Investigation Of Performance Under Loads And Ductility Of Prestressed High Strength Concrete Beams

Prestressed technology combined with high-strength materials (including high-strength concrete and reinforcement) makes prestressed high- strength concrete simply-supported beams has great advantages in reducing beam height and increasing load-bearing capacity. In this paper the prestressed high-strength concrete simply-supported beams are the main analysis object. This paper systematically introduced its developmental history and foreground, the up-to-date state of the prestressing structure, discussed their merits and demerits. In view of these problems, the following research works have been carried out in this dissertation. Several main tasks have been done as following.1 .Twenty-fourth pre-tensioning prestressed high-strength concrete beams were investigated with varying grade of concrete compressive strength, height of section, partial prestressing ratio, reinforcing index and even percentage elongation ratios of strand. At the same times, the complete load-deflection curves were successfully recorded over the entire loading range from initial load to collapse stage. The experiment not only provides necessary data for nonlinear analysis, but also is an independent means of checking computation methods.2. Losses of prestress in different stage is analyzed, and compared it with those predicted by Code proposed model. The available stress state before loading is also given.3. The method used to calculate the stress of critical sections of tested beams before/behind cracking was studied. The analysis results indicates that the stress of section before cracking of prestressed high-strength concrete beams can be calculated as that of material mechanics model, and the stress of section after cracking of partially prestressed high-strength concrete beams can be calculated also as that of Code proposed model, but not suitable to the fully prestressed high-strength concrete beams.4. The crack distributions and its development of tested beams are considered. At the same time, main factors that affecting crack width were Analyzed also. Based on the experiment and the former researches, formulas for calculating crack width that have been accepted by many internal and overseas Codes of the world were presented. Through comparison, we concluded that the crack distribution state and the crack width development model are the same as that of the normal strength concrete beams, while the Code proposed model to calculating the maximum crack width only suits the partially prestressedhigh-strength concrete beams. A calculation model that suits not partially prestressed but fully prestressed high-strength concrete beams were presented.5.the values of anti-arch after cutting off the wires and the deflections under normal service load were studied. Main factors affecting stiffness were analyzed. By comparing with the Code, the suited area of it were shown, at the same time, a emendatory equation not adapted to partially but also to fully prestressed high-strength concrete bending members was given.6.The methods to calculating the ultimate load capacity of prestressed high-strength concrete beams were analyzed. The section stress state of prestressed high-strength beams is illuminated in the destruction conditions. Effect of the elongation of steel strands on failure mode of bending members was discussed.7. Main factors affecting the ductility and failure mode were analyzed also. Based on experimental results, the whole stage nonlinear analysis was conducted by programming corresponding process. The effect of material properties on section ductility of reinforced concrete and prestressed concrete beams was discussed. At the same time, the restrictive conditions ensuring section ductility of member were proposed also.8. A test on high-performance prestressed concrete hollow slab is performed based on the optimum design. It is made of C80 concrete and high strength grade 270 strand. The properties of a hollow slab about the cracking strength, cracking width, deflection and ultimate bearing resistance were studied. Th...