437R-91 Strength Evaluation of Existing Concrete · PDF fileACI 437R-91 (Reapproved 1997) Strength Evaluation of Existing Concrete Buildings Reported by ACI Committee 437 Brian J

ACI 437R-91(Reapproved 1997)

Strength Evaluation ofExisting Concrete Buildings

Reported by ACI Committee 437

Brian J. Pashina’t Paul E. GaudettcChairman Secretary

Joseph A. AmonCraig A. BallingerCharles L BallouMerle E BranderNicholas J. Carino*Claudius A. CamegieSRobert V. GeveckerZareh B. GregorianOtto C GuedelhoeferGrant T. Halvorsent

Roberto HuykeDov KaminetzkyAndrew T. KrauklisJohn MinorTarun R. NaikC. Raymond NowackiSuresh J. PinjarkarPredrag L PopovicAvanti C. ShroffMark S. Suchecki

*Primary Authont Editorial Subcommittee$ Chairman of the Committee while the report was in preparationNote: Associate member Thomas L. Rewerts was committee chairman at the time the majority of the work on thii revision was accomplished.

The strength of existing concrete buildings may be evaluated analytically orby load tests. These recommendations indicate when such an evaluationmay be needed establish criteria for selecting the evaluation method, andindicate the data and background information necessary for an evaluation.Methods of determining material properties used in the analytical investi-gation are described in detail. Analytical investigations should follow the principles of strength design outlined in ACI 318. Procedures for con-ducting static load tests are recommended and criteria indicated fordeflection under load and recovery.

Keywords: Buildings; cracking (fracturing); deflection; deformation;evaluation; instruments; leads; load tests (structural); nondestructivetests; reinforced concrete; reinforcing steel; serviceability static tests;strength; structural design; structures; tests.

CONTENTSDescriptionChapter 1 -- Introduction, p. 437R-2

l.l--Scope1.2--Applications

ACI Committee Reports, Guides, Standard Prac-tices, and Commentaries are intended for guidancein designing, planning, executing, or inspecting con-struction and in preparing specifications. Referenceto these documents shall not be made in the ProjectDocuments. If items found in these documents aredesired to be a part of the Project Documents, theyshould be phrased in mandatory language andincorporated into the Project Documents.

4

1.3--Exceptions1.4--Categories of evaluation1.5-Procedure for a structural evaluation1.6--Commentary1.7--Organization of the report

Chapter 2 -- The preliminary investigation, p. 437R-32.1--Review of existing information2.2--Condition survey of the building

Chapter 3 -- Methods for material evaluation, p. 437R-83.1--Concrete3.2--Reinforcing steel

Chapter 4 -- Assessment of loading conditions andselection of evaluation method, p. 437R-12

4.1--Assessment of loading and environmentalconditions

4.2--Selecting the proper method of evaluation

Chapter 5 -- The evaluation, p. 437R-155.1--Analytical evaluation

This report supersedes ACI 437R-67 (Revised 1982), effective Nov. 1,199l. Ithas been revised to update and give more complete information on proceduresfor strength evaluation of existing concrete buildings.

Copyright 6,1991, American Concrete Institute.All rights reserved, including rights of reproduction and use in any form or by

any means, including the making of copies by any photo process, or by anyelectronic or mechanical device, printed, written, or oral, or recording for soundor visual reproduction for use in any knowledge or retrieval system or device,unless permission in writing is obtained from the copyright proprietors.

37R-1

437R-2 ACI COMMITTEE REPORT

5.2--Supplementing the analytical evaluationwith load tests

Chapter 6-- References, p. 437R-226.1--Recommended references6.2--Cited references

Chapter 1 --INTRODUCTION

1.1 -- ScopeThis report provides recommendations to be

followed in an investigation to establish the loadings thatcan safely be sustained by the structural elements of anexisting concrete building. The procedures may be ap-plied generally to other concrete structures provided thatappropriate evaluation criteria are agreed to prior to thestart of the investigation. This report covers convention-ally reinforced cast-in-place concrete, precast-prestressedconcrete, and post-tensioned, cast-in-place concrete.

1.2 -- ApplicationsThe procedures recommended in this report

apply where the strength evaluation of an existingconcrete building is required in one or more of thefollowing circumstances:

-- Distressed structures which show damagefrom excess or improper loading, vibra-tions, fire, etc.

-- Deteriorated structures where there isevidence of structural weakness, such asexcessive cracking or spalling of the con-crete, reinforcing bar corrosion, memberdeflection or rotation, etc.

-- Defective structures suspected to be sub-standard in design, detail, material, orconstruction

-- Structures where there is doubt as tostructural adequacy with regard to futureloading when the original design criteriaare not known

-- Structures undergoing a change in use oroccupancy where there is doubt concern-ing structural adequacy when the pro-spective loading exceeds the service loadcapacity calculated for the originaldesign criteria

-- Structures which require performancetesting following remedial measures(repair or strengthening)

1.3 -- Exceptions

This report does not address the followingconditions:

-- Performance testing of structures withunusual design concepts

--

--

Product development testing where loadtests are carried out for quality controlor approval of mass produced elements

Evaluation of foundations and/or soilconditions

-- Structural engineering research

1.4 -- Categories of evaluationThere are a number of different characteristics

or levels of performance of an existing concrete structurethat can be evaluated. These include:

--

--

Stability of the entire structure

Stability of individual components of thestructure

-- Strength and safety of individual struc-tural elements

Stiffness of the entire structure

Stiffness of individual structural elements

Susceptibility of individual structuralelements to excess long-term deforma-tion

-- Dynamic response of individual struc-tural elements

-- Durability of the structure

-- Fire resistance of the structure

-- Serviceability of the structure

This report deals with the evaluation of anexisting concrete building for stability, strength, andsafety. Procedures for evaluating the other characteristicsof an existing concrete building are beyond the scope ofthis document.

1.5 -- Procedure for a structural evaluationMost structural evaluations have a number of

basic steps in common. However, each evaluation shouldbe treated as unique and emphasis placed on the dif-ferent steps as dictated by the project. Generally, theevaluation will consist of:

STRENGTH EVALUATION OF CONCRETE BUILDINGS 437R-3

-- Defining the existing condition of thebuilding, including:

(1) Reviewing available informationon the building

(2) Conducting a condition survey ofthe building

(3) Determining the cause and rateof progression of existing distress

Determining the degree of repairto precede the evaluation

-- Selecting the structural elements whichrequire detailed evaluation

-- Assessing past, present, and future load-ing conditions to which the structure hasand will be exposed under the antici-pated use

-- Conducting the evaluation

-- Evaluating the results

1.6 -- CommentaryEngineering judgment is a critical element in the

strength evaluation of reinforced concrete buildings.Judgment of trained structural engineers may take pre-cedence over compliance with rigid code provisions orformulas for analyses. It should be recognized that thereis no such thing as an absolute measurement of structuralsafety in an existing concrete building, particularly inbuildings that are deteriorated due to prolonged expo-sure to the environment, or that have been damaged ina physical event such as a fire. Similarly, there are nogenerally recognized criteria for evaluating serviceabilityof an existing concrete building. Engineering judgmentand close consultation with the owner regarding theintended use of the building is required in this type ofevaluation.

The following conclusions are possible regardingthe integrity of a structure as a result of a strengthevaluation:

-- The structure is adequate for normal useover its expected life if maintainedproperly

-- The structure, although adequate forpresent loading and existing conditions,may not remain so in the future

-- The structure is inadequate for its cur-rent or intended use, but may be ade-quate for alternative use

-- The structure is inadequate or unsafe,and needs remedial work

-- The structure is unsafe and beyondrepair

-- The information or data are not suffi-cient to reach a definitive conclusion

1.7 -- Organization of the reportThe remainder of this report is structured into

the following four chapters:Chapter 2 -- The preliminary investigation, dis-

cusses the information that must be gathered to performa strength evaluation and how that information can begathered. Two primary topics are covered. The first is areview of existing records on the building. The second isthe condition survey of the building, including guidelineson the proper recognition of abnormalities in a concretestructure, and survey methods available for evaluation ofstructural concrete.

Chapter 3 -- Methods for material evaluation,outlines procedures that should be undertaken to assessthe quality and mechanical properties of the concreteand reinforcing steel materials in the structure, in theirpresent condition. Discussion is included on samplingtechniques, petrographic and chemical analysis of con-crete, and test methods available to assess the mechanicalproperties of concrete and steel.

Chapter 4 -- Assessment of loading and selectionof evaluation method, provides information regardingprocedures necessary to properly assess the past, present,and future loading conditions of the structure, or struc-tural component in question. The second part of thechapter is devoted to a discussion of how to select theproper method for evaluating the strength of an existingstructure.

Chapter 5 -- The evaluation, provides commen-tary on the conduct of a strength evaluation for anexisting concrete structure. Analytical techniques arediscussed, and the use of load tests to supplement theanalytical evaluation is considered.

CHAPTER 2 -- THEPRELIMINARY INVESTIGATION

This chapter describes the initial, preliminary,work that should be performed during a strength evalu-ation of an existing concrete building. Sources of infor-mation that should be reviewed are discussed and de-tailed information is presented about procedures forconducting a condition survey.

2.1 -- Review of existing informationAll sources of existing information concerning

the design, construction, and service life of the buildingshould be researched to learn as much as possible aboutthe structure. Attempts should be made to clearly recon-


struct the original design assumptions and theories. Theobjective is to minimize the number of assumptions nec-essary to perform an analytical evaluation. The followingis a comprehensive listing of available informationsources. It is intended as a guide only. It should berecognized that each source need not be consulted in astrength evaluation.

2.1.1 The original design -- The following sourcesof information should be researched to define the para-meters used in the original design:

-- Architectural, structural, mechanical,electrical, and plumbing contractdrawings

--

--

Structural design calculations

Change orders to the original contractdrawings and specifications

-- Records of the local building department

2.1.2 Construction materials -- Project documentsshould be checked to develop an understanding of thetype of materials that were originally specified andactually used for the building. These include:

-- Reports on the proportions and prop-erties of the concrete mixtures

--

--

Reinforcing steel mill test reports

Material shop drawings, including allplacing drawings prepared by suppliersthat were used to place their products(bars, welded wire fabric, and pre-stressing steel) in the original con-struction of the building; formworkdrawings; and mechanical, electrical, andplumbing equipment drawings

2.1.3 Construction records -- In many cases, docu-mentation dating from original construction will be avail-able to the investigator. These often include:

-- Correspondence records of the designteam, the owner, the general contractor,the specialty subcontractors, and thematerial suppliers and fabricators

Field inspection reports

Contractor and subcontractor diaries

Job progress photographs

Concrete cylinder compressive strengthtest reports

-- Field slump and air-entrainment testreports

--

--

--

--

--

Delivery tickets from concrete trucks

As-built drawings

Survey notes and records

Reports filed by local building inspectors

Drawings and specifications kept in thetrailers or offices of the contractor andthe subcontractors during the construc-tion period

2.1.4 Design and construction personnel -- Otherexcellent sources of information concerning the designand construction of the building under investigation arethe individuals involved in those processes. Interviewswith these personnel often will yield valuable informationfor a strength evaluation. This information can be ofparticular value if the members of the design and con-struction teams reveal any problems that may haveoccurred during the design and construction of thebuilding.

