Conceptual design of a building with columns and shear walls
Answer for Question-1:
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Criteria |
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Restraint of Floor shrinkage |
Since all four corners of floor is restricted to experience shortening, this RC wall system possess good control of shrinkage. |
The edges of Floor are restricted to floor shortening. Whereas the corners are prone to shortening/shrinkage with frame system. |
In both the principle directions, the floor is not enclosed with RC wall system at two sides. So this floor will have more shrinkage effect. |
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Lateral Stiffness |
During earthquake excitation, the principle directions will be exposed to lateral movements. At such incidents, since the given RC wall system is not across the principle planes but in diagonal location. So it will possess less stiffness. |
The RC walls are right across the lateral force direction. They possess better stiffness compared to other systems. |
The RC wall system is effective and stiffer in X-direction. But not stiffer in Y-direction due to concentration of RC wall at only one side. |
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Torsion with vertical axis |
Center of mass and center of stiffness will coincide. So less prone to Torsion. |
Center of mass and center of stiffness will coincide. So less prone to Torsion. |
Center of mass and center of stiffness will not coincide in both the principle directions. So this system will experience more torsion during earthquake. |
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Vertical rebar at Base |
As they will experience lesser lateral forces, the amount of reinforcement may be lesser than other systems. |
This system will take all lateral loads in either principle directions. So the amount of vertical rebar will be heavier than the previous system. |
The RC wall arrangement is so eccentric that these walls will experience extreme lateral and torsional moments. This system will have the highest amount of vertical rebar. |
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Static eccentricity |
The system is centric with respect to mass-stiffness comparison. |
The system is centric with respect to mass-stiffness comparison. |
The system is more eccentric with respect to mass-stiffness comparison. |
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System’s redundancy |
Since the RC wall is less effective to collect lateral forces, the frame structures will need to take part in lateral load resisting system. |
RC wall system is effective in this case and mirror with right angle. They possess good redundancy. |
The system is worst in terms of redundancy because of concentration of load at one sides. |
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Foundation system |
Isolated footing with tie beam arrangement is suitable for this system. |
Box type foundation is suitable for this system. |
Strip footing for Y-direction RC wall and isolated footing for X-direction RC wall is suitable. |
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Architectural constraints |
Architecturally very effective, since only corners are obstructed. |
Architecturally may not be recommended since all four side entrances are partially obstructed. This RC wall arrangement may disturb open space requirement. |
Left side is completely arrested. All other sides are okay with respect to architectural point of view. |
Answer for question 2 :
The goal is to evaluate the given structural framing for seismic influence and to offer better alternatives. Additionally, the system in question has to have its torsional flexibility evaluated.
Monitoring the specified system
The given structural drawing effectively addresses the lateral load transferring mechanism from floor to foundation from a seismic perspective. Even though it is only a three-story building, any moderate earthquake will still have an impact on it because of the complicated load-transferring mechanism, as shown in the photographs below.
Alternative Structural Framing:
By strategically placing the columns, we may reduce load path complexity. We can also frame the columns with beams, which will make the movement of lateral forces much easier.
The beam design is effectively changed from column to column by simply adjusting the right top and left bottom columns. This mimics a floor grid design, which will provide improved lateral loading resistance.
Impact of the building's torsion:
Since the building's centre of mass and centre of stiffness are offset from one another, the structure will undoubtedly encounter torsional forces with regard to its vertical axis. Nevertheless, the plan aspect ratio is under 3 (within the bounds of IS1893), therefore we can infer that the supplied system is properly proportioned.
Due to excessive offsets and connections between beams, the given structural floor system is also ineffective at transferring lateral stresses to vertical parts. The poorest response is when a structure is translated in its basic form.
Perhaps still higher than the fundamental mode of torsion are the two fundamental modes of translation.
Answer for Question-3:
The floor space is larger on the left side of the floor plan, so based on the plan dimensions, it makes sense that the centre of mass will be there. Therefore, we must position the lateral load resisting system so that the centre of their stiffness is close to the centre of mass. In order to prevent torsional irregularity, this is necessary.
The appropriate Lateral load resisting mechanism is:
Because the floor layout is an uneven quadrilateral, an earthquake's effects will also be felt in the Y direction and vice versa. In order to withstand seismic forces, a lateral load resisting system should be strong in both directions. So, we can recommend a configuration of an L-shaped corner RC wall.
We have two viable foundation choices for this L-shaped RC wall irregular corner configuration.
One is isolated foundation system with tie beam connection. The other is whole Box type foundation system.