Section K1.1/HSS-to-HSS Truss Connections
AISC 360-22 Chapter K covers HSS connection design addressing chord wall plastification, shear yielding, and geometric limits.
Connections to HSS (tubes and pipes) must account for failure modes that do not occur with open sections (W-shapes, channels). These include chord wall plastification (yielding of the chord wall under the branch member load), chord wall shear yielding, sidewall failure, uneven load distribution in the branch, and chord distortional failure. The capacity of an HSS connection depends on the chord wall thickness, the branch-to-chord width ratio (beta), the chord utilization ratio, and the gap or overlap between branch members. HSS truss connections require specific geometric limitations: minimum gap, maximum branch-to-chord width ratios, and minimum chord wall thickness.
Why this section exists
HSS members have thin walls compared to their overall dimensions. When a branch member frames into the chord of an HSS truss, the concentrated force can punch through, buckle, or plastify the chord wall. These failure modes are different from the bolt shear and plate bearing failures in conventional wide-flange connections. Without the Chapter K provisions, designers might use connection design methods from Chapter J that do not account for these HSS-specific failure modes, leading to unconservative designs.
What plan reviewers look for
Plan reviewers check HSS truss connection details for compliance with Chapter K geometric limits (branch-to-chord ratios, gap distances, wall thickness). They verify the connection strength is checked for all applicable limit states (plastification, shear yielding, sidewall failure). They check that the chord utilization ratio is included in the capacity calculation, as a heavily loaded chord has reduced connection capacity.