Concept on positioning of Columns

Q1) Ans:- Investigation of the framing plan with respect to redundancy in X-direction.

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

• Columns 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 quiet longer spans. The columns are symmetrical in stiffness distribution

- Investigation of the framing plan with respect to redundancy in Y-Direction.

• Columns in Y-direction are comparatively lesser but evenly spaced. So the structure is redundant but lesser than that of in X-direction.

- Investigation with respect to Bi-directional stiffness:

• It is bi-directional. The columns in horizontal direction are connected with straight too straight beams. This means any lateral load (Seismic force in X-direction) passing from left end of the building will have it's path straight till it reaches right end of the building. So no or very less possibility of force diversion takes place.
• The columns in the vertical direction are not connected with straight to straight beams. So a lateral load passing from south sole 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 in Y-Direction 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 columns in x-direction comparative to y-direction. It will result in higher stiffness if the building in x-direction, which would reduce ductility in x-axis.
• Moreover, the x-force will easily pass from one bay to it's next due to beam alignment. Whereas, the y-force will struggle to pass through. The north-south beams are arranged in zig-zag which leads to a discontinuous framing.
• We can conclude that the given framing plan is more ductile in y-direction than that of in x-direction.

Q2)Ans:

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

• Soft-Story: 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.

-1: 5 Stories have larger area compared to other upper floors.

-2: No bracing on the 6th floor, uncovering space it's substories

• 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 IS1893-2016 figure 5C). Few levels may be subjected to soft story.

- There is embankment, slopy ground

- vertical irregularity ( IS1893-2016 table b serial no (iii))

- Soft story - IS1893-2016 Figure 4A

- Soft base IS1893-2016 Figure 5E

Q3)Ans:

As given in the question:

i. Open ground floor (soft story mechanism)

ii. 2,3,4 have one row of rooms along each long side and separated by a corridor

iii. Two sides are infill walls

iv. Staircase near upper left hand corner

• 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 rooms will have a higer 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 periphery is more stiffer during seismic force along north-south.
• Staircase portion at top left corner: Considered to be more stiffer on that part. As usual staircase and lift portion are stiffer because of concentrated concrete elements. More stiffness will lead to more resistance to lateral force. The partition walls arranged within the bay, will lead to mass irregularity in all stories.
• No framing connection along y-direction: 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 axes - The stiffness of column is higher in vertical direction. The columns are having longer dimensions 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 transfer it.
• Variation in column sizes: External columns usually have much lesser lead than internal. The internal columns are having higher sizes compared to exterior columns because load demands. But this will lead to significantly difference in lateral drift of columns. So the concrete floor might have suffered heavy out-of-plane shear which would lead to collapse.