Material properties and mechanical response models for fire design of steel structures are based ... more Material properties and mechanical response models for fire design of steel structures are based on extensive research and experience. Contrarily, the behaviour of aluminium load bearing structures exposed to fire is relatively unexplored. This article gives an overview of physical and mechanical properties at elevated temperature of frequently applied aluminium alloys, found in relevant literature and discusses mechanical response models currently applied for fire exposed aluminium structures. A comparison is made with steel structures exposed to fire. Key words: Physical and mechanical properties of aluminium, fire design of aluminium 1
An existing theoretical model indicates that the behaviour of trapezoidal steel sheeting under co... more An existing theoretical model indicates that the behaviour of trapezoidal steel sheeting under combined web crippling and bending moment may be modelled by only the sheeting's compressed flange. Therefore, this paper presents finite element models that simulate only the compressed flange of the sheeting, applying a prescribed displacement field along the flange longitudinal edges to simulate the loading of the bending moment. Seven different and increasingly complex types of these finite element models of a flange are compared with verified finite element models of sheeting for (a) first yield load; (b) ultimate load; (c) yield line patterns; and (d) out-ofplane deformation patterns. It is concluded that a bottom flange only, or a flange with a rounded bottom corner and load bearing plate do not predict (a) and (b) for sheeting correctly. A moving load bearing plate improves to some extent the prediction of (d) and in combination with an imposed curvature on the flange also (a)....
Markov-based models for predicting deterioration for civil infrastructures are widely recognized ... more Markov-based models for predicting deterioration for civil infrastructures are widely recognized as suitable tools addressing this mechanism. The objective of this paper is to provide insights regarding a network of orthotropic steel bridges in terms of degradation. Consequently, a model combining a dynamic Bayesian network and a Markov chain is first introduced that builds up the network in a concise way. In an attempt to represent a network composed of two general classes of orthotropic steel bridges, the classical method of structured expert judgment is carried out as a quantification procedure. The first objective is to elicit indirectly transition probabilities for a Markov chain that describes how each bridge type deteriorates in time. Second, experts are asked to provide estimates on required conditional probabilities related to the Bayesian network. An in-depth analysis of the results is presented so that remarks and observations are subsequently pointed out and, finally con...
IABSE Symposium, Vancouver 2017: Engineering the Future, 2017
This paper investigates the differences in the predicted fatigue life of transverse butt weld joi... more This paper investigates the differences in the predicted fatigue life of transverse butt weld joints and cover-plated beams considering statistically based fitting methods on fatigue test data and comparing the results with the S-N relation proposed in international standards. The test data fitting are performed by employing the Least Square Method (LSM) and the Maximum Likelihood Method (MLM) taking into account the contribution of the runouts. The Mean curve, the characteristic curve and the design curve have been derived. In order to consider the effect of Variable Amplitude loading, the S-N curves have been extended and the fatigue damage according to the Palmgren- Miner cumulative damage rule is evaluated for a load spectrum that follows a Rayleigh distribution. The results have been compared and discussed together with a Linear Elastic Fracture Mechanics (LEFM) based fatigue prediction.
Orthotropic Steel Decks (OSDs) are widely used in long span bridges because of their extremely li... more Orthotropic Steel Decks (OSDs) are widely used in long span bridges because of their extremely light weight when compared to their load carrying capacity. These deck types typically consist of a grillage of closed trapezoidal longitudinal stiffeners and transverse web stiffeners, welded to a deck plate. As a result, fatigue problems occur due to the extensive use of complex welded connections. Unfortunately, fatigue effects have often been overlooked during design, which was also the case for an important multiple span box girder viaduct in Belgium (1978).Due to a renovation program of the ring road around Brussels, the number of traffic lanes on the viaduct should be extended from three to four. As a result, questions have been raised about the current structural health of the OSD due to fatigue and future fatigue damage accumulation. Therefore, extensive FEM analyses have been performed, taking into account various parameters such as increased traffic volume and accompanying axle ...
