CONCEPTUAL DESIGN OF A BUILDING WITH COLUMNS AND SHEAR WALLS

Q.1 The building shown, 20 x 30m in plan, has column on a 5 x 5m grid and shear walls( with dimensions shown in m, 250mm in thickness) in three alternative arrangements. (a, b, c), all with the same cross sectional area of the shear wall. 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 systems redundancy, foundation systems, architectural constraints etc.,

Ans: 

Parameter	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

Q.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.

*In this structural frame , there is a two-way eccentricity of the center of mass in accordance with the center 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 to 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.

 

*For here, we changed the column of C5 & C8 to considered as a combined footing, because of their need to avoid the loss of center of stiffness due to        occur lateral forces about the structure.

*And more we add one more column of C10 is covered that boundary of plan, should maintain the center of mass as well as the center of stiffness about    the structure during lateral horizontal force action.

Q.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: Observation:-

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. Defiantly a lateral load resisting system for these torsion moments should be accommodated.

Random Internal Column- Internal column are random, so they are unable to transfer lateral loads efficiently can’t achieve desirable response, so we have to assume and design those column for only gravity.

Floor to floor Variations in partitions wall & Beams- Partitions wall provide an important mass control in a building and beams play key role in shear transfer from floor to bream. These entire elements are not in order, so heavy distribution and distortion of lateral loads will happen.

Suggestion on the lateral load system & its foundation- Heavy torsional forces should be controlled by respective lateral load , so corner shear walls are suggested .The proportion of floor area is greater on the left side than right side, so corner shear wall on the left side should be heavier than right. Corner shear wall shall preferably by support over a box foundation. Shear walls should be connected by link beam to transfer shear from on the other.  The internal columns shall be supported by isolated footing .Those isolated footing can be connected with shear walls through is beams.