54.- Miscellaneous Reinforced Brick Masonry Structures

by J. C. GROGAN

Sou/hem Brick & Ti/e Man/lfaclllrers Associa/ioll, Atlamo, Georgia

ABSTRACT

Some struclures in lhe USA, pri­marily fhose olher Ihall buildings, which have utilized reinJorced brick masollry are described and i/Iustrated. Building code requiremellls, desigl1 standards, design procedures, COIl­structiol1 melhods and COS(S are discussed.

Constructions en Mafonnerie en Brique Renforcée de Types Divers

VerscJliedene Konstruktionen be~ wehrten Ziegelmauerwerks

Quelques cons/ruetions aux E/als­Unis, principalement celles qui 0111

wilisé des maçolllleries ell brique renforcée à I' exclusiol1 des immellbles 50111 décrites. L'artic/e cOl1tienl une disClIssioll SUl' les exigences dll code de construcfion, ainsi que sur les "ormes, procédés, méfhodes el COÚls de conSfrUClion. L'ar/icle conliem égale­mell/ des mustrafiolls représenfal1f Wl

cerraillllombre de ces cOl1structions de types diverso

Einige Konstruktiollen ;n den USA , iibcrwiegend keine Gebõude, bei denell bewehrtes Ziegelmauerwerk ver­lVendel wurde, sillll beschrieben und abgebildet. Baugesetzliche Erfor· dernisse, Enlwurfs-Normen um/ -Verjahren sowie KonstruktioJ7sme­thoden ""d die Koslell werden eror/erl.

1. INTRODUCTION In 1813, Mare Isambard Brunel proposed theembedment of iron reinforcement in a brick masonry chimney in order to inerease its st rength , and he is thus eredited wit h the invention of reinforeed briek masonry (RBM). Invented almost half a eentury before reinforeed eon· crete, RBM in the modern sense is, however, a relatively new type of eonstruetion in the USA. It was not until 110 years after the first use of RBM by Brunel that the brick manufacturers and structural engineers in America beca me interested in this type of construction .

This interest was initiated by the publieation by BREBNER,l in 1923 , of the results of an extensive in­vestigation of the performance of RBM structmal members. In order to create greater interest in RBM in the USA, the brick manufactmers, through Iheir association and research foundation, sponsored more research. They also appoinled a Committee on Rein­forced Brick Masonry to suggest and correlate research work to establish design theories and procedures. This effort is lhe basis for lhe currenlly accepted design and eonslruclion praclices for RBM in lhe USA. Since then much additional dala have been obtained through research, construction experience and the performance of slructures . The early history of RBM is reported in greater detail elsewbere. 2

The original tesl data and subsequent investigations indicated that the structural performance of RBM is analogous to that of reinforced concrete and the pro­cedures used in calculations of stresses and deftection in reinforced concrete flexural members (working slress design) can be used in lhe caleulations for similar RBM members. The design procedure for an RBM fiexur al member is, as for eonerele, based on the slraight·line theory of stress distribution which, in turn, is based 00

the assumplions thal a seetion that is plane before bending remains plane after bending, the moduli of elasticity of the masonry and of the reinforcement remain constant, the reinforcement is completely sur­rounded by and bonded to the masonry, and the lensile forces are resisted only by the tensile reinforcemenL

327

Therefore, the designer who is familiar with the design methad af lhe transformed section for co ncrete, that is , the transforming of a com posite steel and concrete section into its equivalent in the one material , concrete, and solving as a homogeneous section, can readily design RBM flexural members by the method of trans­formed section when given lhe alIowable stresses and modulus of elasticity of the masonry. The design procedures for compression members are also based, for the most part, on elastie theory wilh the a lIowable load modified for slenderness. The method of modifying the alIowable load differs lO some degree in lhe various design standards.

There are, in the USA , essentialIy two sta ndards on the requirements for the design of reinforced masonry. The Buildillg Code Reql/irel1lellts for Reinforced Masollry , American National Standard A41.2- 1960, by the Ameri· can National Standards Institule Inc. (formerly the United Slates of America Standards Institute Inc.) is a complete code af minimum requirements for rein­forced masonry construetion ulilizing both holIow and solid masonry units. It includes definitions and require­ments for materiais and structural designo The BI/ildillg Code Requirementsfor EIIgilleered Brick Masonry, SCPI­August 1969, is a complete code of minimum require· ments for the rational design and construction of brick masonry (solid cIay masonry unils only) both plain (non-reinforced) and reinforeed. It also incIudes defini­tions and requirements far materiais and structural design plus construction requirements. The August 1969 edition is the second edition of the SCPI (Structura l Clay Produets Institute) Standard. It contains additional requirements and refinements lO the first edition dated May 1966.

