REINFORCING DETAILING
OF R.C.C MEMBERS
PRESENTED BY
Er.T.RANGARAJAN,B.E,M.Sc(struct.engg),F.I.E,
FACCE,LACI,LISSE,LIASE
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 other professions……is that his works are out in
the open where all can 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…..like the LAWYERS.
He cannot, like the ARCHITECT, cover his figures
with trees and vines.
He cannot, like the politicians, screen his
shortcomings by blaming his opponents….and hope
the people will forget. The ENGINEER simply cannot
deny he did it.
If his works do not work……he is damned.
A design engineer’s responsibility should include
assuring 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
link in the planning and engineering process as
some of the most devasting collapses in history
have been caused 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
proper execution of the structures but for the
safety of the structures.
Detailing is necessary not only for the steel
structures but also for the RCC members as it is
the translation of all the mathematical
expression’s and equation’s results.
For the RCC members for most commonly used for buildings we can
divide the detailing for
1.
2.
3.
SLABS-WITH OR WITHOUT OPENINGS.(RECTANGULAR,CIRCULAR,NONRECTANGULAR-PYRAMID SLAB,TRIANGULAR ETC)
-BALCONY SLAB,LOFT SLAB,CORNER SLAB etc
BEAMS- WITH OR WITHOUT OPENIGS.(SHALLOW & DEEP BEAMS)
COLUMNS.(RECTANGULAR,L-SHAPE,T-SHAPE,
CIRCULAR,OCTAGONAL,CROSS SHAPE etc)
4. FOUNDATIONS.
Detailing for gravity loads is different from the lateral loads specially for
the SEISMIC FORCES.
Apart from the detailing for the above there is a different detailing
required for the Rehabilitation and strengthening of damaged structures.
We will now dwell on the DETAILING OF MEMBERS FOR THE GRAVITY
AND SOME CODAL DETAILINGS AS PER IS CODE IS 13920 AND IS 4326
AS REQUIRED FOR SEISMIC FORCES.
DO’S & DONOT’S FOR DETAILING
DO’S-GENERAL
1.
Prepare drawings properly & accurately if possible label each bar
and show its shape for clarity.
12”
I ¼”dia@12”c/c
1- ¼”dia@12”c/c
Cross section of retaining wall which collapsed immediately after placing of soil
backfill because ¼” rather than 1-1/4” dia. were used. Error occurred because
Correct rebar dia. Was covered by a dimension line.
2.
3.
4.
5.
6.
7.
8.
Prepare bar-bending schedule , if necessary.
Indicate proper cover-clear cover, nominal cover
or effective cover to reinforcement.
Decide detailed location of opening/hole and
supply adequate details for reinforcements
around the openings.
Use commonly available size of bars and spirals.
For a single structural member the number of
different sizes of bars shall be kept minimum.
The grade of the steel shall be clearly stated in
the drawing.
Deformed bars need not have hooks at their
ends.
Show enlarged details at corners, intersections
of walls, beams and column joint and at similar
situations.
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 bars
shall 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.
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.
DO’S – 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 beams
without 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. For
members subjected to torsion and for members likely to be
subjected to reversal of stresses as in Seismic forces.
5.
To accommodate bottom bars, it is good practice to make
secondary beams shallower than main beams, at least by
50mm.
Do’s –COLUMNS.
1.
A reinforced column shall have at least six bars of
longitudinal reinforcement for using in transverse helical
reinforcement.-for CIRCULAR sections.
2.
A min four bars one at each corner of the column in the
case of rectangular sections.
3.
Keep outer dimensions of column constant, as far as
possible , for reuse of forms.
4.
Preferably avoid use of 2 grades of vertical bars in the
same element.
DONOT’S-GENERAL:
1.
Reinforcement shall not extend across an expansion joint
and the break between the sections shall be complete.
2.
Flexural reinforcement preferably shall not be terminated
in a tension zone.
3.
4.
5.
6.
Bars larger than 36mm dia. Shall not be bundled.
Lap splices shall be not be used for bars larger than
36mm dia. Except where welded.
Where dowels are provided, their diameter shall not
exceed the diameter of the column bars by more than
3mm.
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 UP
BARS(CRANKED) ARE NOT ALLOWED IN THE CASE
OF EARTHQUAKE RESISTANCE STRUCTURES.
DETAILING OF SLABS WITHOUT ANY CUT
OR OPENINGS.
The building plan DX-3 shows the
slabs in different levels for the
purpose of eliminating the inflow of
rainwater into the room from the open
terrace and also the sunken slab for
toilet in first floor.
