1. Design of RCC structures Detailing of Reinforcement (IS , IS13920) Pradip Paudel (M.Sc. in Structural Engineering)

2. WHO IS AN ENGINEER?
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.
He cannot bury his mistakes in the grave like the DOCTORS.
He cannot, like the ARCHITECT, cover his figures with trees
A design engineer’s responsibility should include assuring the structural safety of the design, details, checking shop drawing.
Detailing is as important as design

3. Requirements of Good Detailing
Should be simple for fabrication and placing
Check spacing for crack control – maximum spacing
Minimum spacing for concrete placing
Check for splicing requirements and development length
Special care for section of varying depth and sloped slabs
Care for corner joints, beam column junction, openings etc.

4. Cont.…
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.
Detailing codes SP16 and IS
EQ code is as required for seismic forces.

5. Minimum Nominal Cover Clear cover shall be provided
To develop the desired bond strength through out the perimeter of steel
To protect against corrosion and fire
Slab 20mm
Beam 25mm
Column 40mm
Footing 60mm
For detail see Table-16 IS

6. Spacing of reinforcement
The horizontal distance between two parallel main reinforcing bars shall not be less than
The diameter of the bar if the bars are of equal diameter
The diameter of the larger bar
5mm + nominal size of aggregate
Maximum spacing ----as per design
Further reading Page 167 A. K. Jain
Clause , IS

7. Limits for reinforcement
Beam
Min As/bd = 0.85/Fy
Maximum = 4% of bD
Compression = 0.2%
Web reinforcement = 0.1% of web area
Vertical Shear bars not exceeding 0.75d or 300mm whichever is less.
Minimum shear bars = cl
Slab = min 0.12% for Fe415 and 0.15% for Fe250
Clause 26.5, IS

8. The stirrups shall be minimum size of 8mm in the case of lateral load resistance .
The hooks shall be bent to 135 degree .
In column size of bar not less than 12 mm
Spacing of bars not greater than 300mm
Arrangement of lateral ties as per cl

9. DEVELOPMENT LENGTH OF BARS
FOR A CONCRETE GRADE M20 &STEEL STRENGTH Fy=415
SLNO
BAR DIA.
TENSIONmm
COMPRESSION
REMARKS 1 8
376.0
301.0 2 10
470.0 3 12
564.0
451.0 4 16
752.0
602.0 5 20
940.0 6 22
1034.0
827.0 7 25
1175.0 28
1316.0
1053.0 9 32
1504.0
1203.0
APPROXIMATELY USE 50Xdia FOR TENSION

10. Lap splicing -clause 26.2.5.1 IS456-2000

11. Lap splicing as per clause 26.2.5.1 IS456-2000
Lap splices should not be used for bar larger than 36mm
Larger than 36mm bar may be welded
Lap length including anchorage value of hooks in flexural tension is development length (Ld)or 30ϕ whichever is greater.
Lap length including anchorage value of hooks in direct tension is 2Ld or 30ϕ whichever is greater.
The straight lap length should not be less than 200mm or 15ϕ whichever is greater.

12. Lap splicing Cont.….
Lap splices are considered as staggered if the c/c distance of the splices is not less than 1.3 times the lap length.
The lap length in compression is equal to the development length in compression but not less than 24ϕ.
Lap length is calculated on the basis of diameter of smaller bar when bars of different diameters are to be spliced.

13. DO’S For Detailing Prepare drawing properly and accurately
Prepare bar bending schedule, if necessary
Indicate proper cover to the reinforcement
Decide location of the openings/hole and supply adequate details for the reinforcement around openings.
Commonly available size of bars and spirals shall be used for reinforcement.

14. For a single structural member the number of different sizes of reinforcement bar should be minimum.
The grade of reinforcement bars should be clearly mention in the structural drawings
When reinforcement is left exposed for future construction, it should be adequately protected from corrosion and weathering.
Congestion of the reinforcement should be avoided at points where members intersect and make certain that all the reinforcement shown can be properly placed.
Show enlarged details at the corners, beam and column joint and at similar special situations.

15. Do Not's for Detailing
Flexure reinforcement shall not be terminated in a tension zone.
Lap splices should not be used for bars larger than 36 mm dia.
Different types of reinforcing bars such as deformed bars and plain bars and various grades should not be used side by side as this practice would lead to confusion at site.

16. Do’s for Columns
A reinforced column should have min 4 bars for rectangular or square column and minimum 6 bars for circular columns.
Keep outer dimensions of the column constant, as far as possible, for re-use of forms.
Preferably avoid use of two grades of vertical bars in the same element.

