Concept on positioning of Columns

1.Ans

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.
• It is observed that the distribution of mass stiffness is across the plan has good symmetrical aspects.
• This tends to reduce the horizontal displacements in both of the two horizontal displacements in both of the two Orthogonal Horizontal Directions.
• It also has a very good uniformity also

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.
• Symmetric in both the directions and well distributed which helps the transferring the load equally as it is very good to transfer all the vertical loads uniformly. By this symmetricity stiffness of the building will also be improved

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 redundant in x-direction.
• Except the top and bottom column rows are having quite longer spans.
• Redundancy is less as there is no shear walls placed and not resisting the non-lateral forces
• Connection between beam and the columns are not uniform so stronger columns weak beam scenario is preferred and beams should act as the ductile for the building to resist the earthquake forces.

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 in x-direction.
• Redundancy is less as there is no shear walls placed and not resisting the non-lateral forces
• Connection between beam and the columns are not uniform so stronger columns weak beam scenario is preferred and beams should act as the ductile for the building to resist the earthquake forces.

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 & 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 to its 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 bracing.
• We can conclude that the given framing plan is more ductile in y-direction than that of in x-direction.
• The building may not be able resist the elastic earthquake forces in shorter direction (v-axis) so it may result in inelastic Response.
• The reduction in design force in the shorter direction (Y-axis) is to be compensated by Ductility.

2.Ans

• We can see that the building in not uniform along the height in the elevation as the columns at each level are not connected to each other which raises the irregularity of the structure by which vertical load acting will not be distributed equally by this there would be the formation of the kink
• This also arises the stiffness irregularity of the structure for the different levels/storeys. For resisting this, stronger columns have to be provided or size of the columns can be decreased of the top floors orderly.

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 reference 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.

Some provisions to avoid the irregularities:

• the building is torsionally irregular so the building framing must be revised
• The mass irregularity is avoided by providing light weight concrete/ Low weight masonry or by providing structure with more wood materials.
• The structure should be built in a well symmetric manner.
• The columns which are provided on the structure should be of same size and height throughout the building.
• The weight of the building from ground floor should decrease towards top

Mass irregularity: at each floor as seen in the building there is a open floor at the middle of the structure and mass of the above floors are respectively decreasing as there size is decreased

3.Ans

• In buildings, floors play a very important role in the overall seismic response of the structure. They act as horizontal diaphragms
• That collect and transmit the inertial forces to the vertical structural systems and ensure that those systems act together in resisting the horizontal seismic action.
• A soft story at ground level is certainly the most serve situation, because there in the inter-storey shear force is at its maximum and that storey supports the whole building

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 the North-South seismic force.

Beams connected along column minor axis

• The columns are having longer dimension in Y-direction. This means they are 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.