With increasing traffic volumes on Malmbanan (the Ore Line) between the ore fields in Northern Sweden and the harbors in Luleå and Narvik, there is a need to raise the axle load allowed on the track, This, in turn, necessitates the analysis and if needed, enhancement of the capacity of the railway bridges.

To facilitate this, fatigue tests are being conducted on a full-scale model of a reinforced concrete trough bridge. Calculations of the load effects from dead weight and axle loads are performed using the Eurocodes and the fib Model Codes (2010 and 2020).

The results indicate that the axle load on the Ore line can be increased to 35 tons without the risk of bending or shear fatigue failure in the trough bridges. However, the fatigue capacity varies considerably, both between different bridges and across different codes, so continued Structural Health Monitoring is recommended.

A carefully studied evaluation was necessary to replace an existing pre-stressed concrete box girder bridge that had been in service for over 60 years, in Kalix, Northern Sweden. The bridge was 283.6 m long divided into five spans, and it was constructed using the balanced cantilever method. The decision to replace the old bridge created the need to evaluate a demolition procedure for it, one carefully designed not only to avoid damaging the newly built bridge or creating stability-related issues, but also to prevent any debris from falling into the Kalix River, which is part of a Natura 2000 protected area. This article focuses on the comprehensive methodology, on the demolition design, and on the observations related to residual prestress levels in the bridge, indirectly obtained through a reversed-engineering FEM process and on the limitations of the demolition technology to be used in these specific cases. Several variables were monitored during the deconstruction process, to control the structural stability better during all the phases of the project. The main outcome of the full condition assessment is that it provides the information needed to make informed decisions for interventions on these types of structures.

In recent decades, assessing the performance of existing structures has become increasingly crucial, especially as many post-war structures approach the end of their design lifespan. Among these, prestressed concrete bridges are particularly concerning because they are inherently vulnerable to deterioration caused by time-dependent prestress losses. Recent inspections of prestressed concrete bridges with internally grouted tendons have uncovered hidden defects beneath a seemingly intact and robust exterior, raising concerns about their structural integrity. Notable bridge collapses, including the Koror–Babeldaob Bridge (1996), Nanfang’ao Bridge (2019), the Polcevera Viaduct (Morandi bridge, 2018) and Carola Bridge (2024) highlight the critical need for accurately assessing the structural condition of aging bridges. These cases underscore vulnerabilities in prestressing systems and underline key gaps in understanding degradation mechanisms, long-term performance, and failure factors in prestressed concrete structures. Conventional investigation techniques and visual inspections often fail to capture the true condition of these structures, necessitating specialized evaluation methods. As a result, there is a pressing need for reliable, user-friendly, and nondestructive techniques to assess their structural performance throughout their life cycle. Such assessments play a vital role in early diagnostics, helping to prevent cracking and deflections that could jeopardize a bridge’s structural integrity and safety. A major challenge in evaluating the structural performance of existing prestressed concrete bridges is assessing the time-dependent loss of prestress. This loss serves as both an indicator and a warning sign of potential structural deterioration. However, accurately measuring prestress loss is difficult due to uncertainties in material properties, environmental conditions, and long-term degradation processes. Simplified code-conforming models fail to account for the combined effects of environmental wear and fatigue, leading to discrepancies between measured and predicted prestress losses.

This study examines various testing methods for estimating residual prestress, highlighting their features and experimental approaches through a case study of the Kalix Bridge, a 66-year-old prestressed box-girder bridge in northern Sweden. This bridge posed unique challenges due to the complexity of its prestress system, the non-homogenous concrete curing process induced by due to multiple construction stages and the long-term deformations at the pendulum joint associated with creep. A numerical model was developed and calibrated using proof-loading test data and material characterization from extracted concrete cores. This updated model was later used to calculate residual prestress, which was then compared with predictions from standard formulations. Advanced probabilistic methods, including Bayesian updating and time-dependent reliability analysis, were also employed to refine residual prestress estimations and improve longterm reliability assessments. These methods allowed for the probabilistic analysis of uncertainties in estimating the service life of bridges, particularly when updating prestress levels retrieved through testing. By incorporating uncertainties related to material properties, environmental conditions, and degradation processes, these approaches enhance the accuracy of predictions about how long a bridge can remain serviceable after prestress updates. This refined approach provided valuable insights for optimizing maintenance strategies and ensuring extended service life and durability of prestressed concrete structures.

This paper presents a time-dependent reliability assessment that integrates experimental data with Bayesian updates and is applied to a 66-year-old prestressed concrete box-girder bridge. Non-destructive and destructive tests were performed to evaluate its actual serviceability condition. The tests included on-site prestress measurements, material evaluations, a serviceability-proof load test, and refining structural response and boundary conditions using monitoring system data. These tests offered crucial updates to assumptions based on the as-built drawings. The bridge’s structural reliability for serviceability is studied by comparing two approaches: (1) a prior reliability analysis based on traditional Eurocode methods to estimate prestress losses; and (2) a posterior reliability analysis incorporating on-site measurement for residual prestress and material properties. A Bayesian update was performed to refine the estimates of concrete strength and prestress losses and improve the accuracy of the reliability assessment. The results showed that updating material properties doubled the reliability index relative to the initial analysis. Similarly, updating residual prestress measurements via strand cutting and saw cut methods increased the reliability index from 1.75 to 2.84 and 2.35, respectively. These findings highlight the need for on-site prestress measurements and time-dependent reliability analyses to accurately assess the serviceability performance of ageing bridges accounting for long-term degradation.