17. Do’s for Beams and Slabs
Where splices are provided in the reinforcing bars, they should be staggered, and away from the sections of maximum stress.
Where the depth of the beam exceeds 750 mm in case of beams without torsion and 450 mm with torsion side face reinforcement shall be provided.
All spacing shall be c/c spacing of the bars.

18. Deflection in beams/slabs may be reduced by providing compression reinforcement.
At beam column intersection ,ensure that the main beam bars avoid the main column bars.
At beam column intersections , main reinforcement may be so arranged that layers in mutually perpendicular beams are at different levels.
To accommodate bottom bars, it is good practice to make secondary beams shallower than the main beams at least by 50 mm.

19. Curtailment of reinforcement
Clause IS456

20. Cont.…

21. Cont.… Positive moment reinforcement, Cl26.2.3.3
Negative moment reinforcement,Cl
Curtailment of bundled bars,Cl
Further reading A. K. Jain p 172
Simplified rules of curtailment as per BS

22. Bar Bending Schedule Bar Bending Schedule should include:
Identification of structural member
Position of each bar in the member
Bar marks and diameter of each bar
Number of bars
Shape and bending dimension of each bar
Length of each bar
Remark, if any
Typical example for slab, beam and column: see page 180 (A.K. Jain)

23. IS13920:1993,Ductile Detailing of RCC Structures Subjected to Seismic Forces
This code applies to all RCC structures which satisfy one of the four conditions-
The structure is located –
In zone IV or V
In zone III and I> 1.0
In zone III and industrial structure
In zone III and is more than 5 story high

24. What is EQ Resistant Design?
The acceptable response levels of the structure under design earthquake.
Designer should exercise some degree of control on magnitude and distribution of stiffness, mass and relative strength of member and their ductility to achieved desired results.

25. Seismic Design Criteria(IS 1893)
Earthquake
Desired Behavior
Controlling parameters
Minor
No damage to non-structural components
Control deflection by providing stiffness
Moderate
No significant structural damage, minor cracks in beam and columns, Response should be predominantly elastic
Avoid yielding of members or permanent damage by providing strength
Severe, Catastrophic
No collapse of the system which could cause loss of life.
Allow structure to enter into inelastic range and absorb energy by providing ductility

26. If elastic strength of structural elements exceeds the greatest imposed load upon that structure there can be no significant damage.
In severe earthquake some of the resisting elements will be loaded to their full strength. If they are brittle, they will fail, throwing their share of the load on the remaining elements. If they are ductile, they can continue to participate in resisting the lateral force up to their full strength after they yield.

27. DUCTILITY
A ductile material is the one that can undergo large strains while resisting loads
Ductility implies the ability to sustain significant inelastic deformations prior to collapse.
Brittle material is one that fails suddenly upon attaining its maximum load

28. Brittle and Ductile force-deformation behaviorΔy Δu
Deformation
Brittle

30. Significance of Ductility
It can be expected to adapt to unexpected overloads, impact and structural movements due to foundation settlements and volume changes.
Occupants will have sufficient warning of the impending failure thus reducing the probability of loss of life in the events of collapse.
All joints and splices must be able to withstand forces and deformations corresponding to yielding of the reinforcement.

31. Design for Ductility Structural layout should be simple and regular.
Amount of tension reinforcement in beams should be restricted and more compression reinforcement should be provided.

32. Cont.…

33. Cont.…
The shear reinforcement should be adequate to ensure that the strength in shear exceeds the strength in flexure and thus, prevent a non-ductile shear failure before the fully reversible flexural strength of a member has been developed.
See on clause in IS13920

34. BEAMS
At least two bars should be provided continuously both at top and bottom.
The positive moment resistance at the face of the joint should not be less than one –half of the negative moment resistance provided at that face of the joint.
Neither the negative nor the positive resistance at any section along the member length should be less than one-fourth of the moment resistance provided at the face of the either joint
Clause 6, IS13920

35. BEAM REINFORCEMENT MIN 2 BARS FOR FULL LENGTH
ALONG TOP AND BOTTOM FACE
AS > MIN. Bd
AS < MAX Bd
50 mm max
50 mm max d db 2d 2d
HOOP SPACING
> d /2
HOOP SPACING
< d/4 and 8 db
B = BREADTH OF BEAM
db = DIAMETER OF LONGITUDINAL BAR
BEAM REINFORCEMENT

