Elastomeric Bridge Bearings with
Elastomeric Bridge Bearings with
(OP)
I am modeling a concrete deck/steel girder 4-span bridge for seiesmic response in the piers using GT-Strudl. So that I only need a single expansion joint, I am going to fix the superstructure at the third pier and use elastomeric bearings at the other 2 piers and 2 abutments. Using seismic design examples from Federal Highway Administration and from co-workers, I have assembled a model that reasonably approximates the bridge. Elastomeric bearings are modeled as springs. Results show that lateral translation of the superstructure is predicted to be 8" at one of the piers. To minimize this, I propose keeper plates that are placed 0.5" to either side of the elastomeric bearings. These will transfer lateral forces down to the pier.
THE QUESTION - How do I model this? What type of member should I introduce to the model to represent something that will transfer force only after it has deflected 0.5"? The only option that immediately comes to mind is to define the lateral elastomeric bearing restraint as a pin rather than a spring - not 100% accurate, but more conservative than what I have now.
THE QUESTION - How do I model this? What type of member should I introduce to the model to represent something that will transfer force only after it has deflected 0.5"? The only option that immediately comes to mind is to define the lateral elastomeric bearing restraint as a pin rather than a spring - not 100% accurate, but more conservative than what I have now.





RE: Elastomeric Bridge Bearings with
RE: Elastomeric Bridge Bearings with
Often times we have to model bridges with more than one model to encompass the overall seismic behavior. More proof of that statement maybe found in the FHWA and Preistly's book on the matter. Another area of concern is the abutment and the non-linear action there, first due to possible soil yielding and second is the tension/compression nature.
Another note is why the expansion joint within the bridge - this leaves a major substructure unit vulnerable. It would really be best to place the joints (if necessary) at each end at the abutment, where if something needs to be replaces its not impossible to do with regular maintenance workers. Joints at the piers will lead to premature aging of the pier or bent and may cause access problems for the workers if its over road could restrict traffic below.
Also, many states now use jointless bridges for lengths up to 600'. See Tennessee DOT.
RE: Elastomeric Bridge Bearings with
FHWA suggests keeping the bridge symmetric. The spans (85'-105'-105'-85'), however, are such that if the bridge were symmetric it would require a finger joint at Abutment B as well, therefore, the decision was made to fix Pier 3 in order to minimize potential thermal expansion at Abut B. The idea is that there is less risk of damage from an earthquake than from a failed joint.
We occasionally use jointless, but our guidelines recommend not to use integral for steel spans > 200'.
Thanks for your previous response.
RE: Elastomeric Bridge Bearings with
RE: Elastomeric Bridge Bearings with
Most bridges are layed out to have symmetry but most cannont due to anyone of a number of constraints. Hence, the bridge and spans are located such as to optimize where possible but not always. Mostly we consider the exterior to interior span ratios.
It also seems that finger joints as you noted are a bit much for this bridge and that some consideration should be given to the use of compression seals of 4.5 to 5" range.
Just some thoughts.
RE: Elastomeric Bridge Bearings with
RE: Elastomeric Bridge Bearings with