A number of orthotropic deck structures of existing bridges are suffering from fatigue cracks. Ma... more A number of orthotropic deck structures of existing bridges are suffering from fatigue cracks. Maintenance of these deck structures may consist of regular inspections and repair of detected cracks. The usual fatigue design life procedure for aswelded structures based on S-N curves is not feasible for determining the remaining fatigue life after inspection, because S-N curves only give information on the entire fatigue life. An assessment procedure dedicated to determine the residual fatigue life is the fatigue fracture mechanics method, which starts from an initial defect and predicts the growth of this defect to a critical size. The initial defect may be a small crack detected during an inspection, or an inspection threshold value in case no crack was detected. This paper provides approximate stress intensity factors (geometric correction factors) for crack locations in continuous stringer to crossbeam joints with cope holes, which forms essential information for a fracture mechani...
Voor een monitorsysteem dat aan-geeft wanneer groot onderhoud of renovatie van stalen bruggen nod... more Voor een monitorsysteem dat aan-geeft wanneer groot onderhoud of renovatie van stalen bruggen nodig is, is in 2014 een (inmiddels uitgebreide) pilot-studie gestart op de Van Brienenoordbrug met een 'akoestische emissie-meetsysteeml. In combinatie met bestaande rekenmodellen moet het AE-systeem, geplaatst op het brug-dek, preciezere informatie geven die betere voorspellingen mogelijk maken voor brugbeheerders. Het gebruik van de meetgegevens is een belangrijk middel om voorspellingen te verfijnen.
Bolted connections are applied in many aluminium structures. Stainless steel bolts are often pref... more Bolted connections are applied in many aluminium structures. Stainless steel bolts are often preferred over carbon steel bolts in aluminium connections to prevent galvanic corrosion. However, current design standards and guidelines do not allow for using preloaded stainless steel bolts in slip resistant connections, mainly because of a lack of knowledge on the preload loss to be expected in these connections, and this limits the application field of this type of structure. This paper presents a combined empirical and analytical (i.e. mechanical) study into preload losses of stainless steel bolts in aluminium slip resistant connections caused by long-term effects (creep and relaxation), thermal expansion, and lateral contraction. It appears that stainless steel bolts can be applied in aluminium slip resistant connections, but a larger partial safety factor than standards currently prescribe is required for the slip resistance in ultimate limit state.
Probabilistic fatigue life prediction models of welded steel joints are often used to estimate th... more Probabilistic fatigue life prediction models of welded steel joints are often used to estimate the level of safety, which is given in terms of the probability of failure or the reliability index as a function of the applied load cycles. Prediction models based on fracture mechanics allow taking into account the effect of inspections on the estimated level of safety. Recent developments in fracture mechanics based fatigue prediction models allow modeling the behavior of short and long fatigue cracks under constant and variable amplitude loading. Short cracks are relevant since their growth characterizes most of the fatigue life, especially under service loading. A recently proposed model by the authors is considered and compared to a more traditional and simplified model as proposed in the standard BS7910, where no distinction is made between short and long cracks. The effect of the model uncertainty, the type of inspection, and the time of the inspection on the estimated level of sa...
Many developed countries have a national road network including a significant number of bridges i... more Many developed countries have a national road network including a significant number of bridges in need of renovation or replacement in the coming years. The reason for this is their technical and functional capacity becoming insufficient due to aging and changes in societal demands. Therefore, these bridges need to be adjusted or replaced. National authorities in The Netherlands currently require a design life of 100 years for new bridges, however nowadays it seems reasonable to have a certain flexibility for this parameter. Since the selected design life has its implications on structural solutions and choice of materials, the identification of the optimal design life for bridges seems necessary. This paper gives a summary on the issue regarding the optimum design life of bridges and it highlights the framework of the upcoming research activities.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Fatigue verification of bridge structures requires information on the loads induced by heavy vehi... more Fatigue verification of bridge structures requires information on the loads induced by heavy vehicles, which can be obtained from weigh in motion measurement (WIM) systems. The current fatigue load models applied in Europe are based on traffic load measurements in 1986. This paper evaluates the appropriateness of these models for today's traffic by comparing their load effects with those of recent WIM databases, covering the years 2008 to 2018. A procedure is derived to determine the required size of the WIM database for a sound representation of the fatigue loads. The effects of traffic jams are evaluated and the required safety margins or partial factors are derived. As already concluded by others, it appears that the most frequently used fatigue load model is unable to represent the fatigue action effects of today's European traffic. In addition, the paper demonstrates that the other fatigue load models are also inaccurate. A new fatigue load model is proposed that is easy in use and gives a significant improvement in accuracy compared to the existing models. The parameters in this model can easily be calibrated for other WIM databases.