36. Spacing of hoops over a length of 2d at either end of the beam shall not exceed-
8 times the diameter of the smallest longitudinal bar, need not be less than 100 mm
Elsewhere, the beam shall have vertical hoops at a spacing not exceeding d/2.
Clause 6.3.5, IS13920

37. COLUMN

38. Cont.…
The special confining reinforcement shall be provided above and below the beam connections, in a length of the column at each end which is largest of the following-
1/6 of the clear height of the column
Larger dimension of the column
450 mm
When a column terminates into a footing, special confining reinforcement shall extend at least 300 mm into the footing

39. PROVISION OF SPECIAL CONFINING REINFORCEMENT IN FOOTINGS
> 300 mm
PROVISION OF SPECIAL CONFINING REINFORCEMENT IN FOOTINGS

40. COLUMN AND JOINT DETAILINGlO
JOINT REINFORCEMENT
AS PER 8.1 lO
> hc / 4
SPECIAL CONFINING REINFORCEMENT
AS PER 7.4.1
TRANSVERSE REINFORCEENT
AS PER 7.3.3
SPLICE
TRANSVERSE
REINFORCEMENT
AS PER 7.2.1 hC
> hc / 4 lO
CONFINED JOINT WITH BEAMS
FRAMING INTO ALL FOUR SIDES
CONFINING REINFORCEMENT AS
PER 8.2
COLUMN AND JOINT DETAILING

41. The spacing of hoops used as special confining reinforcement shall not exceed –
¼ of the minimum member dimension
need not be less than 75 mm nor more than 100 mm
For further information see on Clause and in IS 13920

42. FIG. 1: ANCHORAGE OF BEAM BARS IN AN EXTERNAL JOINT.
Ld + 10db db
Ld + 10db
Ld = DEVELOPMENT
LENGTH IN TENSION
Db = BAR DIAMETER
FIG. 1: ANCHORAGE OF BEAM BARS IN AN EXTERNAL JOINT.

43. LAP SPLICES IN BEAM
Not more than 50 % of the bars shall be spliced at one section
The longitudinal bars shall be spliced , only if hoops are provided over the entire splice length, at a spacing not exceeding 150 mm
The lap length shall not be less than the bar development length in tension.
Clause IS13920

44. Cont.… Lap splices shall not be provided-
within a distance of 2d from the joint face
within a joint
within a quarter length of the member where flexural yielding may generally occur under the effect of earthquake forces.
Use of welded splices and mechanical connections may also be made as per IS
Clause IS13920

45. Ld db FIG. 2: LAP, SPLICE IN BEAM 150 mm Ld = DEVELOPMENT
LENGTH IN TENSION
db = BAR DIAMETER
FIG. 2: LAP, SPLICE IN BEAM

46. Web Reinforcement
Clause 6.3 IS13920

47. Cont.….

51. CANTILEVER BEAM Ld/2 Ld/2 Ld INCORRECT CLOSE STIRRUPS CORRECT Ldt
crack
INCORRECT
Ldt
CLOSE STIRRUPS
Ldt/2
Ld/2
Ld/2
CORRECT Ld

52. NON PRISMATIC BEAM Ld/2 Ld/2 Ld INCORRECT CLOSE STIRRUPS CORRECT Ldt
crack
INCORRECT
Ldt
CLOSE STIRRUPS
Ldt/2
Ld/2
Ld/2
CORRECT Ld

53. GRID BEAM INCORRECT Hanger bars CORRECT Close rings 1.5d 1.5d 1.5d 300
2#extra bars
Slope 1:10
CORRECT

54. Details of Main & Secondary beams
Main beam
INCORRECT
Secondary beam
Close rings
1.5d
1.5d
1.5d
300
300 d
60degree
Hanger bars
Main beam
CORRECT

55. d INCORRECT d/2 d/2 CORRECT BEAM 1/4OR 1/5 SPAN d/2+d/2Cot(t) 1.5d Ld
LINE OF CRACK
d/2 t
d/2 t
d/2+d/2Cot(t)
1.5d
CORRECT

56. Continuous Beam incorrect correct Span/4 Span/4 Span/4 Span/4 Span/4
1.5d
1.5d
1.5d
correct

57. CONTINUOUS BEAM L1 L2 INCORRECT L1 L2 CORRECT SPAN/4 SPAN/4 SPAN/4
100%
CRACK
100%
CRACK
CRACK L1
.08L1
.08L1 L2
.08L2
INCORRECT
100%
L1/4
L2/4
L1/4
20%
20%
0.1L1
100%
100% L1
.15L1 L2
.15L2
CORRECT

