Search

Steel hollow structure section (HSS) chord-to-branch joints in Vierendeel trusses are concerned for their proneness to fracture due to imperfection in fabrication. In this paper, the stress intensity factors (SIFs) for HSS chord-to-branch joints are examined based on fracture mechanics and finite element modelling. Through a well-prepared sub-modelling strategy, the influences of geometric parameters related to the crack propagation behaviour are analysed and discussed. The crack front of the HSS chord-to-branch joint without the axial stress of the branch is shown to have notably high SIFs at the deepest point and the surface point. Alternatively, the concentration of highest SIFs at the deepest point of the elliptical arc of the crack becomes significant with the increase of the axial stress of the branch. The increase of the chord wall thickness is shown to be beneficial in the reduction of the SIFs for HSS chord-to-branch joints, especially for lower chord width ratio normalized by thickness. Conversely, the influence of the crack shape indicated by larger aspect ratio on the reduced SIFs becomes obvious and consistent for greater chord width ratio normalized by thickness. The SIFs for HSS chord-to-branch joints are decreased with the increase of the normalized crack depth with respect to the chord wall thickness, particular for shallow surface cracks. Such a trend becomes obvious for the joints with lower fillet weld leg length of equal leg fillet welds with respect to the chord wall thickness or with lower weld leg length along the HSS branch with respect to that along the chord. [ABSTRACT FROM AUTHOR]

Bolted spherical joints, due to their prominent merits in installation, have been widely used in modern spatial structures. Despite significant research, there is a lack of understanding of their flexural fracture behaviour, which is important for the catastrophe prevention of the whole structure. Given the recent development to fill this knowledge gap, it is the objective of this paper to experimentally investigate the flexural bending capacity of the overall fracture section featured by a heightened neutral axis and fracture behaviour related to variable crack depth in screw threads. Accordingly, two full-scale bolted spherical joints with different bolt diameters were evaluated under three-point bending. The fracture behaviour of bolted spherical joints is first revealed with respect to typical stress distribution and fracture mode. A new theoretical flexural bending capacity expression for the fracture section with a heightened neutral axis is proposed and validated. A numerical model is then developed to estimate the stress amplification and stress intensity factors related to the crack opening (mode-I) fracture for the screw threads of these joints. The model is validated against the theoretical solutions of the thread-tooth-root model. The maximum stress of the screw thread is shown to take place at the same location as the test bolted sphere, while its magnitude can be greatly reduced with an increased thread root radius and flank angle. Finally, different design variants related to threads that have influences on the SIFs are compared, and the moderate steepness of the flank thread has been found to be efficient in reducing the joint fracture. The research findings could thus be beneficial for further improving the fracture resistance of bolted spherical joints. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the fatigue life estimation of off-centrally cracked aluminum plates. Typical theoretical equations for off-central, central and edge cracks were reviewed and compared in terms of their sensitive parameters and applicability. A finite element model has been validated in its capacity in modelling the influences of eccentricity and crack size on the boundary correction coefficients. The Forman equation has been employed along with numerical results for the prediction of fatigue lives. Based on the test data, the fatigue life results of aluminum plates with and without patched laminate repair have been compared with codified fatigue classes. It is demonstrated that the repair at the crack tip close to the plate edge is effective in the fatigue life improvement for off-centrally crackedaluminum plates. [ABSTRACT FROM AUTHOR]

The aim of this study is to find out the degradation of dynamic behaviour of bridge girders with trapezoidal profiled webs when subjected to different vehicle moving loads. Finite element modelling based parametric analysis is demonstrated to be desirable in capturing the dynamic deflection and stress state of critical structural details of girders. The model is validated in the modal analysis through a comparison with theoretical eigenfrequencies. The vibration characteristics are shown to be significantly affected by the corrugation details. The structural service life results of analysed bridge girders are in close agreement with experimental data. It is shown that the dynamic nodal velocity and deflection of analysed bridge girders are greatly affected by the magnitude of the load corresponding to the overload of the vehicle in contrast to the vehicle travel speed. Similar observations can be made for the fatigue life prediction analysis related to the crack initiation when unfavourable effects of the overload vehicle are concerned. Presented analytical results using a fracture mechanics approach could be taken as a good basis for the service life assessment of related bridges with the desired level of performance or functionality. [ABSTRACT FROM AUTHOR]