Effects of Out-of-plane Patterns on Thin Steel Webs: Fabrication Imperfections and Low-Frequency Sinusoids

Abstract

Thin steel webs can resist large shear forces. When designing large-scale structures, engineers can maximize the shear and flexural strength of steel plate girders by increasing the web depth while minimizing the thickness, which consequently produces slender webs. However, slender webs are susceptible to shear buckling. The objective of this dissertation was to discover, measure, and quantify the relationship between out-of-plane patterns (imperfections) on webs of plate girders and the structural strength via two specific studies: (1) web out-of-flatness imperfections developed during fabrication, and (2) a type of corrugation in the web plate called “low-frequency sinusoids” (LFS). Field measurements, experimental tests, and finite element analyses were the methods employed to meet this objective.The findings of this pioneering research reveal the following: (1) field-measured imperfections exhibit larger shear strength values and do not follow the patterns of the numerical eigenmode shapes, (2) irrespective of the initial imperfection shape and magnitude, the shear buckling behavior in thin webs is a plastic yield mechanism failure penetrating through the web thickness in three stages (elastic stage 1, web mechanism stage 2, and panel mechanism stage 3), (3) the fabrication process of LFS plate girders using the bump and press forming technique will increase the shear strength of plate girders by a maximum of 46% above that of flat webs, and (4) the elastic lateral-torsional buckling (LTB) strength of LFS plate girders with slender webs as compared to flat webs can increase by up to 9%. Overall, this research leads to important conclusions on the effects of imperfections and appropriate methods of their consideration in numerical and experimental studies. The research also enables the development of appropriate fabrication and design specifications for the construction of large-scale structures.