Conceptual design of a building with columns and shear walls
Ans 1.
For figure A.
- Restraint of Floor shrinkage
Observation : Full restraints at all corners.
Conclusion : It will have higher restraint to shrinkage which leads to cracks in the floor.
- The Lateral stiffness
Observation : Comparatively to other figures Lower Lateral stiffness in both X and Y direction.
Conclusion : Provide less lateral stiffness
- Torsion with respect to vertical axis
Observation : The more resistant to twist provided by corner walls.
Conclusion : It will be best option with respect to Torsional resistance.
- Vertical reinforcement for similar base capacity
Observation : Nominal flexural moment and heavy twisting moment at Walls.
Conclusion : It does not require higher vertical reinforcement.
- Static eccentricity
Observation : This is a Symmetric Structure.
Conclusion : It does not have static eccentricity.
- System's Redundancy
Observation : Uniform placement of lateral load supports in both the axes.
Conclusion : It is more Redundant.
- Foundation Systems
Observation : Due to 'L' shaped Walls, the geometry of foundation and its design will be critical.
Conclusion : This is recommended to have peripheral box foundation.
- Architectural constraints
Observation : Walls obstruct only corners.
Conclusion : According to architectural speaking this option is preferred one.
For figure B.
- Restraint of Floor shrinkage
Observation : Corners are left free but restraints along the edge.
Conclusion : It will have average restraint to shrinkage which leads to cracks in the floor.
- The Lateral stiffness
Observation : Uniform and comparatively higher lateral stiffness in both X and Y direction.
Conclusion : It will provide higher lateral stiffness for a pure seismic acceleration in X and Y directions.
- Torsion with respect to vertical axis
Observation : Edge Walls provide good resistance to twist.
Conclusion : It will be 2nd best option with respect to Torsional resistance.
- Vertical reinforcement for similar base capacity
Observation : Nominal twisting moment at Walls.
Conclusion : It does require least vertical reinforcement.
- Static eccentricity
Observation : This is a Symmetric Structure.
Conclusion : It does not have static eccentricity.
- System's Redundancy
Observation : Uniform placement of lateral load supports in both the axes.
Conclusion : It is more Redundant.
- Foundation Systems
Observation : Walls are in line. Easy to fix the geometry and design of foundation
Conclusion : This is recommended to have Isolated footins/striped footings.
- Architectural constraints
Observation : Walls obstruct the faces of the building.
Conclusion : According to architectural speaking this option is subjected to discussion.
For figure C.
- Restraint of Floor shrinkage
Observation : Non uniform restraints.
Conclusion : It will not effectively restrain the shrinkage, so possibly less cracks..
- The Lateral stiffness
Observation :Non-uniform lateral stiffness in both X and Y direction.
Conclusion : It Provides less lateral stiffness.
- Torsion with respect to vertical axis
Observation : Irregular Walls provide very poor resistance to twist.
Conclusion : It will be the worst option with respect to Torsional resistance.
- Vertical reinforcement for similar base capacity
Observation : Walls are subjected to heavy flexural moment and twisting moment.
Conclusion : It will require higher vertical reinforcement.
- Static eccentricity
Observation : This is a Un-Symmetric Structure.
Conclusion : It is significant and does have static eccentricity.
- System's Redundancy
Observation : Concentrated lateral load supports in both the axes.
Conclusion : It is less Redundant.
- Foundation Systems
Observation : Walls are in line & concentrated. Easy to fix the geometry of foundation but critical in design.
Conclusion : This is recommended to have Isolated footins/striped footings.
- Architectural constraints
Observation : There is no passage allowance at vertical walls.
Conclusion : According to architectural speaking this option is not accepted for Architecturally and Commercially.
Ans 2.
Issues in the given Framing plan :
1. Indirect lateral load Transfer in X and Y directions -
The beams are connecting to another beams which is ineffective during lateral load transfer. In such conditions, the primary beam is subjected to shear failure.
2. Strong beam Weak Column possibility -
The size of columns is clearly mentioned in the image as 25 cm x 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 slightly bigger sizes for column.
3. Eccentricity -
The longer the distance between center of mass and center of stiffness, the higher torsional moment of the building. As per the given structural plan eccentricity, the building is subjected to higher torsional moment (Torsional flexibility) in both X and Y directions.
So the changes have to be make in the given plan to construct the structural plan effeciently.... the changes are that we have to arrange the beam and columns at joints and in linear form so that the load transfers from one end to other end which results in reducing of shear failure.
Ans 3.
Observations in the given Framing plan: 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 variations 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. aman .com 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 shall preferably be supported over a box foundation. Shear walls should be connected by Link beams to transfer shear from one to the other. MOHAN The internal columns shall be supported by isolated footings. Those isolated footings can be connected with Shear walls through Tie beams.
Proposed Schematic plan of lateral load system :
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