Concept on positioning of Columns

Question 1:

Comment on the layout of the framing plan concerning earthquake resistance in the two horizontal directions X or Y (dots are columns, lines depict beams). Look into aspects of symmetry, redundancy and bi-directional stiffness and ductility.

Answer:-

Investigation of the framing plan with respect to symmetry in X-direction:-

If we split the plan vertically, it will look mirrored so we conclude the given plan is symmetric in X-direction

Investigation at the framing plan with respect to symmetry in Y-direction:-

if we split the plan horizontally half, it will look mirrored so we coclude the given plan is symmetric in y-direction.

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

The column in X-direction are comparitively more and evenly spaced. so the structure is more redundant in X-direction except the top & bottom column rows are having quite longer spans.

Investigation of the framing plan with respect to redundancy in Y-direction:-

The columns in Y-direction are comparitively lesser but evenly spaced so the structure is redundant but lesser than that of X-direction.

Investigation with respect to Bi-directional stiffness:-

• The column in ghorizontal 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 column is vertical direction are not connected with straightto straight beams. so a lateral load passing from south side of building will get diverted to east 7 south side of the building will get diverted to east of 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-dirction.

Invstigation of the framing plan with resoect to ductility:-

• Prima facie, the aspect ratioof the plan clearly hints more column in X-direction compared to Y-direction it will results in higher stiffness of the building in X-direction, which would reduce ductility in X-axis.
• More over, the X-force will easily pass from one bay to its next due beam alignment, where as the Y-force will struggle to pass through, the north-south beams are arranged in zig-zag which loads to a discontinues bracing.
• We can conclude that the given framing plan is more ductile in Y-direction than that of in X-direction.

Question 2:

What are the possible sources of irregularity in the building shown here? Explain how, as an engineer, each of these irregularities should be dealt with.

Answer:-

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 cross checked 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 partition wall, this will lead to plastic hinge formation at the columns (with reference to IS-1893-2016 fig: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 stiffeness (with reference to IS-1893-2016 fig:5) few levels may be subjected to soft storey mechanism.
• Vertical irregularity - IS:1893-2016 table-16 serial number iii.

Question 3:

A 4-storey hotel building has an open ground floor for the restaurant. Story 2 to 4 have one row of rooms along each long side in plan, separated by a corridor. The two short sides of the perimeter are fully in-filled in all storeys, except for certain openings at the ends of the corridor at storeys 2 to 4 and along the right-hand side of the ground floor. There is a staircase near the upper left-hand corner, with straight flights between landings at floor levels and in-between floors. Cross-section dimensions are written next to the member no. in meters.

Comment on the features of the structural design and of the layout of infills which are important for earthquake resistance and seismic performance. How do they relate to the almost full collapse of this building (the extreme left-hand bay with the staircase survived, as well as one long-side façade in the rear end, and the frame along the right-hand side in plan).

Answer:-

• Open ground floor:- This denotes soft storey mechanism acting in the building.
• Rooms along 2 bays seperated by an open corridor the bays filled with rooms will have higher mass compared to the middle bay left open for corridor. this includes 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 concete elements,so the stair case portion contains more stiffness in the prvided building plan.
• No forming connection along Y-direction we could see no structural beams provided along the vertical direction between columns. This makes the building more vulnerable during north - south seismic forces.
• b=Beams connected along column minor axes - the columns are having longer dimensions in Y-direction. thi 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 harldly transfers it.
• variation in column sizes:- The internal columns are having higher sizes compared to exterior columns(This is common becaue of higher load demands) but this will lead to significant difference in lateral drift of columns. so the concrete floor mght have suffered heavy out of plane shear which would led to collapse.