CBDG 26th Annual Conference

Resilient concrete bridges - The importance of a whole life strategy

Institution of Structural Engineers, London, EC1V 3PS

Held on Wednesday 28th June 2023


Concrete bridges are inherently resilient. Their design working life, an "assumed period for which a structure or part of it is to be used for its intended purpose with anticipated maintenance but without major repair being necessary", is key to sustainability. But will changes in materials, design and construction practice driven by the clamour for decarbonisation unintentionally compromise resilience?

The CBDG's 26th Annual conference will discuss whole life strategies in relation to sustainability and the drive for decarbonation whilst maintaining the inherent resilience of concrete bridges.


Click here past conferences for videos and pdf's of the presentations.

Welcome by CBDG Chairman
Santosh Singh
Opening address: 
National Highways manages a portfolio of 23,000 structures, which includes 8,800 bridges and large culverts. About 60% of the bridges were built pre-1980, and 94% are concrete or composite construction. With over four million journeys taking place daily on our strategic network, the bridges play a vital role in people's lives and in building a stronger and more productive economy. Enhancing, maintaining, and operating the bridges safely, reliably, and efficiently requires us making good consistent decisions throughout their lifecycles. Some of the key challenges we face include, assets value optimisation, asset-lifecycle planning, optimising interventions, delivering low carbon infrastructure, and driving innovation and initiatives such as use of AI, modular construction, and digitisation within the bridges sector. Our ambition for the services delivered to our customers is to have no unplanned closures on highways structures, by undertaking the right intervention at the right time.
The environmental and social impact of bridges and viaducts is undeniable. In this presentation the structural efficiency for various parts of a viaduct structure is outlined based on collected data from current projects. The results of a parametric study showing how varying the sectional form, reinforcement design criteria and post-tensioning arrangement affect the efficiency are presented. The impact of these inputs on the carbon emissions are investigated and benchmarked against published data. The role of CAT.3 Checker in contributing to optimised whole-life solutions without sacrificing safety/robustness will be discussed.
Sustainability is at the heart of asset management. Having a decision support tool that quantifies whole life cost over the design life of a structure can ensure that robust decisions are being made in the early stages of a project. This presentation will cover the approach that Atkins took in developing the Unit Rate Calculator in conjunction with HS2, which allows multiple design options to be compared on a like-for-like basis in order to demonstrate best value over 120 years. By applying up to 300 deterioration curves to an indicative design, a comprehensive whole life cost analysis can be obtained which takes into account construction cost, maintenance, and renewal and O&M costs.
The presentation will show on how preliminary design choices influence the embodied carbon of both bridges and wingwalls. Firstly Jimmy Barratt-Thorne will present on work as part of his dissertation form the University of Cambridge, using a case study of a single span integral bridge to compare how differing substructure choices from PD 6694 influence the embodied carbon, and under what conditions provide an optimal solution. For example how does undertaking ground improvement, thereby removing the need for piled foundations, change the embodied carbon? Secondly, Nick Fenwick will present on a study looking in to wingwall efficiency, and how the embodied carbon differs depending on the orientation of the wingwall with respect to the bridge, as well as how different materials such as reinforced soils can contribute to carbon efficiency. Both speakers will demonstrate how large carbon savings can be readily made through simple design choices.
The passage of time, site specific deterioration, maintenance and past repairs, imbedded complexity of capacity functions introduce a high level of uncertainty for existing reinforced concrete bridges. Due to the strategic importance of bridges such uncertainties need to be accounted for in assessment and decisions about the residual life. Thus, there would be great value in systematic and practical models for evaluation of remaining capacity and likelihood of failure for ageing infrastructure that take into account the uncertainties but also increasing availability of site specific data. The presentation will review advanced models for infrastructure ageing process characterization and will also demonstrate the application of continuous gamma process to characterise remaining capacity of an existing reinforced concrete bridge while taking into account various monitoring sources and imbedded uncertainties. Such an approach could result in a notional estimate of future performance including the potential to account for the effects of climate projections, thus providing a beneficial planning tool.
