Study On Post-tensioned Prestressed Concrete Structure And Constitution Examination And Evaluation

With the great development of prestressed concrete structure in our country, some defects in theory are becoming more and more remarkable. Several considered and difficult problem in the field are studied in the paper, which include the method of prestressed load for statically indeterminate prestressed concrete, the method of integral analysis for unbonded prestressed concrete and the system of examination and evaluation of prestressed concrete for construction quality.Study on the method of prestressed load for statically indeterminate prestressed concreteIt can be observed clearly from the course of construction stretch of post-tensioned prestressed concrete that shrinking force of a tendon make a member bend and compress. Just because of pre-exertion of tensile resistance capacity during load period the tendon's tensile strength "reduce" heavily. Hence, the function of tensile resistance capacity can be divided into two part. One part is prestress and another part is tensile force which is remainder of the pre-exertion. And then, the prestressed action can be separated according to the tendon's function. The prestressed action could be regarded as the same as a dead load and its effects could be considered not only on serviceability limit states but also on ultimate limit states. That is the main ideal of the prestressed load.In terms of traditional method of designing a hyperstatic prestressed structure, secondary internal force must be obtain at first and partial safety factor should be taken into account based benefit or not to structure. Then, used as dead load, the secondary internal force should be considered into combination calculating of internal force. In this method, it is not clear on concept that treating prestressed force as material resistance or action load and besides, calculation process become inconvenience because of secondary internal force is needed.According to a normal tendon duct design, usually, the tendon's stress could increase continuously after efficiency prestress in the course of loading. On the base of the condition, prestressed load can be handle as the same as dead load in internal force analyzing and combining by the use of the method of prestressed load. And then, in cross-section design efficiency prestress should be deducted from pretressing bar's strength. In this way, analysis of secondary internal force is not need in the method of prestressed load and so the design method can be used concisely and conveniently.Calculated by the two method on continue beam and frame structure on ultimate limit states, some of calculation results are not same and fundamental reason is that prestressing load is comprehended in different way. To moment, only secondary moment is regarded as load effects and primary moment is regarded as one part of material resistance by traditional method. By prestressed load method resulting moment that means summation of secondary and primary moment is regarded as load effects, which is confirmed by analysis andcalculation in period of stretching and resisting load. When resulting moment and secondary-moment are benefit or un-benefit to structure at the same time, the results by the two methods is same. And when that is not at the same time, the result by two methods is different and the difference is very weak comparing to general bearing capacity.Study on the method of integrity analysis for unbonded prestressed concreteOwing to specific construction crafts, tendons of unbonded prestressed concrete could move freely and bear little friction force. Through the course of beginning to the ultimate state of resisting load, unbonded structure obtain lower stress increment in unbonded tendon than that of assumed bonded tendon in the same place of the same structure. This is said stress hysteresis phenomena. It is the main characteristic of unbonded structure and so tendon's stress cannot be got by the Bernoulli's principle.Ultimate capacity of cross-section is partly determined by stress value of unbonded tendon. The stress value is determine...