In continuation of my previous post on soft story in buildings, I had discussed about the soft stories and how it induces the stiffness irregularity in the structural system.

There I had left that post on question remark that does it help to have infill in the structure, or a bare frame is better?

[1] The infill walls provide lateral stiffness to the structure depending upon their material, thickness, and length on the floor.

[2] There is a fundamental difference between lateral strength & lateral stiffness, the lateral strength is provided by shear walls, moment frames & other stabilizing units. These take the lateral forces coming to structure & ground it.

[3] So having infill walls in structure will certainly increase the stiffness which in turn reduce the lateral deflection & drift of the building.

Then why not have thick infill walls and control the lateral deflections as much as possible, well there is limit to which the infill walls can help.

[4] That limit is the capacity of those moment frames which are surrounding the infill walls. if the infill walls are stiffer than the beams & columns, it will crack the beam & column junctions.

[5] Hence in the hierarchy of structural members the infill walls are the lowest, so they need to fail first then the beam and then the columns. (I have added a sketch below to explain this)

This is a post on effect of infill walls.

Any comments or suggestions are welcomed.