Conceptual design of a building with columns and shear walls

Restraint of Floor shrinkage

Observation -

For option (a)- Full restraints are provided at all corners

For option (b)- all the Corners are left free but there are restraints provided along the edge

For option (c) - There are Non-uniform restraints

Conclusion -

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

The Lateral stiffness

Observation

For option (a) - Comparatively Lower Lateral stiffness in both X and Y direction

For option (b) - Uniform and comparatively higher lateral stiffness in both X and Y direction

For option (c) - Non uniform Lateral stiffness in both X and Y direction

Conclusion -

As Option(b) has uniform and higher stiffness so option (b) will provide higher lateral stiffness for a pure seismic acceleration in X and Y directions.

Torsion with respect to vertical axis

Observation -

For option (a) - Corner Walls can provide more resistance to twist

For option (b) - Edge Walls can provide good resistance to twist

For option (c) - Irregular Walls provide very poor resistance to twist

Conclusion

Option (a) will be the best option for torsional resistance where option (c) is the bad one

Vertical reinforcement for similar base capacity

Observation -

For option (a) - Walls are subjected to nominal flexural moments and heavy twisting moments

For option (b) - Walls are subjected to nominal twisting moment

For Option(c) - walls are subjected to heavy flexural and twisting moment

Conclusion -

Option (c) will require higher vertical reinforcement and Option(b) will require the least

Static eccentricity

Observation

For option (a) - Structurally symmetric

For option (b) - structurally symmetric

For option (c) - structurally un-symmetric

Conclusion -

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

Systems redundancy

Observation -

For option (a) - Uniform placement of lateral load supports in both the axes

For option (b) - uniform placement of lateral load supports in both the axes

For option (c) - concentrated lateral load supports in both axes

Conclusion -

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

Foundation systems

Observation -

For option (a) - Due to 'L' shaped Walls, the geometry of foundation and its design will be critical

For option (b) - Walls are in line. Easy to fix the geometry and design of foundation

For option (c) - Walls are in line & concentrated. Easy to fix the geometry of foundation but critical in design

Conclusion -

Both Option(b) and Option(c) shall be incorporated with isolated footings/strip footings Option(a) is recommended to have peripheral box foundation.

Architectural constraints

Observation

For option (a) - Walls obstruct only corners.

For option (b) - Walls obstruct the faces of building

For option (c) - Vertical wall will not allow passage

Conclusion -

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

Aim - Conceptual design of a building with columns and shear walls

Problems in the present framing plan -

Indirect lateral load transfer in X and Y direction -

the beams resting on another beam this condition is ineffective during lateral load transfer. In such cases primary beams tend to fail in shear

Eccentricity -

The longer the distance between center of the mass and center of stiffness the higher torsional moment of the building. In the present framing building is subjected to higher torsional moment in both X and Y direction

Strong beam weak column possibility -

The size of the beams are 25/50 and size of the column is 25/25 that means the size of the beam is more than the column sizes. Inertia of the beam is visually higher than column. If the reinforcement of columns is more than beam then this is ok. But as now we don't have reinforcement details so we recommend to increase the size of the column.

Solution -

Aim - Conceptual design of a building with columns and shear walls

Observations in the given Framing plan:

Floor plan - The floor plan of the building is not either uniform or symmetric. So naturally any lateral load induced in the floor will not have 100% influence in the 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 cannot 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.

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.

The internal columns shall be supported by isolated footings. Those isolated footings can be connected with Shear walls through Tie beams.