PRACTICAL IMPLICATION OF DESIGN CRITERIA 2.1 Main Factors Affecting the Fatigue Strengthįatigue of steel structural components, especially welded steel details, is a particularly complex problem, and many factors may exert an influence on the fatigue life. This work has provided an opportunity to re-evaluate existing fatigue test data and allowed for a more consistent approach to the classification of detail categories. To determine the fatigue strength provisions given in Eurocode 3, a compilation of fatigue data of various sources was carried out. In addition to this approach another concept supported mainly by recent developments and research in the field of fatigue for "offshore" structures is referred to in Eurocode 3 as the geometrical stress concentration concept (also called the "hot spot stress" method). The Recommendations define a set of equally spaced fatigue strength curves with a constant slope of m = 3 (for normal stress), or m = 5 (for shear stress, hollow section joints, and some particular details). The concept for fatigue strength design follows the Recommendations of the European Convention for Constructional Steelwork (ECCS). The main provisions of Eurocode 3 rely upon a set of fatigue resistance curves, equally spaced, upon which are classified a set of constructional details. The principal objective of this lecture is to review the main rules which are the basis for Chapter 9 of Eurocode 3 concerning the fatigue strength assessment of steel structural details. Then several factors, introduced in Eurocode 3, affecting the fatigue strength are also discussed. The evaluation is compared with a set of equally spaced S-N curves with a slope constant of m = 3.Įxplanation is given on the choice of a normalised double-slopes S-N curve. The classification of a given detail, either welded or bolted, results from a statistical evaluation of the fatigue test data with a 95% probability of survival for a 75% confidence interval. These fatigue design rules are based on fatigue test results obtained mainly under constant amplitude loading. The lecture discusses the main fatigue design rules contained in Eurocode 3. Lecture 12.2:Ědvanced Introduction to Fatigue SUMMARY Lecture 12.1:ěasic Introduction to Fatigue This lecture contains the background information of the basis of the Eurocodeģ rules concerning the fatigue design of structural elements. The procedure of fatigue strength determination for both normal and shear stresses is obvious from the following pictures.FATIGUE Lecture 12.8: Basic Fatigue Design Concepts in Eurocode 3 OBJECTIVE/SCOPE: These stresses are used for calculation of cycle amplitude according to the formula:įor calculated stress and known endurance limit, the resulting strength of fatigue joint is easily determined according to the selected fatigue curve. Mean cycle stress σ m and upper cycle stress σ h are calculated for the specified mean cycle loading F m and maximum calculated loading F max with the formulas used in static calculation. Calculation of actuating stress in the bolted connection joint This is implemented by using the dynamic stroke factor in the formula for determining the maximum calculated loading:ĥ.
If strokes affect the joint besides the fatigue loading, their influence must be included into the calculation. Mean values for given upper and lower cycle loadings are calculated their mean values according to the following formulas. Calculation of parameters of particular fatigue loadings
Calculation continues with this finite-life fatigue limit.ģ.
The finite-life fatigue limit σ f is calculated for the specified joint life that is in the (N< 10 6 cycles) range of timed strength. In the first step the calculation determines the endurance limit at constant strength σ C for the specified type, design, loading, and material of bolted connection. This description follows step by step the implementation in the program: The description of fatigue loaded bolted connection joints checking follows. Consequently, the fatigue strength of joint is used in check of fatigue loaded joints. Conventional check procedures at fatigue loaded bolted connection (based on the ultimate or yield strength of material) do not provide sufficient guaranty of safe joint design.
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