Date of Thesis
Open web steel joists are structural members often used in long-span roof and floor systems. The geometry of these joists makes them more efficient in flexure than typical I-beams because of their ability to resist bending while being incredibly lightweight. These joists are made up of single and double angles, which are nonsymmetric shapes. The nonsymmetric nature of these sections means that when load is applied at the shear center, no twisting occurs. In most finite analysis programs, elements are loaded through the centroid, not the shear center, so twisting is often not accounted for. In industry today, the elements that make up these joists are modeled as line elements in finite element analysis programs, where their properties are treated as symmetric. This research provides various methods of modeling these joists and assesses the impacts of modeling the sections as symmetric versus nonsymmetric.
The Steel Joist Institute (SJI) requested information on two specific joists: a 30K12 and a 32LH06. The analysis results give insight into how impactful modeling a section as symmetric is and indicate that the effects of modeling a section as symmetric versus nonsymmetric are not significant. The results of the joists with symmetric properties are still less conservative than those with nonsymmetric. As indicated by the modeling parameters measured in this study, recommendations can be given on how best to model an open web steel joist, and the factors that can influence error can be discussed.
finite element analysis, open web steel joists, shear center, lateral torsional buckling, double angles
Honors Thesis (Bucknell Access Only)
Bachelor of Science in Civil Engineering
Minor, Emphasis, or Concentration
Ronald D. Ziemian
Rojahn, Gigi, "Finite Element Modeling of Open Web Steel Joists Comprised of Nonsymmetric Shapes" (2020). Honors Theses. 551.