guide for reinforced concretet detailing
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WHO IS AN ENGINEER?
According to USA President Herbert Hoover, who was an
engineer before he became a politician, said:The great liability of the engineer compared to men of otherprofessionsis that his works are out in the open where allcan see them.
His acts ..step by step are in hard substances.
He cannot bury his mistakes in the grave like the DOCTORS.
He cannot argue them into thin air..or blame the judge..likethe LAWYERS.
He cannot, like the ARCHITECT, cover his figures with treesand vines.
He cannot, like the politicians, screen his shortcomings byblaming his opponents.and hope the people will forget. The
ENGINEER simply cannot deny he did it.If his works do not workhe is damned.
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A design engineers responsibility should includeassuring the structural safety of the design,details, checking shop drawing.
Detailing is as important as design since proper
detailing of engineering designs is an essential linkin the planning and engineering process as some ofthe most devasting collapses in history have beencaused by defective connections or DETAILING.There are many examples explained in the book"DESIGN AND CONSTRUCTION FAILURES by Dov
Kaminetzky.Detailing is very important not only for the properexecution of the structures but for the safety of thestructures.
Detailing is necessary not only for the steel
structures but also for the RCC members as it is thetranslation of all the mathematical expressions andequations results.
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For the RCC members for most commonly used for buildings wecan divide the detailing for
1. SLABS-WITH OR WITHOUT OPENINGS.(RECTANGULAR,CIRCULAR,NON-RECTANGULAR-PYRAMIDSLAB,TRIANGULAR ETC)
-BALCONY SLAB,LOFT SLAB,CORNER SLAB etc
2. BEAMS- WITH OR WITHOUT OPENIGS.(SHALLOW & DEEP BEAMS)
3. COLUMNS.(RECTANGULAR,L-SHAPE,T-SHAPE,CIRCULAR,OCTAGONAL,CROSS SHAPE etc)
4. FOUNDATIONS.
Detailing for gravity loads is different from the lateral loadsspecially for the SEISMIC FORCES.
Apart from the detailing for the above there is a differentdetailing required for the Rehabilitation and strengthening of
damaged structures.
We will now dwell on the DETAILING OF MEMBERS FOR THEGRAVITY AND SOME CODAL DETAILINGS AS PER IS CODE IS13920 AND IS 4326 AS REQUIRED FOR SEISMIC FORCES.
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DOS & DONOTS FOR DETAILING
DOS-GENERAL
1. Prepare drawings properly & accurately if possible label each bar
and show its shape for clarity.
12
I dia@12c/c
Cross section of retaining wall which collapsed immediately after placing of soil
backfill because rather than 1-1/4 dia. were used. Error occurred because
Correct rebar dia. Was covered by a dimension line.
1- dia@12c/c
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2. Prepare bar-bending schedule , if necessary.
3. Indicate proper cover-clear cover, nominal cover or
effective cover to reinforcement.4. Decide detailed location of opening/hole and supplyadequate details for reinforcements around theopenings.
5. Use commonly available size of bars and spirals.For a single structural member the number ofdifferent sizes of bars shall be kept minimum.
6. The grade of the steel shall be clearly stated in thedrawing.
7. Deformed bars need not have hooks at their
ends.
8. Show enlarged details at corners, intersections ofwalls, beams and column joint and at similarsituations.
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9. Congestion of bars should be avoided at points where
members intersect and make certain that all rein. Can be
properly placed.
10. In the case of bundled bars, lapped splice of bundled barsshall be made by splicing one bar at a time; such
individual splices within the bundle shall be staggered.
11. Make sure that hooked and bent up bars can be placed
and have adequate concrete protection.
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12. Indicate all expansion, construction and contraction joints
on plans and provide details for such joints.
13. The location of construction joints shall be at the point of
minimum shear approximately at mid or near the mid points.
It shall be formed vertically and not in a sloped manner.
DOS BEAMS & SLABS:
1. Where splices are provided in bars, they shall be , as far as
possible, away from the sections of maximum stresses and
shall be staggered.
2. Were the depth of beams exceeds 750mm in case of beamswithout torsion and 450mm with torsion provide face rein.
as per IS456-2000.
3. Deflection in slabs/beams may be reduced by providing
compression reinforcement.
4. Only closed stirrups shall be used for transverse rein. Formembers subjected to torsion and for members likely to be
subjected to reversal of stresses as in Seismic forces.
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5. To accommodate bottom bars, it is good practice to make secondarybeams shallower than main beams, at least by 50mm.
Dos COLUMNS.
1. A reinforced column shall have at least six bars of longitudinal
reinforcement for using in transverse helical reinforcement.-forCIRCULAR sections.
2. A min four bars one at each corner of the column in the case ofrectangular sections.
3. Keep outer dimensions of column constant, as far as possible , forreuse of forms.
4. Preferably avoid use of 2 grades of vertical bars in the same element.DONOTS-GENERAL:
1. Reinforcement shall not extend across an expansion joint and thebreak between the sections shall be complete.
2. Flexural reinforcement preferably shall not be terminated in a tensionzone.
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3. Bars larger than 36mm dia. Shall not be bundled.
