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The paper presents a GIS plugin, named Bridge Assessment System via MTInSAR (BAS-MTInSAR), aimed at assessing deformations in existing simply supported concrete girder bridges through Multi-Temporal Interferometry Synthetic Aperture Radar (MTInSAR). Existing bridges require continuous maintenance to ensure functionality toward external effects undermining the safety of these structures, such as aging, material degradation, and environmental factors. Although effective and standardized methodologies exist (e.g., structural monitoring, periodic onsite inspections), new emerging technologies could be employed to provide time- and cost-effective information on the current state of structures and to drive prompt interventions to mitigate risk. One example is represented by MTInSAR data, which can provide near-continuous information about structural displacements over time. To easily manage these data, the paper presents BAS-MTInSAR. The tool allows users to insert information of the focused bridge (displacement time series, structural information, temperature data) and, through a user-friendly GUI, observe the occurrence of abnormal deformations. In addition, the tool implements a procedure of multisource data management and defines proper thresholds to assess bridge behavior against current code prescriptions. BAS-MTInSAR is fully described throughout the text and was tested on a real case study, showing the main potentialities of the tool in managing bridge portfolios. [ABSTRACT FROM AUTHOR]

Several recent studies have investigated the opportunities of differential interferometry synthetic aperture radar (DInSAR) using satellite data for structural health monitoring (SHM) of civil structures. However, its use in structural engineering is still debated because of the lack of a general understanding of the potential and limitations of the technology for bridge SHM. To overcome this issue, specific methods of data processing and displacement assessment with error quantification need to be developed. The present paper aims at giving an insight into the use of small baseline subset-differential synthetic aperture radar interferometry (SBAS-DInSAR) as a remote-sensing technology for civil infrastructure monitoring combining information at a large scale with those associated with a single bridge. In particular, an operational framework for the selection and processing of a measurement time series representative of the structural behavior of the bridge of interest is designed in a way that fully remote characterization and assessment can be carried out by exploiting web-mapping platforms according to the crowd-sensing paradigm. The workflow, designed consistently with a structural engineering perspective, has been tested with reference to a number of bridges crossing the Tiber river in Rome (Italy), showing that the proposed fully remote monitoring procedure can effectively support satellite data processing and interpretation. Moreover, some issues in view of the general use of satellite data for bridge monitoring emerged from the study. Gaps in the measurement point distribution over the bridge decks are frequently observed over all the monitored area, therefore simplified methodologies aimed at estimating expected displacement ranges of different bridge typologies under serviceability loads have been defined enabling a rational interpretation of the data in the light of the selected radar sensor band of operation. Simplified formulations and charts for service and environmental loads are then presented with a twofold objective: (1) supporting the satellite data elaboration and interpretation by means of easy to manage open-source tools; and (2) providing estimates of the expected operational displacements of healthy structures to guide data interpretation and even algorithms for radar signals processing able to incorporate the response of structures to temperature variations. [ABSTRACT FROM AUTHOR]

Evaluation and strengthening of existing bridges – historical outlines and findings regarding the Hessian road bridge inventory Two short histographical sketches introduce the concepts of refurbishment, condition and load‐bearing capacity assessment between 1700 and 2010 and take a look at the development of the recalculation of existing bridges. Based on project sketches, the hidden safety features of existing road bridges are worked out and procedures for achieving efficient structural bridge strengthening are presented. The focus is on the determination of real object‐specific traffic load models, calibrated structural analyses and additive and non‐destructive strengthening methods. Some critical comments on planning acceleration and the current approval system, together with the demand that bridge construction should be reflected in the common objective of "traffic", broaden the definition of strengthening holistically. This offers the opportunity to stimulate a discussion about the sensible handling of existing bridges as part of our road infrastructure. [ABSTRACT FROM AUTHOR]

The management of existing civil infrastructure is becoming more crucial as a large share of bridges is approaching their theoretical end of service duration. Structural performance monitoring aims to verify bridge safety at a given time, and it should be differentiated from structural health monitoring, which aims at detecting structural damage. Possible monitoring techniques include bridge load testing, non-destructive testing, and continuous monitoring of structural behaviour, environmental conditions, and load levels. Nonetheless, selecting the optimal combination of monitoring techniques is challenging as each method provides unique but also redundant information. This study proposes a framework to assess the value of information from multiple bridge monitoring techniques. This framework enables defining the appropriate set of monitoring techniques to ensure that the collected information will potentially correct engineering decisions regarding structural safety. A full-scale bridge in Switzerland is used for validating the framework predictions. Combining four monitoring techniques, the expected average increase of degrees of compliance of structural verification is estimated to 19%, which is consistent with the 36% obtained after performing these monitoring techniques. The methodology supports decision-makers in selecting an optimal combination of monitoring techniques for structural performance monitoring by maximizing the value of information. [ABSTRACT FROM AUTHOR]

