Differences in required structural efficiency of standard commercial steel greenhouses among EU countries: A hellenic experience
Since the climate and seismic conditions vary significantly among European countries (and sometimes even in different areas of the same country) the European Standard for the design and construction of greenhouses for commercial production (EN 13031-1) contains strict provisions concerning load combinations in both serviceability (SLS) and ultimate limit states (ULS) for each individual country. Hence, a standard commercial (steel in particular) greenhouse structure, designed for a specific country, is not likely to meet the requirements for structural efficiency of a different EU country, if constructed as is it. This fact, combined with the overall tendency of growers to import standard commercial greenhouses, raises a very important issue, as far as official approval and structural adequacy are concerned. In the context of the above, the present work deals with the structural analysis of a steel Venlo - type multi-span greenhouse, originally designed and dimensioned in Italy, acted upon by the loads specified in EN 13031-1 for Greece, in conjunction with the Hellenic Anti-Seismic Code. Initially, the sides, gable ends and primary internal bearing steel frames of the structure were modeled as multi-bay single-story frames, including the braces of the original design, and loaded only at the external column tips with the equivalent horizontal seismic forces for both primary directions, as specified by the aforementioned Hellenic Code. The results of the nonlinear elastic analysis showed that the columns and vertical members of the trellis girders were heavily overstressed. The structure was re-designed, without any changes in the geometric characteristics (i.e. distances between columns, member lengths and connectivity), utilizing larger cross-sections and a different bracing system. After numerous attempts, the final design proved efficient in fulfilling all the design requirements of both SLS and ULS, without loss of functionality and global performance.