Research On Ultimate Bearing Capacity Of Unbonded Prestressed Concrete Beams

As one of the most important branches of the system of post-tensioned prestressed concrete structures, unbonded partially prestressed concrete(UPPC) structures has been widely used in civil engineering with the development of prestressed concrete structures. To fix the ultimate stress increment of unbonded prestressed tendons is the key point during the design of UPPC beams,for it directly concerns the reliability of components. Accordingly many models have been proposed based on large numbers of tests and different theories by many experts inside and outside of the country. And one model is also prescribed in current criterion of"Design and Construction of cohensionless prestressed concrete structure"(JGJ/T92-2004) in our country. However, there are many complex factors to affect the ultimate stress increment of unbonded prestressed tendons, and the model in the code has pointed no evident reliability level and the code which is based on to build the model have been reset. Thus, it would make great sense to set a model for ultimate stress increment of prestressed tendons of UPPC beams ,based on the current criteria with evident reliability level.In this paper, the development, application and characteristics of UPPC structures are reviewed,and detail introduce the calculation model of Stress Increment of Unbonded Tendon which constituted by academician at home and abroad.The destroy forms and mechanics performance of UPPC beams are analyzed, the factors to affect the ultimate stress increment of prestressed tendons of UPPC beams are discussed. In order to take various uncertainties in structural design into account, the method to fix the reliability-based ultimate stress increment of prestressed tendons of UPPC beams is proposed with the synthetical ratio of reinforcement, and though the statistical analysis of large numbers of tests the corresponding design model is set up based on the current criteria with evident reliability level. The model is reliable and acceptable and could be beneficial for the improvement of the model from the current criterion through the check and comparison from tests. In additional, the numerical analysis for the factors affecting the ultimate bearing capacity of UPPC beams with ANSYS, the large universal FEA program, has been conducted. From the simulation result the degree of sensitivity for the factors to ultimate bearing capacity of UPPC beams is acquired, and the rationality of the model is proved again, so that the model can be used in the design of UPPC beams.That if the reliability-based model for ultimate stress increment of prestressed tendons of UPPC beams fits the UPPC beams with the T-section, I-section, etc. and if it fits the design of highway bridges should be further studied in order to make UPPC beams be used in various structures more widely and more safely.