Concept on positioning of Columns
1)
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.
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 symmetrical in Y-direction.
Investigation of the framing plan with respect to redundancy in X-direction :-
The column in X-direction are comparatively more and evenly spaced. So the structure is more redundant in X-direction. Except the top and bottom column rows are having quite longer spans.
Investigation of the framing plan with respect to redundancy in Y-direction :-
The columns in Y-direction are comparatively lesser but evenly spaced so the structure is redundant but lesser than that of the X-direction.
Investigation with respect to Bi-directional stiffness :-
* The columns in horizontal direction are connected with straight beams.This means, any lateral loads(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 direction takes place.
* The columns in vertical direction are not connected with straight to straight beams. So 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.
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 its next due to beam alignment. Where as, the Y-force will struggle to pass through. The north-south beams are arranged in zig-zag which leads to discontinuous bracing.
* We can conclude that 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 increases 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 partion wall, this will lead to plastic hinge formation at the columns(with reference to IS:1893-2016 figure 4A). This has tobe checked and sufficiently designed.
Slopy base :-
The building is constructed on the sloping ground at one side. This will lead to give significant variations in the stiffness(with referance to IS:1893-2016 figure 5E). Few levels maybe subjected to soft storey.
3)
Open ground floor :-
This denotes soft storey mechanism acting in the building.
Rooms along 2bays separated by an open corridor :-
The bays filled with rooms will have higher nass compared to the middle bay left open for corridor. This induces mass irregularity along height uniformly.
Two short sides covered with in fill walls :-
This means the building left and right sides periphery is more stiffer during seismic forces(especially along north-south).
Staircase portion at left top corner :-
Usually staircase and liftportios 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 beam provided along the vertical direction between columns. This makes the building more vulnerable during the north-south seismic force.
Beams connected along column minor axes :-
The columns are having longer dimension in Y-direction. This means they are more stiffer along Y-direction. But the beams are running only X-direction which would attract much lesser lateral forces and hardly transfer it.
Variation in column sizes :-
The internal columns are having higher sizes compared to exterior columns(This is common beacuse of higher load demands). But this will lead to significant difference 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.