On a 20-story brick-veneer building, the masonry is bulging and cracking at each relieving angle. The building has no horizontal expansion joints. Could the cracking result from brick expansion? What can be done?
This is fairly common in masonry veneer high-rise buildings where relieving angles are used without horizontal expansion joints. During construction, a small gap generally is left between the bottom of each relieving angle and the top of the brick below. As the masonry grows due to moisture and thermal expansion, the gap between the masonry and the shelf angle narrows. Mortar placed at the tip of the angle creates a solid bridge between the masonry above and below the relieving angle. This portion of the joint cannot compress. Resulting forces often cause bowing and spalling. Also look at tie placement. If the nearest ties are more than 12 inches above and below the relieving angle, bowing is more likely. Corrosion of the shelf angle also can cause bowing. Steel corrosion products are larger than steel itself. This creates pressures that act on the wall similarly to moisture and thermal expansion. These problems are compounded if the building's frame shrinks over time as the masonry expands. Bowing and spalling can be prevented by leaving adequate space beneath each angle during construction. The size of these spaces depends on expected movement. Procedures for sizing joints are given in BIA Technical Note 18A. Before repairing a bowed wall, you must determine what caused the bow. This requires cutting openings in the masonry to examine the condition of the relieving angles. Before cutting new expansion joints, verify that the angles are attached adequately. The pressures developed due to moisture and thermal expansion may have lifted the angles or caused some of the bolts connecting the shelf angles to fail. New expansion bolts may need to be added. Examine ties, too. Supplemental ties may be needed to maintain stability. Bowed walls should not be straightened, as this can cause cracks.