Concept on positioning of Columns

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.

Answer:

• The given layout of the framing plan is symmetric.
• Generally, a well distribution symmetric plan layout of the structural elements like beams, columns are appropriate to achieve uniformity.
• The symmetric nature also makes the structure more reliable to resist earthquake forces.
• Having the same or equivalent resistance and stiffness in all directions is one of the desired features to resist the seismic effect, thus it should also be considered.
• The horizontal seismic motion is a bi-directional phenomenon and, thus the building should be able to resist these horizontal actions in any direction.
• The structural pattern of the building in the plan should be made orthogonal to make it resistant to seismic action in any direction.

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.

Answer:

The building might damage due to various reasons. Identification of a single cause of damage to buildings is not possible. There are combined reasons which are responsible for multiple damages. The cause of damage to buildings is soft stories, vertical geometry irregularities. floating columns, mass irregularities, poor quality of material, faulty construction practices, inconsistent seismic performance.

• Soft story failure: The first story must have lesser strength and stiffness as compared to upper stories which are stiffened by masonry infill walls. Increased flexibility of the first story results in extreme deflections. The damage may also happen due to the collapse and bucking of columns, especially where parking places are not covered appropriately.
• Floating Columns: In the upper stories the perimeter of the ground story is discontinued and floating columns rest at the tip of the taper overhanging beams without considering the increased vulnerability of the lateral load resisting system due to vertical discontinuity. This type of construction does not create any problem under vertical loading conditions but during an earthquake, a clear load path is not available for transferring the lateral forces to the foundations.
• Mass Irregularity: In the upper stories the perimeter of the ground story is discontinued and floating columns rest at the tip of the taper overhanging beams without considering the increased vulnerability of the lateral load resisting system due to vertical discontinuity. This type of construction does not create any problem under vertical loading conditions but during an earthquake, a clear load path is not available for transferring the lateral forces to the foundations even when the seismic weight of any floor is more than 150 percent of the floor of that floor above.

3.

Answer:

1. From the above images, we can observe that:

• The masonry fill provided is very high, which provides higher stiffness.
• Mass irregularity within the building was caused as a result of providing the top and bottom bays as full of room and the middle bay for the corridor, which created the internal collapse of the structure, which we can see from the third figure.
• The dissipation of the lateral force can be also observed as there are no beams provided in the plan, this can also lead to internal collapse of the structure, creating redundancy irregularity, especially during earthquakes.

2. As a solution, we can list out the following:

• Masonry filling should be provided appropriately.
• Adopt lightweight construction material in the lower floors, so that mass of the floors will be equal
• keep the floor width as same as possible to withstand the longitudinal irregularity of the structure to any impact.
• Provide columns and beams, to carry the load uniformly, thus reducing the redundancy irregularities.