This paper addresses the need for accurate and objective safety assessments of bridges in Brazil taking into account the increase in traffic load and limited funding for infrastructure. In Brazil, the usual method of ensuring bridge safety involves strengthening based on design codes using deterministic analysis and partial safety factors. This method leads to an increase in the maintenance cost of the bridges. Structural reliability assessment, a higher-tier assessment method, is recommended globally for assessing the safety of existing bridges beyond current deterministic methods. This paper presents a study that evaluates the structural safety of existing road bridges in Brazil using the semi-probabilistic method defined in Brazilian standards and the full probabilistic method. The study selected six case studies of existing reinforced and prestressed concrete bridges to evaluate their structural safety concerning current normative loads. The results suggest that the partial safety factors defined in the Brazilian standards are consistent with international standards. The reliability analysis can guarantee the bridges' safety, even with increased traffic loads, without additional costs for structural strengthening. Therefore, the paper highlights the importance of promoting reliability analysis in Brazil to ensure the safety of existing bridges and promote cost-effective and objective safety assessments. [ABSTRACT FROM AUTHOR]

A case study was conducted to explore a more rational and robust process for determining the characteristic in-situ compressive strength of concrete structures from core samples. Slabs and girders were obtained from a total of seven bridges, earmarked for demolition due to social and performance considerations. Approximately 600 concrete core samples were extracted from various locations on these bridges. Statistical simulations were carried out using both conventional protocols and a newly proposed method to ascertain the characteristic strength from the cores. This led to a comprehensive discussion on the appropriate sample size, as well as the probabilistic robustness and reliability of the protocols. The proposed method demonstrated the ability to minimize over- or under-estimation of the characteristic strength, providing stable values less affected by fluctuations in core strengths.

The paper presents a GIS plugin, named Bridge Assessment System via MTInSAR (BAS-MTInSAR), aimed at assessing deformations in existing simply supported concrete girder bridges through Multi-Temporal Interferometry Synthetic Aperture Radar (MTInSAR). Existing bridges require continuous maintenance to ensure functionality toward external effects undermining the safety of these structures, such as aging, material degradation, and environmental factors. Although effective and standardized methodologies exist (e.g., structural monitoring, periodic onsite inspections), new emerging technologies could be employed to provide time- and cost-effective information on the current state of structures and to drive prompt interventions to mitigate risk. One example is represented by MTInSAR data, which can provide near-continuous information about structural displacements over time. To easily manage these data, the paper presents BAS-MTInSAR. The tool allows users to insert information of the focused bridge (displacement time series, structural information, temperature data) and, through a user-friendly GUI, observe the occurrence of abnormal deformations. In addition, the tool implements a procedure of multisource data management and defines proper thresholds to assess bridge behavior against current code prescriptions. BAS-MTInSAR is fully described throughout the text and was tested on a real case study, showing the main potentialities of the tool in managing bridge portfolios.

A methodology is introduced that allows to determine the reliability of railway bridges subject to freight trains and which comply with code based assessment according to the Swiss structural code SIA 269. The methodology uses probabilistic models for section forces from freight trains. These models are based on a large database of wheel load measurements. A case study demonstrates how the methodology is applied to determine the reliability of generic bridges and subsequently allows the assessment of the reliability for a portfolio of railway bridges. The results show that the target reliability is achieved according to SIA 269 considering the code format and current set of partial safety factors. The study identifies potential load bearing reserves for bridges with longer spans. [ABSTRACT FROM AUTHOR]

There is great interest in developing an adequate partial factor format for the assessment of existing structures, and in particular bridges, that should be able to take various aspects into account linked to the fact that the structure already exists. As the structure is existing, additional information related to material parameters, loading conditions, local structural defects, etc. can be accounted for. In addition, the degree of conservatism needs to be well balanced to avoid unnecessary investment of resources in replacement or retrofitting. This contribution considers the experience gained in recent years in parallel with some ongoing standardisation work in relation to Eurocodes and the next edition of the fib Model Code for new and existing concrete structures. The current state of the art of partial factors for the assessment of existing structures is explored and the differences are assessed based on a comparison between (i) the use of recommended fixed partial factors as provided in many national and international codes, (ii) adjusted (flexible) partial factors derived for the individual case under consideration, and (ii) reliability-based verification. In order to assess the adequacy of proposals and identify some differences, the available partial factor formats are applied to two case studies of reinforced concrete bridges and they are critically assessed. [ABSTRACT FROM AUTHOR]

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This paper describes the structural effects of ASR expansion in reinforced structures. It proposes models and procedures for calculating the strains in the concrete caused by the reinforcement, the load effects in statically indeterminate structures and the cross-sectional capacities. Three models are described to include variations of the ASR expansion in a section. Model 1 for constant or linearly varying ASR expansion, Model 2 for an expansion variation in different parts of a cross-section and Model 3 for a particular case of different expansion in subsections of the cross-section. The models are exemplified by calculations based on input data from one relevant bridge, the 70 years old Elgeseter bridge in Trondheim, Norway. This is done to illustrate various aspects of the calculation methods and show the structural consequences of the ASR expansion. The results correlate with the bridge’s observed structural behavior and assumed expansion. This paper also illustrates the importance of coordinating inspection, material testing and structural strength analysis to obtain reliable assessment.

