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.
ANS-1
Investigation of the framing plan with respect to symmetry in X- direction :
if we split the plan vertically half it will look mirrored so , we conclude the given plan is symmetric in x direction.
Investigation of the framing plan with respect to symmetry in Y- direction :
if we split the plan Horizontally half it will look mirrored so , we conclude the given plan is symmetric in y direction.
Investigation with respect to Bi-directionnal stiffness :
The columns in horizontal direction are connected with straight to straight beams. this means any lateral load passing from left end of the building will have its path straight till it reaches right end of the building.
The column in vertical direction are not connected with straight to straight beams. so a lateral load passing from south side of building will get diverted to east & west direction to reach next bay.
Investigation of the framing plan with respect to ductility :
Prima facie, the aspect ratio of the plan clearly hints more column in x-direction compared to y-direction
moreover ,the x-force will easily pass from one bay to its next due to beam alignmment. whereas the y-force will struggle to pass through.
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.
ANS-2
Vertical irregularity-
The building plan area is large inn bottom stories. the floor plan areas are getting reduced with increase in height.
Soft storey-
The building has uncovered opening space on 6th floor.as there is no occupancy or a partition wall,this will lead to plastic hinge formation at the columns .
Slopy base-
The building is constructed on a aloping ground at one side.this will lead to significant variations in the stiffness.
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).
ANS-3
Open Ground floor-
This denotes soft storey mechanism acting in the building.
Rooms along 2 bays separated by an open corridor-
The bays filled with rooms will have higher mass compared to the middle bay left open for corridor.
Two short side covered with infill walls-
This means the building's left and right sides periphery is more stiffer during seismis forces.
Staircase portion at left top corner-
usually staircase and lift portions are stiffer than other parts because of concertrated 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 the vertical direction between columns.
Variation in column size-
The internal columns are having higher size compared to exterior columns.but this will lead to significant difference in lateral drift of columns.so the concrete floor might have suffered heavy out-of-plan shear which would led to collapse.