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Pakrashi V.,University College Cork | Kelly J.,Roughan and ODonovan Consulting Engineers | O'Connor A.J.,Innovative Solutions
Bridge Maintenance, Safety, Management, Resilience and Sustainability - Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management | Year: 2012

Tests related to durability studies on structures often feature half-cell potential and resistivity data. An approximately linear relationship between half-cell potential testing and resistivity data has been discussed and well-researched. In spite of criticisms related to environmental sensitivity of resistivity tests it remains as a popular choice for investigations into durability of structures. This paper investigates the correlation between half-cell potentials and resistivity tests on reinforced concrete from field data from tests on six bridges. The empirical interrelationships from the six bridges with widely varying environmental exposure conditions and the variation of such interrelationships are observed. Similar investigations are carried out on different elements of bridges. The paper then discusses problems related to the interpretation and practical application of correlations carried out on absolute values and advocates the use of statistical measures obtained from test data. The percentile correlations are observed to be helpful when considering exceedances of different threshold values. A customised use of such data in an empirically correlated probabilistic format with can be useful in durability ranking and infrastructure maintenance management. The studies presented in this paper emphasize the advantages of using probabilistic formats over traditional formats when interpreting or quantitatively establishing field relationships between half-cell potential and resistivity data. The ability of this empirically correlated probabilistic format to support structure-specific thresholds of serviceability limit states is discussed. The need for a shared repository for the improvement of accuracy of such correlations and for the use of such correlations as a surrogate for other structures is emphasized. © 2012 Taylor & Francis Group.

Caprani C.C.,Dublin Institute of Technology | Gonzalez A.,University College Dublin | Rattigan P.H.,Roughan and ODonovan Consulting Engineers | OBrien E.J.,University College Dublin
Structure and Infrastructure Engineering | Year: 2012

The determination of characteristic bridge load effect is a complex problem. Usually, statistical extrapolation of simulated static load effects is used to derive a lifetime characteristic static load effect. However, when a vehicle crosses a bridge, dynamic interactions occur which often cause greater total load effect. This total load effect is related to the static load effect through a dynamic amplification factor (DAF). Specifications often recommend a conservative level for DAF, based on bridge length, number of lanes, and type of load effect only. Therefore significant improvements in the accuracy of this calculation are possible if a DAF, specific to the considered bridge, is applied. In this paper, the authors develop a novel method that considers site-specific bridge and traffic load conditions and allows for the reduced probability of both high static loading and high dynamic interaction occurring simultaneously. This approach utilises multivariate extreme value theory, in conjunction with static simulations and finite element vehicle-bridge dynamic interaction models. It is found that the dynamic allowance for the sample bridge and traffic considered is significantly less than recommended by bridge codes. This finding can have significant implications for the assessment of existing bridge stock. © 2012 Taylor and Francis Group, LLC.

OBrien E.J.,University College Dublin | Hayrapetova A.,Roughan and ODonovan Consulting Engineers | Walsh C.,Trinity College Dublin
Structure and Infrastructure Engineering | Year: 2012

This paper presents a new approach to the modeling of congested traffic loading events on long span bridges. Conventional traffic load models are based on weigh-in-motion data of non-congested traffic, or something similar to a Poisson Arrival process. In neither case do they account for the mixing between lanes that takes place as traffic becomes congested. It is shown here that cars move out from between trucks as traffic slows down which results in a higher frequency of long platoons of trucks in the slow lane of the bridge. These longer platoons increase some characteristic load effects under the slow lane by a modest but significant amount. Micro-simulation, the process of modeling individual vehicles that is widely used in traffic modeling, is presented here as a means of predicting imposed traffic loading on long-span bridges more accurately. The traffic flow on a congested bridge is modelled using a random mixing process for trucks and cars in each lane, where each vehicle is modelled individually with driver behaviour parameters assigned randomly in a Monte Carlo process. Over a number of simulated kilometres, the vehicles move between lanes in simulated lane-changing manoeuvres. The algorithm was calibrated against video recordings of traffic on a bridge in the Netherlands. Extreme value statistics of measured strains on the bridge are then compared to the corresponding simulation statistics to validate the model. The micro-simulation algorithm shows that the histograms of truck platoon length are moderately affected by lane changing. This in turn is shown to influence some characteristic load effects of the bridge deck. © 2012 Taylor and Francis Group, LLC.

Pakrashi V.,Roughan and ODonovan Consulting Engineers | O'Connor A.,Trinity College Dublin | Basu B.,Trinity College Dublin
Structural Health Monitoring | Year: 2010

This article presents an experimental monitoring of the evolution of a crack in a beam using beam-vehicle interaction response signals for identification of progressively increasing crack-depth ratios. The beam is traversed by a two-axle model vehicle providing excitation in the time domain for the various extents of damage. The response of the beam in the time domain during the period of forced vibration is measured using strain gages. A consistent evolution of damage has been demonstrated in terms of the maxima values of the measured responses. The corresponding distortions of wavelet coefficients of the measured strain data due to the presence of various levels of damage have been identified. The evolution of the phase space and the wavelet transformed phase spaces have been evaluated with damage evolution. The wavelet transformed phase spaces for the undamaged and the damaged cases are observed to be distinctly different at high scales. The importance of denoising of the acquired data and the importance of vehicle configuration has been illustrated. This study presents a basis for a general model free damage assessment and structural health monitoring framework. The study presented is particularly useful in the context of continuous online bridge health monitoring, since the data necessary for analysis can be obtained from the operating condition of the bridge and the structure does not need be closed down. © The Author(s), 2010.

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