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:

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.

The high rise building can produce less frequency during earthquake and it will it will take more time to complete one cycle of vibration in this symmetric position .

The good and symmetric pattern of column placement will deal with uniform distribution load carrying capacity.

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 Stiffness:

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).

The building may led to get collapsed during the high time period beyond resisting frequency

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 ductile property can also save the building from brittle failure.

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 deal with.

Ans:

The possible type of irregularities for the given structure are:

Soft story irregularity:

1. Stiff and strong upper floor due to masonry fill and non- ductile design
2. The column in one storey is longer than the above and the ductility code is ignored completely .
3. The irregular column may be placed in the upper beam which may increase the dead load in the structure .

Some provisions to avoid the irregulrities:

The building is torsional irregular. So the building framing must be revised.

During construction the proper lapping of steel and appropriate dia of the building to be used as per drawing design and recommended by engineer.

The mass irregularity is avoided by providing light weight concrete/ Low weight masonary or by providing structure with more light weight materials .

The structural design should be according to the nature of use of type and the codal load provision to be taken care .

The structure should be built in symmetric manner to provide udl load case though the frame .

The height of the building from ground floor should decrease towards top.

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:

Structure is not symmetric.

Larger strength is provided hence low ductility.

In this building, there is no proper placement of masonry infill walls.

In this building, Redundancy in the vertical direction is not provided properly.

During construction the steel work like lapping zone and proper steel drawing is not being followed .

The irregular material testing may be their .

During structural analysis may be earthquake frequency not been taken in account .