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Abstract: Steel bridges fabricated with Q345qD steels face critical challenges when operating in cold regions with a low ambient temperature. This study aims to investigate, via an experimental program, the low‐temperature fatigue crack propagation behavior of Q345qD bridge steel base material and its butt welds. The testing program comprises a series of Charpy impact tests and fatigue crack propagation tests at the room temperature, −20°C and −60°C. The experimental results demonstrate a reduced crack propagation rate in the base material, but an increasing crack propagation rate in the butt welds, with a decreasing ambient temperature. The base material also shows enhanced fatigue crack propagation thresholds with the decreasing temperature. The ductile‐to‐brittle transition temperature for fatigue is lower than that for fracture in the base material while the weld metal exhibits an opposite trend. Generally, the butt welds present higher resistance against fatigue crack propagation and larger Charpy toughness values than do the base material at all tested temperatures. The Paris‐law parameters measured at the room temperature for the base material leads to a conservative assessment of the crack propagation life for a welded joint under a low ambient temperature. [ABSTRACT FROM AUTHOR]

Current design formulae for circular hollow-section (CHS) T and X joints loaded by brace in-plane or out-of-plane bending moments are based on a limited number of tests available from the early 1980s. In the last three decades, many experimental studies and numerical research programmes have been conducted in this area. This study re-evaluates the brace moment capacity strength of T and X joints. The available data are checked against possible member failures, while the experimental data are carefully screened with respect to outliers. Detailed comparisons are made between finite-element results and 'reliable' test data obtained from different research programmes. Based on the selected data, the existing strength equations are updated. [ABSTRACT FROM AUTHOR]

This paper presents results from a systematic finite-element (FE) study on the static strength of moment loaded thick-walled circular hollow section (CHS) X-joints, and compares the results with CIDECT and ISO/CD 13819-2 recommendations. For thick-walled joints subjected to brace out-of-plane bending, the CIDECT formulation excludes the γ dependency in the joint strength, which is different from the ISO equation and the present FE observations. The current study compares the different load paths mobilized in the X-joint under various brace loading conditions, through a detailed three-dimensional finite-element study. The numerical results reveal the significance of the joint geometric parameters and the tensile chord stress effect on the ultimate joint strength. Based on the present detailed study, a new chord stress function which incorporates the geometric dependency and the tensile chord stress effect is proposed. [ABSTRACT FROM AUTHOR]

Numerical modeling of the fracture effects on the strength of steel circular hollow section joints has not been sufficiently addressed historically. The Gurson model simulates the plastic yield behavior of material with microvoids. It is found in the current study that we can offer an alternative approach in modeling the ductile fracture for the strength analysis of tubular joints. Two loading conditions are investigated on tubular bars with the Gurson model. The effects of void growth and nucleation are observed to be more prominent in the axial tensile mode than the shear mode. Two types of tubular joints are investigated: precracked tubular joints and intact tubular joints. The effect of ductile fracture is reflected by softening of material, which leads to reductions in load–deformation curves which are consistent with test observations. Due to the lack of material data, a sensitivity study is carried out on the Gurson’s material properties. [ABSTRACT FROM AUTHOR]