Conceptual design of a building with columns and shear walls

ANSWER NO 1

AIM :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:

We are compared three alternative arrangements, (a), (b), (c), all with the same total cross-sectional area of the shear walls are

Restraint of Floor shrinkage:

Option(a) will have higher restraint to shrinkage, thus lead to cracks in the floor. Option(b) is average. Option(c) will not effectively restrain the shrinkage, so possibly less cracks.

The Lateral stiffness:

• 0ption 'a'Comparatively Lower Lateral stiffness in both X and Y
• Option 'b' Uniform and comparatively higher lateral stiffness in both X and Y
• Option 'c' Non uniform Lateral stiffness in both X and Y

Torsion with respect to vertical axis

0ption 'a' Corner Walls provide more resistance to twist

0ption 'b' Edge Walls provide good resistance to twist

0ption 'c' Irregular Walls provide very poor resistance to twist

Vertical reinforcement for similar base capacity

Option(a) will require very poor vertical reinforcement

Option(b) will require the least.

Option(c) will require higher vertical reinforcement

Static eccentricity

Only Option(c) will have static eccentricity and it is significant

System's redundancy

Option(a) and (b) are more redundant than Option(c)

Foundation systems

Option(b) and Option(c) shall be incorporated with isolated footings/ strip footings.

Option(a) is recommended to have peripheral box foundation.

Walls obstruct only corners.

Architecturally speaking, Option(a) is the preferred one. Option(b) is subjected to discussion. Option(c) will not be accepted both architecturally and commercially.

Answer no 2

Aim :

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.

Ans:

There are many Issues in the given Framing plan are :

• The Indirect lateral load Transfer in X and Y directions.
• Eccentricity - The longer the distance between center of mass and center of stiffness, the higher torsional moment of the building. As per the given plan eccentricity, the building is subjected to higher torsional moment (Torsional flexibility) in both X and Y directions.
• Strong beam Weak Column possibility The size of columns majorly mentioned as 5cm * 25 cm. But all the beams have much deeper section (50cm). Inertia of beam is visually higher than column. If the column reinforcement is adequately greater than that of beams, we are okay and since we do not have the reinforcement detail, this is doubtful. It is recommended to have slight bigger sizes for column.

Answer no 3

Aim : 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.

Ans :Observations in the given Framing plan and the result are :

• The floor plan of building is not either uniform or symmetric. So naturally any lateral load induced in the floor will not have 100% influence in same direction.
• the internal columns are random, they are unable to transfer lateral loads efficiently and can not achieve desirable building response
• Suggestion on the Lateral load system & Its foundation:

1. Heavy torsional forces should be controlled by respective lateral load system. So "Corner Shear walls" are suggested.
2. The proportion of floor area is greater on the left side than the right side (Irregular quadrilateral). So Corner shear walls on the left side should be heavier than the right.
3. Corner Shear walls shall preferably be supported over a box foundation. Shear walls should be connected by Link beams to transfer shear from one to the other.
4. The internal columns shall be supported by isolated footings. Those isolated footings can be connected with Shear walls through Tie beams."