Concept on positioning of Columns
Answers:-
1
· The given plan is symmetric in X and Y- direction because it will look mirrored images when we split it in to half
· The columns in X- direction is more redundant than that of Y-direction, because columns are more in X-direction and are of evenly spaced except top and bottom while in Y-direction it is evenly spaced but counts are lesser than that of in X-direction.
· For Bi-directional stiffness, in X-direction the columns are connected by straight to straight beams so the lateral loads pass from one end to the extreme next end without any distraction. But in the vertical direction the columns are not connected straight to straight so diversion of force takes place along east and west direction. Thus the framing plan is weak with respect to bi-directional stiffness in Y-direction.
· In X-direction, the no of columns are higher thus results higher stiffness, which will reduce ductility. X- force will pass through one bay to another easily due to beam alignment while Y-force will struggle due to the beam zig-zag arrangement. So the given frame arrangement is more ductile in Y-direction.
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· Vertical irregularity :- As per IS 1893:2016, table 6 serial number (iii), The bottom base area is large compared to the top floor areas.
· Soft storey:- As per IS 1893:2016 Figure 4A, the building has uncovered opening space at 6th floor. As there is no occupancy or partition wall, this will lead to plastic hinge formation at the columns.
· Slopy base:- As per IS 1893:2016 figure 5E, the building is constructed on a sloping ground at one side. This will lead to variations in stiffness, so shows soft storey mechanism.
3
· Open ground floor:- This causes soft storey mechanism.
· Rooms along 2 bays separated by an open corridor:- The bays filled with rooms will posses higher mass compared to the middle bay this induces irregularities.
· Two short sides covered with infill walls:- The building left and right side is more stiffer during seismic activity.
· Staircase portion at left top corner:- The staircase and lift portion are more stiffer than other parts of the building due to concentrated concrete elements.
· No framing connection along y-direction:- there were no structural beams are provided along vertical direction so building becomes more vulnerable during north-south seismic force.
· Beams connected along column minor axis:- The columns are having longer dimension along y-direction. This means they are more stiffer along vertical direction but the beams are running along x-direction which would attract much lesser lateral forces.
· Variation in column sizes:- The internal column sizes are lesser than exterior columns, so leads to significant difference in lateral drift of columns.