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:

Restraint of floor shrinkage:

In case A it is observed that they are fully restraint at allcorners so it is concluded that it will have higher restraint to shrinkage,thus leads to cracks in the floor.

In case B corners left free but restraints along the edge so it is observed that it will have average restraint to shrinkage

In case C it is non uniformly restraint so it is concluded that it will not have effectively restraint to shrinkage ,thus leads to less cracks in the floor

The lateral stiffness:

In case A it is observed that comparatively lower stiffness in both x & y direction

In case B uniform & comparatively higher stiffnesss in both x & y

In case C non uniform lateral stiffnesss in both x & y

so it is concluded that B will provide higher lateral stiffness for a pure seismic acceleration in both x & y directions

Torsion with respect to vertical axis:

In case A corner walls provide more resistance to twist

In case B edge walls provide good resistance to twist

In case C Irregular walls provide very poor resistance to twist

So it is concluded that case A will be the best to Torsional resistance

Vertical reinforcement for similar base capacity:

In case A walls are subjected to nominal flexural moment & twisting moment

Incase B walls are subjected to nominal twisting moment

Incase C walls are subjected to heavy flexural momet & twisting moment

So it is concluded that case C will require higher vertical reinforcement & case B will be least

Static eccentricity:

Both case A & B are structurally symmetric & C is un symmetric

So it is concluded that option C have static eccentricity 7 it is significant

Systems redundancy:

In both case A & B unifrom placement of lateral load supports in both the axes & Incase C concentrated lateral load supports in both the axes

So it is Concluded that both A& B are redundant than case C

Foundation systems:

In case A Due to L shaped walls the geometry of foundation & its design will be critical

In case B walls are in line .easy to fix the geometry & design of fouundation

In case C walls are in line & concentrated .Easy tro fix the geometry of foundation but critical in design

Architectural Constraints:

In case A walls obstruct only corners

In case B walls obstruct the cases of the building

In case C vertical wall will not allow passage

So it is concluded that A is the preferred one ,B is subjected to discussion,C will not be both architecturally & 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.

Issues in framing plan is given below :

INDIRECT LATERAL LOAD TRANSFER IN X AND Y DIRECTION :

The beams are connecting to another beams which is ineffective during lateral load transfer in such conditions the primary beam is prone to shear failure .

ECCENTRICITY :

Longer distance between center of mass and center of stiffness the higer torsional moment of the building .

As per given plan eccentricity , the building is subjected to higher torsional moment in both x and y direction .

STRONG BEAM WEAK COLUMN POSSIBILITY :

As per given information the column having size 25 cm x 25 cm , and beam size is 25 cm x 50 cm . the depth of beam is 50 cm it is large than column size .

If reinforcement of column is greater than beam then ok. but reinforcement details are not given . so it create a confusion .

so increase the size of column . it the size of column is not increased then column is failure first

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.

OBSERVATION IN THE GIVEN PLAN :

1. Floor plan :

The floor plan of this building is non uniform and symmetric .

so that lateral load is induced in floor will not have 100 % influence in same direction .

The special lateral load resisting system for this torsional moments should be accomdated .

2. Random internal column :

The internal column are random so they cant transfer lateral loads efficiently and can not achived desirable building response .

so we have to assume and design those column for only gravity load .

3.Floor to floor variactions in partition walls and beams :

The partition wall provide mass control in building where beam pay key role in shear transfer from floor to beam . and this element is not provided in order. so heavy ditoration and distribution of lateral load will happen

SUGGESTION ON THE LATERAL LOAD SYSTEM AND ITS FOUNDATON :

Heavy torsional force can be controlled by repective lateral load system . so "corner shear walls" is provided

The proportional floor area is greater in left side and less in right side so corner shear walls in left side is heavier than right side .

The corner shear wall is supported over a box foundation and this walls should be connected by link of beam to transfer the shear load from one to another .

Internal column is supported by isolated footing . This footing can be connected with shear wall through tia beam .