Welded anchor rods for column base connections
Creators: name: Ali, Mahmoud
Publisher: name: figshare
Year: 2025
Subjects: classificationCode: 400510
subject: Structural engineering
classificationCode: 400504
subject: Construction engineering
classificationCode: 400506
subject: Earthquake engineering

description: Column base connections serve as the foundational anchor of steel structures, playing a pivotal role in ensuring overall stability and structural integrity. These connections must be meticulously designed to possess sufficient strength and high stiffness against both gravity and lateral forces, enabling them to elastically manage the transmitted demands between the superstructure and foundation. Given their critical importance, this study introduces a novel approach to enhance the overall performance of such connections. The proposed approach involves anchor rods welded beneath the base plate, capable of simultaneously withstanding tensile, compressive, and shear loads, as well as flexural moments. This innovative design aims to address the shortcomings of traditional connections, such as pinching hysteretic loops and uneven shear load distribution. A key focus of this research was the development of robust weld types for connecting the anchor rods to the base plate. To achieve this objective, a comprehensive experimental program was meticulously designed and conducted. This program investigated the tensile behavior of various fillet-welded connections, exploring multiple parameters including weld configurations (both asymmetric and symmetric fillet welds), different weld materials, and different preheating effects. To complement the experimental findings, a sophisticated numerical study was conducted to provide deep insights into several critical aspects of the welded connections, including fracture angle, crack initiation and propagation, and a comparative analysis between idealized specimens. Building upon the comprehensive investigation of fillet welds and the development of static strength formulas, this study extended the concept of welded anchor rods to column base-plate connections to thoroughly examine their overall behavior. A detailed numerical study was carried out using the finite element method. The numerical study commenced with a comparative study, comparing the cyclic behavior and uplift characteristics of typical column base connections against the proposed ones featuring concentric welded anchor rods aligned with the column. Subsequently, the investigation delved deeper, exploring crucial parameters that significantly influence connection performance such as concentric and eccentric layouts of anchor rods, diverse loading regimes, and varying levels of applied axial compressive loads. The results of weld investigations demonstrated that increasing the strength of weld metal enhanced the tensile capacity of all-round fillet welds. Ductility, on the other hand, was primarily influenced by the chemical composition of the weld metal, with carbon and manganese having the most substantial impact. A notable finding was that effective preheating of anchor rods before welding effectively mitigated the softening effects of the heat-affected zone. Perhaps one of the most striking discoveries was the superior performance of asymmetric fillet welds. Those with an optimal toe angle of 30° exhibited a remarkable 14% increase in tensile capacity compared to their symmetric counterparts with a 45° toe angle, despite utilizing identical weld volumes. The results also shed light on the fracture mechanisms, where asymmetric fillet welds also featured a fracture angle of 30°, contrasting with equivalent symmetric welds at 0°. Across all specimens, the initiation point for fractures was invariably located at the root gap of the weld. From this origin, cracks propagated towards the external surface of the weld. The numerical investigation of column base connections utilizing welded anchor rods demonstrated the elimination of pinching from hysteresis loops when employing welded anchor rods. Configurations featuring a concentric layout of anchor rods showed a remarkable 31% increase in uplift stiffness compared to typical column base connections. Also, in such arrangements, the base plate’s influence on cyclic behavior was negligible, functioning primarily as a linking tool between the anchor rods and the column, in contrast with the eccentric arrangement of anchor rods where the base plate plays a more significant role. Furthermore, a positive correlation was observed between compressive load and both the initial stiffness and strength of the connection, which resulted from the prevention of rapid separation between the base plate and the grout, and delayed tensile engagement of anchor rods.