Concept on positioning of Columns

1.

AIM: To comment on the layout of the framing plan concerning earthquake resistance in the two horizontal directions X or Y looking into aspects of symmetry, redundancy and bi-directional stiffness and ductility.

i.Symmertry

Having a look over the aspects of symmetry of the framing plan, it is observed that the distribution of mass,Stiffness is across the plan;it is observed that the distribution of mass, stiffness is across the plan.It is considered for one of the 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.

ii.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.

iii.Bi-directional Stifness:

The building plan may not be able to resist the Horizontal seismic actions in the Shorter Direction (Y-axis);also the Resistance and stiffness in the shorter direction (Y-axis) is less when compared to Longer direction (X-axis).

iv.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.

2.

AIM: To analyze the possible sources of irregularity in the building shown and to explain how, as an engineer, each of these irregularities should be dealt with.

Procedure:

This building's structure may be affected by seismic forces in the categories of soft storey, vertical geometry irregularities, floating columns, mass irregularities, and inconsistent seismic forces.

Failure of a soft storey

• The ground floor of the building is mostly considered soft stories because it has a short column, no shear wall, and a lot of mass properties.
• Damage may also occur, such as a collapse, buckling of the column, etc.

Floating Columns

• The column is regarded as a vertical member of the structure that resists lateral forces.
• If horizontal forces act about the structure, they may transfer through the vertical member and to the base shear foundation.
• As a result, the column is at the structure's discontinuity, and it is unable to withstand lateral forces during earthquakes because the load cannot be transferred to the foundation.

Mass Irregularity

• The seismic response should not be considered because of the structure's mass irregularity at any floor.
• The susceptibility of an irregular frame to seismic excitation has been found to decrease as the mass irregular floor moves towards the top of the building.
• In a structural system, mass irregularity is defined as a variation of more than 150 percent of mass between adjacent stories.

3.

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 (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)

i.Open Ground Floor

• The ground floor of the building is open, which may be a softstorey (having long columns) due to this the Ground floor excitation the columns could have been unable to resist the Earthquake and form collapse.
• This is called as soft storey mechanism.
• This can be avoided by having Strong column-weak beam mechanism.

ii.Two short sides of the perimeter in-filled

• The mass has been undistributed in all the sides of the Building in all storeys because it is given that the two sides of the perimeter of the building is in-filled (may be with the soil) which causes the Irregular distribution of mass called as Mass Irregularity.
• This can be avoided by providing the shear walls in the directions of Two short sides of the perimeter which can resist the Lateral loads (soil due to Infill) by providing stiffness in the Building frame and helps to resist the Earthquake actions.
• Also it adjusts the Mass Irregularity for the plan.

iii.Extreme left hand bay Staircase filled with the Concrete

• The extreme left hand bay has Staircases (made of concrete) due to this the mass got concentrated in the staircase area due to which torsional effects are formed having the base of the concentration of mass in the Staircase.
• To avoid this type of failure the staircases should be kept in the centre of the Building which makes the Torsional effect as Zero by Uncoupling the moment. It also makes the Implications of the Irregularity in plan of the Building.

iv.Columns not in the same line

• It is observed that the columns in the Extreme left hand middle line columns has the deviation in the line of the Construction at the staircase which again a reason for the Irregularity in plan having the Torsional flexibility.
• To avoid this the Eccentricity should be maintained for the deviation to be within the limits of Beam size and the Columns sizes.
• Also the sizes of the Beams and Columns in the Plan should be redesigned in such a way that the line of the columns doesn't deviate even in the staircase area.