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 :-

Structure - A

• It will have higher restraint to shrinkage, thus lead to cracks in the floor.
• It will be best option with respect to torsional resistance.
• It is recommend to have peripherical box foundation.
• For this structure is considered as it is asymmetric in nature.
• Here can not be considered as horizontal irregularities and the shear wall shaped like L.
• There is some uncertainty concerning certain features of the seismic response of non-rectangular walls.
• It occurs lack of tensile capacity and force configuration.
• These walls have high stiffness and strength in boyh direction, hence are subjected biaxial bending and bi-directional shears during Earthquake.
• This Structure is more redundant than Structure-C.
• This structure is more preffered than any of the both.

Structure - B

• This structure frame can be considered as symmetric in placed the Shear walls.
• The Walls of wall system of this frame can be arranged into two horizontal direction with as much two-way symmetric as possible.
• The shear walls are arrangrd in similar and symmetric, so it can be considered at every storey to fairly uniform resistance in seismuc forces and the deformation demand, minimising the uncertainty about the specifications.
• This structure has average higher restraint to shrinkage.
• It will provide higher lateral stiffness for a pure seismic acceleration in X and Y directions.

Structure - C

• It will have not effective restrain the shrinkage, so possibly less cracks.
• This structure has worst torsion with respect to vertical Axis.
• It will require higher vertical reinforcement.
• Walls are subjected to higher flexural moment and twisting moment.
• There are irregular walls provide very poor resistance to twist.
• It Shall be incorporated with isolated footings.
• This structure can be considered as asymmetric in nature, because of the shear wall provided are not arranged in a two orthogonal horizontal direction.
• The centre of mass and centre of gravity of such structure will not lie far away from each other enabling transitional modes in the first two principal modes.
• The foundation, shear wall and columns are arranged the different arrangements, so here take up huge amount moments in case of during earthquake.
• This type of shear wall system will not carry the load equally in either direction so the structure have lack of redundancy.
• On left hand side the wall provide more eccentricity, lateral stiffness is more. So therefore it occurs then the damage or failure will be less.
• This Structutre will not be accepted for both architecturally and commercial.

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 :-

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.

Strong Beam - Weak Column Possibility -

• The size of columns majorly mentioned is 25 cmX25 cm.
• But all the beams have much deeper section.
• Inertia of beam is visually higher than column.
• If the column reinforcement is adequately greater than that of beams, we are ok and since we do not have the reinforcement detail, this is doubtful.
• It is recommended to have slight bigger sizes of columns as centricity.

Eccentricity -

• The longer the distance between centre of mass and centre of stiffness, the higher torsional moment of a building.
• As per given plan is eccentricity, the building is subjected to high torsional moment in both X and Y direction.

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

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 the building is not uniform or symmetric. So naturally any lateral load induced in the floor will not have 100% influence in same direction. Definitely a special lateral load resistance system for these torsional moments should be accommodated.

Random internal columns :- Since the internal Columns are random, they are unable to transfer the lateral loads efficiently and cannot achieve desirable building response. So we have to assume and designed those columns for only gravity loads.

Floor to floor variation in partition walls and beams :- partition was provide an important mass control in and building and Beams plan key role in shear transfer from floor to Beam. All these elements are not in order. So heavy distorsion distribution of loades will happen.

• This plan is totally unacceptable for heavy seismic zone areas.
• In this plan interior columns are in unsymmetric.
• The partition wall are provided through to the base of beam, should support the lateral deformation due to the structure.
• The Interior beams will support the slab, then the lateral load resisting the failed due to earthquakes.
• For this irregular columns in plan, there we provide the flat slab because it directly stay in column centoidal Axis.
• For here the beams at different locations is irregular in plan are the contineuous and is disallowed to resist the seismic load in the region.
• The solution of the structure, we provide the shear wall from the foundation of the structure through vertical components, it should minimise the lord of second failure occur due to lateral forces acting on structure.