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.

Answer:

AIM: To understand the concept on positioning of Columns.

Symmetry:

• If we split the plan vertically half and horizontally half it look like as a mirror. so we conclude the given plan is symmetric in x and y direction.
• The load resistance framing in this symmetrical structure is distributed evenly throughout the structure.
• The reflection of the structure about the axis is identical in geometry, supports, and material properties to the structure itself, the structure is symmetric with respect to an axis of symmetry in its plane.
• This structure has an exact matching of form and arrangement of parts on opposite sides of the boundary at X and Y.

Redundancy:

• Because this structure has perfect redundant, the structure becomes more reliable in resisting any lateral forces acting on the structure.

Redundancy in x direction:

• If we see the plan the column in x direction is more than in y direction. Also more space in x direction, except top and bottom column.
• The redundancy at the top and bottom is less as compair to middle part in the x direction.

Redundancy in Y direction:

• If we see the plan the column in y direction are comparatively less but having evenly spaced.
• The structure in y direction is redundant but comparitively less to x direction.
• So we can conclude that the redundancy in the Y-direction is lesser.

Bi-directional stiffness:

• In the horizontal(x) direction, the width is more compared to vertical(y) direction and as such distribution of structural elements is also more in x direction, hence the stiffness is more. . That is, the stiffness is more in X direction as compared to Y direction.
• The given plan has an orthogonal layout in both the X and Y directions, so it can transfer forces evenly, and its structure will be able to withstand direct action from seismic forces.

Ductility:

• The ductility is always, inversely proportional to stiffness. If the structure is more stiffer, it will be less ductile and vice versa.
• We see that more column in x direction than y direction it will results in higher stiffness in x direction. That reduce ductiliy in x axis.
• So if we compare the ductility in both the direction i.e, X and Y direction then we can say that the frame in the X-direction is more ductile and the frame in the Y-direction is not ductile due to the lesser number of beams in the Y-direction.

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.

Answer:

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.

Vertical Irregularity:

• If we observe the above given plan carefully then we will be able to see that the buiding plan area is bigger in the bottom section and the building plan area keeps reducing as it goes up. In short it means that the building plan area reduces with the increase in the height as we can see clearly in the above image.

• The area in the green rectangle has bigger plan area than that of the area that are in the yellow rectangle.

• The building offset has to be checked out with the reference of IS 1893-2016 table no 6.

• 

Soft Storey:

• As we can see in the above given image that this building at the 6th floor has a soft storey because it has uncovered opening.
• And there is no partition wall or no occupancy or any other shear wall or any other type of support elements etc nothing is there to support the upper blocks of the building during the earthquake and this will also cause plastic hinge at the colums.
• According to the reference IS 1983-2016 Figure 4A, this has to be checked and we have to design the building accordingly. So that there will be no mistake in designing the buiding.
• 

Sloppy Base:

• In the right side of the building, there is an embankment. It means the building is constructed over a sloping ground and this will lead to a significant variation in the stiffness.
• The few levels are subjected to soft story mechanism .
• This irregularity is cross checked with refrance to IS- 1893-2016 FIG 5E.

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.

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).

Answer:

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).

• The frame of the structure is not symmetric.
• If the columns in this structure are not properly aligned in a symmetrical plane, due to which any lateral forces may cause damage.
• There's no proper masonry infill wall placement.
• Redundancy in the vertical direction is inadequate.
• If the framed structure is capable of transferring the load from one direction to another of the foundation's structure.
• The columns in this layout are closely spaced, resulting in the formation of short paths for the transfer of stresses, which is also an important factor in earthquake resistance.
• The interaction of the staircase with other parts of the three-dimensional structure, specifically the interaction with the beam, column, and shear wall, results in patterns of deformation that are not typically studied during the design process.
• The increased strength and stiffness of the structure in the stairway region, for example, will influence the seismic torsional distress of the structure and may lead to shear failure of the staircase or other structural elements.