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 :

1. Symmetry

a) X-direction :

• If we see into the above given plan and split it into two equal portion in the horizontal direction then can say that the plan looks mirrored, if we split the given above plan into equal parts.
• This will conclude that the given above plan in the X-direction is symmetric.

b)Y-direction :

• If we see at the given above plan and if we split the plan into two equal parts in the Y-direction horizontally i.e, Section 1 and Section 2, we will be able to understand that the above plan looks mirrored.
• So here we can conclude that the given above plan in the Y-direction is also symmetry

2. Redundancy :

a) X-direction :

• In the above given plan there are multiple dots and the lines, So these dots represents the columns and the line represents the beams.
• In the above given plan, the columns in the X-directions are more and evenly spread in the middle of the plan, So we can say that the structure is redundant in the X-direction.
• But if we observe the above plan then we can see that the columns in the top and the bottom there are less number of columns as compared to the middle portion of the plan but these columns are evenly spread so we can say the structure in the X-direction is redundant in nature.

(b) Checking the redundancy in the Y- direction:

• In the above given plan there are multiple dots and the lines, So these dots represents the columns and the line represents the beams.
• In the above given plan, the columns in the Y-directions are evenly spread but they are lesser in number.
• So we can conclude that the redundancy in the Y-direction is lesser.

Conclusion:

After checking the redundancy in the X and Y direction we can conclude that the structure is more redundant in the X-direction than the Y-direction.

3. Bi-directional Stiffness :

a) X-direction:

• From the above plan we observe that the columns in the X-directions are connected in a straight line with the beams in the continuous manner.
• It's seen that the loads can be carried out and the loads can be transferred easily in the horizontal direction i.e, X-direction.
• After this study we can conclude that the frame is stronger in the bi-lateral stiffness in the X-direction.

b)Y-direction:

• From the given plan, the columns in the Y-direction connected in a straight line, but as we can see in the above given image that the beams are not connecting all the columns properly.
• As we can see that there are empty space after the each one beam.Therefore the loads cannot be transferred easily in the Y-direction.
• It is concluded that the above given frame is weak in the bi-lateral stiffness in the Y-direction.

Conclusion:

After checking the bi-lateral stiffness in both the direction i.e, X and Y direction it is concluded that the frame is stronger in the X-direction according to the bi-lateral stiffness than in the Y-direction.

4. Ductility :

a) X-direction :

• From the given plan the beams are connecting all the columns in the X-direction and the stiffness is more in the X-direction as the number of columns are more in the X-direction.So it is concluded that the frame is more ductile in the X-direction.

b)Y-direction :

• From the above given plan that the beams are not connected to each and every column of this frame in the Y-direction and the stiffness of this frame in the Y-direction is also less because of the lesser number of the beams in the Y-direction.So it is concluded that the frame is not ductile in the Y-direction.

Conclusion:

Comparing the ductility in both the direction, X and Y direction it is said that the frame in the X-direction is more ductile and the frame in the Y-direction is not ductile.

                                                                  ****************

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 :

• By observing the image we can get to know that the plan in the bottom is large when compared to the top storey. While increase in the height of the of the building the floor plan of the building is getting reduced. It has to be significantly checked with reference to IS 1893 2016 table 6 serial number (iii)  
• It is seen that the 6^th floor of the building has open space which has no walls which leads to plastic hinge formation in the column, it is a soft storey (reference IS: 1893 2016 figure 4A). This has to be significantly designed and checked.
• We can also see that the one side of the building has sloping ground This will lead to significant variation in the stiffness (reference IS: 1893 2016 figure 5E) and also some levels may be subjected to soft storey.

                                                                           ***********************

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 :

• Open ground floor - denotes the soft storey mechanism acting in the building.
• Room along 2 bays separated an open corridor - The bays filled with room will have higher mass compared to the middle bay left open for corridor, this induces mass irregularity along height uniformly.
• Stair case portion at left corner - Usually staircase and lift portions are stiffer than other parts because of concentrated concrete elements.
• Two Short sides covered with infill wall - This means the buildings left and right side periphery is more stiffer during seismic forces.
• No framing along y-direction - It is seen that no structural beams provided along these vertical direction between columns, this makes building more vulnerable during north south seismic force.
• Beams connected along X-direction -  The column are having longer dimension in y- direction that means they are more stiffer along y-direction but the beam are connected only x-direction which could attract much lesser lateral  forces and hardly transfer it.
• Variation in column size - The interior column are having higher size compare exterior column , but this will lead to significant difference in lateral drift of column & so the concrete floor might have suffered heavy plane shear which would be collapse.

                                                     *******************