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6/11/2008
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Engineer’s Responsibility for Detailing Reinforced Concrete Structures
Neal S. Anderson, PE, SE, FACIVice President of Engineering
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Dilbert !!
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What is Rebar Detailing?
The art of placing reinforcing in a concrete member to follow the design intent
Thou shall follow the design & placing rules of ACI , AASHTO, and CRSI . . . .
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Why is Detailing Important?
It is how the project gets builtNot everything gets caughtIt makes the SE thinkIt makes the SE thinkWhen problems occur . . . » Delays in the project» Cost implications» Possible finger pointing
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U.S. Detailing Practice
Structural Design – A/EStructural Design – A/E
BuildingBuilding BridgeBridgeBuildingBuilding
Drawings / Specs
Drawings / Specs
Placing DrawingsPlacing
Drawings
BridgeBridge
Structural –Placing
Drawings
Structural –Placing
Drawings
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Detailing of Rebar in Concrete
BuildingsBridgesRole of SE & DetailerRole of SE & DetailerTwo Case StudiesWhat can we (SEs) do?
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Buildings
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Building Deliverables
Drawings» Structural» ArchitecturalProject Specifications» Section 03200 - ReinforcingGeneral Notes
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ACI 318 – Building Code
Dawn of timeCurrent version is 2008Governs building gdesignContains info on reinforcing
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ACI 318, Section 1.2.1 –Drawings, Details & Specs
Specified strength / grade of reinforcementSize and location of all » Structural elements» Reinforcement» Anchors
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Reinforcement anchorage lengths Lap splices » Location
ACI 318, Section 1.2.1 –Drawings, Details & Specs
» LengthMechanical & welded splices» Type» Location
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Building Drawings
Beams / girdersColumnsWallsWallsFoundationsPlans, sections, & details
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Building Drawings
Beam / girder table
Many elements are shown TYPICAL
gColumn schedule
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Typical Beam Detail
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umn
Det
ails
Typi
cal C
olu
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Building Drawings
Structural (& arch) drawingsMany typical details» chedules tablesS ,» Bar size & spacing (#5 @ 12” o.c.)Detailer’s role» Placing plans development» Bill of material for fabrication
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Bridges
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Bridge Deliverables
Drawings» Structural – rebar placing» Rebar schedules» CivilGeneral / structural notesProject special provisions» Rebar covered in Std Specs.
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Plans – Bar Schedule
A. Bar ID (unique)B. Quantity (or #)C. Rebar sizeD Total lengthD. Total length
(including bends)
E. Depiction of shape
A B C D E
(E) = Epoxy coated19
Plans – Bend DiagramsStirrups
L-bars
Straight with 180° hook
Bar ID from schedule 20
Rebar Markings for Deck
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Plans – splices
Bridge deck plan
Contact lap splice lengthSplice
locations & length
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Bridge Drawings
Structural & placing drawingsVery prescriptive by DOT» a E b E bars ~ deck( ) & ( )» h(E) & v(E) bars ~ wallDetailer’s role» Check engineers layout» Bill of materials
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Buildings vs. Bridges
Buildings - Private
Bidding package» Lump sum
Furnish and install
Bridges - Public
Bidding package» Unit prices» ItemizedFurnish and install
Rebar lumped inChange ordersRFIs
Unique nature - not cookie cutter
» Itemized
Rebar» Weight ~ plain & (E)» Placing unit
Not many COs / RFIs
Bridges are more typical
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Detailing Practice – The Roles
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Detailing Responsibilities
Admittedly, this is more focused on the building sideWhat are the issues / concerns?Why worry?» Costs» Project delays» Structural issues
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Meet Mr. Detailer . . .
Detailer» Technically trained individual » Interprets contract
documentsResponsible for» Placing plans development» Bill of material for fabrication
They are not design professionals
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Meet Mr. SE . . .
Structural Engineer» BSCE, MSCE, or PhD» FE (EIT), PE, or SE
Responsible for» Design of concrete» Preparing design plans &
specifications» Placing / shop drawing review» Anything else to ensure our
designs get built properly
We are licensed design professionals28
What are the perceived “normal” relationships between SE and detailer?
SE Point of View . . . .
How can this relationship be improved?How do we solve the problems?Who takes the lead to avoid problems?
