Experimental and Analytical Investigation of Service-Load Stresses in Cellular Beams

Cellular beams are expanded I-sections with circular web voids that have been used extensively in Europe, and are currently gaining popularity in the United States. For these expanded I-sections, stresses within the web void projection are the manifestation of primary bending and shear-induced Vierendeel bending. The circular shape of the web void and corresponding interaction between primary and Vierendeel bending results in a stress distribution where the critical stress occurs at a location where neither stress component is at its respective maximum. In this paper, the stress distribution in cellular beams at the service limit state is explored using closed-form equilibrium methods, finite-element analysis, and experimental testing. Two different cellular sections are studied, with four identical experimental samples per section type tested in the laboratory under simple support and uniform load conditions. Experimental data are compared with both finite-element results and closed-form predictions, and are used to establish the accuracy of the analytical methods considered. Cartesian and principal stresses are considered in the investigation. The study concludes that critical stress magnitude and location calculated using the closed-form and finite-element methods are in good agreement with experimentally measured data.