I have an interesting dilemma at a building that my firm has been hired to repair. Shrinkage of the concrete frame over the last 30 years, along with expansion of the brick masonry, have caused the masonry to move upward relative to the concrete frame. Angles attached to the concrete spandrel beam use wedge inserts cast into the beams. I am afraid that some of the anchors in these wedge inserts may have become loose as the angles shift upward.
How can expansion joints be added beneath the shelf angles to accommodate any future movement without the angle just shifting down because the anchors are loose?
I have been involved in several projects where vertical growth of masonry has caused the askew head bolts (those with an angled head) in the wedge inserts to loosen. Because of the askew head on the bolt, it tightens under normal gravity loads. However, when the angles are pushed up as a result of differential movement between the brick veneer and the concrete structure, the anchor becomes loose and is not capable of supporting vertical loads.
Shifting likely occurs in at least some locations if expansion joints are merely cut beneath the angles. Besides causing the saw blade to bind up, this shifting can result in cracking, spalling, and other problems in the brick veneer. Also, if some of the anchors are able to support the load and the remaining anchors cannot because they are loosened, there may be failures in the angle due to increased spans or progressive failures of the few bolts that are able to support some load.
When the masonry veneer has shifted upward due to differential movement, expansion joints cannot be cut without opening up the masonry at the shelf angles in order to inspect and tighten the bolts as necessary. The work should begin at the top of the building.
Bolts should be tightened prior to cutting an expansion beneath the shelf angle. Since the bolts are typically spaced at 2 feet on center, the masonry above the shelf angle must be temporarily supported so that the bolts can be tightened and flashings can be repaired or replaced in conjunction with this work. It may be possible to make repairs at every second or third floor to reduce the amount of work required.
In this case, the shelf angle must be strong enough to also carry the masonry at the floors where repairs are not being performed. In many cases, the shelf angles may need to be replaced with larger models sized to carry the increased load due to the additional floors.