Bridge Requirements for Commercial property

[NFExp]

I designed a 5 timber bridges for a resort developer. The bridges are 2 lane and 60-100ft long with 1 bridge 1300feet long. The bridges are about 4-6 feet high, over wetlands. I designed the bridges with an HS20-44 loading and a crash tested guardrail (as originally requested). The pricing came back about 5 times what they had budgeted and they are asking me to reduce my loading requirements..

I think that I can reduce my loading to a H-20 loading but I am having trouble finding the minimum loading for a bridge over commercial property and what is the minimum requirement for a guardrail. The client is asking me to reduce my guardrail considerably

Before I walk away from this project, I curious to what everyone's opinion is regarding the loading and guardrail requirements.

 

[bridgebuster]

Regarding the live load, check with AHJ regarding any requirements they have for an emergency vehicle (EV). There are EV's that weigh more than the HS-20 truck.

Regarding the barrier, check with your state DOT for loading requirements. In NY, TL rating for barrier and railing is based on AADT.

Edit - fixed typo

 

[BridgeSmith]

I think if it's privately owned and on private property, I think the owner can decide what load to design for. If it doesn't have a satisfactory rating for the HL-93 loading, the owner will be required to post load limits, if it's accessible to the public.

As far as the railings, the Test Level (TL) requirements are based on the size of the vehicles and the design speed (maximum posted speed will be dictated by design speed). Especially for a timber bridge, meeting the capacities required for railings 'by the numbers' can be difficult, but the alternative is a crash-tested system that has proven adequate in the real world. Our steel tube-type railings perform far better in the real world than the analysis would predict. I suspect that would be the case for a railing for a timber bridge, as well.

I suggest contacting your state's Bridge division at the DOT, for specific information regarding the loading and railing requirements.

Also, you may get more relevant input if you have this thread moved to the Bridge Engineering forum. Sorry, I'm not sure how to go about that.

 

[SlideRuleEra]

Review US Forest Service "Standard Plans For Timber Bridge Superstructures" as a guide for minimum design.

 

[JStephen]

Consider dump trucks, cement mixers, and trucks hauling trackloaders, etc. into the site during construction.

 

[EdStainless]

And for the future will emergency access be needed, say by firetrucks?

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P.E. Metallurgy, consulting work welcomed

 

[JStructsteel]

Push back. You dont want to design this for less than HL93, due to construction loading, EV, etc.

The issue is the material. Are you clear spanning 130 feet with a wood truss? Steel or concrete would be desirable in this case. You can add timber to give the look you want.

 

[JoelTXCive]

I think that if it is private property, the owner can direct you to design for whatever loading they specify.

The local fire department might refuse to drive over the bridge, which might cause insurance issues for the property owner. I've seen that happen in Texas. Property owners cannot purchase insurance because the fire department will not respond to the property.

If the owner's want to design for less than the HS-20 loading, then I would definitely get something in writing showing that they directed you to design for a specific load. I would also make sure you clearly state the loading assumptions on the plan sheets.

 

[JoelTXCive]

Another idea is a pre-fab bridge with wood aesthetics. Maybe the client could be sold on that. This cuts into your design fee, but might be better than nothing if you are about to walk away from the project.

We have private developers that prefer the pre-fab units due to their speed and cost. We still set up the plan & profile, and then design the abutments. The rest is turnkey from the pre fab bridge company.

Contech has weathered steel units with wood aesthetics that look pretty nice.

 

[dik]

The minimum load I would design it for would be for safety vehicles, such as fire trucks. If the client doesn't want that, I would suggest he find another engineer.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[NFExp]

Thanks all for the responses. I previously suggested the pre-fabricated bridge so I'll mention that option again..

 

[jorton]

I second JStephen. Concrete trucks can exceed H20 loading. I'd be hesitant to design for less.

 

[JLNJ]

If the original cost is 5 times the budget, you probably won't be saving a significant amount by skinnying down the design loads. It sounds like the Owner's problems are bigger than just the capacity of the bridge.

 

[driftLimiter]

Agreed