CBC Handrail Factor of Safety
CBC Handrail Factor of Safety
(OP)
CBC section 2407.1.1 calls for factor of safety 4 to be used for all glass handrail support members. We are already using 200 # point load or 50 # /ft load for designing the support members. Is it not FS is already built in these loads.






RE: CBC Handrail Factor of Safety
Also remember glass is brittle, therefore little 'warning' before failure. You want to make sure it would take something crazy for the railing to shatter.
RE: CBC Handrail Factor of Safety
One thing to keep in mind when applying the FS=4 is that it's calculated against the capacity of the element. I know it may seem obvious to some but I can't tell you how many times I've seen it misapplied as a load factor or taken against an allowable stress. And as strcutSU10 points out glass is a little bit unique as a structural material. There was a thread a week or so ago for a "cantilever glass wall". You might search that one out. I posted a few more comments about how glass is designed that may help.
regards,
Michel
RE: CBC Handrail Factor of Safety
RE: CBC Handrail Factor of Safety
I do agree with your approach for most materials, but glass is different. It's ultimate failure capacity doesn't have a direct proportional linear relationship to load. So using a using a 4 as a LF just isn't right. Glass fails as a result of small defects that can only be addressed in terms of the probability for their size and distribution. Glass is then designed based upon the "probability of breakage"(Pb). Normal glass design assumes a Pb=0.008 and for glass handrails the Pb=0.002. ASTM E1300 Appendix X3 provides procedures to calculate Pb for a given load and configuration. Appendix X8 provides procedures for calculating an "allowable stress" for a given Pb and glass configuration. Results of these will show that to gain an added FS you may only need to reduce the stress level by a smaller amount than you would find by using the 4 as a LF.
Regards,
Michel
RE: CBC Handrail Factor of Safety
RE: CBC Handrail Factor of Safety
It sounds like you may have a different condition than what the Code references assume. If the glass is attached to a vertical post or baluster which includes a top cap and/or handrail then the glass is just an infill panel. In that condition I believe the 200# point load would be applied directly to the supporting steel member and doesn't require a FS=4 since it's not a load applied to the glass (you have a steel framework supporting the 200# load). However the component load of 50# on the glass as a "panel filler" as referenced in 1607.7.1.2 would have a FS=4 on the all connections and supports back to structure. That should change the statics a bit and provide some relief. Just be certain that the glass doesn't support the handrail or act as a top-cap/guard.
regards,
Michel
RE: CBC Handrail Factor of Safety
RE: CBC Handrail Factor of Safety
Good luck,
Michel
RE: CBC Handrail Factor of Safety