Evaluation of Perforated Steel Tubes for Use as an Internal Frame and Partial Rebar Replacement in Precast Concrete Wall Panels

One of the areas that requires improvement in the precast concrete construction industry is the connections between elements which will address issues around inefficiency of the construction process in terms of accumulation of errors and speed and effort for alignment of elements such as walls and floors. The focus of this paper is on the preliminary strength tests of perforated steel tubes that will be used as an internal frame in precast concrete wall panels to accommodate a new bolted connection between precast walls. The connection will be self-aligning and ensure that strict tolerances are met during erection. The connection relies on an internal frame within the concrete wall panel made from perforated steel sections that the structural connection components bolt on to. Due to the location of the internal frame within the wall panel, it is important to understand whether it has some capacity to be also used as a partial replacement of traditional steel reinforcement. Therefore, four tube samples were tested in tension. While loading the samples, the corresponding strain was recorded throughout the testing using cameras and digital image correlation (DIC) software. Significant deformations, and consequently ultimate failure, was observed at the location of holes in these specimens. Strain distributions mapped onto the specimens using DIC process demonstrated large strain concentrations close to the bolt holes, due to significantly smaller net area compared to the gross areas between holes, specifically during the plastic response of the sections. The effective area of the specimens was calculated based on a known modulus of elasticity of 200 GPa and load and strain data. The average effective area of the four specimens was found to be 216 mm2 with a standard deviation of 8.7. This was found to be lower than both the gross cross-sectional area and net cross-sectional area of the specimens which were 377 mm2 and 258 mm2, respectively. The specimens had an average yield strength of 402 MPa and an average ultimate strength of 476 MPa based on the effective area.