Research On The Type Selection And Design Optimization Of Viaduct Based On Comparison Of The Chinese And American Specifications

With the proposal of the Belt and Road Initiative,Chinese enterprises continued to explore overseas markets and undertook overseas bridge construction tasks.Based on the Bangladesh elevated expressway project wich is called DAEEP for short,this dissertation first compared and analyzed the difference between Chinese and American bridge design codes.Then,to obtain an economical,applicable and reliable design scheme,this dissertation studied the viaduct type selection and section optimization design.The results of the study can provide technical support for domestic design and construction enterprises when they enter the international market,also can improve the competitiveness of China’s road and bridge industry into the international construction market.The main research and conclusions are as follows:1)Made a comparison between Chinese and American bridge design specifications and conduct a quantitative and qualitative analysis based on some examples.2)The selection scheme of the superstructure of the viaduct was compared.The results show that T-shaped section is the best scheme.3)Based on the literature and study of the relevant fields,the technical condition of bridge structure optimization design problems were summarized,such as design variables,objective functions,constraints,optimization algorithm.According to the force characteristics of the T-beam,the section design variables were determined,which included the web height,the web thickness,the prestressed steel area,the thickness of the flange plate and the width of the flange plate.According to the AASHTO,the constraint conditions of the section optimization were determined,and the optimization mathematical model was established by taking the overall cost of the bridge superstructure as the objective function.4)The program files of objective function and constraint function were compiled by MATLAB.There were two schemes of 8 beams and 9 beams with 5 spans of 25 m,30m,35 m,40m and 45 m which were optimized by using genetic algorihm.The optimization results show that can improve the section efficiency index and reduce the project cost when we increase the width of flange plate and reduce the thickness of web.T-beam cross-height ratio increases when we consider economic indicators,because the cocrete cost is expensive.After optimization,the span-depth ratio increases,and the value is better to be in the range of 16.6 to 19.2 and the ratio is basically kept the same when the span is more than 40 m.The lower T-beam scheme is appropriate and economic for the selected project.The cost of 25 m,30m,35 m,40m and 45 m spans are reduced by 10.3%,12.1%,12.9%,13.0% and 14.5%,respectively.It can provide a reference for the design of similar overseas engineering projects.5)The optimization results were modeled and checked by Chinese and American specifications respectively.The results show that the control moment of the girder decreases after optimization.The difference of the design moment between winding beam and cantilever beam decreases,and the design bending moment of the main beam is more reasonable.The calculation results of the same section and reinforcement with Chinese and American design specifications,it is lower by American design specifications,which indicates that the design safety is higher.