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 :
TYPES :
- RESTRAINT OF FLOOR SHRINKAGE
- THE LATERAL STIFNESS
- TORSION WITH RESPECT TO VERTIVAL AXIS
- VERTICAL REINFORCEMENT TO VERTICAL AXIS
- STATIC ECCENTRICITY
- SYSTEM'S REDUNDANCY
- FOUNDATION SYSTEM
- ARCHITECTURAL CONSTRAINTS
1.)
1.) RESTRAINT OF FLOOR SHRINKAGE :
OBSERVATION :
- Full restraint at all corners
CONCLUTION :
- It will be have a higher resistant to shrinkage, Thus lead to cracks in the floor.
2.) THE LATERAL STIFNESS :
OBSERVATION :
- Comparatively lower lateral stiffness in both x and y
3.) TORSION WITH RESPECT TO VERTIVAL AXIS :
OBSERVATION :
- Corners walls provide more resistance
CONCLUTION :
- It will be best option with respect to torsional resistant
4.) VERTICAL REINFORCEMENT TO VERTICAL AXIS :
OBSERVATION :
- Walls are subjected to nominal flexural moment and heavy twisting moment
5.) STATIC ECCENTRICITY :
OBSERVATION :
- It will be a Structural symmetric
6.) SYSTEM'S REDUNDANCY :
OBSERVATION :
- Uniform placement of lateral load support in both the axes
7.) FOUNDATION SYSTEM :
OBSERVATION :
- Due to ' L ' shaped wall, the geometric of foundation and its design will be critical
CONCLUTION :
- It will be recommeneded to have peripheral box foundation
8.) ARCHITECTURAL CONSTRAINTS :
OBSERVATION :
- Wall obstruct only corner
CONCLUTION :
- Architectural speaking, and its prefered one
__________________________ X ________________________________________ X _______________________________
2.)
1.) RESTRAINT OF FLOOR SHRINKAGE :
OBSERVATION :
- Corners are left free but restraints along the edge
CONCLUTION :
- It will be average in resitant to shrinkage
2.) THE LATERAL STIFNESS :
OBSERVATION :
- Uniform and comparatively higher lateral stiffness in both x and y
CONCLUTION :
- It will be provide higher lateral stiffness fpr pure seismic acceleration in X and Y direction
3.) TORSION WITH RESPECT TO VERTIVAL AXIS :
OBSERVATION :
- Edge walls provide good resitance to twist
4.) VERTICAL REINFORCEMENT TO VERTICAL AXIS :
OBSERVATION :
- Walls are subjected to nominal twisting moment
CONCLUTION :
- It will be provide a least of vertical reinforcement
5.) STATIC ECCENTRICITY :
OBSERVATION :
- Structural symmetric
6.) SYSTEM'S REDUNDANCY :
OBSERVATION :
- Uniform placement of lateral load support in both the axes
CONCLUTION :
- It's more redundant than (3) option
7.) FOUNDATION SYSTEM :
OBSERVATION :
- Walls are in line. Easy to fix the geometric and design of foundation
CONCLUTION :
- It will be incorporated with isolated footing / strip footing
8.) ARCHITECTURAL CONSTRAINTS :
OBSERVATION :
- Wall obstruct the faces of building
CONCLUTION :
- It subjected to discussion
__________________________ X ________________________________________ X _______________________________
3.)
1.) RESTRAINT OF FLOOR SHRINKAGE :
OBSERVATION :
- Non uniform restraint
CONCLUTION :
- It will be not effectively restrain the shrinkage, so possible less crack
2.) THE LATERAL STIFNESS :
OBSERVATION :
- Non uniform lateral stiffness in both X and Y
3.) TORSION WITH RESPECT TO VERTIVAL AXIS :
OBSERVATION :
- Irregular walls provide very poor resistance to twist
CONCLUTION :
- Here it will be worst one
4.) VERTICAL REINFORCEMENT TO VERTICAL AXIS :
OBSERVATION :
- Walls are subjected to heavy flexural moment and twisting moment
CONCLUTION :
- It will be provide a higher vertical reinforcement
5.) STATIC ECCENTRICITY :
OBSERVATION :
- Un symmetric
CONCLUTION :
- It will have static eccentricity and it is significant
6.) SYSTEM'S REDUNDANCY :
OBSERVATION :
- Concentrated lateral load support in both the axes
CONCLUTION :
- It's less redundant than other option
7.) FOUNDATION SYSTEM :
OBSERVATION :
- Walls are in line and concentrated. Easy to fix the geometric of foundation but critical in design
CONCLUTION :
- It will be incorporated with isolated footing / strip footing
8.) ARCHITECTURAL CONSTRAINTS :
OBSERVATION :
- Vertical wall will not allow passage
CONCLUTION :
- It will not accepted both architectural and commerical
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 :
Issues in the given Framing plan :
Indirect lateral load Transfer in X and Y directions -
- The beams are connecting to another beams which is ineffective during lateral load transfer. In such conditions, the primary beam is prone to shear failure.
Issues in the given Framing plan :
- Eccentricity-The longer the distance between center of mass and center of stiffness, the higher torsional moment of the building. As per the given plan eccentricity, the building is subjected to higher torsional moment (Torsional flexibility) in both X and Y directions.
Issues in the given Framing plan :
Strong beam Weak Column possibility -
- The size of columns majorly mentioned as 25 cm x 25 cm. But all the beams have much deeper section (50cm). Inertia of beam is visually higher than column. If the column reinforcement is adequately greater than that of beams, we are okay and since we do not have the reinforcement detail, this is doubtful.
- lt is recommended to have slight bigger sizes for column.
ALERNATE SCHEME :
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 :
Observations in the given Framing plan:
Floor plan-
- The floor plan of building is not either uniform or symmetric. So naturally any lateral
load induced in the floor will not have 100% influence in 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 can not 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.
- This plan totally unsuitable for heavy seismic Zone areas.
- In this plan, the interior columns arein unsymmetric.
- The partition wall are provided through the base of beam, should support the lateral deformation due to the structure.
- The interiors beams will supports the slab, then the lateral load resisting the failure due to earthquakes.
- For this irregular columns in plan, there we provided the flat slabs, because its directly stay in a column centroidal axis.
- For here, the beams at different locations is irregular in plan and are continuous and is disallowed to resist the seismic load in the region.
- In this plan, the flat sab is more aIppropriate thana regular beam column junctions, because of as its provide support to the columns without any provision of the beam, which reduces the weight of the building and also helps in the ductility of the structure by indirectly.
- For the solution of this structure, we provide the shear wall from the foundation of structure through vertical components, it should minimize the loss of sudden failure occur due to lateral force acting on structure.