Experimental And Numerical Study On The Air-membrane Interaction Of ETFE Cushions

In recent years,ETFE cushions have been widely used in large building structures such as water cubes as external structures.The cushion will show the typical air-membrane interation under load or free vibration.In the static force,the air-membrane interaction is reflected between membrane surface deformation,internal pressure change and cushion stiffness.In terms of power,the air-membrane interation effect is mainly reflected in the additional mass effect of the inner inflatable body.It can be seen that the air-membrane coupling interation has a great influence on the mechanical properties of the cushion,and no literature has yet been found to carry out quantitative studies on the air-membrane coupling interation of the ETFE cushion.Quantitative analysis of the airmembrane coupling interation helps to fully understand the mechanical behavior of the cushion under load and the natural vibration characteristics of the cushion,making the mechanical analysis of the ETFE cushion more accurate.In this paper,the method of combining experiment and numerical value is used to compare the cushion with constant pressure and constant mass in different states to quantitatively study the effect of air-membrane interaction on the static and dynamic characteristics of ETFE cushion.The specific research contents are as follows:(1)According to the boundary conditions and accuracy requirements,we independently design and develop a test device to perform static loading test on the cushion.A uniform load is applied by placing sandbags on the upper membrane surface,and real-time measurement of the membrane surface displacement and the cushion internal pressure are performed by laser displacement sensors and digital micromanometers,respectively.Accurate control is performed from the aspects of device processing,inflation and deflation,loading and measurement to ensure the accuracy of the test results.It aims to study the change of membrane surface displacement and internal inflation pressure with external load under the uniformly loaded state of ETFE cushion.(2)An environmental excitation method was used to test the dynamic characteristics of the ETFE cushion model.Use a rubber hammer to strike the membrane surface to apply pulse excitation,obtain the free vibration time history of each measurement point on the membrane surface through frequency measurement and image speckle recognition technology,and use a combination of peak picking method and cross-spectral recognition State parameters.By analyzing the natural frequency of cushion,the effect of different initial internal pressure and size on the natural vibration characteristics of cushion is studied.(3)Using ADINA finite element analysis software,the effect of air-membrane interaction is considered by equivalent inner air as a potential fluid,and the deformation of ETFE membrane is considered by the geometric nonlinear characteristics of large displacement and small strain,and wrinkle are ignored.The influence of deformation on ETFE membrane material,the establishment of ETFE cushion air-membrane interaction finite element model,and the analysis results are compared with the static test,dynamic test results and the corresponding results in the literature to verify its rationality and accuracy.(4)Using the verified finite element model,static analysis and natural vibration characteristics analysis of the cushion,combined with the static and dynamic test results of the cushion,quantitatively study the stiffness and coupling factors,frequency and mode of the air-membrane interaction.The influence of the state and its changes with the parameters of size,sagittal ratio,film thickness,initial internal pressure and other parameters.The results show that: under the effect of uniform load,the effect of air-membrane interaction decreases with the increase of the initial internal pressure of the cushion,decreases with the increase of the cushion membrane thickness,and increases with the increase of the cushion sagittal ratio Decreases and increases with the size of the cushion;in terms of natural vibration characteristics,the effect of the air-membrane interaction increases with the increase of the initial internal pressure of the cushion,and increases with the increase of the size of the cushion,Decreases with the increase of the cushion membrane thickness,and decreases with the increase of the cushion sagittal ratio.