Foundation, Concrete and Earthquake Engineering

Requirements For Frames in Regions of High Seismic Risk

In region of high seismic risk, structural frames proportioned to resist forces induced by earthquake motion should satisfy the requirements stated below :

1) Tensile steel ratio in flexural members should be well below balance steel ratio,Pb to ensure adequate rotation capacity at plastic hinges.

2) Use of high strength steel (having limited ductility) should be avoided.

3) Lateral reinforcement in column must serve not only their usual functions of column (ties or spiral) but also serve as shear reinforcement to provide adequate resistance to horizontal forces.

4) As much as possible longitudinal beam reinforcement should be carried through beam- column joints without interruption.

But when required special attention must be paid to bar anchorage .

5) At least minimum amount of flexural reinforcement should be used in both top and bottom throughout the length of all beams to allow for

a) possible shifts in points of inflection

b) load combination not accounted in design.

6) At least minimum amount of web reinforcement should be used throughout length of all beams and closed-hoop reinforcement should be provided in regions which can subject to plastic hinging to improve rotational capacity.

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