BRIDGE DESIGN 2

[cdous]

A two span conrete bridge (20m+20m)(solid slab as deck continuous over pier and momolithically casted with abutments) is to be checked for seismic loads. The rigid deck model is to be used, Eurocode states that the earthquake effects shall be determined by specifying aa horizontal static force on the deck.
F=M*Sd(T)
The structure has been modelled in 3D by Finite Elemets
The force is to be applied as a distributed force over the whole deck? Is this ok or do I have to apply it first between span A1-M1 and then between span M1-A2.
Don't I have to aplly the imertia forces to the abutments?
Thanks

 

[paddingtongreen]

I can't help with your question but I don't know of any bridge that is cast monolithically with the abutments. Who would do that?

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[cdous]

I was writting in a hurry..monolithicalyy referred to a proper rigid joint i,e portal frame. As the bridge serves a spillway the requirements/specifications were for no bearings

 

[bd96]

I've seen some decks cast monolithically with abutments, providing a moment connection at the abutment.
You'll want to apply your seismic force to the whole superstructure. Codes in NZ define the seismic weight as the superstructure plus half of the exposed substructure. Rather than applying hundreds of distributed point forces, you might apply the seismic force as a horizontal acceleration in the same way you apply gravity to the model. This won't be exactly right, but it won't be far off either. Both spans should receive the seismic forces.
Hope this helps you get started.

 

[graybeach]

You will make your self crazy doing this with 3D elements. I would use a single line of elements with each one representing the full width of the structure, and I would make sure the supports reflected reality. The results will be 1000 times easier to interpret and easier for someone to check.

 

[cdous]

The reason i want to model it 3-d is to get realistic results due to temperature effects i.e shrinkage, uniform contraction due to temperature fall, deck temperature difference e.t.c.
This type of bridge although is a good and solid structure regarding earthquake, it is is vulnerable to stress arising from temperature effects.
The servbiceability state may and is actual be more crucial than the ultimate state
Actually I have done many underpasses (one spam frames) the way you describe it graybeach.
However I usually solved with finite element the top slab.
Then I would solve the portal frame with 1m width.
The live loads would be concetrated over that one meter width but the loading would be multiplied by the ratio of the value obtained form the slab analysis dibvided by the moment obtained for the 1m width frame.
This was made in order to simulate the "slab" effect.

 

[bridgebuster]

It sounds like you want to construct a two span rigid frame, which are normally designed as a one foot (305 mm) strip. They're not difficult to design.

 

[graybeach]

I might not even use a computer, well maybe to find the live load moments and shears.

For an transverse equivalent static EQ, I would just put half the deck on the middle pier, and a quarter deck at each abutment, applied at the mid-depth of the slab. I'd put the weight of the pier and abuts at their CGs. Then I would calculate a moment at the foundation. For longitudinal EQ, I would just apply the equivalent long. static force directly to the fill.

Might use a computer for differential temperature, but I'd still use one line of beam elements. For constant temperature, alpha* delta t*L.

I think you are going to have a hard time getting usable forces using solid elements. Are you modeling the cracks and the rebar?