2.1.5 Service history of the building -- This in-cludes all documents that define the history of thebuilding from the original construction to the present,such as:

-- Records of current and former owners,their legal representatives, and their in-surers

-- Maintenance records

-- Documents and records concerning pre-vious repair and remodeling

-- Records maintained by owners of ad-jacent structures

-- Weather records

-- Logs of seismic activity

2.2 -- Condition survey of the buildingAll forms and areas of deterioration and distress

existing in the structural elements of the building shouldbe located, inspected and recorded as to type, location,and degree of severity. Procedures for performing thiscondition survey are described in this section. The readershould also refer to ACI 201.1R. A considerable degreeof engineering judgment must be exercised in performinga condition survey. All of the steps outlined below maynot be required in a particular strength evaluation. Theinvestigator performing the evaluation must decide what


information will be needed to determine the existing con-dition of structural elements of the particular buildingthat is being evaluated.

2.2.1 Recognition of abnormalities -- A funda-mental knowledge of the basic characteristics of struc-tural concrete and the types of distress and defects thatmay be observed in a concrete building is essential forsuccessful performance of a strength evaluation. Addi-tional information on the causes and evaluation of con-crete distress is found in ACI 201.1R, ACI 207.3R, ACI222R, ACI 224R, ACI 224.1R, ACI 309.2R, a n d ACI362R.

2.2.2 Survey methods for evaluation of structuralconcrete

2.2.2.1 Visual examination -- All obviousdistress, deterioration, and damage existing in the struc-ture should be located by means of a thorough visual in-spection of all structural components of the building.Liberal use of photographs, notes, and sketches to doc-ument this walk-through inspection is recommended. Allabnormalities found to exist should be recorded as totype, magnitude, location, and severity.

When the investigator conducting the visual ex-amination finds defects that are considered to be of sucha nature as to render a portion or all of the buildingunsafe, the condition should be reported to the ownerimmediately. Appropriate temporary measures should beundertaken immediately to secure the structure before itis placed back in use and the survey continued.

To employ the analytical method of strengthevaluation it is necessary to collect from verified records,as described in Section 2.1, sufficient information on themember properties, physical size, and positioning of thestructural components in the building. If this informationis incomplete, missing, or of questionable accuracy, themissing and unreliable information must be determinedthrough a field survey.

2.2.2.2 In-place tests for assessing thestrength of concrete -- A number of test methods areavailable for estimating the in-place concrete strength orfor locating areas of low strength concrete. These havebeen traditionally referred to as “nondestructive tests” tocontrast them with the drilling and testing of core sam-ples. A more descriptive term for these tests is “in-placetests” because they are performed on concrete as it existsin a structure. Additional information on these methodsmay be found in ACI 228.1R and Malhotra (1976).

The common feature of these methods is thatthey do not directly measure the compressive strength ofthe concrete. Rather they measure some other qualitywhich has been found to have an empirical correlationwith compressive strength. These methods can be used toestimate compressive strength or to compare the relativecompressive strength at different locations in the struc-ture. Depending on which application is desired, differentprocedures are needed.

If these methods are used for estimating the in-place compressive strength, it is necessary to develop a

relationship between compressive strength and the quan-tity measured by the in-place test. Such a relationshipshould be developed by performing the in-place test onthe structure and testing core samples that have beendrilled from areas adjacent to the test locations. Anattempt should be made to obtain paired data from dif-ferent parts of the structure so as to obtain as wide aspread as possible in the range of compressive strength.Regression analysis of the correlation data can be usedto develop a prediction equation along with the con-fidence limits for the predicted strength. These cor-relation relationships have been found to be influencedby the specific materials used in the concrete. The use ofgeneral correlation curves supplied with test equipmentor developed from concrete other than that in the struc-ture being evaluated is not recommended. The use of in-place test procedures can reduce the number of corestaken, but cannot eliminate the need for drilling coresfrom the building.

When using these methods to compare relativeconcrete strength it is not necessary to develop cor-relation relationships. However, the user must be awareof the factors that may influence the in-place test results,otherwise it is possible to draw wrong conclusions con-cerning the relative in-place strength.

Sections 2.2.2.2.1 - 2.2.2.2.4 summarize theoperating principles of a number of currently availablein-place tests, and highlight factors that significantlyinfluence test results.

2.2.2.2.1 Rebound number --Procedures for conducting this test are given in ASTM C805. The test instrument consists of a metal housing, aspring-loaded mass (the hammer) and a steel rod (theplunger). To perform a test, the plunger is placed per-pendicular to the concrete surface and the housing ispushed toward the concrete. This action causes theextension of a spring connected to the hammer. Whenthe instrument is pushed to its limit, the hammer ispropelled toward the concrete and it impacts a shoulderon the plunger. The hammer rebounds, and the rebounddistance is measured on a scale numbered from 10 to100. The rebound distance is recorded as the “reboundnumber” indicated on the scale.

The rebound distance depends on how much ofthe initial hammer energy is absorbed in the interactionof the plunger with the concrete. The greater the amountof absorbed energy, the lower the rebound number. Theenergy absorbed by the concrete depends on its stress-strain relationship. For this reason, there is not a simpledirect relationship between rebound number and com-pressive strength. However, it has been shown empiricallythat for a given concrete mixture there may be good cor-relation between compressive strength and reboundnumber.

The concrete in the immediate vicinity of theplunger has the greatest effect on the measured reboundnumber. Hence, test results are sensitive to the localconditions at the test point. For example, a test per-


formed directly above a hard particle of coarse aggregateresults in a higher rebound number than a test over mor-tar. To account for the variations in local conditions,ASTM C 805 requires the averaging of ten rebound read-ings for a test. Procedures for discarding abnormally highor low values are also given.

The measured rebound number is affected by theproperties of the concrete near the surface and may notbe representative of the rebound value of the interiorconcrete. A surface layer of carbonated or deterioratedconcrete results in a rebound number which is signifi-cantly different from that for the interior concrete. Therebound number increases as the moisture content of theconcrete decreases, and tests on a dry surface can givethe wrong estimation for interior concrete that is moist.Since rebound distance is affected by the direction of theinstrument (sideward, upward, downward), this must beconsidered when comparing readings and using cor-relation relationships. The manufacturer provides cor-rection factors to account for varying hammer positions.

The rebound number is a simple method forquickly obtaining information about the surface prop-erties of a structural member. However, there are manyfactors other than strength that influence the measuredrebound number. These factors are identified in ASTMC 805 and must be considered when evaluating test re-sults.

2.2.2.2.2 Probe penetration -- Theprocedures for performing this method are given inASTM C 803.* The test involves the use of a specialpowder-actuated gun to drive a hardened steel rod(probe) into the surface of a concrete member. Thepenetration of the probe into the concrete is taken as anindicator of concrete strength.

The probe penetration technique is similar to therebound number except that the probe impacts the con-crete with a much higher energy level. A theoreticalanalysis of this test is complex. Qualitatively it involvesthe initial kinetic energy of the probe and the energyabsorption by friction and by failure of the concrete. Asthe probe penetrates the concrete there is crushing ofmortar and aggregate along the penetration path andthere is extensive fracturing within a conic region aroundthe probe. Hence, the strength properties of the aggre-gates and the mortar will influence the penetrationdepth. This contrasts with the behavior of ordinarystrength concrete in a compression test, in which ag-gregate strength plays a secondary role compared withmortar strength. Thus, an important characteristic of theprobe penetration test is that the type of coarse aggre-gate strongly affects the correlation relationship betweencompressive strength and probe penetration.

Because the probe penetrates into the concrete,test results are not highly sensitive to local surfaceconditions such as texture and moisture content. In

* The only commercial test system for performing the test is known as the"Windsor Probe."

practice, the exposed lengths of the probes are measured,and according to ASTM C 803, a test result is the aver-age of three probes located within 7 in. (180 mm) ofeach other.

The probe penetration system enables the use ofa lower power level or a larger probe for testing rela-tively weak [less than 3000 psi, (20 MPa)] or lightweightconcrete. The correlation relationships are only valid fora specific power level and probe type.

The method is useful for comparing relativecompressive strength locations in a structure. However,as is the case with other methods, the strengths of corestaken from the structure are required to estimate com-pressive strength. The probe penetration test is unreliablein the evaluation of high-strength concrete.

2.2.2.2.3 Pulse velocity -- Theprocedures for this method are given in ASTM C 597.The test equipment includes a transmitter, a receiver,and electronic instrumentation. The test consists ofmeasuring the time it takes for a pulse of vibrationalenergy to travel through a concrete member. The vibra-tional energy is introduced into the concrete by thetransmitting transducer, which is coupled to the surfacewith an acoustic couplant such as grease. The pulse tra-vels through the member and is detected by the receivingtransducer, which is coupled to the opposite surface. In-strumentation measures and displays the pulse transittime. The distance between the transducers is divided bythe transit time to obtain the pulse velocity through theconcrete under test.

The pulse velocity is proportional to the squareroot of the elastic modulus and inversely proportional tothe mass density of the concrete. The elastic modulus ofconcrete has been found to vary in proportion to thesquare root of compressive strength. Hence, largechanges in compressive strength produce only minorchanges in pulse velocity. There are factors other thanstrength that affect pulse velocity, and changes in velocitydue to these factors can easily overshadow changes dueto strength. One of the most critical of these is moisturecontent. An increase in moisture content increases thepulse velocity and this could be incorrectly interpreted asan increase in compressive strength. The presence ofreinforcing steel aligned with the pulse travel path canalso significantly increase pulse velocity.

Under laboratory conditions, excellent cor-relations have been reported between velocity and com-pressive strength. However, these findings should not beinterpreted to mean that highly reliable in-place strengthpredictions can be routinely made. Reasonable strengthpredictions are possible only if correlation relationshipsinclude those characteristics of the in-place concrete thathave a bearing on pulse velocity. It is for this reason thatthe pulse velocity method is not generally recommendedfor estimating in-place strength. However, it is an excel-lent technique for locating regions in a structure wherethe concrete is of a different quality, or where there maybe internal defects such as cracking and honeycombing.


