PSC Bridge Beam Bearings

[sponcyv]

I am working on a project where a stream was not located during preliminary design and did not get picked up until drawings were at 100%. We went back and redesigned the last 2 spans to create a 3 span condition to keep the piers out of the stream. When the bridge was 2 span, we had expansion joints at outer two bents and a fixed condition at the interior bent. When the 3 span was created, I left the two outer bents alone, but made the two interior bents fixed. I now have a condition where the beam ends are both in fixed holes, not expansion capable slots. This was commented on by the program director (a third party engineering firm hired by the local municipality to oversee the project). His comment reads "the beams have 2 fixed bearings, thus, not allowing the beams on this span to have any movement at all. This is a design issue, which should be addressed by the designer, not the beam fabricator. Bearing pads, pier, or even the beams may have to be redesigned or re-evaluated." Is it a no-no to have fixed conditions on both beam ends? I have designed my piers to take the thermal forces and I have provided large enough expansion joints to allow the deck to expand. Is it necessary to provided slots on one end of the beam to let the beam expand and if so, do I still need an expansion joint in my deck even if I checked the expansion of the bridge deck and I don't need another expansion joint?

 

[kelowna]

I have seen a number of bridges with more than one fixed pier. They were designed, as you say, for the piers to take the additional horizontal loading from thermal and the deck the additional compression. In one bridge, fixity in two piers was necessary to provide enough restraint to the deck given the poor geotechnical conditions.

Maybe you need to explain to him that you did consider this configuration on the design and the rational behind. As long as you can prove it works, it should not be a problem.

 

[Qshake]

Many bridges, typically small ones, less than 300 feet may have more than one fixed pier depending on the type of construction in that region.

The relief is provided by the flexibility in the pier and it is usually designed for the lateral loads.

If your piers were not designed for the lateral loads due to fixity then you should reconsider your design. If they were then respond to the owner that the condition is designed for.



Regards,
Qshake

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[paddingtongreen]

This is confusing terminology, does the interior span have fixed ends or pinned ends?

Understand that the Third party has the Owner's ear.If you want to defend your design, be prepared, not just to say that your design works, but why it is better, from design and from cost/benefit points of view, than one with an expansion joint at one end.

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