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.
- CASE 1 CASE 2 CASE 3
- ANSWER :
- Compareing is given below
- CASE 1
- CRITERIA FOR CASE 1 :
- 1.Restraint of floor shrinkage :
- Observation :
- full restraints at all corners .
- Conclution :
- In this case will have higher restraint to shrinkage. thus lead to creaks in the floor .
- 2.The lateral stifness :
- Observation :
- It have low lateral stiffness in both x and y .
- 3. Torsion with respect to vertical axis :
- Observation :
- The corner wall provided that is more resistance to twist .
- 4. Vertical reinforcement for simiar base capacity :
- observation :
- The walls in this case are subjected to nominal flexural momet and heavey twisting moment .
- 5. Static ecentricity :
- this case is structural symmetric .
- 6.System redundancy :
- observation :
- the shear walls are uniform placement of lateral load support in both axis .
- conclusion :
- the structure is more redundant .
- 7. Foundation system :
- Observation :
- due to ' L' shaped walls , the geometry of foundation and its design will be critical
- Conclusion :
- for this case recommented to hae peripheral box foundation due to L shape of walls .
- 8. Archictural constrains :
- Observation :
- walls obstruct only corners.
- Conclusion :
- As per archictural point , this case is more preferred because this is obstract less .
- CASE 2 :
- 1. Restraint of floor shrinkage :
- observation :
- corners are left free but restraints along the edge .
- conclusion :
- in this case it provide avarage restrains.
- 2. The lateral stiffness :
- observation :
- it has uniform and comparatively higher lateral stifness in both x and y axes .
- 3. Torsion with respect to vertical axes :
- observation :
- wall edges provided good resistance to twist .
- 4. Vertical reinforcement for similar base capacity :
- Observation :
- the wall are subjected to nominal twisting moment and regular flextural moment .
- conclusion :
- in this case it requried least vertical reinforcement .
- 5. Static eccentricity :
- Observation :
- it is structurally symmetric .
- 6. Systems redundancy :
- observation :
- the uniform placement of lateral load supports in both the axes .
- conclusion :
- the structure is more redundent .
- 7. Fundamental system :
- observation :
- in this case the walls in lines . easy to fix the geometry and design of foundation .
- conclusion :
- for this plan or structure the isolated and strip footings are suitable .
- 8. Architectural constrains :
- observation :
- the walls are obstruct the faces of the building .
- CASE :3
- Restaint of floor shrinkages :
- observation :
- it is not effiecitively restrain the shrinkage , so possibly less cracks .
- 2. The lateral stiffness :
- Observation :
- the uniform lateral stifness in both x and y axes .
- 3. Torsion with respect to vertical axes :
- observation :
- the irregular walls provides very poor resistance to twist .
- conclusion :
- this case have very worst option with respect to torsional resistance .
- 4. Vertical reinforcement for similar base capicity :
- observation :
- walls are subjected to heavey flexural moments and twisting moments .
- 5. Static eccentricity :
- observation :
- it has static eccentricity and it is significant .
- 6. System redundancy :
- observation :
- the concentrated lateral load is supported in bith x and y axes .
- conclusion :
- the structure is less redundant than other 2 cases .
- 7. Foudation system :
- observation :
- the walls are in lines and concentrated . easy to fix the geometry of foundation but critical in design becouse of heaver forces .
- conclusion :
- isolated and strip footing is suitable for the structure .
- 8. Architectural constrains :
- observation :
- vertical walls will not allow passage .
- conclusion :
- it is not accepted both architecturally and commercially becouse it obstruct the full sides.
- 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 framing plan is given below :
- INDIRECT LATERAL LOAD TRANSFER IN X AND Y DIRECTION :
- 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 .
- ECCENTRICITY :
- Longer distance between center of mass and center of stiffness the higer torsional moment of the building .
- as per given plan eccentricity , the building is subjected to higher torsional moment in both x and y direction .
- STRONG BEAM WEAK COLUMN POSSIBILITY :
- As per given information the column having size 25 cm x 25 cm , and beam size is 25 cm x 50 cm . the depth of beam is 50 cm it is large than column size .
- if reinforcement of column is greater than beam then ok. but reinforcement details are not given . so it create a confusion .
- so increase the size of column . it the size of column is not increased then column is failure first .
- 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 IN THE GIVEN PLAN :
- 1. Floor plan :
- the floor plan of this building is non uniform and symmetric .
- so that lateral load is induced in floor will not have 100 % influence in same direction .
- the special lateral load resisting system for this torsional moments should be accomdated .
- 2. Random internal column :
- the internal column are random so they cant transfer lateral loads efficiently and can not achived desirable building response .
- so we have to assume and design those column for only gravity load .
- 3.Floor to floor variactions in partition walls and beams :
- the partition wall provide mass control in building where beam pay key role in shear transfer from floor to beam . and this element is not provided in order. so heavy ditoration and distribution of lateral load will happen
- SUGGESTION ON THE LATERAL LOAD SYSTEM AND ITS FOUNDATON :
- Heavy torsional force can be controlled by repective lateral load system . so "corner shear walls" is provided .
- the proportional floor area is greater in left side and less in right side so corner shear walls in left side is heavier than right side .
- the corner shear wall is supported over a box foundation and this walls should be connected by link of beam to transfer the shear load from one to another .
- internal column is supported by isolated footing . this footing can be connected with shear wall through tia beam .