Structural behavior of the PV-ETFE cushion roof

ETFE (ethylene tetrafluoroethylene) cushion roof integrated photovoltaic (PV-ETFE cushion roof) is an environment-friendly retrofit with advantages of cushion structures and capacity of utilizing solar energy. PV temperature due to photothermal effect could noticeably influence mechanical properties of ETFE foils and temperature boundary conditions of ETFE cushions. For this reason, corresponding experiments were carried out to obtain the indispensable data for numerical simulations. In this paper, numerical simulations focused on design condition and parameter analysis. Results under design condition (pressure of 250 Pa and pre-stress of 1.0 MPa) showed that maximum stress and strain were within the yield region, which validated the feasibility of this PV-ETFE cushion roof. Parameter analysis with normal working ranges (pressure of 250-450 Pa and pre-stress of 1.0-3.0 MPa) could be used to understand effects of pressure and pre-stress on structural behavior. The detailed analysis was divided into one-parameter and two-parameter analysis in terms of average values on the top layer as these values were more significant than those on the bottom layer. The one-parameter analysis showed that maximum stress existed in zone 1 due to the effects of boundary conditions while maximum strain was found in zone 2 because of the high temperature. Moreover, to evaluate effects of pressure and pre-stress on structural behavior, a slope method was employed and the results showed that the effect of the pressure was more significant than that of the pre-stress. For two-parameter analysis, it is obtained that stress increased with pressure and pre-stress and that deformation increased with pressure but decreased with pre-stress.