Recent Italian Guidelines provide a possible solution for mitigating the structural risk of existing bridges. The procedure, which entails a multi‐level approach, from census of the structures to the resilience assessment of the road network, is being applied in several portions of the Italian territory with reference to bridges managed by different administrative bodies and private companies. In this paper, the application of the Italian Guidelines to a stock of 150 in‐service road bridges of the Province of Caserta is addressed. The application refers to the level 2 of the procedure and aims at estimating the structural/foundational and seismic attention class of the considered structures. The obtained results are then discussed, and a preliminary statistic elaboration of the results aimed at highlighting the most influencing parameters of the whole procedure is provided. [ABSTRACT FROM AUTHOR]

The structural reliability of existing post‐tensioned concrete bridges is a non‐trivial topic because of uncertainties affecting many parameters involved in their assessment process. This last is performed according to the current Codes specification through the partial factor method. Such method can be applied considering realistic material properties variability and accounting also for ageing, deterioration, and damage by means of all prior data that can be collected, as stated in present Standards like Fib 80. These data span from existing design specifications up to original design documents and experimental campaigns for the material investigations through in‐situ tests. Regarding existing post‐tensioned concrete bridges, the prestressing cables characteristics are the most important components in the reliability of the final safety verification, but their values (in terms of probability distribution) are affected by many uncertainty sources. This paper focuses on the evaluation of the structural reliability of a real case study by applying the partial factor method and by comparing the results achieved considering the ideal case of perfect knowledge with those achieved considering different levels of knowledge acquired through simulated experimental tests. [ABSTRACT FROM AUTHOR]

Aging infrastructures require huge budgets to preserve their functionality and the lack of effective maintenance leads to increasing deterioration and therefore higher repair costs. For these reasons, assessing the condition of infrastructures becomes mandatory, with particular attention to the ones still in service even when their life limit has been exceeded. In particular, this problem is really important in Countries, like Italy, in which there are several operating bridges at the end of their service life. In this framework, many companies responsible for the management of road networks have turned their interest towards Bridge Management Systems (BMS). This paper presents a fast and low‐cost method for condition rating of reinforced concrete bridges. The proposal is based on visual inspection and non‐destructive testing. A specific parameter is designed to take into account the mechanical degradation of materials and the damage location at the structural sub‐component level. Some benchmark case studies have been discussed in order to compare the proposed method with other approaches available in literature. [ABSTRACT FROM AUTHOR]

The question of maintenance and monitoring of bridges gained attention during the last decade, especially in Italy, after some serious collapses. The first emergency phase was the census and the visual evaluation of the state of maintenance and preservation of existing heritage to highlight the critical conditions for security. For this reason, in 2020 the Italian Ministry of Transport and Infrastructure enacts Guidelines, based on a multilevel approach, which allows to save time and resources by deepening the analysis only on the bridges in the worst state of conservation. After two years of inspections, a lot of data had been collected. The data concerns both the geometrical/typological characteristics and the defectiveness of bridges. In the present work, the authors discuss the data of a sample of inspected bridges belonging to some Regions of the Italian infrastructural system trying to analyse them from a statistical point of view. The objective is to standardize an analysis methodology and apply it to a larger number of samples to obtain useful and significant information to refine the inspection procedure and, eventually, to educate algorithms for the a priori provision of the defectiveness level, suggesting a possible prioritization of the bridges to be inspected. [ABSTRACT FROM AUTHOR]

Autostrade per l'Italia (ASPI) is planning the upgrading of several highway axis for approx. 150 km in the next years. Most of the original bridges, built around '60/'70, have already been widened in the 90s but should now be widened again. The original decks are often made of a grid of post‐tensioned elements, while the further enlargements were built with different solutions (precast pre‐stressed beams or steel beams). To assess the material properties and the internal conditions of the post‐tensioned decks, several investigations with non‐destructive and semi‐destructive testing have been carried out, in accordance with Italian Guidelines. This paper illustrates the main results collected, also highlighting the difficulties encountered to achieve a sufficient understanding of the degradation conditions. The assessment process evidenced that for a large part of the post‐tensioned decks it was more convenient to intervene with the replacement of the existing decks rather than rehabilitate them. The main reasons supporting this choice are explained. [ABSTRACT FROM AUTHOR]

