Now showing 1 - 10 of 161
  • Publication
    Finite Element Updating using Cross-Entropy Combined with Random-Field Theory
    (Civil-Comp Press, 2014-09) ; ;
    In this paper, the possibility of introducing random field theory into the cross-entropy algorithm is studied. Cross-entropy algorithm is an optimization process that Walsh and González (2009) use to estimate the stiffness distribution of a structure given a set of displacements. Although this method has been successfully tested, many lines of improvement are still opened. Random field theory is incorporated into the algorithm in an attempt to account for spatial variability of stiffness throughout the structure. For this purpose, a correlation function, variable in space, is defined and, as a result, a modification of the algorithm is proposed. The modified algorithm is then tested using numerical simulations in a scenario consisting of a simply supported beam.
      332
  • Publication
    Enhancing Student Performance through a Competitive Team Tournament
    In some engineering subjects, the nature of the material requires a maturation time in the student’s mind before being fully understood and the time constraints of modularization can become an impediment to the successful achievement of their learning outcomes. This paper presents a novel and efficient way of helping students to timely meet their learning outcomes by means of a Team Game Tournament. The principle behind a Team Game Tournament is that the success of a team lies on the success of the individuals composing the team. Therefore, team mates help each other and study more than individually because they care for them and for the team. A variation of Team Game Tournament inspired by the UEFA ‘Champions League’ is used here to address learning outcomes for two different age groups, four modules, four engineering degrees and two countries during the 2013/14 and 2014/15 academic seasons. It is noticed that the more games between the teams, the more effective the team work and learning has become. Confidential questionnaires and end-of-semester exams confirm the success of the competition in enhancing student satisfaction and learning.
      669
  • Publication
    Value of inspection in fatigue management of steel structures
    Fatigue cracking is a common problem that needs to be managed in the life cycles of steel structures. Operational inspections and repairs are important means of fatigue crack management. Driven by high relevance in safety control and budget saving, inspection and maintenance planning has been widely studied. However, the value of inspection and repairs has typically not been fully appreciated and quantified rationally before they are implemented. The basic idea of this paper is to address the planning problem with focus on repair other than on inspection. A maintenance strategy without inspection is studied and serves as comparison of a maintenance strategy with inspection. Then the value of repair and the value of inspection relative to repair can be evaluated respectively. An illustrative example is performed on a typical fatigue-prone detail in steel structures.
      142
  • Publication
    Modal analysis of a bridge using short-duration accelerations
    The application of unmanned aerial vehicle technology to bridge structural health monitoring has become a hot research topic due to its low cost, safety and high energy efficiency. However, flight duration and battery life are substantial technical limitations. Is a short data burst sufficient for damage detection? This paper intends to answer this question by developing a novel approach based on frequency domain decomposition to obtain the mode shapes from a short data burst. Then, the modal assurance criterion is used as an indicator of the differences between the estimated mode shapes from the short data burst and the exact eigenvectors from finite element analysis. Here, the short data burst is obtained from the simulated acceleration response of a bridge beam model due to the crossing of two quarter-cars. A new damage indicator based on the modal assurance criterion profile along the beam is proposed to locate and quantify damage.
      201
  • Publication
    Dynamic analysis of the nonlinear response of high density fuel storage racks
    High Density Spent Fuel Storage racks are steel structures designed to hold nuclear spent fuel assemblies removed from the nuclear power reactor. Weighing around 60 tons, they are 5m high free-standing structures resting on the floor of a 12m depth pool and separated by only a few centimetres. Their underwater seismic response is a troubling safety issue, especially after Fukushima nuclear disaster. However, only limited basic guidelines have been provided as regulatory design criteria to date. The racks’ design deals with a very highly nonlinear behaviour, a transient dynamic response and a fluid-structure interaction problem. Industry is currently using available computer-aided finite element analysis software to solve the design problem in a cost-effective manner but some dispersion of results still exists. Hence, the nuclear regulatory authorities are requiring an evaluation of the current uncertainty associated to the assessment of rack displacements, rocking and maximum forces on supports. This paper discusses the main difficulties faced during the seismic analysis and presents an ad-hoc analysis methodology based on the hydrodynamic mass concept which takes advantage of a simplifying thermal analogy. The methodology, implemented in ANSYS FE Mechanical is hereby described for a reduced scale 2-rack model where the coupling effect of water in the dynamic motion of immersed racks is quantified and displacements and forces are provided. Finally, methodology assumptions are discussed and lessons learnt about the behaviour trends are summarized.
