Strain is a direct indicator of structural safety Therefore, strain sensors have been used in most structural health monitoring systems for bridges However, until now, the investigation of strain response has been insufficient This paper conducts a comprehensive study of the strain features of the U ribs and transverse diaphragm on an orthotropic steel deck and proposes a statistical paradigm for crack detection based on the features of vehicle-induced strain response by using the densely distributed optic fibre Bragg grating (FBG) strain sensors The local feature of strain under vehicle load is highlighted, which enables the use of measurement data to determine the vehicle loading event and to make a decision regarding the health status of a girder near the strain sensors via technical elimination of the load information Time–frequency analysis shows that the strain contains three features: the long-term trend item, the short-term trend item, and the instantaneous vehicle-induced item (IVII) The IVII is the wheel-induced strain with a remarkable local feature, and the measured wheel-induced strain is only influenced by the vehicle near the FBG sensor, while other vehicles slightly farther away have no effect on the wheel-induced strain This causes the local strain series, among the FBG strain sensors in the same transverse locations of different cross-sections, to present similarities in shape to some extent and presents a time delay in successive order along the driving direction Therefore, the strain series induced by an identical vehicle can be easily tracked and compared by extracting the amplitude and calculating the mutual ratio to eliminate vehicle loading information, leaving the girder information alone The statistical paradigm for crack detection is finally proposed, and the detection accuracy is then validated by using dense FBG strain sensors on a long-span suspension bridge in China

https://iopscience.iop.org/article/10.1088/1361-665X/aa7600/pdf

Strain features and condition assessment of orthotropic steel deck cable-supported bridges subjected to vehicle loads by using dense FBG strain sensors

Damping Identification of Bridges Under Nonstationary Ambient Vibration

Cost-Safety tradeoff analysis is one of the most challenging tasks of structural maintenance. Undoubtedly, developing an economic and efficient schedule for structural maintenance and rehabilitation is highly acknowledged. While meta-heuristic optimization algorithms have been used widely to determine the best maintenance strategies to provide more economical structures, we present a mathematical programming model to overcome the limitations of previous studies. In this paper a Mixed Integer Non-linear Programming (MINLP) has been presented to find the optimal time of applying maintenance intervention in a deteriorating structure. While, considering the time value of money, postponing the maintenance actions will be more economic, this postponement may cause a decrease in the safety of structures. Due to this contradictory relation between the objectives, it is vital to find a reasonable trade-off between cost-safety. Our proposed approach considers different values of the discount rate of money. We apply our mathematical programming model to solve two optimization examples, which are found in the structural maintenance literature. It is shown that our proposed model is able to determine the optimal time of applying maintenance intervention to the structures with less total life cycle cost, and higher level of safety.

A mathematical programming model for solving cost-safety optimization (CSO) problems in the maintenance of structures

Two conventional methods, the nominal stress method and the hot spot stress method, are examined for the fatigue assessment of a steel box girder bridge while considering the effect of the modeling options on the estimated fatigue life Two analytical models, a simplified global analytical model and a refined local finite element analytical model, are developed for the evaluation of the stress ranges induced by a fatigue truck The field tests are conducted for validating the analytical models as well as for direct fatigue assessment via an ambient vibration test The local modeling options that are examined are the inclusion of the fillet weld itself in the refined analytical model and the mitigation of the concentrated stress at the web plate, considering stress dispersion over the width of the attachment The fatigue life is estimated for three different nonexceedance probabilities, considering different partial factors according to the accuracy of the analysis method as well as the reliability of the estimated fatigue loading for a specific bridge site Through a comparative analysis, the potential differences in estimated fatigue lives according to the assessment methods and the modeling options are quantitatively discussed

Fatigue life assessment for a composite box girder bridge

Human-induced vibrations of a curved cable-stayed footbridge

An efficient method for constructing multiple candidate finite element (FE) models which are consistent with the measured dynamic properties of a civil structure is presented. A parameterised sensitivity-based FE model updating method was developed to permit a feasible FE model set for the target structure to be produced. In this method, an aggregated multi-objective function, which is defined by the weighted sum of the error functions, is parameterised by its relative weighting factors. By introducing multiple parameter sets for the weighting factors, a number of optimal updated FE models are produced that permit both the natural frequency errors and mode shape errors to be simultaneously minimised. The effectiveness of the proposed method is illustrated by an example using an existing cable-stayed bridge. The findings show that error-minimised, well-distributed FE models can be obtained in terms of modal frequency errors and mode shape errors. The high quality of the candidate model sets is also verifie...

Candidate model construction of a cable-stayed bridge using parameterised sensitivity-based finite element model updating

The load carrying capacity of a composite open-top steel box girder bridge was evaluated, based on a reliability-based method, and potential differences from conventional approaches were evaluated. A practical analysis model was utilized in evaluating the Rating Factor (RF) after verification with a rigorous full finite element analysis model with solid and plate elements. The accuracy of the analysis models was validated in terms of displacements and distribution factors through static loading tests. Dynamic effects were also estimated from the dynamic loading tests. The load factors, proposed for the purpose of evaluation based on recently accumulated statistical data, were utilized in evaluating RF. The RFs were evaluated for maximum positive flexure, negative flexure, and shear regions along the bridge. The calculated RF with the load factors for evaluation purposes was higher by 35% than that with design load factors. The proposed method also produces a 29% increase in RF compared to the conventional allowable stress design approach. Consequently, the proposed reliability-based procedure would be expected to permit a more economical assessment of bridge performance to be made.

Reliability-based Evaluation of Load Carrying Capacity for a Composite Box Girder Bridge

Not all loads contribute to fatigue crack propagation in the welded detail of steel bridges when they are subjected to variable amplitude loading. For fatigue assessment, therefore, non-contributing stress cycles should be truncated. However, stress range truncation is not considered during typical fatigue reliability assessment. When applying the first order reliability method, stress range truncation occurs mismatch between the expected number of cycles to failure and the number of cycles obtained at the time of evaluation, because the expected number of cycles only counts the stress cycles that contribute to fatigue crack growth. Herein, we introduce a calibration factor to coordinate the expected number of cycles to failure to the equivalent value which includes both contributing and non-contributing stress cycles. The effectiveness of stress range truncation and the proposed calibration factor was validated via case studies.

JunYong Park

Papers

Candidate model construction of a cable-stayed bridge using parameterised sensitivity-based finite element model updating

Fatigue life assessment for a composite box girder bridge

Reliability-based Evaluation of Load Carrying Capacity for a Composite Box Girder Bridge

A Methodology for Fatigue Reliability Assessment Considering Stress Range Distribution Truncation

Finite Element Model Update of Cable Supported Bridges Using Large Scale Global Optimization Technique