Fatigue Assessment Of Welds Research Articles

Methods for Structural Stress Determination according to EN 13445-3 Annex NA – Comparison with other Codes for Unfired Pressure Vessels

The European Pressure Vessel Standard EN 13445 provides in its part 3 (Design) a simplified method (Clause 17) and a detailed method for fatigue assessment (Clause 18). Clause 18 “Detailed Assessment of Fatigue Life” is under revision within the framework of the European working group CEN/TC 54/WG 53 – Design methods with the aim of reaching a significant increase in user-friendliness and a clear guideline for the application. This paper is focused on the new informative annex NA ”Instructions for structural stress oriented finite elements analyses using brick and shell elements”. As an essential amendment for the practical user, the determination of structural stress ranges for fatigue assessment of welds is further specified in this new annex. Different application methods for the determination of structural stresses are explained in connection with the requirements for finite element models and analyses. This paper will give a short overview of the proposed approaches of structural stress determination in annex NA of the revised EN 13445-3. It will present the status of the approaches based on the results of fatigue analyses according to EN 13445-3 Clause 18 for different application examples. For verification purposes, the results of the approaches proposed in EN 13445-3 are compared with the results of other pressure vessel design codes for nuclear and non-nuclear application.

Wind-Induced Fatigue Analysis of High-Rise Steel Structures Using Equivalent Structural Stress Method

Welded beam-to-column connections of high-rise steel structures are susceptive to fatigue damage under wind loading. However, most fatigue assessments in the field of civil engineering are mainly based on nominal stress or hot spot stress theories, which has the disadvantage of dependence on the meshing styles and massive curves selected. To address this problem, in this paper, the equivalent structural stress method with advantages of mesh-insensitive quality and capability of unifying different stress-life curves (S-N curves) into one is introduced to the wind-induced fatigue assessment of a large-scale complicated high-rise steel structure. The multi-scale finite element model is established and the corresponding wind loading is simulated. Fatigue life assessments using equivalent structural stress method, hot spot stress method and nominal stress method are performed, and the results are verified and comparisons are made. The mesh-insensitive quality is also verified. The results show that the lateral weld toe of the butt weld connecting the beam flange plate and the column is the location where fatigue damage most likely happens. Nominal stress method considers fatigue assessment of welds in a more global way by averaging all the stress on the weld section while in equivalent structural stress method and hot spot method local stress concentration can be taken into account more precisely.

Linear fracture envelopes for fatigue assessment of welds in bridges

Presently welded components are designed using S/N curves which predict only the fatigue life of the component. In order to ascertain the condition of the weld at any intermediate period of its life inspection is carried out. If cracks are detected in a weld fracture mechanics is used to find their remaining life. A procedure for assessment is developed here that can be used to verify the condition of a weld before inspection is carried out to detect cracks. This simple method has been developed using linear fracture envelopes by combining S/N curves with linear elastic fracture mechanics.