Quantification of the conditional value of SHM data for the fatigue safety evaluation of a road viaduct

Fatigue safety verification of existing bridges that uses ‘‘re-calculation’’ based on codes, usually results in insufficient fatigue safety, triggering invasive interventions. Instead of “re-calculation”, Structural Health Monitoring (SHM) should be used for the assessment of the existing bridges. Monitoring systems provide data that can reduce uncertainties associated with the fatigue loading process and the structural resistance. The objective of this paper is to quantify the value of the SHM system implemented in a 60-years-old road viaduct to investigate its fatigue safety, through modeling of the fundamental decisions of performing monitoring in conjunction with its expected utility. The quantification of the conditional value of information is based on the decision tree analysis that considers the structural reliability, various decision scenarios as well as the cost-benefit assessments. This leads to a quantitative decision basis for the owner about how much time and money can be saved while the viaduct fulfills its function reliably and respects the safety requirements. The originality of this paper stands in the application of the value of information theory to an existing viaduct considering the fatigue failure of the system based on the monitoring data and the cost-benefit of monitoring method.

Through-thickness performance of adhesive connections between FRP bridge decks and steel main girders

Martin Schollmayer

FRP bridge decks offer several advantages compared with conventional concrete bridge decks, particularly their much lower weight, but also their resistance against corrosion as well as easier installation and maintenance. The poorly conceived methods available for connecting FRP bridge decks with their supporting structures – normally steel girders – nonetheless constitute a disadvantage. Connections involving studs or bolts are not appropriate in this case, since FRP is a very brittle material that offers no ductile properties. Bolted connections usually result in much higher stress concentrations, while adhesive bonding is a more material-adapted connection method since larger surfaces can be linked together, thus ensuring reduced stresses. The bridge system investigated in this thesis consists of a pultruded FRP bridge deck bonded to steel main girders, the bridge's main structural components, which have to transmit the dead and traffic loads to the supports, whereas the bridge deck is spanned in the transverse direction perpendicular to the steel girders. Uplift forces caused by the load-bearing behavior of the bridge deck transverse to the bridge axis lead to through-thickness tensile stresses in the adhesive joint. The main objective of this thesis is the description of the structural behavior in the transverse direction. This includes analysis of the stresses in the adhesive connection as well as determination of the strength of the joints. Analytical and experimental investigations were carried out. It was shown, that the tensile stress distribution in the adhesive joint is non-uniform with high stress concentrations below the FRP deck webs of the cellular deck and above the steel girder web. Alternately inclined deck webs thereby induce significantly higher stresses below the vertical webs. A method for the calculation of the stress state in the adhesive layer is proposed which is validated by numerical and experimental results. The material strength of the connection in terms of a combination of tensile through-thickness and shear stresses is established. The total safety factor of the joint was higher than the safety factor of the FRP deck for bending between the main girders. A possible failure process would not start in the adhesive connection between bridge deck and steel girder which eventually could lead to additional failure of other structural members. The system is redundant. Fatigue loading up to 10 million cycles showed no stiffness degradation. The results of this thesis prove the existence of a good load-bearing behavior under static and fatigue loads of adhesively-bonded joints between pultruded FRP bridge decks and structural steel girders, where the adhesive connection is loaded with uplift forces and moments acting in the bridge deck, in addition to the shear in the connection layer due to composite action. The basis for a design method for adhesively-bonded connections between pultruded FRP bridge decks and steel girders is provided.

EPFL2009

Size effects in the fatigue behavior of welded tubular bridge joints

Luís Costa Borges, Alain Nussbaumer

Tubular space trusses for bridge applications use thick-walled tubes. The reduction in fatigue resistance due to geometrical size effects is thus an important issue. In order to carry out a thorough study, both fatigue tests on large-scale specimens and advanced 3D crack propagation modelling were carried out at ICOM/EPFL. The study is limited to circular hollow sections (CHS) K-joints. An alternate current potential drop (ACPD) system is used to measure crack depth on nodes of the tested truss specimens. The results obtained from the tests are given in the paper in terms of S-N data, crack depth versus number of cycles and deduced crack propagation rates. The numerical model was developed using the dual boundary elements method (DBEM), software BEASYTM, and was validated with fatigue tests data. The stress intensity factors (SIF) along the doubly curved crack front at different crack depths were obtained.With this model, a parametric study investigates the influence of geometry, size and load case on fatigue life. The results of both proportional and non-proportional sizing effects on fatigue strength are presented. The paper shows that size effects (proportional and non-proportional) can be expressed as a function of the non-dimensional parameters and chord thickness. Keywords: Structural steel, fatigue, size effects, large-scale tests, boundary element method.

Wiley-Blackwell2008

Prediction of fatigue life of reinforced concrete bridges using Fracture Mechanics

Eugen Brühwiler, Marina Rocha Pinto Portela Nunes

With the occurrence of higher and more frequent axle loads, bridges are more solicited by fatigue loading. Bridge elements like deck slabs are subjected to a high number of stress cycles at relatively small stress magnitudes. The application of Fracture Mechanics as a useful tool for the analysis of fatigue crack growth in steel elements was demonstrated by Paris et al. in the early 1960s. With respect to reinforced concrete, the fatigue strength of the steel reinforcement is determinant. The fatigue behaviour of the steel reinforcement is similar to that of structural steel. The fatigue relevant parameters are the stress ranges, the number of fatigue cycles and stress concentrations. This paper presents a study to predict the fatigue life of steel reinforcement based on the Paris law. The method will be validated by a case study.

CRC Press/Balkema2012

Through-thickness performance of adhesive connections between FRP bridge decks and steel main girders

Martin Schollmayer

EPFL2009