Arch Bridge

[lnavarro]

I am now learning to use STAAD to load rate arch bridges.
Does anyone have a tip on how to model the arch in STAAD? Is there a way to import from Microstation? Or is creating several grids with different dimensions the only way to do it?

Thanks.

 

[edward1]

Inavarro,
Is the arch a slab or beam with vertical posts supporting deck (open spandrel)or beam with solid plate supporting deck (closed spandrel?

 

[lnavarro]

It is a closed spandrel stone arch. I think the best way is to draw it in Microstation and set a coordinate system and then type the points on STAAD.
Any other tips on how I should do it?

Thanks!

 

[edward1]

Does this file look like the bridge?

 

[lnavarro]

Yes, but I'm going to create a 2D model to get the member forces.
I see you have the arch members and a grid that doesn't look like members with several supports. Why did you do that?

Thanks!

 

[edward1]

I modelled the entire bridge with plates in order to get a more accurate distribution of the truck wheel loads in the structure instead of using S/6 for the distribution factor for a two dimension structure modelled with beams.

 

[lnavarro]

How can I model the fill between the deck and the arch? Or should I neglect that and apply all the loads directly to the arch?

Thanks for you help!

 

[edward1]

It sounds as if you have a CONSPAN arch bridge. This design depends on the soil structure interaction for the live load distribution. The fill height varies from maximum at abutment end to minimum at midspan. The dead load will vary by height x soil density. The live load will be distributed over a width = 1.75 x fill height for LFD or 1.15 x fill height for LRFD. So you can model the bridge with beams 1 foot wide by thickness of arch and put a trapezoidal load for the dead load and put several different wheel loads at axle spacing divided by the distributed width on this location until you get maximum moment (at midspan) and maimum shear (at arch depth from abutment breast wall).

 

[lnavarro]

That was very helpfull, thanks!
Can I apply the distributed wheel loads directly to the arch or do I have to model top of deck members?
Is there a way to define a moving truck load or do I have to add the loads manually at different points?

 

[edward1]

Inavarro,
Attached is some output from BRASS-CULVERT for 2 feet fill using LFD for HS20 Truck. This shows the axle loads, spacing, impact and distribution factor to multiply by the axle weights to get loads on 1 foot width of arch bridge. I put loads on arch member model as different loads until I got maximum moments on center member since the arch was not in same vertical elevation. Once you get maximum live load + impact, dead load, and moment capacity of center member you can rate arch for moment.
Ed

 

[lnavarro]

I now have a bridge with concrete arch beams. Do you know how I can load rate those?
Thanks!

 

[edward1]

Rating Factor for reinforced concrete at operating level=
(Mu/1.3-Mdl)/Mll+impact. Mu= Moment Capacity, Mdl= Moment due to Dead Load, Mll+impact= Moment due to Truck + impact. After you calculate Rating Factor multiply this by the weight of particular truck. For example assume RF= 1.45, then capacity of bridge for HS20 truck would be 1.45 x 36 tons = 52.2 tons