Brick Veneer, Metal Studs and Smashed Cars

[mbryan]

In the early 80's somewhere in Texas (I believe Houston) a whole section of brick veneer fell from the exterior of a high rise building literally smashing a parked car below. This incident was the first indication that the marriage of brick veneer and metal stud wall construction was going to be a major problem in high rise construction.
What led to this disaster? The chain of small failures that led to the major failure are logical and fascinating. The chronology and key contributing factors are as follows:
1.) Wind, Barometric Pressure and Stack Affect: When we enter a very tall building often you will hear that low howl of feel the ruch of air into or out of the building. Changes in barometric pressure cause an imbalance between internal and external pressure in large buildings that takes a while to equalize.
2.) An inflexible veneer over a flexible structure: When you put a brittle veneer over a flexible structure, something's got to give!
Wind and quick changes in barometric pressure exerted considerable force upon the flexible metal wall envelope of the building. This constant in and out flexing caused the mortar to brick bond in bed joints between floors to fail.
3.) Moisture Intrusion: Unequal barometric pressure within and without of large buildings casts a whole new light on moisture intrusion forensics. Negative internal pressure can literally draw moisture into the cracks and crevices of a building by the gallon.
4.) Corrosion: Wet steel rusts and corrodes away.
These last two factors sealed the fate of a sysem that appeared to be well thought out. Negative building pressure literally sucked water in through the failed bed joints. This in turn was wetting the anchorage. Although the metal studs and the wall ties were galvanized steel, the self-tapping screws through the studs revealed raw unprotected steel. Eventually the steel stud around the anchorage fastening screw failed. Finally, high wind or extreme pressure caused the entire brick veneer to literally fall out of the wall to the street below.