Building Information Modelling is receiving increasing attention as an emerging technology for enhancing the life‐cycle performance of facilities. The cooperation between all professionals involved in the construction chain allows to reproduce digital twins of the structures including information related to different disciplines, such as structural and architectural aspects. In this context, the use of Building Information Modelling, combined with an automatic tool to predict risk indices, could be particularly useful when dealing with existing bridges due to the significant structural deficiencies recently demonstrated by numerous bridge collapses worldwide. This paper explores the development of a BIM‐based procedure to bring greater value in the design, construction, maintenance, and inspection stages. The procedure is applied to existing bridges and it allows to estimate a structural risk prioritization class of bridges according to maintained activities, periodical inspections, structural detailing and modelling uncertainties. The automatic BIM‐based tool uses a workflow developed in Dynamo, and is able to automatically update the structural risk class and to provide warning if the structural safety index exceed defined thresholds. [ABSTRACT FROM AUTHOR]

In professional practice, the design and verification of Reinforced Concrete (RC) and Prestressed Reinforced Concrete (PRC) structures are performed using a simplified calculation provided by the Eurocodes that limits resistance but that also includes a certain level of structural safety. Some aspects that directly affect the simplified methods involve the use of linear constitutive laws of materials. The use of non-linear laws is evident in the exploitation of reservoirs of strength and deformations of plastic materials in the Ultimate Limit State. The purpose of this research is to evaluate the increase in resistance to bending actions during the plasticization of the beam of existing bridges to support the decision-making process of the engineer in the assessment of existing structures. To achieve this, two codes (MEG Ductility, MEG Fiber Sections) were developed to provide the moment–curvature diagram of RC and PRC sections using non-linear bonds, and in this paper, the study of RC sections is reported. Furthermore, through a push-down analysis, two RC and PRC viaducts have been analyzed using the moment–curvature characteristics obtained from the realized codes and by varying the non-linear constitutive bonds. The results of this study provide valuable insights into the behavior of RC structures under bending actions and demonstrate the importance of considering non-linear material laws for accurate structural assessments. The findings contribute to the enhancement of the decision-making process of engineers when dealing with existing infrastructures. [ABSTRACT FROM AUTHOR]

The safety of existing bridges represents a serious problem in Italy since these structures are fundamental for the national transportation system and, at the same time, can be subject to significant deterioration phenomena linked to the fact that the construction period typically dates back to the 1960s. This study involves the seismic analysis of five case study bridges belonging to the Italian Road Network. Using nonlinear time–history analysis with sets of code-spectrum compatible ground motions, analytical fragility curves have been constructed for each of the five bridges. The results obtained interpreting the analytical fragility curves agree with the fact that the seismic behavior of existing bridges can be problematic and that higher seismicity can be associated with more detrimental behavior. In particular, the results reveal that in regions with higher seismicity, the main problems in bridges are related to bearings and connecting elements located in the piers. Five case studies have also been analyzed to determine the Structural and Foundational Class of Attention and Seismic Class of Attention, following the approach proposed by the 2020 Italian Guidelines. In this way, it is possible to compare two different assessment approaches with different safety levels. The results obtained with the two approaches are in good agreement considering bridges in high seismicity regions, while the procedure of the Guidelines could lead to not reflecting the seismic behavior of bridges when the seismicity of the area is lower. [ABSTRACT FROM AUTHOR]

The examination of existing civil structures must be differentiated from designing new structures. To have sustainable and circular asset management, the behavior of these existing structures must be better understood to avoid unnecessary maintenance and replacements. Monitoring data collected through bridge load testing, structural health monitoring, and non-destructive tests may provide useful information that could significantly influence their structural-safety evaluations. Nonetheless, these monitoring techniques are often elaborate, and the monitoring costs may not always justify the benefits of the information gained. Additionally, it is challenging to quantify the expected information gain before monitoring, especially when combining several techniques. This paper proposes several definitions and metrics to quantify the information gained from monitoring data to better evaluate the benefits of monitoring techniques. A full-scale bridge case study in Switzerland is used to illustrate the information gain from multiple monitoring techniques. On this structure, static load tests, three years of strain monitoring, weigh-in-motion measurements, and non-destructive tests were performed between 2016 and 2019. The influence on structural-safety examination is evaluated for each combination of monitoring techniques. Results show that each technique provides unique information and the optimal combination depends on the selected definition of information gain. When data from monitoring techniques are combined, significant reserve capacity of the bridge is determined. [ABSTRACT FROM AUTHOR]

