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:

observing by dividing in the x-direction

If we split the plan vertically in half,it will look like a mirror so it is concluded as symmetric in the x-direction.

observing by dividing in the y-direction

If we split the plan vertically in half,it will look like a mirror so it is concluded as symmetric in the y-direction.

Investigation with respect to BI-directional stiffness:

the columns in horizontal are connected with straight-to-straight beams. This means any lateral load passing from the left end of the building will have its path straight till it reaches the right end of the building. so no or less possibility of force diversion takes place.

The columns in the vertical direction are not connected with straight-to-straight beams, so a lateral load passing from the south side of the building will get diverted to the east and west directions to reach the next bay. there will be a major force diversion taking place with seismic force in the Y-direction.

observing the framing plan with respect to ductility:

the aspect ratio of the plan clearly hints at more columns in the x-direction compared to the y-direction. it will result in the highest stiffness of the building in the x-direction. which would reduce ductility in the x-axis.

moreover, the x-force will easily pass from one bay to the next bay, whereas in y -the direction the beams are aligned in zig zag so which leads to discontinuous bracing.

we can conclude that the given framing plan is more ductile in the y-direction than that in the 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 is large at the bottom and decreased with height need to check the offsets as per is 1893-2016 table-6 serial number.

soft story: the building has uncovered opening space on the 6th floor. as there is no occupancy or partition wall this will lead to plastic hinge formation at the columns, this has to be checked and sufficiently designed. we should check as per IS 1893-2016.

story base: the building is constructed on slopping ground at one side it will lead to significant variations in the stiffness.

we should check as per IS 1893-2016 .

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:

Opened ground floor- This denotes the soft story mechanism acting in the building.

Rooms and 2 bays separated by an open corridor: the bays filled with rooms will have higher mass compared to the middle bay left open for the corridor. this induces mass irregularity along the height uniformly.

Two short sides covered with infill wall: - 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 the concentrated concrete elements. so the staircase portion contains more stiffness in the provided building plan.

No framing connection along the 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 axes- The columns are having longer dimensions in Y -Y-direction. this means they are stiffer in Y -direction. but the beams are running only along the 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. but this will lead to significant differences in the lateral drift of columns. so the concrete floor might have suffered heavy out-of plane shear which would lead to the collapse.