Thermomechanical Modeling of Welding and Galvanizing a Steel Beam Connection Detail to Examine Susceptibility to Cracking

Abstract

Hot-dip galvanizing is the process of submerging steel elements into molten zinc to form a metallurgically bonded zinc coating that serves as corrosion protection for the steel substrate. Used with great success on an industrial scale for many decades, hot-dip galvanizing is a ubiquitous process. On occasion, cracks in steel members develop during galvanizing. While such cracking remains a poorly understood phenomenon, previous research has attributed the formation of cracks to the combined effects of residual strains introduced by welding and temperature-induced deformations caused by the hot-dip galvanizing process.This article presents thermomechanical analyses of a structural steel beam with a welded double-angle connection detail where cracking occurred during hot-dip galvanizing. Three-dimensional finite element models of the beam and connection detail were analyzed using the finite element analysis software Abaqus (Dassault Systèmes, Vélizy-Villacoublay, France). The welding process was simulated using the Abaqus Welding Interface, maintaining the welding sequence of the connection. After welding, the entire beam was subjected to a temperature field that was specified through a user subroutine in Abaqus, simulating the hot-dip galvanizing process. The temperature field had a bath temperature of 450°C and a thermal cycle that included dipping, dwell time, and removal from the bath. Material properties used in the simulation were nonlinear Manuscript and temperature dependent. The parameters of the study were the welding sequences, heat input during welding, and the depth of the double-angle connection. It was observed that strain demands due to welding and hot-dip galvanizing were high magnitude at the cracked location in the beam. The relative significance of strain demands due to welding and of hot-dip galvanizing on the propensity for the beam to develop cracks are discussed. Keywords welding residual stress, thermal stress, cracking, hot-dip galvanizing, steel building structures, finite element analysis 75 mm FIG. 1 Beam detail with crack after hot-dip galvanizing.structures, so this failure raised concern among designers, fabricators, and galvanizers and highlighted the need to investigate the problem.Since physical tests are expensive and highly challenging, especially in hot-dip galvanizing conditions where testing devices are submerged in a high-temperature (450°C) liquid zinc environment, computational simulations offer a useful tool with which to study the cracking phenomenon. Even so, thermomechanical analyses that simulate both the welding and galvanizing processes are technically challenging and require large computer platforms, which explains the sparse literature pertaining to such simulations. Toi, Kobashi, and Iezawa [5] analyzed the behavior of welded bridge girders during hotdip galvanizing but did not account for the effect of welding. Later, Toi and Lee [6] incorporated measured welding residual stress into the finite element model as an initial condition. An important study was perf...

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