Testing of Pile Extension Connections to Slab Bridges
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The California Transportation Department (Caltrans) has a large number of highway bridges; and many of them are slab bridges. Although slab bridges are a common type of bridge, the current version of the Bridge Design Specification and the Seismic Design Criteria provide limited design guidance for pile extension connection details for slab bridges. Unlike the column to box-girder bridge connections which have been discussed and tested extensively, slab-bridge connections have not been tested. The objectives were to develop standard details that can be used to update the existed details for the slab bridge joints and to establish design procedure for the joint regions with and without drop caps. To accomplish these objectives eight large-scale pile-slab bridge connection specimens (16-in. diameter piles) were tested under cyclic loading at the University of Nevada, Reno (UNR). The first two specimens were based on the existing Caltrans specification. The primary difference was that one specimen had a flat-slab detail while the second specimen had a drop-cap detail. The remaining six specimens were based on 24-in. diameter piles. Since there are no standard details for 24-in. diameter piles, box-girder design methodology was used. Both the drop cap T-joint and Knee-joint with the 24-in. diameter piles had plastic hinging in the pile. The flat-slab T-joint and Knee-joint both did not perform well with failure in the slab. From the experimental visual observations and the reinforcement strains recorded for 24-in. pile specimens, strut-and-tie models (STM's) were used to develop the last two specimens. The modified specimens performed well and provided the basis for revised design methodology and standard details for the connection of larger diameter piles in slab bridges. Overall the results have shown that the specifications for the box-girder design are good for slab-bridge joints with some modifications. Guidelines for the modification of the slab bridge joints are discussed in detail.
Report No. CCEER-10-06