| Metal composite roof system is widely used in large span roof structures.The limited stiffness and high damping of composite roof panels will change the pulsation characteristics of the wind load and affect the wind-induced vibration response of the sturctures,which is ignored in current design.The thesis tests three full-scale specimens of the polyurethane sandwich roof panel and the rock-wool sandwich roof panel,to investigate the actual dynamic properties of them.According to the experimental results,the ideal finite element model of these two types of roof panels is modified to obtain the physical parameter values which can effectively characterize the actual stiffness,mass and damping performance.The main work of this thesis and conclusions are listed as follows:(1)Based on the damping theory of elastic-viscoelastic combined system,the initial(ideal)finite element models of two kinds of metal composite roof panels are established.According to the initial models,the natural frequency and vibration modes of the two types of roof panels are analyzed,and the modal damping properties are analyzed by the modal strain energy method.(2)According to the rationale of PolyLSCF method and the drawing principles of stabilization diagram,the related program is written with MATLAB.The validity of the method and the correctness of the program are verified by four typical examples.It is proved that PolyLSCF method can be used to identify the modal parameters of the metal composite roof panels.(3)The dynamic experiment and modal parameter identification of these two kinds of roof panels are carried out.The experimental result shows that the frequencies of the first 7 modes of the polyurethane sandwich panel are close,between 24?60 Hz,when the modal damping ratios are between 1%and 3%.The stiffness of the rock-wool sandwich panel is so small that the natural frequencies of the first 6 modes are between 15?25 Hz.The frequencies are close,of which the closest two modes differ only by 0.3 Hz.Meanwhile,the damping ratio of the rock-wool sandwich panel is large,about 8%each mode.(4)Modify the initial finite element models of these two kinds of roof panels with the natural frequencies and vibration modes,which are identified by the experiment.The necessity of considering the bearing stiffness of purlins is clarified.The sensitivity analysis shows that the vertical elastic modulus,density and vertical poisson ratio of the sandwich material are the key parameters affectiong the dynamic performance of the polyurethane sandwich panel.It also shows that the rock-wool sandwich panel is most sensitive to the density,lateral elastic modulus,thickness and vertical elastic modulus of the sandwich material.(5)Before the models were corrected,the frequency errors of the polyurethane sandwich panels were all at a high level,mostly around 10%.The errors of the rock-wool sandwich panel were higher,half of which were more than 20%.After the models are corrected,the frequency errors of the two types of roof panels are obviously reduced.The modified design parameters retain clear physical meanings and can be used to further studies on the wind-induced dynamic effect and damping properties of the metal composite roof panel. |
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