Conceptual design of a building with columns and shear walls

Question 1:
The building shown, 20 × 35 m in plan, has columns on a 5 × 5 m grid and shear walls (with dimensions shown in m, 250 mm in thickness) in three alternative arrangements, (a), (b), (c), all with the same total cross-sectional area of the shear walls. Compare the three alternatives, taking into account the restraint of floor shrinkage, the lateral stiffness and the torsional one with respect to the vertical axis, the vertical reinforcement required for the same total flexural capacity at the base, the static eccentricity, the system’s redundancy, foundation systems, architectural constraints etc.

restraint of floor shirankage

in figure a, the shear wall is in both x and y direction with equal dimension and at the corner of the floor there is no chance of floor shirankage

in figure b,the shear wall at the pheriphery of the structure in all sides,but the corner are open so there is shirankage in the floor

in figure c, shear wall is not symetrical, most likly shirankage occur in both long and short direction,length of shear wall in left side is 1o meter but corner is open so chances of shirankage is more in this side.

lateral stiffness

in figure a , as the shear wall at the corner of floor in both axis,the earthquake force tends to act along the edge of the floor either x and y direction so lateral stiffness will be less.

in fig b ,the shear wall at the pheriphery of the floor,during movement of structure the lateral stiffness is more as compared to fig a

in fig c, the two shear wall along the x axis and one shear wall along y axis ,so y direction insatble as compared to x axis.

torsion

in fig a there is no chances of torsion as shear wall is symmetric and in corner and no eccentricity arise between center of mass and center of stiffness.

in fig b, the shear wall is symmetric, and along the periphery of the structure, and no eccentricity where as in fig c shear wall not symmetric there is ceccentricity between center of mass and center of stiffness,so there is torsional movement.

static eccentricity

in fig a and b the the wall is symmetric and center of mass and center of stiffnees are in same plane so there os no question of eccentricity

in fif c , wall is not symetric, and havier mass of wall in y axix and other side no wall, in x axis wall at corner , there is eccentricity developed between center of mass .

redundency

in fig a and b, equal force shared by all the corner wall and pheriphery wall, so structure is less redundent

in fig c, force are not shared equally by the shear wall, so structure is less redundent.

Question 2:
Discuss the suitability for earthquake resistance of the moment resisting framing plan of a three-storey building depicted here (cross-sectional dimensions in cm), the eccentricity of the centre of mass (as centroid of floor plan) to the centre of stiffness (from the moments of inertia of the columns) are shown. Suggest an alternative. Also, is there torsional flexibility? Are the two fundamental translational modes of vibration larger than the fundamental torsional mode of vibration. Discuss qualitatively.

ANS

The provided column is not symmetric in plan as well as column to column distance .

The position of beam should be continue from column to column without offset or intruption so that the reinforcement should be continue.

Here also case of strong beam and weak column.

The pheriphery beam B7 should be primary it should rest on column here it rest on anther beam B4

Here as the eccentricity between center of mass and center of stiffness given ,so there is movement in building

Question 3:

A multi-storey building with basement, with a quadrilateral (non symmetrical floor plan) plan as, has interior columns in an irregular (not in a grid) pattern in plan that serves architectural and functional considerations. Partition walls and interior beams supporting the slab have different layout in different stories. However, there is no constraint to the type, location and size of the lateral force resisting components and sub-systems on the perimeter. Proposals are to be made and justified for the choice of the lateral-load-resisting system and its foundation.

ANS

The above plan is not symmetrical , the center of mass and center of stiffness is diffrent ,here the eccentricity developed, as every floor has different patrition wall and beam location.

Proposal for such type of structure is flat slab or drop panel slab, the foundation should be raft foundation.