Ductile deatailing

ductile detailing as per is 13920-2016 for earthquake resistant design of a framed structure

1. DUCTILE DETAILING as per IS 13920:2016 Prof. Ram Meghe Institute Of Technology And Research – Badnera , Amravati By Aniket Chavan Welcome

2. INTRODUCTION The basic approach of earthquake resistant design should be based on lateral strength, deformability and ductility capacity of structure with limited damage but no collapse. The code IS 13920-2016 “ Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Force Code of Practice” based on this approach. This standard covers the requirements for anchorage, specially bar cut-offs and joint details.

3. DUCTILITY Ductility in concrete is defined by the appropriate percentage of steel reinforcement present in it. Mild steel is an example of ductile material that can be bent and twisted without rupture. A ductile material is one that can undergo large strain while resisting loads. In case of reinforced concrete building, the term ductility implies the ability to sustain significant inelastic deformation prior to collapse.

4. A convenient measure of ductility is a ratio of the curvature at the ultimate strength of the section ( øu ) to that of the curvature at the first yield of tension steel in the section ( øy ).

5. Importance of Ductility Ductility in the structure will arise from inelastic material behaviour and detailing of reinforcement in such a manner the brittle failure is avoided and ductile behaviour is induced by allowing steel to yield in control manner. Ductile failure of the structure will not be sudden, hence the people occupying the structure get sufficient time to escape. It allows the structure as a whole, to develop its max. potential strength, through distribution of internal forces, which is given by the combination of max. strength of all componets .

6. Beam failure Longitudinal bars to resist bending moment while vertical stirrups resist shear force. Beams sustain two basic types of failure, Flexural failure Shear failure

7. General requirements for Ductile detailing Minimum grade of concrete is now M20 for any building and M25 for buildings with height > 15 m Steel reinforcement of grade Fe-415 However, TMT bars of grade Fe-500 & Fe-550 may be used

8. Ductile detailing of beam Clause 6.1 The factored axial stress on the member under eq. loading shall not exceed 0.1fck. The member shall have Width/depth ratio of more than 0.3 Width of the member shall not less than 200mm. Depth of the member (D) should not be more than ¼ of clear span.

9. Diameter at least 6mm but not less than 8mm for beam longer than 5m. 135 hook at both end and 10 times diameter extension. Max. spacing less than half the depth of beam. Max. spacing less than quarter the depth of beam for twice the depth of beam for support.

10. At the location of lap, the bars transfer large forces from one to another Laps of the longitudinal bars are: Made away from the face of column. Not made at locations where they are likely to stretch by large amounts and yield

11. Transverse reinforcement The min. dia. of the bar forming hoop shall be 6mm. In lc > 5m min. bar dia. 8mm The spacing of hoops over a length 2d at either end of beam shall not exceed a) d/4 b) 8 * dia. of smallest longitudinal bar, whichever is smaller The first hoop shall be at a distance not exceeding 50mm from the joint face.

12. Ductile detailing of column Clause 7.1 Column can sustain 2 types of damage a) axial flexural (combined compression bending ) failure b) shear failure (brittle damage) & must be avoided by providing lateral ties

13. Design -width to depth ratio >= 0.4 -0.8 <= steel percent <= 4.0% -No. of bars in rectangular section >= 4 -longitudinal bar diameter >= 12mm -clear cover >= 40mm - min. width of column = 300mm

14. Closely spaced horizontal closed ties help in 3 ways, They carry the horizontal shear forces induced by eq. and thereby resist diagonal shear cracks. They hold together the vertical bars and prevent them from excessively bending outwards , and They contain the concrete in the column within the closed loops . The ends of the ties must be bent as 135 degree hooks. Such hook ends prevent opening of loops and consequently.

15. In column where spacing between the corner bar exceeds 300 mm: Additional links with 180 hook ends for ties to be effective in holding the concrete in its place and to prevent the buckling of vertical bars.

16. Special Confining Reinforcement Ht. of confinement zone Larger of D, h c /2 or 450mm Spacing of ties in CZ: <= D/4 But >= 75mm and <= 100mm Spacing of ties in lap zone: <= D/2 and <= 150mm Spacing of ties in rest <=D/2

17. References [1] IS 13920:1993 - Indian Standard Ductile Detailing of Reinforced Concrete Structures subjected to seismic forces - Code of Practice [2] The Indian Concrete Journal VOL-77, NOV2003, No-11 (Special Issue Earthquake Engineering) [3] Earthquake Reconnaissance Report (Bhuj, India; 26-01-2001) : National Information Centre of Earthquake Engineering (NICEE) IIT, Kanpur. [4] Design of Reinforced Concrete Structures For Earthquake Resistance -By D.S. Joshi, R. L. Nene, M. D. Mulay , S. Salegaonkar , N. D. Joshi, Published By Indian Society of Structural Engineers, Dadar West, Mumbai [5] Imaging the Indian Subcontinent beneath the Himalaya -Schulte- Pelkum , V., A. Sheehan, F. Wu, R. Bilham, , Nature,435, 1222-1225, 30 June 2005.

18. Thank you….!