Futuristic bridge inspection with advanced technology.

Bridge Over Troubled Waters: Can We Trust Our Aging Infrastructure?

Soraya Malik in Tech & Innovation September 2025 • 4 min read.

"Innovative assessment models offer new hope for evaluating the safety of existing concrete bridges."

For decades, the assessment of existing concrete bridges has been a critical task for civil engineers. These structures, vital to transportation and commerce, require continuous evaluation to ensure their safety and longevity. However, significant changes in industry standards have complicated this process, often making it difficult to verify the structural integrity of older bridges using current regulations.

In response to these challenges, the Technical University (TU) of Wien has developed a novel assessment model designed to more accurately reflect the actual load-bearing behavior of these bridges. This innovative approach promises a more realistic evaluation of structural capacity, potentially reducing the need for costly and disruptive reinforcement measures or even complete bridge replacements.

Initially applied to single-span bridges, this model is now being tested on multi-span prestressed concrete bridges. Eight experiments were conducted at the interior supports of these bridges to validate the model’s assumptions. The experimental setup and specimens were designed to mimic real-world conditions, specifically the stress configurations of post-tensioned bridges at a 1:2 scale. This research marks the first systematic investigation into the influence of factors such as prestressing levels, cross-sectional shapes, shear reinforcement, and shear slenderness under realistic conditions.

Why Current Shear Resistance Assessments Fall Short?

Futuristic bridge inspection with advanced technology.

Modern building codes are intended to reflect the latest advancements in knowledge and technology while also meeting the demands of future generations. However, major revisions to these codes can inadvertently render existing structures non-compliant, posing a significant challenge for civil engineers. This is particularly critical for infrastructure, where the high costs of replacement necessitate accurate and reliable assessment methods.

The introduction of the Eurocode series [1-3] for European construction standards has highlighted this dilemma in assessing the load-bearing capacity of prestressed concrete bridges. To address this issue, Germany [4] and Austria [5] have implemented recalculation guidelines for bridges, allowing engineers to deviate from current norms during structural evaluations. Yet, even with these guidelines, verifying shear force resistance often remains problematic [6-8], potentially leading to expensive reinforcement projects or even the need for new construction.

Many bridges built in the 1960s and 1970s have proven their functionality through years of safe operation, indicating a clear need for more precise assessment models.
Current methods often underestimate the actual load-bearing capacity of these structures, leading to unnecessary interventions.
The economic implications of inaccurate assessments are substantial, given the high replacement costs of bridge infrastructure.

In response to these shortcomings, a new assessment concept was developed at TU Wien as part of the “Traffic Infrastructure Research” initiative by the Austrian Research Promotion Agency (FFG). This concept aims to realistically represent shear force behavior [9, 10] and comprises various shear force models, including the FSC model (flexural-shear crack), ST model (shear-tension), and principal tensile stress verification. The assessment concept is already being used in engineering practice to evaluate shear force capacity at the end supports of prestressed concrete bridges [11]. Unlike current standards [1, 12], this new approach recognizes the significant contribution of concrete to shear force transfer, aligning with other newly developed approaches [13-15].

The Future of Bridge Assessment

The development and validation of innovative models like the FSC model represent a significant step forward in ensuring the safety and longevity of our existing bridge infrastructure. By providing a more accurate assessment of shear resistance, these models can help engineers make informed decisions about maintenance, reinforcement, and replacement, ultimately safeguarding our transportation networks and minimizing economic impact.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

What are the key challenges in assessing the safety of aging concrete bridges, and how do these challenges impact infrastructure management?

Assessing the safety of aging concrete bridges is challenging due to several factors. Firstly, changes in industry standards and building codes, like the Eurocode series, can render older bridges non-compliant, even if they have proven their functionality over decades. Secondly, current assessment methods often underestimate the actual load-bearing capacity of these structures, leading to unnecessary and costly interventions. The economic implications are substantial, considering the high replacement costs of bridge infrastructure. These challenges necessitate accurate and reliable assessment methods. The introduction of the Eurocode series for European construction standards has highlighted this dilemma. Germany and Austria have implemented recalculation guidelines for bridges, allowing engineers to deviate from current norms during structural evaluations. Even with these guidelines, verifying shear force resistance often remains problematic, potentially leading to expensive reinforcement projects or even the need for new construction.

How does the new assessment model developed at TU Wien improve the evaluation of concrete bridge safety compared to existing methods?

The innovative assessment model developed at the Technical University (TU) of Wien aims to more accurately reflect the actual load-bearing behavior of concrete bridges. Unlike current methods, which often underestimate the load-bearing capacity, the TU Wien model provides a more realistic evaluation of structural capacity. This improved accuracy is crucial because it potentially reduces the need for expensive and disruptive reinforcement measures or even complete bridge replacements. The model's development is part of the “Traffic Infrastructure Research” initiative by the Austrian Research Promotion Agency (FFG). It comprises various shear force models, including the FSC model (flexural-shear crack), ST model (shear-tension), and principal tensile stress verification. The new approach recognizes the significant contribution of concrete to shear force transfer, aligning with other newly developed approaches. This contrasts with current standards that may overlook this critical factor.

What is the significance of the experiments conducted on multi-span prestressed concrete bridges to validate the new assessment model?

The experiments conducted on multi-span prestressed concrete bridges were crucial for validating the assumptions of the new assessment model developed at TU Wien. These experiments, conducted at the interior supports of the bridges, were designed to mimic real-world conditions, particularly the stress configurations of post-tensioned bridges at a 1:2 scale. This research represents the first systematic investigation into how factors such as prestressing levels, cross-sectional shapes, shear reinforcement, and shear slenderness influence the bridge's behavior under realistic conditions. The validation process ensures that the model accurately reflects the actual performance of these bridges, increasing the reliability of its assessments and its applicability in engineering practice.

Can you explain the different shear force models mentioned in the new assessment concept and how they contribute to evaluating shear force behavior?

The new assessment concept developed at TU Wien incorporates several shear force models to realistically represent shear force behavior in concrete bridges. These models include the FSC model (flexural-shear crack), the ST model (shear-tension), and principal tensile stress verification. The FSC model, for instance, likely focuses on the behavior of cracks that develop due to combined flexural and shear stresses. The ST model probably addresses the tensile stresses within the concrete caused by shear forces. Principal tensile stress verification involves checking the maximum tensile stresses within the concrete to ensure they remain within acceptable limits. By combining these different models, engineers can get a comprehensive understanding of the shear force capacity of a bridge, leading to more accurate and informed decisions regarding maintenance and reinforcement.

How do advancements like the FSC model impact the future of bridge assessment and infrastructure management?

The development and validation of innovative models like the FSC model signify a major step forward in ensuring the safety and longevity of existing bridge infrastructure. By providing a more accurate assessment of shear resistance, these models help engineers make informed decisions about maintenance, reinforcement, and replacement. This contributes significantly to safeguarding transportation networks and minimizing economic impacts. The more precise assessments reduce the likelihood of unnecessary interventions, leading to cost savings and less disruption. Moreover, as these models are integrated into engineering practice, they can help bridge owners effectively manage their infrastructure assets, prioritize repairs, and extend the lifespan of existing bridges. This overall approach to bridge assessment is crucial for the safety and economic stability of communities relying on these essential structures.