4. Lap splices shall be not be used for bars larger than
36mm dia. Except where welded.
5. Where dowels are provided, their diameter shall notexceed the diameter of the column bars by more than
3mm.
6. Where bent up bars are provided, their contribution
towards shear resistance shall not be more than 50% of
the total shear to be resisted. USE OF SINGEL BENT UPBARS(CRANKED) ARE NOT ALLOWED IN THE CASE
OF EARTHQUAKE RESISTANCE STRUCTURES.
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DETAILING OF SLABS WITHOUT ANY CUT
OR OPENINGS.
The building plan DX-3 shows theslabs in different levels for the
purpose of eliminating the inflow of
rainwater into the room from the openterrace and also the sunken slab for
toilet in first floor.
The building plan DX-A3 is one inwhich the client asked the architect to
provide opening all round.Refer the 3d
elevation
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Different shapes of slabs used in the
buildings. 6depression for OT &9 for sunken slabs.
Portico slab in elevation
19-6
9-6suareopening
5wide corridor all
round
Portico and other rooms
roof slab in plan
Portico slab in plan
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Minimum and max.reinforcement % in beams, slabs and
columns as per codal provisions should be followed.
SLABS:
It is better to provide a max spacing of 200mm(8) for main
bars and 250mm(10) in order to control the crack width and
spacing.
A min. of 0.24% shall be used for the roof slabs since it is
subjected to higher temperature. Variations than the floor
slabs. This is required to take care of temp. differences.
It is advisable to not to use 6mm bars as main bars as this
size available in the local market is of inferior not only with
respect to size but also the quality since like TATA and SAILare not producing this size of bar.
BEAMS:
A min. of 0.2% is to be provided for the compression bars in
order to take care of the deflection.
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The stirrups shall be min.size of 8mm
in the case of lateral load resistance .
The hooks shall be bent to 135degree .
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Ld/2Ld/2
Ld
crack
INCORRECT
CORRECT
CLOSE
STIRRUPS
Ldt
Ldt/2
CANTILEVER BEAM
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NON PRISMATIC BEAM
Ld/2 Ld/2Ld
INCORRECT
CORRECT
CLOSE
STIRRUPS
crack
Ldt/2
Ldt
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GRID BEAMGRID BEAM
INCORRECT
1.5d1.5d1.5d
Close rings
Hanger bars
Slope 1:10
2#extra bars
300300
d
CORRECT
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Details of Main & Secondary beams
INCORRECT
1.5d1.5d1.5d
Close rings
Hanger bars
300300
d
CORRECT
Secondary beam
Main beam
Secondary beam
60degree
Main beam
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d
1/4OR
1/5 SPAN
1.5d
CORRECT
INCORRECT
d/2+d/2Cot(t)
tt
Ld
d/2
d/2
Ld
LINE OF CRACK
BEAM
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Continuous beam
continuous beamSpan/4
Span/4Span/4
Span/4
incorrect
Span/4
Span/4
1.5d1.5d
Span/4
correct
1.5d
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100%
L1
100% CRACKCRACK
.08L2.08L1 L2
SPAN/4 SPAN/4
CONTINUOUS BEAM
INCORRECT
.08L1
.08L1
SPAN/4
CRACK
100%
L1
100%
.15L2 L2
L1/4 L2/4
CORRECT
0.1L1
.15L1
L1/4100%
20%20%
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D
D
CRACK
INCORRECT
NONPRISMATIC
SECTION OF BEAM
D
D
DCORRECT
D
CLOSE RING
CLOSE RING
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COLUMN
INCORRECT
CANTILEVER BEAM PROJECTING
FROM COLUMN
CORRECT
NOT LESS THAN GREATER OF 0.5L OR Ld50mm
0.25Ast
NOT LESS
THAN 0.5Ast
COLUMN
Ld
Ld/3
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CRACK
SLOPING BEAM
CORRECT
Ld
Ld
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CRACKCRACK
INCORRECT
HAUNCH BEAMS
CORRECTL/8 TO
L/10 L/8 TO
L/10
L
L
Ld Ld
Ld Ld
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STRESSES AT CORNERS
C
C-COMPRESSION
T-TENSION
t
t
C
RESULTANT TENSILE STRESS FOR
ACROSS CORNER(ONE PLANE)
t
c
RESULTANT TENSILE STRESS FOR
ACROSS CORNER(DIFFERENT PLANE)t
c
CRACK
CRACK
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SHEAR AND TORSION REIN. IN
BEAMS
INCORRECT
Min 0.2%bd to control deflection as
well as for seismic requ.
b
D100 to
200mm
d
D-n>500mm
D/5
Skin rein.10dia is
required when depth
exceeds 450mm(0.1%of web area distributed
equally on two faces)
Stirrups taken round outermost
bars spacing
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CANTILEVER BEAM WITH
POINT LOAD
CORRECT
INCORRECT
2/3dd
Shear rein.
