Refined structural modeling of thick-walled closed section composite beams

An analytical theory, based on Vlasov theory, is developed that accurately models the cross-sectional elastic properties of thick-walled composite multi-celled closed section beams. The model includes a correction to the shear strain equation to account for the non-uniform distribution of the shear strain through the wall thickness. A higher order transverse shear theory is also incorporated into the plate segment equations. The refined model is validated against three-dimensional solid finite element results. The validation studies reveal that the baseline Vlasov theory does not accurately capture the thick-walled effects (as much as a 24% error) while the results generated by refined theory closely match (less than 4% error) the finite element results. Parametric studies are conducted to determine the limits of Vlasov theory in predicting the cross-sectional properties of thick-walled beams. Because of the shear strain related effects, differences in baseline Vlasov theory and the refined theory start to become noticeable (10% error) at wall thickness to depth ratios of approximately 20% and become significant (greater than 25% error) at thickness ratios of 30%. Results show that neglecting transverse shear in the plate segments has a noticeable effect (10% error) on transverse shear stiffness and lateral deflections of uniform lay-up beams of ply angle range 15°-45°, for thickness to depth ratios larger than 25%.