Experimental Research On Hooping Strengthening Technique For Existing Reinforced Concrete Arch Bridge

Bridge structure is the controlling engineering of the entire transportation network. To ensure the safety of bridge structures is of great social significance and economic value. There are many deterioration problems of the early built reinforced concrete(RC) arch bridge, such as aging, poor integrity, lower capacity, and so on. Because these bridges can not meet the needs of local transportation and economic development, they must be strengthened in order to increase the load carrying capability and traffic capacity. The hooping strengthening technique not only can resolve defects and deterioration problems of existing reinforced concrete arch bridge, but also can improve integrity performance and increase carrying capacity. However, research either domestic or oversea about the calculation theory and its failure mechanism and characteristics of hooping reinforced composite section is less. Considering above all. combined the sub-research of "the study of the repairing and strengthening method for existing bridge" with the fund supported by the Ministry of Education, several aspects were mainly concerned with as following:1. Based on the research of previous studies and data collection, and combined the on-site bridge inspection, evaluation, and strengthening work that the author has engaged in. the status of deterioration problems for the existing reinforced concrete arch bridge were summarized, and the generating mechanisms were analyzed. Those can provide reliable technical information for the future design, maintenance and strengthening of the similar structures. At the same time, the related deterioration problems resolved by the hooping strengthening technique were pointed out, which leads to the necessity of the research about the hooping technique strengthening existing RC arch bridge.2. Aiming at the technical selection problem appeared frequently in the bridge strengthening about the young-old concrete interface treatments between bonded rebars and grooved.6groups of specimens were made to compare with the shear performance and failure modes of the young-old concrete interface. The test results showed that the young-old concrete interface shear strength of the specimens which embedded steel bars was distinctly stronger than that of the slotted specimens. And the failure characteristics of specimens which embedded steel bars are ductile, but the failure characteristics of specimens which slotted are brittle. For the case of bonded rebars treatment, some amendments on the shear bearing capacity formulas were executed. The bonded rebars ratio of the young-old concrete interface was discussed. And some reasonable suggestions of young-old concrete interface treatment were proposed. 3. By use of the proposed suggestions about young-old concrete working together in the third chapter, and considering the different influence factors.8groups with25column specimens were designed and manufactured. The failure tests and nonlinear FEM analysis of the RC hooping strengthening columns were executed. It verifies that the proposed suggestions about young-old concrete working together in the third chapter are feasible.The failure process and failure mechanism for the composite section after strengthening and the influence of the different factors to the bearing capacity were studied. At the same time, combined with the results of test and FEM, the influence on shear stress of young-old concrete interface and carrying capacity induced by different loading method was analyzed. The counter-measures of unfavorable force mode appeared possibly in hooping technique strengthening were put forward.4. Based on the related research achievements about bearing capacity of eccentric compression member, the defects in the formulas of the current specifications have been pointed out. And the relatively accurate and unified formulas of eccentric compression member have been derived. The formula of bearing capacity for the hooping strengthening columns were proposed, which can consider various influence factors. Then, combined with the specific treatment in this experiment, the formula were appropriatly simplified. By comparative analysis of the calculation and test results, it tests that the simplified formula are reliable.5. Based on the basic design principles of RC structure, combined with the research results of hooping strengthening columns, the formula for the bearing capacity of hooping strengthening structure considered various influence factors was proposed. And considering the existing strengthening technical specifications, the formula was appropriately simplified. The stress states of the secondary loading process for hooping strengthening eccentric compression members were analyzed, and the influence on the sectional stress induced by the shrinkage and creep of fresh concrete was considered. With the feature of RC arch bridge, the bearing capacity formulas of composite section under different conditions were derived. Meanwhile, the simplified critical state equations about the thickness of hooping reinforcement layer were established according to the stress calculation process. Combination of the requirements of the thickness for bridge strengthening construction, the minimum reasonable thickness of hooping reinforcement layer can be initially determined.6. Considering the practical application of engineering and the proposed suggestions about young-old concrete working together in the third chapter, the RC arch rib specimen with hooping strengthening and the integrated pouring specimen were designed and manufactured. The failure process, failure mode and the bearing capacity of the composite section after hooping strengthening were studied. The test results showed that the crack features, failure mode and failure load of the two specimens were basically consistent, and the proposed suggestions about young-old concrete working together in the third chapter were feasible. At the same time, it verified that the hooping strengthening technique used in RC arch bridge was reliable.7. Combining with the practice of repairing and strengthening engineerings about two long-span RC arch bridges, the application of hooping strengthening technique was analyzed. Combining with the research results of theoretical analysis and tests, the strengthening design schemes of the bridges and the bearing capacity of key sections after hooping strengthening were analyzed and calculated. Then, the normal working performance of the composite section after strengthening under operating load was analyzed. The load test results after bridges strengthening showed that the hooping strengthening technique was feasible and reliable for the existing RC arch bridges.8. The key issues of the design and analysis about hooping techinique strengthening the existing RC arch bridge were summarized, and the reasonable suggestions were pertinently proposed. Finally, the standardization proposals about calculation procedure of the hooping strengthening techinique were recommended.