Probabilistic fatigue life updating accounting for inspections of multiple critical locations

Many steel structures contain multiple fatigue sensitive details that have similar geometries and are subjected to similar load fluctuations. Examples are orthotropic (bridge) decks and stiffened (ship) hulls where tens to thousands of similar details are present in one structure. Generally only visual inspections on fatigue cracks are considered for these structures because more accurate techniques are considered to be too expensive and time consuming when so many details need to be inspected. Visual inspections are known to have a low probability of detection. Consequently Bayesian update techniques usually show a marginal effect of the result of visual inspections on the reliability of structures with respect to fatigue failure. On the other hand the inspection result of one location also provides information on similar details at other locations and thus the significance of the inspection result may be larger if multiple potential crack locations occur and cracks are not detected at any of these locations. This paper provides a probabilistic fatigue crack growth (fracture mechanics) model of a system containing a fatigue sensitive detail at multiple locations that accounts for the results of inspections. Spatial correlations of loading, resistance, and uncertainty variables between the different locations are evaluated and estimated through a literature review and are accounted for in the model. The model is demonstrated on a practical example of an orthotropic bridge deck containing a detail at 100 locations. The paper shows that visual inspections may be effective provided that a certain minimum inspection reliability can be guaranteed, that the structure is relatively tolerant to large cracks, and that the geometry and loading conditions are similar for a large number of locations

Inspectie-interval is geen toeval – vermoeiing van bruggen (2) : bepalingsmethode voor stalen brugdekken

Het verstrijken van de vermoeiingslevensduur vna stalen verkeersbruggen stelt beheerders ervan voor een aantal dilemma's. Wanneer moet ik de eerste inspectie laten plaatsvinden en bij welke details? Wat is het inspectie-interval voor voldoende veiligheidsniveau? Als er een scheur gevonden wordt, hoeveel tijd heb ik om een reparatie uit te voeren? Welke inspectiemethode moet ik toepas-sen? Dit artikel geeft een (berekenings)methode om een gefundeerd antwoord te kunnen geven op deze vragen

Numerical investigation into strong axis bending-shear interaction in rolled I-shaped steel sections

Clause 6.2.8 of EN 1993-1-1 covers the design rules on bending-shear resistance, taking presence of shear into account by a reduced yield stress for the shear area. Numerical research on bending-shear interaction by means of the Abaqus Finite Element modelling software is presented. The numerical model is validated against the experimental results. A material model based on various tensile test coupons was used incorporating the actual mate-rial properties within the tested cross-section. Strong axis three-point bending tests were simulated by means of continuum solid elements. Good agreement was achieved between numerical and experimental result, both are compared with the EN 1993-1-1 design rule

Fire exposed aluminium structures

Material properties and mechanical response models for fire design of steel structures are based on extensive research and experience. Contrarily, the behaviour of aluminium load bearing structures exposed to fire is relatively unexplored. This article gives an overview of physical and mechanical properties at elevated temperature of frequently applied aluminium alloys, found in relevant literature and discusses mechanical response models currently applied for fire exposed aluminium structures. A comparison is made with steel structures exposed to fire

Fire safe buildings with thin-walled steel + insulation systems

BackgroundIt is important that buildings should be able to withstand a fire during evacuation and extinguishment. To determine a building’s fire resistance ability, full scale experiments would be ideal, but these are very expensive. Therefore an existing simulation approach will be extended, whichenables theoretical models and design rules to be developed to predict system failure as a function of component failure

Fatigue assessment for deck plates in orthotropic bridge decks

Since the 1960s, orthotropic deck plates of highway bridges have been built with large cold-formed trapezoidal stiffeners supporting a deck plate with a thickness of approx. 12 mm. The maximum cross-beam spacing is approx. 4 m. A number of these bridge decks in The Netherlands suffer from fatigue cracks in the deck plate. First cracks have been observed after about 30 years in service. In one particular movable bridge, the cracks were found after only seven years. In many other countries, this type of crack has not yet been observed. This article provides a fatigue assessment procedure for deck plates. The procedure is calibrated with the conditions and observations in The Netherlands. It gives a fatigue life prediction and takes account of inspection results quantitatively. Although aspects such as the type and thickness of the surface finishes and the traffic load may vary between countries, the principles of the assessment procedure in this article are generally applicable and can be used to identify reasons for differences in fatigue life and to develop strategies for increasing the life

Determining the moment-curvature diagram of aluminium cross-sections in fire; a numerical code and practical examples

The use of aluminium as a construction material has been increasing since its first invention. At present, limited knowledge of the behaviour of aluminium beams in fire gives rise to excessively high insulation demands, decreasing its competitiveness. To study the behaviour of (statically undetermined) bending members in fire, it is required to know the moment-curvature diagram. For aluminium and stainless steel at both room and elevated temperatures, and for steel at elevated temperatures, this curve cannot be calculated analytically, but needs to be obtained numerically. A versatile numerical code is presented, capable of calculating the moment-curvature diagram for arbitrary geometries along any axis with arbitrary temperature and initial strain distributions