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Seismic Design Principle

Lateral loads like wind and earthquake comes under dynamic loading category. Although nature and intensity of both the loads are different. One thing common between both is, both induces differential shear stress along the structure height. These days keeping everything in mind structures were designed earthquake resistant. Different materials and construction practices are adopted for high rise buildings in higher seismic zones. Shear wall is one of the element, which is used frequently to counteract to the lateral forces. Earthquake forces are random and time variant. For the force based design shear force is calculated after considering multiple factors like type of soil, Seismic zone, Importance factor etc. As per the Indian Seismic Code IS:1893 (Part 1) – 2007, Design Base Shear VB is given by:


where Z is the Seismic Zone Factor, I the Importance Factor, R the Response Reduction Factor, and (S a / g) the Design Acceleration Spectrum Value. W is the seismic weight of the building. To estimate the seismic weight of the building, full dead load and part live load are to be included. Percentage of imposed load depends on the height of the floor. Seismic zone factor depends on the location of the structure and how much prone it is to the earthquake. Importance factor depends on the purpose of the building, increase with important buildings. Design acceleration value depends on the structure’s fundamental time period and soil type. Time period depends on the mass and stiffness of the structure. It is directly proportional to mass and inversely related to stiffness. Response reduction factor depends on the type of the structure like whether it is RC frame or not.


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