<p>The failure mechanisms of hollow steel sections can be divided into six main categories (i.e., chord plastification, chord web failure, chord shear failure, punching shear, brace failure, and local buckling). Chord plastification represents the primary governing factor in these failures and the dependence on chord material yielding imposes limitations on structural efficiency. To overcome these limitations, an innovative strengthening method using internal concrete infill applied to both the chords and bracing elements of hollow sections is investigated in this paper. While there have been many studies concerning the behaviour of concrete-filled chord members, the role of concrete-filled bracing members has yet to be fully investigated; this represents a significant gap in the existing body of knowledge. The objective of this study is to examine how parameters including chord thickness, concrete infill length, and concrete compressive strength affect the overall joint performance. Both experimental and numerical approaches were employed. The testing program consisted of eight specimens with varying infill configurations. All eight specimens were subjected to axial compressive loading applied to the brace member and characterised in terms of strength, stiffness, and failure mode. A finite element (FE) model was developed in ABAQUS and validated against the experimental results. Once validated, the model was used to perform parametric study. The test data show an increase in maximum loads that can be supported by joints of as much as 198% for the bare steel control condition based on geometrically identical sections with different types of infills. A transition in failure mode was also observed, from chord face plastification to localised buckling of the brace member. Additionally, numerical increases were found through the parametric studies where the chord thickness was varied along with the type of infill used. Further evaluation demonstrated that currently available code-based design provisions are not applicable to this composite configuration. Consequently, a new capacity prediction equation for composite T-joint configurations is presented and incorporates terms for concrete bearing on the chord face, chord thickness, concrete infill length, and concrete compressive strength. The predicted capacities obtained from the ABAQUS finite element model, and the proposed equation showed good agreement with the experimental results.</p>