However, it is not possible to determine the nature of thedefect based solely on the measured pulse velocity (seeSection 2.2.2.3).

2.2.2.2.4 Pullout test -- The pull-out test consists of measuring the load required to pullan embedded metal insert from a concrete member. Theforce is applied by a jack which bears against the con-crete surface through a reaction ring concentric with theinsert. As the insert is extracted, a conical fragment ofthe concrete is also removed. The test produces a well-defined failure in the concrete and measures a staticstrength property. However, there is currently no consen-sus on which strength property is measured and so a cor-relation relationship must be developed between com-pressive strength and pullout strength (Stone and Carino,1983). The relationship is valid only for the particulartest configuration and concrete materials used in thecorrelation testing.

ASTM C 900 describes procedures for per-forming pullout tests. However, the standard methoddeals with inserts cast in the concrete during con-struction. Recent developments have been made inadapting the pullout test to existing structures by usingvarious types of anchors that can be placed in a holedrilled in the structure (Mailhot et al. 1979). Some ofthese methods produce a failure pattern similar to thestandard test (Peterson 1984) and others produce an en-tirely different pattern (Chabowski and Bryden-Smith1979). Presently, there are no standard procedures forperforming “drilled in” pullout tests on existing structures.

2.2.2.3 Nondestructive tests for identifyinginternal abnormalities -- A strength evaluation may alsoinclude determining if internal abnormalities exist whichmay adversely affect structural capacity. For example, itmay be necessary to determine if there are internal voids,cracks, or regions of inferior concrete quality. Thissection describes some of the available methods for theseapplications. Compared with methods of strength deter-mination, some of the techniques for locating internaldefects require more complex instrumentation and spe-cialized expertise to perform the tests and interpret theresults. However, the investigator should be aware thatsuch procedures are available.

2.2.2.3.1 Sounding -- Hollowareas or planes of delamination below the concrete sur-face can be detected by striking the surface with ahammer or a steel bar. A “hollow” or “drum-like” soundresults when the surface over a defective area is struck,compared with a “ringing” noise over sound concrete. Forslabs, a heavy steel chain can be dragged over the con-crete surface. Sounding is a simple and effective methodfor locating regions with subsurface fracture planes.However, the sensitivity and reliability of the methoddecreases as the depth of the defect increases. Pro-cedures for using sounding in pavements and slabs maybe found in ASTM D 4580.

2.2.2.3.2 Pulse velocity -- Theprinciple of the method is discussed in Section 2.2.2.2.

Pulse travel time between the transmitting and receivingtransducers is affected by the concrete properties alongthe travel path and the actual travel path distance. Ifthere is a region of low quality concrete between thetransducers, the travel time increases and a lower velocityvalue is computed. If there is a void between the trans-ducers, the pulse travels through the concrete around thevoid. This increases the actual path length, increases thetravel time, and a lower pulse velocity is computed.While the pulse velocity method can be used to locateabnormal regions, it cannot by itself identify the natureof the abnormality. Therefore, cores are recommendedto determine the nature of the indicated abnormality.

2.2.2.3.3 Pulse (impact)-echo --This technique also involves measuring the transit timeof a pulse of vibrational energy. Unlike the pulse velocitymethod, in this case the pulse is generated and receivedon the same surface. The measured transit time repre-sents the elapsed time for the pulse to travel through theconcrete and travel back after reflection from an inter-face. A reflecting interface is a boundary betweenmaterials having different acoustic impedances (productof mass density and pulse velocity). For a sound member,reflection occurs from the member boundary oppositefrom where the pulse is generated. If there is an internalinterface, such as that created by a crack or a void, thepulse is reflected from this interface and the echo isreceived sooner. By knowing the pulse velocity throughthe concrete and the measured transit time, the depth ofthe interface can be computed.

While the principle of this method is rathersimple, a pulse-echo test system that is reliable andsimple to use is not commercially available. However, thisis an area of active research and tools may be availablein the near future. A technique under development usesa short-duration, mechanical impact to create a transientresonance between the impact point and reflecting inter-face. It has been demonstrated that this method, whichis called “impact echo,” is capable of detecting a varietyof defects within concrete (Sanalone and Carino 1986,1989).

2.2.2.3.4 Ground probing radar --This method is in principle, similar to the pulse-echotechnique except that electromagnetic radiation isintroduced into the material. An antenna placed on theconcrete surface sends out an extremely short-durationradar pulse. A portion of the pulse is reflected back tothe antenna, which also acts as receiver, and a portionpenetrates into the concrete. If the concrete membercontains boundaries between materials with differentelectrical properties, some of the pulse is reflected backto the antenna. Knowing the velocity of the radar pulsein the concrete, the depth of the interface can bedetermined. Recording systems are available which dis-play a profile view of the reflecting interfaces within themember as the antenna is moved over the surface. Inter-pretation of the recorded profiles is the most difficultaspect in using commercially available radar systems. This


method has been used successfully to locate embeddedmetal, such as reinforcing steel, and to locate regions ofdeterioration in pavements. The penetrating ability of theradar pulse depends on the electrical conductivity of thematerial and the frequency of the radiation. As electricalconductivity increases radar penetration decreases. Intesting concrete, a higher moisture content reduces thedepth of penetration.

2.2.2.3.5 Infrared thermography --A surface having a temperature above absolute zeroemits electromagnetic energy. At room temperature, thewave length of this radiation is in the infrared region ofthe electromagnetic spectrum. The rate of energy emis-sion from the surface depends on its temperature, so byusing infrared detectors it is possible to “see” differencesin surface temperature. If a concrete member contains aninternal defect, such as a large crack or void, and thereis heat flow though the member, the presence of thedefect may influence the temperature of the surfaceabove the defect. A “picture” of the surface temperaturecan be created by using an infrared detector to locate“hot” or “cold” spots on the surface. The locations ofthese hot and cold spots serve as indications of thelocations of internal defects in the concrete. Thetechnique has been successfully used to locate regions ofdelamination in concrete pavements and bridge decks.

There must be heat flow through the member touse infrared thermography. This can be achieved by thenatural heating from sunlight or by applying a heatsource to one side of the member. In addition, thissurface of the member must be of one material and havea uniform value of a property known as emissivity, whichis a measure of the efficiency of energy radiation by thesurface. Changes in emissivity cause changes in the rateof energy radiation which can be incorrectly interpretedas changes in surface temperature. The presence of anymaterial on the surface, such as paint or grease, willaffect the results of infrared thermography by changingthe temperature of the surface. It is often useful to takea photographic or video record of the same areas of theconcrete surface so that it may be compared to theinfrared photographic record. In this manner surfacedefects can be eliminated from consideration as internaldefects in the concrete.

2.2.2.3.6 Radiography -- Radio-graphy can determine the internal condition of a struc-tural member or locate embedded steel by using pene-trating radiation, such as x rays or gamma rays. As theradiation passes through the member its intensity isreduced according to the thickness, density and absorp-tion characteristics of the materials within the member.The quantity of radiation passing through the member isrecorded on x ray film similar to that used in medicalapplications. Reinforcing bars absorb more energy thanthe surrounding concrete and show up as light areas onthe exposed film. Cracks and voids, on the other hand,absorb less radiation and show up as dark zones on thefilm. Crack planes parallel to the radiation direction are

detected more readily than cracks perpendicular to theradiation direction.

Produced by an electrical device, the penetratingability of x rays can be varied. However, the penetratingability of portable x ray units is limited [the techniqueworks best on members less than 12 in. (300 mm) thick]and gamma radiation is used more commonly in field ap-plication. Gamma rays result from the radioactive decayof unstable isotopes. As a result, a gamma ray sourcecannot be turned off and extensive shielding is needed tocontain the rays when not used for inspection. The shieldrequirements make gamma rays sources heavy and bulky,especially when high penetrating ability is required. Thepenetrating ability of gamma rays depends on the typeand age of the isotope source. Gamma ray sources areavailable that can penetrate up to 18 in. (450 mm) ofconcrete. For thicker structural elements, a hole may bedrilled and the source placed inside the member.

Radiographic inspection poses health hazards ifproper operating procedures are not followed and mustbe performed by licensed and trained personnel. Onedrawback to radiography is that it can interrupt tenant orconstruction activities because the exposure areas mustbe evacuated.

CHAPTER 3 -- METHODS FORMATERIAL EVALUATION

This chapter describes procedures that should beundertaken to assess the quality and mechanical prop-erties of the concrete and reinforcing steel in a structure.Sampling techniques, petrographic and chemical analysisof concrete, and test methods available to assess themechanical properties of concrete and steel arediscussed.

3.1 Concrete3.1.1 Techniques for proper sampling of concrete--

Samples of concrete in an existing structure may beretrieved to determine strength as well as physical andchemical properties. It is essential that the samples beobtained, handled, identified (labeled), and stored inproper fashion to prevent damage or contamination.Sampling techniques are discussed in this section.

Guidance on developing an appropriate samplingprogram is provided by ASTM C 823. Samples are usu-ally taken to obtain statistical information about theproperties of concrete in the entire structure, or tocharacterize some unusual or extreme conditions in spe-cific portions of the structure. In the first case, samplelocations should be randomly distributed throughout thestructure. The number and size of samples depends onthe necessary laboratory tests and the degree of con-fidence desired in the average values obtained from thetests.

The type of sampling plan which is required ona particular project depends on whether the concrete is


generally believed to be uniform, or if there are likely tobe two or more regions which are different in compo-sition, condition, or quality. The preliminary investigationand other sources of information should be consideredbefore a detailed sampling plan is prepared. Where aproperty is believed to be uniform, sampling locationsshould be distributed randomly throughout the area ofinterest, and all data treated as one group. Otherwise,the study area should be subdivided into regions believedto be relatively uniform, with each region sampled andanalyzed separately.