The effect of embedding in concrete on the fatigue performance of steel reinforcement bars is not... more The effect of embedding in concrete on the fatigue performance of steel reinforcement bars is not evident. Some test series provided in literature demonstrate a higher fatigue resistance of embedded bars as compared to bars in air, whereas others provide a lower resistance. In addition, debate exists on the mechanisms behind the difference between tests in air and tests in concrete, if any. These mechanisms mentioned in literature are empirically based. This paper provides a numerical (finite element) study on the stress concentration factors and the stress intensity factors for the two conditions. It shows that the locations of cracks in concrete relative to the ribs on rebars and the distance between concrete cracks have little influence on the stress peaks in the rebar and hence on the fatigue performance of the rebar. Mechanical interlock or pressure of concrete against the ribs slightly contributes to the rebar stress concentrations. No significant difference should be expected in fatigue resistance between rebars in air and rebars embedded in concrete. Variations in local geometry at the root of ribs appear of more significant influence.
This present paper concerns the application of probabilistic fatigue life prediction models based... more This present paper concerns the application of probabilistic fatigue life prediction models based on S-N curves aiming at the estimation of the safety level for a nonload carrying cruciform joint. The safety level is expressed in terms of the reliability index as a function of the number of applied cycles. Estimating the reliability of a structural component against fatigue failure is relevant for both new and existing structures. The analysis is executed considering three models. For each of them, the input random variables are given in a probabilistic manner, based on fatigue test data from the scientific literature. The effect of the model uncertainty on the model response is quantified for both the load and the resistance side, demonstrating its relevance. Moreover, it has been shown that a 0.5 to 1 increase in the reliability index is achievable by applying the newly proposed, more complex model.
This paper presents a probabilistic fatigue life prediction model for welded details subjected to... more This paper presents a probabilistic fatigue life prediction model for welded details subjected to variable amplitude random loading, using the nominal stress approach. The proposed model makes use of CA S-N curves in combination with the relative damage rule which allows to globally account for load interaction effects, and the damage limit concept that permits the estimation of the damage for the stress ranges lower than the fatigue limit and is based on linear elastic fracture mechanics. Epistemic (sampling) and aleatory (statistical) uncertainties are estimated in a statistical framework, making the model applicable for structural reliability analyses.
Hot-riveted connections have been widely used in the past for metallic bridges, of which a large ... more Hot-riveted connections have been widely used in the past for metallic bridges, of which a large part is still in service, making relevant the assessment of their fatigue life. Previous studies have shown that the fatigue behavior of hot-riveted connections depends on many factors; among these, the residual tensile force in the rivets that clamps the plates together, i.e. the clamping force, is one of the most prone to uncertainty and scatter. Investigations p in the past made use of specimens produced in controlled laboratory conditions, potentially leading to optimistic results. This paper presents an experimental investigation on the clamping force of as-built hot-driven rivets extracted from an old steel bridge. On average, the clamping stress was found to be ∼100 MPa and ∼60 MPa, but with large scatter, for two or three plates being clamped, respectively, and for grip length over diameter ratios close to unity. This significant dependency on the number of clamped plates, as well as the lower values observed as compared to earlier studies, are attributed to larger imperfections in rivets installed in-service, as compared to the controlled laboratory environment. In addition, a finite element model is presented that simulates the development of the clamping force following the installation of the rivet. The finite element model was validated on the basis of the experimental data and it appears able to predict the effect of the grip length on the clamping force. The larger the grip length over diameter ratio, the larger is the clamping force.
