Case 2

Cause of Defects

Corners of openings such as a window are subjected to higher stress concentration. Stress concentrations occur when the flow of stress is disrupted by irregularities in the geometry or material of a structural component. These disruptions can be caused by holes, especially at sharp corners. This may be part of the reasons why windows of airplanes are rounded [1].

The transference of load around openings will mean that the walling immediately below the openings carries a considerably higher loading. The redistribution of forces produces shear cracking and differential movement. There is an effect on the bonding of masonry walls (Figure 1).

Weakness in the bonding are likely to occur at any structural discontinuity or where the loading is reduced surrounding windows.

This concentration of stresses into bands between openings where the construction is continuous occurs both horizontally and vertically. If there is viability in the materials within an elevation, it is likely that any stresses will be relieved as cracking at the connection of materials and near the openings (Figure 2).

When openings are made in walls for windows and doors installation, the corners of these openings are areas where stress is greatest. The plaster around such weak areas will suffer from cracks upon the slightest movement.

Besides at the junction of such interface, without the proper design detailing to accomodate the openings it will result in cracks that occur diagonally to the opening.