AGG - 2006 - May/June

Volume 20 • Issue 3 • May / June 2006

Glass and the Multi-Hazards of Nature
by Jim W. Sealy

On August 18, 1983, Alicia, a category 3 hurricane, made landfall on the west end of Galveston Island, Tex., with sustained winds of 96 miles per hour and gusts of 127 mph. Her winds went streaking up the Houston ship channel and destroyed virtually every pane of glass in the high-rise office buildings of downtown Houston. It wasn’t the wind itself that caused that damage, however, but flying missiles that were generated by the wind.

One of the most plentiful sources of missiles was the roofing ballast that had become a popular construction technique of that era. The ballast became like pellets from a gargantuan shotgun and sprayed every office building in its path. The destruction left by Alicia caused changes in how buildings are built. Rather than changing the way we designed and detailed glass and glazing systems, however, we made changes in the way we designed, detailed and constructed roofs. In retrospect, no weather event, or any other hazard of nature, has caused us to drastically modify the way we detail and install glass.

The Requirements
The International Building Code (IBC) includes requirements for the thicknesses of glass such that it will be of appropriate strengths to withstand the direct forces of wind, and the average architect and builder easily interpret those provisions. After those basic exercises, when designing for the forces of wind, what architects and builders alike do is to rely solely on the glass and glazing systems manufacturers to verify that the selected glass thickness will satisfy the code and to make certain that the glass will stay in the selected setting mediums.

If anything more is required, or if the building is in a geographic area that is subject to high winds, architects and builders will make provisions for wind shutters to be installed when high winds are predicted. Most of those devices work well when buildings are faced with the wind forces of hurricanes, but there is little that we can do in the event of sudden, unexpected wind gusts, such as tornadoes. Shutters likely would be of little use, if any, if the building were in the direct path of a tornado, not only because of the totality of the destruction but also because the lack of time to install or operate shutters prohibit their use.

Quake and Break
In addition to wind events, another unexpected event of nature is an earthquake. Even though we can predict areas where earthquakes may occur (fault lines), we do not know when the actual event (which is sudden) will occur and therefore the application of “protective devices” are of no value.

It’s not as though architects ignore the fact that glass breaks or that we believe nothing can be done to prevent the breakage. The plain truth is that there is little, if anything, we can do to overcome the sudden and unexpected forces of nature. In the midst of a tornado that completely destroys houses, there is little that can be done to protect the integrity of glass and glazing systems. Even when buildings are on the fringes of the effects of a tornado, there is little that can be done, simply because of the sudden timing of the event and the overwhelming and destructive forces that it brings.

Protection
While we cannot predict the actual timing of earthquakes, we can take measures to protect the glass and glazing systems that we have designed to be installed in our buildings. Earthquakes may impart twisting and wracking motions, which can be instantaneous and then immediately subside, or they can be motions that last for several seconds, or even up to several minutes. If it were possible to survey the thousands of architects attending the AIA’s national convention in Los Angeles (where this magazine is being distributed), I believe we would find that few of them have ever considered whether or not a natural hazard will or will not impact the glass and glazing systems they have designed.

The Test
Some clients, such as owners and operators of medical facilities, require that architects specify the glass and glazing systems of their projects be subjected to physically wracking tests before the systems are allowed to be installed in their buildings. From a commonsense perspective, this is good practice and one that should be adhered to by more architects simply as a loss preventative measure for our clients. There are a few jurisdictions, or governmental agencies, that mandate wrack tests for wall assemblies. If an architect is unaware of what the jurisdictions that are controlling a project may require, it is also good practice to “check it out.” A simple phone call may save everyone involved some grief the next time Mother Nature comes calling.

Jim W. Sealy, FAIA, is an architect and consultant based in Dallas who has more than 40 years of experience.