AASHTO Pedestrian Guardrail Service Load Combination 2

[BS2]

Please excuse my relative lack of experience with AASHTO load combinations. I am being asked to include checks for a service limit state in addition to the strength load combinations for a typical pedestrian guardrail. I have not been able to find what this includes besides a load factor of 1.0 instead of 1.75. I would appreciate it if someone could point me in the right direction.

Thanks!

 

[bridgebuster]

Are they asking for Service II? If so the load factors are 1.0 for dead load & 1.3 for live load & impact.

 

[BS2]

Thank you for the response!

This is their exact quote: "These checks appear to apply to strength only. Please include checks for the service limit state."

If the load factors are 1.0 and 1.3, what do I need to check at these levels? Deflection?

I am already applying a 1.75 load factor for strength on a 530 lb pedestrian guard rail load. I can't imagine that there is a serviceability problem with a pedestrian guardrail designed for 930lb but I want to make sure I am doing all of the checks.

Thanks again!

 

[bridgebuster]

The Service II is check for slip critical connections at yield. The LRFD railing specs only require Strength and Extreme Load checks.

 

[BridgeEI]

Agree with bridgebuster. If it’s concrete you would need Service I for crack control or if they’re asking you to check deflection. Other than that you should only need to check the combinations bridgebuster suggested.

 

[BS2]

Thank you bridgebuster and BridgeEI!

I read through the sections I thought were applicable but couldn't find any service requirements. I didn't think to look under slip critical connections as I don't have any.

Thanks again!

 

[BridgeSmith]

I concur that there are no service load combinations for steel pedestrian railings in the AASHTO spec.

The way we read the spec, the 200lbs and 50plf railing loads are the "design loads" as stated in Section 13.8.2, and in accordance with Section 3.6.1.7, no load factors are applied to those loads. Bridgebuster and BridgeEI, is that how you read the provisions?

 

[BridgeEI]

HotRod10 - I’ve always factored them but I see your point. My argument would be AASHTO calls it a “design truck” and we factor it. It’s vague enough I could see the argument either way.

BS2 - As a FYI, if you look at 3.4.1 it gives a description of each load combination limit state and what it’s intended for. I know designers that will run every combination even though they aren’t applicable to the description given by AASHTO.

 

[bridgebuster]

Hotrod10 - I read the spec as requiring load factors because the spec also requires resistance factors. If we don't use factors then it's a working stress design (which would suit me just fine). The Standard Specs used 200/50 loads.

 

[BridgeSmith]

I read through what I think are all the applicable provisions in AASHTO, and I'm still not sure whether to factor the railing loads. Is my understanding correct that in the other US codes, there were not load factors applied to the 200lbs + 50plf? If so, I would think the AASHTO loads would be consistent with the others.