QUESTION
I am an architect currently working on a design competition for a project that will require blast resistant windows. I’m curious about the note stating the connections will be difficult for small windows. What dimension would you define as a small window? Our schematic has some smaller windows in stairs and in this phase of competition we certainly want to show something that is feasible.
5) Connections and anchors under static equivalent method is changed. The connections and anchors must be designed for either 1x or 2x the glazing resistance instead of the typical loop holes that we have seen 2x the 3-second load (usually 100psf). Anchors and connections at these loads will be difficult if the controlling glazing lite in an elevation is small. I think anchors into masonry and wood and light-gage steel will not be workable with this method.
ANSWER
Well – lets take this example a 20” x 30” window – Insulated glass (1/4” Tempered outside pane and ¼” Heat strengthened inside). When we run the ASTM E-1300 glass resistance numbers on this we are at 680 psf. (See below)
So if the anchor design loads are just 1x the resistance then it would be 680 psf, but if it is 2x then it would be 1360 psf. 680 psf is severe enough, because originally before the UFC change many specs and criteria that we would see would be 2x the 3-sec equiv blast load (usually 2x 50psf = 100psf). So the question is can someone design anchors for this in whatever your substrate is? – This example is almost 7x as much design load as before (a little less than that because we can use ultimate strength methods now – but that’s little relief).
Stewart P. Jeske, P.E.
