## Equivalent Lateral Force Analysis (Static Analysis)

Seismic Analysis Using UBC And IBC Codes,Equivalent Lateral Force Analysis in STAAD Pro v8i

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Basic principle

•When a building is subjected to an earthquake, it undergoes vibrations.

•The weights of the structure, when accelerated along the direction of the earthquake, induce forces in the building.

•Normally, an elaborate dynamic analysis called time history analysis is required to solve for displacements, forces and reactions resulting from the seismic activity.

•UBC and IBC provide a static method of solving for those values.

Generalized Procedure

Step 1:

Calculate

Base Shear = Factor f * Weight W

where,

f – is calculated considering

•Importance factor of the building,
•Site Class
•and soil characteristics, etc.

W is the total vertical weight derived from dead weight of the building and other imposed weights.

Generalized Procedure

Step 2:

The base shear is then distributed over the height of the building as a series of point loads.

Generalized Procedure

Step 3:

The model is then analyzed for the horizontal loads generated in step 2. 