恒载性超载对在役桥梁受弯构件可靠性的影响规律

Influence of Dead-load Based Overload on Reliability of Flexural Members of In-service Bridges

为深入研究恒载性超载对在役桥梁安全性的影响程度,以加固后桥梁名义恒载效应与原名义恒载效应之比作为恒载超载系数,详细分析了在役桥梁受弯构件可靠指标随恒载超载程度的变化规律。鉴于新老桥梁设计规范极限状态设计表达式的不同,采用《公路工程可靠度设计统一标准》建议的抗力与荷载效应的统计参数,分别计算了与不同恒载超载系数对应的受弯构件可靠指标。计算结果表明,随着恒载标准值效应所占比重的增加,恒载性超载对桥梁结构安全性的影响愈明显。桥梁结构或构件隐含的可靠度越高,相应结构或构件的抗恒载性超载能力越强。在满足目标可靠指标要求的前提下,结构或构件容许一定程度的超载作用。

To study the influence of dead-load based overload on the security of in-service bridges, the variation of the reliability index of tlexural members with dead-load based overload of existing bridges was analyzed in detail according to the dead-load based overload coefficient, which is expressed as the ratio of the nominal dead-load effect of the strengthened bridge to the original nominal dead-load effect. With consideration of the difference of the limit state design expressions between the current bridge design codes and the previous ones, the reliability indexes of flexural members of bridges related to different dead-load based overload coefficients were calculated separately by using the statistical parameters of variation of resistance and load effects from Unified Standard for Reliability Design of Highway Engineering Structures .The result indicates that （1） along with the proportion of the dead-load characteristic value effect adopted in the design of bridges increases, the influence of dead-load based overload on security of bridge structures would be more obvious; （2） along with the implicit reliability of the bridge structures or components increases, their capability to anti dead-load based overload intensifies; （3） on condition that the objective reliable target requirement is satisfied, the structure or the component allows certain degree of overload.