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Long-term structural performance of pre-stressed concrete bridges: A risk-based monitoring informed framework for life-cycle asset management

Periodic Reporting for period 1 - LoStPReCon (Long-term structural performance of pre-stressed concrete bridges: A risk-based monitoring informed framework for life-cycle asset management)

Reporting period: 2015-11-01 to 2017-10-31

• What is the problem/issue being addressed?
A recent re-assessment of the collapse in 1996 of the Koror-Babeldaob Bridge, a pre-stressed concrete bridge built by the cantilever method, concluded that this was due to excessive deflections linked to creep and shrinkage that appeared and grew non-linearly some years after construction. Similar trends have been found for a group of 56 similar bridge spans, raising the question whether such concerns could influence the maintenance and service life of a high number of pre-stressed bridges in Europe and beyond with important socio-economic impact.

• Why is it important for society?
Long-span bridges are key elements in the European transportation networks underpinning mobility of citizens and goods. In this respect, bridge safety and durability are essential attributes of a well-functioning infrastructure, attracting significant investment from national budgets. Improving our understanding on how bridges behave under increasing loads and possible deterioration will help in spending the maintenance funds effectively, minimising owner and user costs and reducing risks to people.

• What are the overall objectives?
Although individual material and structural factors have been researched, this problem can only be solved by integrating physical and probabilistic models and benefiting from the increasing use of monitoring data. In this context, the five objectives of the LostPreCon project were set as follows:

– Objective 1: Review existing models for shrinkage and creep at specimen level.
– Objective 2: Establish robust hybrid FE models for medium/long-term performance predictions.
– Objective 3: Develop a novel monitoring approach based on Digital Image Correlation (DIC).
– Objective 4: Formulate a time-dependent reliability assessment framework, addressing creep and shrinkage uncertainties.
– Objective 5: Produce representative performance-time profiles for pre-stressed bridges based on the proposed framework and models.
In accordance with these objectives, work led to the following tangible deliverables, including journal publications currently under review:

– Objective 1: A state-of-the-art review covering nine creep and shrinkage models available in the literature and highlighting the four models that best suit the main problem under analysis,
– Objective 2: Discussion and quantification of issues in relation to geometry modelling at the structural level by taking into account the specificities of creep and shrinkage phenomena,
– Objective 3: A better understanding on how to use and extract relevant information from available monitoring data to be incorporated into the time-dependent reliability assessment framework,
– Objective 4: Formulation of a time-dependent reliability assessment framework that can integrate prior knowledge and engineering judgement with field data obtained through inspection and structural health monitoring methods
– Objective 5: Application and utilisation of monitoring data in the context of asset management by an industrial stakeholder, building on the work undertaken in earlier tasks, and demonstration of the potential benefits from structural health monitoring in predicting creep deformations.

These results have been highly disseminated by means of a set of common and innovative channels of communication such as: international conferences and journal papers; COST Action TU1402 through leadership of the Innovation Committee, webinars available in YouTube, lectures and seminars to students on MSc courses and the general public by means of the official website:

Aiming at the highest possible impact, the Fellow actively engaged with several stakeholders, from both academia and industry, in order to promulgate the work. The most direct and immediate payback from the outreach activities that were conducted is a five-year industry-based project that the Fellow has agreed with one of the major highway agencies in Europe in which the objective is to embed the developed framework into the current protocols of asset management and to create a new paradigm for the use of structural health monitoring data in asset management.
The major innovative steps that have been achieved are highlighted by the following, the majority presented in publications resulting from the project work:

– Increase in creep/shrinkage model applicability to include special concrete mixes.
– Identification of and quantification of geometric features of the bridge affecting long-term deflections due to creep and shrinkage phenomena.
– Assessment and quantification of the effect of heterogeneities within the structure towards the reduction of deflections in cantilever structures.
– Identification and formulation of monitoring-based Performance Indicators devoted to the long-term performance of pre-stressed bridges.
– Quantification of the minimum frequency sampling rate, with meaningless loss of accuracy, towards manageable monitoring databases.
– Set up of the Value of Information (VoI) analysis flow chart for the case study of the Lezíria Bridge.
– Set up and demonstration of a Bayesian framework applied to creep deformations at the specimen level in a real case study through performance-time profiles at specimen level.
– Method for quantification of monitoring requirements at specimen level.

The work is being highly appreciated in the COST Action TU1402, where the Fellow, as the leader of the Innovation Committee, is promoting the awareness of legal authorities, such as bridge owners/concessionaires, to the utility of the developed framework in the context of asset management. Under the Fellow’s leadership, an event called Industry Innovation Days is currently being planned with peers, which will result in the compilation of an official technical recommendation that gathers the most relevant outcomes from a set of case studies across Europe. Ultimately, this document is intended to be useful to authorities across Europe, responsible for the management of Civil Engineering structures, including the Portuguese highways authority Brisa who are responsible for the case study investigated in this Fellowship, namely the Lezíria Bridge.

In this context, further work is in progress, mainly regarding the application of the developed framework at the structural level, not only based on the case study of the Lezíria Bridge, but also taking some inputs from other case studies that the Fellow has been involved with through successful networking activities.

For those with interest to follow-up further developments on this topic, the Fellow invites all to keep an eye in the official website of the Fellowship project –
Official image/logo of the project