In Situ Determination of Stress Distribution of Inflatable Membrane Structure Using Force Finding Method

Abstract

Stress distribution on a membrane surface plays a key role in the structural safety and bearing capacity of an inflatable membrane structure, especially for the state under service condition. This paper presents an in situ method to determine the stress distribution of an inflatable membrane structure by using a force-finding method based on measured configuration. On the basis of the previous in situ measurement of geometrical shape and internal pressure, the target inflatable membrane structure is simplified to a membrane link structure with external forces on connection nodes. As a result, the stress distribution of the target structure can be determined based on the optimal solution of force equilibrium between the membrane internal force and internal pressure, as well as the thickness of the constructive membrane material. In order to validate the proposed method, the stress distribution of an experimental model of ETFE (ethylene–tetrafluoroethylene) cushion structure is evaluated following the suggested determining procedure. By carefully comparing the determining results with the numerical results for the forming process of the ETFE cushion model, acceptable agreement is obtained in terms of the stress distributions in the x-direction and maximum principle stress. Furthermore, the influence of mesh size on the stress distribution is also investigated by using four mesh sizes during the determining process. It is thus demonstrated that the proposed method is suitable for determining the stress distribution of an inflatable membrane under service conditions, which only requires the geometrical shape and inflated internal pressure of the final state, as well as the thickness of constructive material.