A Step-by-Step Summary of the Equivalent Lateral Force Procedure for the Seismic Design of Structures

May 15, 2017 Abdul Siraj, P.E.

In this post, I will provide a step-by-step summary of the equivalent lateral force procedure for the seismic design of structures.

 

The first step is to determine the seismic design category and choose the proper seismic importance factor, IE, of the structure.

 

The second step is to choose the appropriate response modification factor from Table 12.2-1 of ASCE 7-10.

 

The third step is to calculate the elastic fundamental period of the structure, T, which is a function of the mass and stiffness of the structure. It can be found using Section 12.8.2.1 of ASCE 7-10.

 

The fourth step is to calculate the seismic response coefficient, Cs, from Section 12.8.1.1 of ASCE 7-10. It is equal to the design spectral response acceleration coefficient for short periods, SDS, times the seismic importance factor, IE, divided by the response modification factor, R.

 

The fifth step is to compute the effective weight of the structure.

 

The sixth step is find the the seismic base shear, which is defined as the total seismic force acting at the base of structure during an earthquake. According to Equation 12.8-1 of ASCE 7-10, it is equal to the product of the seismic response coefficient, Cs, and the effective weight of the structure, W.

 

The seventh step is to determine the seismic lateral load, Fx, for each level of the structure from Equation 12.8-11 of ASCE 7-10. The lateral seismic force is equal to vertical distribution factor, Cvx, times the total design lateral force or base shear.