Concept on positioning of Columns
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 framing plan with respect to symmetriy in X direction
If we split the plan vertically half, it will look mirrored so we conclude the given plan is symmetric in X direction
Investigation of the framing plan with respect to symmetry in Y direction
If we split the plan horizontally half, it will look mirrored so we conclude the given plan is symmetric in Y direction
Contd:
Investigation of the framing plan withb respect to redundancy in X direction
The column in X direction are comparitevly more and evenly spaced so the structure is more redundant in X direction Except the top and bottom column rows are having quite longer span
Investigation of the framing plan withb respect to redundancy in Y direction
The column in Y direction are comparitevly lesser but evenly spaced so the structure is redundant but lesser than that of in X direction
Contd:
Investigation with respect to Bi directional stiffness
the columns in horizontal direction are connected with streight to sreight beams, this means any lateral load seismic force in X direction passing from left end of the building to the right end, so no or less possibilty of force diversion take place
the columns in y direction (vertical) are not connected with streight to streight beam so lateral load p[assing from south side of building will get diverted to east and west directioin to reach next bay there will be major force diversion take place with seismic force in Y direction the framing plan is weak with respect to biodirectional stiffness in Y direction
Investigation of the framing plan with respect to ductility
Prima facie the aspects ratio of the plan clearly hints more column in X direction compared to y direction it will result in higher stiffness of the building in the X direction which would reduced ductility in X axis
moreover the x force will easily pass from one bay to its next due to beam allignment. whereas the Y force will struggle to pass through the north south beam are arranged with zig zag which leads to discontinuous bracing
we can conclued that the given framing plan is more ductile in Y direction than that of in 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) Vertical irregularity:
The building plan area is larger in bottom stories The floor plan areas are getting reduced with increasing in height these building offsets has to be crosschecked with trefrence to IS 1893-2016 table 6 serioel number 3
2) Soft storey -
The building has uncoverd opening space in 6th floor, as trhere is no accurancy or a partition wall this will lead to plastric formation at the column this has to be checked and sufficiently designed
3) slopy base :
The building on a sloping ground at one side this will lead to significant variation in the stiffness few level 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:
Open ground floor: This denotes soft storey mecanism acting in the building
Rooms along 2 bay seperated by an open corridor: The bay filled with rooms will have higher mass compared to middle bay left open for corridor. This induces mass irregularityalong height uniformly
Two short side coverd with infill walls: This meance building left and right sides pheriphery more stiffer than front and back side during seismic force
Staircase portion at left top corner: Usually staircase and lift portion are stiffer than other parts because of concentated concrete elements so the staircse portion contains more stiffness in the provided building plan
Contd. :
No framing along Y direction:
We could see no structural beam provided along the verticall direction between columns This makes the building more vulnerable during the north south seismic force
Beams connected along column minor axes:
The column are having longer dimension in Y direction this meance they more stiffer along y direction but the beam are arunning along the x direction which would attract much lesser lateral force and hardly transfer it
Variation in column sizes:
The internal column are having heigher sizes compared to exterior columns but this will lead to signifoicant difference in lateral drift to column so the concrete floor might have suffered heavy out of plane shear which would led to collapse