Concept on positioning of Columns

1 ans : SYMMETRY-

when we have a look over the aspect of symmetry of the framing plan , it is observed that the distribution of mass,stiffness is across the plan it is considered as one of the good symmetrical aspects .

this tends to reduce the horizontal displacements in both of the two orthogonal horizontal directions .

it is also in the good uniformity.

REDUNDANCY-

there are missing structural elements in the periphery of the plan . this causes the uneven distribution of earthquake action effects in non linear range across the plan . the energy dissipation across the structure is very low which results in the non reliable structure.

BIDIRECTIONAL  STIFFENESS -

the building plan may not be able resist the horizontal sedismic actions in shorter direction  (y axis) also the resistance and stiffness in shorter direction (y axis) is less when compared to longer direction (x axis). 

DUCTILITY-

The building may not be able to resist in elastic earthquake forces in shorter direction (y axis) so it may result in inelasic response. the reduction in design force in shorter direction (y axis) is to be compensated by ductility.

2ans  : flexible structures in torsion , soft storeys

STIFFNESS IRREGULARITY

the lateral stiffness of the storey at the mid height which is open is very less compared to the above levels  because the main reason is the structural which is discontinued at the midheight.

it is observed that the open storey causes reduction in the stiffness in the building and attracts lateral seismic exicition is more in that floor which causes severe damage to the upper floors .

the irregularity can be solved dy providing the shear walls to high sismic action prone floor . 

MASS IRREGULARITY 

The open storey also causes th mass irregularity in the building bcause the high mass concentration is present above the open floor. that is the upper floors carry  more mass than the open floor , also the number of floors are higher above  the open    floor .

VERTICAL GEOMETRY IRREGULARITY -

there is a changewith the horizontal dimension of the lateral force resisting the open storey in mid height and also the vertical geometry of the building which means the length of top storey are varying along the building unit.

this causes torsional effects in the building which needs to be decoupled by providing the shear walls or decoupled moments.

the flexibility provided due to variation needed to be compensated by providing ductility.

3ans - The building collapse is due to ground exicition in both orthogonal horizontal direction and also due to torsional effects.

inspite of having earth quake resistance for two mentioned actions .

these are some of the resopnsible factors for failure -

1 OPEN GROUND FLOOR 

2 TWO SHORT SIDES OF THE PERIMETER IN FILLED

3 EXTREME LEFT HAND BAY STAIRCASE FILLED WITH CONCRETE

4 COLUMNS NOT IN SAME LINE

1 open ground floor-

the ground floor of the building is open which may be a softstorey (having long columns) due to this the ground floor exicition the columns could have been unable to resist the earthquake and form collapse   and this is called the soft storey mechanism.

this can be avoided by having strong column -weak beam mechanism.

2 two short sides of the perimeter in filled-

the mass has been undistributed in all sides of the building in all storeys because it is given that the two sides of the perimeter of the building is in filled which causes the irregular distribution of mass called as mass irregularity.

loads(soil due to infill) by providing stiffness in the building frame and helps to resist the earthquake actions and it adjusts the mass irregularity for the plan.

3 extreme left hand bay staircase filled with concrete-

the extreme left hand bay staircase due to this the mass got concentrated in the staircase due to which torsional effects formed having the base of concentration of mass in the staircase .

to avoid failure staircase should be kept in centre of building which makes torsional effect zero bu uncou[ling the moment .

4. columns not in same line 

it is observed that the columns in extreme left hand middle line columns has the deviation in the line of construction at staircase which again is the reson for irregularity in plan having the torsional flexibility .

also the sizes of beams and columns in the plan should be redesigned in such a way that the line of the column doesnt deviate in the staircase area.