Analysis On System Design Theories Of Single Pylon Steel Cable-stayed Bridges

Single pylon steel cable-stayed bridges have a flexible layout and a beautiful appearance,that is the reasons why they have been widely used in the field of bridge engineering.But the researches on the system of single pylon steel cable-stayed bridges are seldom seen now at home and abroad,which causes designers difficult to start the design of this king of bridges or even enter design misunderstandings,and diseases finally occur commonly after the bridges put into service.This thesis starts with some diseases of a completed single pylon steel cable-stayed bridges,and another single pylon steel cable-stayed bridges which completed in the same period and approximate in shape has been put to compared.Comparisons find that diseases occurs the former frequently but the latter is flawless and perfect.The root cause of this phenomenon is that there are differences in the system between the two bridges.Those differences are cable-plane,auxiliary pier,material of main beam and boundary between beam and pylon.This thesis takes those differences as main line,mainly studies torsion of main beam and applicable conditions of single-cable-plane or twin-cable-plane,influences of auxiliary pier and position optimization of it,selection method of main beam material,influences of boundary between beam and pylon and so on of single pylon steel cable-stayed bridges,aming at supplementing the system design theories of single pylon steel cable-stayed bridges.Following the main line,an analysis method—from special to general or from concrete to abstract,have been used in main chapters.First a finite element analysis software called Midas has been uesd to analysis this bridge to point out that the design of this bridge is unreasonable.Then a large number of finite element models have been built and statistical analysis software called SPSS has been uesd to summarize the mechanical law of single pylon steel cable-stayed bridges.Finally some theoretical methods of single pylon steel cable-stayed bridges system design have been proposed.Under this analysis framework,this thesis find that torsion of main beam does not happen under symmetrical load.Under partial load,torsional normal stress takes the center line of the main beam as the center,roughly distributes anti-symmetrically;torsional shear stress decreases gradually from loading side to unloading side;distortion can be obviously seen.Then,Orthogonal Experiment and Analysis of Variance(ANOVA)have been used to prove that span length and form of cable-plane are the most significant factors of influencing main beam's torsion.The Dimensional Analysis and the Structural Equation method have been used to find a function expression of torsion angle and single-cable-plane or twin-cable-plane,which can help designers to select form of cable-plane quantificationally.Next,the Multi-Objective Optimization method and the Regression Analysis help to obtain an optimum setting position estimation formula of single pylon steel cable-stayed bridges' auxiliary pier.The ANOVA and the Regression Analysis have been used to obtain a fundamental frequency of vertical bending estimation formula of single pylon steel cable-stayed bridges,and it is proved feasible.Then,by setting control tests and studying how main beam material affects the bridges' mechanical properties,the influence rule between main beam material and single pylon steel cable-stayed bridges system has been proposed,which can be seen as a principle of selecting main beam materials of single pylon steel cable-stayed bridges.And at the last,a comprehensive method of evaluating the influence of different tower-beam-connection boundary forms and the bridges has been proposed by setting multiple control tests,and the laws how boundary conditions effect single pylon steel cable-stayed bridges have been summarized.This thesis starts with mechanical characteristics of single pylon steel cable-stayed bridges,by builting a large number of finite element models.In this thesis,some system design theories which can be used to guide to design the single pylon steel cable-stayed bridges have been proposed,simultaneously the method of syetem analysis has been supplemented.