For tests intended to measure the average valueof a concrete property, such as strength, elastic modulus,or air content, the number of samples should be deter-mined in accordance with ASTM E 122. The requirednumber of samples generally depends on:

-- The maximum allowable difference (orerror) that one is willing to acceptbetween the sample average and the trueaverage

-- The variability of the test results, and

-- The risk one is willing to accept that theallowable difference is exceeded

Fig. 3.1 illustrates how ASTM E 122 may beused to determine the sample size. The vertical axisindicates the number of samples as a function of themaximum difference (as a percentage of the true aver-age) and as a function of the coefficient of variation ofthe test results. In Fig. 3.1 the risk that the allowable
error will be exceeded is 5 percent, but other levels maybe used depending on the particular situation. Since thevariability of test results is usually not known in advance,an estimate should be made and adjusted as test resultsbecome available. Economy should also be considered inthe selection of sample sizes. In some cases increasingthe sample size may only result in a minimal decrease inthe risk that the error is exceeded. The cost of additionalsampling and testing would not be justified in these situ-ations.
The investigator must recognize that concrete isnot isotropic and properties will vary depending on thedirection that samples are taken. Particular attentionshould be given to vertical concrete members, such ascolumns, walls, and deep beams, because concrete pro-perties will vary with elevation due to differences inplacing and compaction procedures, segregation, orbleeding. Typically the strength of concrete decreases asits elevation within a placement increases.

3.1.1.1 Core sampling -- The proceduresfor properly removing concrete samples by core drillingare given in ASTM C 42. The following guidelines are ofparticular importance in core sampling:

-- Equipment: Cores should be taken using

diamond-studded core bits when thecores will be tested for strength. A shotdrill may be acceptable for other appli-cations when the core is drilled vertically.However, diamond-studded core bits arerecommended for other drill orien-tations

-- The number, size, and location of coresamples should be carefully selected topermit all necessary laboratory tests. Ifpossible, use virgin samples for all testsso that there will be no influence fromprior tests

-- Core diameter: Cores to be tested for astrength property should have a mini-mum diameter of three times the maxi-mum nominal size of the coarse aggre-gate, or 2 in. (50 mm), whichever isgreater

-- Core length: Where possible, cores to betested for a strength property shouldhave a length of at least twice theirdiameter

-- Reinforcing steel should not be includedin a core to be tested for strength

-- Caution should be exercised to avoidcutting electrical conduits or prestressingsteel

-- Where possible, core drilling shouldcompletely penetrate the concrete sec-tion to avoid having to break off the coreto facilitate removal. If through-drillingis not feasible, an extra 2 in. (50 mm)should be drilled to allow for possibledamage at the base of the core

-- Where cores are taken to determinestrength, at least three cores should beremoved at each location in the struc-ture. The strength value should be takenas the average of the cores. A single coreshould not be used to evaluate or diag-nose a particular problem

3.1.1.2 Random sampling of broken con-crete-- Sampling of broken concrete generally should notbe used where strength of concrete is in question. Thismethod is most frequently used when evaluating chemicalproperties of deteriorated concrete members.

3.1.2 Petrographic and chemical analysis -- Aqualified petrographic and chemical laboratory can behelpful in determining characteristics and properties of

437R-10

5% Risk Error is Exceeded

5 10 15 20

ALLOWABLE PERCENTAGE ERROR IN AVERAGEFig. 3.1--Sample size based on ASTM E 122, risk equals 5 percent

concrete from an existing structure which may be impor-tant in a strength evaluation. A qualified petrographerwho is familiar with problems commonly encounteredwith concrete should be consulted prior to the removalof samples from an existing structure. The petrographershould be provided with information regarding the pre-construction, construction, and postconstruction historyand performance of the structure.

3.1.2.1 Aggregates -- The followingproperties of aggregates can be determined by petro-graphic evaluation of concrete samples (ASTM C 856):

-- Particle shape, size distribution, andcomposition

-- The extent to which the particles arecoated, and the nature of the coatingsubstance

-- The potential for deleterious reactionsbetween the aggregate and cementalkalies, sulfates, and sulfides

-- Presence of unsound aggregates(fractured, porous, and degree ofweathering)

Mielenz (1978) describes petrographic examin-ation of concrete aggregates in more detail.

3.1.2.2 Concrete -- The fol lowingcharacteristics of the concrete can be determined bypetrographic analysis in accordance with ASTM C 856:

-- Density of the cement paste, and color

--

--

--

--

--

--

--

--

Matherr (1978) provides additional information

of the cement

Homogeneity of the concrete

Occurrence of settlement and bleedingin fresh concrete

Presence of deterioration caused byexposure to freezing and thawing

Occurrence and distribution of fractures

Characteristics and distribution of voids

Presence of contaminating substances

Proportion of unhydrated cement

Presence of mineral admixtures

Volumetric proportions of aggregates,cement paste, and air voids

Air content and various dimensionalcharacteristics of the air void system(including entrained and entrapped air)

Weathering patterns from surface-to-bottom

Presence of deterioration due toabrasion or fire exposure


on petrographic examination of hardened concrete.3.1.2.3 Chemical tests -- Chemical tests

can determine the cement content, content of solublesalts, depth of carbonation, and chloride content. Wherethe structure is exposed to deleterious substances it isoften useful to develop a profile of the property throughthe thickness of the member. This is particularly im-portant for structures where chlorides are present.

3.1.3 Testing concrete for compressive strength3.1.3.1 Destructive testing -- Compressive

strength of concrete cores taken from an existing struc-ture should be determined in accordance withASTM C 39 and C 42. A number of key points should beobserved in this procedure.

-- For core length-to-diameter ratios lessthan 2.0, apply the appropriate strengthcorrection factors given in ASTM C 42

-- When the concrete in the portion of thestructure in question will always be dryin service, cores should be air-dried[temperature 60 to 80 F (15 to 25 C) andrelative humidity less than 60 percent]for at least 7 days before testing andshould be tested dry. If the concrete inthe structure will be more than super-ficially wet under service conditions,cores should be immersed in lime-sat-urated water for at least 40 hr andshould be tested wet. Concrete with anoutdoor exposure should be tested wetunless fully protected from water absorp-tion

-- Compression tests for comparison withcompressive strength tests on standard-cured cylinders should be performed wet

-- Depending on age and strength level,compressive strength values obtainedfrom core tests can either be lower orhigher than those obtained from tests ofstandard 6 by 12-in. (150 by 300-mm)cylinders molded from samples of con-crete taken during construction. Formature concrete, the core strength variesfrom 100 percent of the cylinder strengthfor 3000 psi (20 MPa) concrete to 70percent for 9000 psi (60 MPa) concrete(Mindess and Young 1981)

-- Core compressive strengths may beexpected to be lower for cores removedfrom the upper portions of slabs, beams,footings, walls, and columns than fromlower portions of such members

3.1.3.2 Nondestructive testing -- The in-vestigator performing a strength evaluation is cautionedthat currently there are no nondestructive tests whichyield direct compressive strengths of concrete in anexisting structure. Nondestructive tests are commonlyused in conjunction with tests of drilled cores to reducethe amount of coring required to establish compressivestrengths throughout the structure. Considerable care isrequired to established valid estimates of compressivestrength based on nondestructive testing. See Section2.2.2.2 for further information.

3.2 -- Reinforcing steel3.2.1 Locational survey methods -- The size,

number, and location of steel reinforcing bars can bedetermined by the following methods, or combinationthereof:

3.2.1.1 Magnetic tests -- Magnet icinstruments for locating reinforcing steel embedded inconcrete are based on the fact that the presence of steelaffects the alternating magnetic field produced by ahand-held search unit. As the search unit is moved alongthe concrete surface, a meter indicates when the unit islocated directly above a reinforcing bar. With propercalibration, these meters can be used to estimate thedepth of a bar if its size is known, or estimate the barsize if the depth of cover is known. Dixon (1986) andSnell, Wallace, and Rutledge (1987) report additionaldetails.

Magnetic tests are limited to detectingreinforcement located within 7 in. (175 mm) of theexposed concrete surface. This method may not beeffective in heavily reinforced sections, particularlysections with two or more adjacent bars or nearlyadjacent layers of reinforcement. Battery poweredequipment will give erroneous readings at ambienttemperatures less than 32 F (0 C). It is possible tooperate the equipment at lower ambient temperatures ifit is kept warm with external heat pads.

The accuracy of these devices depends on barspacing and thickness of concrete cover. Inaccurateresults may occur when the depth of concrete cover isequal to or close to the spacing of the reinforcing bars.Care should be taken to insure that the search unit is notused close to other ferrous materials, as inaccurateresults may be obtained.

Results from tests should be calibrated orcorrelated by drilling or chipping to confirm concretecover and bar size, see Section 3.2.1.4.

3.2.1.2 Radiographic evaluation -- Asdiscussed in Section 2.2.2.3, radiography may be used todetermine the size, position, and configuration of embed-ded reinforcing steel. Inspection by x ray is especiallyuseful in locating post-tensioning strands in concreteslabs. Gamma ray inspection may be used in concrete upto 18 in. (450 mm) thick and is generally acceptable as afield test method because of its portabilitv.


Results from radiographic tests should becalibrated or correlated by drilling or chipping to confirmactual concrete cover and bar size.

3.2.1.3 Radar -- Pulsed radar systemsmay also be used to locate embedded reinforcement. Itoffers advantages over magnetic methods when searchingfor bars in heavily reinforced concrete or when searchingfor nonferrous metals. Interpretation of the results of aradar survey requires an experienced operator.

3.2.1.4 Removal of concrete cover -- Thismethod can take the form of actual removal of concretecover to locate and determine the size of embedded rein-forcing steel, or power drilling to determine the depth ofcover for embedded reinforcing steel. These methods areused primarily for verification and calibration of theresults of the nondestructive methods outlined above.

Removal of concrete cover is the only reliabletechnique available to determine the condition ofembedded reinforcing steel in deteriorated structures.

3.2.2 Determination of yield strength -- The yieldstrength of the reinforcing steel used in the building canbe established by two methods. Information from testsdata furnished by the manufacturer of the reinforcingsteel may be used if it is agreed to by the investigatorand the building official. However, tensile strengths frommill test reports tend to be greater than those obtainedfrom tests of field samples. Where this is not possible ordesirable, sampling and destructive testing of specimenstaken from the structure will be required. Guidelines forthis method are given in Section 3.2.3. Concrete Rein-forcing Steel Institute (1981) provides additional infor-mation on reinforcing systems in older structures.

