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

• In this structural frame , there is a two-way eccentricity of the center of mass in accordance with the center of stiffness , which is eccentricity of x-direction is larger than y-direction.
• In this structure beams are provided at stronger than column, so it can consider as Weak column strong beam design in nature.
• Therefore this structure need some shear wall to resist the column failure, when the lateral forces acting about the structure.
• Combination of shear wall and column tends to prevent the failure about the structure during the seismic forces occur.
• As the frame plan, we can see about the alignment of beam is uniformly continuous of B1 and B2 at X- direction, and B11 & B12, B9 & B10 at Y-direction.
• But another all beams are provided at discontinuous of structural frame, so here cause to difficult of transmission of load evenly at entire structure due to action of lateral forces.
• Beams with long span may have their top reinforcement at the supports governed by factored gravity load, rather than by the seismic design situations.
• Therefore,this structure will alternate to better portal of better offset at symmetric in nature.
• The column beams connections should be in proper cross section area, then it achieve lateral stiffness, mass regularity, moment resisting factor.
• As we consider beam-sway mechanism in strong column/ weak beam design frames is better, because of its achieve a uniformly spread, global inelastic displacement demand at roof level, to all storeys.

• For here, we changed the column of C5 & C8 to considered as a combined footing, because of their need to avoid the loss of center of stiffness due to occur lateral forces about the structure.
• And more we add one more column of C10 is covered that boundary of plan, should maintain the center of mass as well as the center of stiffness about the structure during lateral horizontal force action.

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.