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.

CRITERIA
Restraint of floor shrinkage	Observation conclusion	full restraints at all corners it will have higher restraints to shrinkage,thus leads to cracks in the floor.	corners are left free but restraints along the edge it is average .	non uniform restraints it will not effectively restraints the shrinkage , so possibly less cracks
The lateral stiffness	Observation conclusion	comparatively lower lateral stiffness in both x and y obtion b will provide higher lateral stiffness for	uniform and comparatively higher lateral stiffness in both x and y a pure seismic acceleration in x and y directions	non uniform lateral stiffness in both x and y
Torsion with respect to vertical axis	Observation conclusion	corner walls provide more resistance to twist option (a) will be best option with respect to	edge walls provide good resistance to twist torsional resistance whereas option (c) is the worst one.	irregular walls provide very poor resistance to twist
Vertical reinforcement for similar base capacity	obseravtion conclusion	walls are subjected to nominal flexural moments and heavy twisting moment option (c) will be require higher vertical	walls are subjected to nominal twisting moment reinforcement and option (b) will require the	walls are subjected to heavy flexural moment and twisting moment least.
static eccentricity	observation conclusion	structurally symmetric onlyn option (c) will have static eccentricity	structurally symmetric and it is significant.	un-symmetric
System redundancy	Observation conclusion	uniform placement of lateral load supports in both the axes option (a) and (b) are more reduntant than	uniform placements of lateral load supports in both the axes option(c).	concentrated lateral load supports in both the axes
Foundation systems	observation conclusion	due to L shaped walls the geometry of foundations and its design will be crictical option (b) and option (c) will be incorporated	walls are in line, easy to fix the geometry and design of foundation with isolated footings /strip footings , option(a)	walls are in line & concentrated easy to fix the geometry of foundation but crictical in design is recommended to have pheripheralbox foundation.
Archietectural constraints	obseravtion conclusion	walls obstruct only corners. Archietecturally speaking , option (a) is the preferred one .	walls obstruct the face of building option (b) is subjected to discussion	vertical wall will not allow passage option (c) will not be accepeted both archietecturally and commercialy

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 :

ISSUSES in the given framing plan :

Indirect lateral load Transfer in X & Y directions,.

• The beams are connected 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 center of mass and center of stiffness , higher torsional moment of the building
• as per the given plan eccentricity , the building is subjected to higher torsional moment (torsional flexibilty) in both X & Y directions

STRONG BEAM WEAK COLUMN POSSIBILTY :

• The size of columns majorly mentioned as 25cm * 25cm.
• but all the beams have much deeper section (50cm)
• Inertia of beam is visually higher than column
• if the column reinforcement is adequately graeter than that of beams , we are okey and since we do not have the reinforcemnt detail, this is doubtfull
• it is recommended to have slight bigger sizes for column

ALTERNATE SCHEME :

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 :

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
• Definetly a special lateral load resisting system for these torsional moments should be accomodated

RANDOM INTERBAL COLUMNS :

• Since the internal columns are random , they are unable to transfer lateral loads efficiently and can not achieve desirable building response.
• So we have to assume and design those columns for only gravity loads

FLOOR TO FLOOR VARIATIONS IN PARTITION WALLS AND BEAMS :

• Partition walls provide an important mass control in a building and beams play key role in shear transfer from floor to beam
• all these elements are not in order, so haevy distortion and distribution of lateral loads will happen.

SUGGESTION ON THE LATERAL LOAD SYSTEM & ITS FOUNDATION :

• Heavy torsional forces should be controlled by respective lateral load system , "so corner shear walls" are suggested
• The proportion of floor area is greater on the left side then the right side (irregular quadrilateral) , so corner shear walls on the left side should be heavier than the right
• corner shear walls shall preferably be supported over a box foundations .
• shaer walls should be connected by link beams to transfer shear from one to another
• The internal columns shall be supported by isolated footings
• Those isolated footings can be connected with shear walls through tie beams.

PROPOSED SCHEMATIC PLAN OF LATERAL LOAD SYSTEM :