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.

ANS:

STRCTURE (a)

• Full resistense at all corners.
• will have higher restrain to shrinkage, thus lead to cracks in the floor
• Comparatively lower lateral stiffness in both x and y
• corner walls provide more resistence to twist
• walls are subjected to nominal flexural moment and heavy twisting moment
• will be best option with respect to toetional resistence
• structurally symmentric
• uniform placement of lateral load supports in both the axes
• walls obstruct only corners

STRCTURE (b)

• corners are left free but restraints along the edge
• it is average restrain to shrinkage
• uniform and comparatively hogher lateral stifness in both x and y
• provide higher lateral stiffness for a pure seismic acceleration in x and y direction
• edge walls provide good resistence to twist
• walls are subjected to nominal twisting moment
• its require least vertcal reinforcement
• structurally symmentric
• uniform placement of lateral load supports in both the axes
• walls obstruct the faces of building

STRCTURE (c)

• non uniform restrains
• it will not effectively restrain the shrinkage,so possibly less cracks
• non uniform lateral stiffness in both x and y
• irregular walls provide very poor resistence to twist
• walls are subjected to heavy flextural moment and twisting moment
• will require higher vertical reinforcement
• structurally un-symmentric
• concentrated lateral load supports in both the axes
• vertcal wall will not allow 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:

ISSUES: -

Indirect lateral loadtransfer in x and y direction: THe beams are connecting to another beams which is ineffective during lateral load transfer. in such conitions, the primary beams is prone to shear failure.

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 momentin both x and y direction.

Strong beam weak column: The size of column majorly mentioned as 25cmx25cm. but all the beams have much deeper section (50). inertia of beam is visully higher than column. if the column reinforcement is adequately greater than that of beams we are okey and since we do not have the reinforcement detail this is doubtful. it is recommended to have slight bigger sizes for column.

Alternate plan:-

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:

• The floor plan of building is not either uniform or symentric. so naturally any lateral load induced in the floor will not have 100% influence in same direction.
• The internal column are random they are unable to transfer lateral loads efficiently and can not achieve desirable building responce.
• havey torsional forces should be controlled by respective lateral load system. so corner shear walls suggested.
• the proportion of floor area is greater on the left side than the right side. so corner shear walls on the left side should be heavier than the right.
• corner shear walls shall preferably be support 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 footing. those isolated footing can connected with shear walls through tie beams.