Conceptual design of a building with columns and shear walls
Answer to the Question No. 1
Question:1
he 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:
OBJEECTIVE:
- TO INVESTIGATE THE SUITABILITY OF GIVEN PLAN WITH RESPECT TO SEISMIC BEHAVIOR
- TO SCHEMATICALLY DRAW A SEISMIC VIAVBLE STRUCTURAL PLAN.
CRITERIA: RESTRAINTS FLOOR SHRINKAGE
(a)
Observation: Full restraints at all corners
(b)
Observation: Corners are left free but restrained along the edge.
(c)
Observation: Non-uniform restraints.
Conclusion: Option a will have higher restraint to shrinkage, thus lead to cracks in the floor. Option(b) is average. Option (c) will not effectively restrain the shrinkage, So possibly less cracks.
CRITERIA: THE LATERAL STIFFNESS
(a)
Observation: Comparatively Lower lateral stiffness in box X and Y
(b)
Observation: Uniform and comparatively higher lateral stiffness in both X and Y
(c)
Observation: Non uniform Lateral stiffness in both X and Y
Conclusion: Option(b) will Provide higher lateral stiffness for a pure seismic acceleration in X and Y directions.
CRITERIA: TORSION WITH RESPECT TO VERTICAL AXIS
(a)
Observation: Corner walls provide more resistance to twist
(b)
Observation: Edge walls provide good resistance to twist
(c)
Observation: Irregular walls provide very poor resuistance to twist
Conclusion: Option(a) will be best option with respect to Torsional resistance whereas Option(c) is the worst one.
CRITERIA: VERTICAL REINFORCEMENT FOR SIMILAR BASE CAPACITY
(a)
Observation: Walls are subjected to nominal flexural moment and heavy twisting moment
(b)
Observation: Walls are subjected to nominal twisting moment
(c)
Observation: Walls are subjected to heavy flexural moment and twisting moment.
Conclusion: Option (c) will require higher vertical reinforcement and Option (b) will require the least.
CRITERIA: STATIC ECCENTRICITY
(a)
Observation: Structural symmetric
(b)
Observation: Structural symmetric
(c)
Observation: un- symmetric
Conclusion: only Option (c) will have static eccentricity and it is significant
CRITERIA: SYSTEM REDUNDANCTY
(a)
Observation: Uniform placement of lateral load supports in both the axes
(b)
Observation: Uniform placement of lateral load support in both the exes
(c)
Observation: Concentrated lateral load supports in both the exes.
Conclusion: only Option (a) and (b) are more redundant then Option(c)
CRITERIA: FOUNDATION SYSTEMS
(a)
Observation:Due to 'L' shaped walls the geometry of foundation and its design will be critical
(b)
Observation: Walls are in line. Easy to fix the geometry and design of foundation
(c)
Observation: Walls are in line & concentrated. Easy to fix the geometry of foundation but critical in design
Conclusion: Option (b) and Option (c) shall be incorporated with isolated footings/. Option(a) is recommended to have peripheral box foundation.
CRITERIA: ARCHITECTURAL CONSTRAINTS
Observation: Due to 'L' shaped walls the geometry of foundation and its design will be critical
(b)
Observation: Walls are in line. Easy to fix the geometry and design of foundation
(c)
Observation: Walls are in line & concentrated. Easy to fix the geometry of foundation but critical in design
Conclusion: Architectural speaking, Option (a) is the preferred one. Option (b) is the is subjected to discussion, Option (c) will not be accepted both architecturally and commercially.
Answer to the Question No. 2
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:
OBJEECTIVE:
- TO INVESTIGATE THE SUITABILITY OF GIVEN PLAN WITH RESPECT TO SEISMIC BEHAVIOR
- TO SCHEMATICALLY DRAW A SEISMIC VIAVBLE STRUCTURAL PLAN.
Issues in the given Framing plan:
(a) Indirect lateral load Transfeer in X and Y directions- The beams are connecting to another beams which is ineffective during lateral load transfer. in such conditions. in the primary beams is prone to shear failure.
INCOMPLETE LATERAL LOAD TRANSFER IN X-DIRECTION: WE CAN SEE THE BEAM NOT CONNECTED TO THE COLUMN.SO THE LATERAL LOAD TRANSFER ONLY SHEAR BEAMS NOT TO THE COLUMN AND MAIN BEAM SUBJEECTED TO SHEAR FAILURE.
IMPROPER LATERAL LOAD TRANSFER IN Y- DIRECTION.
INCOMPLETE LATERAL LOAD TRANSFER IN X-DIRECTION
Issues in the given Framing plan:
(b) 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 (Tosional flexibility) in both X and Y directions.
Issues in the given Framing plan:
STRONG BEAM WEAK COLUMN POSSIBILITY:
The size of column majorly mentioned as 25cmx 25cm . But all the beams is visually higher than column. if the column reinforcement is adequtly greater than of beams, we are okey and since we do not have the reinforcement details. this is slight bigger sizes for column.
BEAM SIZE 25CM X 50CM
COLUMN SIZE 25CM X 25 CM
ALTERNATE SCHEME:
Answer to the Question No. 3
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:
OBJEECTIVE:
- TO INVESTIGATE THE SUITABILITY OF GIVEN PLAN WITH RESPECT TO SEISMIC BEHAVIOR
- TO SCHEMATICALLY DRAW A SEISMIC VIAVBLE STRUCTURAL PLAN.
first, we should Observation 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 responce. 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 beams. 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 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 with shear walls throughout tie beams.