Tensile Strength Characterization of Quenched and Self-Tempered (QT/TMT) Reinforcing Coupled and Welded Steel Bars

Abstract

Considering that the Philippines located in Seismic Zone 4, concrete structures are commonly reinforced using reinforcing steel bars, or commonly referred to as rebars. The production of rebars is limited to certain lengths like 6.0m, 7.5m, 9.0m, 10.5m and 12.0m and mostly are produced using quenched and tempering process. These rebars are commonly referred to as Quenched Tempered Thermo-Mechanically Treated (QT/TMT) Steel Reinforcing Steel Bars. This study concentrated on this kind of rebars. The concerns of structural builders and manufacturers arise when design of high-rise structures is involved, particularly those employing the process of joining QT/TMT rebars to meet the required design heights. When QT/TMT rebars are subjected to various joining or coupling process, the mechanical properties are affected, thus, influencing the structural integrity of the design. This study considered six kinds of joining process of rebars, where each one was subjected to tensile test, hardness test, chemical analysis and micro- examination to determine the tensile characteristics after undergoing a certain joining procedure. Samples were taken from three major QT/TMT rebar manufacturing companies in the Philippines through the coordination from the Bureau of Philippine Standards. The tensile tests were conducted using a Universal Testing Machine while chemical analysis used an Optical Emission Spectrometer. The results showed that out of six kinds of joining process, only two complied with the technical requirements of PNS 49: 2002 in terms of Tensile Strength, Yield Strength, Percent Elongation and TS/YS Ratio. Micro-examination was performed on several samples to determine how the tempered martensite regions were affected by the joining process used which eventually affected the mechanical properties.