Are the anchors for your blast resistant glazing systems appropriately designed?
There are many misinterpretations of UFC requirements for blast resistant design among engineers. Some engineers solely design anchors for two times the static equivalent blast load determined from ASTM F2248.
However, UFC 4-010-01 (2007) also requires a minimum anchor design equivalent to the resistance of the glass determined from ASTM E1300.
Many engineers miss this requirement, but UFC, under section B-3.1.1.4 Connection Design, state, "The actual connection design load is dictated by the glass type and thickness determined by ASTM E 1300."
Therefore, the correct design load is the maximum of either two times the static equivalent blast load from ASTM F2248 or the resistance of the glass from ASTM E1300. The intent of UFC is to design anchors such that they will not fail before the glass.At JEI Structural, we stay up-to-date on the latest codes and offer many value-added services.
Let's build together,
Stewart P. Jeske, P.E.
President
www.JEIstructural.com
"Expert engineers for commercial glazing calculations."
This topic has generated quite a buzz. Clearly, this is an item we need to understand. One person replied,
ReplyDelete"Please understand we request ASTM E1300 reports from all our customers to perform calculations. However, in most cases either
they are unaware of what they are requesting or the glass maufacturer / fabricator is unable to supply due to generic information from the
architecturals. For UFC projects we use the static equivalent method.
There are three methods that can be used to show compliance of the window framing members and their connections to the structure that are acceptable per the UFC code. They are by testing, a dynamic analysis, or a static equivalent analysis.
The UFC code lists the requirements for performing a static equivalent analysis of the framing members and their connections within Section B-3.1. Those requirements are as follows:
· The framing member design consists of checks for both deflection and stress. The criteria for both deflection requirements and allowable stress levels within the aluminum are listed within the UFC code. The blast load that is used for these checks is a static equivalent load that is given within the UFC code. This load is predetermined and is independent of the laminated glass make-up or thickness.
· The framing members shall allow for proper engagement of the glazing so as to allow for an adequate sealant joint to be applied around the perimeter of each glazing lite.
· The connection of the framing members must follow the same stress requirements as the framing members. The loads used for the design of the connections are elevated but are based on the static equivalent load given within the UFC code. As is the case of the framing members, these loads are predetermined and are not dependent on the laminated glass make-up or thickness.
The UFC makes no stipulation for the design of the framing member and their connections to the surrounding structure when using the equivalent static design load method for glazing make-up. The only considerations that most must make with regard to the glazing is that we can accommodate the thickness and provide enough engagement to allow for an adequate sealant bead around each lite. It was not then, nor is it now, a requirement to know the exact make-up of the glazing to be used in order to perform our analysis of the framing system and its connection to the surrounding structure.
For GSA and other government entities our engineers use the appropriate proprietary software to satisfy the specified requirement i.e. WINGARD P.E. on GSA projects.
To which I replied,
ReplyDelete"Please note from your response "The connection of the framing members must follow the same stress requirements as the framing members. The loads used for the design of the connections are elevated but are based on the static equivalent load given within the UFC code. As is the case of the framing members, these loads are predetermined and are not dependent on the laminated glass make-up or thickness." is not quite right. The statement in your response does ingore the intent of the requirement in UFC 4-010-01 (2007 version) B-3.1.1.4 Connections Design where it states, "Note: The actual connection design load is dictated by the glass type and thickness determined by ASTM E 1300. Therefore, in order to keep the connection loads reasonable, use a glass type and thickness that just exceeds the required glazing resistance."
I have sat in may training sessions with some of the same people behind the writing of the governing codes. There has been much debate about this and the misunderstanding in the industry. That is why they have issued a new ASTM F2248-09 (Equivalent 3-Second Duration Design Loading for Blast Resistant Glazing) which takes care of the mis-interpretations. I've attached the new ASTM F2248 as a reference. The issue of connection design is addressed in paragraph 1.6. Ultimately, the connections do need to be designed considering the load resistance of the glazing.
They have not issued an updated UFC 4-010-01 yet, but I understand that it is coming very soon - some say this year.
If you have any questions or would like to discuss this, please comment here, send me an email or give me a call.
Stewart Jeske, P.E.
JEI Structural Engineering
Glazed Systems & Blast Engineering
11108 N. Oak Trwy, Suite 208
Kansas City, MO 64155
http://www.jeistructural.com
816-734-8345
816-734-7013 fax