Advanced reliability assessment can be required when evaluating existing bridge structures through proof load testing. The target load of a proof load test typically requires input from resistance models; however, bridges with a low documentation level are often the most relevant for proof load testing, and resistance models thus involve significant uncertainties. This paper presents a different approach to proof loading and target proof load, in which the resistance model is not included in the determination of this load. Instead, the target proof load is determined based on load models coupled to the desired target failure probability, thus ensuring sufficient safety of the existing bridge. The method is in line with the proposal for a new Eurocode on assessment of existing structures and is deemed to be superior to existing approaches. An essential assumption of the method is that monitoring systems can identify stop criteria before irreversible damage occurs. The approach was applied in a case study, where an OT-slab bridge with a span of 6.5 m was proof-load-tested and reclassified for capacity upgrading of a road stretch in Denmark. [ABSTRACT FROM AUTHOR]

This paper provides a discussion and thoughtful application on a large sample of the procedures for the classification of existing bridges recently adopted in Italy and defined within the Italian Guidelines for the classification, risk management, safety evaluation and monitoring of existing bridges and the early published Operating Instructions. Focusing on the classification at the territorial level, first the logic flows to the classification on the base of the structural risk are shown, resulting in the definition of the "structural warning class", providing the motivations that support the criteria for the definition of such procedures. Then, a statistical analysis of the results obtained from the classification of 661 existing Italian bridges is performed, focusing on the vulnerability classification and on the influence of each parameter on its evaluation. [ABSTRACT FROM AUTHOR]

In structural engineering and bridge construction, probabilistic calculations are only performed in a few exceptional cases. The ability to directly use information from the existing structure is an important advantage of probabilistic methods. Geometric data or the position and quantity of the installed reinforcing steel and tendons can be measured. Results from monitoring of the traffic can be used to generate structure-specific load models. Many clients are still very sceptical about the results of probabilistic calculations, even though there are several examples of successful application. The use of probabilistic verification formats is explicitly permitted by the German guideline for the assessment of existing bridges (German: Nachrechnungsrichtlinie). Since a high degree of special knowledge is required for the application of probabilistic calculations, it is difficult to establish the potential of this verification method in practice. It is necessary to enable the practical engineer to utilize the advantages of probabilistic calculations and to include the actual structural conditions into the calculation model, but without the need for all the special knowledge. Structure-specific partial safety factors include measured data and can be used for the well-known and in the codes established semi-probabilistic design concept. The authors present examples for the successful application of probabilistic methods and of data measurement during the reassessment of two existing bridges in Germany. The capabilities of full-probabilistic calculations for the reassessment of existing structures are described and concepts for the calculation of structure-specific partial safety factors are shown.

The Italian road network comprises many bridges that were constructed around the middle of last century and are now close to, or have exceeded, their intended design lives. The advanced state of degradation of many of the bridges has been a contributing factor in a number of collapses in recent years, with the problem being particularly prevalent in prestressed concrete construction. In response to the need for improvements in the reliability of existing Italian bridges, the Ministry of Transport and Infrastructure published in 2020 a new set of guidelines for assessment and monitoring. This article undertakes a critical review of the guidelines, which are currently in a trial phase, through the multilevel assessment of a case‐study prestressed concrete road bridge. Four key areas for potential improvement in future revisions are identified: refinement of the level 3 preliminary assessment approach, greater emphasis on assessment rather than design thinking, objective Knowledge Levels, and treatment of elements with unknown levels of degradation. [ABSTRACT FROM AUTHOR]

The heritage of existing road infrastructures and in particular of bridges consists of structures that are approaching or exceeding their designed service life. Detrimental causes such as aging, fatigue and deterioration processes other than variation in loading conditions introduce uncertainties that make structural assessment a challenging task. Experimental data on their performances are crucial for a proper calibration of numerical models able to predict their behavior and life-cycle structural performance. In this scenario, an experimental research program was established with the aim of investigating a set of 50-year-old prestressed concrete bridge girders that were recovered from a decommissioned bridge. The activities included initial non-destructive tests, and then full-scale load tests followed by a destructive test on the material samples. This paper reports the experimental results of the full-scale tests conducted on the first group of four I-beams assumed to be in good condition from visual inspection at the time of testing. Loading tests were performed using a specifically designed steel reaction frame and a test setup equipment, as detailed in the present work. Due to the structural response of this first group of girders, a uniform behavior was found at both service and ultimate conditions. The failure mechanism was characterized by the crushing of the cast-in-situ top slab corresponding to a limited deflection, highlighting a non-ductile behavior. The outcomes of the experimental research are expected to provide new data for the life-cycle safety assessment of existing bridges through an extended database of validated experimental tests and models. [ABSTRACT FROM AUTHOR]

