Concept on positioning of Columns

1) AIM: To Comment on the layout concerning earthquake resistance in the two horizontal directions with aspects of symmetry, redundancy, bi-directional stiffness and ductility.

1) Irregularity in terms of Symmetry

• From the above images, it is clear that the building layout is symmetric about both X-axis and Y-axis. So, it holds good symmetrical property in both the orthogonal asis.
• Due to symmetry, the centre of ma willie near to the centre of stiffness if the loads are distributed uniformly.
• The torsional response will be far lesser because of the reduced eccentricity between the centre of mass and the centre at stiffness

2) Regularity in terms of Redundancy

• The load path between toe and bottom edee columns are more as compared to other columns, thus a large portion of the lateral forces will be transfered to these columns
• The blue circled vertical clements will hold higher loads than other vertical elements due to their longer spans.
• Ultimately, these columns wil bear higher lateral forces.
• Hence, the redundancy is compromised at these two locations.

3)Irregularity in terms of directional stiffness

• The number of structural members in X-direction is more as compared to Y-direction
• Elx>Ely
• So, the stiffnex of building in X-direction is higher than that of in Y-direction

4) Irregularity in terms of Ductility

• The ductility of the building is inversely proportional to the stiffness of that building in any particular direction
• Considering this, the given building is less ductile in X-direction (high stiffness) and more ductile in Y-direction (lesser stiffness)
• So, the lateral force in the X-direction will be larger than the lateral forces in Y-direction

2) AIM: To find the possible sources of irregularity in the building shown above and explain how as an engineer these irregularity can be dealt.

ANSWER:

The possible sources of irregularity in the building are listed and discussed below:

• Failure at the middle of the building due to the soft-storey.
• Vertical irregularity.
• Slopy base.

(i) 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.
• As we can see that 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.
• Below are the images showing the stiffness irregularities(soft storey):
• 

(ii) Vertical irregularities:

• 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 serial no (iii). The image regarding this reference is given below:
• 

(iii) Slopy base:

• If we observe properly then we can see that at the right hand side of the image there is slopinf ground and this building is constructed at that sloping area.
• Which means that the there are risks that this building may collapse during the earthquake.
• And this will lead to the variation in the stiffness as we can conclude properly.
• So according to the IS 1893-2016 FIG 5E we have some standards in order to design a building insuch slopy areas and if we follow these standards then there is high possibility that we can save the structure from collapse during the earthquake attack.

3) AIM: To comment on the features of the structural design and of the layout of the building and the cause of the collapse of this building after the earthquake.

(a) Open ground floor:

• As it is already mentioned in the question that the hotel building has an open ground floor for the restaurant, it means that the restaurant has a soft storey mechanism acting on the building that cause the damage to the building. And this is one of the reasons why this restaurant building collapse.

(b) Rooms along two bay separated by an open space:

• The bay that are filled with the rooms will have higher mass than the middle bay whic is opened for the corridor.
• So this will cause mass mass irregularity along the height uniformity.

• As we can see at the above image that the upper portion and the bottom portion is for the rooms and because of that rooms these portions have higher mass because of the various furniture load,live loads etc.

• And the middle portion they left for the corridor as we can see in the above given image.

(c) Two short sides coveres with the infill walls:

• - As we can see that the two shorter sides of the perimeter are not in filled in all the storeys,except for the certain openings at the ends of the corridor at the 2nd and the 4th floor and along the right-hand side of the ground floor.
• This means that the building at the left and the right of the given building is more stiffer during the earthquake.
• And they have built non structural wall.

(d) Staircase portion at the left top corner:

• As we can see that the staircase and the lift portion of the building is not affected with the seismic force. These are the only elements that are not affected during the earthquake force.
• This is because the usually the staircase and the lift portion are more stiff than the other members of the building. It m eans it does not bend easily with the external forces and that is the reason that the staircase and the lift is intact in the polsition with much harm.
• 
• As we can see in the image only the staircase part is intact because of the concrete elements.
• So the staircase is the only intact portion which contains more stiffness in the given structure or hotel.

(e) No frame connection along the Y-direction:

• 
• As we can see in the above image that there are no structural beams that are provided along the Y-direction between the columns.
• This means that the building is more vulnerable during the earthquake because of the no frame connection along the Y-direction.
• Thats why we have to be more careful while designing the structures because a little mistake can lead to a very serious problem.

(f) Beams connected along column minor axis:

• As we can see in the above image that the columns have the longer direction in the Y-direction.
• But there is no direct connection or frame in the Y-direction which may connects the beam in the Y-direction.
• There are columns that are connected in the X-direction but the large side of the column is in the Y-direction which means that they are more stiffer in that direction whic can attract more lesser lateral force and this is one of the reason for the collpase of this building.

(g) Variation in column sizes:

• As we can see in the above given image that the sizes of the columns are different.
• We can say that the size of the interior column is big in size and the size of the exterior column is smaller as wecan see in the above image.
• And because of the difference in the size of the columns the structure collapse because it may suffered heavy out of plan shear.