ME USGlass September 2011 : Page 26

PROTECTIVE GLAZING continued from page 25 specifications,” Jeske says. “They end up getting burned on the back end.” For example, Jeske sees, “they’re sup-posed to submit calculations on down the road and, a lot of times, they haven’t been thoroughly educated in the specs what to look for … Or they don’t un-derstand that it requires three times the amount of anchors that they were orig-inally thinking about, or that the system that was originally tested under blast loads does not really meet the require-ments that were specified. So they get into a lot of messes that way.” Cornellier has worked on enough projects with blast requirements to know that they take a lot more time, a lot more money and a lot more experi-Future Changes Coming to UFC by Matt Quinlivan or the past several years, the Unified Facilities Criteria (UFC 4-010-01) has been the governing code for all U.S. Department of Defense (DOD) blast mitigation projects. Referencing ASTM F2248-03, Standard Prac-tice For Specifying An Equivalent 3-Second Duration Design Loading For Blast Resistant Glazing Fabricated With Laminated Glass , the UFC provides a guide-line for determining an appropriate static design blast pressure for both fram-ing and connections of blast-resistant glazing systems. Surprisingly, many engineers and glazing contractors are unaware of the re-quirements set forth by ASTM F2248-03 for the design of framing connections for blast-resistant glazing systems. ASTM F2248-03 specifies connection de-sign loads of at least 2.0 times the magnitude of the 3-second equivalent de-sign load or the glazing resistance as determined from ASTM E1300, Standard Practice For Determining Load Resistance Of Glass In Buildings , whichever is greater. Often the glazing system connections to the main structure are only de-signed to resist 2.0 times the 3-second equivalent design load, despite the glazing resistance of the system. The UFC 4-010-01 currently is undergoing revisions that should clarify blast design loads and reference a more stringent version of the ASTM F2248 stan-dard—ASTM F2248-09. ASTM F2248-09 sets forth the following criteria for the design of blast-resistant framing connections to the main structure: a. 2.0 times the magnitude of the load resistance of the blast-resistant glaz-ing if the maximum air blast pressure is greater than one half the magnitude of the load resistance of the blast-resistant glazing. b. 1.0 times the magnitude of the load resistance of the blast-resistant glaz-ing if the maximum air blast pressure is less than one half the magnitude of the load resistance of the blast-resistant glazing. Currently, UFC 4-010-01 (the 2007 revision) references ASTM F2248-03, and not the more up-to-date F2248-09 edition. It is our understanding that ASTM F2248-09 is not required in the design of blast-resistant systems until referenced in the most current version of the UFC, which is anticipated before the end of this year. The changes may be difficult to accommodate with static equivalent analy-sis and may require a larger push for dynamic blast analysis to maintain rea-sonable connections. F ence than non-blast projects. Walking through the process, he ex-plains, “You end up having to design to calculations based upon requirements that are set forth in the specifications. Then the owners, be it the government or individual companies, hire a blast consultant. They give you design crite-ria and then you have to submit calcu-lations that show that you’re meeting that design criteria.” From there, “All the data is interpreted: you have to under-stand what the intent of the design is, then you have to interpret it, then you submit your interpretation, and they tell you whether you got it right or you got it wrong.” Cornellier says he sees as much as 75-percent additional time spent on en-gineering and submittals for these proj-ects compared to non-blast. Carrillo agrees that the calculations required often pose a problem—but in a different way. He recalls bidding a government project where the specifi-cation required a specific tool for ana-lyzing the effects of blast/dynamic forces upon glazing. “It utilized infor-mation other than the traditional equivalent static forces methods employed by most consulting engi-neering firms to design safety and blast resistance glazing.” Problem was, he found, access wasn’t granted “unless you were already a government-approved contractor.” As the market segment grows, more resources are becoming available to help glazing contractors and their customers (see sidebar on page 28) . Product Evolution Valerie Block, senior marketing spe-cialist with DuPont Glass Laminating Solutions based in Wilmington, Del., notes that while building codes have not adopted security glazing require-ments that address terrorism, an in-creasing number of architects on government and many high profile commercial projects are including blast continued on page 28 Matt Quinlivan, E.I.T., is an engineer with JEI Structural Engineering. This ar-ticle is reprinted courtesy of JEI Structural Engineering. 26 USG lass, Metal & Glazing | September 2011

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