HS-20 loading on a 3D space structure bridge grid

[Meesamali512]

Dear All,
I am working on a model of 3D space structure for bridge span. The space structure will ultimately support the bridge slab for taking various loadings. Structure is modeled in STAAD and the members are tubular with 2mm wall thickness and 20cm squares in plan. I have attached a model picture as an attachment here. Now I want to apply a traffic load i.e. HS-20 to verify whether or not the structure is adequate enough to take this load. Can anybody help me how to apply this HS-20 loading i.e. on what part of structure and how much exact loads with separation in-between?
Any help is appreciated.
Regards

 

[bridgebuster]

We need more to go on. Is this a simple span or continuous? If it's a simple span, for maximum moment put the center axle at the centerline, unless your a purist then the axle is about 2' from the CL. One line of wheels is placed 2' off of the barrier; the next line is 6' away; if you're putting another truck next to it the first line of wheels will be 4' away.Then you have to distribute the wheel loads and add impact.

For maximum shear put an axle at the end.

 

[Meesamali512]

Hi Bridgebuster,
thanks for the response. Width is very less and is 2.4m. Length of one span is 6m. Right now i have modeled the frame elements (i.e. 3D truss) and the actual load will come on slab which will cover the 3d grid. But i am NOT modeling slab right now. So how can i apply the load accurately on bridge grid? To make it more clear, if you look at my post as an attachment then you see that its an open hollow structure in plan view with lots of nodes of 3d grid. Which nodes should i apply the load and much better if somebody can mention how much exactly to match HS-20 specification?
Much appreciated.

 

[bridgebuster]

At 6m you'll never have more than 2 axels on the bridge. Doesn't STAAD have a moving lad feature? At your width all you can do is run one truck over the bridge.

I'm sure you have your reasons but why go to all this trouble modeling a bridge like this? There are standard designs you could have used.

 

[Meesamali512]

Hi bridgebuster,
Actually this project is related to a research project where we are trying to find out optimum usage of space structures as they have lesser weight and are easier to construct / assemble. I just wanted to do analysis to find out main forces and compare with some other models. Still thanks for the response and will try to check them out.