The paper presents a systematic review about the use of artificial intelligence (AI) in the field of structural health management of existing bridges. Using the PRISMA protocol, 81 journal articles were analysed. Three areas of investigation were addressed: (1) use of computer vision (CV) to automatize visual inspection of existing bridges; (b) use of AI with data provided by sensors employed in structural health monitoring (SHM); (c) use of AI for enhancing prediction of existing bridges deterioration, to improve risk estimation. The findings indicated that while the first two areas are covered by the scientific literature, the most intriguing challenges regard the use of AI in the field of bridge performance and risk assessment, in which new technologies could be exploited for predicting structural decay over time and residual life. This synthesis could significantly contribute to facilitate the indispensable fusion between the traditional civil-structural engineering and the contemporary technological progresses. [Display omitted] • AI methods for structural health management of existing bridges are reviewed. • CV techniques to improve current practices of visual defect detection were discussed. • AI methods for improving input and output from SHM of existing bridges were defined. • Improvements given by AI in assessing bridge performance and risks were shown. • Open challenges and future research directions were highlighted. [ABSTRACT FROM AUTHOR]

In recent years, several catastrophic collapses of existing bridges have highlighted the need for rapid risk analysis methods aimed at supporting infrastructure managers in the prioritisation of detailed assessments and, if any, risk mitigation actions. A large percentage of existing road bridges were built between the 1960s and 1980s, having thus already reached or even exceeded their design lifetime. Several studies have also shown that bridges often collapse due to either natural or human-related events, such as floods, collisions or overloading that, in addition to earthquakes, should be duly considered in risk assessment. This calls for multi-hazard approaches that provide an integrated perspective of the risk of bridge portfolios, to identify critical structures to support decision-makers. This study proposes a multi-hazard risk-based prioritisation methodology for application to a large number of bridges under limited level of knowledge. Specifically, the risk level is quantified through indices, accounting for uncertainties, that are used for comparative purposes among bridges. The methodology is applied to a highway bridge portfolio located in northern Italy, producing a risk-based ranking that is critically discussed. Analysis results are then compared with the outcome of the current Italian guidelines for safety assessment and maintenance of existing bridges. • Multi-hazard risk assessment of existing road bridges for prioritisation. • Proposal and investigation of alternative formulations of a multi-hazard risk index. • Application to bridge portfolio under traffic, earthquake, fire and impact hazards. • Bridge ranking and classification based on statistical thresholds. • Incorporation of visual inspection data. [ABSTRACT FROM AUTHOR]

In structural engineering and bridge construction, probabilistic calculations are only performed in a few exceptional cases. The ability to directly use information from the existing structure is an important advantage of probabilistic methods. Geometric data or the position and quantity of the installed reinforcing steel and tendons can be measured. Results from monitoring of the traffic can be used to generate structure-specific load models. Many clients are still very sceptical about the results of probabilistic calculations, even though there are several examples of successful application. The use of probabilistic verification formats is explicitly permitted by the German guideline for the assessment of existing bridges (German: Nachrechnungsrichtlinie). Since a high degree of special knowledge is required for the application of probabilistic calculations, it is difficult to establish the potential of this verification method in practice. It is necessary to enable the practical engineer to utilize the advantages of probabilistic calculations and to include the actual structural conditions into the calculation model, but without the need for all the special knowledge. Structure-specific partial safety factors include measured data and can be used for the well-known and in the codes established semi-probabilistic design concept. The authors present examples for the successful application of probabilistic methods and of data measurement during the reassessment of two existing bridges in Germany. The capabilities of full-probabilistic calculations for the reassessment of existing structures are described and concepts for the calculation of structure-specific partial safety factors are shown. [ABSTRACT FROM AUTHOR]

To accommodate increased seismic hazard in Indonesia, provisions regarding structural details in seismic regulations have been tightened. In this paper, variations in seismic hazard and detailing requirements in bridge codes from before 1990 to the present are provided. To examine bridge performance, pushover analysis was carried out based on the latest Indonesian bridge code, SNI 2833:2016/Seismic Map 2017. From the analysis results, the performance of older bridges would typically be less than that of more recently designed structures. The performance level of bridges designed in the era before SNI 2833:2016/Seismic Map 2017 will be Operational-Life Safety (LS), whereas the performance level of bridges designed according to SNI 2833:2016 will be Elastic-Operational. Referring to NCHRP 949 for bridge performance level evaluation, the results of this study showed that the performance level of the bridges still satisfies the requirements of NCHRP 949 which is Life Safety under upper-level earthquakes. Therefore, existing bridges still have adequate capacity under the current seismic load in Seismic Map 2017 (7% probability of exceedance in 75 years (RP = 1000 years)). Evaluation of seismic vulnerability needs to be done to ensure the safety of existing bridges in Indonesia, most of which are located in earthquake-prone areas, especially those that were designed under older version regulations. [ABSTRACT FROM AUTHOR]

