Virtual structural health monitoring and remaining life prediction of steel bridges

In this study a Structural Health Monitoring (SHM) system is combined with Bridge Weigh-in-Motion (B-WIM) measurements of the actual traffic loading on a bridge to carry out a fatigue damage calculation. The SHM system uses the 'Virtual Monitoring' concept, where all parts of the bridge that are not monitored directly using sensors, are 'virtually' monitored using the load information and a calibrated Finite Element (FE) model of the bridge. Besides providing the actual traffic loading on the bridge, the measurements are used to calibrate the SHM system and to update the FE model of the bridge. The newly developed Virtual Monitoring concept then uses the calibrated FE model of the bridge to calculate stress ranges and hence to monitor fatigue at locations on the bridge not directly monitored. The combination of a validated numerical model of the bridge with the actual site-specific traffic loading allows a more accurate prediction of the cumulative fatigue damage at the time of measurement and facilitates studies on the implications of traffic growth. In order to test the accuracy of the Virtual Monitoring system, a steel bridge with a cable-stayed span in the Netherlands was used for testing

Assessment of Fatigue Behaviour of Orthotropic Steel Bridge Decks using Monitoring System

AbstractDuring the last decades orthotropic steel decks have become a widely used component of steel bridges, however high numbers of fatigue cracks have been recently detected in these structure types. It is well known, that the orthotropic decks are sensitive to fatigue damage, therefore safe fatigue design is important for the safety assessment of bridge structures. The fatigue damage assessment and life prediction of steel bridges can be carried out by using online structural health monitoring systems (SHM). By using the SHM system, it is possible to detect deterioration, determine anomalies and assess the safety level which will allow optimum maintenance strategies. On-structure long-term monitoring systems have been already successfully implemented on bridges all around the world in order to detect cracks just like on the orthotropic steel deck structure of M0 Háros Danube highway Bridge in Hungary. The purpose of the current research program is the investigation and analysis of the fatigue behaviour of this orthotropic steel bridge deck and the evaluation process improvement of the data rows collected by the monitoring system. Additional laboratory tests are carried out at 6 large scale test specimens at the Budapest University of Technology and Economics, Department of Structural Engineering to determine the fatigue resistance of closed section longitudinal stiffeners. In parallel finite element model is developed to simulate the fatigue behaviour of the analyzed components and to investigate its fatigue behaviour by numerical analysis. The aim of the current study is to analyze and verify the structural behaviour of the orthotropic steel deck on the basis of the executed test results, numerical simulations and the strain-time history data from the online structural health monitoring system implemented on the studied bridge

Fatigue Reliability Assessment of Orthotropic Bridge Decks under Stochastic Truck Loading

A steady traffic growth has posed a threat to the fatigue safety of existing bridges. Uncertainties in traffic flows add to the challenge of an accurate fatigue safety assessment. This article utilizes a stochastic traffic load model to evaluate the fatigue reliability of orthotropic steel bridge decks. The traffic load model is simulated by site-specific weigh-in-motion measurements. A response surface method is presented to solve the time-consuming problem caused by hotspot stress simulations in the finite element model. Applications of the stochastic traffic load model for probabilistic modeling and fatigue reliability assessment are demonstrated in the case study of a steel box-girder bridge. Numerical results indicate that the growth rate of the gross vehicle weight leads to a rapid decrease of the fatigue reliability in comparison to the traffic volume growth. Even though the traffic volume growth is rapid, the control of overloaded trucks in comparison to the traffic volume is an effective way to ensure the fatigue safety of the steel bridges.National Basic Research Program of ChinaNational Science Foundation of ChinaKey Research Program in Civil Engineering from Changsha University of Science and Technolog

Damage identification in bridge structures : review of available methods and case studies

Bridges are integral parts of the infrastructure and play a major role in civil engineering. Bridge health monitoring is necessary to extend the life of a bridge and retain safety. Periodic monitoring contributes significantly in keeping these structures operational and extends structural integrity. Different researchers have proposed different methods for identifying bridge damages based on different theories and laboratory tests. Several review papers have been published in the literature on the identification of damage and crack in bridge structures in the last few decades. In this paper, a review of literature on damage identification in bridge structures based on different methods and theories is carried out. The aim of this paper is to critically evaluate different methods that have been proposed to detect damages in different bridges. Different papers have been carefully reviewed, and the gaps, limitations, and superiority of the methods used are identified. Furthermore, in most of the reviews, future applications and several sustainable methods which are necessary for bridge monitoring are covered. This study significantly contributes to the literature by critically examining different methods, giving guidelines on the methods that identify the damages in bridge structures more accurately, and serving as a good reference for other researchers and future works

Fatigue Life Assessment of Rib to Deck Welded Joint of the Hardanger Bridge – a Realistic Traffic Loading of FEM

