Project spotlight: Exploring the trilemma of integral bridges

The PLEXUS research project explored the benefits of integral bridges and how they might provide other services.
Project spotlight: Exploring the trilemma of integral bridges
UKCRIC Communications, Marketing and Events Manager (UCL)

All physical infrastructure systems rely upon ground support in some way. Despite this, soil-structure interaction generally, and dynamic and seismic loads particularly, are inadequately understood. Separate codes of practice cover structural and geotechnical sub-systems, with interaction effects crudely represented and often neglectful of subtle, sometimes counterintuitive, systemic responses, especially for extreme loads. Frequently though, holistic soil-structure interaction (SSI) studies are perceived as prohibitively costly.

Advances in infrastructure must also consider their impact on climate change and provide low carbon solutions. Heating and cooling represents approximately 50% of energy consumption in Europe and North America. Thus, for the UK to make a meaningful contribution to reductions in carbon emissions it is essential to deliver renewable and low- or zero-carbon heat. Ground heat exchange and storage offers such low-carbon opportunities but uptake is low, restricted by high capital costs and adverse electricity and gas price ratios making payback times prohibitive for investors. A novel way to achieve affordable ground heat exchange is to use existing or to-be-constructed infrastructure; and in serving a dual purpose, this reduces capital costs and makes the idea feasible.

Completing the trilemma, despite concrete being one of the most used building materials in the world, how different cement mixes behave over time and in extreme loading and blast conditions isn’t well understood. The pervasiveness of concrete also means that its potential to make a positive contribution to reducing the construction industry’s carbon footprint is huge, but technical unknowns are preventing the adoption of low-carbon concrete. The Priming Laboratory Experiments on Infrastructure and Urban Systems project – or PLEXUS – explored the benefits of integral bridges by tackling three important technical challenges: intense physical interdependency of urban infrastructure systems, harvesting energy from buried infrastructure systems and accelerated deterioration of infrastructure materials due to extreme loading.

The diversity of SSI problems, from buried pipes, through soil-retaining structures, deep excavations, piled foundations, highway & railway foundations and offshore structures, to the seismic response of whole urban areas, dictates a generic, systemic and tailorable approach. Many of the crucial epistemic uncertainties are associated with the lack of knowledge of how real infrastructure behaves; uncertainties that conventional laboratory scale modelling cannot address.

One of the principal motivations of the UKCRIC facilities is to enable investigation of prototype, or near-to-prototype, scale infrastructure behaviour. UKCRIC laboratories of Birmingham, Southampton and Bristol represent a unique, integrated research infrastructure and environment in which these crucial epistemic uncertainties can be explored to devise a new, holistic and systemic SSI framework.

PLEXUS’s research into the three technical challenges: the design and performance of integral bridges (universities of Birmingham, Southampton, Bristol and Cambridge), energy harvesting from buried infrastructure systems (Universities of Leeds, Sheffield, Newcastle, Cambridge and Cranfield) and the properties of aged (hence carbonated) concrete manufactured using different types of cement and when subjected to blast and fire loading (Universities of Leeds, Imperial and anchester), can be combined in a proposition for more sustainable and resilient, and more economic, holistic integral bridge systems. Through its research, PLEXUS demonstrated that the widespread adoption of integral bridges has huge potential for reducing bridge construction and maintenance costs, and for improving their long-term resilience. Following UKCRIC’s first call for research projects in 2021 ‘PLEXUS PLUS’ was awarded funding to further understanding of the seasonal bridge-abutment interaction through the combined application of large-scale testing, state-of-the-art modelling and in-soil monitoring.

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Image credit: Eduardo Goody via Unsplash