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1. 1
Ductile Detailing for
Earthquake Resistant
R C Structures
Dr. S. K. PRASAD
Professor of Civil Engineering
S.J. College of Engineering
Mysore – 570 006

2. 2
Ductile Detailing
Objective
To provide adequate toughness and ductility
to resist severe earthquake shocks without
collapse
IS 13920 : 1993 (Reaffirmed 2003)
Code of Practice for Ductile detailing of
reinforced concrete structures subjected to
seismic forces

3. 3
Ductile Detailing
Where is this required?
Structure in Seismic Zone IV or V.
Structure in Seismic Zone III with
Importance factor (I) greater than 1.0.
Structure in Seismic Zone III and is an
industrial structure, and
Structure is located in Seismic Zone III and
is more than five storeys high.

4. 4
Ductile Detailing
Design of structures : IS : 456 – 2000
(modified by the provisions of IS 13920 : 1993)
All structural buildings
Grade of concrete: Minimum fck = 20 MPa
Grade of steel : Fe 415 or less shall be used

5. Flexural member
Two types of
Damage
 Flexure
 Shear
Flexural failure
is preferred
5

6. 6
Ductile Detailing … Flexural members
Factored axial stress under earthquake
loading 0.1 fck.
Preferably width to depth ratio > 0.3.
Width, b 200 mm.
Depth, D ¼ of clear span.
1

7. 7
Ductile Detailing … Flexural members
LONGITUDINAL REINFORCEMENT
At least two bars throughout the member length at
both top and bottom.
Tension steel ratio on any face at any section
Maximum steel ratio on any face at any section
Positive steel at a joint face half the negative
steel at that face.
1

8. Flexural detailing
8

9. 9
Ductile Detailing … Flexural members
LONGITUDINAL REINFORCEMENT … Contd.
1
Steel provided at each
of top and bottom face
of member at any
section along its length
1/4 of maximum
negative steel
provided at the
face of either joint

10. 10
Ductile Detailing … Flexural members
LONGITUDINAL REINFORCEMENT … Contd.
1
External Joint
For both the top and bottom bars of the beam
Anchorage length = Ld + 10 dia - allowance for 90
degree bends.

11. Anchorage of beam bars in exterior joints
11

12. 12
Ductile Detailing … Flexural members
LONGITUDINAL REINFORCEMENT … Contd.
1
Internal Joint
For both faces of beam, bars shall be taken
continuously through the column.

13. Failure at internal joint
13
Shear failure of R C beam – column joint during the
1985 Mexico earthquake when beam bars are
passed outside the column cross section (EERI)

14. 14
Ductile Detailing … Flexural members
LONGITUDINAL REINFORCEMENT … Contd.
1
Splicing
In region of splicing
of longitudinal bars
Hoops to be provided over the
entire splice length, at a
spacing not exceeding 150 mm
Lap length shall not be less
than the bar development in
tension

15. Splicing or lapping of longitudinal bars
15

16. 16
Ductile Detailing … Flexural members
Splicing of Longitudinal Reinforcement … Contd.
Lap splices shall not be provided
1. Within a joint
2. Within a distance of 2d from joint face, and
3. Within a quarter length of the member where
flexural yielding may generally occur under the
effect of earthquake forces.
Not more than 50 percent of the bars shall be spliced
at one section.
1

17. 17
Flexural members
WEB REINFORCEMENT
Shall consist of vertical hoops.
Closed stirrup having a 1350 hook with a 10 dia
extension ( min of 75 mm) that is embedded in the
confined core
1

18. Vertical Stirrups
18

19. 19
Vertical Stirrups

20. 20
Flexural members
WEB REINFORCEMENT
In compelling circumstances, it may also be made of
TWO pieces of reinforcement;
• a U – stirrup with a having a 1350 hook and a
10 dia extension ( min of 75 mm), and
• a crosstie.
1

21. 21
Flexural members
WEB REINFORCEMENT
Crosstie – bar having a 1350 hook and a 10 dia
extension ( min of 75 mm) at each end. The hooks
shall engage peripheral longitudinal bars.
Minimum bar dia for hoops
• For spans less than 5 m is 6 mm
• For spans more than 5 m is 8 mm
Contribution of bent up bars and inclined hoops to
resist shear shall not be considered.
1

22. 22
Flexural members
WEB REINFORCEMENT
1

23. 23
Flexural members
WEB REINFORCEMENT
1

24. 24
Flexural members
Spacing of hoops
a) At either end of the beam
Over a length of 2d, spacing shall not exceed
• d/4
• 8 times the dia of smallest longitudinal bar
Minimum spacing is 100 mm
First loop 50 mm from joint face
1

25. 25
Flexural members
Spacing of hoops
b) On either side of a section where flexural yielding
may occur
Over a length of 2d, spacing shall not exceed
• d/4
• 8 times the dia of smallest longitudinal bar
c) Elsewhere
Spacing d/2
1

