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:
COMMENTS ON THE LAYOUT OF THE FRAMING PLAN IS GIVEN BELOW :
a) SYMMETRY :
- If we split the plan vertically half and horizontally half it look like as a mirror . so we conclude the given plan is symmetric in x and y direction .
- This structure has an exact matching of form and arrangement of parts on opposite sides of the boundary at X and Y.
- The load resistance framing in this symmetrical structure is distributed evenly throughout the structure.
- If the reflection of the structure about the axis is identical in geometry, supports, and material properties to the structure itself, the structure is symmetric with respect to an axis of symmetry in its plane.
b) REDUNDANCY :
1) Redundancy in x direction :
- If we see the plan the column in x direction is more than in y direction . also more space in x direction , except top and bottom column .
- The redundancy at the top and bottom is less as compair to middle part in the x direction .
2) Redundancy in Y direction :
- if we see the plan the column in y direction are comparatively less but having evenly spaced .
- the structure in y direction is redundant but comparitively less to x direction .
- Because this structure has perfect redundant, the structure becomes more reliable in resisting any lateral forces acting on the structure.
- Furthermore, it tends to prevent any extent of degradation that the structure may suffer without losing some specified elements of its functionality.
c) BI-DIRECTIONAL STIFFNESS :
- The column in horizontial direction are connected to stright beam if any lateral load in x direction which are passing from left to right direction of the building i.e. throughout the layout's framing., we see that path is stright there was less or no possibility of the force diversion.
- but in y direction the column is not connected to stright beam so , the lateral load passing through south side of the building get diverted into the opposite direction that is east nd west direction to reach at a next bey .
- therefore major force diversion is take place with sesmic force in y direction .
- the framing plan is weak with respect to bi-directional stiffness in y direction .
-Because this structure can distribute seismic forces due to its bidirectional nature, it can withstand and resist any horizontal motion of forces.
- The given plan has an orthogonal layout in both the X and Y directions, so it can transfer forces evenly, and its structure will be able to withstand direct action from seismic forces.
d) DUCTILITY :
- We see that more column in x direction than y direction it will results in higher stiffness in x direction . that reduce ductiliy in x axis.
- we see that the x force is easly passes through one bay to another bay . but y force is doing more strugle for passing .
- the given floor plan is more ductile in y direction than 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.
ANS:
Sources of possible of irregularity in the building exlplain below :
1. vertical irregularity
2. Failure of soft storey
3. Slopy base
4. Floating Columns
5. Mass Irregularity
1) Vertical irregularity :
- This irregularity is cross checked with refreance to IS-1893-2016 table 6 - serial no (iii)
- we see in above picture at the bottom the floor plan area is large and then area is reduced as per height is increased .
2) Soft Story :
- If we look at the 6th floor where concorved opening space is provided
- there was no partition wall is provided that leads with plastic hinged formation at the column .
- this irregulrity is cross checked with reference to IS-1893-2016 FIG 4A
- The ground floor of the building is mostly considered soft stories because it has a short column, no shear wall, and a lot of mass properties.
- Damage may also occur, such as a collapse, buckling of the column, etc.
- checked this and then design properly .
3) Slopy Base :
- In picture looking to right side we see slopy base at a one side . that leads to significient variations in the stiffness .
- the few levels are subjected to soft story mechanism .
- this irregularity is cross checked with refrance to IS- 1893-2016 FIG 5E.
- This building's structure may be affected by seismic forces in the categories of soft storey, vertical geometry irregularities, floating columns, mass irregularities, and inconsistent seismic forces.
4) Floating Columns:
- The column is regarded as a vertical member of the structure that resists lateral forces.
- If horizontal forces act about the structure, they may transfer through the vertical member and to the base shear foundation.
- As a result, the column is at the structure's discontinuity, and it is unable to withstand lateral forces during earthquakes because the load cannot be transferred to the foundation.
5) Mass Irregularity:
- The seismic response should not be considered because of the structure's mass irregularity at any floor.
- The susceptibility of an irregular frame to seismic excitation has been found to decrease as the mass irregular floor moves towards the top of the building.
- In a structural system, mass irregularity is defined as a variation of more than 150 percent of mass between adjacent stories.
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:
- Looking toward the plain we see that it consist of one way slabs , beam and columns in the structural plan.
- the reinforced concrete beam is provided in x direction .
- no beams are provided in y direction thats way structure is failure .
- we see at bottom floor looking open at may lead soft story failure mechanism acting in the building .
- as per the given instructions, the middle portion is the corridor which means that portion has no mass as compaired to other sides having room and which results in greter mass , due to this irregularity building may collaps.
- The structure's frame is not symmetric.
- If the columns in this structure are not properly aligned in a symmetrical plane, then any lateral forces may cause damage.
- There is no proper masonry infill wall placement.
- In this structure. Redundancy in the vertical direction is inadequate.
- If the framed structure is capable of transferring the loaf from one direction to another of the foundation's structure.
- The columns in this layout are closely spaced, resulting in the formation of short paths for the transfer of stresses, which is also an important factor in earthquake resistance.
- The interaction of the staircase with other parts of the 3D structure, specifically the interaction with the beam, column, and shear wall, results in patterns of deformation that are not typically studied during the design process.
- The increased strength and stiffness of the structure in the stairway region, for example, will influence the seismic torsional distress of the structure and may lead to shear failure of the staircase or other structural elements.