Research On Safety Evaluation And Optimization Method Of Complex Support System In Concrete Bridge Construction

In order to adapt to the development trend of bridge to long span and high altitude,the complex support system of bridge construction composed of full framing,bailey beam and steel tube column has been widely used in the construction of concrete cast-in-place bridge because of its great bearing capacity,strong adaptability,simple erection and reusable advantages.But the complex support system of bridge construction has many components and complex structure,and there is no specific design standard and specification.How to achieve the win-win of security and economy in design is worth exploring and researching.In this paper,the methods of theoretical research,numerical simulation and machine learning are combined to study the comprehensive safety evaluation and structural optimization methods of complex support systems for bridge construction.The following research works have been carried out:(1)Based on the analysis of the force transmission mode and stress characteristics of the complex support system for bridge construction,a comprehensive safety evaluation index system is established.The concept of comprehensive safety degree is put forward as the quantitative evaluation result of structural safety reserve.Entropy weight method of objective assignment method is used to determine the weight of indexes,and the conflict between indexes is introduced to correct the weight.A comprehensive safety evaluation model for bridge construction complex support system is established.(2)A structural optimization method based on support vector machine approximation model and genetic algorithm is proposed.The basic concepts and steps of genetic algorithm are studied.The penalty function method is used to solve the limitations of genetic algorithm in constrained optimization problems.The principle of support vector machine regression algorithm,training sample selection and parameter selection optimization method are studied.A method for constructing an approximate model of structure by support vector machine is proposed to replace a large number of finite element calculations in structural optimization by genetic algorithm.(3)Based on the basic theory of structural optimization design,an optimization method for the complex support system of bridge construction is proposed.Taking the total steel consumption of the structure as the objective function,and taking the cross-sectional dimensions of each component as the design variable,the comprehensive safety of the structure reaching a certain target value and the stress or displacement of each component meeting the safety requirements are the constraints.The optimization mathematical model of complex support system is established.The steps to solve the optimization model using the optimization method based on the support vector machine approximate model and genetic algorithm are studied.(4)The cast-in-place construction of the main girder of a cable-stayed bridge adopts a complex support system composed of full framing,Bailey beam and steel pipe column.The safety evaluation and structure optimization of the support system are carried out.The comprehensive safety degree of the support system is2.51 under the original design parameters.The safety reserve is relatively sufficient,and there is certain room for optimization.The optimization goal is to minimize the total steel consumption when the comprehensive safety of the complex support system reaches 2.0.The comprehensive safety degree of the optimized structure is 2.09,and the total steel consumption is reduced by 20.99%compared with the original design.It shows that the optimization method of complex support system in bridge construction can make the structure achieve the optimal economic consumption while maintaining a certain safety reserve.