Abstract:This article establishes a numerical analysis method based on incremental deformation, which is applicable to both bonded partially prestressed concrete beams and unbonded partially prestressed concrete beams throughout the entire process of loading. The method proposed in this article can simulate the performance of components in the descending section after reaching their peak bearing capacity, and can consider the changes in material stress-strain relationships caused by the unloading of non prestressed steel bars and concrete due to the structure entering the descending section of bearing capacity. Using the method established in this article, the effects of different loading methods, span to height ratio, comprehensive reinforcement index (CRI), partial prestressing ratio, and concrete compressive strength on the ductility performance of unbonded partially prestressed concrete beams were studied. Research has shown that the curvature ductility coefficient of unbonded partially prestressed concrete beams decreases with the increase of the comprehensive reinforcement index (CRI). For a given comprehensive reinforcement index (CRI), the difference in curvature ductility coefficients between bonded and unbonded prestressed concrete beams was compared and analyzed. Analysis shows that when the comprehensive reinforcement index (CRI) is between 0.15 and 0.20, the curvature ductility coefficient of unbonded prestressed concrete beams is close to that of corresponding bonded prestressed concrete beams; When the comprehensive reinforcement index (CRI) is greater than 0.20, the curvature ductility coefficient of unbonded prestressed concrete beams is greater than the corresponding curvature ductility coefficient of bonded prestressed concrete beams; When the comprehensive reinforcement index (CRI) is less than 0.15, the curvature ductility coefficient of unbonded prestressed concrete beams is smaller than the corresponding curvature ductility coefficient of bonded prestressed concrete beams

Abstract:Prestressed concrete Box girder bridge has been widely used in modern long-span bridge structures because of its good overall structural mechanical performance. However, in the concrete Box girder bridge built so far, the phenomenon of box girder cracking and excessive downward deflection during the operation stage is common. The lack of understanding of concrete shrinkage and creep effect and its effect in actual concrete Box girder bridge is one of the possible reasons. The current calculation formulas for concrete shrinkage and creep are mostly based on the results of laboratory model tests. Due to the large size of actual concrete box girder structures and their complex natural environment, it is particularly important to conduct long-term testing on the actual structure to obtain measured data that can verify the current specifications for concrete shrinkage and creep calculation formulas. Combined with the construction and operation of two large-span prestressed concrete Box girder bridge on an expressway, the real response of Box girder bridge in natural environment under the action of concrete shrinkage and creep is tested, and the test data are analyzed in detail. On this basis, a calculation method of concrete shrinkage strain and creep coefficient is proposed, taking into account the factors such as concrete temperature, environmental relative humidity, local theoretical thickness of box girder and their changes, And it is applied to the analysis of shrinkage and creep effect of actual bridges, and some conclusions with practical value are obtained, which provide reference for the calculation of shrinkage and creep of actual Box girder bridge

Abstract:Analyze the deformation calculation of prestressed steel concrete continuous composite beams under normal service limit state. Analyze and consider the slip effect between steel and concrete, establish a simplified calculation model, and based on this, propose a calculation formula for the length of the crack zone of the concrete support and the internal force increment of the prestressed reinforcement. Provide a calculation chart for the mid span deflection of a two span prestressed continuous composite beam. The analysis results indicate that the deformation calculation formula for two span prestressed continuous composite beams has a high accuracy in calculating the internal force value of prestressed reinforcement in the normal use limit state. The deformation calculation value without considering the internal force increment of prestressed reinforcement is larger than the experimental value. The accuracy of the deformation calculation value considering the internal force increment of prestressed reinforcement has significantly improved, which is in good agreement with the experimental results and can be used as a reference for engineering design. Finally, a general method for calculating the deformation of prestressed continuous composite beams is proposed based on the formula for calculating the deformation of two span prestressed continuous composite beams

Abstract:Tensioning integral structure is a new type of structure composed of continuous cables and intermittent compression bars. Research on cylindrical and spherical tensioned monolithic structures has been widely carried out, but another basic geometric topology form - circular tensioned monolithic structures - has received little attention. Propose a new type of ring tensioned integral structure, study its topology and shape finding problems, and use the balance matrix method to solve the self stress mode and mechanism displacement mode of the structure. A new type of cable dome is proposed by introducing a circular tensioned integral ring beam into the cable dome structure, and the initial prestress distribution and structural performance are analyzed. The calculation results show that the new cable dome is a tensioned integral structure with good stiffness and complete self-supporting and self balancing. This study enriches the existing forms of tensioned integral structures and their applications

Abstract:The corrosion characteristics of prestressed steel bars are the basis for studying the durability failure and prevention of prestressed concrete structures. Therefore, two methods, internal salt addition and external salt immersion, were used to conduct comparative tests on the corrosion of steel bars in three groups of concrete under natural climate conditions: steel strand and hot-rolled ribbed steel bars, steel strand and hot-rolled plain round steel bars, steel strand center steel wire and hot-rolled plain round steel bars. Through testing the corrosion current density during the corrosion process and comparing and analyzing the broken shape observation and weighing after the experiment, the following results were obtained: the degree of corrosion on the outer surface of the steel bar is significantly more severe on the side facing the protective layer than on the side facing the protective layer; The corrosion on the outer surface of the steel strand and its central steel wire is relatively uneven, with severe local corrosion - pit corrosion morphology, followed by ribbed steel bars, and smooth round steel bars are relatively the most uniform and comprehensive; The internal surface of the steel strand undergoes relatively comprehensive and uniform corrosion similar to that in air; The average external surface corrosion rate of steel strands is lower than that of hot-rolled ribbed steel bars and hot-rolled plain round steel bars, but severe local corrosion is extremely detrimental to their tensile performance. In addition, electrochemical mechanism analysis was conducted on the above corrosion characteristics