IS:13920- 1993- Detailing of reinforced concrete structures subjected to seismic forces
This standard covers the requirements for designing and detailing of monolithic reinforced concrete buildings so as to give them adequate toughness and ductility.
Clause gives the general requirement, which flexural members should satisfy.
a) Longitudinal Reinforcement:
-The top as well as bottom reinforcement shall consist of at least two bars throughout the member length.
- The positive steel at a joint face must be atleast equal to half the negative steel at that face.
- The steel provided at each of the top and bottom face of the member at any section along its length shall be at least equal to one- fourth of the maximum negative moment steel provided at the face of either joint.
- in an external joint, both the top and the bottom bars of the beam shall be provided with anchorage length, beyond the inner face of the column, equal to the development length in tension plus 10 times the bar diameter minus the allowance for 90 degree bend.
- Clause no. 6.2.6 gives about the lap, splice in beam.
- Web reinforcement shall consist of vertical hoops. A vertical hoop is a closed stirrup having a 135 degree hook with a 10- diameter extension (but not<75mm) at each end that is embedded in the ocnfined core. Itmay be made up of two pieces of reinforcement,a U- stirrup and a crosstie.
- The minimum diameter of the bar forming a hoop shall be 6 mm. However, in beams with clear span exceeding 5 m, the minimum diameter shall be 8 mm.
- The spacingof hoops ovwe a length of 2d at either end of a beam shall not exceed (a)d/4, and (b) 8 times the diameter of the smallest longitudinal bar, however, it need not be less than 100 mm. The first hoop shall be at a distance not exceeding 50 mm from the joint face. Elsewhere, the beam shall have vertical hoops at a spacing not exceeding d/2.
Columns and frame members subjected to Bending and Axial Load
Clause in it gives the general requirement, which columns and frame members should satisfy
a) Longitudinal Reinforcement
-The minimum longitudinal and transverse reinforcement is given as per IS 456- 2000
b) Transverse Reinforcement
- Transverse reinforcement for circular columns shall consist of spiral or circular hoops. In rectangular columns, rectangular hoops may be used.
- The parallel legs of rectangular hoops shall be spaced not more than 300 mm center to center.
-The spacing of hoops shall not exceedhalf the least lateral dimension of the column.
c) Special Confining Reinforcement:
-This requirement is used when large amount of transverse reinforcement is required for shear strength considerations.
- Special confining reinforcement shall be provided over a length lo from each joint face, toward midspan, and on either side of any section, where flexural yielding may occur under the effect of earthquake forces. The length 'lo' shall not be less than (a) larger lateral dimensions of the member at the section where yielding occurs, (b) 1/6 of clear span of the member, and (c) 450mm.
- The spacing of hoops used as special confining reinforcement shall not exceed 1/4 of maximum member dimension but need not be less than 75mm nor more than 100mm.
d) Joints of frames:
- A joint which has beams framing into all vertical faces of it and where each beam width is at least 3/4 of the column width, may be provided with half the special confining reinforcement required at the end of the column.
- Hoops spacing shall not exceed 150mm.
e) Shear walls:
- They are part of the lateral force resisting system of the structure.
- The thickness of any part of the wall shall preferably, not be less than 150 mm.
-Shear wall shall be provided with reinforcement in the longitudinal and transverse directions in the plane of the wall.
- The diameter of the bars to be used in any part of the wall shall not exceed 1/10th of the thickness of that part.
- Reinforcement shall be provided along the edges of openings in walls. The vertical bars should extend for the full storey height. The horizontal bars should be provided with development length in tension beyond the sides of the opening.
-Horizontal reinforcement shall be anchored near the edges of the wall.
-Welded splices and mechanical connections shall confirm to IS 456: 2000.