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.

1.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. 

2.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.

3.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).

4.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.

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.

Soft Storeys

Flexible structures in Torsion

1.Stiffness Irregularity

• The lateral stiffness of the story at the mid height which is open is very less when compared to the above levels bexause the main reason is the structure is discontinued at the mid-height.
• It is obseverved that the open storey causes reduction in the stiffness in the Building and attracts lateral seismic Exicitation more in that floor which causes severe damage to the upper floors.
• The Irregularity can be solved by providing the Shear walls to this high seismic action prone floor.

2.Mass Irregularity

• The open story also causes mass irregularity in the Building because the high mass concentration is present above the open floor.That is the upper floors carry more mass than the open floor.
• Also the number of floors are higher above this open floor.

3.Vertical Geometrical irregularity

• There is a change with the horizontal dimension of the lateral force resisting due to the open storey in mid height and also the vertical geometry of the Building which means the length of the Top storeys are varying along the Building unit.
• This causes Torsional effects in the Building which need to be Decoupled by providing shear walls or Decoulped moments.
• The Flexibility provided due the variation need to be compensated by providing Ductility.

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.

(a) Open ground floor:

 A 4-storey hotel building has an open ground floor for the restaurant.

• 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: 

  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.

• 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:

 There is a staircase near the upper left-hand corner,with straight flights between landings at floor levels and in between floors. 

• 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.