A continuous brick veneer column located between windows was 18 m (60 ft) or six floors tall, with moisture expansion of 9 mm (0.36 in.). This is calculated with:
(0.06 x 6)
= 0.36 in.
This occurred in addition to thermal expansion at the south elevation of 9.3 mm (0.37 in.), calculated with:
(0.0624 x 6)
= 0.37 in.
Total brick veneer expansion was 19 mm (3/4 in.), accumulating at the top of the building and shifting up the sixth-floor loose lintel for 19 mm. It was calculated with:
(0.36 + 0.37)
= ¾ in.
The CMU backup wall shrinkage would be 16 mm (5/8 in.), calculated with:
(0.1 x 6)
= 0.6 in.
This means the top floor windows attached to the CMU backup wall will shift down for 16 mm.
Total differential movement between the expanding brick veneer and shrinking CMU backup wall would be 35 mm (1 3/8 in.) at the sixth floor, calculated with the following:
(3/4 + 5/8)
= 1 3/8 in.
Brick veneer was anchored to the CMU backup wall with adjustable hook and eye masonry ties, and at the sixth floor, the hooks could be off the eyes due to this differential movement. Therefore, continuous shelf angles should be provided to support the brick veneer at every floor level.
Conclusion
When differential movement between expanding brick veneer and shrinking CMU accumulates at the top of the building, it can cause shifting of the parapet coping stones, and unsafe conditions. With introduction of the continuous shelf angles bolted to the CMU bond beams at every floor level, and a horizontal expansion joint under each shelf angle, this accumulation—and all its associated problems—can be eliminated.
Michael Gurevich is a masonry consultant at the New York City Brickwork Design Center (NYCBDC), which conducts seminars on a variety of brick masonry topics. He has more than three decades of experience working with exterior masonry walls. Gurevich holds a master’s degree in structural engineering from Belarussian State Polytech University in Minsk. He can be contacted via e-mail at nycbdc@aol.com.
