Research Publications

 

All titles published by the School are listed in the yearly President's reports classified by type of publication and author and can be downloaded for each academic season from the links in the right hand side menu. 

Full text for some of these titles are available in the Open Access Institutional Repository of UCD Research. The top 10 downloads from the School repository are listed in the right hand side menu and can be accessed by clicking each title. The most recent uploads to the repository can be accessed in the list below. Following this list, an archive of news involving publications by the School is provided.

Methodologies for Crack Initiation in Welded Joints Applied to Inspection Planning

Methodologies for Crack Initiation in Welded Joints Applied to Inspection Planning Zou, Guang; Banisoleiman, Kian; González, Arturo Crack initiation and propagation threatens structural integrity of welded joints and normally inspections are assigned based on crack propagation models. However, the approach based on crack propagation models may not be applicable for some high-quality welded joints, because the initial flaws in them may be so small that it may take long time for the flaws to develop into a detectable size. This raises a concern regarding the inspection planning of high-quality welded joins, as there is no generally acceptable approach for modeling the whole fatigue process that includes the crack initiation period. In order to address the issue, this paper reviews treatment methods for crack initiation period and initial crack size in crack propagation models applied to inspection planning. Generally, there are four approaches, by: 1) Neglecting the crack initiation period and fitting a probabilistic distribution for initial crack size based on statistical data; 2) Extrapolating the crack propagation stage to a very small fictitious initial crack size, so that the whole fatigue process can be modeled by crack propagation models; 3) Assuming a fixed detectable initial crack size and fitting a probabilistic distribution for crack initiation time based on specimen tests; and, 4) Modeling the crack initiation and propagation stage separately using small crack growth theories and Paris law or similar models. The conclusion is that in view of trade-off between accuracy and computation efforts, calibration of a small fictitious initial crack size to S-N curves is the most efficient approach.
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On the estimation of bridge mode shapes from drive-by measurements

On the estimation of bridge mode shapes from drive-by measurements Malekjafarian, Abdollah; O'Brien, Eugene J. This paper summarizes the latest approaches proposed on indirect bridge monitoring and provides recommendations for future development. The possibility of the estimation of bridge mode shapes from indirect measurements, is investigated. The Hilbert transform is applied to the responses measured from two following axles to extract the amplitudes of the signals. The global bridge mode shapes are constructed by applying a rescaling process to the local mode shapes obtained from the amplitudes. The performance of the proposed method is demonstrated using a numerical case study. 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Rhodes Island, Greece, June, 2017
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Direct Field Measurement of the Dynamic Amplification in a Bridge

Direct Field Measurement of the Dynamic Amplification in a Bridge Carey, Ciaran; O'Brien, Eugene J.; Malekjafarian, Abdollah; Lydon, Myra; Taylor, Su E. In this paper, the level of dynamics, as described by the Assessment Dynamic Ratio (ADR), is measured directly through a field test on a bridge in the United Kingdom. The bridge was instrumented using fiber optic strain sensors and piezo-polymer weigh-in-motion sensors were installed in the pavement on the approach road. Field measurements of static and static-plus-dynamic strains were taken over 45 days. The results show that, while dynamic amplification is large for many loading events, these tend not to be the critical events. ADR, the allowance that should be made for dynamics in an assessment of safety, is small.
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Rigid body stiffness matrix for identification of inertia properties from output-only data

Rigid body stiffness matrix for identification of inertia properties from output-only data Malekjafarian, Abdollah; Ashory, M. R.; Khatibi, M. M.; SaberLatibari, M. Identification of inertia properties (mass, location of the center of mass and inertia tensor) is essential for designing of engineering structures. Using modal testing is a possibility for estimation of the inertia properties in which they can be identified using the orthogonality property of mass-normalized rigid body mode shapes. However, identification of rigid body mode shapes using modal testing is not always possible, because it is not possible to excite the structure at all degrees of freedom. In this paper, output-only modal analysis in which the structure can be excited in different directions is used to identify the rigid body modes of the structure. It is shown that all of the rigid body modes of the structure can be extracted using the data extracted from output-only modal analysis. As the obtained rigid body mode shapes from output-only modal analysis are not scaled, a new method is proposed for scaling them using rigid body stiffness matrix. The inertia properties of the structure are obtained from the scaled mode shapes. The accuracy of the proposed method is studied using a numerical case study of a steel structure as well as an experimental case study of a steel frame.
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Application of empirical mode decomposition to drive-by bridge damage detection

