Conceptual design of a building with columns and shear walls
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.
AIM: To compare the three alternatives of the building taking into account the restraint of floor shrinkage, 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 redundancy, foundation system and architectural constraints
INTRODUCTION: Three alternatives of the building is going to be compared with step by step explanation which are as given below
EXPLANATION:
a) Shrinkage: In the first case all the corners of the wall are held together by four L-shaped walls which are held together in rigid manner. Hence they are resistant to shrinkage but there will be developement of cracks due to restrained which are non structural in nature.
In the second case shear walls are placed together symmetrical in nature which means it is better stable in nature. But the shrinkage occurs at the corner of the wall.
In the third case walls are placed together assymetrical in nature. So the higher chances of shrinkage may occur
b) Lateral stiffness: In the first case shear walls are placed at the corner of the walls. So when there is a earthquake there is possibility of earthquake effects along the corners which means there is low lateral stiffness.
In the second case shear walls are placed symmetrical which is redundant in nature. They are having better stiffiness along principal directions in both x-axis and y-axis
In the third case shear wall are place ayymetrical in nature which is having less stiffiness as compared to the second one.
c) Vertical reinforcement at the base: In the first case since there is low lateral stiffness hence there is less amount of vertical reinforcement required at the base
In the second case since there is good stiffness required to resist the lateral forces hence there is good amount of vertical reinforcement required at the base.
In the third case shear walls are assymetric in nature.Hence there is large amount of vertical reinforcement required at the base as compared to second one
d) Static eccentricity: In the first case walls are placed symmetric in nature hence there is no eccentricity. Here the centre of mass and centre of stiffness coincides with the given plan.
In the second case walls are placed symmetric in nature in both x and y directions hence there is no eccentricity. Here the centre of mass and centre of stiffness coincides with the given plan.
In the third case walls are assymetric in nature. Hence there is more eccentricity and the stiffness is more shifted towards the left side of the wall.
e) System redundancy: In the first case the wall takes less amount of shear forces hence it is less redundant in nature.
In the second case the walls take more amount of shear forces and it is having symmetric in nature, Hence it is more redundant in nature.
In the third case shaer walls are placed assymetric in nature hence it is less redundant in nature.
f) Foundation: In the first case box type of foundation can be adopted
In the second case raft type of foundation can be adopted for better structural integrity
In the third case combined type of footing can be adopted in Y-direction whereas strip type of foundation can be adopted along x-direction.
g) Architectural Constraint: In the first case there is no architectural constrained because of the wall properly blends with the architectural one
In the second and third case there is a possibility of chances of clashes of wall with the architectural one.
RESULT: Three alternatives of the building has been illustrated properly.
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.
AIM:- To discuss the suitability for earthquake resistance of the moment resistance frame of the three-storied building.
INTRODUCTION: Earthquake resistance of the moment resistance frame of the three storied building is going to be explained which are as given below.
EXPLANATION:
From the above observation of the above given figure, it can be seen that:-
a) Columns are not arranged in a proper layout manner.
b)
From the above figure it can be stated that columns are not properly connected together hence it will be difficult to transfer of lateral forces from one end to another end.
c) Proper symmetry is not achieved.
d) Beam sizes are more as compared to column hence it is a strong beam-weak column design which is not acceptable.
e) Beams are not placed in a proper grid position.
f) Torsional flexibility will be created since there is an eccentricity developed between centre of mass and centre of stiffness. So there will be more vibration developed in torsion as compared to vibration developed in two main principal directions. i.e linear vibration
Alternative way is to resolve this structural issues which are as given below:
a) Columns and beams has to be arranged in a proper layout manner.
b) Beam sizes need to be increased as compared to column for strong column- weak beam design concept.
c) Shear walls can be provided at better alternative positions to make the structure redundant in nature.
RESULTS: Earthquake resistance of the moment resistance frame of the three storied building has been explained properly.
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.
AIM: To justify the choice of the lateral load-resisting system and its foundation of multi-story building and its proposals
EXPLANATION:
From the above observation it can be stated that:-
a) Plans are not symmetrical in nature
b) Interior column area unsymmetric
c) This plan is not suitable for area which is having high seismic zone region
d) Partition walls are provided to transfer shear tansfer from floor to beam. All these elements are not in order. Hence heavy distortion will occur.
Proposals:- Proposals can be made which are as given below:
a) Isolated foundations can be adopted
b) Flat slabs can be provided with drop panel without the use of beam.
c) Provide shear wall from the foundation of the structure so that it can minimise the lateral effects.
b) Flat slabs can be adopted if it is difficult to provided beam with drop panel
RESULTS: Choice of the lateral load-resisting system and its foundation of multi-story building and its proposals has been illustrated properly.