Combined Wind Load and Live load on Handrail Systems 1

[JDV22]

I am looking for some guidance on load combinations for a rooftop guardrail system. The railing consists of 5'-0" wide shoe mounted glass panels with a continuous top cap. ASCE 7-10 ASD load combination 6a indicates that when combining wind load to live load, you can use 1.0*D + 0.75*L + 0.75*(0.6*W) (unless another LC controls). With these parameters in mind, my question is: Has anyone come across anything in the code that allows me to not combine the required railing live load with the wind load? I would imagine that nobody would be on the roof during a major wind storm event.. but I can also see that if they do happen to be on the roof, that guardrail would be pretty important!


Thanks for any insight and advice!

 

[Stenbrook]

What are the chances that you have full wind load (a hurricane!) and someone is on the roof? very low I would say. Design for live load or wind load. See what is worse.

 

[msquared48]

I would also argue that the two loads could be working against one another rather than in the same direction.

Mike McCann, PE, SE (WA, HI)

 

[EZBuilding]

The High Velocity Hurricane Zone (applicable in Broward and Miami-Dade County) section of the Florida Building Code has the following section which provides some consideration for this topic.

1620.4
For wind force calculations, roof live loads shall not be considered to act simultaneously with the wind load.

Even based upon this, one could argue that the railing load is a live load and not a roof live load.

This is one of those situations where meeting the intent of the code conflicts with the written letter of the code. If you don't design for the combined forces a lawyer and their expert witness would gladly charge 5x your billing rate to tell you that you did not meet the standard of care. If you do design for the combined forces you will rack your brain trying to make standard connections work and your client will likely find a new engineer.

I would not consider both forces acting simultaneously.

 

[JDV22]

Thanks for the insight everyone!

msquared48: Per ASCE, the railing load must be designed to act in the direction resulting in the greatest impact to the rail structure, so I cannot make the argument that they would be acting in opposite directions from one another.


EZBuilding: Thanks for the code reference! I feel if any argument can be made to take the greater of the wind load and live load rather than the combination of the wind load and live load, its 1620.4. I'm assuming that is a local code, but it has to reference IBC somewhere so I will dig that up.


Thanks again everyone!!

 

[EZBuilding]

JDV22:

The high velocity hurricane zone is applicable only to two counties in the state of Florida. A project a mile away in a different county would not be required to meet the provisions of this section of the code.