An innovative steel-concrete joint for integral abutment bridges

Integral abutment bridges are becoming rather common, due to the durability problems of bearings and expansion joints. At the same time, among short- and medium-span bridges, multi-beam steel-concrete composite deck with hot-rolled girder is an economical and interesting alternative to traditional pre-stressed concrete solutions. The two concepts can be linked together to design integral steel-concrete composite bridges with the benefits of two typologies. The most critical aspect for these bridges is usually the joints between deck and piers or abutments. In this paper, an innovative beam-to-pier joint is proposed and a theoretical and experimental study is introduced and discussed. The analyzed connection is aimed at combining general ease of construction with a highly simplified assembly procedure and a good transmission of hogging and sagging moment at the supports in continuous beams. For this purpose, the traditional shear studs, used at the interface be- tween steel beam and upper concrete slab, are also used at the ends of steel profiles welded horizontally to the end plates. To better understand the behaviour of this kind of joints and the roles played by different components, three large-scale specimens were tested and an FE model was implemented. The theoretical and experimental results confirmed the po- tential of the proposed connection for practical applications and indicated the way to improve its structural behaviour.

The optimal shapes of piles in integral abutment bridges

Integral abutment bridges （IABs） can be used to avoid the durability issues associated with bearings and expansion joints. For this type of bridge, the design of the optimal pile foundation, especially with respect to the horizontal stiffness, is a challenging issue. A structural optimization approach is proposed in this paper to optimize the pile foundation shape in integral abutment bridges. A procedure was implemented based on linking MATLAB, where an optimization code was developed, and OpenSees, which was used as the finite element solver. The optimization technique was compared with other techniques developed in previous researches to verify its reliability; the technique was then applied to a real 400 m-long IAB building in Verona, Italy, as a case study. The following two possi- bilities were considered and compared： （a） a pile with two different diameters along the depth and Co） a pile with a pre-hole. In fact, to increase the lateral and rotational flexibilities of the pile head, piles for an integral abutment bridge foundation are often driven into pre- deep holes filled with loose sand. Finally, the case of super-long integral abutment bridges （L = 500 m） with a corresponding displacement on one bridge end of approximately 50 mm was analysed. The following four pile design optimization eases were considered with similar study criteria as the Isola della Scala Bridge： （a） a pinned pile head for semi-integral abutment, Co） a fixed pile head without a pre-hole, （c） a fixed pile head with a pre-hole of any depth, （d） a fixed pile head of a pre-hole with a depth limit （〈 2 m） allowing for enoughembedded length for the friction pile. The case studies confirmed the potential of the proposed optimization techniques for finding the optimal shape of piles in integral abut- ment bridges.