Concept on positioning of Columns
1. ANS:
COMMENT ON THE LAYOUT OF THE FRAMING PLAN CONCERINING EARTHQUAKE RESISTANCE:
LOOK INTO ASPECTS OF SYMMETRY, REDUNDANCY AND BI-DIRECTIONAL STIFFNESS AND DUCTILITY:
1. SYMMETRY:
Having a look over the aspects of symmetry of the framing plan, it is observer that the distribution of mass, stiffness is across the plan; it is observed that the distribution of mass, stiffness is across the plan.
It is considered for one of the good symmetrical aspects.
This tends to reduce the horizontal displacements in both of the two horizontal displacements in both of the orthogonal horizontal directions.
IT IS ALSO HAS A VERY GOOD UNIFORMITY ALSO.
2. REDUNDANCY:
There are missing structural elements in the periphery of the plan. This cause the uneven distribution of earthquake action effects in linear range across the plan.
The energy dissipation across the structure in very low which results in non reliable structure.
3. BI - DIRECTIONAL STIFFNESS:
The building plan may not be able to resist the horizontal seismic actions in the shorter direction(Y-axis); also the resistance and stiffness in the shorter direction (Y - axis) is less when compared to longer direction (X - axis).
4. DUCTILITY:
The building may not be able resist the elastic earthquake forces in shorter direction (Y - axis) so it may result in inelastic response. The reduction in design force in the shorter direction ( Y- axis) is to be compensated by ductility.
2. ANS:
SOFT STOREYS
FLEXIBLE STRUCTURES IN TORSION:
1. STIFFNESS IRREGULARITY:
The lateral stiffness of the story at the mid height which is open is very less when compared to the above levels because the main reason is the structure is discontinued at the midheight.
It is observed that the open storey causes reduction in the stiffness in the building and attrracts lateral seismic exicitation more in that floor which causes severe damage the upper floors.
The irregularity can be solved by providing the shear walls to this seismic action prone floor.
2. MASS IRREGULARITY:
Th open storey is also causes mass irregularity in the building because the high mass concentration is present above the open floor. That is the upper floors carry more mass than the open floor.
Also the no.of floors are higher above this open floor.
3. VERTICAL GEOMETRICAL IRREGULARITY:
There is a change with the horizontal dimension of the lateral force resisting due to the open storey in mid height and also the vertical geometry of the building which means the length of the top storey are varying along the building unit.
This causes torsional effects in the building which need to be decoupled by providing shear walls or decoupled moments.
The flexibility provided due to the variation need to be compensated by providing ductility.
3.ANS:
THE BUILDING COLLAPSE OCCURED DUE TO THE GROUND EXICITATION IN BOTH ORHOGONAL DIRECTIONS AND ALSO DUE TO THE TORSIONAL EFFECTS. INSPITE OF BEING HAVING THE EARTHQUAKE RESISTANCE FOR THE TWO MENTIONED ACTIONS.
THE FOLLOWING ARE THE RESPONSIBLE FACTORS:
1. OPEN GROUND FLOOR.
2. TWO SHORT SIDES OF THE PERIMETER IN FILLED.
3. EXTREME LEFT HAND BAY STAIRCASE FILLED WITH THE CONCRETE.
4. COLUMNS NOT IN THE SAME LINE.
1. OPEN GROUND FLOOR:
The ground floor of the building is open which may be a softstorey due to this the ground floor excitation the columns could have been unable to resist the eathquake and form collapse is called soft storey mechanism.
This can be avoided by having string column - weak beam mechanism.
2. TWO SHORT SIDES OF THE PERIMETER IN FILLED.:
The mass has been distributed in all the sodes of the building in all storeys because it is given that the two sides of the building is in filled which may causes the irregular distribution of mass called as mass irregularity.
This can be avoided by providing the shear walls in the directions of two short sides of the perimeter which can resist the lateral loads by providing stiffness in the building frame and helps to resist the earthquake actions.
Also it adjusts the mass irregularity for the plan.
3. EXTREME LEFT HAND BAY STAIRCASE FILLED WITH THE CONCRETE.:
The extreme left hand bay staircase due to this mass got concentrated in the staircase area due to which torsional effects are formed having the base of the concentration of mass in the staircase.
To avoid this type of failure the staircases should be kept in the centre of the building which makes torsional effect as zero by uncoupling the moment, it also makes the implications of the irregularity in plan of the building.
4. COLUMNS NOT IN THE SAME LINE:
It is observed that the columns in the extreme left hand middle line columns has the deviation in the line of the construction at the staircase which again a reason for the irregularity in plan having the torsional flexibility.
To avoid this the eccentricity should be maintained for the devition to be with in the limits of the beam size and the column sizes.
Also the sizes of the beams and columns in the plan should be redesigned in such a way that the line of the columns doesn't deviate even in the staircase area.
THESE ARE THE BASIC CONCEPTS OF THE POSITIONIG OF BEAMS AND COLUMNS: