Example calc of Differential Temperature on bridge deck 1

[blihpandgeorge]

Hi

I am looking at analysing a simple support beam, released axially at one end, under differential thermal loads from AS5100. The beam is for a pedestrian bridge, it is a composite 1200WB249 with a 200 slab spanning 28m.

I can derive the temperature, but i am looking for a sample calc to show how to take the temperature load and how to convert these into design actions i can then add to other loads such as dead / live etc.

Can anyone provide any advice?
Thanks
Blihp

 

[bridgebuster]

For a simply supported beam under the conditions you are describing, there shouldn't be any temperature forces taken by the beam. However, you do need to know the range of motion to design your joints and bearings.

 

[rapt]

Bridgebusted,

There could be some stresses induced if the temperature profile has any discontinuities in it or does not reach full depth.

blihpandgeorge
If you are design a bridge like this, you should have a good text book on it. Read it.

 

[blihpandgeorge]

thanks bridgebuster, what you described is what i was hoping but having a very asymmetric temperature distribution was making me second guess this. I believe this is because with an induced strain, there can be no corresponding stress unless there is restraint?

how do account for the longitudinal stress on shear studs by the induced curvature?

 

[blihpandgeorge]

hi rapt - can you recommend a text that is based on Aus Standards? I mainly works on buildings (and these don't deal with temperature effects well) and thus don't have too many bridge texts

thanks

 

[bridgebuster]

See attached, which might be of some help; I found it in my files. It's from the mid-80's; looks like it was originally published by AISC.

Again, for a shallow steel bridge I don't see any point in a thermal analysis; even the current AASHTO specs leave wiggle room. However, from the paper I posted that's how it's done Down Under.

 

[IDS]

It is standard practice in UK (and I presume now Eurocode) and Australian bridge codes to include differential temperature effects in pretressed concrete and composite bridge deck design for stress.

The procedure in outline is:
1. Calculate the stresses that would be induced if the section was rigidly restrained against longitudinal strain.
2. Calculate the force and moment that would be induced by these stresses.
3. Calculate the stresses on the composite section due to application of the negative restrained force and moment (which restores longitudinal equilibrium after removal of the imaginary rigid restraint).
4. Add 1 and 3.

Hambley's "Brick Deck Behaviour" has a chapter on it.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[blihpandgeorge]

Thanks Bridgebuster and IDS for info, i also found this website that also mirrors your advice.

Link


Cheers
Phil