The orthotropic steel decks in the Hardanger Bridge, as is common for long span suspension bridges, have welded joints that are susceptible to fatigue cracks. The rib-to-deck welded joints under the wheel load are the most common crack initiation sites. Crack in the weldment accelerates the degradation of other components of the bridge deck and ultimately shortens the fatigue life of the road bridge. The fatigue life of the rib-to-deck welded joint is determined by using Miner’s damage accumulation rule of the rainflow cycle counted stress ranges of the nominal and Hot Spot stresses. A full-scale 20 m long finite element model of the box girders in the Hardanger Bridge was built following the design drawings provided by the Norwegian Public Road Administration (NPRA). The model was loaded with fatigue load models (FLM) in Abaqus. A realistic dynamic design of the FLM traffic loading on the bridge was achieved by user subroutine. The thesis compared the fatigue life of two fatigue load models, the national (FLM-N) and Eurocode’s FLM4. The effect of velocity on fatigue life of the welded joint was assessed by simulating vehicle with three different velocities while ensuring equal sampling rate. A validated whole span global model of Hardanger Bridge was provided for this thesis. The global model was loaded by vehicle equivalent concentrated load and corresponding moment of FLM-N and FLM-4. Stress response calculated from moment and axial force was used to estimate fatigue life. The fatigue load models cause high cycle fatigue damage on the welded joints of the orthotropic steel decks of the Hardanger Bridge. The Hot Spot stress fatigue life of the welded rib-to-deck joint was 135 years (FLM-N) and 24 years (FLM4). The corresponding nominal stress fatigue life was 1180 years (FLM-N). Stresses from loading the global model with a single vehicle at a time did not induce fatigue damage. The effect of velocities of the vehicles loaded resulted in insignificant changes of the fatigue life of the welded joint

Fatigue performance of existing bridges under dynamic loads from winds and vehicles

During the life cycle of bridges, varied amplitude of stress ranges on structural details are induced by the random traffic and wind loads. The progressive deteriorated road surface conditions might accelerate the fatigue damage accumulations. Micro-cracks in structural details might be initiated. An effective structural modeling scheme and a reasonable fatigue damage accumulation rule are essential for stress range acquisitions and fatigue life estimation. The present research targets at the development of a fatigue life and reliability prediction methodology for existing steel bridges under real wind and traffic environment with the capability of including multiple random parameters and variables in bridges’ life cycle. Firstly, the dynamic system is further investigated to acquire more accuracy stresses for fatigue life estimations for short and long span bridges. For short span bridges, the random effects of vehicle speed and road roughness condition are included in the limit state function, and fatigue reliability of the structural details is attained. For long-span bridges, a multiple scale modeling and simulation scheme based on the EOMM method is presented to obtain the stress range history of structural details, while the calculation cost and accuracy are saved. Secondly, a progressive fatigue reliability assessment approach based on a nonlinear continuous fatigue damage model is presented. At each block of stress cycles, types and numbers of passing vehicles are recorded to calculate the road surface’s progressive deterioration and nonlinear cumulative fatigue damage, and the random road profiles are generated. Thirdly, this study discussed the fatigue design of short and long span bridges based on the dynamic analysis on the vehicle-bridge or vehicle-bridge-wind system. For short span bridges, a reliability-based dynamic amplification factor on revised equivalent stress ranges (DAFS) is proposed. For long span bridges, a comprehensive framework for fatigue reliability analysis under combined dynamic loads from vehicles and winds is presented. The superposed dynamic stress ranges cannot be ignored for fatigue reliability assessment of long-span bridges, although the stresses from either the vehicle loads or wind loads may not be able to induce serious fatigue issues alone

Assessment of Existing Steel Structures - Recommendations for Estimation of the Remaining Fatigue Life

Due to the demand for freight volume on rail and road, traffic has increased significantly in the past years leading to an increasing number of heavy vehicles in the traffic flows and greater exploitation of their loading capacities. Because of environmental considerations there is also a tendency to further enhance the admissible loads in the design of new heavy vehicles (e.g. by increasing axle loads or using road trains). This all may affect the safety, serviceability and durability of existing bridges. Bridge authorities are therefore interested in agreed methods to assess the safety and durability of existing bridges and to make appropriate provisions for more refined maintenance methods, possible restriction of traffic, bridge-rehabilitation or substitution of old bridges by new ones where necessary. For steel bridges including the old riveted ones there are numerous approaches to such assessments, partly standardized by national codes or recommendations. In the light of the development of the European single market for construction works and engineering services there is thus a need to harmonize them and to develop agreed European technical recommendations for the safety and durability assessment of existing structures. These recommendations should follow the principles and application rules in the Eurocodes and provide a scheme with different levels of analysis: a basic level with general methods and further levels with higher sophistication that call for specific expertise. This technical report on ¿Recommendations for the estimation of remaining fatigue life¿ supported by the ECCS could be used as a basis for harmonizing National procedures and for the further evolution of the Eurocodes.JRC.G.5-European laboratory for structural assessmen