Study On Mechanical Properties Of Polyurethane Sandwich Metal Roof Panel And Its Effects On Wind--induced Vibration Responses Of Roof Structures

Currently, the light metal roofing system is widely used in large span roof structures, while the effect of roof panel is ignored in design. Actually, the wind pressure acts on the roof panel first, then passes through the roof panel to the purlins and arrived in the main structure finally. The article studies on the frequently-used polyurethane sandwich metal roof panel, focusing on its effect of finite stiffness and damping on the mechanical properties of roofing system, especially on the wind-induced vibration, the main parts as follow:(1) The article investigates the basic mechanical and damping properties of the polyurethane sandwich layer. Studies have found that the tensile and compression performance as well as the mechanical properties of different direction of polyurethane foam are different. So it can’t be considered as isotropy material. Parameters of transverse isotropic model are fitted according to the test data. The loss factor curve of polyurethane foam is measured by DMA, during witch, the factor loss-frequency and factor loss-temperature cure are obtained.(2) The damping properties of the polyurethane sandwich metal roof panel are investigated here. The model loss factor of the polyurethane sandwich metal roof panel is obtained, which is found to cause high damping energy dissipation on external high-frequency stimulation. Parameter analysis shows that the damping properties of the polyurethane sandwich metal roof panel are decisive to the damping properties of the whole roofing system. The finite stiffness of roof panel and the damping properties of sandwich layer will both change the characteristics of fluctuating wind pressure, by investigating the response of roof panel with different stiffness and damping properties under the action of pulsating wind load of dynamic response.(3) The pressed metal layer is equaled to orthogonal anisotropy plate, while polyurethane sandwich metal roof panel is also equaled to orthogonal anisotropy sandwich plate with different thickness of top and bottom layer. Based on the Hoff sandwich plate theory, the static equation of roof panel is obtained, and dicussed the analytic solutions. Complex modulus method is taken to represent the viscoelastic properties of polyurethane sandwich layer. Futher, the dynamic equation of the panel transverse vibration with the damping properties of sandwich layer is derived.(4) Based on the Hoff sandwich plate theory, a new kind of sandwich plate element is established, which is established on the middle surface of the sandwich layer as a rectangular element with eight nodes, each of which contains five freedoms:3linear displacements and2angular displacements.The roof panel simulated by this element has the same displacement as what is got in the accurate model, while the natural frequency of vibration is close to the accurate model. So, it is found to be effective enough to simulate the static and dynamic properties.(5) Effect of the stiffness and damping of roof panel on the wind vibration of the roof structures is investigated by two examples. The analysis result shows that whether to take the roof panel into account is definitely different on the calculation results of wind vibration.The stiffness of roof panel is the main factor to consider to the wind-induced vibration. The damping of sandwich layer has obvious effect on the roof structure with large stiffness, and how mcuh it causes depands on its stiffness.