The building plan DX-A3 is one in
which the client asked the architect to
provide opening all round.
Refer the 3d
elevation
Different shapes of slabs used in the
6”depression for OT &
buildings.
9” for sunken slabs.
Portico slab in elevation
19’-6”
5’wide corridor all
Portico slab in plan
9’-6”suare
opening
Portico and other rooms
roof slab in plan
round
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 SAIL
are 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.
The stirrups shall be min.size of
8mm in the case of lateral load
resistance .
The hooks shall be bent to 135
degree .
CANTILEVER BEAM
crack
INCORRECT
Ldt
CLOSE
STIRRUPS
Ldt/2
Ld/2
Ld/2
Ld
CORRECT
NON PRISMATIC BEAM
crack
INCORRECT
Ldt
CLOSE
STIRRUPS
Ldt/2
Ld/2
Ld/2
Ld
CORRECT
GRID BEAM
GRID BEAM
INCORRECT
Close rings
1.5d
1.5d
300
300
d
2#extra bars
Slope 1:10
Hanger bars
CORRECT
Details of Main & Secondary beams
Secondary beam
Main beam
INCORRECT
Secondary beam
Close rings
1.5d
300
1.5d
300
d
60degree
Hanger bars
CORRECT
Main beam
BEAM
d
INCORRECT
1/4OR
1/5 SPAN
Ld
Ld
LINE OF CRACK
d/2
t
1.5d
t
d/2
d/2+d/2Cot(t)
CORRECT
Continuous beam
• continuous beam
Span/4
Span/4
Span/4
Span/4
Span/4
incorrect
Span/4
Span/4
1.5d
1.5d
1.5d
correct
CONTINUOUS BEAM
SPAN/4
SPAN/4
.08L1
100%
SPAN/4
CRACK
100%
CRACK
CRACK
.08L1
L1
L2
.08L2
INCORRECT
L1/4
0.1L1
100%
L1/4
L2/4
20%
20%
100%
100%
L1
CORRECT
.15L1
.15L2
L2
NONPRISMATIC
SECTION OF BEAM
D
CRACK
D
D
INCORRECT
CLOSE RING
D
D
CORRECT
CLOSE RING
D
CANTILEVER BEAM PROJECTING
FROM COLUMN
COLUMN
INCORRECT
NOT LESS
THAN 0.5Ast
NOT LESS THAN GREATER OF 0.5L OR Ld
50mm
Ld
0.25Ast
COLUMN
CORRECT
Ld/3
SLOPING BEAM
CRACK
Ld
Ld
CORRECT
HAUNCH BEAMS
CRACK
CRACK
L
INCORRECT
Ld
Ld
CORRECT
Ld
L/8 TO
L/10
L
L/8 TO
L/10
Ld
C-COMPRESSION
STRESSES AT CORNERS
T-TENSION
C
t
C
CRACK
t
RESULTANT TENSILE STRESS FOR
ACROSS CORNER(ONE PLANE)
t
RESULTANT TENSILE STRESS FOR
ACROSS CORNER(DIFFERENT PLANE)
CRACK
c
t
c
SHEAR AND TORSION REIN. IN
BEAMS
Stirrups taken round outermost
bars spacing<=x1
<=(x1+y1)/4
<=300mm
Min 0.2%bd to control deflection as
well as for seismic requ.
INCORRECT
n
d
Skin rein.10dia is
required when depth
exceeds 450mm(0.1%
of web area distributed
equally on two faces)
y1
D
100 to
200mm
D-n>500mm
D/5
x1
b
CORRECT
CANTILEVER BEAM WITH
POINT LOAD
Shear rein.
INCORRECT
2/3d
d
Ld
CORRECT
Ld
Extra ties
INCORRECT
opening
crack
crack
OPENING IN WEB OF BEAM
d/2
opening
d/2
Closed stps
for d/2
Closed stps
for d/2
Ld
OPENING IN WEB OF BEAM
CORRECT
BEAM COLUMN JUNCTION-EXTERIOR COLUMN
INCORRECT
2”max
CLOSED STPS
U TYPE BARS
Ld
IN TENSION-Ld
CORRECT
SPLICE DETAIL FOR COLUMN
COVER
CLOSE
TIES @S/2
SLOPE 1:6
S-SPACING
INCORRECT
CORRECT
REDUCTION
COLUMN BOTH
SIDES
INCORRECT
SLOPE 1:8 FROM
BEAM BOTTOM
SPLICE
3NO.CLOSE TIES
3NO.CLOSE TIES
CLOSE STPS SPACIN
<=75mm
CORRECT
TERMINATION OF COLUMN BARS INSIDE BEAM
INCORRECT
Ld
CORRECT
*COL.CORE HAS TO
EQ REGION-BEAM-COL JN-EXTERIOR
BE CONFINED BY
CIRCULAR OR
RECTANGULAR TIES
IN ACCORDANCE
WITH END REGION
SPACING OF
LATERAL
TIES <=d/2
COL.
