Conceptual design of a building with columns and shear walls

AIM : CONCEPTUAL DESIGN OF BUILDING WITH COLUMNS AND SHEAR WALLS.

OBJECTIVE:

• TO INVESTIGATE THE SUITABILITY OF GIVEN PLAN WITH RESPECT TO SEISMIC BEHAVIOUR.
• TO SCHEMATICALLY DRAW A SEISMIC VIABLE STRUCTURAL PLAN.

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 1.

STRUCTURE 1.

1. The structure is considered asymmetrical according to the regulations and the grid system.

2. Structural components do not have sufficient tensile capacity and force configuration.

3. The design will have some uncertainty regarding certain seismic response properties of non-rectangular walls.

4. This construction cannot be considered as horizontal unevenness and shear wall shape as L.

5. Structural walls have high stiffness and strength in both directions and are therefore subject to biaxial bending and bidirectional shear during earthquakes.

STRUCTURE 2.

1. The frame of the structure can be considered symmetrical in the grid-located shear wall according to the symmetrical ideology of the design.

2. The wall system of this frame can be arranged in two horizontal directions with as much two-way symmetry as possible to distribute the load in a balanced transfer from multiple sides.

3. Shear walls are arranged similarly and symmetrically so that they can be considered at each level fairly, minimizing uncertainty about seismic response and transferring loads uniformly across the frame.

STRUCTURE 3.

1. In the floor plan of the structure, the placement of the columns is inherently asymmetrical and is not acceptable by ordinance and is a code provision.

2. The foundation or foot may interfere with the placement of the foundation foot, and in practice, this may not be possible

3. The left wall provides more eccentricity, and the lateral stiffness is greater. Therefore, if this happens, then the damage or failure will be less.

4. The center of mass and center of gravity of such a structure will not be reliable according to the structural design, it does not satisfy the equation of equilibrium for the transfer of loads

5. This type of shear wall system will not carry the load equally in both directions. the structure lacks redundancy.

6. We are analyse the criteria listed below in structure 1 , 2, 3 .

• RESTRAINT OF FLOOR SHRINKAGE
• THE LATERIAL STIFFNESS
• TORSION WITH RESPECT TO VERTICAL AXIS
• VERTICAL REINFORCEMENT FOR SIMILAR BASE CAPACITY
• STATIC ECCENTRICITY
• SYSTEM REDUNDANCY
• FOUNDATION SYSTEM
• ARCHITECTURAL CONSTRAINTS

QUESTION 2 .

Discuss the suitability for earthquake resistance of the moment resisting framing plan of a three-story building depicted here (cross-sectional dimensions in cm), the eccentricity of the center of mass (as the centroid of floor plan) to the center 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 2.

PROBLEM IN THE GIVEN FRAMING PLAN:

1. INDIRECT LATERAL 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 .

2. 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, the building is subjected to higher torsional moment (Torsional flexibility) in both X and Y directions.

3.STRONG BEAM WEAK COLUMN POSSIBILITY:

The size of columns is majorly mentioned as 25 cm x 25 cm. But all the beams have a much deeper section (50cm).

The inertia of the beam is visually higher than the column.

If the column reinforcement is adequately greater than that of beams, we are okay and since we do not have the reinforcement detail, this is doubtful.

It is recommended to have slightly bigger sizes for the columns.

ALTERNATE DESIGN OF STRUCTURE( FRAMING) PLAN AFTER SOLVE THE PROBLEM :

For the Alternate option of this plan, we can add some changes as per the following.

QUESTION 3.

A multi-story building with a basement, with a quadrilateral (nonsymmetrical floor plan), plan as, has interior columns in an irregular (not in a grid) pattern a plan that serves architectural and functional considerations. Partition walls and interior beams supporting the slab have a 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.

ANSWER3.

OBSERVATIONS IN THE GIVEN FRAMING PLAN :

1.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.

A Special lateral load resisting system for these torsional moments should be accommodated.

2.RANDOM INTERNAL COLUMNS:

Since the internal columns are random, they are unable to transfer lateral loads efficiently and can not achieve desirable building responses.

So we have to assume and design those columns for only gravity loads.

3. FLOOR TO FLOOR VARIATION IN PARTITION WALLS AND BEAMS:

Partition walls provide an important mass control in a building and beams play a 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.

SUGGESTIONS ON THE LATERAL LOAD SYSTEM AND ITS FOUNDATIONS:

1. Heavy torsional forces should be controlled by the respective lateral load systems. So "Corner Shear walls” are suggested.

2. The proportion of floor area is greater on the left side than on the right side (Irregular quadrilateral). So Corner shear walls on the left side should be heavier than on the right.

3. Corner Shear walls shall preferably be supported over a box foundation. Shear walls should be connected by Link beams to transfer shear from one to the other.

4. The internal columns shall be supported by isolated footings. Those isolated footings can be connected with Shear walls through Tie beams."

Proposals are to be made and justified for the choice of the lateral-load-resisting system and its foundation.

• The above plan that is given is totally unsuitable for normal areas and also in Earthquake prone area.
• In seismic region the lateral and vertical loads play important criteria because it helps in resisting the failure against the earthquake as the loads.
• Resultant will not co inside with the centre of the mass of the structure it becomes eccentric and not suitable for any type of areas.
• In this plan a flat slab is more appropriate than a regular beam column junction as it provides support to the columns without any provision of the beam
• which reduces the weight of the building and also helps in the ductility
• which indirectly helps to maintain the structure in the earthquake prone areas.
• Apart from flab slab a wooden structure is also appropriate which reduces the weight of the building .
• Also helps to maintain the structure in the earthquake prone areas.