DESIGN ENGINEER MUST FOLLOW LINE OF THE REQUIRED RESISTANCE TO PROVIDE BOTH , STRENGTH AND THE DUCTILITY, NECESSARY FOR THE EARTH QUAKE RESISTANT.

The design of earthquake resistant structure should aim at providing the appropriate dynamic and structural characteristics so that acceptable response levels results under the design earthquake.The design Engineer can exercise some degree of control on magnitude and distribution of stiffness and mass ,relative strengths of members and their ductility to achieve the desired results.The performance criterion implicit in most earthquake codes and provision required to make it able for (1) To resist earthquakes of minor intensity without damage .A structure would be accepted to resist such frequent but minor shocks within its elastic range of stresses. (2) To resist moderate earthquakes with minor structural and some non -structural damage.With proper design and construction,it is believed that structural damages due to the majority of the earthquakes will be limited to repairable damages ,and (3) To resist major catastrophic earthquakes without collapse.Severe structural damage is expected . For satisfactory performance in an earthquake 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.But in order to accomplish this,it would require designing the structure for lateral forces several times greater than those specified in a seismic code for construction and use .It must be assumed that in a severe earthquake some of the resisting elements may be loaded to their full strength.If they are brittle,they will fail , throwing their share of the load on to the remaining elements.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.Thus it is necessary for the designer to follow the line of resistance providing both the strength and the ductility.A ductile material may undergo large strains while resisting the loads, when applied to reinforce the concrete members and the structures .The ductility implies the ability to sustain significant inelastic deformations prior to the collapse and the brittle material as well as the structure may fail suddenly upon attaining it's maximum load .It is therefore necessary to protect the line of resistance after consultation of the code for consideration and improvement suggested by the earthquake resistant construction.