Study On Stress Behavior Of Partially Prestressed Concrete Beams With HRB500 Steel Bars

HRB500 reinforced bars developed by China's metallurgical industry are adapt to high-strength steel reinforced concrete structure. Various performance indicators of the bars are conform to our country's steel products standards "hot and roll steel used in the reinforced concrete" (GB1499-199 8), and are met or exceeded the level of the same strength class reinforced bars developed in the foreign advanced industrial countries. That replacing HRB335 and HRB400 reinforced bars by HRB500 reinforced bars has good social and economic efficiency. The construction technology of the fold line pre-tensioned method has many advantages over the straight line pre-tensioned method and the curve pre-tensioned method. Combined with the National Natural Science Foundation-funded project "study on the force properties of HRB500 level reinforced concrete structures" (NO.50578148) and the Transportation Office of Henan province-funded project "study on a set of suitable techniques of the broken-tendon of pre-tensioned pre-stressed concrete beams" (NO.2005P338), the research work on the following aspects are mainly done with the fold line pre-tensioned pre-stressed beams and the curve post-tensioned pre-stressed concrete beams with HRB500 reinforced bars:1. Ten part pre-stressed concrete beams supported simply (6 of them are pre-tensioned, the other 4 are post-tensioned) are designed, and the main study parameters are: the strength of concrete, the strength of non-pre-stressed bars, the reinforcement ratio of non-pre-stressed bars, the strength ratio of the pre-stressed reinforced bars, the layout form and tension methods of the pre-stressed reinforced bars and so on. Various stresses are monitored in the production process of the test beams. The calculation methods suggestion is proposed about the friction loss on the fold line reinforced pre-tensioned pre-stressed concrete beam devices and other pre-stressed loss. Especially, the force performance in the construction phase is analyzed about the fold line reinforced pre-tensioned pre-stressed concrete beams. Thus, the basis is provided for promoting the use of fold line pre-tensioned pre-stressed concrete construction technology. 2. The static load test of the 7 concrete beams (4 pre-tensioned, 3 post-tensioned) supported simply are completed, as well as a test study on the characteristics of the force of the beam in every phase. The stress characteristics and damage patterns are analyzed about the HRB500 reinforced bars part pre-stressed beams. Meanwhile, the relationship between load and strain about the concrete, non-pre-stressed reinforcement and strand is analyzed during the whole process of the test beam from the load start to damage, and so is the development law of the cracks and deflection of the test beams. The main trial results are summarized, and the reliable data are provided for the following test analysis accordingly.3. The bearing capacity, crack, crack width, stiffness and deformation characteristics is analyzed about the HRB500 reinforced bars part pre-stressed beams in the static load based on the test data. Then, the corresponding calculation method is proposed, and the design strength value about the HRB500 reinforced bars used in pre-stressed concrete structures is known clearly. Also, the ductility characteristics and impact factors of the ductile is investigated about the beams. Meantime, the design method is proposed about the fold line reinforced pre-tensioned part pre-stressed concrete beam with HRB500 reinforced bars. Thus, the foundation is laid for that HRB500 bars will be included in the reinforced concrete structure design codes in China, and the basis is provided for the great efforts to promote the use of fold line pre-tensioned pre-stressed concrete beams.4. The non-linear analysis about the HRB500 reinforced bars part pre-stressed concrete beam for the entire process of loading is carried out by ANSYS finite element analysis software. By comparing the results with the test results, the ANSYS numerical model and parameters are verified reasonably and feasibly, also, the accuracy can meet the requirements. Thus, the finite element analysis results are in line with the test results, and the finite element analysis method can be used as a further study technique.5. The fatigue stress test of the 3 concrete beams (2 pre-tensioned, 1 post-tensioned) supported simply are completed, meanwhile the test method and fatigue test of the adding load system is discussed about the fatigue performance test. Then the fatigue damage patterns and destruction features are revealed about the broken line reinforced pre-tensioned pre-stressed concrete beam. The stress changing law of the non-pre-stressed reinforced bars and pre-stressed strand and fatigue strength of the non-pre-stressed reinforced bars is analyzed under the action of the fatigue load. Following, the fatigue performance of the HRB500 reinforced bars is evaluated. After that, the cracks, deflection changing law and calculation method are discussed about the test beam under fatigue load, and the remaining capacity calculation method after the action of the fatigue load is proposed. Accordingly, the test data are provided for the including HRB500 bars in the reinforced concrete structure design codes in China in the future, and it is proved that fold line pre-tensioned method can be applied to the structural elements bearing the duplicate load with adequate security.