These standards are written in such a form that lhey may be incorporated verbatim or adopted by reference in a general building code. Three of the fom model building codes utilized in the USA ; the Basic Buildillg Code, lhe SOl/tilem Stalldard Buildillg Code, and the Natiollal BI/i1ding Code, accept by referenee bOlh the ANS-A41.2- 1960 and the SCPI Standard. The fourth

328 Miscellaneous Reinforced Brick Masonry Structures

model building code, lhe Uniform Building Code, con­lains provisions wilhin lhe body of lhe code for lhe design of reinforced masonry. MoSl local building codes (State, Counly, etc.) are based on one of lhe four medel codes and, therefore, contain provisions for the use ofRBM.

The melhod of conslruclion of RBM is very similar to that af non-reinforced brick masonry with the ex­ceplion of lhe placing of lhe reinforcing steel and the grout. AIlhough in some cases lhis portion of lhe work is claimed by olher trades, in lhe majority of lhe projects in lhe USA utilizing RBM the bricklayer lays lhe brick, places lhe steel and grouts the member. Of lhe lwo melhods of construction , low-lift and high-lifl grouting, there has been a trend in recent years toward the use af pumping equipmenl and lhe high-lifl technique. In some instances concrete buckets and tremies are used wilh high-lift grouting. Although not used to lhe same degree as in the past, low-lift grouting is still in lIse but primarily for small projects or for isolated RBM members.

2. EXAMPLES OF THE USE OF REINFORCED BRICK MASONRY

Reinforced brick masonry is not promoted in the USA as a competitive material to reinforced concrete ar structural steel sections for ali applications. However, in most instances where the savings due to a built-in finish are considered, RBM can provide an economical solution. An example of this is the RBM girder used in the construction of SI. Hedwig's Church in SI. Louis, Missouri. This church was designed by J. T. Golabowski (architect) and William A. Herrman (structural eng­ineer) and built in 1957. The design incorporated a modified clerestory Ihat extends the length of the church from ffaot to rear. In arder to keep the nave and sanc­luary clear of interior columns, the side walls of the clerestory were supported only at the ends. Exposed bricks were used extensively both outside and inside the church. Structural members, 65 ft long, were required that would have a brick finish on both sides, and carry the roof load from above and part of the loads from the side roofs .

Three types of girders were considered :

1, Prestressed concrete girders. These were eliminated because, wilh masonry on both sides, they would be 100 thick for the desired appearance.

2. Brick-encased steel plate girders. These would have been end-supported on steel columns buill inlo the masonry walls .

3. RBM girders. These would be supported on RBM columns buill integrally with lhe front and rear masonry walls.

Contractors in the St. Louis area were not at lhat time familiar wilh RBM construction, so alternate bids were taken on both the brick-encased plate girder and RBM girder systems. Ali ten bidders indicated savings would be made Wilh lhe RBM system. The successful contractor, C. Rallo Contracting Co. Inc., reported that the lotai cost of lhe two RBM girders and supporting columns was only $8000 ; columns alone cost 3600. The bid figures show two steel girders and four steel columns would have cost $8200 without lhe brick encasing.

The 65-ft RBM girders are 17-in. thick and 10-ft 2i-in. deep. The depth was dictated by the clereslory proportions. Six No. 9 and six No. 10 bottom bars were used for tensile reinforcing. Two No. 7 and Iwo No. 8 bars provided top reinforcement. Ten No. 4 stirrups were placed at each end of the girder. The morlar was a 1:~:4t cement:lime:sand mixo A 1:3 cement:sand mix was used for the grouting. Where the grout space was more than 2-in. wide pea gravei was added to lhe grou!. During the construction of the two girders, the only form needed was a work scaffold seI to lhe bottom elevalion of the girder. Soffit bricks were laid out first with the bOllom steel being placed next. Stirrups were then added and tied near lhe tops for stability. After lhat, it was just a malter of laying brick and placing grout in increments of lhree or four courses (Figure I).

~ -~';;s.., - _ ~_ ... ~ ~ ~ '.---:; -'~"-

FIGURE 1- 51. Hedwig's Church: 65-ft RBM girder under construct íon.

