Control effect of seismic action in the load combination of greenhouse

Abstract: Most agricultural greenhouses generally present low structural rigidity, self-weight, and seismic response in recent years. The structure design also varies significantly in different locations, if the seismic effect is considered in the load combination. Therefore, this study aims to investigate the effect of seismic action on various greenhouse structure under a load combination in China. The glass greenhouse was also taken as the research object, particularly for the heaviest material of roof glazing in all greenhouses. Two regular and one irregular plane layouts of greenhouses were selected, according to the regulation of seismic action in the structure design. Midas Gen software was used to analyze the structure stress in the components. The load combinations were compared with or without the seismic action (remarked as class-e and class-a). The maximum stress ratio of components was set as the evaluation index, while, the seismic intensity was used as the variable from 7° (0.10g), 7° (0.15g), 8° (0.20g), 8° (0.30g) to 9° (0.40g). The results show that the greenhouse with the regular and irregular plane layouts performed the greater stress ratios under the load combination of class-a without considering the seismic action, when the seismic intensity was 7° (0.1g and 0.15g), indicating there was no controlling effect of seismic action. In the inner and side wall posts of the regular plane layout in the greenhouse structure, the stress ratio of load combination of class-e considering the seismic effect was already very close to that of class-a, when the seismic intensity reached 8° (0.20g). In some individual corner posts of irregular plane layout in the greenhouse structure, the maximum stress ratio of load combination of class-e (0.31) was slightly larger than that of class-a (0.29). In the individual structural components of the regular plane layout in the greenhouse, the maximum stress ratio of load combination of class-e (0.36) was greater than that of class-a (0.29), when the seismic intensity reached 8° (0.30g). It infers that the maximum stress ratio was controlled by the seismic action. The seismic intensity was also combined with the smallest wind load in the study areas. Consequently, the areas of 8° (0.20g) and below cannot be considered for the seismic combination, whereas the areas of 8° (0.30g) and above were preferred in the structural design of the glass greenhouse. Additionally, the seismic action cannot be considered in the load combination, particularly in the plastic structures, including gutter-connected plastics, solar and plastic tunnels. The finding can provide a sound theoretical basis to implement the structural design of a glass greenhouse.