Conceptual design of a building with columns and shear walls
Answer (1).
|
Criteria |
Observation/Conclusion |
For Dig. A |
For Diag. B |
For Dig. C |
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1.Restraint of floor shrinkage |
Observation |
Full restraints at all corners |
There is no restraint at corners but on edges. |
Either corner or edges, non-uniform restraints. |
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Conclusion |
Drg.A will have higher restraints to shrinkage, thus lead to cracks in the floor. |
Drg.B will have average restraints to shrinkage |
Drg.C will not have effective restraints to shrinkage, thus lead to less cracks. |
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2.Ltereral stiffness |
Observation |
Comparatively lower lateral stiffness in both X and Y. |
Uniform and Comparatively higher lateral stiffness in both X and Y. |
Non uniform lateral stiffness in both X and Y. |
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Conclusion |
Option B will provide higher lateral stiffness for a pure seismic acceleration in X and Y directions. |
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3.Torsion with respect to vertical axis. |
Observation |
Corner shear wall provide more resistance to twist. |
Edge walls provide good resistance to twist. |
Irregular walls provide very poor resistance to twist. |
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Conclusion |
Option A will be best option with respect to Torsional resistance whereas Option (c) is the worst one. |
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4.Vertical reinforcement for similar base capacity. |
Observation |
Walls are subjected to nominal flexural moment and heavy twisting moment. |
Walls are subjected to nominal twisting moment. |
Walls are subjected to heavy flexural moment and twisting moment. |
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Conclusion |
Option C will require vertical reinforcement and option B will require the least. |
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5.Static eccentricity. |
Observation |
Structurally symmetric. |
Structurally symmetric. |
Structurally Non- symmetric. |
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Conclusion |
Option C will have static eccentricity and it is significant. |
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6.Systems redundancy |
Observation |
Uniform placement of lateral load supports in both X and Y axes. |
Uniform placement of lateral load supports in both X and Y axes. |
Concentrated lateral load supports in both X and Y axes. |
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Conclusion |
Option A & B are more redundant than C. |
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7.Foundation system |
Observation |
Due to L – shaped walls, geometry and design of foundation is critical. |
Walls are in line, Easy to fix the geometry and foundation design. |
Walls are in line & concentrated. Easy to fix the geometry but and foundation design is critical. |
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Conclusion |
Option B & C shall be incorporated with isolated footings/strip footings. Option A is recommended for peripheral box foundation. |
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8.Architectural constraints |
Observation |
Walls obstruct only corners. |
Walls obstruct the faces of building. |
Vertical wall will not allow passage. |
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Conclusion |
Architecturally option A is the preferred one. Option B is subjected to discussion. Option C will not be accepted for both architecturally and commercially. |
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Answer – (2)
Indirect lateral load Transfer in X and Y directions – The secondary beams are connecting to primary 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 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 in both axes.
Strong beam weak column possibility – The size of the column majority mentioned as 25cm x 25cm. But all the beams have much deeper section (500mm). Inertia of beam is visually higher than column. If the column reinforcement is adequately greater than that beams, then it okay and as the reinforcement details are not provided here, this is doubtful. Hence it is recommended to have bigger sizes for column.
Alternate Scheme are detailed below :
Answer - (3)
Floor plan : The floor pla of the 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 this torsional moment should be structured.
Random internal column : Since the internal columns are random, they are unable to transfer lateral loads effectively and can not achieve desirable building response. So we need 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 from floor to beam. All these elements are not in order. Therefore, heavy distortion and distribution of lateral loads will happen.
SUGGESTIONS:
- Heavy torsional forces should be controlled by respective lateral load system. So corner shear walls are suggested.
- 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.
- Corner shear walls should 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 should be supported by isolated footings. Those isolated footings can be connected with shear walls through Tie beams.