3.2.3 Sampling techniques -- When the yieldstrength of embedded reinforcing steel is to be deter-mined by destructive testing of specimens taken from thebuilding, the recommendations listed below should befollowed:

-- Test specimen characteristics, specimenselection, and specimen preparation arerecommended in ASTM A 370. Wholebars can also be tested

-- Specimens should be removed at loca-tions of minimum stress in the rein-forcement

-- No two specimens should be removedfrom the same cross section of astructural member

-- Locations of specimens in continuousconcrete construction should be sepa-rated by at least the development lengthof the reinforcement to avoid excessiveweakening of the member

-- For single structural elements having a

span of less than 25 ft (7.5 m) or aloaded area of less than 625 ft2 (60 m2),at least one specimen should be takenfrom the main longitudinal rein-forcement (not stirrups or ties)

-- For longer spans or larger loaded areas,more specimens should be taken fromlocations well distributed through theportion being investigated to determinewhether the same strength of steel wasused throughout the structure

-- Samples should be at least 16 in. (400mm) long. However, smaller samples canbe obtained and then machined ac-cording to the requirements ofASTM A 370 for testing and deter-mination of mechanical properties

CHAPTER 4 -- ASSESSMENT OF LOADINGCONDITIONS AND SELECTION

OF EVALUATION METHOD

4.1 -- Assessment of loading and environmentalconditions

The most fundamental aspect of any strengthevaluation, regardless of the method of evaluationemployed, is the assessment of the loads and environ-mental conditions to which the structure has been ex-posed and to which the structure will be exposed in itsremaining life. It is imperative that these factors beaccurately defined so that the results of the strength eval-uation process will be accurate and realistic.

4.1.1 Dead loads -- Dead loads can be estimatedusing unit material weights as recommended in ANSIA58.1, and using the field measured dimensions of thevarious components of the structure. Design dimensionsshould be used with caution because significant dif-ferences can exist between dimensions shown on originalconstruction drawings and actual, as-built dimensions.Similarly, significant differences are often found inmaterial densities due to variations in moisture content.If such differences are suspected, field samples should beobtained and analyzed to quantify the unit weights.

4.1.2 Live loads -- The magnitude, location, andorientation of live loads on a structural component isdependent on the use of the particular area of thebuilding. It is imperative that past, present, and futureusage conditions be established accurately, so that ap-propriate assumptions can be made for the selection oflive loads to use in the strength evaluation. When evalu-ating a structure for safety, code-defined live loads, basedon usage, can be used. In the absence of an applicablelocal building code the live loads specified in ANSI A58.1can be used.

When evaluating a structure for serviceability, an


attempt must also be made to evaluate the probable liveloads that will be present during normal conditions of oc-cupancy of the building.

4.1.3 Wind loads -- ANSI A58.1 can provideguidance in developing wind loads for use in the strengthevaluation. The investigator should also research thelocal wind conditions at the specific building site. Suchinformation can be obtained from the nearest local officeof the United States Weather Bureau, or directly fromthe National Oceanic and Atmospheric Administration(NOM).

4.1.4 Snow and ice loads -- Care should beexercised in selecting appropriate superimposed loads forsimulation of anticipated snow and ice conditions. Con-sideration should be given to the possibility of build-upof snow and ice at changes in the building roof profile, ordue to the presence of adjacent, higher structures.

Consideration should also be given to local, aswell as regional, geographical locations, when estimatingground snow loads. In the absence of specific code re-quirements, reference should be made to ANSI A58.1and information available from NOAA.

4.1.5 Seismic loads -- Loading conditions due toseismic events are usually well defined in local buildingcodes. In the absence of such guidance ANSI A58.1 orthe Uniform Building Code (UBC) can be used.

4.1.6 Thermal effects -- When restraint exists,expansion and contraction of a concrete building due todaily and seasonal variations in ambient temperature cancause significant forces in the structural elements. Theinvestigator should consult local weather records orNOM to determine the range of temperatures which thestructure may experience. Approximate data regardingseasonal temperature variations is available in the PCIDesign Handbook (Prestressed/Precast Concrete Institute1985).

Large concrete sections do not respond quicklyto sudden changes in ambient temperature. Therefore,effects of rate of heat gain and loss in individual concreteelements may also be important.

Variations in the temperature within a buildingshould also be considered. Consideration should be givento conditions such as areas of the building where heatingor cooling is turned off at night, inadequately or over-insulated areas, existence of cold rooms, etc.

4.1.7 Creep and shrinkage -- The effects of long-term creep and shrinkage are important concerns forconcrete elements (see ACI 209R). Cracks or other dis-tress may be caused by restrained shrinkage, see ACI224R. Internal stresses may exist in a concrete structuredue to restrained shrinkage and long-term creep of con-crete elements. These stresses can be significant whencombined with other loads on the structure. Examples ofthis are a reinforced concrete column under sustainedloading, where stresses in the embedded reinforcing steelcan increase over time due to creep of the concrete, orpost-tensioned structures, where creep and shrinkageinduced problems have been frequentlv found in the past.

4.1.8 Soil pressure -- Significant lateral loads canbe imposed on a building from soil pressure. These mustbe fully and accurately defined. Unit weights of soil canvary significantly, as can the lateral pressure exerted bythe soil. It is often prudent to sample and establish actualsoil weights and properties such as the internal angle offriction. Variations in moisture content can also result inlarge variations in the lateral pressure exerted on the sideof a structure from soil surcharges. Overall stability canbe critical in structures that are built on a slope, due tounbalanced soil pressure that may be present.

Consideration should also be given to loads ordamage caused by frost heaving of soil, soil shrinkage orswelling, differential soil settlement, and improperdrainage.

4.1.9 Fire -- If the building being evaluated hasbeen exposed to fire, consideration must be given to theeffects of localized damage that may have been caused bythe heat of the fire or by the fire-fighting efforts. Carefulattention must be paid to the overall thermal effects onthe structure from the heat of the fire. Volume changesof concrete elements during a fire can cause significantdamage. Potential damage to reinforcing steel or pre-stressing tendons, must also be evaluated carefully. Thisdamage must be considered in the evaluation process.Additional information on damage due to fire may befound in ACI 216R.

4.1.10 Loading combinations -- For purposes ofstrength evaluation load factors and load combinationsshould conform to the requirements of ACI 318 (see alsoACI 318R) and the local building code. If factors otherthan those of ACI 318 are used, the resulting evaluationwill imply a different level of structural safety. Whereserviceability is also to be evaluated, consider using loadfactors equal to 1.0 for all load cases. Load combinationfactors may also be used, such as when wind load effectsare checked. In some situations a serviceability checkmay use a live load different than the full live loadrequired by the local building code.

4.2 -- Selecting the proper method of evaluationThe following recommendations are provided to

assist in selecting the most appropriate method ofstrength evaluation. The choice of the evaluation methodis dependent on such factors as the nature of the struc-ture and how much information is known about its ex-isting condition. The typical choices are evaluation byanalysis, evaluation by analysis and full scale load testing,and evaluation by analysis and structural modeling.

4.2.1 Evaluation by analysis4.2.1.1 Applications -- Evaluation solely

by analysis is recommended where:

Sufficient information is available, orreadily obtainable by field investigation,about the physical characteristics, mater-ial properties, and structural behaviorand loadingss to which the structure will

437R-14 ACI COMMlTTEE REPORT

be subjected

-- Load testing is impractical or unsafebecause of the magnitude, complexity ofthe loads and testing arrangements re-quired, or both

-- Load testing members which are sus-pected of being susceptible to suddenfailure, would endanger the safety of thestructure and those persons conductingsuch tests. This would include columnsor arches likely to fail in compressionand cases susceptible to shear oranchorage failure

4.2.1.2 Conditions for using this method--Analytical evaluation is considered appropriate if all ofthe following conditions are satisfied:

-- There exists a verified theory for theanalysis of the type of structural systemsunder consideration. Information onanalysis methods for reinforced concretebuildings may be found in ACI 442R

-- Characteristics of the structural elementsunder consideration can be determinedand modeled within acceptable limits oferror

-- There is no distress of such a nature ormagnitude that uncertainties are intro-duced which render the application ofthe theory excessively difficult or impos-sible

4.2.2 Evaluation by analysis and physical loadtesting -- Since the previous edition of this report, con-siderable experience has been assembled and reported onthe subject of full-scale load tests of existing structures.Refer to Bares and FitzSimons (1975), FitzSimons andLonginow (1975), Ivani (1976), Guedelhoefer and Janney(1980), Raths and Guedelhoefer (1980) and Elstner et al.(1987) for further information.

4.2.2.1 Applications -- Evaluation byanalysis and physical load testing is recommended in thefollowing cases:

-- The complexity of the design conceptand lack of experience with such types ofstructural elements make evaluationsolely by analytical methods impracticalor uncertain in outcome

-- The loading and material characteristicsof the structural element(s) under con-sideration cannot be readily determined

The nature of existing distress introducessignificant uncertainties into the para-meters necessary to perform an analy-tical evaluation

-- For structural elements suspected to besubstandard in design, materials, or con-struction where the degree of suchdefects cannot be readily determined

-- Where there is doubt concerning ade-quacy of the structural element(s) whenthe likely future loading exceeds theservice load capacity calculated using theoriginal design criteria

4.2.2.2 Preliminary analytical evaluation --Preliminary approximate analytical evaluation should pre-cede evaluation by load test methods. These analysesshould be used to determine the location and magnitudeof the test loading, to determine the effects of existingload effects in the structure (i.e. volume change forces,differential settlement, etc.), to plan the test, and topredict the results of the load test.

4.2.2.3 Vertical loads -- Generally, loadtesting is recommended only for evaluating the strengthof a structure with respect to vertically-applied gravity-type loads. With some exceptions, in-situ load testing isnot recommended for evaluating the strength of a struc-ture to resist lateral loads such as wind and seismicevents. Analytical and/or structural modeling evaluationmethods are recommended in those cases.

4.2.2.4 Sudden failure -- If the structureor element under consideration is known to containdefects that may cause brittle behavior, load testing isspecifically not recommended. This condition may mostfrequently be encountered when evaluating structuralelements for shear capacity. Refer to Section 5.2.8 foradditional guidance.

4.2.3 Evaluation by analysis and structuralmodeling -- In some cases the construction and testing ofstructural models may be a feasible alternative to con-ducting a full-scale load test (Harris 1980). Sabnis et al.(1983) provide a detailed treatment of structuralmodeling and experimental techniques. ACI 444R dis-cusses the specifics of models for concrete structures.

4.2.3.1 Applications -- This method ofevaluation may be appropriate when:

-- Analytical evaluation, alone, results inindefinite conclusions regarding the ade-quacy of the structural element(s) underconsideration

--

--

Load testing is physically impractical

Load testing of members which areprone to sudden failure may endanger


the safety of the building

-- It is desired to evaluate the strength ofa portion of the building, but testing ofthe component to failure is not practical

-- The complexity of the design conceptand lack of experience with such types ofstructural elements make other methodsof evaluation impractical or impossible

-- For structural elements where the mag-nitude of existing load effects due torestrained volume changes (shrinkage,creep, temperature, differential settle-ment, etc.) is significant, alone, or incombination with vertical loads

4.2.3.2 Conditions for using this method--Evaluation by using tests of structural models is consid-ered appropriate only if:

-- The material properties, nature andmagnitude of loading, structural boun-dary conditions, and physical details andconnections are capable of being realisti-cally simulated so as to result in anaccurate portrayal of the existing con-dition of the structural element(s) beingevaluated

-- The investigator is knowledgeable in theprinciples of structural modeling

-- The influence of adjacent structuralelements or whole structures can be ac-counted for in conducting the tests andevaluating the results

CHAPTER 5 -- THE EVALUATION

5.1 -- Analytical evaluationThe information gathered from the preliminary

investigation and material evaluations should be used todetermine analytically the safe load-carrying capacity ofthe structure or portion of the structure being evaluated.This chapter provides guidelines for performance of theevaluation, and criteria for interpreting the results of theevaluation.

