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