Concept on positioning of Columns

OBJECTIVE=

1. To understand the impact of vertical and horizontal load members in a seismic behavior of a structure structure

2. To understand different irregularities in the building

Question 1:

Comment on the layout of the framing plan concerning earthquake resistance in the two horizontal directions X or Y (dots are columns, and lines depict beams). Look into aspects of symmetry, redundancy, and bi-directional stiffness and ductility.

ANSWER=

1.1 Investigation of framing plan concerning symmetric in X- direction:

-If we split the plan vertically half, it will look mirrored so we conclude the given plane is symmetric in the x-direction

1.2 Investigation of framing plan concerning symmetric in Y- direction:

-If we split the plan horizontally it will look mirrored so we conclude the given plane is symmetric in the y-direction

2.1 Investigation of framing plan concerning Redundancy in X- direction:

-The column in the X-direction is comparatively more evenly Spaced, so the structure is more redundant in the X-direction. Except for the top and bottom columns, rows hprettyuite a large span

2.2 Investigation of framing plan concerning Redundancy in Y- direction:

- The column in Y-direction are comparatively fewer but evenly spaced so the structure is redundant but lesser than that of in X-direction

3.1 Investigation of framing plan concerning Bi- Direction stiffness in X- direction:

- The column in the horizontal direction is connected with a straight-to-straight beam. This means any lateral load (seismic force in the X-Direction) Passing from the left end of the building will have its path straight till it reaches the right end of the building. So no or less possibility of force diversion taking place.

3.2 Investigation of framing plan concerning Bi- Direction stiffness in Y-direction:

- The column in the vertical direction is not connected with straight-to-straight beams. So a lateral load passing from the south side of the building will get diverted to the east and west direction to reach the next bay. There will be a major force diversion taking place with seismic force in Y-direction. The Framing plane is weak Concerning Bi-directional stiffness in Y-Direction

4.1 Investigation of the framing plan concerning ductility:

- Prima facie, the aspect ratio of the plan hints at more columns in x- the direction compared to the y-direction. It will result in higher stiffness of the building in the x-direction, which would reduce ductility in the x-axis.

The x-force will easily pass from one bay to the next due to beam alignment. Whereas, the y-force will struggle to pass through. The north-south beams are arranged in a zig-zag which leads to discontinuous bracing.

-We can conclude that the given framing plan is more ductile in the y-direction than in the x-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=

1.Vertically irregularity:

- The plane area is large on the bottom stories.

- The floor plane area is getting reduced with increases in height.

- These buildings were cross-checked with reference to IS 1893-2016 Table-6 Number-3

2. Soft story:

Soft storey - The building has uncovered opening space in 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 Figure 4A). This has to be checked and sufficiently designed.

3. Slopy Base:

Slopy base - The building is constructed on a sloping ground at one side. This will lead to significant variations in the stiffness (with reference to IS- 1893-2016 Figure 5E). Few levels may be subjected to soft storey mechanism.

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:

1.Open ground floor - This denotes soft storey mechanism acting in the building

2.Rooms along 2 bays separated by an open corridor - The bays filled with rooms will have higher mass compared to the middle bay left open for corridor. This induces mass irregularity along height uniformly.

3.Two short sides covered with infill walls - This means the building's left and right sides periphery is more stiffer during seismic forces (especially along North-south)

4.Staircase portion at Left top corner - Usually staircase and lift portions are stiffer than other parts because of concentrated concrete elements. So the staircase portion contains more stiffness in the provided building plan.

5.No framing connection along Y-direction - We could see no structural beams provided along the vertical direction between columns. This makes the building more vulnerable during the North-South seismic force.

6.Beams connected along column minor axes - The columns are having longer dimension in Y-direction. This means they are more stiffer along y-direction. But the beams are running only along x-direction which would attract much lesser lateral forces and hardly transfers it.

7.Variation in column sizes - The internal columns are having higher sizes compared to exterior columns (This is common because of higher load demands). But this will lead to significant difference in lateral drift of columns. So the concrete floor might have suffered heavy out-of-plane shear which would led to collapse.