Experimental and numerical analyses on stress concentration factors of concrete-filled welded integral K-joints in steel truss bridges

Abstract

A novel fully welded concrete-filled integral K-joint incorporating longitudinal perfobond ribs welded to the inner faces of the chord is proposed to improve the fatigue behavior. To evaluate the stress concentration factor (SCF) of such joints, a 1:5 scale truss specimen was fabricated and tested to measure the SCF distribution in the fatigue prone joint. A finite element model was also developed to evaluate the SCFmax of concrete-filled welded integral K-joints and was validated against the test results. A parametric study was carried out and a comprehensive database was obtained considering the effects of brace width-to-chord thickness ratio (2γ), brace-to-chord thickness ratio (τ), the angle between braces and chord (θ) on the SCFmax. Also, the following three basic loading conditions were examined: brace axial force, chord axial force and chord in-plane bending. Based on the results of 192 numerical models, new equations to predict the SCFmax of concrete-filled welded integral K-joint were derived for design purposes. Finally, the fatigue behavior of three different designs is compared in terms of SCFmax and hot spot stress range Sh-N curves. These systems are rectangular hollow section (RHS) K-joints, concrete-filled rectangular hollow section (CFRHS) K-joints and concrete-filled welded integral K-joint. It was shown that the concrete-filled integral welded K-joint has the best fatigue behavior, followed by the CFRHS K-joint, while the RHS K-joint has the poorest fatigue behavior.