5.1.1 Forms of analysis -- In the evaluation ofconcrete structures by analytical methods, “analysis” hastwo different meanings. One deals with finding the valuesof forces and moments which exist in the structure. Thesecond uses the characteristics of the structure ormember to predict how it will respond to the existingload effects.

A structure must be “analyzed” to determine the

bending moments, shear forces, axial forces, etc., at thesections which are believed to be critical. This analysisinvariably involves computations and calculations, per-haps using a computer. Most engineers will conduct thispart of the analysis using methods which assume that in-dividual members have linear and elastic material proper-ties, even though this is not strictly true for reinforcedconcrete. The alternative, “plastic analysis” is notroutinely feasible and requires special capabilities notfound in most engineering offices. However, this is not asignificant drawback, since an analysis done by elasticmethods provides a reasonable estimate for the values ofimportant load effects.

In the second form of analysis, an assumption ismade about the behavior of structures. For an evaluationof structural performance at service loads, it may bereasonable to assume that concrete and reinforcing steelbehave in a linearly, elastic manner. However, it is nec-essary to account for the fact that concrete has a rela-tively low tensile strength, and cracked section propertiesare often used. Where structural safety is the principalconcern, the strength of the member or structure must beestablished. The principles of strength design, as appliedin ACI 318 provide a basis for establishing a nominal ca-pacity for structural members. The average core com-pressive strength may be divided by 0.85 to arrive at theconcrete strength value to be used in strength calcu-lations (Bloem 1968).

5.1.2 Levels of analysis -- “Exact” or“approximate” analyses may be used in strength eval-uation.

5.1.2.1 Exact analysis -- Analysis based onexperimentally verified theories of structural mechanicsare useful under the following conditions:

-- Loading conditions for the building areknown with a high degree of certaintyafter examining existing data

-- Detailed structural engineering drawingsand material specifications for thebuilding are available, and the infor-mation given therein is believed to bereliable or has been confirmed or sup-plemented with data obtained by thecondition survey. For example:

1) Dimensions of the structure andits members can be determineddirectly by field measurements,and these can be used to estab-lish the dead loads of the struc-ture

2) The location, size, and depth ofconcrete cover of embedded re-inforcing steel can be deter-mined by field investigation


3) Material characteristics basic tothe analysis can be determined,or estimated reasonably, by theuse of destructive or nondestruc-tive tests

4) Estimates of the strength of thefoundations can be obtainedthrough consultations with foun-dation engineers and by conduct-ing appropriate soil tests

-- Sufficient data can be collected to makean adequate assessment of the existingphysical condition of the structure in-cluding estimation of the effects ofdistress, deterioration, and damage

5.1.2.2 Approximate analysis -- Use of ap-proximate methods of analysis requires considerable ex-perience with the type of structural system under eval-uation and its behavior. Most importantly, approximatemethods require the exercise of sound engineering judg-ment. Approximations must be applicable to the specificcircumstances. Two basic guidelines should be followed:

-- All assumptions necessary for completionof the structural analyses should beclearly documented. Particular careshould be taken to describe thoseassumptions made to reduce strength inaccounting for existing distress, deter-ioration, or damage

-- All assumptions necessary to conduct thetheoretical structural analysis should bemade to provide a conservative lowerbound for the safe load-carrying capacityof the structure

5.1.3 General considerations -- The assumed be-havior of the structure and the results of the theoreticalanalyses must be compatible with the observed behaviorof the structure. The analyses should consider fully, andmodel appropriately, characteristics of the structure suchas:

-- The effects of nonprismatic members onthe relative stiffness of components inthe structure

-- Torsional characteristics of structuralmembers

--

--

Two-way load response in slab systems

Column support and structural fixities interms of moment-rotation characteristics

-- Column base characteristics as influ-enced by soil conditions

Modifications may be made to the results of thetheoretical structural analyses to account for the anti-cipated future condition of the structure. These modi-fications should include full consideration for anyanticipated repairs and continuing maintenance of thestructure, as well as any future anticipated deteriorationof the structure.

5.1.4 Acceptance criteria -- The structure orstructural component being evaluated may be deemed tohave sufficient strength if the analytical evaluation clearlydemonstrates that the predicted design capacity of theelements under consideration satisfies the requirementsand the intent of ACI 318.

Where field work has established the actualmaterial strengths of steel and concrete; indicated thesize, location, and configuration of reinforcement; andidentified member and structural dimensions, uncertaintyabout the structure is clearly reduced. Some investigatorsbelieve that this supporting work can serve as justificationfor using a different capacity reduction factor 4 forevaluation, as opposed to design. There is a great poten-tial for developing this concept, but at present there is noconsensus or appropriate methodology. Experience andengineering judgment of the investigator are extremelyimportant in this case.

In case the analytical evaluation shows thestructure does not satisfy the intent of ACI 318, thebuilding official may approve a lower load rating for thestructure based on the results of the evaluation.

5.1.5 Findings of the analytical evaluation -- Threescenarios may describe the findings of an analyticalstrength evaluation:

1. Analyses show that the building orstructural element has an adequatemargin of safety according to the pro-visions of the applicable building code.In this case the design capacity (nominalcapacity multiplied by capacity reductionfactor 4) exceeds that required forfactored loads.

2. Analyses show that the design capacityis less than that required for factoredloads, but greater than required for ser-vice loads (load factors equal to orgreater than 1.0 for all load cases). Thissituation may be particularly difficult toresolve where there is no evidence ofstructural distress in the building orelement.

In this case the building or structuralelement is not adequate. Considerationmay be given to load testing the struc-


d

ture if this is agreeable to all parties in-volved. In some cases restricted use ofthe structure which limits the appliedloads in recognition of the computed ca-pacity may be permitted. In cases wherethe structure is only slightly understrength, engineering judgment of theparticular circumstances may indicatethat the structure can be used withoutfurther restriction.

3. Analyses show that the design capacityof the structure is less than required forservice loads under the applicablebuilding code. In such cases, the ownershould be notified and considerationgiven to the installation of shoring,severe restriction of use, or evacuationof the structure until remedial work canbe done.

5.2 -- Supplementing the analytical evaluation with loatests

5.2.1 Conditions for use -- In-situ load testing isrecommended only if all of the following conditions aremet:

-- The test results will permit rationalinterpretation of the structural capacityof the element to be tested

-- The influence of adjacent structuralmembers, components, or whole struc-tures can be accounted for in conductingthe tests and in evaluating the results ofthe tests. This influence includes fullaccounting of alternate load paths whichare available in the building

-- The structure can be monitored ade-quately and safely by appropriateinstrumentation so as to provide thenecessary data to make an evaluation ofthe structural capacity

-- The safety of all participants in the testand all passersby can be assured duringsetup and performance of the test

An analytical evaluation of some type shouldalways be done before conducting a load test. This evalu-ation may employ approximate methods. The analysisshould be performed to allow for a reasonable predictionof the performance of the structure during the load test.One should recognize that theoretical calculations forpredicting deflections of concrete structural elements arein many cases unreliable. Considerable care and engi-neering judgment are required when comparing cal-

culated deflections with those that actually occur duringa load test. Reports are available to assist the investigatorin calculating deflections of reinforced concrete structures (ACI 435.1R, ACI 435.2R, ACI 435.4R, ACI435.5R, ACI 435.6R, ACI 435.7R, ACI 435.8R).

5.2.2 Identifying the form of test to be conducted--Evaluation of structural adequacy may be performedusing analytical methods aided by one or both of thefollowing forms of in-situ load testing:

-- Static tests

-- Dynamic tests, using special test pro-cedures developed specifically for thecharacteristics of the structure to betested. Such procedures are beyond thescope of this report

5.2.3 General requirements -- The following gen-eral requirements are applicable to the process of con-ducting a load test:

A qualified investigator, acceptable tothe building official, should design anddirectly supervise and control the tests

A load test should not be made untilthat portion of the structure to be testedis at least 56 days old. Earlier testingmay be permitted if mutually acceptableto all parties involved. In such cases it isimportant to consider carefully the ageof the concrete in the structure as itrelates to the strength of that concrete

The structure or portion of the structureto be load tested should be loaded insuch a manner as to adequately test thesuspected source of weakness

Load tests that are conducted on envi-ronmentally exposed structures should beconducted at a time when the effects ofsunlight on the structure and themonitoring devices are minimized (i.e.,early morning, late evening, or at night)

Load tests on exposed concrete struc-tures should preferably be conducted attemperatures above 32 F (0 C)

The environmental conditions, especiallythe ambient temperatures should berecorded accurately at frequent intervalsduring the performance of a load test onenvironmentally exposed structures

5.2.4 Test loads-- The following guidelines may


be useful for selecting the type of test load or loadingdevice in conducting a load test of a concrete structure:

-- When the test load is applied by usingseparate pieces, such as iron bars, bricks,concrete block, etc., the pieces must beseparated throughout the duration of thetest to prevent arching action. The sepa-rate pieces or stacks of pieces shouldhave a largest base dimension less thanone-sixth of the span of the structuralelement being tested. These pieces orstacks should be separated by a clearlateral distance of at least 4 in. (100 mm)

-- If test loads are applied by using sepa-rate pieces, the pieces should be of uni-form shape and weight. The weight ofeach piece should not differ by morethan 5 percent from the average weight.The average weight should be deter-mined by weighing at least 20 piecestaken at random. If nonuniform load ele-ments are used, each separate pieceshould be measured (i.e., determine sur-face contact area), weighed, and markedappropriately

-- The weight of the loading elementsshould be easily measurable

-- The load devices should be easy to applyand readily removable

-- Hygroscopic materials should not beused as test load devices

-- Test load devices applied to slopingsurfaces must be securely anchored toprevent shifting. Load components,which may be applied to the structure,must be accounted for in all directions

-- It is usually preferable to apply test loadswith hydraulic or pneumatic devices be-cause of the ease of application andspeed of removal (unloading)

-- When using hydraulic or pneumatic load-application systems, it is necessary toprovide properly and safely for thereactions of those devices, except wherethese reactions are part of the loadingscheme. It is also necessary to insure thatthese loading devices will continue tofunction in a uniform fashion, even withsignificant deformation of the structureduring application of the test load.

