地震作用在温室荷载组合中的控制效应

农业温室结构刚度小、自重轻、地震响应小,对抗震的要求各国不同。为探讨中国农业温室合理的抗震设计方法,该研究以屋面透光覆盖材料中最重的玻璃温室为研究对象,按照《建筑抗震设计规范》要求,选择两个规则形和一个不规则形平面布局,运用MidasGen计算软件,以恒活风雪荷载为基础,对不考虑地震作用的a类荷载组合和考虑地震作用后增加的e类荷载组合进行比较,以构件的最大应力比为评判指标,以地震烈度为变量,分别选取7度(0.10g)、7度(0.15g)、8度(0.20g)、8度(0.30g)和9度(0.40g)(g为重力加速度)来研究地震作用的控制效应。计算结果表明在地震烈度为7度时,规则和不规则平面的温室,均是不考虑地震作用的a类荷载组合下的应力比更大,即地震作用不起控制作用。地震烈度达到8度(0.20g)时,对于规则平面温室的中柱和侧墙柱,考虑地震作用的e类荷载组合应力比已经非常接近a类荷载组合;对于不规则平面温室的个别凹角立柱,e类应力比(0.31)略大于a类(0.29);当地震烈度达到8度(0.30g)时,对于规则平面温室的个别构件,e类应力比(0.36)大于a类(0.29),最大应力比已经受地震作用控制。结合中国最小风荷载地区地震烈度表,提出在中国玻璃温室设计时,8度(0.20g)及以下地区可不考虑地震作用计算,8度(0.30g)及以上地区应考虑地震作用计算,此外,以塑料薄膜为透光覆盖材料的连栋塑料温室、塑料大棚以及日光温室在任何情况下都可以不考虑地震作用。该研究结果可为国内温室结构设计规范的制定和具体工程设计提供理论依据。

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.