Prognosis and Mitigation of Weldment Cracking in High-mast Illumination Poles Due to Hot-dip Galvanization
Cracks that develop during galvanizing at the pole-to-base plate connection of High Mast Illumination Poles (HMIPs) are a major source of concern to fabricators and highway officials in the United States. Due to life safety concerns, substantial resources are spent performing detailed inspections of welded connections, and financial losses are incurred every time a damaged connection is found. One of the most important causes of connection damage are thermally-induced deformations during the galvanizing process, also known as hot-dip process. Therefore, there is an essential research need to identify the factors contributing to the initiation of weldment cracking during the hot-dip process of steel highway structures and propose improved design, materials, and construction specifications to help alleviate such cracking.
A crucial step toward addressing this need is to accurately quantify the structural response of the poles during the four stages of galvanizing, which are dipping, dwelling, extraction and cooling. Typically, thermocouples and strain gauges are attached to specific locations of the high mast illumination poles (HMIPs) to measure temperature and strain, respectively. Nonetheless, local discrete measurements are not good indicators for evaluating the overall structural integrity of a structure exposed to a spatial temperature gradient.
In this study, a comprehensive set of finite element models for simulating the hot-dip galvanizing procedure of HMIPs has been developed using the commercial finite element software ABAQUS. Linear and nonlinear coupled temperature-displacement analyses have been performed to quantify the stress/strain demands of the HMIPs during galvanizing. In addition, an extensive parametric study was performed, evaluating the effects of geometric configurations and galvanization practices on thermally-induced stress/strain demands during the galvanization of HMIPs. Geometric configurations including plate-to-pole thickness ratio, pole shaft geometric shape, connection type, bend radius, and the addition of stiffeners, along with galvanization practices encompassing of dwell time, speed and angle of dipping, dipping cross-section orientation, and preheating were thoroughly investigated to determine how these parameters contribute to the crack initiation phenomenon.