Conceptual design of a building with columns and shear walls

CHALLENGE 5

Aim: The main aim of this challenge is to gain the knowledge about the concept of placing of the shear walls and the positions of the columns. The effects that may cause due to the wrong planning of the position of the shear walls or the columns are learnt through this challenge.

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.

Ans:

Parameters	Shear Wall arrangement (a)	Shear Wall arrangement (b)	Shear Wall arrangement (c)
Restraint of floor shrinkage	The shear walls are arranged at the corners therefore it will restraints at all  the four corner	The shear wall are arranged on the periphery region , thus restraints occurs along the edges	The shear wall arrangement has non-symmetric therefore non uniform restraints occurs
Lateral Stiffness	The lateral stiffness becomes comparatively low along both the direction	Uniform and comparatively higher lateral stiffness along x and y directions	Non-uniformity in lateral stiffness
Torsion	Torsional resistance will be more at corner walls on the structure	Torsion resists at the edge sides of the wall	Less torsional resistance due to non-uniform arrangement of walls
Vertical Reinforcement	Walls are subjected to nominal flexure moment with more twisting moment	Walls are subjected to nominal twisting moment	Walls are subjected to heavy flexural moment and twisting moment
Static eccentricity	Symmetrical structure	Symmetrical structure	Unsymmetrical
System Redundancy	As the wall arrangement are symmetric uniform lateral load supports on both axis	As the wall arrangement are symmetric uniform lateral load supports on both axis	Concentrated lateral load supports in both the axes
Foundation System	Due to L shaped wall the foundation design will be critical	Walls are in the form of  straight line, the foundation design will be easy to fix	Walls are in straight line and concentrated. therefore it is easy to fix but critical at design
Architectural Constraints	Obstruction occur at corners	Obstruction at the face of the buildings	Obstruction at passage

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.

Ans:

• In this structural frame, there is a two-way eccentricity of the centre of mass in accordance with the centre of stiffness, which is eccentricity of x-direction is larger than y-direction.
• In this structure beams are provided at stronger than column, so it can consider as Weak column strong beam design in nature.
• Therefore this structure need some shear wall to resist the column failure, when the lateral forces acting about the structure.
• Combination of shear wall and column tends to prevent the failure about the structure during the seismic forces occur.
• As the frame plan, we can see about the alignment of beam is uniformly continuous of B1 and B2 at X- direction, and B11 & B12, B9 & B10 at Y-direction.
• But another all beams are provided at discontinuous of structural frame, so here cause too difficult of transmission of load evenly at entire structure due to action of lateral forces.
• Beams with long span may have their top reinforcement at the supports governed by factored gravity load, rather than by the seismic design situations.
• Therefore, this structure will alternate to better portal of better offset at symmetric in nature.
• The column beams connections should be in proper cross section area, then it achieve lateral stiffness, mass regularity, moment resisting factor.
• As we consider beam-sway mechanism in strong column/ weak beam design frames is better, because of its achieve a uniformly spread, global inelastic displacement demand at roof level, to all storeys.

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.

Ans:

Floor plan: - The floor plan of the building is not 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 resistance system for these torsional moments should be accommodated. 

Random internal columns: - Since the internal Columns are random, they are unable to transfer the lateral loads efficiently and cannot achieve desirable building response. So we have to assume and designed those columns for only gravity loads.

Floor to floor variation in partition walls and beams :- Partition was provide an important mass control in and building and Beams plan key role in shear transfer from floor to Beam. All these elements are not in order. So heavy distortion distribution of loads will happen.

• This plan is totally unacceptable for heavy seismic zone areas.
• In this plan interior columns are in unsymmetrical.
• The partition wall are provided through to the base of beam, should support the lateral deformation due to the structure.
• The Interior beams will support the slab, then the lateral load resisting the failed due to earthquakes.
• For this irregular columns in plan, there we provide the flat slab because it directly stay in column centroid Axis.
• For here the beams at different locations is irregular in plan are the continuous and is disallowed to resist the seismic load in the region.
• The solution of the structure, we provide the shear wall from the foundation of the structure through vertical components, it should minimise the lord of second failure occur due to lateral forces acting on structure.

Conclusion:

From the challenge carried out it can be concluded that the concept of placing of the shear walls and the positions of the columns. The effects that may cause due to the wrong planning of the position of the shear walls or the columns are learnt through this challenge.

Vijayalakshmi S H