Random Vibration And Structural Reliability Analyses Of Saddle Membrane Structure Excited By Wind-Driven Rain Load

With the progress of the construction industry,the architectural forms in contemporary society have gradually diversified,and the spatial structure is one of them,which has developed rapidly in recent decades.As a new spatial structure,membrane structure is composed of envelope system(membrane material)and supporting system(cable,supporting skeleton).Membrane structure has features like light weight,low stiffness,good tensile strength and flexibility,so it is widely used in modern long-span space structures.However,due to those features,the membrane structure becomes a wind sensitive structure,that is,the wind load is the main control load of the membrane structure.In fact,strong wind is often accompanied by heavy rainfall in nature.If only the effect of wind load on the membrane structure is considered and the influence of raindrops on the wind field and the impact of raindrops are ignored,the reliability of the membrane structure will be overestimated in the design,and even lead to engineering accidents.Additionally,most of the current theoretical research and design of membrane structure are based on deterministic analysis.However,the parameters(physical parameters of materials,loads and etc.)are almost random variables in the actual situation.Therefore,it is apparently unreasonable to adopt deterministic methods for research.At the same time,in order to ensure that the membrane structure can complete its intended function within their serving period,the membrane structure must be definitely reliable when it is in the design.Accordingly,it is of great significance to study the random vibration and reliability of membrane structures under wind-driven rain loads.The skeleton supported saddle membrane structure is selected as a research object in this dissertation,and the specific contents are as follows:(1)A theoretical study on the random vibration of saddle membrane structures under wind-driven rain load is carried out.First,the basic governing equations of saddle membrane structures are established by utilizing von Karman’s large deflection theory,moment-free theory of thin shells and flat shell theory.Then,based on the experimental wind speed-time history data,the constant and time-varying wind-induced aerodynamic model are established utilizing the wind pressure formula,the theory of potential flow and thin airfoil.Subsequently,the raindrop spectrum is used to establish the rain load model,which is coupled with the wind-induced aerodynamic forces to obtain the wind-driven rain load.The deterministic and random vibration differential equations of saddle membrane structure under wind-driven load can be obtained by applying the governing equation and wind-driven load.The equations are solved by perturbation method and equivalent linearization method separately to obtain the statistical parameters of theoretical model concerning structural random vibration displacement response.Finally,the parameter analyses of the statistical parameters of theoretical model are performed to explore the random vibration response of the membrane structure excited by the wind-driven rain load.The theoretical model shows that rain load is the main parameter of mean value and wind load is the main parameter of standard deviation of vibration displacement response;The vibration response of membrane structure can be reduced effectively by increasing the initial pretension force and rise-span ratio.(2)According to the theoretical model of random vibration of membrane structure,the reliability of membrane structures is studied.First,the displacement first passage failure criterion is introduced to establish the structural performance function of membrane structure in serviceability limit state.Further,the third moment method is derived based on the second moment method.Finally,the reliability index of saddle membrane structure under wind-driven rain load are calculated by utilizing the second order and the third order moment methods respectively,and the parameters analyses are conducted.It is found that when the vibration of the membrane structure is weakly nonlinear,the third-order moment reliability index can be approximately replaced by the second-order moment reliability index;The third-order moment reliability index is more accurate than the second-order moment reliability index;The rise-span ratio has more significant influence on the structural reliability than the pretension force.(3)The random vibration and structural reliability of saddle membrane structures under wind-driven rain load are studied by wind tunnel test with scaled aeroelastic model.According to the features of the membrane structures,the aeroelastic similarity ratios are established,which convert the time-history data of wind speed,rain intensity and vibration displacement of the membrane surface into the input parameters and response data of the corresponding prototype.The theoretical model of random vibration is validated by the statistical parameters of the response data obtained by probability statistic method.Moreover,Monte Carlo method is applied to analyze the experimental data to obtain the reliability index,which are compared and analyzed to the theoretical model for verifying the rationality of the theoretical model.Based on the theoretical and experimental results,the variation laws and mechanism of random vibration and reliability of saddle membrane structures under wind-driven and rain loads are analyzed.The relationship between the random vibration and reliability of saddle membrane structures and loads combinations,pretension force and rise-span ratio are discussed,which provides theoretical reference and technical guidance for the design of membrane structure under wind-driven rain load based on the reliability theory.