Structural performance evaluation and optimization of sliding thermal-blanket-adapted solar greenhouses under vertical loads

Sliding thermal blanket systems have been widely used as an energy-saving facility in solar greenhouses. However, the opening mechanism is still lacking in the structural skeleton and load conditions for better mechanical performance. It is also required to specifically optimize the structural safety, standardized design, and performance of such greenhouses, particularly under critical vertical loads, like snow accumulation. In this present study, a sliding thermal-blanket-adapted solar greenhouse was proposed with the skeleton of a 13.6 m span, typically for Shenyang City, Liaoning Province, Northeast China. A systematic investigation was conducted to integrate a 1:1 full-scale skeleton loading test with Finite Element Analysis (FEA) simulation using Midas-Gen software. The mechanical response of the greenhouse structure was validated under vertically applied loads. The experimental and numerical protocols were designed to simulate realistic loading conditions. Vertical load was also applied to the front roof surface. Load-displacement curves were obtained from three measurement points: the base connection of the rear roof, the inflection point of the rear wall column, and the mid-span section of the front roof. The global and local deformation behavior was analyzed after measurement. Furthermore, the internal force distribution over the entire skeleton was obtained to identify structural vulnerabilities and potential failure initiation zones. The bearing capacity of the structure under the defined vertical load case was determined using experimental and numerical approaches. The results showed that there was high-level consistency between the measurement and the computation. Both the experimental skeleton and the FEA model also exhibited a two-stage trend of the load-displacement curves under identical loading and boundary conditions: an initial linear elastic stage followed by a nonlinear deformation, indicating better agreement. Quantitatively, a slightly higher overall structural strength was predicted using the FEA model. Meanwhile, the ultimate bearing capacity was numerically derived as 24.19 kN, which was marginally greater than the experimental average of 23.35 kN. The relative error between them was only 3.62%. The accuracy and reliability of the FEA model were effectively validated to simulate the structural behavior of the greenhouse type. The geometric parameters of the greenhouse skeleton (span, ridge height, and purlin spacing) remained constant for the subsequent structural optimization. Two modification strategies were explored to enhance the performance: 1) The weak point was identified at the inflection point of the rear wall column; 2) The structural boundary conditions were modified to reinforce local weaknesses and then redistribute internal stresses for the global efficiency. The actionable insights were yielded after optimization. Firstly, the out-of-plane lateral bracing was enhanced at the rear column inflection point. Once the spacing of these additional lateral constraints was reduced to 1.5 m and even to 1.2 m, the ultimate load capacity of the skeleton increased substantially, with the maximum enhancement of 26.90%. The strength was accompanied by a concurrent increase in the displacement at the measurement points, highlighting a trade-off between load-bearing capacity and deformation. Secondly, the boundary conditions were altered to pose a profound impact on both the overall load-bearing capacity and the fundamental failure mode of the structure. Specifically, when the support condition at the base of the rear wall column was shifted from a typical pinned or partially restrained connection into a fully fixed (embedded) condition (denoted as GG in engineering terms), a significant redistribution of internal forces occurred. The redistribution led to a shift in the location of the relatively weak section within the skeleton. Consequently, the ultimate load capacity of the optimal structure increased by 16.99% under the boundary conditions. In conclusion, the overall mechanical performance of solar greenhouse skeletons was achieved in the sliding thermal blanket systems. Two practical measures were substantially improved: The out-of-plane lateral constraints increased at the critical inflection point of the rear columns, while the rotational and translational fixity were enhanced at the base of these rear column footings. The local weak areas were effectively strengthened to promote a more favorable redistribution of internal stresses for the structural safety margin. Ultimately, a reliable full-scale experimentation was combined with the advanced simulation and optimization for the structural safety, performance, and design of the solar greenhouses under vertical loading. The findings can greatly contribute to the structural engineering and protected horticulture facility in modern agriculture.