Concept on positioning of Columns

1)

i) Symmetry:

The given plan is symmetrical in both the X and Y directions.

• This is concluded by splitting the plan by exactly two halves across both the directions and checking if bot halves mirror each other.

ii) Redundancy:

The structure is more redundant in X and less redundant in Y direction.

• The columns in X direction are comparatively more and evenly spaced, they have more columns except in top and bottom rows.
• The columns in Y directrion are also evenly spaced but are comparatively lesser than in number.

iii) Bi-directional stiffness:

The framing plan is weak with respect to bi-directional stiffness in Y axis.

• The columns in X axis are all connected in a single straight line from end to end, therefore any lateral load passing through the X direction will reach the other end in a straight path without any force diversion taking place.
• The columns in Y axis are not connected in a single straight line from end to end, therefore any lateral load passing through the Y direction will undergo major force diversion and get diverted to East and west directions in X axis to reach the next bay.

iv) Ductility:

The framing plan is more ductile in Y axis than the X axis.

• The columns in X direction are comparatively more than the Y direction causing in higher stiffness in X axis, thsi results in less ductility in X axis.
• Any lateral load passing through the X direction will reach the other end in a straight path due to the beam alignment, whereas lateral load passing through the Y direction will struggle to pass through due to discontinuos bracing caused by the beam alignment in Y direction.

2)

i) Vertical irregularity:

• The building is larger in the bottom stories with the floor plan are getting reduced with increase in height.
• These building offsets must checked with reference to IS-1893-2016 Table 6 (iii).

ii) Soft storey:

• The 6th floor of the building is an uncovered open space with no partition wall or occupancy, this leads to plastic hinge formation at the column.
• It must be checked with reference to IS-1893-2016 Figure 4A and designed appropriately.

iii) Sloped base:

• There is a sloped ground on one side of the building.
• Few levels maybe subject to soft storey mechanisms.
• It will lead to significant variations in stiffness with reference to IS-1893-2016 Figure 5E.

3)

Open ground floor: therefore soft storey mechanism acts in the building.

Rooms along two bays seperated by open corridor: the bays with rooms will have higher mass than the bays with the open corridors resulting in mass irregularity.

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: because of concentrated concrete elements staircase and lift parts are stiffer than others.

No framing connection along Y-direction: no structural beas provided in the Y direction, this makes the building vulnerable to seismic forces acting in that direction.

Beams connected along column minor axes: The columns are longer along Y direction therefore a lot more stiffer in Y direction. But the beams run along X axis which attract less lateral force and is hardly transfered.

Variation in column sizes: Interior columns are bigger than exterior columns, it leads to significant difference in lateral drift of columns. So the concrete floor suffered heavy out of plane shear which leads to collaps.