Conceptual design of a building with columns and shear walls

ANSWERS

1.

CRITERIA		Option a	Option b	Option c
Restrain of floor shrinkage	Observation	Full restraints at all corners	Corners are left free but restraints along the edge	Non-uniform restraints
Lateral stiffness	Observation	Comparatively lower lateral stiffness in both X & Y axes	Uniform and comparatively higher lateral stiffness in both X & Y	Non-uniform lateral stiffness in both X & y axes
Torsion concerning vertical axis	Observation	Corner walls provide more resistance to twist	Edge walls provide good resistance to twist	Irregular walls provide very poor resistance to twist
Vertical reinforcement for similar base capacity	Observation	Walls are subjected to normal flexural moment and heavy twisting moment	Walls are subjected to nominal twisting moment and regular normal flexural moment	Walls are subjected to heavy flexural moment and twisting moment
Static eccentricity	Observation	Structurally symmetric	Structurally symmetric	Unsymmetric
System's redundancy	Observation	Uniform placement of lateral load supports in both axes	Uniform placement of lateral load supports in both axes	Concentrated lateral load supports in both axes
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 & concentrated. Easy to fix the geometry of foundation but critical in design
Architectural constraints	Observation	Walls obstruct only corners	Walls obstruct the faces of building	Vertical walls won't allow passage

CONCLUSIONS

• Option a will have higher restrain to shrinkage, that leads to cracks in the floor. Option b is avg. Option c won't effectively restrain shrinkage, so possibly less cracks.
• Option b will provide higher lateral stiffness for pure seismic acceleration in X & Y axes.
• Option a will be best option with respect to Torsional resistance whereas Option c is the worst one.
• Option c will require higher vertical reinforcement & Option b will require the least.
• Only Option c will have static eccentricity and it's significant.
• Option a & b are more redundant than Option c.
• Option b & Option c shall be incorporated with isolated footings/strip footings. Option a is recommended to have peripheral box foundation.
• Architecturally, Option a is the preferred one. Option b is subjected to discussion. Option c won't be accepted both architecturally and commercially.

2.

a) Indirect load transfer in X & Y directions

Incomplete Lateral load transfer in X-direction Incomplete Lateral load transfer in Y-direction

The beams are connecting to another beams which is ineffective during lateral load transfer. In such conditions, the primary beams is prone to shear failure.

b) Eccentricity

The longer the distance between the centre of mass and the centre of stiffness, higher the torsional moment of the building. As per the given plan eccentricity, the building is subjected to higher torsional moments in both X & Y directions.

c) Strong beam Weak column possibility

The size of the columns is majorly mentioned as 25 x 25 cm. But all the beams are much deeper ie, 50 cm. The inertia of the beam is visually higher than the column. If the column reinforcement is adequately greater than the beams, we're okay and since we don't have the reinforcement to have slightly bigger sizes for the column.

Alternate scheme

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3.

Observations

• Floor plan - The floor plan isn't either uniform or symmetric. So naturally any lateral load induced in the floor won't 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're unable to transfer lateral loads efficiently and can't 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 - Partion walls provide an important mass control in a building and beams play a key role in shear transfer from floor to beam. All these elements aren't in order. So heavy distortion of and distribution of lateral load will happen.

Suggestions

• Heavy torsional forces should be controlled by respective lateral load system. So, "Corner shear walls" are suggested.
• The proportion of the 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.

Proposed Schematic plan for Lateral load resisting system

Superstructure Substructure