无粘结预应力混凝土构件的可靠度分析

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。

Reliability Analysis of Unbonded Prestressed Concrete Members

Unbonded prestressing (including inside and outside of the member) is widely adopted in bridge engineering. The main difficulty in the analysis of unbonded prestressed concrete members is the coupling behavior of flexural strength and structural deformation. By use of unbonded prestressing tendons, the number of possible failure sections in structure are increased, and the reliability of structure is affected. According to the theory of extreme values of independent and identically distributed random variables, the reliability of unbonded prestressed concrete bending members is analyzed in the present paper. It is shown that the decrease of reliability is existing when longitudinal probability distributions of cross sections of unbonded prestress tendons are considered, and the index of reliability is reducing with the increase of the number of independent and identically distributed random variables. It seems reasonable in practice to increase the safety margin of unbonded members by 15% in comparison with the bonded prestressed concrete bending members . It is also shown that the less variation coefficient of cross section area of prestressing tendons, the less will be the reduction of index of reliability in unbonded prestressed concrete bending members. Therefore, the quality of prestress tendons must be strictly controlled in practice.