by Jim W. Sealy

Hurricane Ike had sustained winds averaging over 100 miles per hour and gusts up to 145 mph. Its winds destroyed virtually every pane of glass in the high-rise office buildings of downtown Houston. And, it wasn’t the wind itself that caused the damage, but flying missiles generated by the wind.

In the May/June 2006 issue of this magazine I wrote: On August 18, 1983, Alicia, a Category 3 hurricane made landfall on the west end of Galveston Island, Texas, 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 modify the way we detail and install glass drastically.

Some of you may remember that article, but even if you don’t, I’d like to revisit the point I made then—if for no other reason than to remind architects and contractors that Mother Nature is a powerful force and glass does not deal well with such power.

This time the article reads: On September 6, 2008 hurricane Ike made landfall on Galveston Island, with sustained winds averaging over 100 miles per hour and gusts up to 145 mph. Ike was a hugh storm, in terms of its physical dimension, and this made it more destructive than Alicia even though it was a category 2 storm. Ike’s winds also went up ship channel and destroyed virtually every pane of glass in the high-rise office buildings of downtown Houston. Again, it wasn’t the wind itself that caused the damage, but flying missiles that were generated by the wind. Whereas Alicia’s glass damage resulted primarily from roofing ballast, the broken debris of small structures, pieces of wood, caused Ike’s damage. Galveston Island was virtually destroyed and the aerial photographs taken immediately afterwards showed the thousands of wood frame structures that were reduced to heaps of broken wood. Not only did Galveston take a big hit but so did the smaller communities that border the Houston ship channel and Ike just kept gathering more ammunition with which to attack the glass of downtown Houston.

IBC
Nothing about the International Building Code (IBC) has changed. It still includes requirements for the thicknesses of glass such that it will be the appropriate strength to withstand the direct forces of wind, and the average architect and builder can easily interpret those provisions. After those basic exercises what architects and builders do is simply rely on the glass and glazing systems’ manufacturers to verify that the selected glass thicknesses will satisfy the code and make certain that the glass will stay in the selected setting mediums. If anything above that is required, or if the building is in a geographic area that is subject to very high winds, architects and builders sometimes make provisions for wind shutters to be installed. 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 the sudden and unexpected wind gusts, such as tornadoes, that nature can impose. It is also likely that shutters would be of little use if the building is in the direct path of a tornado, not only because of the totality of the destruction but also because of the lack of time to install or operate shutters. In addition to wind events, another unexpected event of nature is earthquakes. Even though we can predict areas where earthquakes may occur (adjacent to fault lines), and we have advanced warnings of hurricanes, our ability to predict tornadoes is still in a fledgling state. 

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 we can do to overcome the unexpected and extreme forces of nature. In dealing with tornados, there is little we can do 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 events and the overwhelming and destructive forces they bring. That is not to say we can’t design for tornadoes in some respects, because we can. The Wind Engineering Research Center at Texas Tech University has made significant advances in designs for tornadoes, but all of their research has a flaw as far as architects are concerned. That flaw is aesthetics. It seems that what will resist the winds of tornadoes is likely to be unattractive and architects are not inclined to use them.

Down to Earthquakes
While we cannot predict the actual timing of earthquakes, we can take measures to protect the glass and glazing systems that we have designed. 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 architects were surveyed, I believe we would find that few have ever considered whether or not any natural hazard has the potential of impacting the glass and glazing systems of their designs.

Some clients, such as owners and operators of medical facilities, will require architects to specify that the glass and glazing systems of their projects will be physically subjected to wracking tests before the systems are allowed to be installed in their buildings. From a common sense perspective, this is good practice and one that should be followed by more architects, simply as a loss prevention measure for our clients. Other than it being a good practice to look out for your client’s interests, it’s another way of protecting yourself if a natural hazard does occur. Remember, there are several cases on file where huge buildings have experienced total failures of their glazing systems and it is prudent for all architects and builders to pay more attention to the glazing systems they design and install. And, one more time, just pick up the phone and call the building official where your next project will be built and ask the question, “Do you have any special requirements for exterior glazing systems in jurisdiction?” You may discover that the jurisdiction has more restrictive or less restrictive requirements for glazing systems. Be very careful when you find that the requirements are less than the minimum standard of the IBC. That usually signals special interest groups have played a part in the reduction and it may not be in the best interest of your client, or you. Always review such things with your clients and advise them of the implications of not complying with the minimum. Too often architects are sued because an event takes place and an unhappy owner makes the claim, “You didn’t tell me that this could happen.” Be very careful! 

Jim W. Sealy, FAIA, is an architect and consultant based in Dallas who has more than 40 years of experience. A principal in J.W. Sealy Consulting, his expertise ranges from zoning and conceptual design to forensic architecture. He is also a member of the Architects’ Guide to Glass & Metal editorial board.

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