Brent Cross Interchange northwest London, forms part of one of the most heavily congested sections of highway network in Europe. The Interchange includes a 190m, 10-span flyover supporting the A41 over a mid-level elevated roundabout complex. Built in a period of rapid development of design theory and construction techniques for structural concrete, it includes some unusual features. The articulation of the flyover and elevated roundabout incorporates double pinned and sometimes highly slender columns with Mesnager-type hinges. Additionally, the structures were built with minimum structural reinforcement and distribution steel. This talk will focus on the assessment Arcadis undertook in 2022. The experimental nature of the design necessitated a first principles approach to some of the analysis, providing opportunities for development of assessment standards. The approach taken has enabled reserves of strength to be identified, providing a sustainable outcome for the management of these assets.
The 27km long Sultan Haji Omar Ali Saifuddien Bridge in Brunei (known as Temburong Bridge) is the longest bridge in Southeast Asia. One of the main components is the 12km long viaduct across the peat swamp forest in Temburong. The swamp forest has unique and endangered flora and fauna. The soil conditions consist of soft peat overlying soft marine clay with depths exceeding 70m. With tight programme and limited access for construction, the design maximises the use of precast concrete elements and repetition, enabling erection by normal crawler cranes in a three-day cycle per span. The construction was done from deck level (top-down), without ground level temporary road and minimised environmental impact. The presentation will describe the design development, the construction, the lessons learnt and reflections on what could be done differently now with the clamour for decarbonisation.
Network Rail commissioned the testing of four no. post-tensioned beams that were extracted from the demolished Granby Terrace Bridge. This presented a unique opportunity to carry out a variety of tests on post-tensioned bridge beams that were in service for nearly 60 years. The tests included non-destructive testing, large scale structural testing and forensic demolition. Ramboll has been commissioned to interpret the test results and compare the factual findings with theoretical assessment results. The aim of the investigation is to support the development of NR standards for the management of post-tensioned structures. The presentation will cover a brief description and history of the demolished bridge, a review of the test programme and findings, the interpretation of the test results considering current asset management practices and comparison with theoretical assessment results.
The N22 Macroom bypass in County Cork is a project which has pushed the boundaries of engineering. It has proven that prestressed concrete bridges can be a viable long-span alternative to steel and that projects can reap the benefits of prestressed concrete beams manufactured offsite – increased sustainability and durability, improved site safety, reduced onsite programmes and the elimination of maintenance. The presentation will take you on the design journey of the Laney River Bridge record-breaking concrete beams along with details on how Eurocode 2 achieved a saving of 100 tonnes on the scheme. This significant project came to fruition in December 2020 with the safe installation of 7 Banagher W19 beams, each measuring an impressive 50 metres long, 2.5 metres high and weighing 155 tonnes. Intense collaboration was required along with precision engineering, manufacturing and logistical planning to ensure the success of this record-breaking structure.
The recent drive towards net zero and low carbon materials has intensified interest in exploring natural and sustainable materials as internal reinforcement for concrete, such as basalt which is not itself susceptible to corrosion unlike ordinary carbon steel. The work presented investigates the use of basalt as an alternative to steel reinforcement of concrete beams. By considering concrete beams with a given loading demand, the performance of steel and basalt reinforced concrete (BRC) is evaluated in terms of SLS (crack width and deflections), ULS (moment and shear resistance), embodied carbon emissions and initial cost. The outputs are compared for the two materials and the results show that the BRC beam generally matches the performance of the steel reinforced concrete beam in terms of ULS and SLS performance for embodied carbon, but the initial cost of manufacturing a BRC beam is high compared to a traditional concrete beam. However, the cost of using basalt is lower than stainless steel for applications where corrosion resistance is a key issue, as is the whole life carbon footprint.