Typical damage patterns in masonry buildings

Masonry is brittle, weak in tension and heavy, so damage is typically cracking, separation and collapse in recognisable patterns.

1. Diagonal X-cracks in piers and walls (in-plane shear)

Caused by in-plane shear when the principal tensile stress exceeds the masonry tensile strength. Cracks reverse with cyclic motion and form an X.

 +-------+
 |\     /|
 | \   / |      X-cracks in
 |  \ /  |      pier or wall
 |  / \  |
 | /   \ |
 |/     \|
 +-------+

2. Cracks at openings

Stress concentration at the corners of doors and windows leads to diagonal cracks starting at the opening corners, and horizontal cracks at sill and lintel levels; narrow piers between openings fail first.

3. Vertical cracks at wall corners and junctions

Orthogonal walls vibrate out of phase, so the corner or T-junction separates (vertical crack). It is worse if there is no bonding or bands.

4. Out-of-plane bulging, overturning and collapse

Long, tall or thin walls bend outward; horizontal cracks at mid-height or at floor level result, and the wall falls out. Gable walls and parapets overturn because they are not restrained at the top.

5. Delamination of wall leaves and collapse of stone walls

In rubble masonry the outer leaves separate from the loose core, and the wall sheds as a pile of stones.

6. Roof and floor damage

Heavy roofs on weak walls cause collapse; timber joists pull out of walls because of poor anchorage.

7. Damage due to irregular plan and torsion

Irregular plans (L, T shapes), unsymmetrical openings or stiff walls on one side lead to torsion and concentrated damage at re-entrant corners.