Concept on positioning of Columns

1) Aim: To understand the impact of vertical and horizontal members in seismic behavior of a structure

To understand different irregularities in a building

a) Investigation of the framing plan with respect to symmetry in X- direction

If we split the plan vertically half, it will look mirrored. So we conclude the given plan is symmetric in X-direction

b) Investigation of the framing plan with respect to symmetry in Y direction

If we split the plan horizontally half, it will look mirrored. So we conclude the given plan is symmetric in Y- direction

c) Investigation of the framing plan with respect to redundancy in X- direction

The columns in x- direction are comparatively more and evenly spaced. So the structure is more reduntant in x-direction. Expect the top and bottom column rows are having quite longer spans

d) Investigation of the framing plan with respect to reduntancy in Y- direction

The columns in y-direction are comparatively lesser but evenly spaced. So the structure is reduntant but lesser than that of in x-direction

e) Investigation with respect to Bi directional stiffness

The columns in horizontal direction are connected with straight to straight beams. This means, any lateral load( Seismic force in X-direction) passing from left end of the building will have its path straight till it reaches right end of the building. So no or less possibility of force diversion takes place

The columns in vertical direction are not connected with straight to straight beams. So a lateral load passing from south side of building will get diverted to east and west direction to reach next bay. There will be major force diversion take place with seismic force in Y-direction. The framing plan is weak with respect to bi- directional stiffness in Y- direction

f) Investigation of the framing plan with respect to ductility

Prima facie, the aspect ratio of the plan clearly hints more column in x- direction compared to y- direction. It will result in higher stiffness of the building in x-direction, which would reduce ductility in x-axis

Moreover, the x-force will easily pass from one bay to its next due to beam alignement. Whereas, the y-force will struggle to pass through. The north-south beams are arranged in zigzag which leads to a discontinous bracing

We can conclude that the given framing plan is more ductile in y-direction than that of in x-direction

2) Vertical irregularity- The building plan area is large in bottom stories. The floor plan areas are getting reduced with increase in height. These building offsets has to be crosschecked with references to IS- 1893-2016 Table-6 serial number(iii)

Soft storey- The building has uncovered opening space in 6th floor. As there is no occupancy or a partition wall this will lead to plastic hinge formation at the columns(with reference to IS-1893-2016 Figure 4A). This has to be checked and sufficiently designed

Slopy base - The building is constructed on a sloping ground at one side. This will lead to significant variations in the stiffness (with reference to IS- 1893-2016 figure 5E). Few levels may be subjected to soft storey mechanism

Vertical irregularity- IS -1893- 2016 Table-6 serial number(iii)

Soft storey- IS-1893- 2016 Figure 4A

Slopy base- IS -1893-2016 Figure 5E

3) Open ground floor- This denotes soft storey mechanism acting in the building

Rooms along 2 bays separated by an open corridor- The bays filled with rooms will have higher mass compared to the middle bay left open for corridor. This induces mass irregularity along height uniformly.

Two short sides covered with infill walls- This means the building's left and right sides periphery is more stiffer during seismic forces( especially along North- south)

Staircase portion at left top corner- Usually staircase and lift portions are stiffer than other parts because of concentrated concrete elements. So the staircase portion contains more stiffness in the provided building plan

No framing connection along y-direction- We could see no structural beams provided along the vertical direction between columns. This makes the building more vulnerable during NOrth south seismic force

Beams connected along column minor axis- The columns are having longer dimension in y-direction. This means they are more stiffer along y-direction. But the beams are running only along x- direction which would attract much lesser lateral forces and hardly transfers it.

Variation in column sizes- The internal columns are having higher sizes compared to exterior columns( This is common because of higher load demands). But this will lead to significant difference in lateral drift of columns. So the concrete floor might have suffered heavy out-of plane shear which would led to collapse