Risk Analysis Research For Long-span Continuous Rigid-frame Bridges During Construction

The remarkable development of long span continuous rigid-frame bridges has taken place in recent years. With the innovations of structures and the increase of the span length, all kinds of uncertainty have been arisen, and the engineering construction is faced with unprecedented high risk. The engineering accidents which endanger safety of structures, properties and people's lives, may take place if enough attention has not be paid. This dissertation focuses on the construction risk of long span continuous rigid-frame bridges, which includes the following aspects:1.The theoretical skeleton is established. In this paper, the risk conception and its analysis principle are discussed. The definition of risk and the selection principle of risk analysis methods are put forward, and the theoretical skeleton of construction risk analysis for bridges is built firstly on the basis of giving definition of structure risks of bridges during construction.2. Conventional methods of wind-resistant performance of bridges deal with uncertain parameters by simple means. The modern approach in assessing the wind-resistant performance of bridges is first to be investigated from the point of risk assessment. The system of risk assessment and analyses of buffeting when bridge structures under wind are built, and lost assessment model is also established. The principle of risk acceptance criteria is introduced, and the strategy and techniques of risk response of bridge structures under wind is also built.3.In this paper, an approach of the systematic artificial neutral net was introduced into the analysis on the ship-against-bridges probability with a computer programs. Based on the basis data of the present typical bridges as the sample, chief influential factors as the input coefficient, such as the bridge span, the water flow rate, the incline angle between water flow direction and the direction normal to bridge axis, and the curve in the course near the bridge area, with the ship-against-bridge probability as the output coefficient, the intelligent judging system of the ship-against-bridges probability reflecting the influence of the above input parameters is obtained after training. So, a general framework for the risk analysis of the ship impact against bridges is set up. The specific suggestions to decreasing ship collisions on the bridge have been presented.4. Due to the performance functions of long-span continuous rigid-frame bridges construction, a method, combining finite element methods and RBPNN neural network and Monte-Carlo simulation, is presented, which is called F-R-M. The principle of construction risk assessment for bridges is discussed. The principle for building a model of risk assessment is presented. The model of comprehensive risks assessment for bridges is built. The principle for establishing risk assessment indices is put forward. The construction risk assessment index system for bridges, which includes risk acceptance criteria and risk grade assessment standard, is built. This makes it possible to comprehensively assess construction risk of bridges in all round way5. Basic bridge risk assessment approach, multi-objective bridge risk assessment method and public safety oriented bridge risk assessment investigated in detail after single objective bridge risk assessment. Compared with other risk assessment methods, multi-objective bridge risk assessment system based on AHP-GRAP and ALARP is built. Due to Bei Shan bridge, risk assessment and risk decision-making for long-span continuous rigid-frame bridges construction multi-objective bridge risk are studied6. In this paper, the scientific, rational, synthetical and comprehensive guides are put forward. This makes how to select best construction project and optimum treatment strategies for construction risk of bridges possible, and provides important decision references to risks decision makers.