Concept on positioning of Columns

Answer – 1:

• Checking framing plan for Symmetry in X- direction

We get mirror image of plan if we cut vertically half, so the given framed plan is symmetry in X-direction.

• Checking framing plan for Symmetry in Y- direction

We get mirror image of plan if we cut horizontally half, so the given framed plan is symmetry in Y-direction.

• Checking framing plan for redundancy in X- direction

The column along X direction is more and evenly spaced, So the structure is more redundancy in X direction. Except the top(A) and bottom (B) as shown below.

• Checking framing plan for redundancy in Y- direction

The column along Y direction is less as compared to X direction and evenly spaced, So the structure is lesser redundancy in Y direction than X direction.

• Investigating framing plan with respect to Bi-directional stiffness:

The columns in the X direction are connected straight to straight beams. This shows any lateral load in X direction passing from left to right side of building would have its path straight. So less or no force diversion might occur.

The columns in the Y direction are not connected straight to straight beams. This shows any lateral load in Y direction passing from bottom to top side of building would get diverted to left/right to reach its bay instead of top as shown in A, B, C & D. So, the framing plan is weak in bi-directional stiffness in Y-direction.

• Checking framing plan for redundancy in Y- direction

The column along Y direction is less as compared to X direction and evenly spaced, So the structure is lesser redundancy in Y direction than X direction.

• Investigating framing plan with respect to Bi-directional stiffness:

The columns in the X direction are connected straight to straight beams. This shows any lateral load in X direction passing from left to right side of building would have its path straight. So less or no force diversion might occur.

The columns in the Y direction are not connected straight to straight beams. This shows any lateral load in Y direction passing from bottom to top side of building would get diverted to left/right to reach its bay instead of top as shown in A, B, C & D. So, the framing plan is weak in bi-directional stiffness in Y-direction.

• Investigating of framing plan with respect to ductility:

The aspect ratio of the plan clearly shows more column in X direction as compared to Y direction. It will result in higher stiffness in X direction which would reduce ductility in X-axis.

The x-force will easily pass from one bay to its next due to beam alignment. Whereas, the Y-force will struggle to pass through. The north and south beams are arranged in zig-zag which leads to discontinuous bracing.

We can conclude that the framing plan is more ductile in Y-direction.

Answer – 2:

• Vertical irregularity :

The building plan area is large in bottom stories (1-5).The floor plan areas are getting reduced with increase in height. As per IS code 1893(P-1):2016,Table No.6 Sl.No.(iii), the offsets are to be checked as per below mentioned para.

• Soft Story:

The building has uncovered opening space in the 6^th floor. There is no occupancy or partition wall exists, this will lead to plastic hinge formation at the columns vide reference to IS code 1893(P-1):2016,Fig.4A as below. This issue should be taken into consideration for designing frame plan.

• Slopy base:

This building is connected on a slopy ground at on side (Right side). This will lead to significant variations in the stiffness with reference to IS code 1893(P-1):2016,Fig.5E as below. Few levels may be subjected to soft story mechanism.

Answer – 3:

• Open ground floor:

This denotes soft story mechanism acting in the building.

• Rooms along 2 bays separated by an open corridor:

The bays filled with room have higher mass compared to middle bay (corridor). This would induce mass irregularity along height uniformity.

• 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 direction.

• Staircase portion at top corner:

Usually staircase and lift portions are stiffer than other parts because of concentrated concrete elements. So the staircase portions are more stiffer in the building.

• No framing connection along Y-direction :

There is no structural beams provided along the vertical direction b/w columns. This makes the building more vulnerable during the north-south seismic force.

• Beams connected along column minor axis:

The columns are having longer dimensions along vertical directions. This means they are stiffer along Y direction but the beams connections are only along X directions which will literally attract fewer lateral forces and hardly transfer it.

• Variation in column sizes:

The internal columns are having higher sizes as compared to exterior columns. This will certainly lead to significant drift in columns. Therefore, the concrete floor might have suffered heavy out of plane shear which would led to collapse during earthquake.