Conceptual design of a building with columns and shear walls

Conceptual design of a building with columns and shear walls

Question 1:
The building shown, 20 × 35 m in plan, has columns on a 5 × 5 m grid and shear walls (with dimensions shown in m, 250 mm in thickness) in three alternative arrangements, (a), (b), (c), all with the same total cross-sectional area of the shear walls. Compare the three alternatives, taking into account the restraint of floor shrinkage, the lateral stiffness and the torsional one with respect to the vertical axis, the vertical reinforcement required for the same total flexural capacity at the base, the static eccentricity, the system’s redundancy, foundation systems, architectural constraints etc.

Answer :-

	Arrangement 'a'	Arrangement 'b'	Arrangement 'c'
Restraint of floor shrinkage	Shear walls are placed at corners, so it restricted to experience the shortening has the good restraint against floor shrinkage	The edges of floors are restricted to shortening, therefore the corners are prone to shortening with frame system	The floor is not enclosed symmetrically with reinforced wall, so this floor will have more shrinkage effect
Lateral Stiffness	The RC walls are not prasent in the principal plane, so this arrangement possess the less stiffness	The RC walls are in the direction of principal plane, so this arrangement possess greater stiffness as compared to other arrangements	The RC wall is arranged only along X-axis, so this arrangement is stiffer along X-axis and not stiffer along with Y-axis.
Torsion with Vertical Axis	There is no eccentricity, so the centre of mass and centre of stiffness coincids and it shows results in less prone to torsion	There is no eccentricity, so the centre of mass and centre of stiffness coincids and it shows results in less prone to torsion	The centre of mass and centre of stiffness does not coincids and it shows results in more torsion
Vertical Rebar at Base	The RC walls are not prasent in the principal plane, so the amount of reinforcement required for these walls is less as compared to other walls	The RC walls are in the direction of principal plane, so this arrangement will resist greater force, so this arrangement required much more reinforcement to resist these forces	The RC wall is arranged only along X-axis, so this arrangement required heavily reinforcement to the left wall to resist the lateral forces
Static Eccentricity	The walls are symmetrically placed and due to this, the centre of mass and the centre of stiffness coincides, so there is no any eccentricity occurs	The walls are symmetrically placed and due to this, the centre of mass and the centre of stiffness coincides, so there is no any eccentricity occurs	The walls are not symmetrically placed and due to this, the centre of mass and the centre of stiffness doess not coincides, so eccentricity occurs to this arrangement
System's Redundency	The RC walls are not prasent in the principal plane, so these wall not carry much more load created due to lateral forces, so this arrangement results in less redundency	The RC walls are prasent in the principal plane, so these walls carry much more load created due to lateral forces, so this arrangement results in good redundency	The walls are not symmetrically placed and due to this arrangement it has the poor redundency
Foundation System	Isolated footing connected with tie beam is suitable	Wall footing is suitable for this	Strip footing for X-directionn RC walls and Isolated footing for Y-direction RC walls
Architectural Constrains	The walls are prasented at the corners and hence it will not obstruct to any other elements	The walls are prasented at the centre of all sides and hence it will obstruct to any other elements	Except the left side, this arrangement is ok by architectural constrains

Question 2:
Discuss the suitability for earthquake resistance of the moment resisting framing plan of a three-storey building depicted here (cross-sectional dimensions in cm), the eccentricity of the centre of mass (as centroid of floor plan) to the centre of stiffness (from the moments of inertia of the columns) are shown. Suggest an alternative. Also, is there torsional flexibility? Are the two fundamental translational modes of vibration larger than the fundamental torsional mode of vibration. Discuss qualitatively.

Answer :-

Observation :-

• From the seismic point of view, the earthquake with moderate intensity will affect this structure due to complexity in load transferring mechanism.
• The columns and beams are not placed in grid patterns infact they are offseted from their path due to which load does not transfer effectively.
• Proper symmetry is not achieved
• Some beams like B3, B6, B7 are supported by column on one side and at other side they are supported on beam

Alternatives

• We can rearrange the columns so that it will transfer load effectively.
• Arrange the beam framing from column to column for the easy flow of lateral forces.
• All the columns and beams should be placed in the form of grid pattern.
• Provide the RC walls wherever possible to resist the lateral forces

Torsional Flexibility :-

• The centre of mass and centre of stiffness does not coincides so the building will definately experience the torsion about the vertical axis
• Yes, two fundamental modes of translation are greater than the fundamental modes of torsion

Question 3:

A multi-storey building with basement, with a quadrilateral (non symmetrical floor plan) plan as, has interior columns in an irregular (not in a grid) pattern in plan that serves architectural and functional considerations. Partition walls and interior beams supporting the slab have different layout in different stories. However, there is no constraint to the type, location and size of the lateral force resisting components and sub-systems on the perimeter. Proposals are to be made and justified for the choice of the lateral-load-resisting system and its foundation.

Answer :-

Observation :-

• The floor area is not uniformly distributed
• The structure shown in picture is complex structure.
• Simplicity, regularity and symmetry is not achieved in the plan.
• Rectangular shaped or square shaped building is always preffered as compared to trapezoidal shaped.
• The columns and beams are not placed as per the grid pattern.

Lateral Loading System :-

• As we can see in the figure, the floor plan is an irregular quadrilateral. So during the occurance of seismic forces both the directions of earthquake will have influence on each other because of geometory. so the best option is to provide the L-Shaped corner RC wall arrangement which will have bi-directional strength to resist seismic forces.

• The foundation suitable for this arrangement is Isolated footing with tie beam connection or Box type foundation