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:

AIM- 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.

1. The layout is symmetric in X and Y both the directions.
2. The column in X-direction are compartively more evenly placed and are more reducntant there are 7 colmuns in X-direction.
3. The column in Y-direction are less evenly spaced and are lesser redundant than x-direction there are 6 columns in Y-direction.
4. The structure can resist the semsimc load when then laods are evenly distibuted.
5. But the framing plan is weak with respect to bi-directional stiffness in Y-direction.
6. The given framing plan is more ductile in Y-direction than that of in X-direction
7. The layout is in orthogonal pattern.

Symmertry:

It is observed that the distribution of mass,stiffness is across the plan has good symmetrical aspects.

This tends to reduce the horizontal displacements in both of the two horizontal displacements in both of the two Orthogonal Horizontal Directions.

It also has a very good uniformity also.

Redundancy:

There are missing structural elements in the Periphery of the plan.This causes the uneven distribution of earthquake action effects in non linear range across the plan.

The energy dissipation across the structure is very low which results in non -reliable structure.

Bi-directional Stifness:

The building plan may not be able to resist the horizontal seismic actions in the shorter direction (Y-axis) and also the resistance and stiffness in the shorter direction (Y-axis) is less when compared to longer direction (X-axis).

Ductility:

The building may not be able resist the elastic earthquake forces in shorter direction (Y-axis).So it may result in inelastic Response.

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:

AIM- To name the possible sources of irregularity in the building shown here? Explain how, as an engineer, each of these irregularities should be dealt with.

• A building is said to be torsionaly irregular when the maximum horizontal displacements of any floor in the direction of the lateral force at one end of the floor is more than 1.5 times its minimum horizontal displacement at the far end of the same floor in that direction.
• In such a case the building configuration must be revised.
• Out of the many possible irregularities in building structures, the final structural design should, in absolute terms, avoid the two most dangerous irregular situations

1) Soft storeys

2) Extremely flexible Structure in torsion

• Both cases correspond to extremely irregular stiffness distributions: the former regarding the distribution in height/elevation with a very weak story and the latter regarding the distribution in plan, with the concentration of the stiffness at the center or at a corner.

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:

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. How do they relate to the almost full collapse of this building.

1. It has a open ground floor so it will have soft storey mechanism.
2. There will be mass irregularities as middle bay is left open.
3. The structure also have strong beam and week column.
4. The staircase is sperated from building so it must be provided with required reiforcement whiich resist the sesmic loads
5. Two short sides are coverd with infill wall which will cause cracks
6. The secondary beam in vertical direction is absent.
7. The stiffness of coulmn is more in Y-direction while beams are provided in X-direction which would lead to less load transmission.
8. Structure is not symmetric.
9. Larger strength is provided hence low ductility.
10. In this building, there is no proper placement of masonry infill walls.
11. In this building, Redundancy in the vertical direction is not provided properly.