Application of empirical mode decomposition to drive-by bridge damage detection O'Brien, Eugene J.; Malekjafarian, Abdollah; González, Arturo A new method is proposed in this paper for bridge damage detection using the response measured in a passing vehicle. It is shown theoretically that such a response includes three main components; vehicle frequency, bridge natural frequency and a vehicle speed pseudo-frequency component. The Empirical Mode Decomposition (EMD) method is used to decompose the signal into its main components. A damage detection method is proposed using the Intrinsic Mode Functions (IMFs) corresponding to the vehicle speed component of the response measured on the passing vehicle. Numerical case studies using Finite Element modelling of Vehicle Bridge Interaction are used to show the performance of the proposed method. It is demonstrated that it can successfully localise the damage location in the absence of road profile. A difference in the acceleration signals of healthy and corresponding damaged structures is used to identify the damage location in the presence of a road profile. The performance of the method for changes in the transverse position of the vehicle on the bridge is also studied.
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On the use of a passing vehicle for the estimation of bridge mode shapes

On the use of a passing vehicle for the estimation of bridge mode shapes Malekjafarian, Abdollah; O'Brien, Eugene J. This paper presents a novel algorithm for the estimation of bridge mode shapes using the response measured on a passing vehicle. A truck-trailer system is assumed, equipped with an external excitation at a frequency close to one of the bridge natural frequencies. The excitation makes the bridge response dominant at its natural frequency. The acceleration responses are measured on two following axles of the vehicle. It is shown that the amplitude of the signal includes the operational deflected shape data which can be used to estimate the bridge mode shapes. The energy of the responses measured on two following axles is obtained using the Hilbert Huang Transform. It is shown that the bridge mode shape can be estimated with high resolution and accuracy using a rescaling process. The presence of road roughness introduces additional contributions to the response measured on the vehicle, in addition to the bridge response. The concept of subtraction of the responses measured from two identical axles is used to remove the effect of road roughness.
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Uncertainty quantification and calibration of a modified fracture mechanics model for reliability-based inspection planning

Uncertainty quantification and calibration of a modified fracture mechanics model for reliability-based inspection planning Zou, Guang; Banisoleiman, Kian; González, Arturo Efficient inspection and maintenance are important means to enhance fatigue reliability of engineering structures, but they can only be achieved efficiently with the aid of accurate pre-diction of fatigue crack initiation and growth until fracture. The influence of crack initiation on fatigue life has received a significant amount of attention in the literature, although its im-pact on the inspection plan is not generally addressed. Current practice in the prediction of fatigue life is the use of S-N models at the design stage and Fracture Mechanics (FM) models in service. On the one hand, S-N models are relatively easy to apply given that they directly relate fatigue stress amplitude to number of cycles of failure, however, they are difficult to extrapolate outside the test conditions employed to define the S-N curves. On the other hand, FM models like the Paris propagation law give measurable fatigue damage accumulation in terms of crack growth and have some ability to extrapolate results outside the test conditions, but they can only be a total fatigue life model if the initial crack size was known given that they do not address the crack initiation period. Furthermore, FM models generally introduce large uncertainties in parameters that are often difficult to measure such as initial crack size, crack growth rate, threshold value for stress intensity factor range, etc. This paper proposes a modified FM model that predicts the time to failure allowing for crack initiation period. The main novelty of the modified FM model is the calibration using S-N data (i.e., inclusive of crack initiation period) for an established criterion in fatigue life and reliability level. Sources of uncertainty associated to the model are quantified in probabilistic terms. The modified FM model can then be applied to reliability-based inspection planning. An illustrative example is performed on a typical detail of ship structure, where the optimum inspection plan derived from the proposed model is compared to recommendations by existing FM models. Results demonstrate to what extent is the optimum inspection plan influenced by the crack initiation period. The modified model is shown to be a reliable tool for both fatigue design and fatigue management of inspection and maintenance intervals.  12th International Conference on Structural Safety & Reliability (ICOSSAR 2017), Vienna, Austria, August, 2017
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Development of probabilistic fracture mechanics method for fatigue life prediction based on EIFS concept

