Changes to Bridge Support Conditions

[Ipetu]

Existing bridge has pin - hanger hinges at two locations. Due to their inherent weakness, the pin-hanger details are to be removed by making the girders continuous at the hinge locations. Furthermore, bearings adjacent to the hinge locations have to be changed from fixed to expansion to accommodate the expansion / contraction capability lost by removing the hinges. Please see attached drawing. Original design had 3 fixed and 4 expansion bearings per girder line. Proposed design will have 1 fixed and 6 expansion bearings per girder line.

Assuming that the girder strength is not an issue, what are all the implications associated with changing bearings from fixed to expansion? One such effect would be that the longitudinal braking force is now resisted by only one bearing per girder line.

Thanks.

 

[yakpol]

Some of the items to check:
1. End piers expansion joints will have to replaced for larger movement.
2. Old expansion bearings need to be checked for larger movements.
3. Fixed pier will take majority of seismic force along the bridge.

Yakpol

 

[Ipetu]

Forgot to mention...there are no seismic forces to be considered at this location.

 

[BridgeEI]

You will have to check the piers for thermal effects as well. Out of curiosity, do you plan on redecking the structure or jacking the structure up, replacing the bearings & making the girder continuous at the hinges?

 

[chicopee]

The state of Ct. retrofitted all pin and hanger hinges with supports instead of doing what you are proposing.

 

[graybeach]

You should also check if stress ranges increase in the retrofitted structure.

 

[Ipetu]

Bridge EI,

Proposal is to jack at bearing location, replace bearings, disable pins, make girders continuous at the hinges and then re-deck.

 

[BridgeEI]

Thanks for the info, sounds like it could get quite messy but interesting at the very least. One other thought is if you're using elastomeric bearings, they will probably be quite tall due to the length of expansion. This may cause you problems w/ your abutment pedestals (not able to match structure depth & finish grade).

 

[huntley101888]

I know you said "assuming...girder strength is not an issue," but I just wanted to mention that making the beams continuous will cause the previously zero moment section of the beam to see moment. You'll likely need to add cover plates. I worked on a bridge a few years ago that was supposed to only be a concrete deck replacement. Since the bridge had a center span suspended by pin and hanger connections, we convinced the DOT to replace the entire superstructure (adding cover plates would have been too expensive on a bridge that was already 50 years old).

Alternately, you could add a support under the connection like I believe chicopee was referring to. I found a detail online:

http://www.pbworld.com/news_events/publications/network/issue_28/images/charter_fig3.jpg