The Experimental Researches On Unbonded Partially Prestressed Concrete Continuous Beams

Due to their advantages of mechanical properties, the unbonded partially prestressed concrete (UPPC) continuous beams have been applied in civil engineering more and more popularly. However, the calculation principle of stress increment of unbonded tendons in continuous beams is still derived from results of simply supported beams. Accordingly, it is necessary to improve the calculation principle. The test data of UPPC continuous beams on redistribution law of plastic internal force have rarely been reported at home and overseas, and differences exist in the value of recommended moment redistributions. Consequently, it is worthwhile to do an in-depth research on redistribution law of plastic internal force. The secondary moment caused by prestressing has an impact on redistribution law of plastic internal force of UPPC continuous beams, which is expected to further be investigated.According to above problems, 9 UPPC continuous beam tests have been conducted, the experimental process and phenomenon have been described in detail and test results have been analyzed. Two variation factors, nonpretressed reinforcement and secondary moment, are considered in this batch of beams. Through the tests, development and distribution of cracks of each specimen have been obtained; the characteristics of load–deformation curves and flexure lines have been compared and analyzed; the testing data of stress increment under different loads of unbonded tendons of each beam are gained and compared with the data calculated by the recommended calculation formulas of codes. For the sake of establishing validation calculation formulas of stress increment of unbonded tendons, which is in accord with the stress mechanism of continuous beams, the experimental foundation is provided; the characteristics of load–strain curves have been compared and analyzed.Ultimate bearing capacity of the key section of test beams has been calculated and analyzed. The ductility data of the key sections of the specimens have been summarized and compared. The factors which influence the ductility of the key sections of UPPC continuous beams are also discussed in this thesis. Based on it, the influence of the secondary moment on the moment redistribution and the ductility is mainly analyzed, and the general rule of the redistribution law of plastic internal force is obtained in this paper.The width of maximum cracks and the average space of cracks have been given out, and are compared with the values calculated by the recommended formulas; the statistic analysis of width of cracks and the cracks spaces has been conducted, in order to provide test basis for further investigating the rule of the crack; the influence of non-prestressed reinforcement on the rule of crack development is also discussed.Experimental data of 9 UPPC continuous beams are assorted in this thesis, and are compared with the data calculated by the recommended formulas. Finally, some valuable conclusions have been gained.