Material properties and mechanical response models for fire design of steel structures are based ... more Material properties and mechanical response models for fire design of steel structures are based on extensive research and experience. Contrarily, the behaviour of aluminium load bearing structures exposed to fire is relatively unexplored. This article gives an overview of physical and mechanical properties at elevated temperature of frequently applied aluminium alloys, found in relevant literature and discusses mechanical response models currently applied for fire exposed aluminium structures. A comparison is made with steel structures exposed to fire. Key words: Physical and mechanical properties of aluminium, fire design of aluminium 1
An existing theoretical model indicates that the behaviour of trapezoidal steel sheeting under co... more An existing theoretical model indicates that the behaviour of trapezoidal steel sheeting under combined web crippling and bending moment may be modelled by only the sheeting's compressed flange. Therefore, this paper presents finite element models that simulate only the compressed flange of the sheeting, applying a prescribed displacement field along the flange longitudinal edges to simulate the loading of the bending moment. Seven different and increasingly complex types of these finite element models of a flange are compared with verified finite element models of sheeting for (a) first yield load; (b) ultimate load; (c) yield line patterns; and (d) out-ofplane deformation patterns. It is concluded that a bottom flange only, or a flange with a rounded bottom corner and load bearing plate do not predict (a) and (b) for sheeting correctly. A moving load bearing plate improves to some extent the prediction of (d) and in combination with an imposed curvature on the flange also (a)....
Markov-based models for predicting deterioration for civil infrastructures are widely recognized ... more Markov-based models for predicting deterioration for civil infrastructures are widely recognized as suitable tools addressing this mechanism. The objective of this paper is to provide insights regarding a network of orthotropic steel bridges in terms of degradation. Consequently, a model combining a dynamic Bayesian network and a Markov chain is first introduced that builds up the network in a concise way. In an attempt to represent a network composed of two general classes of orthotropic steel bridges, the classical method of structured expert judgment is carried out as a quantification procedure. The first objective is to elicit indirectly transition probabilities for a Markov chain that describes how each bridge type deteriorates in time. Second, experts are asked to provide estimates on required conditional probabilities related to the Bayesian network. An in-depth analysis of the results is presented so that remarks and observations are subsequently pointed out and, finally con...
IABSE Symposium, Vancouver 2017: Engineering the Future, 2017
This paper investigates the differences in the predicted fatigue life of transverse butt weld joi... more This paper investigates the differences in the predicted fatigue life of transverse butt weld joints and cover-plated beams considering statistically based fitting methods on fatigue test data and comparing the results with the S-N relation proposed in international standards. The test data fitting are performed by employing the Least Square Method (LSM) and the Maximum Likelihood Method (MLM) taking into account the contribution of the runouts. The Mean curve, the characteristic curve and the design curve have been derived. In order to consider the effect of Variable Amplitude loading, the S-N curves have been extended and the fatigue damage according to the Palmgren- Miner cumulative damage rule is evaluated for a load spectrum that follows a Rayleigh distribution. The results have been compared and discussed together with a Linear Elastic Fracture Mechanics (LEFM) based fatigue prediction.
Orthotropic Steel Decks (OSDs) are widely used in long span bridges because of their extremely li... more Orthotropic Steel Decks (OSDs) are widely used in long span bridges because of their extremely light weight when compared to their load carrying capacity. These deck types typically consist of a grillage of closed trapezoidal longitudinal stiffeners and transverse web stiffeners, welded to a deck plate. As a result, fatigue problems occur due to the extensive use of complex welded connections. Unfortunately, fatigue effects have often been overlooked during design, which was also the case for an important multiple span box girder viaduct in Belgium (1978).Due to a renovation program of the ring road around Brussels, the number of traffic lanes on the viaduct should be extended from three to four. As a result, questions have been raised about the current structural health of the OSD due to fatigue and future fatigue damage accumulation. Therefore, extensive FEM analyses have been performed, taking into account various parameters such as increased traffic volume and accompanying axle ...
