Structure Fatigue Strength Evaluation

This paper presents the finite-element procedure for fatigue evaluation of reinforced concrete bridge deck under the application of truck wheel load. The approach is based on the smeared crack concept with the introduction of the fatigue tests of concrete and reinforcing steel available in the literature and the Palmgren-Miner linear criterion of cumulative damage in the analysis. The models are validated with the fatigue test of 1/6.6-scale AASHTO bridge deck under the application of fixed-point repetitive loading presented in previous study. Results are in good agreement. Significant contribution of the developed approach to the fatigue evaluation of bridge deck is a series of S-N relations which can be simulated at any desired levels of damage. This permits the investigation of the deterioration of bridge deck which is appeared to be useful information for highway agencies to prolong the life of their bridge decks. S-N relations are simulated at crack areas of 10%, 20%, 30%, and 40% of the bottom surface area of the deck slab to represent the propagation of crack. Deterioration of bridge deck subjected to passages of five-axle double-unit trucks in Thailand is investigated to demonstrate the application of the simulated S-N relations.

Concrete paving blocks ideal materials on footpath for easy lying, aesthetic look and finish. It was found that rapid
deterioration occurred on pavers and blocks became unserviceable within few year of utility. The application of paver block has
extended to the traffic area and due to movement of vehicle, there is a formation of cracks on the paver blocks.re is a formation
of cracks on the paver blocks. By considering this as a matter of grave concern to the serviceability of paver blocks and with the
aim of manufacturing durable as well as visible paver blocks an attempt is made by inclusion of Chicken wire mesh as
reinforcement in paver blocks. The strength and durability characteristics study is been carried out in order to analyze the
suitability of such paver blocks in practical.

The costs and times associated with Full Scale Fatigue Tests (FSFTs) are enormous, but to date, they have proved to be the only reliable means for verification and validation of aircraft durability and safety and are thus mandated by aviation regulators for any new aircraft type. At the same time, however, analyses or models have been playing an increasing role in the qualification/certification process, and the question beckons whether the FSFT can one day be dispensed with.  In this paper, rationale for both sides of the argument is presented, but concludes that the important question is not so much whether the FSFT can be done away with, but rather how FSFT can be performed more efficiently?  To this end, a new concept is proposed that is a hybrid of the conventional FSFT and the complete digital model.  Borrowed from the control systems engineering field, the hardware-in-the-loop simulation (HiLS) approach is adapted to provide the best of both worlds – the realism of actual testing for the critical components, together with the flexibility and cost-effectiveness of modelling.  Whilst this approach has been made possible by a unique DSTO-developed technology that allows fatigue hotspots to be identified, its eventual success will also require some other technical problems to be solved.  However, whilst these hurdles may be challenging, it is shown that they are not insurmountable and some suggestions are presented on how these may be tackled.

Thick walled components such as high pressure (HP) steam turbine casings operating under high parameter conditions are subjected to a complex stress state. As a result of that stress state, some parts of HP turbine casing undergo to the creep fatigue caused by the combination of thermal fatigue resulted from repeated start/stop operation and the creep which occurs during long-term operation at high temperature and high-pressure. It is well known that domestic thermal power plants have been in use over 100000 h which means that significant cost is required not only for maintenance, but often for renewal of equipment. Based on comprehensive investigation, the results of residual life assessment of one high pressure steam turbine casing, which belongs to the older turbine generation, taking into account simultaneous action of thermal fatigue and creep, are presented in this paper. Also, the critical flaw crack size of HP turbine casing is determined because this parameter has a strong influence on casing integrity and residual life. The results of residual life assessment provide not only a basis for further maintenance, but also estimated time for reparation or renewal.