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.

Answers:-

Obectives:-

• To understand the imapct of vertical & horizontal members in seismic behavior of a structure
• To understand different irregularities in a building

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

• If we spilt the plan vertically half, it will look mirrored. so we conclude the given plan is symmetric in X- direction.

Ivestigation of the framing plan with respect to symmetry in Y- direction:

• If we spilt the plan horizontally half, it will look mirrored. so we conclude the given plan is symmetric in Y- direction.

Investigation with respect to BI-directional stiffness:

• The columns in horizontal direction are connected with straight beams.This means any lateral load (seismic force in y-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 connect with straight to straight beams. so a lateral load passing from south side of building will get diverted to est & west direction to reach next day. There will be major force diversion 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 compared to y-diection . It will result in higher stiffness of the buildings in x- direction, would reduce ductilty in x-axis
• Moreover , the x-force will easyily 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 discontinous 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.

Answers:-

Obectives:-

• To understand the imapct of vertical & horizontal members in seismic behavior of a structure
• To understand different irregularities in a building

Vertical irregularity-

The buildings plan area is large in bottom stories. the floor plan areas are getting reduced with increase the height. These buildings offsets has to be crosschecked with reference to IS-1893-2016 Tble -6 seral 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 thecolumns ( 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 FIGURE5E).Few levels may be subjected to soft storey mechanism.

Vertical irregularity-IS-1893-2016 Table-6 serail number(iii)

Soft storey-IS-1893-2016 Figure 4A

Slopy base-IS-1893-2016 Figure5E

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).

Answers:-

Obectives:-

• To understand the imapct of vertical & horizontal members in seismic behavior of a structure
• To understand different irregularities in a building

Open ground floor - This denotes soft storey mechanism acting in the building

Rooms along 2 bays separeted by an 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 buildings left and right sides periphery is more stiffer during seismic forces (especially along north-south)

Stairs portion at left top corner- Usually stairscase and lift portions are stiffer than other parts becaud=se 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 thw vwrtical direction between columns. This makes the buildings more vulnerable during the north-south seismic force.

Beams connected along column minor axis- The columns are havimg 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 transfers it.

Variations in columns sizes- The interanl 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 laterl drift of columns. So the concrete floor might have suffered heavy out of plane shear which would led to collapse.