A building permil was issued for the job with a proviso thal one of the girders be successfully load­tesled afler complelion. The specification required a tesl load equal lo the design dead load plus twice the live load, in accordance with the Building Code Require­ments for Reinforced Concrete of the American Con­crete Institute. Test loads of 67 500 Ib were applied at each third point of the girder. This was in addition to the dead load of bOI h lhe girder and lhe concrete roofs it supports. Pittsburgh Testing Laboratory performed the tesls with calibrated hydraulic jacks through a fulcrum system. All deftection measurements checked out within the allowable limits. After 24 h under full load , the maximum girder deftection was only half the amount allowed by lhe test provisions. Recovery after load release was 94 %. J

More recently, Griffey & Slroll Associates (architects) and William Blanton (structural engineer) utilized RBM in the design of the Alexander Art Center in Athens, Wesl Virginia, which was completed in 1968. The designers were confronted with the problem of spanning over the maio auditorium proscenium opening. A structural member having a fire-resistant brick finish was required to support steel trusses which, in tum, support the roof loads over a clear span of 39 ft and a monorail system spaced I ft on centre connected to the boltom chord of the trusses. The monorails provide a flexible system for lighting and scenery movement. The encasing operations for a steel girder would require scaffolding similar to that used in the construction of RBM girders. Also, RBM was being utilized on lhe project in retaining walls and in load-bearing walls.

J. C. Grogan 329 These factors resulted in the final selection of an RBM girder spanning 50 ft 8 in. to solid brick masonry columns on either side of the proscenium. The RBM girder is 24-in. thick and 8-ft 21·-in. deep. Ten No. II bars provi de the tensile reinforcement and two No. 5 bars are located at the topo The stirrups are No. 5 bars . The girder was constructed of 80001bf/in2 brick and a I : *: 3 cement: lime: sand mortar (see Figure 2).

FtGURE 2- Alexander Art Center: 50·ft 8·in. RBM girder under construction.

The Alexander Arl Center also includes an RBM girder which spans a 24-fl stage. This girder is loaded similarly to lhe 50-ft 8-in. girder plus an additional load of a prestressed concrete roof which spans 46 ft 6 in . The RBM girder is 16-in. thick and 4-ft 9i-in. deep. Two No. 10 and four No . 9 bars provi de the tensile reinforcement and tWQ No. 5 bars are located at lhe topo The stirrups are No. 4 bars. These and other examples of RBM girders are reported in greater detail elsewhere.4

During the first part of 1970 the offiee of Southern Briek & Tile Manufaeturers Assoeiation (SBTMA) was involved in the decision by an Atlanta, Georgia structural engineer to use several RBM lintels in plaee of the orig­inally proposed struetural steel Iintels. The project was the Allanta Auto Auetion building designed by the arehiteetural firm of Thompson- Ventulett & Stainbeek and the struetural engineering firm of Lagerstrom. A problem arose with the deeision to build the exterior non-Ioadbearing cavity wall of the one-storey building prior to the completion of the steel frame . This decision was made to expedi te the eompletion of the building since the bricks were available, but there was a delay in the shipment of the structural steel. The problem resulted from the fact that the exterior walls contained a number of openings ranging in size up to approximately 27 f1. The structural engineer had designed the lintels for the smaller openings, the largest of which weighed ap­proxjrnately 35 Ib per ft and was composed of two angles and a spacer plate. However, lhe engineer was having difficulty providing a lintel for the 27-ft opening which would accommodate the architectural detail. A meeting was called by the architect in order to solve this problem, and included the architect, the structural engineer, the general contractor, the mason contractor and Mr Z. A. Snipes of SBTMA. Mr Snipes suggested the use of RBM for ali of the lintels. The designers thoughl lhat RBM would probably be the simplest solution but expensive. This led to a discussion on lhe comparative cost between the steel and RBM system. The general contractor estimated the cost of the fabricated-steel Iintel at ap-

proximately 5400 per tono The average cost of the structural steel for the rest of the job was approximately 5200 per ton, but since the lintels would be a special arder, require shop fabricating and would necessitate a crane on the job at an unscheduled time, it was felt that the higher cost was more realistic. Assuming the weight of the lintel for the 27-ft span to be in the same range as the lintel for the next smaller opening, 35 Ib per ft , the cost of the structural steellintel would be a minimum of 83·50 per linear ft and could go as high as 57·00 per linear ft. Since the cavity wall section over the opening is required with both systems, steel and RBM , the additional cost items for the RBM Iintel include only the grout , the reinforcing steel , the shoring and the necessary treatment to produce fini shed morta r joints on the soffit of the member. A 4-ft-deep RBM section was assumed which, it was considered , would eliminate fhe need for stirrups and reduce the amount of tensile reinforcement required . The grout required to Im the nominal 4-ft by 21-in. core of the lO-in . cavity wall , I ft' per linear ft including waste, was estimated by the general contractor at $27 per yd' in place or 51·00 per ft '. The required reinforeement was estimated bythe structural engineer at 2 to 3 Ib per linear foot at an in-plaee cost of approximately 10 to 15 cents a Ib. The mason contrac­tor estimated the cost of shoring at a maximum of SI·OO per linear ft and the joint treatment at approxi­mately 5 cents per linear fI. The total cost, therefore, of converting the cavity wall over the opening to an RBM beam was estimated at $2·50 per linear ft:

Grout I ft3 per linear ft at SI-00 per fl 3 Reinforcing sleel:

3 Ih per linear fI at SO-15 per Ih Shoring Morlar joint treatment

TOlal

SI -OO per linear ft

80-45 per linear ft SI -00 per linear ft 80-05 per linear ft

S2-50 per linear ft

It was therefore agreed that not only would the RBM section be the simplest solution, but it would also be the most economical.

