Tree Composites Joints (TC-joints)

TC-joints replaces the traditional welding in TKY joints delivering a lightweight structure with higher fatigue resistance, reduced steel volume (up to 60%) and an increased lifetime. This innovation originates from the faculty of Civil Engineering of the TU Delft. Since 2017 over 120 wrapped composite joints have been manufactured and tested on various sizes of joints at the Stevin Lab of Tu Delft and at OCAS Belgium. The results of these test conclude that the wrapped composite joint outperforms welds in fatigue resistance, maximum load resistance and joint stiffness.

The improvement of the TC-joint compared to welding is that the load is transferred through a dedicated composite wrap and not through the small surface of the weld. The brace members (diagonals) are bonded to the chord members (legs) through a coupling formed by composite wrapping. 

The composite wrap is tailored (length and thickness) to deal with static and dynamic loads transferred by the joint. The optimized, nature-like, shape of the composite wrap, with increasing thickness towards the root of joint, reduces the stress concentration in the composite material and bonded interface, thereby solves issues in fatigue prone/driven design. The substantial improvement of the fatigue resistance of the Circular Hollow Section (CHS) joints is achieved by 1) completely circumventing stress concentrations in steel that normally are present due to local wall bending, and 2) avoiding residual stresses, embrittlement and notch effects due to welding.

A TC-joint is made by the application (lamination) of glass fibres on the non-welded steel tubes. This provides outstanding bonding strength and flawless quality.