STUDY OF BEHAVIOR UNDER EXCESSIVE NEGATIVE PRESSURE AND CYCLIC LOADING CONSIDERING MATERIAL NON-LINEARITY: Study on basic mechanical properties of sealed ETFE air cushion

In recent years, the adoption of the rectangular ETFE cushion as a roof cladding element has become widespread. It is anticipated that this trend will continue and that the size and shape of the panels made of ETFE will become more diverse. The cushion structure allows non-linear material behavior until the second yield stress, because the supply of air to the cushion can increase the volume of air even if elongation of membrane caused by residual strain has occurred. However, the behavior of the cushion structure exceeding the 1st yield point hasn’t been studied and investigated yet. In this paper, the behavior of ETFE sealed air cushion under Excessive Negative Pressure and Cyclic Loading was examined. As a result of comparative studies using experiments and numerical analyses, - It was confirmed that there was a trend that both the upper and lower membranes deformed almost equally keeping the initial cushion depth under full monotonous negative pressures. - The internal pressure gradually decreased and showed a tendency to become negative after initially maintaining zero Pa under full negative pressures. - Although the residual strain remained in the membrane and the initial internal pressure reduced due to the material non-linearity after the excessive load was applied, it was confirmed that the system did not collapse within the scope of this study. - Under cyclic loading, the residual strain occurred and the initial internal pressure decreased which is a typical characteristic of the sealed air cushion. However, it was confirmed that the system did not collapse within the scope of this study. In addition, because of numerical analyses, - By increasing the initial internal pressure, it was able to delay the disappearance of the tension of the upper membrane on the unloaded side and to delay the deformation of the upper membrane into a flat shape. However, regardless of the difference in the initial internal pressure, the load at which the lower membrane reached the first yield point was constant, and the displacement of the lower membrane associated therewith was almost constant. - When the aspect ratio was 1.5 or more, the results of internal air pressure of the cushion, membrane displacement and maximum membrane stress showed approximately equivalent values. - Even if the panel scale was different, the decrease in internal pressure could be reduced and the cushion stiffness was increased by using thicker film. In the elastic range, it was confirmed