Earlier it was stated that when savings due to built-in finish are considered, RBM can provide an economical solution. However, one project in which RBM was bid in competition with reinforced concrete as strictly a structural member was the United of America Building in downtown Chicago (Figure 3). The forty-storey building, designed by the firm of Shaw Metz & Associates of Chicago, IIIinois, was completed in 1962. The building is a structural steel frame with the columns encased in concrete. The base design provided reinforced concrete piers, 4-ft wide, as lhe backup for the Chcrokcc White Georgia marble exterior finish . The alternate piers engage the steel columns. However, the architect also submitted sketches with the bidding information showing the piers which were not engaging the steel colurnns designed in RBM. Ali piers were required to be finished on the interior with metallath and plaster. The successful contractor, A. L. Jackson & Co., used the RBM alter­nate. The RBM piers, which span between fioor and ceiling beams, a distance of approximately 10 ft, are 4-ft wide and 9-in. thick. They are built with two wythes of nominal 4-in. brick. The reinforcing steel , which consists of four vertical No. 4 bars and No. 3 horizontal bars at about 2 ft on centre, is contained in the collar join!.'

One of the most effective uses of RBM as a fiexural

330 Miscellaneous Reinforced Brick Masonry Structures

FIGURE 3- United of America Building: under construction.

member is in the construction Df retaining walls designed to withstand lateral earth pressure. Adding reinforcing steel allows the designer to greatly reduce the mass of a brick masonry gravity-type wall and, hence, the cost of such wall. At the same time it is still possible to provide a wall which when fini shed \ViII have an integral surface, the colour and texture of which \ViII harmonize with other structures in the area (Figure 4). RBM retaining walls have been used to a great extent in certain parts of the USA and the Structural Clay Products Tnstitute has available a design aid6 which contains design details and lables to assist the engineer in developing an economical and safe design for a given location and set of conditions.

Another application of RBM is in garden walls and fences. Kettler Bros. Inc. utilized RBM fences at Mont­gomery Village, a planned community in Gaithersburg, Maryland (Figure 5). To achieve privacy between houses, \Vhich were luxury homes built in compact clusters (h ouses as little as 5 ft apart), Kettler constructed high fences creating the community courtyard. These rences were 4-in. thick, one-brick wythe, reinforced with

FIGURE 4-Buffalo Presbyterian Church: RBM retaining wall.

~.

FIGURE 5- Monlgomcry Village: RBM fences.

prefabricated joint reinforcement and spanned bctwecn RBM piers, 12-io. square.'

3. CONCLUSIONS

It is the purpose of this paper to review so me applications in the USA of RBM miscellaneous structures and structural members. RBM bearing-\Vall buildings were not discussed since it was assumed these would be covered in great detail in other papers. Various other applications of RBM such as sanitary structures, swimming pools, drainage canais, culvert end walls and precast RBM panels which can be found in lhe USA are also not covered. Discussions of most of these appli­catioos can be fouod in the Technical Notes on Brick and Tile Construction published by lhe Slructural Clay Products Institute.

REFERENCES 1. BREBNER. A., Notes on Reinforced Brickwork. Government of

India, Public Works Department, Tech. Paper No. 39,1923. 2. PLUMMER, H . C. and BLUME. J. A., Reinforced Brick Masonry

and Lateral Force Design. Structural C1ay Products Institule , 1953.

3. ANoN. Brick Girders Spanning 65 feet. Engllg. News. Rec. July3 1, t958.

4. STRUCTURAL CLAY PRODUCTS l NsTITuTE, Tech. Notes on Brick and Tile Construction, 17 M. July, 1968.

5. ANoN, Pier Design Alternate Lets Bidder Cu! Costs. Dl/ild. COl/s/r. June, 1961

6. GROGAN. J. C. and PLUMMER. H . c., Reinforced Brick Masonry Retaining Walls. Struclllral Clay Prodllcts lnstitule, August, 1965.

7. STRUCTURAL CLAY PRODUCTS I NSTITUTE. Tech. Notes on Brick and Tile Conslruction, 29A, rcvised Nov. 1968.