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:

Criteria		A Image	B Image	C Image
Restraint of floor shrinkage	observation	full restrains at all corners	corners are left free but restraints along the edge	Non-uniform restraints
	conclusion	will have higher restrains to shrinkage it may cause higher shrinkage cracks	average of shrinkage cracks	will not affect the restrains so possibly less cracks
The lateral stiffness	observation	comparatively lower lateral stiffness in both X and Y.	uniform and comparatively higher lateral stiffness in both X and Y	Nonuniform lateral stiffness in both X and Y.
	conclusion		higher stiffness in both X and Y directions
Torsion with respect to the vertical axis.	observation	corner walls provide more resistance to twist	edge walls provide good resistance	irregular wall provides poor resistance
	conclusion	best i torsional resistance		worst in torsional resistance
Vertical reinforcement for similar base capacity	observation	wall are subjected to nominal flexural moment and heavy twisting moment.	nominal twisting moment	walls are subjected to heavy flexural moments and twisting moments.
	conclusion		vertical reinforcement required less	vertical reinforcement required more
static eccentricity	observation	structurally symmetric	structurally symmetric	structurally un-symmetric
	conclusion			it will have static eccentricity and it is significant.
systems redundancy	observation	uniform placement of lateral load supports in both the axes	uniform placement of lateral load supports in both the axes	concentrated lateral load supports in both the axes
	conclusion	more redundant	more redundant	less redundant

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:

Indirect load transfer in X and Y directions- The beams are connecting to another beam which is ineffective during lateral load transfer. in such conditions, the primary beam is prone to shear failure.

Eccentricity- The longer the distance between the center of mass and the center of stiffness, the higher the torsional moment of the building,as per the given plan eccentricity is subjected to higher torsional moments in both X and Y directions.

Strong beam Weak column possibility - The size of columns is majorly mentioned as 25cm x 25cm. but all the beams have much deeper sections 50cm. inertia beam is visually higher than the column. if the column reinforcement is adequately greater than that of beams. we are ok since we don't have reinforcement details it is recommended to have slightly bigger size of columns.

Question 3:

A multi-story 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:

Observations in the given framing plan:

Floor plan- The floor plan of the building is not either uniform or symmetric. so naturally any lateral load induced in the floor will not have 100% influence in the same direction. Definitely, a special lateral loading system of these torsional moments should be accommodated.

Random internal columns- columns are restrained we can define them for live loads so we can simply use this column for live loads.

Floor-to-floor variation in partition walls and beams-partition walls provide an important mass control in building and beams play key role in shear transform floor to floor beam.all these elements are not in order. so heavy distortion and distribution of lateral loads will happen.

Suggestion on the lateral load system and its foundation:

• heavy torsional forces should be controlled by respective lateral load systems. so "corner shear walls" are 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 side.
• corner shear wall preferably is supported over a box foundation.shear walls should be connected by the link beams to transfer shear from one to another.
• The internal columns shall be supposed to isolated footings. those isolated footings can be connected with a shear wall through tie beam.