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:

Symmertry:

If we split the plan vertically half, it will look mirrored.so we conclude the give plan is symmetric in x direction.

If we split the plan horizontally half, it will look mirrored.so we conclude the give plan is symmetric in y direction.

It also has a very good uniformity also.

Redundancy:

The column in x-direction are comparativey more and evenly spaced. so the structure is more redundant in x-direction.Except the top and bottom column rows are having quite longer spans.

The column in y-direction are comparativey lesser but evenly spaced. so the structure is redundant but lesser than of in x-direction.

Bi-directional Stifness:

The column in horizontal direction are connected with straight to straight beams.this means,any lateral load paasing 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 in vertical direction are not connected with straight to straight beams. so a lateral load paasing from south side end of the building will get diverted to east & west direction to reach next day.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 direction.

Ductility:

prima facie, the aspect ratio of the plan clearly hints more column in x-direction compared to y-direction. it will result in higher stiffness of the building in x-direction, which would reduce ductility in x-axis.

The x-force will easily pass from one bay to its next due to beam alignment. the y-force will struggle to pass through.the north south beams are in zig zag which leads to a discontinuous bracing.

The reduction in design force in the shorter direction (Y-axis) is to be compensated by Ductility.

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:

vertical irregularity - The building plan area is large in bottom stories. the floor plan area are getting reduction with increase in height. these building ofsets has to be cross checked with reference to IS-1893-2016 table 6 serial no(iii)

soft story - The building has uncoverd opening space in 6th floor. as there is no occupancy or a partition wall, this will lead to plastic hongr formation at the columns IS 1893-2016 figure 4A.

slopy base - The building is constructed on a sloping ground at one side. this will lead to significant variation in the stiffness IS-1893-2016 figure 5E.

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:

• This denotes soft story mechanism acting in the building
• The bays filled with rooms will have higher mass compared to the middle bay left open for corroder.this induces mass irregularity along height uniformly
• This means the buildings left and right sides periphery is more stiffer during seismic forces
• Usually straicase and lift portion are stiffer than other parts because of concentrated concrete elements. so the staircase portion contains more stiffness in the provided building plan.
• no framing connection along y-direction.
• beams connected along column minorb axes.
• variation in column sizes.