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.
      334
  • Publication
    Contributions by Marie Sklodowska-Curie TRUSS-ITN towards reducing uncertainty in structural safety of buildings, roads, energy and marine infrastructure
    There is multitude of models available to assess structural safety based on a set of input parameters. As the degree of complexity of the models increases, the uncertainty of their output tends to decrease. However, more complex models typically require more input parameters, which may contain a higher degree of uncertainty. Therefore, it becomes necessary to find the balance that, for a particular scenario, will reduce the overall uncertainty (model + parameters) in structural safety. The latter is the objective of the Marie Sklodowska-Curie Innovative Training Network titled TRUSS (Training in Reducing Uncertainty in Structural Safety) funded by the EU Horizon 2020 research and innovation programme (http://trussitn.eu). This paper describes how TRUSS addresses uncertainty in: (a)  structural reliability of materials such as basalt fiber reinforced polymer, (b) testing techniques in the assessment of concrete strength in buildings, (c) numerical methods in computing the non-linear response of submerged nuclear components subjected to an earthquake, (d) estimation of life of wind turbines, (e) the optimal inspection times and management strategies for ships, (f) characterization of the dynamic response of ship unloaders and (g) the relationship between vehicles fuel consumption and pavement condition. 
      332
  • 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.
      238
  • Publication
    COST 345 – Procedures Required for Assessing Highway Structures, Work packages 4 and 5 report
    (European Co-operation in the Field of Scientific and Technical Research, 2004-09) ; ; ; ; ; ; ;
    This document treats the following aspects of the assessment of existing highway structures: • Levels of assessment: Five levels of assessment are recommended varying from simple but conservative to complex but accurate. • Uncertainty modelling: An integrated approach to traffic loading, structure condition and structural response is described. • Load modelling: There can be considerable unused capacity in highway structures that are not subjected to the full design levels of traffic loading. This can be calculated from traffic weight statistics obtained from a weigh-in-motion system. • Modelling materials for assessment: The processes are reviewed by which material properties in existing structures can be estimated. • Structural response modelling: The types of analysis appropriate to the five recommended levels of assessment are proposed. • Target reliability levels: The levels of reliability considered appropriate for highway structure assessment are discussed. • Reliability analysis: The available procedures for full reliability analysis of highway structures are reviewed. All of these topics are covered in detail in the following chapters. It is not possible in a report of this nature to provide sufficient details for an engineer to use all of the methods by reading this report alone. The report aims to provide sufficient information for engineers and network managers and authorities to choose the appropriate methodology for assessing their structures. It also aims to inform Engineers charged with assessment about some of the procedures available. It is sincerely hoped that this report will contribute to the continued safety and serviceability of the land transport fixed assets in Europe and elsewhere.
      131
  • Publication
    The TRUSS ITN project (2015-19): a Marie Skłodowska-Curie innovative training network on reducing uncertainty in structural safety
    (CERAI, 2018-08-30)
    The structural deterioration of aging structures is often aggravated by an increase in loads that were not foreseen at the design stage and an insufficient maintenance spending as a result of the economic downturn of recent years. A management strategy guaranteeing structural safety with the best use of the resources available is clearly needed. TRUSS (Training in Reducing Uncertainty in Structural Safety, http://trussitn.eu/, 2015-2019) is a €3.7 million Marie Skłodowska-Curie innovative training network funded by the European Horizon 2020 Research and Innovation Programme, with the main objectives of: (1) carrying out research that will ensure structural safety levels for buildings, energy and transport infrastructure, and (2) providing training to a new generation of researchers for dealing with an aging infrastructure stock. The network is composed by 6 Universities, 11 companies and 1 research institute from 5 European countries, joining forces to identify, quantify and reduce uncertainties associated to the structural response, to the imposed loads, and to the probability of structural failure.
      119
  • Publication
    Using instrumented vehicles to detect damage in bridges
    (Faculty of Engineering, University of Porto, 2012-07-22) ; ; ;
    Bridge structures are subject to continuous degradation due to the environment, ageing and excess loading. Monitoring of bridges is a key part of any maintenance strategy as it can give early warning if a bridge is becoming unsafe. This paper will theoretically assess the ability of a vehicle fitted with accelerometers on its axles to detect changes in damping of bridges, which may be the result of damage. Two vehicle models are used in this investigation. The first is a two degree-of-freedom quarter-car and the second is a four degree-of-freedom halfcar. The bridge is modelled as a simply supported beam and the interaction between the vehicle and the bridge is a coupled dynamic interaction algorithm. Both smooth and rough road profiles are used in the simulation and results indicate that changes in bridge damping can be detected by the vehicle models for a range of vehicle velocities and bridge spans.
      767
  • Publication
    Application of the cross-entropy method to estimate stiffness distribution in plate-type structures
    This paper examines the use of the cross-entropy (CE) method to estimate the structural parameters of a plate structure, given data from a simulated non-destructive static loading test. Finite element models of plates are created, with properties close to that of a bridge of similar dimensions. Damage is introduced to the models by local reductions in the longitudinal Young’s modulus (Ex). In practice, reduced values of Ex may result from material irregularities, poor construction methods and structural degradation due to weathering and/or impact. By assembling combinations of Ex values, the CE method searches the solution space of possible combinations of Ex values. The location and severity of the damage is varied to test the ability of the algorithm to identify different damage events.
      427
  • Publication
    Response of a Simply Supported Beam with a Strain Rate Dependent Elasticity Modulus when Subjected to a Moving Load
    The structural response of a material to a load that is applied rapidly (dynamically) or applied very slowly (statically) can be considerably different. A vehicle moving across a concrete bridge represents an example of a dynamic load that is applied to a structure within a limited period of time that will depend on the velocity of the load. This paper explores the variation in the response of a beam when using a typical constant value or a time-variant value that depends on the strain experienced by the structure. Previous research has demonstrated that the static modulus of elasticity is smaller than the dynamic modulus. Some of this research is based on compression and tensile tests using samples where deformation is measured at one single location for different strain and stress rates, and they have led to formulas that allow characterizing the dynamic modulus as a function of strain rate. The latter is used in this investigation to quantify the effect of considering a time-varying modulus of elasticity in a structure traversed by a moving load. The simulation of a moving load across a simply supported beam is implemented in MATLAB for two different scenarios: (i) using a constant modulus of elasticity as it is common practice in vehicle-bridge interaction literature, and (ii) using a time-varying dynamic modulus of elasticity. A sensitivity study is carried out to evaluate the percentage of increase in the elasticity modulus with respect to its static value as a function of the load velocity and magnitude. Finally, a graph of dynamic amplification factor versus speed is provided for both the constant modulus and the time-varying modulus scenarios for comparison purposes. Results show that the influence of a time-varying modulus becomes significant for high load magnitudes travelling at high speeds. 
      592
  • Publication
    Dynamic effects of a five-axle truck on a short-span bridge
    (Bridge Research Group UCD, 2002-08-30)
    Five-axle trucks produce the critical load cases for the design of short span bridges. This paper uses theoretical simulations to analyse the effect of a five-axle articulated truck on the dynamic response of a short-span bridge. Three-dimensional finite element bridge and truck models are developed with NASTRAN software. The bridge model is a 20 m long single span structure discretised into isotropic plate elements. The truck model is composed of bar, mass, damping, friction, spring and rigid elements. The road profile is generated stochastically from power spectral density functions. Then, the dynamic interaction problem between bridge, truck and road profile is solved using a Lagrange multiplier technique. Dynamic amplification factors are obtained for a combination of static weights, speed, road roughness and damping and compared to the Eurocode recommendation.
      145
  • 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.
      327