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

Investigation of the framing plan with respect to symmetry in X and Y direction

If we split the plan vertically half, it will look like a mirrored image. So we conclude the given frame is symmetry in Y-direction.

If we split plan in horizontally half, it will look mirrored. So we can conclude the given plan is symmetric in Y -dirrection

Investigation of the framing plan with respect to redundancy in X direction:

The coloumn in X-direction are comparitivly more and evenly spaced. So the structure is more redundant in X-direction. Except the top and bottom column rows are having quite longer spans.

Investigation of the framing plan with respect to redundancy in Y direction:

The columns in Y-direction are comparitively lesser but evenly spaced. So the structure is redundant but lesser than that of in x direction.

Investigation with respect to Bi-directional stiffness:

The columns in horizontal direction direction are connected with straight to straight beams. This means, any lateral loads (seismic forces in x direction ) passing from left end of the building will have its path straight till it reaches rightend of the building. So no orless possibility of forces direction takes place

The coloumns in vertical direction are not connected with straight beams. so a lateral load passing from south side of building will get diverted to east & west direction to reach next bay. There will be major force diversion take place with sesmic force in Y-direction. The framing plan is weak with respect to bi-directional stiffness in 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

Vertical irregularity:The building plan area is larger in bottom stories. The floor plan areas are getting reduced with increase in height. These building offsets has to be crosschechedith increase in height. These building offsets has to be crosschecked with reference to Is-1893-2016 Table-6 serial number 3

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 formationat the columns (with reference to IS-1893-2016 Figure 4A). This has to bechecked and sufficiently designed.

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

Vertical irregularity-IS 1893-2016 Table-6 serial number 3

Soft storey-IS-1893-2016 Figure 4A

Slopy base - IS 1893-2016 Figure 5E

Question 3

A 4-stoorey hotel building has an open grounnd floor for the restorent. Story 2to 4 have one row of rooms along each long side in plan, sperated 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 2to 4 and along the right-hand corner, with straight fkights 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 ofinfills which are important for earthquake resistance and seismic performance. How do they relate to the almost full collapse of this building (extreme left -hand bay with the staircase survied, as well as one long-side fasadein the rear end, and the frame along the right-hand side in plan).

Aswwer:

Open ground floor-THis denotes soft storey mechanism acting in the building

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

Two short side covered with infill walls- this means the buildings left and right sides periphery is more stiffer during seismic forces (especially along North-Sounth)

Staircase portion at left top corner- Usually stairecase and lift portions are stiffer than other parts beacause of concentrated concrete elements. So the staircase portion contains mors stiffness in the provided building plan

No framing connecting along y-direction - We could see no structural beams provided along the vertical direction between the columns. This makes the building more vulnerable during the north-south sesmic force.

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

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