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.

PROCEDURE:

• Observation of the given framing plan with respect to Symmetry in X-direction:
  • If we draw a line on the framing plan as shown below, it will look as if it is mirrored. So we conclude that the given plan is symmetric in X- direction.

• Observation of the given framing plan with respect to Symmetry in Y-direction:
  • If we draw a line on the framing plan as shown below, it will look as if it is mirrored. So we conclude that the given plan in symmetric in Y-direction.

• Observation of the framing plan with respect to the redundancy in X-direction:
  • The columns in X-direction are comparatively more and also evenly spaced. So the structure is more redundant in X-direction. Except the top and bottom column rows which have longer spans and less number of columns comparitively.
• Observation of the framing Plan with respect to the redundancy in Y-direction:
  • The columns in Y-direction are comparitively less but evenly spaced.So the structure is redundant but lesser than that of in the X-direction.
• Observation of the framing Plan with respect to the bi-directional stiffness:
  • The Columns in horizontal direction are connected with continuous straight beams. This means,any lateral load(like Seismic Force in X-direction) passing from left end of the building will have its path straight till it reaches right end of the building. So no or less possibility of force diversion takes place.
  • The columns in vertical direction are not connected with continuous straight beams, So there is a chance of lateral load passing from South side of building to get diverted to east and west direction to reach next bay. There will be major force diversion taking place with seismic force in Y-direction. The framing plan is weak with respect to bi-directional stiffness in Y-direction.
• Observation of the Framing Plan with respect to Ductility:
  • Ductility is inversely proportional to stiffness. If the structure is more stiff, it will be less ductile and vice versa. Here, the structure is more stiff in the X direction, i.e it will be less ductile in X direction whereas in Y direction, the structure is less stiff, hence it will be more ductile in Y direction.

Result:

Observations and comments have been passed on the framing plan of the building with respect to the Symmetry, Redundancy, Bi-directional Stiffness and Ductility.

2)

Aim:

To discuss the possible sources of irregularity in the building shown in the below figure and to also explain how as an engineer, each of these irregularities should be dealt with.

PROCEDURE:

The possible sources of irregularities in the above building are as follows:

• Vertical Irregularities
• Slopy Base Irregularities
• Soft Storey Irregularities.

Vertical Irregularities:

• The building plan area is large in bottom stories. The floor plan areas are getting reduced with increase in height.
• A structure is said to be irregular when its bottom edge is 25% more than the top edge.
• Hence, this building is subjected to vertical irregularity.
• These building offsets has to be crosschecked with reference to IS-1893:2016 table-6.

Slopy Base Irregularities:

• The building is constructed on a slopy ground at one side.
• This will lead to significant variations in the stiffness (with reference to IS-1893:2016).
• Therefore, few levels may be subjected to soft storey mechanism.

Soft Storey Irregularities:

• A soft storey is the storey whose lateral stiffness is less than that of the storey above it.
• The building has uncovered opening space in its 6th floor.
• As there is no occupancy or a partition wall, this will lead to plastic hinge formation at the columns (with reference to IS 1893:2016).
• This has to be checked and sufficiently designed according to the issue.

Result:

All the possible irregularities that can occur and the solutions that as an engineer we should use to deal with all these irregularities has been discussed in the above points.

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 from the given plan of the hotel building.

GIVEN PLAN:

GIVEN BULDING VIEWS:

PROCEDURE:

• Let us discuss various features of the structural design and of the layout of infills which are important for earthquake resistance and seismic performance from the given plan of the hotel building.
• GROUND FLOOR: As this is open it denotes soft storey mechanism acting in the building.
• ROOMS VISIBLE ALONG THE BAYS SEPARATED BY THE CORRIDOR: The bays with the rooms will have higher mass compared to the middle bay which is left open for corridor. So, on the top and bottom portion of the plan it will have heavier mass and hence there is more stiffness compared to the middle portion which is left unoccupied. This leads to irregularity in mass. So during earthquake excitation, the middle portion will get collapsed due to lower stiffness whereas the other two sides may sustain.This includes mass irregularity along the height of the building uniformly.
• TWO SIDES COVERED WITH THE INFILL WALLS: This means that the building's left and right periphery is more stiff during seismic forces. Since, the lateral force resisting systems, i.e the walls are continuous from the foundation, this impart greater strength and stiffness to the structure in these locations. That is the reason why the left and right edges remain intact even after the earthquake excitation.
• STAIRCASE AT THE TOP LEFT CORNER: Usually staircase and lift portions are stiffer than others parts because of the concentrated concrete elements. There is also redundancy in the staircase portion due to increased number of columns. This is the reason why the left-hand bay survived even after the excitation.
• From the plan it is clear that there is no structural member to transfer the load from the floor to the columns. This may cause the floor to become flexible and due to this the column will be subjected to irregular loading and increases the chances of collapse, especially when the direction of earthquake is along Y-direction.

Result:

Comments on the features of the structural design and of the layout of infills which are important for earthquake resistance and the seismic performance has been made.