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:

Symmetry:

In the above layout the structural column is uniformly distributed so it has the good symmetrical aspects .This tends to reduce the horizontal displacements in both of the two orthogonal directions .The mass and stiffness across the plan has good symmetrical aspects.

Redundancy:

They are some missing elements in periphery of the plan which causes the uneven distribution of earthquake action effects. And the energy dissipation is also very low which results in non reliable structure

Bidirectional resistance:

In the above orientation Bidirectional resistance as the structural element is arranged in an in-plan orthogonal structural pattern .so the building will be able to resist the seismic resistance action in any direction.

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 is to be given 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:

There will be several possible reasons for the irregulaties like soft storey,geometery irregularities ,mass of the materials ,poor quality of the materials used in the constructions,faulty construction practices

Some of the reasons to avoid the irregulaties:

Avoiding the soft storey effect where due to extreme deflections may occur and also due to buckling of columns

The mass of the building materials used in the construction must be light weight concrete or by providing more wood materials.

The buildings should be in symmetrical in plan

The size of the columns provided on the structure should be of same size and height through out the building.

And the floating columns due to which the upper stories perimeter of the ground story is discontinued and floating columns rest at the tip where overhanging beams without the increased vulnerability of the lateral load resisting systems due to vertical discontinuity .

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 ):In this figure provided above must have several reasons for the collapse

The masonry filling must have been very high which have more mass and high stiffness which also results in larger strength and low ductility .

The structure is not symmetric is one the reason .

The lateral load resisting systems are not present as there are no beams mainly in case of during earthquake criteria.