END REGION
CORE*
SPACING OF
LATERAL
TIES
<=100mm
END REGION
BEAM COL. JUNCTION-EQ
REGION
INCORRECT
SPACING OF
LATERAL
TIES <=d/2
CORRECT
BEAM COL. JUNCTION-EQ
REGION
COLUMN DETAILS IN EQ REGIONS
incorrect
First stirrups
50mm from beam
face
END
REGION
correct
END REGION-h/6 or D or
450MM whichever is
greater
h
b
d
D
END
REGION
Spacing of shear rein. In
columns
END
REGION
Spacing of shear rein. In
columns
EQ-REGION-CONTINUOUS BEAM
INCORRECT
50mmmax
CONTINUOUS BARS NOT LESS THAN ¼
AREA OF BARS AT COL.FACE
A=L1/3
A=L1/3
CORRECT
A=L1/3
Ld
stp@maxd/2
2d
Stirrup spacing=d/4 or
100mm or 8dia which
ever is the least
2d
2d
stp@maxd/2
FOOTING-DETAILS(INDEPENDENT)
INCORRECT
COLUMN
BARS
STARTER
BARS
NATURAL
G.L
COVER TO
STARTER
Lb
3” SIDE COVER
Ldt
Min.300
Ldt
CORRECT
COVER50mm
IF p.c.c below
or 75mm
INCORRECT
TYPICAL REIN DETAILS OF
HAMMER FOUNDATION BLOCK
CORRECT
Ld
Ld
SECTION OF TRENCH
INCORRECT
CRACK
CORRECT
Ld
Ld
Ld
STAIRCASE-WITH WAIST SLAB
INCORRECT
Extra bar
Ld(min)
Ld(min)
Ld(min)
CORRECT
SLABLESS STAIRCASE
Dist.
Alternate 1
Main bar
Main bar
SLABLESS STAIRCASE
Main bar
L=horizontal span
Alternate 2
A=0.25L
DEVELOPMENT LENGTH OF BARS
FOR A CONCRETE GRADE M20 &STEEL STRENGTH Fy=415
SLNO
BAR
DIA.
TENSION
mm
COMPRESSION
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
REMARKS
APPROXIMATELY USE 50Xdia FOR TENSION
CONCLUSION:
Before concluding I will show some more details drawn
in autocad exported in wwf format
1.
2.
3.
4.
5.
6.
7.
As there is no time to elaborately explaining ,the following topics are not
covered :
Flat slabs, Folded plates, shell structures-cylindrical shells, silos,
Staircases- helical staircase, central beam type, cantilever type etc.
Different types of foundations-raft, pile foundation, strap foundation etc.
Retaining wall structures,
Liquid retaining structures.
Deep beams.
Shear wall, walls.
Hope that I have enlighten some of the detailing technique for the most
commonly 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 immense
help not only for me but to other young engineers who should learn in wright
ways and not wrong lessons.
REFERENCES:
1.
2.
3.
4.
5.
6.
7.
HANDBOOK ON CONCRETE REINFORCEMENT AND
DETAILING-SP:34(S&T)-1987.
MANUAL OF ENGINEERING & PLACING DRAWINGS
FOR REINFORCED CONCRETE STRUCTURES(ACI 315-80
MANUAL OF STANDARD PRACTICE –CONCRETE
REINFORCING STEEL INSTITUTE.
TWARD BOARD MANUAL FOR RURAL WATER SUPPLY
SCHEMES.
DESIGN PRINCIPLES AND DETAILING OF CONCRETE
STRUCTURES. By D.S.PRAKASH RAO.
SIMPLIFIED DESIGN-RC BUILDINGS OF MODERATE
SIZE AND HEIGHT-BY PORTLAND CEMENT
ASSOCIATION,USA.
DESIGN AND CONSTRUCTION FAILURES BY DOV
KAMINETZKY.
8.
9.
10.
11.
12.
IS:2502-1963 CODE OF PRACTICE FOR BENDING AND
FIXING OF BARS FOR CONCRETE REINFORCEMENT.
IS:1893:2000.
IS:4326.
IS:456:2000
REINFORCED HAND BOOK BY REYNOLD.
THANK YOU.