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.

Ans: As structure is more restrained there will be shrinking. If cross section consists of rectangularparts with aspect ratio greater than 4, then element is classified as wall. The figure L-shape walls are given, that walls have high stiffness and strenght, So during earthquake they are subjected to biaxial and bi-directional shears. Shear walls in structure decide whether floor vibration is more or less, it will reduce cracks at the corners in the structure. High lateral stiffness of walls reduce non structural damage. Strcuture C is more laterally stiff compared to strcuture A and B as there will be eccentricity in structure C which cannot carry load equally in either direction.

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: In above figure there are two eccentricity in X and Y direction with stiffness eccentricity in X-direction is larger compared to Y-direction. Only two continous beam those are B1 and B2 in X-direction. B9,B10 and B11,B12 in the Y-direction where as all beams are broken at the midway in frame. Single plane frame should run continously from one side to other side of building without interruption .Beams with long span may have their top reinforcement at the supports governed by factored gravity loads this will result in beam overstrength. Fundamental translation mode of vibration is larger than the fundamental torsional mode of vibration.

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 In above plan it is unstable for earthquake prone areas. General layout and certain details of the geometry of an individual plane frame have a major impact on its seismic behaviour frames with concentric connections and regular geometry have well known and understood seismic performance. Earthquake resistance requirements on frames lead to large columns, interferring with architectural functions. Apart from slab a wooden structure is also appreciate which reducesthe weight of building and helps in maintain earthquake prone areas.