Study Of Incremental Launching Technology Of Space Arch Combination Bridges

Beam-arch association bridge is an important type of structures in modern urban construction. Owing to the beautiful shape and large span capacity, this kind of bridge has a wide application prospect. For building urban bridges, proper and reasonable construction method should be adopted considering the limitation of economy, site and environment. Incremental launching is such a method which could meet all the requirements. Although this method was first carried out half a century ago and the skills got mature by now, it was mostly employed in construction of beam bridges and not used in beam-arch association bridge as a unity. However, the popularization and application of steel arch-composite beam in bridges gives a chance for the steel structure of beam-arch association bridge to be increment launched as a unity, and this method was likely to be widely used. Based on the construction of Hangzhou Eighth Qianjiang Bridge, some issues were studied on the incremental launching of beam-arch association bridge as a unity.During the process of incremental launching, the cyclic change of tensile and compressive stress of the structure made the suspender unable to work, thus, temporary compressive bar was needed. By homogenizing the suspenders to solid thin plate, the unity of beam-arch association bridge could be seen as a solid-web variable section beam. According to the stress distribution on the solid thin plate under various constraint conditions, number and locations of temporary compressive bars could be determined.Design of nose of beam-arch association bridge was studied, taking length, stiffness and mass into consideration. Keeping the structure style and stiffness of main beam unchanged, the relevance between nose and main arch was proved. The nose of beam-arch association bridge could not be designed by the theory of designing nose for beam bridge, but should be analyzed specifically by optimization method.A finite element model of Hangzhou Eighth Qianjiang Bridge was established by degenerated solid element. With the help of this model, the incremental launching of the bridge unity was carried out and variation patterns of stress and displacement of beam and arch along the launching path were gained, so as to the patterns under representative loadcases. Analysis of axial forces of compressive bars during launching showed that the bars played an important role in the construction.After launching, temporary components should be removed and suspenders be stretched. This was an important issue for launching of beam-arch association bridge. The system transformation was analyzed and construction scheme was worked out. And also the optimal distribution of cable forces of suspenders after stretching was calculated.In the end, construction of the bridge decks of composite beam after launching was analyzed. By assuming the interfacial bonding between concrete deck and steel beam to be rigid at the construction stage, only self-weight to be count, and installed decks could carry load as part of the structure, three plans of installing the bridge decks were proposed. Among them, one was selected after comparing the cable forces of suspenders.