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.

AIM: To comment on the layout of the framing plan concerning earthquake resistance.

IRREGULARITIES

A) SYMMETRY:

Symmetry in X-direction:

• If we split the plan horizontally in X-direction the plan looks mirrored.

Symmetry in Y-direction:

• If we split the plan Vertically in Y-direction the plan looks mirrored.

B) REDUNDANCY:

• The columns in X-direction are comparatively more and evenly spaced so the structure is more redundant in X-direction except for the top and bottom column rows are having quite longer spans.
• The columns in Y-direction are comparatively lesser but evenly spaced so the structure is redundant but lesser than that of in X-direction.

C) BI-DIRECTIONAL STIFFNESS:

• Columns in the horizontal direction are connected with straight to straight beams such that any lateral load passing from left end to right end has a straight path and less possibility of force diversion takes place.
• Columns in verticle direction are not connected with straight to straight beams so lateral load passing from the southside of the building will get diverted to the east to the west direction to reach the next bay.
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D) DUCTILITY:

• From the plan columns 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-direction.
• The force will travel freely from one bay to the other because of even beam alignment in X-direction whereas in Y-direction travel of force is difficult due to the zig-zag alignment of beams.

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.

AIM: To detect the possible irregularities in the given building and also suggestions for that irregularities.

ANSWER:

The building may damage due to various reasons. Identification of a single cause of damage to buildings is not possible. There are combined which are responsible for multiple damages. The Possible damages to the shown building are

A) SOFT STOREY FAILURE:

• The building has uncovered opening space on the upper floor as there is no occupancy or partition wall, this will lead to plastic hinge formation at the columns (IS 1893 -2016 FIG 4A).

B) VERTICAL IRREGULARITY:

• The building plan area is large in bottom stories and the floor plan area is getting reduced with an increase in height. These building offsets have to be crosschecked with reference to IS 1893-2016 table-6 (iii) and Fig 4c.
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C) SLOPY BASE:

• The building is constructed on the slopy ground on one side. This will lead to significant variations in the stiffness (with ref to IS1893[-2016 FIG 5E) few levels may be subjected to the soft storey.
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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).

AIM: To comment on the features of the structural design and of the layout of infills which are important for earthquake resistance and seismic performance.

ANSWER:

Comments on the features of the structural design and of the layout of infills which are important for earthquake resistance and seismic performance

A) STAIRCASE PORTION AT LEFT TOP CORNER:

• Usually, staircase and lift portions are stiffer than other parts because of concentrated concrete elements. So the staircase portion contains more stiffness in the provided building plan

B) NO FARMING CONNECTION ALONG Y-DIRECTION:

• We can see clearly that no structural beams are provided along the verticle direction between columns. his makes the building more vulnerable when the occurrence of lateral force in Y-direction.

C) TWO SHORT SIDES COVERED WITH INFILL WALLS:

• This means the building's left and right side periphery is stiffer during seismic forces
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D) VARIATION IN COLUMN SIZES:

• The internal columns are having higher sizes compared to exterior columns this is done for the higher load demands but this will lead to a significant difference in the lateral drift of columns. So the concrete floor might have suffered heavy out of plane shear which would lead to collapse.