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SE Relationship Perception
Detailer prepares placing drawings» SE and architectural drawings» CRSI “Manual of Standard Practice”
SE provides background drawings toSE provides background drawings to Detailer to “assist” in starting plans » Detailer verifies their scale & redraws if
necessarySE expectations:» Detailer to be properly trained or » Working under the supervision of an
experienced detailer 30
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SE Relationship Perception
SE expects interpretation questions during the preparation stage & prior to reviewing placing drawings» SE will provide quick response to» SE will provide quick response to
questionsPlacing drawings to be complete with unanswered issues cloudedSE will review promptly and clearly mark comments
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SE Relationship Perception
SE will not transmit design changes during the placing drawing preparation» During mark-ups
Detailer addresses mark-ups prior to fabricating & issuing final drawings
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How Can SEs Get Better?
Recognize the tools available» PublicationsGet familiar with rebar detailing
Part 1
» Make buildable designs» Aids in placing drawing reviewField issues cannot always be solved with a BFH
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CRSI – Manual of Std. Practice
First published by CRSI in 1927Industry “Standard Practices” for all activities related to steel reinforcing barsEssential reference for the A / E
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ACI Committee 315 Report
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ACI Detailing Manual
Current Edition ~ 2004Contains ACI 315 reportIllustrative standardsExample drawingsExample drawings» Slabs» Walls» Footings» Bridges» Etc.
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ar B
ends
Typi
cal B
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ar B
ends
Typi
cal B
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Typical Stirrups
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Typical Column Ties
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End Hook Dimensions
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Stirrups and Ties
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Two “What Went Wrongs”
Continuous beamsSlab folds
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Continuous Beam
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SE Typical “Screw Ups”
Conflicting reinforcing over support» Different sizes called on adj. beams
Too many bars for beam width» Specify layers» Specify layers
No direction on rebar location at intersecting beamsFull length bars not taken into accountCongestion over columns» Take column reinforcing into consideration
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Slab Folds
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Slab Folds Again
Two Way SlabsDifficult for detailersSlab elevation differences and the complexity of a two-way slab
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SE Typical “Screw Ups”
Detail is not cut on planExtent of fold not clearly shownFold not coordinated with architecturalNo inst uctions are provided foldNo instructions are provided when fold depth exceeds “maximum fold allowed”Fold location – many bar lengths» Framing bars » Fill bars spliced to longer bars
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Typ. Detailer “Screw-Ups”
Slab reinforcing is “replaced” by fold reinforcing» Two-way reinf. not consideredOther structural components in vicinity are effectedIncorrect laps» Location , length
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Problem Resolution
Identify issues ASAP & communicate to all partiesShare possible solutionsDocument but “do not point fingers”Document, but “do not point fingers”Implement best solution ASAP» Keeps job movingLearn from problems & don’t repeat» At least not on the same job
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Improving the Relationship
Allow communication between partiesProvide Detailer with latest set of contract documents» Including architectural drawings
Encourage detailer to contact SE during placing drawing preparationShare “lesson learned” experience from previous projects
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Improving the Relationship
Identify potential problems ahead of timeSim lif and standardize detailsp yFollow latest codes & practicesKeep Detailers trained and current
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Meetings !!
If needed, call early project meeting» Detailer, Subs, & GC» Discuss project “misunderstandings”Sub / Detailer may request meeting» Details confusing or not clear» He/she proposes alternate detail» Without changing intent, if these have
worked previously
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Stretch Time . . . .
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How Can SEs Get Better?
Take the lead !!Identify potential issues in desi n hase
Part 2
g p» Draw details to scale to visualize» Detail / think out the “tuffys”» Go beyond dots & lines» Recognize congestion issues
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SE Takes the Lead . . .
