Research On Reliability Assessment And Operation Load Limits Of The Active Duty Sub-health Multi-span Simply-supported Beam Bridge

Based on the spirit of sustainable development and conservation of resources, countries all around the world consider the active duty bridge as a great asset. They all try to take a variety of systems, policies and technical means to do everything possible to extend the active duty service period of the bridge. However, as the sub-health bridge promotion and retrofit covers a wide range, and the risk has not been fully demonstrated, in the case of transport infrastructure maintenance funds are limited, people tend to focus on reinforcement of the bridges in critical condition, but not to take the rational use of them into account. For sub-health bridge both safety and moderate play its role in the traffic network, avoiding the "little horse cart" phenomenon and preventing them from the deterioration of existing disease or produce a new disease in its continued use process which cause serious accidents, the scientific and rational assessment and load limit has become an imperative for the bridge maintenance and management.First of all, The paper conducts a relatively systematic analysis on structural reliability theory combining the issue of sub-health bridge operation reliability assessment; in terms of reliability assessment of bridge, summarizes the criteria and models for reliability assessment of bridge structures, and distinguish the main failure mode for multi-span simply-supported beam bridge after consider the significance level of all the potential failure modes; Based on this, puts forward the reliability analysis method by introduces the Analytic Hierarchy Process and the Invalid Index Method, through which to conduct the multi-span simply-supported beam bridge reliability assessment progressively according to the hierarchical structure in sequence.Secondly, in order to assess the current situation of the sub-health bridge, the concept of damage limit state and usable carrying capacity are introduced; analysis the inertia and stiffness changes of the bridge section before and after cracking and its solution; in the assessment of bridge usable carrying capacity aspects, taking static load test results as the criterion, proposes an assessment method for the sub-health simply-supported beam bridge through the five evaluation index system which constructed by three bending usable carrying capacity (normal section crack width,stress value and stress amplitude) and two shearing usable carrying capacity (principal stress,inclined section crack width), At the same time, for the gravity-type piers and the pile-type pier, the overthrow (collapse) mechanism is analyzed, and elaborate the bridge structure damage caused by the overturning (collapse) of the piers.Finally, preliminary analysis the contents about the operation load limit of the sub-health to provide a reasonable scientific basis.