Masonry Failures

When determining coverage for the failure of an older masonry wall, the cause of the failure should be investigated by an engineer. Most failures involving older masonry walls are caused by one, or a combination of, three factors; improper design/construction, long-term material deterioration and a change in the intended use of the structure.


Fig. 1 Cracked unreinforced masonry wall	Fig. 2 Deteriorated mortar

Even as recently as 20 years ago, masonry structures in some areas were built without the benefit of a professional engineer’s design or supervision. This resulted in structures that do not meet proper design standards and, therefore, are vulnerable to long-term structural failure due to their lack of durability. An underdesigned or poorly built masonry structure can exist for decades with no apparent problems, but small loading changes over time, that a properly designed masonry structure would withstand, can cause it to fail. These small loading changes can be brought about by weather changes such as El Nino, or changes adjacent to the masonry structure such as new construction. A typical example would be a masonry retaining wall that was not properly reinforced and lacked proper drainage, Fig. 1. During periods of unusually heavy rain, such as El Nino, this wall could fail due to the increased lateral pressure on the filled side of the wall. Structural fatigue, brought on by the masonry being overstressed over a long period of time, can also lead to failure in an improperly designed wall.

Some mortars from as recent as the 1960’s have been known to deteriorate and loose their cohesiveness, Fig. 2. Masonry has never been recognized as having the ability to resist large tensile forces. As the mortar deteriorates, the masonry begins to lose its tensile strength, much of its shear and compressive strength also. When this occurs, small loading changes that would not affect sound mortar, could cause failure in a masonry structure. Again, the small loading changes could be weather related or changes around the structure that change the nature of the loading of the structure.

The use of any structure can change with time and ownership. If a masonry wall that was intended for use as an interior wall becomes an exterior wall and it is exposed to wind loads, it could become overstressed and fail. If a load-bearing masonry wall has its loading condition changed by adding additional floors or floor area, the wall could fail in compression or buckling due to overstressing. Another example of a change in use would be an open field above a masonry retaining wall that was changed into a parking lot for automobiles. The surcharge from the automobile loading would induce unanticipated lateral loading in the masonry retaining wall and could cause it to fail.

A recent storm or other event may appear to be the cause of failure in a masonry structure when actually the primary cause could be a design/construction defect, mortar deterioration or improper use.

Summit Engineering can investigate masonry failures and identify the cause(s) of the failure and recommend repair procedures. Please contact Neil R. Baer, P.E. for additional.


	Specialists In Engineering Analysis of Accidents