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24 CHAPTER 4 CONCLUSIONS AND SUGGESTED RESEARCH 4.1 CONCLUSIONS It is feasible to integrally connect reinforced concrete columns to box-beam pier caps by extending the column lon- gitudinal reinforcement through holes in the pier cap flange and filling the pier cap compartment directly above the col- umn with concrete. The resulting connection is sufficient to develop the plastic hinging of the column, given that anchor- age adequate to fully develop the column longitudinal rein- forcement inside the pier cap is provided. The first test spec- imen, which had a deeper pier cap and longer anchorage length of the column longitudinal reinforcement, reached a ductility of 嵉 = 6.0 before failure. The second test specimen, with a shallower pier cap, reached a ductility of 嵉 = 4.0 before failure. The failure at this lower ductility essentially resulted from the loss of bond between the col- umn bars and the concrete in the integral connection region. Integral pier connections are most likely to be used for bridges with high skew angles and are supported on single- column piers. The use of the integral pier connections results in lower elevation of the bridge deck and the approaches with- out reducing the bridge underclearance. The cost of bridges with integral connections is expected to exceed conventional bridges; however, because of the lower approach elevation, the combined cost of the bridge and the approaches is expected to be lower than that of a conventional bridge. Extending the column spiral reinforcement into the con- nection region is required to ensure adequate confinement of the connection region. The required spiral reinforcement in the connection region may be taken as the greater of the min- imum spiral reinforcement required by the design specifica- tions and one-half the required column spiral reinforcement next to the integral connection region. The live load distribution factors in the current design specifications, which were developed for use with bridges supported on conventional bearings, may be used for bridges with integral connections. Using grillage models to analyze bridges with integral connections is expected to yield high accuracy. 4.2 SUGGESTED RESEARCH Parametric studies to further verify the simplified analysis method for typical structures as included in the proposed design specifications is needed. Some of the parameters that need to be included are the skew angle, variation in adjacent span length, number of continuous spans, and number of the girders in the cross section. The shear connectors on the outside of the bottom flange of the pier cap may complicate construction. Testing to prove that the column longitudinal reinforcement is sufficient to transfer the column shear force to the connection region is needed.
