This study numerically investigates the limitations of structural hot-spot stress (SHSS) methods and proposes a guideline for the calculation of hot-spot stresses, which can be used for the better evaluation of fatigue-related problems. Four different SHSS evaluation methods have been applied to the rib-to-deck (RD) welded joint in orthotropic steel deck (OSD). These methods are used to calculate SHSS at this critical joint utilizing finite element analyses (FEA) based software Siemens NX.12. The limitations and the accuracy of these methods have been observed under different element types and meshing techniques. Moreover, the effect of the nodal-averaging feature is being studied. Two types of governing stresses are produced by the application of Eurocode fatigue load model-4. Essentially, the bending in deck-plate produces highly non-linear stress at the deck-toe, and the membrane effect in rib-plate generates linear stress at the rib-toe. Guidelines are proposed considering different parameters on these two stress states by applying SHSS evaluation methods. In comparison to other SHSS approaches, the International Institute of Welding (IIW) quadratic stress extrapolation (QSE) method shows better results for solid single-element, and the American Society of Mechanical Engineers (ASME) through thickness stress linearization (TTSL) method stands out in solid cubic-mesh technique. In general, shell elements have more consistent SHSS results as compared to solid elements for both stress states.

When adopting the trapezoidal section of ribs in orthotropic steel decks, the torsional rigidity of ribs losses radically because of rib distortion especially when the load is eccentric from the axis of the rib. Hence, the rib distortion causes high stress concentrations at the rib-to-crossbeam joint which makes this joint easily prone to fatigue. In this paper, the influence of 4 conventional design parameters on distortional behaviour is investigated by numerical simulation adopting the hot spot stress approach and the sub-model analysis technique. A refined finite element model of an orthotropic steel deck specimen with the dimension of 8.2 m × 4.1 m is built. Research results indicate that the distortional stress rises with the increment of the spacing of crossbeam or the weld length of rib-to-crossbeam joint. The thickness of rib is negatively correlated with the distortional stress. The influence of the spacing of rib on distortional stress depends on the relative size between the width of load area and the spacing of rib. The most unfavourable load position is determined by rib geometries, i.e. the thickness of ribs, whereas rest three parameters do not have obvious influence.

Longitudinal ribs with the trapezoidal section are broadly adopted in orthotropic steel decks especially for long span bridges. When the tire load is eccentric from the axis of the rib, the torsional rigidity of ribs is critically reduced by distortion which impedes the horizontal dispersal of load. Because of the existence of cutouts in crossbeam, the high stress concentration at the rib-to-crossbeam joint caused by the rib distortion makes the joint easily prone to fatigue damage. In this paper, based on the parametric analysis of several classical design parameters, static load experiments of an orthotropic steel deck specimen are performed. Measurement results support the positive correlations between the weld length of rib-to-crossbeam joint and the distortional stress. The most unfavorable load position of stress concentration induced by rib distortion is also verified, which is about 1600 mm away from the investigated crossbeam. Experimental results indicate that ribs are deformed toward different directions at the midspan section and the crossbeam section separately when the load is eccentric from the axis of rib.