Glowing lines visualizing shear strength in a bridge, blending new and old architecture.

Bridge Over Troubled Waters: Reassessing Shear Strength in Aging Concrete Structures

Reese Marlowe in Tech & Innovation August 2025 • 4 min read.

"New research offers innovative models to ensure the safety and longevity of existing multi-span prestressed concrete bridges with minimal reinforcement."

The world's infrastructure is aging, and with that comes the critical task of ensuring the safety and reliability of existing structures. Concrete bridges, vital arteries of transportation networks, are particularly susceptible to the ravages of time and evolving engineering standards. Significant changes in structural norms have led to situations where older, prestressed concrete bridges no longer meet the latest requirements for shear strength, creating a pressing need for innovative assessment methods.

Engineers at TU Wien (Vienna University of Technology) have stepped up to this challenge, developing a novel assessment model that promises a more accurate representation of how these bridges actually behave under stress. This new approach could save significant costs by avoiding unnecessary reinforcements or even complete reconstructions. The model challenges current standards, especially for bridges built in the mid-20th century, which have proven their functionality through decades of service.

This new research focuses on refining our understanding of shear strength in multi-span bridges—structures supported by multiple points. These bridges often feature continuous beams that handle both positive and negative bending moments, adding complexity to shear force distribution. Eight experiments have been done that are essential to validating the new model. By realistically replicating the forces at play within these bridges, the research team aims to unlock a more precise method for assessing their true strength and resilience.

The Science of Shear: A New Approach

Glowing lines visualizing shear strength in a bridge, blending new and old architecture.

The cornerstone of this research lies in a series of meticulously designed experiments that mimic the conditions within multi-span prestressed concrete bridges. The experimental setup uses scaled-down models, representing bridge sections at a 1:2 scale. These models are subjected to forces that simulate the combined bending moments and shear forces typically found at the intermediate supports of multi-span bridges. This approach allows researchers to study, in a controlled environment, how different factors influence shear capacity.

Several parameters were systematically investigated during the experiments:

Prestressing Level: The amount of initial compression applied to the concrete, affecting its resistance to cracking.
Cross-Sectional Shape: Whether the beam is T-shaped or I-shaped, influencing load distribution.
Shear Reinforcement: The quantity of steel stirrups within the concrete, providing resistance against shear forces.
Shear Slenderness: The ratio of moment to shear force, indicating how prone the beam is to shear failure.

The findings from these experiments were then evaluated using established codes such as the Austrian recalculation guidelines, Eurocode 2, and the fib Model Code 2010, as well as the new Flexural-Shear Crack (FSC) model developed at TU Wien. The FSC model is based on the idea that shear failure often initiates with flexural cracks, and that the propagation of these cracks determines the bridge's ultimate capacity. By incorporating this mechanism, the FSC model provides a more realistic assessment of shear strength. The engineers examined this potential in-depth for real-world scenarios.

A Safer Future for Our Bridges

The implications of this research are significant for the future of bridge maintenance and safety. By adopting more accurate assessment methods like the FSC model, engineers can better understand the true capacity of existing bridges, potentially avoiding costly and unnecessary interventions. This approach not only ensures the continued safety and reliability of these vital structures but also promotes sustainable infrastructure management by extending their lifespan and optimizing resource allocation. As our infrastructure continues to age, such innovations will be crucial in keeping our bridges strong and safe for generations to come.

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.

This article is based on research published under:

DOI-LINK: 10.1002/best.201800025, Alternate LINK

Title: Nachrechnung Der Querkrafttragfähigkeit Von Mehrfeldrigen Spannbetonbrücken Mit Geringer Bügelbewehrung

Subject: Building and Construction

Journal: Beton- und Stahlbetonbau

Publisher: Wiley

Authors: Tobias Huber, Patrick Huber, Michael Kleiser, Johann Kollegger

Published: 2018-08-05

Everything You Need To Know

How does the new assessment model developed at TU Wien improve the evaluation of shear strength in aging concrete bridges?

The new assessment model developed at TU Wien offers a more precise evaluation of how multi-span prestressed concrete bridges behave under stress. This model focuses on shear strength and considers factors like prestressing level, cross-sectional shape (T-shaped or I-shaped), shear reinforcement, and shear slenderness. By using this model, engineers can potentially avoid unnecessary reinforcements or reconstructions, leading to significant cost savings and sustainable infrastructure management.

What is the Flexural-Shear Crack (FSC) model, and how does it provide a more realistic assessment of shear strength compared to traditional methods?

The Flexural-Shear Crack (FSC) model, developed at TU Wien, operates on the principle that shear failure often begins with flexural cracks. The model assesses shear strength by focusing on the propagation of these cracks. By incorporating this mechanism, the FSC model aims to provide a more realistic assessment of a bridge's shear capacity than traditional methods, especially in multi-span prestressed concrete bridges. Unlike established codes such as the Austrian recalculation guidelines, Eurocode 2, and the fib Model Code 2010.

Can you describe the experimental setup used to validate the new assessment model for multi-span prestressed concrete bridges?

The research involved conducting meticulously designed experiments using scaled-down models (1:2 scale) that represented sections of multi-span prestressed concrete bridges. These models were subjected to forces that simulated bending moments and shear forces typically found at intermediate supports. During these experiments, researchers systematically varied parameters such as prestressing level, cross-sectional shape, shear reinforcement, and shear slenderness to observe their impact on shear capacity and validate the new assessment model.

What do 'prestressing level', 'shear slenderness', 'shear reinforcement', and 'cross-sectional shape' mean in the context of assessing concrete bridge shear strength?

Prestressing level refers to the amount of initial compression applied to the concrete in a bridge. This compression affects the concrete's resistance to cracking. Shear slenderness is the ratio of moment to shear force, indicating how prone the beam is to shear failure. Shear reinforcement is the quantity of steel stirrups within the concrete, providing resistance against shear forces. Cross-sectional shape refers to whether the beam is T-shaped or I-shaped, which influences how loads are distributed throughout the structure. All these parameters were systematically investigated during the experiments to evaluate the new assessment model.

What are the broader implications of using more accurate assessment methods, like the FSC model, for maintaining and ensuring the safety of aging bridges?

By adopting more accurate assessment methods like the FSC model, engineers can better determine the actual capacity of existing bridges, potentially avoiding unnecessary and costly interventions. This ensures the ongoing safety and reliability of vital infrastructure, promoting sustainable management by extending bridge lifespans and optimizing resource allocation. In the face of aging infrastructure and evolving engineering standards, this approach is crucial for preserving our bridges for future generations.