Semi intergral end screen wall

[RME1]

Hi,

I am designing a semi integral bridge in the UK. It is a 2 span bridge (both spans approx 30m), with fixed bearings at the central pier and free bearings at the abutments to allow for expansion.
The deck is continuous steel plate girder with a RC deck slab. At the ends of the bridge the deck continues round the ends of the girders to form an end screen wall (i.e. the ends of the girders are protected by a continuation of the deck, perpendicular to the carriageway surface above.)
This end screen wall projects about 2-2.5m into the embankment, so it will retain some earth and will therefoe be subjected to associated earth pressures. I'm also concerned about the forces on the wall from thermal expansion of the plate girders.
Does anyone have experiance designing a similar detail?

 

[bridgebuster]

Hi,

A few years ago I worked on a similar type bridge - the "end screen", or as we called it the "end diaphragm" or "end block", was 2 meters deep. We took a simple design approach: Case 1 - earth pressure loads; Case 2 - wheel load + self weight. Minimum reinforcement controlled. We didn't bother to include a thermal force in the end block.

 

[RME1]

Thanks for your response.
Most of examples I've seen have a vertical plate welded accross the ends of the girders, with shear studs on the other side going into the end block. I'm not sure if this is just a 'good practice' detail or if there are any design calculations behind it. Did you include a similar detail on your design or were your girders actually cast into the end block?

 

[Qshake]

Even an integral steel bridge will likely have a end crossframe for the purpose of construction stability that will be encased in concrete.

As such I don't such a plate is really necessary for the final arrangement but if I were to place such a plate I can see the point of making sure it is composite with the end diaphragm (screen wall).

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[MichSt]

Most, if not all, details I know of for integral abutments are ‘good practice’ or empirical type details. In the US each state has its own way of going about detailing integral abutments based on their own experience with them. There are not a whole lot of hard, well established design procedures that I know for these type bridges.

For thermal expansion, you’re girders will push the ‘end screen’ in to your fill. This may or may not mobilize full passive pressure from the soil, but typically you will just be conservative and design the concrete for full passive pressure. That will take into account the thermal forces in your concrete design.

As for details, here’s one detail that I have seen used:

http://www.dot.state.oh.us/se/standard/english/revisions/07-19-02 mailing/pdf/2002cms/icd182.pdf

Also, the reinforcement in the ‘end screen’ is typically continued through drilled holes in the girders. If you have a skew, make sure the holes are oversized enough to fit the skewed rebar.

 

[yakpol]

Some engineers design end diaphragms for lateral earth pressures as a continuous beam spanned between the girders. In the case of steel girder expansion it will be passive pressure...