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.
Symmetry:
X-Direction: If we split the frame structure in half then both sides will be an exact mirror image so we can say that structure is symmetrical along the X-direction.
Y-Direction: If we split the frame structure in half then both sides will be an exact mirror image so we can say that structure is symmetrical along the Y-direction.
Redundancy:
X-Direction: There is a sufficient number of columns in the x-direction and equally spaced except in the 1st and last row, so we can consider that the structure is redundant in the x-direction except in the 1st and last row.
Y-direction: If compare to the x-direction numbers the columns in the y-direction are less but equally spaced so we can say that structure is redundant but less than the x-direction.
Bilateral Stiffness:
In the x-direction, columns are connected with the beam from one end to the last end so the lateral load can transfer one column to the last, but along Y-direction because of the non-continuous beam, the load coming from the north will get transferred in the east and west direction. So the structure is stiffer in the x-direction compared to Y-direction.
Bilateral Ductility:
Ductility is the inverse of stiffness, so the frame is more ductile in Y-direction compared to 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.
Vertical Irregularity:
The Area of the building in the bottom stories is more compared to the upper stories, so the structure is Irregular vertically.
Soft Storey:
The structure on the 6th floor has open space means it is less stiff than the floor above and below, so it has soft storey irregularity.
Inclined Base:
The structure is constructed on an Inclined base so the stiffness changes along the slopy base.
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).
Open Ground Floor
Soft story mechanism, Low stiffness.
Story 2 to 4 have one row of rooms along each long side in the plan.
Mass irregularity, uneven distribution of mass.
The two short sides of the perimeter are fully in-filled
It means the two short sides of a building are more stiffer during lateral loads.
There is a staircase near the upper left-hand corner
Stiffness on the upper left-hand corner is more so it generates a torsional effect in the first mode.
No beams are connected along the Y-direction except two ends so the lateral load comes from north on the column directly and transfers in Y-direction.
Orientation of column is vertical leads to attract more lateral force in Y-direction but because of missing beam connection may lead to collapse.
The size of the column in the 1st and 4th row is small so the drift of the column may differ, this might leads to of plane shear in floors.