Research On Static Optimization And Fatigue Behaviours Of Loukouni Bridge Of The 1st National Road Project In Congo(Brazzaville)

With the development and innovation of the bridge technology, the bridge structure is becoming more and more diversified. How to balance security and economy has become the focus of bridge design. Loukouni Bridge is deck type arch bridge with box section in the 1st national road project of the Republic of Congo. In order to make the bridge design in optimal structure and good safety performance at least cost, improve its service life, as well as give support to the design and research of similar arch bridges in the future, it is of great significance to make static optimization analysis and study fatigue behaviours of Loukouni Bridge. In this paper, the main research contents included:(1) ANSYS software was used to establish the finite element model of whole bridge of Loukouni, the arch axis coefficient of arch bridge, section dimensions of arch rib, and the connection form of arch rib and column connected nodes were optimized. The results showed that it was in the most reasonable situation when the arch axis coefficient was 1.543; Arch rib section of Loukouni Bridge had certain optimization space, and in the four key parameters of the section, the section stress value was the most sensitive to the change of cross section height h; the connection of both ends of the column in rigid connection was recommended.(2) Arch rib and cross arm were chosen as the fatigue details, vehicle fatigue load models in different countries were refered to, through the most unfavorable loading method into the impact surface, the fatigue stress amplitude of the fatigue details were calculated. The results showed the two fatigue details were safe and the fatigue calculation under European specifications was the most conservative. It was recommended to use European standard in the design process in order to ensure the safety of the bridge fatigue design.(3)Fatigue experiment researchs on the two selected fatigue details were carried out. For each type of fatigue details 21 valid data were obtained for the nominal stresslife curve fitting which were compared with curves in national norms, showing that the result fitted well with China standard and European standard. The results showed that the fatigue behaviours of details could be well described by the experiments and the fitting curves could be applied to the fatigue details of similar projects in the future.(4) ANSYS software was used to establish the stricted finite element model of the two fatigue details. The stress concentration factor of fatigue details of arch rib was obtained using linear extrapolation path method given in the International Institute of Welding and the hot spot stress- life curve fitting was conducted on this detail which was compared with curves in national norms. The results showed that the safety of the hot spot stress- life curve given in the specifications was yet to be proven. Also, fatigue life evaluation and fatigue life prediction were made on the two details. It was recommended that safety inspection should be made on the fatigue details of Loukouni Bridge before it reached fatigue life in order to prevent the dangerous accidents.This study can provide technical support for future researches on static properties and fatigue behaviours of bridges. Also, it can facilitate the in-depth understanding of national standard and give reference to future learning, revision and development of the relevant specifications.