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    Item type:Publication, Access status: without files ,
    Fatigue crack repair by TIG-remelting
    (2021-04)
    Al-Karawi, Hassan
    ;
    Manai, Asma
    ;
    Al-Emrani, Mohammad
    ;
    von Bock und Polach, Rüdiger Ulrich Franz
    ;
    Friedrich, Nils
    Fatigue is one of the most detrimental Problems that often limits the service life of steel bridges. Because of that, different post weld treatment methods have been studied to extend the fatigue life and repair any existing cracks resulted from the traffic loading. The aim of this paper is to study the fatigue life extension of cracked structures by means of Tungsten Inert Gas (TIG) remelting. Fatigue tests were conducted at stress ratio of 0.29 on a transverse attachment of 16 mm, thick-walled specimens. The specimens were instrumented with multiple strain gauges along the weld to detect the strain drop caused by crack growth. The specimens were pre-fatigued until a crack of around 1 mm- deep was obtained at the weld toe. After crack detection, the weld toes were treated by TIG-remelting to remove any existing cracks and to reduce the local stress concentration. The weld parameters were controlled so that the fusion depth was always larger than the crack depth. A substantial fatigue life extension could be achieved and the testing led to ran-out after 10 million cycles, which was attributed to the improvement in geometry and residual stress. Weld toe radius were measured before and after treatment by laser scanner. Hole drilling was used to measure the residual stresses in as-welded state and after TIG-remelting. In this paper, a fatigue damage model is also presented. It is shown that the model gives a good prediction of the effect of TIG-treatment in repairing fatigue loaded welded details.
    Publicationtype: Conference Paper
      39
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    Item type:Publication, Access status: without files ,
    A methodology for assessment and retrofitting by TIG dressing of existing pre-fatigued welded steel joints
    (2021-04)
    Manai, Asma
    ;
    von Bock und Polach, Rüdiger Ulrich Franz
    ;
    Hedegård, J.
    Several fatigue life extension methods of a welded structure are coveted in the industry such as Tungsten-Inert-Gas Dressing (TIG dressing). This paper presents a framework for a fatigue assessment and retrofitting of welded structures by TIG dressing. The proposed framework provides in detail the parameters that have an influence on fatigue life which can be divided into two groups, the first is related to the structure prior to treatment such (e.g: crack dimension, toe radius, and residual stresses) while the second is related to the state of the structure following the treatment (e.g: treatment depth, residual stresses and resulted toe radius). Experimental results, from the current work, were complemented with tests from literature to verify the proposed framework. An analysis between our predictions and reported values of fatigue life from literature show an absolute error of 20%.
    Publicationtype: Conference Paper
      34
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    Item type:Publication, Access status: without files ,
    Eccentric-wing flutter stabilizer - Effectiveness and costs
    (2021-04)
    Starossek, Uwe
    A device for preventing bridge flutter is presented. It consists of wings running parallel to the bridge deck. In contrast to similar devices proposed in the past, the wings are positioned far outside the bridge deck to achieve a large lateral eccentricity with regard to the bridge axis. This is accomplished by attaching the wings to the bridge deck by means of lateral cantilever structures. The wings do not move relative to the bridge deck. Hence they constitute a passive aerodynamic damping device without moving parts. This is an advantage over devices with moving parts as these meet resistance with bridge owners due to reliability and maintenance concerns. The results of finite element flutter analyses are presented. Furthermore, a simplified approach for the analysis of torsional flutter of a bridge equipped with this device is presented. It leads to a simple equation for determining the flutter speed, in which the influence of all relevant parameters becomes apparent. The simplified approach is applied to the first Tacoma Narrows Bridge. All analyses and tests confirm a high flutter-suppression effectiveness of the wings provided their lateral eccentricity is large. The main findings concerning flutter analysis, flutter-suppression effectiveness, and cost-efficiency of the eccentric-wing flutter stabilizer are outlined.
    Publicationtype: Conference Paper
      36