Tubular Bridge Joints Research Articles

Determining the SCFs of tubular bridge joints with an alternative method

Circular hollow sections are being used in various modern bridges. Although these bridges are highly appreciated because of their aesthetic value, they are considered to be costly, mainly due to the use of cast or welded joints. The fatigue strength of these structures is important since stress concentrations are reached near the weld toe of the joints. These are due to geometric discontinuity and to the welding process, thus making this type of bridge prone to fatigue damage caused by varying traffic loads.There are various methods to determine the stress concentration factors (SCFs) of a welded tubular joint. The existing methods are not suitable for complex tubular joints or require vast computing time. An alternative method for determining the SCFs of complex tubular bridge joints is being proposed. This method is applicable to any tubular joint and accurately determines all SCFs of the joint. These SCFs allow fast computation of the hot spot stresses of the tubular joint loaded with any realistic load condition.

Residual Stresses in As-Welded Joints: Finite Element Modeling and Neutron Difraction Stress Measurements

This paper describes the numerical analysis method used to estimate welding induced residual stresses in K-shape tubular bridge joints. The knowledge of residual stress distribution is required to design the geometry of K-joints loaded under fatigue stresses. Numerical simulations are focused on the arc welding MAG process, generally used to weld joints in bridge construction. Thermo-mechanical analyses are performed in 3D using two finite element codes:ABAQUS® and MORFEO® . ABAQUS has the advantage to offer large analysis capabilities(nonlinear, transient, dynamic, etc.) whereas MORFEO is more dedicated to welding processes and offers the possibility to analyze crack propagation under fatigue loads. Computed residual stresses in the region surrounding the weld are compared with measured residual stresses in order to estimate the ability of the codes to reproduce these stresses. Position, orientation and magnitude of the highest residual stress components are discussed.

Size effects in the fatigue behavior of welded steel tubular bridge joints

AbstractTubular space trusses for bridge applications use thick‐walled tubes. The reduction in fatigue resistance due to geometrical size effects is thus an important issue. In order to carry out a thorough study, both fatigue tests on large‐scale specimens and advanced 3D crack propagation modelling were carried out at ICOM/EPFL. The study is limited to circular hollow sections (CHS) K‐joints. An alternate current potential drop (ACPD) system is used to measure crack depth on nodes of the tested truss specimens. The results obtained from the tests are given in the paper in terms of S‐N data, crack depth versus number of cycles and deduced crack propagation rates. The numerical model was developed using the dual boundary elements method (DBEM), software BEASY™, and was validated with fatigue tests data. The stress intensity factors (SIF) along the doubly curved crack front at different crack depths were obtained. With this model, a parametric study investigates the influence of geometry, size and load case on fatigue life. The results of both proportional and non‐proportional sizing effects on fatigue strength are presented. The paper shows that size effects (proportional and non‐proportional) can be expressed as a function of the non‐dimensional parameters and chord thickness.

A probabilistic model for determining the effect of post-weld treatment on the fatigue performance of tubular bridge joints

Herein, a probabilistic model for predicting the effect of post-weld treatment on the fatigue performance of the welded joints in tubular truss bridges is described. Specifically, a probabilistic LEFM-based model is first developed for the fatigue analysis of single untreated and treated crack sites in tubular K-joints. A systems reliability approach is then proposed for the analysis of tubular structures with multiple potential crack sites. Using this approach, it is then demonstrated that significant improvements in the fatigue reliability of tubular joints with dimensions common to bridge structures can be obtained with post-weld treatment, even when the influences of the various untreated and treated potential crack sites are considered.