Conceptual design of a building with columns and shear walls

1. The building shown, 20 x 30m in plan, has column on a 5 x 5m grid and shear walls( with dimensions shown in m, 250mm in thickness) in three alternative arrangements. (a, b, c), all with the same cross sectional area of the shear wall. 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 systems redundancy, foundation systems, architectural constraints etc.,

ANSWER

STRCTURE (a)

• For this structure is considered as it is asymmetric in nature.
• Here cannot to be considered as a horizontal irregularities and the shear wall shape like L.
• There is some uncertainty concerning certain features of the seismic response of non-rectangular walls.
• It occurs lack of tensile capacity and force configuration.
• These walls have high stiffness and strength in both direction, hence are subjected biaxial bending and bi-directional shears during earthquakes.

STRUCTURE (b)

• For this structure frame can be considered as symmetric in placed the shear walls.
• The walls of a wall system of this frame could be arranged in two horizontal directions with as much two-way symmetric as possible.
• The shear walls are arranged in similar and symmetric, so it can be considered at every storey to fairly uniform resistant in seismic forces and deformation demands, minimizing the uncertainty about the seismic response.

STRUCTURE (c)

• For this structure can be considered as asymmetric in nature, because of the shear wall are provided are not arranged in a two orthogonal horizontal directons.
• The center of mass and center of gravity of such structure will not lie far away from each other enabling transitional modes in the first two principles modes.
• The foundation , shear wall and columns are arranged different arrangements, so here take up huge amount moments in case of during earthquakes,
• This type of shear wall system will not carry the load equally in either directions. So this structure have lack of redundancy.
• On left hand side the wall provide more eccentricity, lateral stiffness is more. Therefore it occurs then the damage or failure will be less.

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 center of the mass ( as centroid of floor ) to the center of stiffness ( from the moment of inertia of the column ) as 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.

ANSWER

There is a two way eccentricity in the frame along X direction and Y direction also with stiffness the eccentricity in X direction is larger when compared to Y direction.

There is only two continuous frames in the structure that is B1 and B2 in the X direction and B9, B10 and B11,B12 in the Y direction and all other beams are broken at the midway in the frame.

There will be Torsional flexibility in the structure.To avoid torsional restraints it is better to make the room dimensions even in both X and Y direction and placing the columns at the junction of two wall if it is feasible better to provide shear wall at appropriate location.

The fundamental translation mode of vibration is larger than the fundamental torsional mode of vibration.

3. A multi-storey building with basement, with a quadrilateral ( non symmetric floor plan) plan as, has interior columns in an irregular(not in a grid) pattern in plan that serves architectural and functional considerations. Partition wall 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-system in the perimeter. Proposals are to be made and justified for the choice of the lateral-load-resisting system and its foundation.

ANSWER

• This plan totally unsuitable for heavy seismic zone areas.
• In this plan, the interior columns are in unsymmetric.
• The partition wall are provided through the base of beam, should support the lateral deformation due to the structure.
• The interiors beams will supports the slab, then the lateral load resisting the failure due to earthquakes.
• For this irregular columns in plan, there we provided the flat slabs, because its directly stay in a column centroidal axis.
• For here, the beams at different locations is irregular in plan and are continuous and is disallowed to resist the seismic load in the region.
• In this plan, the flat sab is more appropriate than a regular beam column junctions, because of as its provide support to the columns without any provision of the beam, which reduces the weight of the building and also helps in the ductility of the structure by indirectly.
• for the solution of this structure, we provide the shear wall from the foundation of structure through vertical components, it should minimize the loss of sudden failure occur due to lateral force acting on structure.