--

--

--

If water, loosely sprinkled sand, or othersimilar materials are used for the testload, they should be contained withinsmallcompartments to prevent “ponding”effects or shifting of the test load duringsignificant deformation of the structurethat may occur while the test load isacting

The total accumulated test load shouldbe within 5 percent of the intended value

Arrangement of the test load shouldconsider the following:

1) The test load should be arrangedas close as possible to the ar-rangement of the load for whichthe structure was designed

2) If the test load cannot be ar-ranged as described above, itshould be designed and arrangedin such a fashion as to produceload effects in the structure sim-ilar to those that would be pro-duced by the design load

3) If uniform design loads are ap-proximated with converging(concentrated) load systems,such systems must be designedso that significant stress con-centrations do not occur at thepoints of load application

4) Consideration should be given indesigning the application of thetest load to produce maximumload effect in the area of thestructure being tested. This in-cludes use of checkerboard orsimilar type pattern loads

_5.2.5 Instrumentation-- The following guidelines

are applicable to installation of instrumentation systemsfor monitoring the performance of a structure or struc-tural element during a load test. Russell (1980) providesadditional background on field instrumentation.

-- Instrumentation should be provided formonitoring deflections, lateral deforma-tions, support rotations, support set-tlement or shifting, etc., during appli-cation of the test load

-- Strain measurements should be made onflexural members at critical locations


--

--

Deflection and strain measurementdevices should be duplicated in criticalareas

The acceptable error in instruments usedfor measuring displacements should notexceed 5 percent of the calculated theo-retical deformation, or 0.005 in. (0.13mm)

Measurement devices should be providedand mounted so that it is possible todetermine relative changes in the shapeof the structure or structural elementduring the test

Instrumentation should be protectedduring the load test from environmentalinfluences such as direct sunlight, sig-nificant temperature variations, and wind

All instrumentation should be installedin advance of the start of the load test toallow for determination of the effects ofdaily thermal changes on the deforma-tions of the structure and on the instru-ments themselves. If necessary, compen-sation factors can be developed for ap-plication to the data obtained from theload test

Deflection of structural members can bemeasured with electronic or mechanicaldevices, or with conventional surveyingequipment

Displacement transducers and resistancestrain gage are available and may allowrapid electronic collection of data froma large number of points. However, theirinstallation can be time consuming andcostly, particularly on sites exposed tothe weather

Mechanical devices, such as dial gages,are typically more reliable, but collectionof data can be slow, and requires thatsomeone enter into the structure duringperformance of the test, which can bedangerous. These devices are valuablefor measuring small deflections in stiffstructures

Large deflections can be easily measuredby suspending graduated scales from crit-ical points and reading them remotelywith a surveyor’s level

-- Deflection measurement devices shouldbe placed at the point(s) of maximumexpected deflection. Devices should alsobe placed at the supports to detectcolumn shortening, if deemed appro-priate by the investigator

-- Crack width can be measured by usinggraduated magnifying glasses, or “crackcomparators.” Their use during a loadtest is, of course, restricted for safetyreasons. If they are used, marks shouldbe placed at each point on the crackswhere readings are to be taken so thatsubsequent readings are taken at thesame positions

-- Crack movement (opening or closing)can be measured with dial gages, dis-placement transducers, or mechanicalstrain gages. Crack movement can alsobe measured accurately by using gagepoints and a mechanical extensometer

-- Thermometers or thermocouples shouldbe used to measure the ambient temper-ature during a load test. Temperaturereadings should be taken in all areas ofa structure that are affected by the loadtest. For structural slabs, thermometersshould be placed above and below theslab surface. Accurate records of vari-ations of sunlight should be maintainedfor roof slabs and other areas of thestructure which are exposed to directsunlight during performance of a loadtest

5.2.6 Shoring --Shoring should be provided priorto a load test, whether the whole structure or only aportion is involved, to support the structure in case offailure during the test. The shoring should be strongenough to carry the existing dead load and all additionalsuperimposed test loads on the portion of the buildingfor which collapse is possible. The effects of impactloading on the shoring, which is likely if a structure ormember fails during the test, should be considered in theselection of shoring elements. For horizontal members,shoring should clear the underside of the structure by notmore than the maximum expected deflection plus anallowance not to exceed 2 in. (50 mm). Similar arrange-ments should be made for other types of members. Inany case, shoring should not influence or interfere withthe free movements of the structure under the test load,and should be designed and constructed to protect allpeople working on, below, or beside the structure to betested, in case of excessive deformation or collapse.


5.2.7 Static load tests of flexural members5.2.7.1 Guidelines -- The following

guidelines are presented for conducting static load testsof flexural members:

-- Install shoring and instruments beforeany test load is applied

where

Take a series of base elevation readingsimmediately prior to the application ofthe test load, to serve as a datum formaking deflection readings on the var-ious elements of the structure during theload test

A load which simulates the effect of anyportion of the service dead load D whichis not already present should be appliedand should remain in place until afterthe load test has been declared com-pleted. This application of additionaldead load is most often done when loadtesting is performed during rehabilitationor before a structure has been com-pleted, and various partitions, ceilings,ductwork, etc., have not yet been in-stalled. Deflection readings should bemade immediately after this additionaldead load is applied. This additionaldead load should be in place for at least48 hr before additional increments of thetest load are applied

-- No portion of the test load which repre-sents live loads should be applied beforethe deflections due to the simulateddead load have effectively reached con-stant values

-- After dead load deflections havestabilized, existing cracks and otherdefects should be observed, marked, andrecorded

-- Immediately before applying any in-crement of the test load, the readings ofall measuring devices should be recorded

-- The portion of the structure selected forloading should be subjected to a totaltest load TL, including all dead loadsalready acting, equivalent to thefollowing:

TL = 0.85(1.4D + 1.7L)

D = dead loadsL = live loads

--

--

--

--

In continuous structures the test load TLshould be defined as the load whichproduces a load effect (bending moment,shear force, or axial force, as appro-priate) equal to 0.85(1.4D + 1.7L) at thesection being studied. Elstner et al.(1987) discuss the determination of testloads in reinforced concrete construction

The determination of the test loadshould include live load reductions aspermitted by the applicable generalbuilding code

The test load should be applied in thepredetermined pattern in at least fourapproximately equal increments. If ser-viceability is a criterion in the evaluationof the structure, an intermediate loadincrement equivalent to 1.0D + 1.0Lshould be included, so that the servicebehavior of the structure can beevaluated

The test loads should be applied withoutimpact and without causing vibration ofthe structure

After applying each increment of the testload, deflection measurements should bemade at equal time intervals until thedeflections attain effectively constantvalues. For this purpose, if the changebetween successive deflection readingstaken at least 2 hr apart does not exceed10 percent of the initial total deflectionrecorded for the current load increment,it may be considered that the deflectionshave effectively stabilized. If the mea-sured deflections reach or exceed pre-calculated values, the test should bestopped and only be continued with therecorded permission of the supervisingengineer

The investigator should inspect closelythe structure following application ofeach load increment for the formation orworsening of cracking and distress, aswell as for the presence of excessive de-formations, rotations, etc. The invest-igator should analyze the significance ofany distress and determine whether it issafe to proceed with the test

Load-deflection curves should be devel-oped during the load test for all criticalpoints of deflection measurements. Var-


ious types of electronic data-gatheringand plotting equipment are available toautomatically plot such curves. Thesecurves should be closely monitoredduring the load test. They are a valuabletool in determining the load-deflectionresponse of the structure, and for deter-mining if the structure is approaching itsultimate capacity

-- After the maximum test load has been inposition for 24 hr, deflection readingsshould be taken. The load should thenbe removed in decrements not greaterthan twice the increments used to applythe test load. Deflection readings shouldbe taken before and after each loaddecrement has been removed. Final de-flection readings should be taken 24 hrafter removal of the entire test load.

5.2.7.2 Criteria for evaluation of the flexural load test-- The procedures and criteria for inter-preting the data should be established completely beforea load test is conducted. If structural safety is the onlycriterion for the evaluation of the structure, and if thestructure under the test load does not show visible evi-dence of failure, it may be considered to have passed thetest if it meets the following criteria specified in ACI 318:

(1) If the measured maximum deflection ofa beam, floor, or roof is less thanLt

2/20,000 h; where Lt = span of themember (in.) under load test and h =the total depth of the member (in.). Thespan of a member is the distance be-tween centers of supports, or cleardistance between the supports plus thedepth of the member, whichever issmaller. In determining limiting de-flection for a cantilever, Lt should betaken as twice the distance from thesupport to the end, and the deflectionshould be adjusted for movement of thesupport

2) If the measured maximum deflection ofa beam, floor, or roof exceeds Lt

2/20,000 h, the deflection recovery within24 hr after removal of the test loadshould be at least 75 percent of themaximum deflection for nonprestressedconcrete, or 80 percent for prestressedconcrete

Note: “Visible evidence of failure” includescracking, spalling, crushing, deflections,or rotations of such a magnitude and ex-

tent that it is obviously excessive and notcompatible with the safety requirementsfor the structure

Nonprestressed concrete construction failing toshow 75 percent recovery of deflections may be retestednot earlier than 72 hr after removal of the first test load.The portion of the structure which is retested should beconsidered satisfactory if:

-- There is no visible evidence of failure inthe retest, and

-- Deflection recovery after the retest is atleast 80 percent of the maximum deflec-tion in the second test

If serviceability is a criterion, the deflectionscaused by the test load corresponding to 1.0D + 1.0Lshould not exceed that stipulated prior to the test. Thesignificance of any cracks should be considered.

If the structure fails the load test on the basis ofthe deflection criteria, but shows no evidence of struc-tural or material failure, either all necessary repairs orchanges should be made to make the structure adequatefor the rated capacity, or a lower rating should be estab-lished. No retesting of a structure, or any portion thereofwhich has previously failed a load test, should be permit-ted, unless, appropriate structural repairs and strength-ening are employed to upgrade the structure.