Orthotropic steel deck (OSD) bridges are lightweight constructions which are convenient, especially for the achievement of long spans. Conversely, due to the stress concentration in correspondence to the numerous and unavoidable welded construction details, this bridge typology is prone to fatigue cracking under the effect of cyclic loading with high-stress amplitudes. Existing OSD bridges are particularly vulnerable to fatigue damage accumulation because of the dated standards adopted at the time of their design and the fact that heavy lorries have increased in travel frequency and weight. In the present paper, a case study of a northern Italian existing highway viaduct, built in the 1990s, is presented and analyzed. The fatigue damage accumulation was carried out according to the fatigue load models for road bridges reported in Eurocode EN 1991-2 and the assessment criteria indicated in EN 1993-1-9. The stress amplitude, in correspondence to the critical details of the bridge, is assessed by means of detailed finite-element calculations carried out with the software MIDAS GEN®. The amplitude and frequency of the travelling weights are assessed based on real traffic monitoring from the highway. Moreover, an automatic "rain-flow" algorithm is implemented, which is able to detect each nominal stress variation above the fatigue limit. In general, the bridge is not fully compliant with today's standards when considering the entire duration of the prescribed life of the design. Countermeasures, like lane number reductions and lane reshaping, are critically analyzed since their effectiveness is questionable as far as the reduction in heavy traffic is concerned. Other interventions, like the replacement of the pavement in order to improve the stress redistribution upon the connection details below the wheel footprint, and continuous bridge inspections or monitoring, look more promising. [ABSTRACT FROM AUTHOR]

In professional practice, the design and verification of Reinforced Concrete (RC) and Prestressed Reinforced Concrete (PRC) structures are performed using a simplified calculation provided by the Eurocodes that limits resistance but that also includes a certain level of structural safety. Some aspects that directly affect the simplified methods involve the use of linear constitutive laws of materials. The use of non-linear laws is evident in the exploitation of reservoirs of strength and deformations of plastic materials in the Ultimate Limit State. The purpose of this research is to evaluate the increase in resistance to bending actions during the plasticization of the beam of existing bridges to support the decision-making process of the engineer in the assessment of existing structures. To achieve this, two codes (MEG Ductility, MEG Fiber Sections) were developed to provide the moment–curvature diagram of RC and PRC sections using non-linear bonds, and in this paper, the study of RC sections is reported. Furthermore, through a push-down analysis, two RC and PRC viaducts have been analyzed using the moment–curvature characteristics obtained from the realized codes and by varying the non-linear constitutive bonds. The results of this study provide valuable insights into the behavior of RC structures under bending actions and demonstrate the importance of considering non-linear material laws for accurate structural assessments. The findings contribute to the enhancement of the decision-making process of engineers when dealing with existing infrastructures.

The safety of existing bridges represents a serious problem in Italy since these structures are fundamental for the national transportation system and, at the same time, can be subject to significant deterioration phenomena linked to the fact that the construction period typically dates back to the 1960s. This study involves the seismic analysis of five case study bridges belonging to the Italian Road Network. Using nonlinear time–history analysis with sets of code-spectrum compatible ground motions, analytical fragility curves have been constructed for each of the five bridges. The results obtained interpreting the analytical fragility curves agree with the fact that the seismic behavior of existing bridges can be problematic and that higher seismicity can be associated with more detrimental behavior. In particular, the results reveal that in regions with higher seismicity, the main problems in bridges are related to bearings and connecting elements located in the piers. Five case studies have also been analyzed to determine the Structural and Foundational Class of Attention and Seismic Class of Attention, following the approach proposed by the 2020 Italian Guidelines. In this way, it is possible to compare two different assessment approaches with different safety levels. The results obtained with the two approaches are in good agreement considering bridges in high seismicity regions, while the procedure of the Guidelines could lead to not reflecting the seismic behavior of bridges when the seismicity of the area is lower.

