Conceptual design of a building with columns and shear walls

1.

CRITERIA		Figure (a)	Figure (b)	Figure (c)
Restraint floor shrinkage	Observation	Full restraints at all corners	Corners are left free but restraints along the edge	Non uniform restraints
	Conclusion	Figure (a) will have higher restraint to shrinkage. thus lead to cracks in the floor. Figure (b) is average. Figure (c) will not effectively restrain the shrinkage. so possible less cracks.
The lateral stiffness	Observation	Comparetively lower lateral stiffness in both X and Y.	Uniform and Comparetively high lateral stiffness in both X and Y.	Non Uniform lateral stiffness in both X and Y.
	Conclusion	Figure (b) will provide higher lateral stiffness for a pure seismic acceleration in X and Y directions
Torsion with respect to vertical axis	Observation	Corners Walls provide more resistance to twist	Edge wall provide good resistance to twist	Irregular walls provide very poor resistance to twist
	Conclusion	Figure (a) will be the best option with respect to torsion resistance whereas Figure (c) is the worst one.
Vertical reinforcement for similar base capacity	Observation	Walls are subjected to nominal flexural moment and heavy twisting moment.	Walls are subjected to nominal flexural moment.	Walls are subjected to heavy flexural moment and heavy twisting moment.
	Conclusion	Figure (c) will require higher vertical reinforcement and figure (b) will require the least.
Static eccentricity	Observation	Structurally symmetric	Structurally symmetric	Un symmetric
	Conclusion	only option (c) will have static eccentricity and it is significant.
System redundancy	Observation	Uniform placement of lateral load support in both axes.	Uniform placement of lateral load support in both axes.	Concentration lateral load support in both axes.
	Conclusion	Figure (a) and figure (b) are more redundant than figure (c)
Foundation systems	Observation	Due to 'L' shaped walls, the geometry of foundation and its design will be critical	Walls are in line . Easy to fix the geometry and design of foundation.	Walls are in line & concentr ated. Easy to fix the geometry of foundation but critical in design of foundation.
	Conclusion	Figure (b) & figure (c) shall be incorporated with isolated footing/strip footings. Figure (a) is recommended to have peripheral box foundation.
Architectural constraints	Observation	Walls obstruct only corners.	Walls obstruct the face of the building.	Vertical wall will not allow passage.
	Conclusion	Architectural speaking, figure (a) is preffered one. Figure (b) is subjected to discussion. Figure (c) will not be accepted both architectural and commercially

2.

Issues

Indirect lateral load transfer in X and Y directions- The beam are connecting to another beams which is ineffective during lateral load transfer. In such conditions, The primary beam is prone to shear failure.

Eccentricity- The longer the distance between centre of mass and centre 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 25cm x 25cm. But all the beams have much deeper section (50 cm). 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.

Alternate scheme:-

3.

Observation

• Floor plan- 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. Definitely a special lateral load resisting system for these torsional moments should be accommodated.
• Random internal columns- Since the internal columns are random, they are unable to transfer lateral loads efficiently and can not achieve desirable building response. So we have to assume and design those columns for only gravity loads.
• Floor to floor variation in partition walls and beams- Partition walls provide an important mass control in a building and beams play key role in shear transfer from floor to beam. All these elements are not in order. So heavy distortion and distribution of lateral loads will happen.

Suggestion on the lateral load system & its foundation:

• Heavy torsional forces should be controlled by respective lateral load system.So "corner shear walls" are suggested.
• The porsion 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.
• 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.
• The internal columns shall be supported by isolated footings. Those isolated footings can be connected with shear walls through tie beams.