Study On Old Bridge Strengthening In Transforming Simply Supported Into Continuous System By Self-stressing Method

Simply supported bridges are designed to function over long periods of time in China. The incidence of structural deterioration increases with bridge age due to traffic development, such as bearing capacity decreasing, and design capacity shortage. Transforming simply supported into continuous systerm is a feasible way to strengthen the old simply supported bridges in order to enhance the bearing capacity, extend the service life of the bridge and save the maintaining expense. But the concrete in the longitudinal joints and the negative bending moment areas is easy to crack due to the lardge negative bending moment. Once the rain water and Cl~- enter the bridge through the cracks, it's a hidden trouble to the durability and security of the continuous bridge. So there are an increasing need and a great challenge to search a feasible material and deduce a logical calculated method for old bridge strengthening with this material.Steel fiber reinforcement self-stressing concrete (SFRSSC) is a new type of fiber reinforced composite. The tensile strength of the concrete can be extremely improved by the chemical pre-stressing, which is caused by the restricted expansion of SFRSSC induced by steel bars and steel fibers. The combination of the steel bars, steel fibers and self-stressing concrete enhances the crack resistance, tensile performance, flexural toughness, impact resistance and durability of the composite, and make SFRSSC a wonderful strengthening material to the old bridge rehabilitation. The research on SFRSSC mainly concentrates on reinforced mechanism and mechanical properties. However, there is no literature on structural properties and bridge strengthening applications.Therefore, based on the Liaoning Province Communication Department Key Science Foundation Project (No.200514) Strengthened Technique and Construction Craft of the Continuous Beams after Continuing Simply Supported Beams by Exerting Prestressing Loads, this thesis will focus on the following aspects:1. Based on the experimental investigation of the strengthening materials containing SFRSSC, steel fiber reinforced concrete (SFRC), Polypropylene fiber reinforced concrete, large diameter synthetic fiber reinforced concrete and hybrid fiber reinforced concrete, the mix proportion, the working performance, the fundermental mechanical property and durability are evaluated. The experimental results show that SFRSSC is validated to be a promising material in the longitudinal joints and the negative bending moment areas, satisfying the engineering requirements of the bearing capacity, crack control and durability;2. Based on the experimental observation of SFRSSC during 9 years, the long-term restricted expansion performance is studied. The long-term restricted expansion curves and calculated method of self-stressing loss are given;3. Based on the model experiment of 9 composite concrete inverted T-beams, the crack resistance and flexural performance of SFRC and SFRSSC in negative bending moment areas are evaluated. With the experimental results, the formulas to calculate the self-stressing and crack resistance of the layers are deduced;4. Based on the model experiment of 10 continuous composite concrete T-beams, the deformation, cross-section strain, crack and new-existing concrete bonding are observed. The influence of pre-damage on continuous beams flexural performance is researched and a method to calculate the crack resistance and bearing capacity under ultimate phase of the continuous composite T-beams are carried out;5. Based on the computer analysis, the influence of SFRSSC on the internal force of continuous T-beams are studied. The restricted strain range and the appropriate position of SFRSSC in continuous bridge are deduced for references in bridge strengthening design.