Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/506694
Eliminate approach 'end bumps' with new slab system Differential settlement in Louisi- ana leads to what are called "end bumps" at the approaches to bridg- es there, posing a safety hazard as well as being disruptive to motor- ists. But researchers at Louisiana State University say they've come up with a new construction design incorporating precast deck slabs paired with geotextile-reinforced approach embankments that will solve the problem. These bridge approaches, which connect the bridge deck to the adjacent pavement, are normally built with reinforced concrete slabs. The Louisiana Department of Transportation and Development, however, received complaints about the roughness of the transi- tion between the bridge abutments and embankments: "Field observations indicated that either faulting at the roadway pavement/approach slab joint (R/S joint) or a sudden change in the slope grade at the approach slab/ bridge joint (S/D joint, shown in Fig. 1) causes this 'bump'," say the research authors 1 . To solve the problem the LaDOTD considered changing the design of approach slabs where differential settlement is expected. The state wanted to fi nd a solution that makes approach slabs strong enough to allow them to lose a portion or all of their contact supports without caus- ing detrimental defl ection. "In this solution, the fl exural rigidity of the approach slabs is increased through increasing both the slab thickness and the rein- forcement ratio," the authors write. "Consequently, some embankment settlement will be allowed without decreasing the ride quality. As a result, the slab dead load and traffi c live loads will be carried by the two ends of the slab rather than distrib- uted over the length of the slab." Accordingly, the local soil pres- sures beneath the strip footing (or "sleeper slab") increase, resulting in an increase in the faulting defl ec- tion. This can be solved by use of road science | by Tom Kuennen EquipmentWorld.com | May 2015 41 TRB: NEW RESEARCH CHANGING HOW YOU WILL BUILD BRIDGES For more information about the 2016 meeting, or to obtain the full papers, visit www.trb.org. E liminating the "end-bump" in construction of bridge approaches ... precast deck pan- els speeding bridge construction ... quick seismic retrofi ts for bridge piers ... and how rockets can speed construction of suspen- sion bridges in isolated areas. Each of these topics will change how bridges will be built in the future, and they were among the themes in bridge design and construction that were presented at the 2015 Transportation Research Board meeting. 1 Mitigating the Bridge End Bump Problem: A Case Study of a New Approach Slab System with Geosynthetic Reinforced Soil Foundation, by Qiming Chen, Ph.D., P.E., and Murad Y. Abu-Farsakh, Ph.D., P.E., Louisiana Transportation Research Center, Louisiana State University, Baton Rouge. Fig.1: Illustration of approach slab and its interaction with soil in Louisiana. Image: Chen and Abu-Farsakh