Shear strength assessment of bridge girders using refined design approaches The unfavourable age structure of bridges of the federal highway system in Germany and the considerable increase in goods traffic are the main reasons for the generally poor overall condition of numerous bridge structures. In addition, the further development of the standards in connection with the Eurocodes often results in computational deficits. More precise verification formats are offered by Level 2 of the assessment guideline, which was first published in 2011 and extended in 2015. Recent findings on the shear behaviour of prestressed concrete bridges with low shear reinforcement ratios in the range of ρw,min form the basis for the 2nd extension to the assessment guideline, which will appear in BEM‐ING Part 2. For the evaluation of the shear capacity of the main system, an extended truss model with additive concrete contribution is introduced, which is explained in the following and presented by means of two case studies. [ABSTRACT FROM AUTHOR]

In this study, the overall carbonation depth of existing bridges was investigated to establish practical guidelines for diagnosing structural carbonation. Carbonation depth was measured by obtaining cross-sections and core samples of girder-slabs from six existing concrete bridges scheduled for dismantling. The variation in carbonation depth based on the structures' location was analyzed. Moreover, various protocols were proposed for deriving the characteristic values of in-situ carbonation depth for concrete structures and each protocol was verified through probabilistic simulations. Carbonation depth exhibited inconsistency across the cross-section, varying significantly depending on the location, but a deeper carbonation was especially noticeable in locations subjected to bending or tensile stress by design. The method to select the largest value from the core data obtained are considered suitable to prevent both underestimation and overestimation. • Carbonation depth varies widely (0–100 mm) across bridge sections. • Normal distribution of carbonation depth observed in experiments. • Upper girder sections showed relatively consistent carbonation. • Lower flange portions exhibited deeper carbonation due to stress. • Method selecting the largest core value suitable to prevent bias. [ABSTRACT FROM AUTHOR]

Advanced reliability assessment can be required when evaluating existing bridge structures through proof load testing. The target load of a proof load test typically requires input from resistance models; however, bridges with a low documentation level are often the most relevant for proof load testing, and resistance models thus involve significant uncertainties. This paper presents a different approach to proof loading and target proof load, in which the resistance model is not included in the determination of this load. Instead, the target proof load is determined based on load models coupled to the desired target failure probability, thus ensuring sufficient safety of the existing bridge. The method is in line with the proposal for a new Eurocode on assessment of existing structures and is deemed to be superior to existing approaches. An essential assumption of the method is that monitoring systems can identify stop criteria before irreversible damage occurs. The approach was applied in a case study, where an OT-slab bridge with a span of 6.5 m was proof-load-tested and reclassified for capacity upgrading of a road stretch in Denmark.

The assessment of existing road bridges as parts of infrastructure networks is required in consideration of their deterioration and age. Advanced monitoring and management tools are mainly used for landmark bridges while the decision making process for small to medium bridges, which constitute the majority of the bridge network, mainly relies on condition assessment based on experience and conservative analysis related to design codes. In the analysis of the load-carrying capacity of theses bridges, loads imposed by the passing traffic are predominant due to their variable nature and level of uncertainties. The research presented in this paper outlines the value of additional traffic data, collected with both traffic counters and Weigh-in-Motion (WIM) method in the scope of assessment procedures for these bridges. Adequate processing of collected traffic data is crucial for subsequent extrapolation of maximum load effects on a particular bridge over a certain period in time. By taking into account all related costs, the purpose of this paper is to prove the benefits of employing traffic load monitoring data in structural assessment and subsequent decision-making process in service life management of bridges. [ABSTRACT FROM AUTHOR]

This paper provides a discussion and thoughtful application on a large sample of the procedures for the classification of existing bridges recently adopted in Italy and defined within the Italian Guidelines for the classification, risk management, safety evaluation and monitoring of existing bridges and the early published Operating Instructions. Focusing on the classification at the territorial level, first the logic flows to the classification on the base of the structural risk are shown, resulting in the definition of the “structural warning class”, providing the motivations that support the criteria for the definition of such procedures. Then, a statistical analysis of the results obtained from the classification of 661 existing Italian bridges is performed, focusing on the vulnerability classification and on the influence of each parameter on its evaluation.

The heritage of existing road infrastructures and in particular of bridges consists of structures that are approaching or exceeding their designed service life. Detrimental causes such as aging, fatigue and deterioration processes other than variation in loading conditions introduce uncertainties that make structural assessment a challenging task. Experimental data on their performances are crucial for a proper calibration of numerical models able to predict their behavior and life-cycle structural performance. In this scenario, an experimental research program was established with the aim of investigating a set of 50-year-old prestressed concrete bridge girders that were recovered from a decommissioned bridge. The activities included initial non-destructive tests, and then full-scale load tests followed by a destructive test on the material samples. This paper reports the experimental results of the full-scale tests conducted on the first group of four I-beams assumed to be in good condition from visual inspection at the time of testing. Loading tests were performed using a specifically designed steel reaction frame and a test setup equipment, as detailed in the present work. Due to the structural response of this first group of girders, a uniform behavior was found at both service and ultimate conditions. The failure mechanism was characterized by the crushing of the cast-in-situ top slab corresponding to a limited deflection, highlighting a non-ductile behavior. The outcomes of the experimental research are expected to provide new data for the life-cycle safety assessment of existing bridges through an extended database of validated experimental tests and models.