EARTHQUAKE RESISTANT DESIGN AND SCOPE AND CYCLIC BEHAVIOUR OF CONCRETE AND REINFORCEMENT .

It is necessary to aim at design of earthquake resistant in structures which may provide appropriate dynamic structural characteristics with acceptable response and results under the provision made however it is necessary to exercise degree of assessment and control required on magnitude and distribution of stiffness and the mass ,relative strength of members and their ductility to achieve the desired results. The performance criteria implicit in most earthquake codes and provisions requires that a structure be able to:--(1) Must resist earthquake of the minor intensity without damage .A structure would be expected to resist such frequent but minor shocks with in its elastic range of stresses .(2) Resist moderate earthquakes with minor structural and some non structural damage .With proper Design and construction,it is believed that structural damage due to the majority of earthquakes will be limited to repairable damage and (3) resist major catastrophic earthquakes without collapse. Severe structural damage is expected. As such a structure must have strength as well as ductility. If the elastic strength of each element in a structure exceeds the greatest load imposed upon it there can be no significant structural damage however it may require designing the structure for lateral forces several times greater than those specified in a seismic code .It must be assumed that in a servere earthquake some of the resisting elements will be loaded to their full strength,if they are brittle,they will fail and if they are sufficiently ductile,they can continue to participate in resisting the lateral force nearly up to their full strength after they yield throwing only the excess load to the remaining elements .Plain concrete is a brittle material where as reinforcing steel has much more ductility than plain concrete .The ultimate strain in mild steel is of the order of 25percent where as,in concrete it is of the order of 0.3percent .