Multistory Frame Building Essay

CHAPTER 4 PROBLEM OF STATEMENT & METHODOLOGY

4.1 Selection of building plan

A multistory frame building is taken into consideration. Building having a RCC shear wall throughout the height of building. Details of multistory frame building are as follows.

Storey of building : G+ 12 storey

Frame type : Special moment resisting frame structure

Floor to floor height : 3.5 m

Seismic zone : Zone III

Soil type : Medium soil (Type II)

Shear wall : 230 mm thick

4.2 Analyze the building plan.

Analyze the building plan is as follows.

1. Center of mass.

2. Center of Rigidity.

4.2.1 Center of mass

Centre of mass (CM) is the point where entire mass of the system is concentrated. During an earthquake, acceleration induced inertia forces will be developed at each floor level,

It is also referred as centre of stiffness of a system. If, as a result of lateral forces, one floor of the building translates horizontally as a rigid body relative to the floor below, a constant inter-story displacement say ‘Δx’ will be imposed on all frames and walls in that story. Therefore, the induced forces in these elastic frames and walls, in the relevant planes, will be proportional to the respective stiffness. The resultant total force, Vj=Vx, induced by the translational displacement Δx, will pass through the centre of rigidity (CR).

The position of CR may be different in each story. It is relevant to story shear forces applied in any direction in a horizontal plane. Such a force may be resolved into two components, such as Vx & Vy, which will cause simultaneous story translations ‘Δx’ & ‘Δy’ respectively. The displacement due to story twist are proportional to the distance of the element from the centre of rotation i.e. CR.

Calculation of centre of rigidity:

X coordinate = Σ (Kyi x Xi)/ Σ Kyi ; Y coordinate = Σ (Kxi x Yi)/ Σ