Conceptual design of a building with columns and shear walls
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.
Answer:
CASE A
Restraint of floor shrinkage
obesrvation full restraint at all corner
conclusion option a will have higher restraint to shrinkage thus lead to crack in the floor, option B is average option C will not effectively restraint the srinkage so possibly less cracks
The lateral stiffness
obesrvation comparatively lower lateral stiffness in both X and Y
conclusion option b will provide higher lateral stiffness for a pure seismic acceleration X and Y direction
Torsion with respective vertical axis
observation Corners walls provide more resistance to twist
coclusion option a will be the best option respect to torsional resistance wheras option c is the wrost one
Vertical reinforcement for similar base capacity
observation walls are subjected to nominal flexural moment and heavy twisting moment
conclusion only c will required heigher vertical reinforcement and option b will required least
static eccentricity
observation structurally symmetric
conclusion only option C have static eccentricity and it is significant
system redundancy
obseravation uniform placement of lateral load support in both the axes
conclusion option a and b are more retundant than c
foundation system
observation Due to L shaped wall the geometry of foundation and its design will be critical
conclusion option B and C will be incorporated with isolated/strip footing option a is recommended to have peripheral box foundation
Architectural constraints
observation walls obstruct only corners
conclusion Architecturally speaking option a the preffered one option b is subjected to discussion option c will not be accepted both architecturally and commercially
CASE B)
Restraint of floor shrinkage
obesrvation corners are left free but restrain along the edge
conclusion option a will have higher restraint to shrinkage thus lead to crack in the floor, option B is average option C will not effectively restraint the srinkage so possibly less cracks
The lateral stiffness
obesrvation comparatively higher lateral stiffness in both X and Y
conclusion option b will provide higher lateral stiffness for a pure seismic acceleration X and Y direction
Torsion with respective vertical axis
observation edge walls provide good resistance to twist
coclusion option a will be the best option respect to torsional resistance wheras option c is the wrost one
Vertical reinforcement for similar base capacity
observation walls are subjected to nominal twisting moment
conclusion only c will required heigher vertical reinforcement and option b will required least
static eccentricity
observation structurally symmetric
conclusion only option C have static eccentricity and it is significant
system redundancy
obseravation uniform placement of lateral load support in both the axes
conclusion option a and b are more retundant than c
foundation system
observation walls are in line easy to fix the geomentry and design of foundation
conclusion option B and C will be incorporated with isolated/strip footing option a is recommended to have peripheral box foundation
Architectural constraints
observation walls obstruct the faces of building
conclusion Architecturally speaking option a the preffered one option b is subjected to discussion option c will not be accepted both architecturally and commercially
CASE C)
Restraint of floor shrinkage
obesrvation non uniform restraints
conclusion option a will have higher restraint to shrinkage thus lead to crack in the floor, option B is average option C will not effectively restraint the srinkage so possibly less cracks
The lateral stiffness
obesrvation non uniform lateral stiffness in both X and Y
conclusion option b will provide higher lateral stiffness for a pure seismic acceleration X and Y direction
Torsion with respective vertical axis
observation irregular walls are provide very poor resistance to twist
coclusion option a will be the best option respect to torsional resistance wheras option c is the wrost one
Vertical reinforcement for similar base capacity
observation walls are subjected to nominal flexural moment and twisting moment
conclusion only c will required heigher vertical reinforcement and option b will required least
static eccentricity
observation structurally un-symmetric
conclusion only option C have static eccentricity and it is significant
system redundancy
obseravation concentrated lateral load support in both the axes
conclusion option a and b are more retundant than c
foundation system
observation walls are in line & concentrated easy ton fix the geomentry of foundation but critical in design
conclusion option B and C will be incorporated with isolated/strip footing option a is recommended to have peripheral box foundation
Architectural constraints
observation vertical wall will not allow passage
conclusion Architecturally speaking option a the preffered one option b is subjected to discussion option c will not be accepted both architecturally and commercially
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.
Solution:
Indirect Lateral load Transfer in X and Y direction :
the beam are connecting to another beam which is ineffective during lateral load transfer in such condition the primary beam is prone to shear failure
Eccentricity
the longer the distance between center of mass and center of stiffness the heigher torsional moment of the building as per the given plan eccentricity the bilding is subjected to heigher torsional moment in both X and Y direrction
Strong beam Weak column possibility
the size of column majorly as 25 cm X 25cm but all the beam have much deeper section inertia of beam vertually higher than the column if the column reinforcement is adequetly geater than that of beam we are ok and since we do not have the reinforcement detail this is doubtfull it is recmmended 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:
observation 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 same direction definately a special lateral load resisting system for these tortional moment should be accommodated
Random internal column:
since the internal column are random they are unable to transfer lateral load effectively and can not achieve desire building responce so we have to assume and design those columns for only gravity load
Floor to floor variations in partition walls and beams
partition wall provide an importance mass control in a building plan key role in shear transfer from floor to 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 tortional forces should be contrrolled by respective lateral load system so corner shear walls are suggested
the propotion of floor area is greater on ther left side than the right side so corners shear walls on left side should be havier than the right
corner shear wall shall preferably be supported over a box foundation shear walls should be connected by link beam to transfer shear from one to the other
The internal columns shall be supported by isolated footing those isolated footing can be connected with shear walls through tie beam