A number of orthotropic deck structures of existing bridges are suffering from fatigue cracks. Ma... more A number of orthotropic deck structures of existing bridges are suffering from fatigue cracks. Maintenance of these deck structures may consist of regular inspections and repair of detected cracks. The usual fatigue design life procedure for aswelded structures based on S-N curves is not feasible for determining the remaining fatigue life after inspection, because S-N curves only give information on the entire fatigue life. An assessment procedure dedicated to determine the residual fatigue life is the fatigue fracture mechanics method, which starts from an initial defect and predicts the growth of this defect to a critical size. The initial defect may be a small crack detected during an inspection, or an inspection threshold value in case no crack was detected. This paper provides approximate stress intensity factors (geometric correction factors) for crack locations in continuous stringer to crossbeam joints with cope holes, which forms essential information for a fracture mechani...
Voor een monitorsysteem dat aan-geeft wanneer groot onderhoud of renovatie van stalen bruggen nod... more Voor een monitorsysteem dat aan-geeft wanneer groot onderhoud of renovatie van stalen bruggen nodig is, is in 2014 een (inmiddels uitgebreide) pilot-studie gestart op de Van Brienenoordbrug met een 'akoestische emissie-meetsysteeml. In combinatie met bestaande rekenmodellen moet het AE-systeem, geplaatst op het brug-dek, preciezere informatie geven die betere voorspellingen mogelijk maken voor brugbeheerders. Het gebruik van de meetgegevens is een belangrijk middel om voorspellingen te verfijnen.
Bolted connections are applied in many aluminium structures. Stainless steel bolts are often pref... more Bolted connections are applied in many aluminium structures. Stainless steel bolts are often preferred over carbon steel bolts in aluminium connections to prevent galvanic corrosion. However, current design standards and guidelines do not allow for using preloaded stainless steel bolts in slip resistant connections, mainly because of a lack of knowledge on the preload loss to be expected in these connections, and this limits the application field of this type of structure. This paper presents a combined empirical and analytical (i.e. mechanical) study into preload losses of stainless steel bolts in aluminium slip resistant connections caused by long-term effects (creep and relaxation), thermal expansion, and lateral contraction. It appears that stainless steel bolts can be applied in aluminium slip resistant connections, but a larger partial safety factor than standards currently prescribe is required for the slip resistance in ultimate limit state.
Probabilistic fatigue life prediction models of welded steel joints are often used to estimate th... more Probabilistic fatigue life prediction models of welded steel joints are often used to estimate the level of safety, which is given in terms of the probability of failure or the reliability index as a function of the applied load cycles. Prediction models based on fracture mechanics allow taking into account the effect of inspections on the estimated level of safety. Recent developments in fracture mechanics based fatigue prediction models allow modeling the behavior of short and long fatigue cracks under constant and variable amplitude loading. Short cracks are relevant since their growth characterizes most of the fatigue life, especially under service loading. A recently proposed model by the authors is considered and compared to a more traditional and simplified model as proposed in the standard BS7910, where no distinction is made between short and long cracks. The effect of the model uncertainty, the type of inspection, and the time of the inspection on the estimated level of sa...
Many developed countries have a national road network including a significant number of bridges i... more Many developed countries have a national road network including a significant number of bridges in need of renovation or replacement in the coming years. The reason for this is their technical and functional capacity becoming insufficient due to aging and changes in societal demands. Therefore, these bridges need to be adjusted or replaced. National authorities in The Netherlands currently require a design life of 100 years for new bridges, however nowadays it seems reasonable to have a certain flexibility for this parameter. Since the selected design life has its implications on structural solutions and choice of materials, the identification of the optimal design life for bridges seems necessary. This paper gives a summary on the issue regarding the optimum design life of bridges and it highlights the framework of the upcoming research activities.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Fatigue verification of bridge structures requires information on the loads induced by heavy vehi... more Fatigue verification of bridge structures requires information on the loads induced by heavy vehicles, which can be obtained from weigh in motion measurement (WIM) systems. The current fatigue load models applied in Europe are based on traffic load measurements in 1986. This paper evaluates the appropriateness of these models for today's traffic by comparing their load effects with those of recent WIM databases, covering the years 2008 to 2018. A procedure is derived to determine the required size of the WIM database for a sound representation of the fatigue loads. The effects of traffic jams are evaluated and the required safety margins or partial factors are derived. As already concluded by others, it appears that the most frequently used fatigue load model is unable to represent the fatigue action effects of today's European traffic. In addition, the paper demonstrates that the other fatigue load models are also inaccurate. A new fatigue load model is proposed that is easy in use and gives a significant improvement in accuracy compared to the existing models. The parameters in this model can easily be calibrated for other WIM databases.