26. 26
Columns and Frame Members
Factored axial stress under earthquake loading
0.1 fck.
Minimum Dimension 200 mm.
In frames which have beams of span > 5m,
• Minimum dimension 300 mm
For columns having unsupported length > 4m,
• Minimum dimension 300 mm
Preferably b/D ratio > 0.4.
1

27. 27
Columns and Frame Members
Lap Splicing
• Shall be provided only in the central half of the
member length
• Length = Tension splice
• Hoops to be provided over the entire splice length
• Spacing of hoops 150 mm
• Not more than 50 percent of the bars shall be
spliced at one section.
1
LONGITUDINAL REINFORCEMENT

28. 28
Columns and Frame Members
Any area that extends more than 100 mm beyond the
confined core due to architectural requirements shall be
detailed as follows:
Structural – Minimum
longitudinal and
transverse reinforcement
as per IS 13920 : 1993
Non-structural –
as per IS 456-2000
1
LONGITUDINAL REINFORCEMENT

29. 29
Columns and Frame Members
Circular columns - Spiral or circular hoops
Rectangular columns - Rectangular hoops
• Closed Stirrups
1350 hook with a 10 dia extension ( min of 75 mm)
that is embedded in the confined core
Spacing of parallel legs of rectangular hoops
300 mm
Provide crosstie if the length of any side of the
hoop is > 300 mm
1
TRANSVERSE REINFORCEMENT

30. Ties or hoops
30

31. 31
Columns and Frame Members
• Closed Stirrups
1
TRANSVERSE REINFORCEMENT

32. 32
Columns and Frame Members
• Alternative Closed Stirrups
A pair of overlapping hoops may be provided
Spacing of hoops b/2, where b = least dimension
1
TRANSVERSE REINFORCEMENT

33. Shear failure
Large spacing of ties
and lack of 135 o hook
ends caused brittle
failure during 2001 Bhuj
earthquake spacing
33

34. Cross ties
34

35. 35
Columns and Frame Members
Special Confining Reinforcement
Shall be provided over a length
l0 from each joint face towards midspan
l0 on either side of any section where flexural
yielding may occur under the effect of earthquake
forces
The length of l0 shall not be less than
larger lateral dimension of the member
1/6 of clear span of the member, and
450 mm
TRANSVERSE REINFORCEMENT

36. 36
Columns and Joint Detailing

37. Beam column joint
Critical - Need to be designed properly
37

38. Closed loop ties in beam column joints will resist
the ill effects of distortion of joints
38
Beam column joint

39. Providing
horizontal ties
at joints
Three stage
procedure
39
Beam column joint

40. Reinforcement details for Shear Wall

41. 41
Columns and Frame Members
Special Confining Reinforcement
Column terminates into a footing or mat, special
confining reinforcement shall extend at least 300 mm
into the footing or mat.
TRANSVERSE REINFORCEMENT

42. 42
Columns and Frame Members
Special Confining Reinforcement
Spacing of hoops used as special confining
reinforcement
1/4 of minimum member dimension.
minimum 75 mm
shall not be more than 100 mm
TRANSVERSE REINFORCEMENT

43. 43
Columns and Frame Members
Special Confining Reinforcement
Area of cross section, Ash, of the bar forming circular
hoops or spiral is
Area of cross section, Ash, of the bar forming
rectangular hoops is
TRANSVERSE REINFORCEMENT

44. 44
Joints of Frames
Special confining reinforcement as required at the
end of the column shall be provided through the
joint as well.
For joints which have
• beams framing into all vertical faces of it
• where each beam width is at least 3/4 of the
column width
provide half the special confining reinforcement
required at the end of the column.
Spacing of hoops 150 mm.
TRANSVERSE REINFORCEMENT

45. 45
Shear Walls
Resist lateral forces coming on structures
Thickness 150 mm
Reinforcement in longitudinal and transverse
directions
Minimum pt = 0.25% of gross area
If wall thickness is > 200 mm, reinforcement shall
be provided in two curtains.
Diameter of bars 1/10 of wall thickness.
Spacing should be the least of
• lw/5
• 3 tw , and
• 450 mm
where, lw is the horizontal length of wall, and
tw is the thickness of the wall.

46. 46
Joints of Frames
Special confining reinforcement as required at the
end of the column shall be provided through the
joint as well.
For joints which have
• beams framing into all vertical faces of it
• where each beam width is at least 3/4 of the
column width
provide half the special confining reinforcement
required at the end of the column.
Spacing of hoops 150 mm.
TRANSVERSE REINFORCEMENT

47. IS - 13920: 1993
• Requirements of detailing R C structures
to give adequate toughness and ductility
to resist earthquake shocks better
without collapse.
• Particularly necessary in structures
located in Zones 3, 4 and 5.
• Distinction between Toughness &
Resilience.
• Steps to enhance ductility and toughness
in R C structures

48. Horizontal earthquake force
48

49. Structural action under earthquake
49

50. Earthquake shaking
reverses tension and
compression in
members.
Reinforcement is
required in both faces
of members
50

51. Columns should be stronger than beams
Two distinct designs of building that result in
different earthquake performances
51

52. 52