Extra ties
Ld
Ld
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opening
CORRECT
OPENING IN WEB OF BEAM
crackcrack
opening
INCORRECT
OPENING IN WEB OF BEAM
Ld
d/2 d/2
Closed stps
for d/2Closed stps
for d/2
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BEAM COLUMN JUNCTION-EXTERIOR COLUMN
CORRECT
INCORRECT
CLOSED STPS2max
IN TENSION-Ld
U TYPE BARS
Ld
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CORRECT
SPLICE DETAIL FOR COLUMN
INCORRECT
COVER
CLOSE
TIES @S/2
S-SPACING
SLOPE 1:6
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REDUCTION
COLUMN BOTH
SIDES
INCORRECT
CORRECT
3NO.CLOSE TIES
SPLICE
CLOSE STPS SPACIN
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TERMINATION OF COLUMN BARS INSIDE BEAM
INCORRECT
CORRECT
Ld
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BEAM COL. JUNCTION-EQ
REGION
EQREGION-BEAM-COL JN-EXTERIOR
CORRECT
BEAM COL. JUNCTION-EQ
REGION
INCORRECT
END REGION
END REGION
COL.
CORE*
SPACING OF
LATERAL
TIES
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EQ REGION CONTINUOUS BEAM
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EQ-REGION-CONTINUOUS BEAM
INCORRECT
Ld
A=L1/3
CONTINUOUS BARS NOT LESS THAN
AREA OF BARS AT COL.FACE
A=L1/3 A=L1/3
2d
50mmmax
Stirrup spacing=d/4 or
100mm or 8dia which
ever is the least
2d2d 2dstp@maxd/2 stp@maxd/2
CORRECT
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INCORRECT
FOOTING-DETAILS(INDEPENDENT)
CORRECT
COVER TO
STARTER
STARTER
BARS
COLUMN
BARS
NATURAL
G.L
Ldt
Lb3 SIDE COVER
LdtCOVER50mm
IF p.c.c below
or 75mm
Min.300
TYPICAL REIN DETAILS OF
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TYPICAL REIN DETAILS OF
HAMMER FOUNDATION BLOCKINCORRECT
CORRECT
Ld
Ld
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SECTION OF TRENCH
CRACK
INCORRECTINCORRECT
CORRECT
LdLd
Ld
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STAIRCASE-WITH WAIST SLAB
INCORRECT
CORRECT
Ld(min)Extra bar
Ld(min)
Ld(min)
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Main bar
Dist.
Main bar
Alternate 1
SLABLESS STAIRCASE
S SS S C S
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Main bar
Alternate 2
A=0.25L
L=horizontal span
SLABLESS STAIRCASE
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DEVELOPMENT LENGTH OF BARS
SLNO BAR DIA. TENSIONmm COMPRESSION REMARKS
1 8 376.0 301.0
2 10 470.0 376.0
3 12 564.0 451.0
4 16 752.0 602.0
5 20 940.0 752.0
6 22 1034.0 827.0
7 25 1175.0 940.0
8 28 1316.0 1053.0
9 32 1504.0 1203.0
FOR A CONCRETE GRADE M20 &STEEL STRENGTH Fy=415
APPROXIMATELY USE 50Xdia FOR TENSION
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CONCLUSION:
Before concluding I will show some more details drawnin autocad exported in wwf format
As there is no time to elaborately explaining ,the following topics are notcovered :
1. Flat slabs, Folded plates, shell structures-cylindrical shells, silos,
2. Staircases- helical staircase, central beam type, cantilever type etc.
3. Different types of foundations-raft, pile foundation, strap foundation etc.
4. Retaining wall structures,
5. Liquid retaining structures.
6. Deep beams.
7. Shear wall, walls.
Hope that I have enlighten some of the detailing technique for the mostcommonly encountered RCC members in buildings.
In the above statements if my senior colleagues and ACCE members
can find different method or any new detailing system it will be of immensehelp not only for me but to other young engineers who should learn in wrightways and not wrong lessons.
REFERENCES
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REFERENCES:
1. HANDBOOK ON CONCRETE REINFORCEMENT ANDDETAILING-SP:34(S&T)-1987.
2. MANUAL OF ENGINEERING & PLACING DRAWINGSFOR REINFORCED CONCRETE STRUCTURES-
(ACI 315-80
3. MANUAL OF STANDARD PRACTICE CONCRETEREINFORCING STEEL INSTITUTE.
4. TWARD BOARD MANUAL FOR RURAL WATER SUPPLYSCHEMES.
5. DESIGN PRINCIPLES AND DETAILING OF CONCRETESTRUCTURES. By D.S.PRAKASH RAO.
6. SIMPLIFIED DESIGN-RC BUILDINGS OF MODERATESIZE AND HEIGHT-BY PORTLAND CEMENT
ASSOCIATION,USA.7. DESIGN AND CONSTRUCTION FAILURES BY DOV
KAMINETZKY.
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8. IS:2502-1963 CODE OF PRACTICE FOR BENDING AND
FIXING OF BARS FOR CONCRETE REINFORCEMENT.
9. IS:1893:2000.
10. IS:4326.11. IS:456:2000
12. REINFORCED HAND BOOK BY REYNOLD.
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THANK YOU.