Theory And Method Of Wind-induced Fatigue Safety Prewarning For High-rise Structure

High-rise structures like guyed mast and power transmission tower are influenced by climate obviously,whose main load is wind load.Due to structural highness and slenderness and the randomicity of wind load,high-rise structures are especially sensitive to the action of wind and tend to produce wind-induced fatigue rupture of structural members that may cause the collapse of the whole structure. Since the wind-induced fatigue is a cumulative effect,if we can establish a safety prewarning system for wind-induced fatigue which will inform customers when a structural member come up to 80%or 90%of limit fatigue lifetime,then we can replace this member accordingly to avoid the collapse of the whole structure caused by wind-induced fatigue.Hence,it is completely necessary to carry out the research on safety prewarning theory,method and system integration method for wind-induced fatigue of high-rise structures,which can improve the security capacity of structures in use.Taking guyed mast for instance mainly,this dissertation studied every integral part of structural safety prewarning system for wind-induced fatigue in detail including the finite element analysis model,analysis method of nonlinear system's wind-induced response,dynamic load identification,model updating,safety prewarning system integration and so on.In this dissertation,nonlinear finite element model establishment method of the guyed mast is studied.The equivalent nonlinear spring model of the guyed cable by polynomial expression is deduced and the multi-node isoparametric curved element is also proposed to represent a cable.The beam element and truss element are discussed to build the mast model respectively.The simulation method of multidimensional cross-correlation fluctuating wind loads and the nonlinear static and dynamic response analysis method in time domain for guyed mast are studied. The methods of model building and dynamic analysis for guyed mast in this dissertation are also suitable for the power transmission tower.Since the determination of dynamic load is difficult especially for structures with a great many degrees of freedom and nonlinearity such as guyed mast and power transmission tower,few researches have focused on this problem.In this dissertation,the concept of equivalent two-dimensional dynamic wind load of high-rise structure is presented and the load identification models of the guyed mast and transmission tower considering nonlinearity are built.The direct load identification based on simplified model,the method of dynamic load identification based on precise time integration and the dynamic load identification method based on modal analysis are proposed to identify high-rise structural equivalent two-dimensional dynamic wind load.Simulation results demonstrate that the methods in this dissertation are effective.In a structural safety prewarning system,difference between the structural theoretical model and the actual structure may lead to inaccuracies and failure of the whole safety system.Therefor,structural finite element model updating is necessary. This dissertation analyzes and summarizes the applicablility,advantages and disadvantages of commonly used FEM updating methods.Taking guyed mast for instance,high-rise structural FEM updating method based on the principle of optimization is proposed according to the characteristics of structure.The element model with adjustable end stiffness is established.Then,combinatorial elements FEM is built to carry on the guyed mast model updating.This dissertation established a fine FEM of bolt connecting joint widely used in high-rise structures.Based on equaling the semi-rigid connecting as the reduction of member end section bending stiffness,an optimization equivalent method is put forward on the principal of minimizing the error term between stiffness matrix of fined model and one of equivalent simple model.In this dissertation,structural fatigue cumulative damage and residual life assessment of wind-induced fatigue safety prewarning system is studied.S-N curve method and fracture mechanics method for fatigue analysis are discussed. Calculation method and procedure of wind-induced fatigue cumulative damage and residual life for high-rise structure like guyed mast is presented.The basic principles and programming procedures of modified simplified rain-flow method are proposed. Methods of improve structural members' fatigue performance and structural wind-induced vibration control are studied.Numerical sumulation of a guyed mast in use by both S-N curve method and fracture mechanics method is made.Based on "structural dynamic wind load identification—FEM updating—assessment of wind-induced accumulative fatigue of structural members", the system composition and working principle of guyed mast's wind-induced fatigue safety prewarning system is studied in this dissertation.The system principle and sub-system function is then discussed.Finally,the use of fatigue life gage to structural health monitoring and wind-induced fatigue safety prewarning is put forward.