Conceptual design of a building with columns and shear walls

CHALLENGE 5

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.

(a) picture:

• The structure is believed to be symmetrical in nature.
• It is more resistant to shrinkage, which causes floors to crack.
• There is some uncertainty about the lateral stiffness falloff along the x and y direction.
• Lack of traction and power configuration occurs.
• These walls have high stiffness and strength in both directions, so they are subjected to biaxial bending and he bidirectional shear duringan an earthqueake.

(b) picture:

• A structure is considered symmetrical if shear walls are in place.
• The walls of this frame work wall system can be placed as symmetrically as possible on two horizontal he two sides.
• Higher lateral stiffness in the x and y direction.
• The shea rwalls are similarly symmetrically arranged so that fairly uniform resistance to seismic force and deflection requirements can be accommodated on each floor, thus minimizing uncertainty regarding seismic response.

(c) picture:

• This is because the structure can be considered inherently asymmetric due to the provision of two orthogonal, non-horizontally aligned shear walls.
• The centroids and centroids of such structures are not far apart, allowing transition modes in the first two principal modes.
• This type of shear wall system does not carry loads evenly in both This structure is there for einherently less redundant.
• There is static On the left, the wall is more eccentric and has greater lateral stiffness. Asaresult, less damage and failures occur.
• The structure is in herently less redundent.

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 mass (as centroid of floor plan) to the center 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 bi-directional This is the center of mass aligned with the center of stiffness.
• The eccentricity in the x direction is greater than the eccentricity in the y direction.
• In this structure, the beams provided are stronger than the stanchions, so it can be considered as a weak support structure with in herently strong beams.
• Therefore, the structurer equires shear walls to resist column failure when lateral forces act around the structure.
• The combination of seismic walls and columns prevents the structure from collapsing due to seismic force.
• Column-beam connections must be of appropriate cross-sectional Lateral stiffness, mass uniformity, and moment coefficient of resistance are then achieved.
• As the frame work indicates, the beam alignment is uniformly continuous from B1 and B2 in the X direction, B11 and B12 in the Y direction, and B9 and B10.
• But since all other beams are designed in breaks in the structural frame, he redue to the action of lateral forces it is difficult to evenly transfer the load through out the structure.
• For longer span beams, reinforcement at the top of the column can be determined by the considered gravity load rather than the seismic design situation.
• Thus, the structure turns in to a better portal with betteroffset symmerty.
• The fundamental translational vibration mode is larger than the fundamental torsional vibration mode.
• We believe the beam pivot mechanism is better with a strong column/ weak beam frame, so this achieves a global, inelastic roof-level displacement requirement that is evenly distributed across all floors.
• 

3.A multi-storey building with basement, with a quadrilateral (unsymmetrical 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.

• The above plan is completely unsuitable for normal or earthquake-prone areas.
• In this plan the inner columns are asymmetrical.
• Internal beams support the slabs and resist lateral loads that resist seismic failure.
• Partitions are placed through the base of the beam and should support lateral deflection by the structure.
• At earthquake sites, lateral and vertical loads are important criteria as they help resist failure against seismic Beams in different locations have irregular plans and are continuous, unable to with stand the seismic loads in that area.
• A flat plate is better for this plan than a regular truss column This also contributes to the weight reduction and ductility of the building by supporting the columns without trusses,and indirectly helps keep the structure with in seismic limits.
• In this structure, shear walls are provided by vertical components from the foundation of the structure to minimize catastrophic failure losses caused by shear forces acting on the structure.