Concept on positioning of Columns

Ans1:

Structural Simplicity: The structure is simple structure as can be seen from 2D plane figure. The shape of the structure in 2d plane is almost square. If the structure is assumed uniform(column and beam sizes and position in elevation), there is direct load transfer from one point to another(except at four corners).

Uniformity and Symmetry : The structure is uniform and symmetric about both axis. There is even distribution of structural elements(beams and columns) in the shown 2d plane. Therefore, there is short and direct transmission of inertial forces produced in the distributed masses of building. The eccentricity between centre of stiffness and centre of mass is zero if the mass of slab or floor is uniformly distributed in plane.

Redundancy : The structure is redundant as there are many structural elements (beams and columns) evenly distributed in plan. As it is redundant, it is reliable for even distribution of earthquake forces. But if there is presence of shear walls it will be more redundant.

Bi directional Stiffness : The stiffness in both the orthogonal directions is almost the same. The stiffness in y axis is less than in x axis slightly. The reason is the end spans between columns along x axis is less than in end spans between columns along y axis.

Ductility : We can provide more ductility in the structure with more reduction factor because the structure is symmetric and simple without any irregularities.

Ans 2 :

Sources of irregularities :

(1) : The structure is irregular in both 2d plan and 3d elevation. In elevation there is sudden change in length, width and height of the structure.

(2) : The Columns in the middle storey are not provided with masonry walls for architectural purposes. This may leads to soft storey mechanism at that storey. It can be seen that height of that storey is also more than other storeys which is also cause of soft storey mechanism due to reduction in stiffness at that storey.

(3) : The same reduction factor cannot be applied for the whole structure because there is major difference in dimensions in the upper block of the structure and the lower block.

(4) The less reduction factor must be used and more elasticity must be provided.

Ans 3 : We can see from the figure that there is staircase at the left top corner which breaks the symmetry of the whole structure. The back side of the structure becomes more stiff because of staircase columns and beams. The length of columns in middle two bays is more than that of the columns at the top and bottom ends. And the depth of the beam in the middle two bays is less than the beam at the top and bottom ends.

On the middle columns the load is acting on the two sides and on the end columns the load is acting on one side only.

On the other hand the diaphragmatic behavior of the slab, the length along y axis is less than along x axis of the

diaphragm(slab). Due to this during seismic action along y axis in plan two times the total lateral load is applied on middle

columns that of the lateral load at the end columns. Along x axis there are more beams present than along y axis, which

makes the structure more stiffer along x axis than that of along y axis.

Therefore, during seismic action left and right end frames remains non-destructed, and the bottom (in plan) and

middle frames gets destructed due to seismic action along y axis (no beams present in middle along y axis, less stiffer).