Submitted by DonHester on Sat, 05/03/2014 - 18:36.
Reflection on Deflection for Guardrails, it is much tougher than we think.
Q: How do we know what is the acceptable deflection for guardrails?
A: There is no standard acceptable deflection.
We have design standards, the requirement of 200 lb concentrated load as described in R301.5. But there is no standard acceptable deflection.
So what is the test? Well to achieve a 200 lb concentrated load they use 2.5 (500lb) safety factor to test the assembly (for glass rails the safety factor is 4). This is based on defined testing procedure from the International Building Code (IBC).
(Glass Guardrail deflection with minimal pressure)
So based on this criteria it was found that most common guardrail assemblies most likely do not meet the requirement defined by the code.
Per Simpson Strong-Tie "The railing connection is a crucial deck connection, and it is often inadequately constructed. In order to provide the required load resistance at the hand rail, the post must not only be fastened to the rim joist, but also be tied back into the joist framing. Machine bolts or lag screws through the post and rim joist alone do not typically meet the performance requirements of the building code. " Link to Strong-Tie PDF - Code Compliant Guard Rail Post Connections
The 200 lb. point load requirement in the code is not new. Research and testing conducted at Virginia Tech on post-to-rim-joist connections indicated common bolted or lag screwed connections to a rim joist alone did not meet the load requirements in the code.
So what does this mean for us as Home Inspectors in the field inspecting deck? We need to be extra careful of our evaluations. If nothing else presenting proper information to our client so they can make informed decisions when it comes to deck guardrail requirements.
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