The question I most often hear about from property managers is about cracks in concrete, masonry or interior finishes, such as drywall or plaster. A common attribute of these materials is that they are all weak in tension and cracks most often occur as a result of excess tensile stresses. Detrimental tensile stresses are usually due to unexpected building movement caused by changes in temperature, foundation settlement or abnormal deflections. The question is, "When does a crack become a structural concern?" The answer is not always clear. Here are some items to keep in mind when evaluating cracks.
1. To a great extent, cracking in conventionally reinforced concrete is unavoidable. As it cures, concrete loses water and therefore mass. It shrinks. Something has to give. Proper design concedes this and incorporates measures to control cracking. Among the potentially problematic, non-shrinkage related types of cracks in concrete are:
a. Diagonal cracks in concrete beams near their bearing points;
b. Radial cracks in concrete slabs near columns;
c. Numerous cracks in one location;
d. Cracks that appear to extend completely through a beam or column; and
e. Cracks greater than one-quarter of an inch in width.
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Most other cracks in concrete are not structural concerns. However, if exposed to weather, they can allow water and/or chlorides to penetrate the concrete and corrode the reinforcing steel.
2. Cracks in interior finishes are usually in indication that the structural frame has moved. The cracks themselves are seldom structural concerns. But they could indicate a more significant problem. Try to expose the structural framing around the area of the crack.
3. Cracks in exterior masonry usually indicate building settlement. Building settlement is not necessarily a structural concern unless the settlement is severe. Settlement cracks in masonry should be monitored to determine whether the building has stabilized or is continuing to move. Cracks should be sealed to prevent moisture from entering the system.
4. Any cracks in structural steel should be examined by a qualified structural engineer immediately. Structural steel should not crack under any circumstances and any unintended discontinuity, fracture or other break is symptomatic of a serious structural problem.
If you are not sure if a crack is a structural concern, I look forward to hearing from you!
John McIsaac |
