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.

ANSWER :

By observing all the given plan the following problems and discussion are mentioned :

• For Structure (A)

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

• For Structure (B)

1. The structure frame can be considered as symmetric in placed the shear walls.
2. In wall system, the walls of this frame could be arranged in two horizontal directions with as much two-way symmetric as possible.
3. The shear walls are arranged in similarity and symmetric.
4. It can be considered at every storey to fairly uniform resistant in seismic forces and deformation demands, minimizing the uncertainty about the seismic response.

• For Structure (C)

1. The structure is considered to bs asymmetric in nature, because of the shear wall are provided are not arranged in two orthogonal horizontal directons.
2. 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.
3. The foundation, shear wall and columns are arranged different arrangements, so here take up huge amount moments in case of during earthquakes.
4. This structure have lack of redundancy because of shear wall system will not carry the load equally in either directions.
5. On left hand side the wall provide more eccentricity, lateral stiffness is more. Therefore it occurs then the damage or failure will be less.

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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.

ANSWER :

• By observing the given structural frame, we can say that :

1. 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.
2. In this structure beams are provided at stronger than column, so it can consider as Weak column strong beam design in nature.
3. This structure need some shear wall to resist the column failure, when the lateral forces acting above the structure.
4. Combination of shear wall and column tends to prevent the failure about the structure during the seismic forces occur.
5. 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.
6. But other all beams are provided at discontinuous of structural frame, so here it causes the difficulties in transmission of load, evenly at entire structure due to action of lateral forces.
7. This structure will alternate to better portal of better offset at symmetric in nature.
8. The column beams connections should be in proper cross section area, then it achieve lateral stiffness, mass regularity, moment resisting factor.
9. As we consider beam-sway mechanism in strong column/weak bear design frames is better, because it achieves uniformly spread global in-elastic displacement demand at roof level, to all storeys.

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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.

ANSWER :

As we observe the given plan, we can state that :

1. It is totally unsuitable design for heavy seismic zone areas.
2. here, the interior columns are in unsymmetric nature.
3. The partition wall are provided through the base of beam, should support the lateral deformation due to the structure.
4. The interiors beams will supports the slab, then the lateral load resisting the failure due to earthquakes.
5. For this irregular columns, we can provided the flat slabs, because it directly stay in a column centroidal axis.
6. Here, the beams at different locations is irregular in plan and are continuous and is disallowed to resist the seismic load in the region.
7. In this plan, the flat sab is more appropriate than a regular beam-column junctions, because it provides 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 indirectly.

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