Design process begins with EOR / SEIn-house training of young engineers» Starts ASAP upon hiring from college» Mentoring from experienced engineers» Mentoring from experienced engineers» In-house seminars, site visits, lessons
learnedClarify intent at pre-constr. meeting Contact detailer early» Initial placing drawings indicate a lack of
understanding of design intent56
U.S. Bar Sizes
Diameter approx.Based on weight
Bar Size[metric]
#
Nominal Weight, lb/ft[Nominal Mass, kg/m ]
Diameter, in. [ mm ]
CrossSectional Area, in.2[mm2]
3 [10] 0.376 [0.560] 0.375 [9.5] 0.11 [71]
4 [13] 0.668 [0.994] 0.500 [12.7] 0.20 [129]
5 [16] 1 043 [1 552] 0 625 [15 9] 0 31 [199]5 [16] 1.043 [1.552] 0.625 [15.9] 0.31 [199]
6 [19] 1.502 [2.235] 0.750 [19.1] 0.44 [284]
7 [22] 2.044 [3.042] 0.875 [22.2] 0.60 [387]
8 [25] 2.670 [3.973] 1.000 [25.4] 0.79 [510]
9 [29] 3.400 [5.060] 1.128 [28.7] 1.00 [645]
10 [32] 4.303 [6.404] 1.270 [32.3] 1.27 [819]
11 [36] 5.313 [7.907] 1.410 [35.8] 1.56 [1006]
14 [43] 7.650 [11.38] 1.693 [43.0] 2.25 [1452]
18 [57] 13.60 [20.24] 2.257 [57.3] 4.00 [2581] 57
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U.S. Bar Sizes
Figure 6-1 fromCRSI’s Manual of Standard Practice
Bar Size
Nominal Diameter( in. )
Outside Diameter( in. )
3 3/8 7/164 1/2 9/165 5/8 11/165 5/8 11/166 3/4 7/87 7/8 18 1 1-1/89 1.128 1-1/4
10 1 270 1-7/1611 1.410 1-5/814 1 693 1-7/818 2 257 2-1/2 58
Common Problem Areas
Beam – column jointsBrackets / haunches / ledgesIntegrity steelIntegrity steelT-JointsTop of columns
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Avoid Congestion
Beam-Column Joints
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Beam-Column Joints
Perimeter of Column Reinf.
Think curtains or planes of steel reinforcing
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Beam-Column Joints
Congestion is a givenConsider making beams wider» B 4 in 2 in each sidey ,» Corner beam bars don’t interfereConsider ⊥ beams» Different depths or elevations» Top & bottom bar interferences
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Beam-Column Joint
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Column Brackets
Where located on column?What is the size?Bar s acin ?p gHow does this effect the strut-and-tie model?
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Bottom Integrity Rebar
Lap outside column to avoid congestion
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Retaining Wall T-Joints
Easier for contractor
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Retaining Wall T-Joints
Performs better
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Coupling Beams
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Scale Drawing of Rebar
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nfig
urat
ion
Fina
l Con
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Shear Wall Ends – L to M
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Shear Wall Ends – L to M
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Shear Wall Ends – Special
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Shear Wall Ends – Special
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Shear Wall Ends – Special
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Column Ends – Headed Bars
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Punching Shear Studs
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SE Need to Knows - Rebar
Standard rebar stock length» (40 to) 60 ft» S ecial len ths ossible coordinate p g p (
with mill or fabricator)Try to use same steel grade throughout project#14 & #18 may require lead time
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Use largest bar size possibleRepeat bar sizes & lengthsProvide minimum 4 - 6 in. gap
SE Need to Knows - Rebar
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Provide minimum 4 6 in. gap between top barsFollow ACI 315 for bending detailsMinimize bar bends & hooksKeep bars in one plane
SE Need to Knows - Columns
Multi-story construction, usual practice» Limit column bar lengths to one storyFor larger bars & couplers» Two and three story heights possible» Bar sizes of #9 & > have sufficient
stiffness to use free standing two story heights.
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SE Need to Knows - Columns
Use same column size, vary» Bar size» Concrete strength gLap splices permitted up to #11#14 & #18 bars have to be mechanically spliced or welded, if tension splice
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Rebar Splicing - Coupler
Couplers are:» Grouted» Threaded» Screw typeManufacturer’s literature
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Rebar Splicing - Couplers
Couplers take up space» Greater diameter than rebarStagger couplersgg pCan they be installed?» Grouting» Set screws
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Better SEs - Review
Identify potential issues» Draw details to scale to visualize» Detail / think out the “tuffys”y» Go beyond dots & lines» Recognize congestion issuesGet familiar with rebar detailing
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What Can Mr. CRSI Do?
Manuals of Standard Practice» Keep current / up to date» Reflect latest Code changes
Encourage & promote detailer trainingEncourage & promote detailer trainingPromote field experience importance» Young engineers
Work with college professors» Discuss importance of detailing» Properly expressing design in contract docs
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Questions?
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