Acoustic emission and ultrasonic testing for fatigue damage detection in a RC bridge deck slab

There is a significant need to examine precisely the conditions of concrete road bridges because of the increasing traffic and axle loads and the fact that most existing bridges were not designed with respect to fatigue. In-situ investigations are challenging in terms of long-term monitoring of deformations and displacements, the difficulty of access to relevant zones of bridges in service, and limitations in current measurement methods and techniques. This paper presents the case study of a specifically designed continuous monitoring system, installed in the reinforced-concrete slab of a 60-year road viaduct, in order to detect possible initial fatigue damaging events due to traffic loading, since the slab currently does not show any sign of fatigue damage in terms of cracks. The originality of the paper lies in the combination and synchronization of four nondestructive-testing techniques, i.e. an acoustic emission system, an ultrasonic system, strain gauges, and thermocouples, to perform long-term monitoring of the RC deck slab of this viaduct under service conditions. It is found that the monitoring system is efficient to detect acoustic emission parameters as a function of traffic and temperature variations.

Quantiﬁcation of traﬃc and temperature eﬀects on the fatigue safety of a reinforced-concrete bridge deck based on monitoring data

Imane Bayane, Eugen Brühwiler, Amol Mankar

For assessment of existing reinforced-concrete bridges, only few rules and recommendations are available, and engineers meanwhile apply design codes for new bridges to evaluate the fatigue safety of existing bridges leading to non-realistic approaches and conclusions. Design codes for new structures are often based on the worst scenarios, and they are not made to assess existing structures with specific loadings and material properties. Direct monitoring provides an important source of information about the actual structural loading and response. This article presents an integral approach to identify fatigue damage of a reinforced-concrete deck as a function of the relevant actions for fatigue using monitoring data. This includes a long-term monitoring system to measure strain and temperature in the most loaded parts, an inverse method using monitoring data to reconstruct traffic actions from the structural response, and a simulation of traffic loading and its effects using a compiler and a finite element model to estimate fatigue damage. The presented approach can be used as a base on how to monitor and analyze recorded data to evaluate the fatigue safety of existing reinforced-concrete slabs in road bridges.

2019

Probabilistic reliability framework for assessment of concrete fatigue of existing RC bridge deck slabs using data from monitoring

Imane Bayane, Eugen Brühwiler, Amol Mankar

Assessment of existing bridge structures for inherent safety level or for lifetime extension purposes is often more challenging than designing new ones. With increasing magnitude and frequency of axle loads, reinforced concrete bridge decks are susceptible to fatigue failure for which they have not been initially designed. Fatigue verification and prediction of remaining service duration may turn out to be critical for civil infrastructure satisfying the required reliability. These structures are exposed to stochastic loading (e.g. vehicle loads, temperature loads); on the resistance side, reinforced concrete also behaves in a stochastic way. This paper presents a probabilistic reliability framework for assessment of future service duration, which includes probabilistic modelling of actions based on large monitoring data and probabilistic modelling of fatigue resistance based on test data. A case study for the steel - reinforced concrete slab of the Cret de l'Anneau Viaduct is presented along with calibration of resistance partial safety factors for lifetime extension.

ELSEVIER SCI LTD2019

FATIGUE EXAMINATION OF REINFORCED-CONCRETE BRIDGE SLABS USING ACOUSTIC EMISSION AND STRAIN MONITORING DATA

Imane Bayane

The examination of bridges under service loading is key for understanding their condition and thus for their sustainable and efficient use. The need to extend the service duration of existing bridges is increasing, and therefore, efficient tools for examining and maintaining them are required. Monitoring of structures is recognised as an efficient method for investigating structural behaviour and evaluating structural performance. However, there is a lack of methods for choosing suitable sensors and performing monitoring on-site. The main challenges associated with monitoring include environmental conditions, complex loading, big data storage, and measurement calibration. Thus far, no research has developed and implemented a complete strain-acoustic-emission monitoring method, from instrumentation to data interpretation, to evaluate long-term changes in the internal state of reinforced-concrete road bridges. The general objective of this thesis is to characterise fatigue-related damage in the reinforced concrete of bridge-deck slabs using nondestructive methods. The influence of low fatigue stress on reinforced-concrete behaviour was studied at a microscale structural level, and this research was then used to define two indices that quantify existing damage and fatigue-damage increase over time. For this aim, an extensive long-term monitoring campaign was conducted on a bridge in service to understand the fatigue behaviour of reinforced-concrete slabs under operational loadings and to evaluate the effectiveness of different nondestructive methods. The instrumentation and calibration of the used nondestructive measurements produced recommendations for the examination of reinforced-concrete bridge-deck slabs. The methods provide a solid understanding of how to quantify the influence of traffic loading and environmental changes on structural behaviour, such as fatigue behaviour, and structural characteristics such as the connection between bridge components. The results derived from the monitoring data indicate that the instrumented bridge is safe with respect to the fatigue limit despite the potential difference between the present and original design conditions. The developed inverse method identifies the probabilistic distribution of the position and the load of vehicles crossing the instrumented slab. The results of this method define the link between the fatigue-damage distribution and the position and the load of vehicles, and reveal the sensitivity of fatigue damage to different sources of uncertainties associated with the compressive strength of concrete, the level of stresses, and the magnitude of annual traffic. Combining information from monitoring data and structural analysis models allows for accurate data interpretation and model development. The results reveal that the identification of structural parameters and the prediction of fatigue endurance of the noninstrumented structural elements can be performed accurately. Integrating acoustic emission and strain measurement results is a comprehensive method for analysing the fatigue of reinforced-concrete members by which microcracks in the concrete volume can be localised and visualised under operational loading. The stationary movement of existing microcracks and low microcrack growth govern the concreteâs behaviour under low fatigue stresses. Reinforced concrete was found to be in the stage of new-microcrack nucleation and stable microcrack growth.

EPFL2021

FATIGUE EXAMINATION OF REINFORCED-CONCRETE BRIDGE SLABS USING ACOUSTIC EMISSION AND STRAIN MONITORING DATA

Imane Bayane

EPFL2021