Development of probabilistic fracture mechanics method for fatigue life prediction based on EIFS concept Zou, Guang; Banisoleiman, Kian; González, Arturo A problem with fracture mechanics (FM) based fatigue analysis is that reliable information on initial crack/flaw size is often unavailable. Also, FM method cannot be applied directly to welded joints with relatively small initial flaws and long crack initiation life. This paper proposes a novel probabilistic FM method based on the equivalent initial flaw size (EIFS) concept. The initial crack size is substituted with EIFS to take both the crack initiation and propagation life into account. Three methods are tested to obtain mean value of EIFS: calibrating to S-N curve, Kitagawa-Takahashi (KT) diagram and fitting to test data. The obtained EIFSs are evaluated by comparing the predicted fatigue lives and crack evolutions with S-N curve and test crack evolution data. The suggested procedure is to derive the mean value of EIFS from S-N curve and the coefficient of variation from KT diagram. 36th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2017), Trondheim, Norway, June, 2017
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Static and dynamic moments for any plane within a straight solid slab bridge caused by the crossing of a truck

Static and dynamic moments for any plane within a straight solid slab bridge caused by the crossing of a truck Mohammed, Omar; González, Arturo A lot of research has been carried out to explain the manner in which longitudinal moments of a bridge respond to traffic. The total longitudinal bending moment is made of 'static' and 'dynamic' components, which vary with time as a result of the inertial forces of the bridge and changes in value and point of application of the forces of the vehicle. However, there is limited evidence about how bending moments at planes other than longitudinal, or twisting moments, act in response to a moving vehicle. For the first time in the literature, this paper analyses the total resultant moments ('static' + 'dynamic') for any plane orientation (from 0 to 360°) at any location of a solid slab deck due to the crossing of a vehicle. The bridge is modelled as a simply supported straight orthotropic plate and the vehicle is modelled as a three-dimensional 5-axle articulated system composed of interconnected sprung and unsprung masses. Simulations are performed for three vehicle transverse paths and three speeds. Using Wood and Armer equations, the resultant moment at any plane orientation can be obtained from equilibrium of bending and twisting moments acting on longitudinal and transverse planes. Maximum twisting moments develop in planes at 45° with longitudinal and transverse planes. Bending moments reach maximum and minimum values at longitudinal and transverse planes. Nevertheless, the moments acting on other plane orientations cannot be ignored in order to accurately assess whether the moment capacity of the bridge provides adequate safety. Therefore, the amount of slab reinforcement will be sufficient provided that the moment capacity exceeds the applied moment for any location and plane. Critical locations with highest values of sagging, hogging and twisting are identified in the bridge, and the dynamic amplification associated to the applied moments is evaluated. Bridge codes such as the Eurocode employ a unique built-in dynamic amplification factor for moment that depends only on the bridge length and the number of lanes. This paper shows how to perform an improved assessment allowing for changes in dynamic behaviour with location and plane orientation, which may prevent needless expense in bridge rehabilitation.
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Developments in damage assessment by Marie Skłodowska-Curie TRUSS ITN project

Developments in damage assessment by Marie Skłodowska-Curie TRUSS ITN project González, Arturo The growth of cities, the impacts of climate change and the massive cost of providing new infrastructure provide the impetus for TRUSS (Training in Reducing Uncertainty in Structural Safety), a €3.7 million Marie Skłodowska-Curie Action Innovative Training Network project funded by EU's Horizon 2020 programme, which aims to maximize the potential of infrastructure that already exists (http://trussitn.eu). For that purpose, TRUSS brings together an international, inter-sectoral and multidisciplinary collaboration between five academic and eleven industry institutions from five European countries. The project covers rail and road infrastructure, buildings and energy and marine infrastructure. This paper reports progress in fields such as advanced sensor-based structural health monitoring solutions - unmanned aerial vehicles, optical backscatter reflectometry, monitoring sensors mounted on vehicles, ... - and innovative algorithms for structural designs and short- and long-term assessments of buildings, bridges, pavements, ships, ship unloaders, nuclear components and wind turbine towers that will support infrastructure operators and owners in managing their assets. 12th International Conference on Damage Assessment of Structures (DAMAS 2017), Kitakyushu, Japan, July, 2017
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