The direct socio-economic consequences of the deterioration of aging infrastructure systems have triggered a continuous process of revising and updating current design standards and guidelines for critical network components. Specifically, long-term degradation processes demand the analysis and evaluation of vital structural assets such as prestressed concrete bridges. It is crucial to develop theoretically consistent, user-friendly, and non-destructive methodologies that engineering professionals can employ to prevent and mitigate potential catastrophic outcomes during the service life of these bridges. This study provides a thorough review of the available testing methods employed over the years for prestressed concrete bridges and introduces a comprehensive framework for evaluating existing methods for residual prestress force assessment. Through a multi-criteria selection process, the three most feasible tests were designed and carried out on an existing 66-year-old balanced cantilever box girder bridge exposed to freezing temperatures that affected the instrumentation plan and test execution. Finally, predictive models compliant with standard codes were calibrated based on the experimental results and the life cycle loss of prestress forces was evaluated to assess relevant bounding intervals. Findings reveal limited on-site testing and discrepancies between calculated residual forces and predictions by standard codes. The saw cut method showed a 18% difference from the initial applied prestress according to the prestress protocol, suggesting the use of a cover meter and concrete modulus evaluation for improved accuracy. The strand cutting method resulted in a 14% difference, emphasizing the need for stress redistribution assessment. The second-order deflection method showed a 6% difference, indicating a focus on enhanced boundary conditions and thorough sensitivity analysis for future investigations.

The transport infrastructure consists of roads, bridges, and tunnel networks. Among these, bridges, viaducts, and tunnels are particularly vulnerable due to structural degrad-ation caused by environmental conditions, overloading, and other factors. Ensuring the safety of these assets, especially at the network level, is a significant challenge. The emergence of Bridge Management Systems (BMS) addresses the need for comprehensive information in managing inspections, condition assessments, and optimizing investments in bridge maintenance. Despite the benefits, many countries face challenges in identifying high-risk bridges. Issues include the lack of high-quality data, mixed ownership of assets, diverse management system platforms, varying condition rating schemes, and the absence of a risk-based assessment. This review aims to highlight current practices and research efforts in evaluating bridge condition indices/ratings (BCI) for existing bridges. The identified knowledge gaps emphasize the need for national authorities to develop policies leading to a unified and functional approach for condition rating.

Examples are given of time dependent prestress losses in prestressed concretestructures caused by friction, creep, shrinkage and relaxation. The total losses varywith time and is often between 10 to 25 % after 50 years. The variation of resultsbetween different assessment and monitoring methods is considerable and more workis needed.

Over the last decades, economic growth and sustained development have enforced the need to ensure reliable and long-lasting infrastructure network to guarantee serviceability and safety. Nevertheless, detrimental effects can lead over time to insufficient structural performance under increasing service loadings and extreme events. Hence, Structural Health Monitoring (SHM) arises as a solution to cope with the need of having timely and continuous data to assess the state of crucial structural assets, such as prestressed concrete bridges. On this matter, the validation of the retrieved data becomes essential for the risk-based decision making in the assessment of bridges, where selecting the most suitable monitoring system could allow to addressed main causes to the right phenomena of deterioration during the service life of the bridge. Consistently with these efforts, this paper deals with a comparative study between the data acquired by different strain-based sensors such as Fiber optic systems (FOS) and strain gauges that were installed to monitor a proof loading test developed on a 65-year-old balanced cantilever prestressed concrete bridge located in Northern Sweden. The monitored data led to establish main differences between emerging types of monitoring systems such as FOS to the well-based strain gauges when exposed to low temperature conditions. Conclusions regarding the influencing parameters between both retrieved data are drawn when evaluating the structural response under serviceability loading conditions is performed, supporting decision makers when different levels of structural assessment are required.

The backbone of European infrastructure was built after the end of the second World War and has reached, or is near to, the end of its nominal design life. This issue urges the development of structural assessment procedures that can provide infrastructure managers the information to make decisions for repairing, upgrading, or replacement. In this paper, a methodology based on load testing and Structural Health Monitoring (SHM) for the assessment of a 65- year-old prestressed concrete bridge located in Northern Sweden is presented. The retrieved data is used to develop and calibrate structural models with different levels of data completeness. The SHM procedure includes the evaluation of material properties by diagnostics, definition of the layout and installation of the instrumentation, test execution, and data analysis. A preliminary structural model is developed based only on the original design parameters, and it is sequentially updated with monitoring data retrieved during a performed proof loading test of the bridge.

The reduction of the structural capacity and eventual collapse of existing concrete bridges is often related to the loss of the initial prestressing forces. This loss can be associated to immediate or time dependent factors such as elastic shortening, creep, relaxation, loading, and cracking, among others. In addition, environmental factors can lead to corrosion of the strands with the subsequent reduction of their area, loss of bond with the concrete and additional cracking which in turn will influence the value of the residual prestress force and the bridge capacity. Therefore, the evaluation of such losses is critical in the decision-making process of defining a financial and environmental cost optimized intervention strategies (e.g., strengthening or replacement). In this paper, a detailed literature review regarding destructive and non-destructive methods for measuring the residual force in prestressed concrete bridges is carried out and used to develop a database of existing experimental tests.