Dynamic geometrical shape measurement and structural analysis of inflatable membrane structures using a low-cost three-camera system

Inflatable membrane structures have gained considerable popularity in recent years owing to the advantages of light weight, beautiful surface and durability. This paper concerns the dynamic geometrical shape in-situ measurement and structural analysis of inflatable membrane structures using a low-cost three-camera system. The measurement system was developed based on three-dimensional (3D) digital photogrammetry. In order to acquire the high-quality measurement results, accuracy influence factors of the system were evaluated. Based on these considerations, dynamic geometrical shapes of inflatable membrane structures can be real-timely measured through the data processing which is used to determine the 3D coordinates of the target points pasted on membrane surfaces from the two-dimensional (2D) photographs captured by three cameras. Following the in-situ measurement of geometrical shape, the stress distributions of inflatable membrane structures can be determined based on the force equilibriums of membrane surfaces between the in-plane forces and out-of-plane loads. For verifying the proposed method, a selected ethylene-tetrafluoroethylene (E I PE) inflated cushion structure model was manufactured and employed for the experimental study of pre-inflated forming and normal working. By carefully analyzing and comparing the experimental results, it is observed that the measurement accuracy was better than 1/11000. More importantly, the geometrical shape of ETFE cushion still deformed with + 5.81% difference during the normal working process of 6 months, resulting in that the maximum stress decreased with - 3.49% difference. In general, this paper could provide an efficient and accurate method to measure the dynamic geometrical shapes of inflatable membrane structures, which is the basic information for the further structural analysis.