Study on the Reliability of Steel-Concrete Composite Beams Based on the Third-Order Moment Method

Abstract

Abstract Study on the Reliability of Steel-Concrete Composite Beams Based on the Third-Order Moment Method Steel-concrete structure is a new type of structure developed on the basis of steel structure and reinforced concrete structure. Because of its high strength, good durability, material saving and convenient construction, it has been widely used in the field of bridge engineering. However, because the influencing factors of composite beam resistance are very complex, there are still some problems that need to be further studied and solved in its theoretical design and practical use. Therefore, more and more scholars are studying steel-concrete composite beams. The research on the structural reliability of steel-concrete composite beams in China started late and is still in the development stage. Therefore, the research on the reliability of steel-concrete composite beam structure is carried out, so as to explore an analysis and calculation method with simple calculation process and accurate and reliable results, which is of great significance for the design and analysis of steel-concrete composite beam structure and the reliability evaluation in the use process. Compared with the traditional Monte Carlo simulation method and the first-order second-moment method, this paper uses the third-order moment method with higher calculation accuracy and wider application range to analyze several factors affecting the reliability of steel-concrete composite beams. Then, the reliability performance function based on different theories, different models and different states is established, and the calculation is verified by an example. Finally, Monte Carlo method, FORM method and third-order moment method are used to analyze the sensitivity of the main indexes affecting the flexural performance of composite beams. The main work done in this paper is as follows: III 吉林大学硕士学位论文 (1)The Monte Carlo simulation method(MCS) and the first-order second-moment method including the center point method, the checking point method and the JC method commonly used in reliability calculation are summarized. Combined with the formula derivation and the research status of the two methods, the advantages and disadvantages of the two methods are analyzed and summarized. (2)The calculation process of the reliability calculation method-the third-order moment method is analyzed. Compared with the commonly used first-order second-order moment method, the third-order moment method further considers the third-order moment of the structural performance function, namely the skewness, which can more accurately simulate the performance function image of the structure, and then more accurately calculate the reliability index of the structure. (3)According to the reliability theory, the performance function of the flexural performance of steel-concrete composite beams is established. Taking a steel-concrete composite beam as the research object, according to the load effect of the beam, the resistance of the steel member, the resistance of the concrete member and the resistance of the shear connector are calculated by considering the material performance, geometric parameters and calculation mode. The corresponding reliability index is calculated by the third-order moment method, and the applicability, efficiency and accuracy of the calculation results of the third-order moment method are analyzed. Reliability of bending resistance of normal section ; (4)Based on the performance function model of the test beam, the performance function of the combined component resistance, dead load effect and live load effect is derived. Based on the bearing capacity function based on elastic theory and the bearing capacity function based on plastic theory, the bearing capacity function of steel beam concrete slab and shear connector bearing capacity model are established respectively. Reliability performance function of normal section bending based on mid-span section bending model. The three models established the performance function of the ultimate state of the bearing capacity and the performance function of IV Abstract the normal use limit state, the component resistance, the dead load effect, and the live load effect. (5)The sensitivity analysis of the main indexes affecting the flexural performance of steel-concrete composite beams is carried out by Monte Carlo method, FORM method and third-order moment method respectively. According to the calculation and analysis, it is concluded that the third-order moment method is consistent with the Monte Carlo method with higher accuracy, and the calculation efficiency is significantly improved compared with the Monte Carlo method. It is proved that the third-order moment method is effective for the sensitivity analysis of flexural performance of steel-concrete composite beams. The calculation results show that the web thickness of the composite beam and the grade strength of the steel beam have the greatest influence on the flexural performance of the steel-concrete composite beam, followed by the shear connection strength and the reinforcement ratio, while the concrete strength has only a small influence. Key words：Steel-concrete composite beam; third-order moment method; reliability index; sensitivity analysis