The effect of embedding in concrete on the fatigue performance of steel reinforcement bars is not... more The effect of embedding in concrete on the fatigue performance of steel reinforcement bars is not evident. Some test series provided in literature demonstrate a higher fatigue resistance of embedded bars as compared to bars in air, whereas others provide a lower resistance. In addition, debate exists on the mechanisms behind the difference between tests in air and tests in concrete, if any. These mechanisms mentioned in literature are empirically based. This paper provides a numerical (finite element) study on the stress concentration factors and the stress intensity factors for the two conditions. It shows that the locations of cracks in concrete relative to the ribs on rebars and the distance between concrete cracks have little influence on the stress peaks in the rebar and hence on the fatigue performance of the rebar. Mechanical interlock or pressure of concrete against the ribs slightly contributes to the rebar stress concentrations. No significant difference should be expected in fatigue resistance between rebars in air and rebars embedded in concrete. Variations in local geometry at the root of ribs appear of more significant influence.
This present paper concerns the application of probabilistic fatigue life prediction models based... more This present paper concerns the application of probabilistic fatigue life prediction models based on S-N curves aiming at the estimation of the safety level for a nonload carrying cruciform joint. The safety level is expressed in terms of the reliability index as a function of the number of applied cycles. Estimating the reliability of a structural component against fatigue failure is relevant for both new and existing structures. The analysis is executed considering three models. For each of them, the input random variables are given in a probabilistic manner, based on fatigue test data from the scientific literature. The effect of the model uncertainty on the model response is quantified for both the load and the resistance side, demonstrating its relevance. Moreover, it has been shown that a 0.5 to 1 increase in the reliability index is achievable by applying the newly proposed, more complex model.
This paper presents a probabilistic fatigue life prediction model for welded details subjected to... more This paper presents a probabilistic fatigue life prediction model for welded details subjected to variable amplitude random loading, using the nominal stress approach. The proposed model makes use of CA S-N curves in combination with the relative damage rule which allows to globally account for load interaction effects, and the damage limit concept that permits the estimation of the damage for the stress ranges lower than the fatigue limit and is based on linear elastic fracture mechanics. Epistemic (sampling) and aleatory (statistical) uncertainties are estimated in a statistical framework, making the model applicable for structural reliability analyses.
Hot-riveted connections have been widely used in the past for metallic bridges, of which a large ... more Hot-riveted connections have been widely used in the past for metallic bridges, of which a large part is still in service, making relevant the assessment of their fatigue life. Previous studies have shown that the fatigue behavior of hot-riveted connections depends on many factors; among these, the residual tensile force in the rivets that clamps the plates together, i.e. the clamping force, is one of the most prone to uncertainty and scatter. Investigations p in the past made use of specimens produced in controlled laboratory conditions, potentially leading to optimistic results. This paper presents an experimental investigation on the clamping force of as-built hot-driven rivets extracted from an old steel bridge. On average, the clamping stress was found to be ∼100 MPa and ∼60 MPa, but with large scatter, for two or three plates being clamped, respectively, and for grip length over diameter ratios close to unity. This significant dependency on the number of clamped plates, as well as the lower values observed as compared to earlier studies, are attributed to larger imperfections in rivets installed in-service, as compared to the controlled laboratory environment. In addition, a finite element model is presented that simulates the development of the clamping force following the installation of the rivet. The finite element model was validated on the basis of the experimental data and it appears able to predict the effect of the grip length on the clamping force. The larger the grip length over diameter ratio, the larger is the clamping force.
Uploads
Papers by Johan Maljaars