All bridge beams are initially chambered upward, and then they flatten out as the deadweight of the bridge deck is added. Pre-stressed concrete beams have a much more noticeable chamber initially than steel beam because the lower part of the beam is pre-stressed into compression. Even after the deadweight is applied concrete beams will retain some chamber since they design the pre-stress high enough to ensure the bottom of the beam is always kept in compression (concrete cracks with just a slight amount of tension).
Since the beams will retain chamber after the deck is applied, when they pour the decking they pour a variable thickness "haunch." The haunch is basically the concrete that connects the deck to the beams. If you closely look at the underside of a concrete beam bridge you can easily see this variable thickness between the beams and the decking.
Basically every other state requires the engineers to do the haunch thickness calculations and put them on the drawings. Oklahoma, however, leaves it up to the bridge construction company. Not only are these calculations fairly complicated for the non-engineers, the state further ties their hands by limiting the min/max thickness range. So even if the contractor did the calcs perfectly, they may still not be able to create a smooth bridge.
Each hump you feel on these bridges is one beam span. The Creek Turnpike South Loop in Tulsa has this problem in a big way too. But it is an issue all over the state. Notice that Texas uses concrete bridges all over the place, including a lot of the new I-635, not a single one has this issue because the engineers do the haunch calculations.
More info:
http://uknowledge.uky.edu/cgi/viewco...ontext=ce_etds
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