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无粘结预应力(包括体内无粘结和体外无粘结)在桥梁工程中的应用逐步广泛起来,分析无粘结预应力混凝土梁桥的主要困难在于构件的截面强度和构件整体变形耦合;另外,结构采用无粘结配筋后,其可能的失效截面增多,从而影响到构件的整体可靠度。论文利用独立同分布随机变量的极值理论,分析了无粘结配筋对梁式构件可靠度的影响问题。结果表明,考虑无粘结预应力筋截面积沿长度方向的分布特性而引起的可靠指标的降低比较明显,可靠指标随着独立同分布随机变量的数目的增大而减小。工程设计实践中将无粘结预应力混凝土梁的安全贮备比有粘结预应力的计算结果提高15%有一定的合理性。分析还表明,严格控制预应力筋质量,减小预应力筋截面积的变异系数,能有效改善因采用无粘结配筋而引起的可靠指标降低问题。
The application of unbonded prestress (including in-vivo unbonded and in-vitro unbonded) is widely applied in bridge engineering. The main difficulty in analyzing unbonded prestressed concrete girder bridges lies in the fact that the cross-sectional strength of the member and the overall deformation of the member are coupled. In addition, the structure of non-bonded reinforcement, the failure of the section may increase, thus affecting the overall reliability of components. In this paper, using the extreme value theory of independent and identically distributed random variables, the influence of unbonded reinforcement on the reliability of beam members is analyzed. The results show that the reliability index decreases obviously when the cross-sectional area of the unbonded prestressing tendon along the length direction is considered, and the reliability index decreases with the increase of the number of independent and identically distributed random variables. In engineering practice, it is reasonable to increase the safety reserve of unbonded prestressed concrete beams by 15% compared with that of prestressed cement. The analysis also shows that strictly controlling the quality of prestressing tendons and reducing the coefficient of variation of cross-sectional area of prestressing tendons can effectively reduce the problem of reducing the reliable index due to the use of unbonded tendons.