Conceptual design of a building with columns and shear walls

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 concerning 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:

Option A

• The structure is considered to be symmetric.
• It will have higher resistance to shrinkage, which will lead to cracks in floors.
• There is some uncertainty concerning lower lateral stiffness along the x and y direction
• It occurs lack of tensile capacity and force configuration.
• These walls have high stiffness and strength in both directions, hence are subjected to biaxial bending and bi-directional shears during earthquakes.

Option B

• The structure is considered symmetric in 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.
• It has higher lateral stiffness in the x and y direction.
• The shear walls are arranged in a similar and symmetric, so it can be considered at every storey to be fairly uniform and resistant to seismic forces and deformation demands, minimizing the uncertainty about the seismic response.

Option C

• this structure can be considered asymmetric because the shear walls provided are not arranged in two orthogonal horizontal directions.
• The centre of mass and centre of gravity of such structure will not lie far away from each other enabling transitional modes in the first two principles modes.
• This type of shear wall system will not carry the load equally in either direction. So this structure is less redundant.
• it has static eccentricity.
• On the left-hand side the wall provides more eccentricity, and lateral stiffness is greater. Therefore it occurs then the damage or failure will be less.
• The structure is less redundant.

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

Question 3]

A multi-storey building with a basement, with a quadrilateral (non-symmetrical floor plan) plan, 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 layouts 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 that is given is unsuitable for normal areas and also in earthquake-prone areas.
• In this plan, the interior columns are unsymmetric.
• The interior beams will support the slab, then the lateral load resisting the failure due to earthquakes.
• The partition wall is provided through the base of the beam and should support the lateral deformation due to the structure.
• In seismic region the lateral and vertical loads play important criteria because it helps in resisting the failure against the earthquake as the loads.
• the beams at different locations are irregular in plan and are continuous and are disallowed to resist the seismic load in the region.
• In this plan a flat slab is more appropriate than a regular beam-column junction as it provides support to the columns without any provision of the beam which reduces the weight of the building and also helps in ductility which indirectly helps to maintain the structure in the earthquake-prone areas.
• For this structure, we provide the shear wall from the foundation of the structure through vertical components which should minimize the loss of sudden failure that occurs due to lateral force acting on the structure.