58. NONPRISMATIC SECTION OF BEAMD
CRACK D D
INCORRECT
CLOSE RING D D
CORRECT D
CLOSE RING

59. CANTILEVER BEAM PROJECTING FROM COLUMN
INCORRECT
NOT LESS THAN 0.5Ast
NOT LESS THAN GREATER OF 0.5L OR Ld
50mm Ld
0.25Ast
COLUMN
CORRECT
Ld/3

60. SLOPING BEAM
CRACK Ld Ld
CORRECT

61. L INCORRECT CORRECT L HAUNCH BEAMS Ld Ld Ld Ld CRACK CRACK L/8 TO L/10

62. C-COMPRESSION T-TENSION STRESSES AT CORNERS C t C CRACK t
RESULTANT TENSILE STRESS FOR ACROSS CORNER(ONE PLANE)
RESULTANT TENSILE STRESS FOR ACROSS CORNER(DIFFERENT PLANE) t
CRACK c t c

63. Stirrups taken round outermost bars spacing<=x1
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 y1
Skin rein.10dia is required when depth exceeds 450mm(0.1% of web area distributed equally on two faces) D
100 to 200mm
D-n>500mm
D-n>500mm
D/5 x1
CORRECT b

64. Shear rein. INCORRECT 2/3d d Ld CORRECT Ld Extra ties
CANTILEVER BEAM WITH POINT LOAD
Shear rein.
INCORRECT
2/3d d Ld
CORRECT Ld
Extra ties

65. opening
crack
crack
INCORRECT
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

66. BEAM COLUMN JUNCTION-EXTERIOR COLUMN
INCORRECT
CLOSED STPS
2”max
U TYPE BARS Ld
IN TENSION-Ld
CORRECT

67. SPLICE DETAIL FOR COLUMN
COVER
CLOSE
SLOPE 1:6
S-SPACING
CORRECT
INCORRECT

68. REDUCTION COLUMN BOTH SIDES
INCORRECT
SPLICE
SLOPE 1:8 FROM BEAM BOTTOM
3NO.CLOSE TIES
CLOSE STPS SPACIN <=75mm
3NO.CLOSE TIES
CORRECT

69. INCORRECT Ld
CORRECT
TERMINATION OF COLUMN BARS INSIDE BEAM

70. EQ REGION-BEAM-COL JN-EXTERIOR
*COL.CORE HAS TO BE CONFINED BY CIRCULAR OR RECTANGULAR TIES IN ACCORDANCE WITH END REGION
SPACING OF LATERAL TIES <=d/2
COL.
CORE*
END REGION
SPACING OF LATERAL TIES <=100mm
END REGION
BEAM COL. JUNCTION-EQ REGION
INCORRECT
CORRECT
SPACING OF LATERAL TIES <=d/2
SPACING OF LATERAL TIES <=d/2
BEAM COL. JUNCTION-EQ REGION
EQ REGION-BEAM-COL JN-EXTERIOR

71. First stirrups 50mm from beam face correct
incorrect
First stirrups 50mm from beam face
correct
END REGION
END REGION-h/6 or D or 450MM whichever is greater
COLUMN DETAILS IN EQ REGIONS h b d D
END REGION
END REGION
Spacing of shear rein. In columns
Spacing of shear rein. In columns

72. EQ-REGION-CONTINUOUS BEAM
INCORRECT
50mmmax
CONTINUOUS BARS NOT LESS THAN ¼ AREA OF BARS AT COL.FACE
CORRECT
A=L1/3
A=L1/3
A=L1/3 Ld 2d 2d 2d 2d
Stirrup spacing=d/4 or 100mm or 8dia which ever is the least

73. FOOTING-DETAILS(INDEPENDENT)
INCORRECT
COLUMN BARS
STARTER BARS
NATURAL G.L
COVER TO STARTER Lb
3” SIDE COVER
Ldt
Min.300
COVER50mm IF p.c.c below or 75mm
Ldt
CORRECT

74. INCORRECT
INCORRECT
CRACK
CORRECT Ld Ld Ld
SECTION OF TRENCH

75. INCORRECT
Extra bar
Ld(min)
Ld(min)
Ld(min)
CORRECT
STAIRCASE-WITH WAIST SLAB

76. Dist.
Alternate 1
Main bar
Main bar
SLABLESS STAIRCASE

77. SLABLESS STAIRCASE
Main bar
L=horizontal span
Alternate 2
A=0.25L