Surprisingly, many engineers and glazing contractors are unaware of the requirements set forth by ASTM F2248-03 for the design of framing connections for blast resistant glazing systems. ASTM F2248-03 specifies connection design loads of at least 2.0 times the magnitude of the 3-second equivalent design load or the glazing resistance as determined from ASTM E1300, whichever is greater. Often the glazing system connections to the main structure are only designed to resist 2.0 times the 3-second equivalent design load, despite the glazing resistance of the system.
The UFC 4-010-01 is currently undergoing revisions that should clairify blast design loads and reference a more stringent version of the ASTM F2248 standard (ASTM F2248-09). The revised 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 glazing 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 glazing 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 (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 this year or early next year.
The changes may be difficult to accommodate with static equivalent analysis and may require a larger push for dynamic blast analysis to maintain reasonable connections.
Written by Matt Quinlivan, E.I.T.