Bridge Safety Assessment Based On Interval Approach

The fundamental objectives of bridge design are safety, serviceability, economy and elegance, and the safety is the foundation and premise for the other three ones. So, how to ensure the safety of bridge structures in their life cycle is becoming the most important issue for all of bridge engineers over the world. For example, in U.S.A and Japan, large numbers of bridge structures built after the Word War Two, most of which are about in their six decades, inevitably need to be taken necessary safety assessments to make sure them safe enough because of degradation, load variation and natural factors. And some domestic bridges built in the fifties of twentieth century are also in their sixties, and they also need safety assessments due to degradation, low-level class of loading and natural factors. Some domestic bridges built after nineteen eighties are already 20-30 years old, although the bridges built in this period can fulfil the requirements of higher class of loading, the valid safety evaluation is also needed because of the construction quality problems. For all these reasons, it is becoming a focal problem in the research of bridge engineering how to establish a reasonable, reliable bridge structure safety assessment method.It is inevitable to deal with structural or load uncertain parameters in the bridge structure safety assessment, the key point of bridge structure safety assessment is how to consider the influences of the uncertainties of these parameters reacted upon the safety of bridge structure. On the base of the existing study results, this thesis discussed the method of structural stiffness matrix assembly based on the interval method, the solving method of interval equilibrium equation using factorization of interval parameters, element by element(EBE) detachment method, penalty method and coordinate conversion delay and symbolic manipulation, etc. Besides, bridge structure safety assessment software was also developed with object-oriented langage of VC++in this thesis. The validity and effectiveness of the software developed in present thesis were tested through several numeric examples, and the safety assessment of a multispan prestressed simply supported bridge considering uncertain parameters was performed based on the software developed. The detailed contents of the thesis are listed as follows:First, the state-of-the-art of the safety of bridges both aboard and at home was reviewed. The methods of bridge structure safety assessment were also classified with evaluation principles and relative merits.Second, the theory of the combination between the interval algorithm and the finite element method was elaborated, the emphasis is about the interval structural stiffness matrix assembly and the solution of the interval equilibrium equation.Third, the brief introduction of the object-oriented method was present, and definitions and the implementations of the interval finite element method were illustrated and interpreted in details. The structure analysis software based on interval FEM method was developed.Fourth, the validity and effectiveness of the structural analysis software based on interval FEM method developed in present thesis were verified. A three spans continuous beam and two stories frame were analyzed taking account the uncertainties of loads, materials and geometries using the software developed in present thesis, the numerical results were compared with the results of Monte Carlo simulations of ANSYS and published papers, and the validity and effectiveness of the software developed in present thesis were verified.Fifth, this chapter presented the flow of bridge structure safety assessment based on the interval method by taking an example of a multispan prestressed simply supported bridge considering uncertain parameters.