5.2.8 Static load tests of elements in shear -- Loadtests to evaluate the shear capacity (see ACI 426R) ofstructural elements are not recommended except in unu-sual circumstances. This recommendation is due to theuncertainty associated with the brittle and sudden char-acteristics of shear failures. A great deal of reliance isplaced on the judgment of the supervising engineeringconducting a load test for shear capacity. Each test isunique in terms of the characteristics of the structuralelements being evaluated. Therefore, specific guidelinesfor conducting such tests cannot be simply listed as forload tests of flexural members. However, the followingguidelines are presented for consideration by the investi-gator who determines that a load test for evaluation ofshear capacity must be conducted:

-- The structure must be thoroughly ex-amined prior to the test. It is importantto establish the concrete strength and theshear reinforcement details, as variationsin these items greatly impact on theshear capacity of a structural element

-- The test load should in no case exceed0.85(1.4D + 1.7L)

-- The load test should be preceded by astructural analysis to closely predict the


performance of the structure under ap-plication of the test load

-- Shoring of the structure is imperative.Provide shoring similar to that discussedfor testing flexural members

-- Instrumentation of the structure shouldconcentrate on crack width monitoringin addition to deflections

-- The critical components of the structuremust be monitored continuously duringthe test

-- Acceptance criteria for the load testmust be developed based on a mutualunderstanding of the investigator and thebuilding official. Such acceptance criteriawill likely be based on crack formationand movements at and along existingcrack planes

5.2.9 Interpretation of load test results -- Con-siderable engineering judgment must be exercised in de-veloping an appropriate interpretation of the results of aload test conducted on a concrete building, or elementswithin the building. Confusion often arises when a con-crete structure, which is believed to be deficient, passesa load test. This confusion, or perhaps misunderstanding,may be the result of any of the following reasons:

-- Many concrete structures have been de-signed conservatively. There are anumber of reasons for .a high degree ofconservatism in reinforced concrete con-struction. These include the use of sup-plemental reinforcing steel placed arbi-trarily in the structure to minimizecracking, providing larger areas of rein-forcement than required by calculationwhen selecting bars, use of conservativedesign theories, overestimation of deadloads, and inaccurate modeling ofboundary and support conditions

-- Actual concrete compressive strengthsare often greatly in excess of thespecified design strengths

-- The structural analyses do not accuratelymodel the load-sharing characteristics ofthe structure

The structure is repaired or strengthenedprior to the load test

CHAPTER 6 -- REFERENCES

6.1 -- Recommended references

American Concrete Institute (ACI)201.1RR Guide for Making a Condition Survey of

Concrete in Service201.2R207.3R

209R

216R

Guide to Durable ConcreteGuide for Evaluation of Concrete in ExistingMassive Structures for Service ConditionsPrediction of Creep, Shrinkage, and TemperatureEffects in Concrete StructuresGuide for Determining the Fire Endurance ofConcrete Elements

222R224R224.1R

Corrosion of Metals in ConcreteControl of Cracking in Concrete StructuresCauses, Evaluation, and Repair of Cracks inConcrete Structures

228.1RR In-Place Methods for Determination of Strengthof Concrete

309.2R

318

Identification and Control of Consolidation-Related Surface Defects in Formed ConcreteBuilding Code Requirements for ReinforcedConcrete

318R Commentary on Building Code Requirements forReinforced Concrete

362R426R435.1R435.2R435.4R

435.5R435.6R

435.7R

435.8R

442R444R

State-of-the-Art Report on Parking StructuresShear Strength of Reinforced Concrete MembersDeflections of Prestressed Concrete MembersDeflections of Reinforced Concrete MembersVariability of Deflections of Simply SupportedReinforced Concrete BeamsDeflections of Continuous Concrete BeamsDeflection of Two-Way Reinforced ConcreteFloor Systems: State-of-the-Art ReportState-of-the-Art Report on Temperature-InducedDeflections of Reinforced Concrete MembersObserved Deflections of Reinforced ConcreteSlab Systems, and Causes of Large DeflectionsResponse of Buildings to Lateral ForcesModels of Concrete Structures -- State of the Art

American National Standards Institute (ANSI)A58.1

ASTMA 370

C 39

C 42

C 597

C 803

Building Code Requirements for MinimumDesign Loads in Buildings and Other Structures

Standard Method and Definitions for MechanicalTesting of Steel ProductsStandard Test Method for Compressive Strengthof Cylindrical Concrete SpecimensStandard Method of Obtaining and TestingDrilled Cores and Sawed Beams of ConcreteStandard Test Method for Pulse VelocityThrough ConcreteStandard Test Method for Penetration


C 805

C 823

C 856

C900

D 4580

E 122

Resistance of Hardened ConcreteStandard Test Method for Rebound Number ofHardened ConcreteStandard Practice for Examination and Samplingof Hardened Concrete in ConstructionsStandard Practice for Petrographic Examinationof Hardened ConcreteStandard Test Method for Pullout Strength ofHardened ConcreteStandard Practice for Measuring Delaminationsin Concrete Bridges by SoundingRecommended Practice for Choice of SampleSize to Estimate the Average Quality of a Lot orProcess

International Conference of Building Officials (ICBO)Uniform Building Code

Recommended references are available from:

ACI

ANSI

ASTM

ICBO

American Concrete InstitutePO Box 9094Farmington Hills MI 48333-9094

American National Standards Institute, Inc.1430 BroadwayNew York NY 10018

ASTM1916 Race StreetPhiladelphia PA 19103

International Conference of Building Officials5360 South Workman Mill RoadWhittier CA 90601

6.2 -- Cited references

Bares, R., FitzSimons, N. (1975), “Load Tests of BuildingStructures,” Journal of the Structural Division, Pro-ceedings ASCE, V. 101, No. ST5, May, pp. 1111-1123.

Bloem, Delmar L. (1968), “Concrete Strength in Struc-tures,” ACI JOURNAL, Proceedings V. 65, No. 3, Mar., pp.176-187.

Chabowski, A.J., and Bryden-Smith, D. (1979), “A SimplePull-Out Test to Assess the In-Situ Strength of Con-crete,” Concrete International: Design and Construction, V.1, No. 12, American Concrete Institute, Dec., pp. 35-40.

Concrete Reinforcing Steel Institute (1981), “Evaluationof Reinforcing Steel Systems in Old Reinforced ConcreteStructures,” Schaumburg, Ill., 16 pp.

Dixon, D. (1987), “Analysis of Cover Meter Data,” Com-puter Use for Statistical Analysis of Concrete Test Data,

ACI SP-101, American Concrete Institute, Detroit, pp.47-64.

Elstner, R.C.; Gustafson, D.P.; Hanson, John M.; andRice, Paul F. (1987), “Application of ACI 318 Load TestRequirements,” CRSI Professional Members’ Bulletin, No.16, Concrete Reinforcing Steel Institute, Schaumburg,Ill., Nov., 11 pp.

FitzSimons, N., and Longinow, A. (1975), “Guidance ForLoad Tests of Buildings,” Journal of the StructuralDivision, Proceedings ASCE, V. 101 , No. ST7, July, pp.1367-1380.

Guedelhoefer, O.C., and Janney, J.R. (1980), “Evaluationof Performance by Full Scale Testing,” Full-Scale LoadTesting of Structures, ASTM STP 702, W.R. Schriever,Ed., ASTM, pp. 5-24.

Harris, H.G. (1980), “Use of Structural Models as anAlternative to Full Scale Testing,” Full-Scale Load Testingof Structures, ASTM STP 702, W.R. Schriever. Ed., pp.25-44.

Ivanyi, Milos (1976), Discussion of “Load Tests ofBuilding Structures,” Journal of the Structural Division,Proceedings ASCE, V. 102, No. ST6, June, pp. 1260-1261.

Mailhot, G.; Bisaillon, Al; Carette, G.G.; and Malhotra,V.M. (1979), “In Place Concrete Strength: New PulloutMethods,” ACI JOURNAL, Proceedings V. 76, No. 12,Dec., pp. 1267-1282.

Malhotra, V.M. (1976), Testing Hardened Concrete: Non-destructive Methods, ACI Monograph No. 9, AmericanConcrete Institute, Detroit, 204 pp.

Malhotra, V.M. (1977), “Concrete Strength Requirements-- Cores Versus In-Situ Evaluation,” ACI JOURNAL,Proceedings V. 74, No. 4, Apr., pp. 163-172.

Mather, K. (1978), “Petrographic Examination,” Sig-nificance of Tests and Properties of Concrete and Concrete-Making Materils, Part II, Tests and Properties of Concrete,ASTM STP 169B, pp. 132-145.

Mielenz, R.C. (1978), “Petrographic Examination,” Sig-nificance of Tests and Properties of Concrete and Concrete-Making Materials, Part III, Tests and Properties of ConcreteAggregates, ASTM STP 169B, pp. 539-572.

Mindess, S., and Young, F. (1981), Concrete, PrenticeHall, Inc., p. 671.

Peterson, C.G. (1984), “LOK-test and CAPO-test Devel-opments and Their Applications,” Proceedings, Institutionof Civil Engineers (London), Part 1, 76, May, pp. 539-


549.

Prestressed/Precast Concrete Institute (1985), PCI DesignHandbook, 3rd Edition, Chicago, 212 pp.

Sansalone, M., and Carino, N.J. (1986), “Impact Echo, AMethod For Flaw Detection in Concrete Using TransientStress Waves,” Report No. NBSIR 86-3452, NationalBureau of Standards, 234 pp.

Sansalone, M., and Carino, N.J. (1989), “DetectingDelaminations in Concrete Slabs With and WithoutOverlays Using the Impact Echo Method,” ACI MaterialsJournal, V. 86, No. 2, Mar.-Apr., pp. 175-184.

Raths, C.H., and Guedelhoefer, O.C. (1980), “Correlationof Load Testing With Design,” Full-Scale Load Testing ofStructures, ASTM STP 702, W.R. Schriever, Ed., ASTM,pp. 91-113.

Russell, H.G. (1980), “Field Instrumentation of ConcreteStructures,” Full-Scale Load Testing of Structures,ASTM STP 702, W.R. Schriever, Ed., ASTM, pp. 63-77.

Sabnis, G.M.; Harris, H.G.; White, R.N.; and Mirza, M.S.(1983), Structural Modeling and Experimental Techniques,Prentice-Hall Inc., Englewood Cliffs N.J., 585 pp.

Snell, L.M.; Wallace, N.; and Rutledge, R.B. (1988),“Locating Reinforcement in Concrete,” Concrete Inter-national: Design and Construction, V. 10, No. 4, AmericanConcrete Institute, Apr., pp. 19-23.

Stone, W.C., and Carino, N.J. (1983), “Deformation andFailure in Large-Scale Pullout Tests,” ACI JOURNAL ,Proceedings V. 80, No. 6, Nov.-Dec., pp. 501-513.

This report was submitted to letter ballot of the Committee andapproved according to Institute procedure.