<p>Through-bolts have demonstrated efficacy as a circular hollow section (CHS) T-joint strengthening method; however, the absence of design guidelines necessitates further investigation. Therefore, using non-linear finite element analysis, numerical research has been conducted to establish robust design equations for predicting the axial capacity of CHS T-joints strengthened using through-bolts under axial brace loading. Focusing on chord face plastification as the primary failure mode, validated finite-elements models were utilized in an extensive parametric study, varying parameters such as the number of through-bolts, spacing between them, chord diameter-to-thickness ratio (<i>γ</i> = <i>d</i>₀/2<i>t</i>₀), and brace-to-chord diameter ratio (<i>β</i> = <i>d</i>₁/<i>d</i>₀). Subsequently, four equations were formulated to account for different through-bolt arrangements, delivering the through-bolt impact factor (<i>Q</i>_TB), which can be applied to the design equations for accurate strengthened capacity of the T-joints across a wide validity range. Additionally, empirical ratios were derived to estimate the force in the through-bolts, so that the cross-sectional diameter of the through-bolt can be chosen.</p>