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Novel assessment of bridge retrofitting measures through Interface Efficiency Indices (InterFeis) using a Guided Wave-based monitoring method

Periodic Reporting for period 1 - BriFace (Novel assessment of bridge retrofitting measures through Interface Efficiency Indices (InterFeis) using a Guided Wave-based monitoring method)

Reporting period: 2019-06-01 to 2021-05-31

Problem issued: With approximately two million highway and railway bridges, of which almost 10% are characterised as structurally deficient and 14% as functionally obsolete, there is a huge challenge for assessing, repairing and strengthening bridges in Europe and worldwide. Indicatively, the average bridge is 43 years old and almost half a trillion trips are taken on a daily basis across structurally deficient bridges, on which world economies and travellers safety heavily rely upon Thus, ageing bridges require urgently strengthening and efficient monitoring, to avoid incidents like the very recent failure of the bridge in Italy. Notably, deck deficiencies are not necessarily the result of deterioration and strength degradation, e.g. corrosion and/or cumulative fatigue effects, but might be related to increases in traffic volumes and loads, e.g. permissible axle weights, or increases in code requirements. Hence the widening and strengthening of bridges are among the most pressing needs for enhancing mobility in EU networks, and this is the main motivation of this Fellowship for pursuing an integrated framework for the efficient and sufficient strengthening of bridges and their monitoring on the basis of long-distant inspection using guided waves (GW), examining and improving the interface response to achieve full embedment.

Importance to society: It is accepted that bridgeworks within Europe have a total value of around €50bn and a moderate 2% increase in their load capacity or life would result in savings of the order of €1bn. Notwithstanding the number of EU bridges that need retrofitting, there is a lack of integrated legislation frameworks and code provisions within the EU and worldwide, whilst the new Eurocode 8-3 is expected to cover only the seismic retrofit of bridges, yet is it not expected to provide guidance on the urgent need for the enhancement of the capacity of existing bridge decks against increased traffic loads. Also, in engineering and monetary terms, there is an urgent need for efficient asset management and plan a strategy based on performance, monitoring and resilient data.

Objectives
Obj. 1 To define the Interface Efficiency Indices (InterFeis). The indices will be correlated to the stiffness of the
strengthened structural element and the properties of the interface using spectral elements. These InterFeis will be defined for the most critical bridge decks with deficiencies, for a reasonable number of representative types of decks (e.g. voided slab decks, precast beams, box girder).
Obj. 2 To utilize an expedient, long-distant inspection method of GW for the first time in bridge inspection in order to
detect, map and characterize the potential discontinuities within the interfaces. To achieve this, the spectral approach will assist in examining different zones and damages within the bridge deck, defining the range of values of InterFeis taking into consideration the bridge performance and exposure conditions.
Obj. 3 To increase the interface efficiency using novel adhesive bond layers containing nanoparticles towards the
development of advanced strengthening systems for bridges. The improved efficiency will be measured with InterFeiS, both numerically and experimentally.
Obj. 4 To use IntereFeiS as a reliable tool towards the quantification of the redundancy of the retrofitted bridge. The
crucial loss of stiffness/capacity of existing bridge decks locally in critical cross sections will be matched with IntereFeis which will be ready to use for rapid decisions of further time-efficient intervention on the bridge
The work towards implementing the project was made in the following stages:
1. state of the art,
2. design and implementation of the experimental campaign,
3. characterization of interface properties (i.e. the shear capacity after cracking, bond slip response, shear strains and failure modes.),
4. design of the strengthening FRP systems (combination of FRP type and adhesive layer),
5. proposal of a semi-empirical prediction model for the interface response, quantifying efficiency based on i) mechanical and geometrical properties of the system and ii) the failure propagation on the concrete,
6. expanded numerical simulations using finite element models and cohesion zone models to represent the interface,
7. diagnostic analysis numerically using guided waves,
8. interpreting the scattering and stress field for discontinuities and different type of epoxy adhesives,
9. development of a holistic roadmap towards resilient asset management based on monitoring data and technological tools.

exploitation and dissemination:
1. journal papers,
2. conference papers,
3. seminar presentations,
4. research proposals,
5. further development of the FRP systems in collaboration with the industrial partner,
6. further development of the holistic roadmap taken into account interoperabilities of networks.
Based on the objectives of the project and the needs of society and science, the following progress beyond the state of the art was accomplished:
1. Quantification of the interface efficiency of strengthening schemes using composites (Fiber Reinforced Polymers) based on the i) failure propagation of the substrate and ii) the mechanical characteristics of the strengthening system: FRP type and adhesive layer.
2. Use of guided waves to expediently detect discontinuities at the interfaces of adhesively bonded FRPs to concrete substrates by observing the stress and scattering field.
3. Development of Carbon FRP strengthening systems in laminated fabrics or prefabricated plates type in combination with toughened and standard epoxies depending on the retrofitting scheme and stiffness demands. The toughened epoxy adhesives enhance the interface capacity of the system by absorbing more energy due to rubber-like nanoparticles that the mixture includes.
4. Development of a novel road map for the quantification of resilience in transport assets based on monitoring data and emerging technologies.

Impact & Societal implication of the project:
the Briface projects introduces solutions and ideas that have the following impact:
1. bring a new mentality in R7D and the design of retrofitting schemes for existing concrete bridge decks and structures based on the interface response,
2. quantifies the effectiveness with simple to use semi-empirical model which can be applied straightforward by designers,
3. contribute towards expedient applications of strengthening measures and as such permit the damaged assets to recover faster,
4. helps define the effectiveness of a strengthening measure and as such work towards minimizing the quantity and cost of the integrated material,
5. introduces a cost-efficient and smart yet complicated method to detect hidden discontinuities and decide on the structural integrity of the concrete without other resources,
6. introduces a ready to use roadmap for civil protection planning based on resilience,
7. introduces the tools to make assets safer and in continuous use and adaptation despite the stressors, the increasing loads and climate change,
8. introduces the methodology to monitor the assets and permit timely decision-making on mitigation measures.
Diagnosis or overloaded areas with GW- FEM
Road map for delivering resilience
Strengthened bridge monitoring and failures
Interface capacity indices
resilience curves 2
Paths along the interface
resilience curves 1