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Flood Risk Assessment and mitigation for Masonry Arch Bridges

Periodic Reporting for period 1 - FRAMAB (Flood Risk Assessment and mitigation for Masonry Arch Bridges)

Reporting period: 2015-10-01 to 2017-09-30

Masonry arch bridges constitute a significant proportion of existing bridges in Europe. Many of these structures are built on rivers or channels and thus are exposed to the flooding. Although masonry arch bridges are very vulnerable to flood effects, no accurate procedures have been proposed thus far to systematically assess the risk of their damage and failure due to flood hazard. Given the large number of masonry-arch bridges and their socio-economic and cultural heritage value, the accurate prediction of their capacity against floods is a task of paramount importance, requiring further research and the development of appropriate analysis tools.
The FRAMAB project aims at defining a flood risk assessment framework for masonry arch bridges combining a realistic description of the hazard (probability of exceeding a given flood discharge) with an accurate assessment of the structural vulnerability (probability of exceeding a given damage level in the bridge components for a flood with a given intensity). The development of such a risk assessment framework entails i) the advancement of computational tools for the response prediction of masonry bridges subjected to flood-induced actions and ii) the accurate propagation of uncertainties inherent in the loading, the problem parameters and the simulation models. The project outcomes contribute to the preservation of cultural heritage and can support decision makers in mitigating the flood risk of infrastructural systems and prioritising retrofit interventions.
To achieve the project objectives, the following actions have been taken:
- A review of the effects of floods on masonry arch bridges has been carried out to identify the most critical actions induced by floods on bridges (scour, impact of floating masses, buoyancy) and the relevant failure modes and damage mechanisms (e.g. pier cracking, arch barrel cracking, damage of spandrel walls). The information and data collected, mainly based on news reporting damages or collapses of bridges during recent floods, have shown that scour is the most common cause of failure.
- An evaluation of state-of-the-art in modelling masonry arch bridges, including a critical assessment of the tools already developed at the Computational Structural Mechanics (CSM) group at Imperial College, has been performed, and the parts of the modelling strategy requiring further development have been identified.
- A modelling strategy has been defined for simulating the effects of scour and of other flood-induced actions, by accounting for the complex geometry of multi-span arch bridge models and the interaction between the various components (arch, backfill, foundation, soil). The proposed strategy employs the nonlinear structural analysis code ADAPTIC, developed in the CSM group at Imperial College. The adopted mesoscale masonry model implemented in ADAPTIC enables an accurate representation of the actual masonry bond for the masonry arch barrel and the piers. Moreover, this detailed 3D description for masonry components is incorporated within a partitioning modelling strategy enabling parallel computation, which significantly enhances computational efficiency when used in combination with the high performance computing resources available at Imperial College.
- A validation study of the proposed modelling strategy has been carried out by simulating experimental tests carried out on single-span and multi-span arch bridges under vertical loads and under scour-induced settlements.
- A probabilistic framework for flood risk assessment analysis, with particular focus on the scour accumulation problem, has been developed, also based on the continuous collaboration with the partner of the secondment, Prof. Costantino Manes, and visits to University of Southampton University and Polytechnic University of Turin.
- The study results have been published/submitted for publication in journals and presented at various international conferences and seminars. The outcomes and capabilities of the proposed modelling strategy have been presented also to engineering firms and agencies involved in the flood risk assessment of bridges in the UK. The participation to the Imperial College festival in 2018 is envisaged as an additional outreach activity.
The modelling strategy proposed within the FRAMAB project advances significantly the current state-of-the-art tools for the evaluation of the behaviour of masonry arch bridges under flood effects. In fact, existing numerical models have seldom considered the three-dimensional (3D) nature of the behaviour of masonry arch bridges and the influence of the masonry bond on the response of the arches and piers. Moreover, the presence of the substructures with their foundations and their interaction with the soil has yet to be fully explored. Finally, no modelling strategy has been proposed thus far for describing the vulnerability of masonry arch bridges to scour effects.
The flood risk assessment framework developed within the FRAMAB project constitutes also an important advancement towards an accurate evaluation of the risk of masonry arch bridges. It offers a common platform for hydrologist, hydraulic engineers, structural engineers, and transport engineers to share and combine the results of their studies and communicate efficiently the flood risk of a masonry arch bridge to stakeholders and decision makers.
The developed tools provide an important contribution to (1) the preservation of cultural heritage for the vitality of the living engagements within and across European cultures, (2) the development of innovative technologies and solutions to reduce the perception of insecurity from natural disasters, and (3) the achievement of a resource efficient economy and society. The output of the proposed risk assessment procedure can support decision making in flood risk management of bridges. More generally, the flood-risk assessment and mitigation for structures responds to the safety and socio-economic needs of many nations, and it is a topic within the Societal Challenges of Horizon 2020 and the objectives of the European Programme for Critical Infrastructure Protection.
Cracking pattern in the model of Copley Bridge subjected to scour
Damage patter observed in the simulations of the bridge tested at Polytechnic University of Turin
Illustration of the flood risk assessment framework
Some results concerning the validation of the proposed modelling strategy