      324
  • Publication
    Probabilistic maintenance optimization for fatigue-critical components with constraint in repair access and logistics
    There is a need to consider repair delay and incurred failure risk in maintenance optimization for some fatigue-critical structural details in marine and offshore structures. For example, in some cases, immediate repair may not be feasible due to weather, geographical location and/or technical restrictions. Also, immediate repair may be much more expensive than well-organized delayed repair. Moreover, detected cracks may sometimes be left unattended until more cracks are found and repaired together. This paper investigates a probabilistic maintenance optimization method allowing for repair delay and the incurred failure risk. The maintenance strategy considering repair delay is optimized based on uncertainty modeling, reliability and life-cycle cost analysis. Special features of the maintenance strategy and its impacts on fatigue reliability and life-cycle costs are discussed on an illustrative example. A method to quantify the risk incurred by repair delay is proposed. It is found that repair delay can result in a significant decrease in fatigue reliability if inspection is scheduled in the late stage of service life. The benefits of the maintenance strategy to fatigue reliability and life-cycle costs are very sensitive to the inspection method. The failure risk incurred by repair delay would be the predominant risk in the life cycle.
      179
  • Publication
    Dynamic axle force and road profile identification using a moving vehicle
    The axle forces applied by a vehicle through its wheels are a critical part of the interaction between vehicles, pavements and bridges. Therefore, the minimisation of these forces is important in order to promote long pavement life spans and ensure that bridge loads are small. Moreover, as the road surface roughness affects the vehicle dynamic forces, the monitoring of pavements for highways and bridges is an important task. This paper presents a novel algorithm to identify these dynamic interaction forces which involves direct instrumentation of a vehicle with accelerometers. The ability of this approach to predict the pavement roughness is also presented. Moving force identification theory is applied to a vehicle model in theoretical simulations in order to obtain the interaction forces and pavement roughness from the measured accelerations. The method is tested for a range of bridge spans in simulations and the influence of road roughness level on the accuracy of the results is investigated. Finally, the challenge for the real-world problem is addressed in a laboratory experiment. 
      411
  • Publication
    Vibration tests of an underwater free-standing 2-rack system
    Nuclear power plants are responsible for the spent fuel management. Closely spaced racks submerged in a pool are generally used to store and to cool the nuclear fuel. A free-standing design allows to isolate the rack base from the pool floor and therefore to reduce the impact of seismic loads. However, the seismic response of free-standing racks is difficult to predict accurately using theoretical models given the uncertainties associated with inertial forces, geometrical nonlinearities, and fluid-structure interactions. An ad-hoc analysis methodology has been developed to overcome these difficulties in a cost-effective way, but some dispersion of results still remains. In order to validate the analysis methodology, experimental tests are carried out on a scaled 2-rack mock-up equipped with fake fuel assemblies. The two rack units are submerged in free-standing conditions inside a rigid pool tank and subjected to accelerations on a unidirectional shaking table. A hydraulic jack induces a given acceleration time-history while a set of sensors and gauges monitor the transient response of the system. Accelerometers track the acceleration of the pool and units. Load cells measure the impact forces on the rack supports as well as the fluid forces at the centre of the rack faces. Video cameras record the transient displacements and rotations. Results provide evidence of a water-coupling effect leading to an in-phase motion of the units.
      193
  • Publication
    Characterisation of pavement profile heights using accelerometer readings and a combinatorial optimisation technique
    Pavement surface profiles induce dynamic ride responses in vehicles which can potentially be used to classify road surface roughness. A novel method is proposed for the characterisation of pavement roughness through an analysis of vehicle accelerations. A combinatorial optimisation technique is applied to the determination of pavement profile heights based on measured accelerations at and above the vehicle axle. Such an approach, using low-cost inertial sensors, would provide an inexpensive alternative to the costly laser-based profile measurement vehicles. The concept is numerically validated using a half-car roll dynamic model to infer measurements of road profiles in both the left and right wheel paths.
      1976
  • Publication
    Impact of a moving trolley on the dynamic response of a ship unloader boom
    (University of Western Australia, 2018-02-02) ; ;
    Container cranes represent an important link in the maritime transport system. Assessment of residual life for such cranes is important both in terms of safety and cost of repair and maintenance. These cranes usually have a hoisting trolley system which can move along the boom for lifting, carrying and lowering the payload, loading/unloading vessels in the harbour. This paper investigates the dynamic response of the lifting boom using a non-linear finite element analysis. A number of such moving trolley systems, with different degrees of complexity, are modelled to assess the impact of their influence on the boom dynamic response parameters. Results from the finite element analysis are compared to a pseudo-static analysis and are presented in terms of a Dynamic Response Factor (DRF).
      300