Optimize Truss Beam In The Large Column By The Relative Stiffness Similar Criterion

Truss beams, a familiar configuration in civil and building engineering, have beenintroduced to the petrochemical industry because of their superiority in bendingstiffness and compatibility of deformation. These structures, assembling channel steel,angle steel and steel plate, are employed as the support for internal parts in the largecolumn. But their basic sizes are defined based on the engineering experience whenapplied in the column, which sometimes can result in stress concentration. In themeantime, as the support in the column, truss beams are of great importance in liquiddistribution in slot distributors or packings. Therefore, optimizing their structure,improving stress distribution and bending stiffness, and gaining detailed mechanicalperformance become an urgent research subject. Based on ANSYS, a truss beam witha span of11000mm is optimized and reinforced locally on three counts, that is,cross-section shape of the chord members, the height of the truss beam and the pairsof the web members. But the results from ANSYS can’t precisely detail the propertiesof the truss beams. In view of that, regarding of the truss beam’ characters, based onthe similarity criterion of bridge and construction designing, a novel similarityprinciple named relative stiffness similar criterion is proposed for designing testmodels. Uniform loadings are performed on these test models to explore the stress andstrain distribution, failure mechanism and the effect of imperfections on the trussbeam’s behaviors.Given that the truss beam is a kind of thin-walled structure and has a lot ofwelding points, this paper employs polymethylmethacrylate (PMMA) as the materialof the scale-reduced test models to effectively decrease the effect of the welding onthe experimental results. The test models are fabricated according to the novelsimilarity. Uniform loads are gradually performed on the test models. The results findthat the strains are evenly distributed along the span. The strains both in the quarterand in the middle of the truss beam are sensitive to the loading change, but the weld inthe quarter of the truss beam will firstly fail. Simultaneously, considering thepossibility of flaws during the manufacture, namely bubbles and crack on the weldsurface, truss beams under four types of imperfections are also investigated. The results show that imperfections in the sensitive area mentioned above have asignificant impact on the truss beams’ performance, while those in insensitive areahave little influence on their behaviors. Besides, some precautions of improving thewelding detection in the quarter of the truss beam are alarmed.Based on the relative stiffness similar criterion, studies on the truss beam systemapplied in the packing column were further performed to speculate the properties ofthe whole support system. Good agreement between experimental results andsimulation results is reached, which proves this developed similar criterion to be validin designing testing model of thin-walled large structures.