Concept on positioning of Columns

1) 

Symmetry :

If we divide the structure in X axis and Y axis the column positioning is symmetrical in both axis. Therefore mass and stiffness is distributed symmetrical in both axis arrangement of strutural elements is good in this arrangement.

Redundancy:

Perimeter columns are distributed unevenly in the above arrangement of top and bottom area which leads to more redundancy. 

Bi-directional stiffness:

Beam and column arrangements in X directions are uniform and regular when compared with the Y direction. Lateral force are uniformly distributed in the X direction.

Ductility:

 A ductile structure is ability to contort and dissipate energy during an earthquake is, therefore, also advantageous as it will keep deforming without reaching ultimate failure or collapse. For seismic analysis it is important to design the structure for ductility. In the above structure Y direction is more ductile than X.

2). Types of irregularities in buildings:

• Vertical stiffness irregularity
•  Weight (mass) irregularity
• Vertical geometric irregularity
•  In-plane discontinuity
•  Out-of-plane offsets
•  Discontinuity in capacity (weak storey)

In this condition we have vertical stiffness irregularity due to base in different levels.

There is a set back in the above floor which leads to mass irrregularity.

Due to irregularity in plan and column and structural arrangements load distribution will not be uniform and it will be more reduntant.

3) Reasons for failure:

• Column orientation -  All the columns are placed along the Y direction more stiffness in Y direction and less stiffness in X direction.
• Beam connection - Beam connections are provided only in X directions no beams are provided in Y direction which makes the slab to behave in one way slab.
• Torsion - As per the description the staircase RC wall is located at one corner of the building which leads the structure to have more torsion.
• In-fill loads - Wall loads are distributed only at one end which is mass irregularity which may lead to the failure mechanism of the building due to lateral load.