Distributed optical fiber sensors (DOFS) are modern-day cutting-edge monitoring tools that are quickly acquiring relevance in structural health monitoring engineering. Their most ambitious use is embedded inside plain or reinforced concrete (RC) structures with the scope of comprehending their inner-workings and the functioning of the concrete-reinforcement interaction. Yet, multiple studies have shown that the bonding technique with which the DOFS are bonded to the reinforcement bars has a significant role on the quality of the extracted strain data. Whilst this influence has been studied for externally bonded DOFS, it has not been done for embedded ones. The present article is set on performing such study by monitoring the strain measurement quality as sampled by DOFS bonded to multiple rebars with different techniques and adhesives. These instrumented rebars are used to produce differently sized RC ties later tested in tension. The discussion of the test outputs highlights the quasi-optimal performance of a DOFS/rebar bonding technique consisting of incising a groove in the rebar, positioning the DOFS inside it, bonding it with cyanoacrylate and later adding a protective layer of silicone. The resulting data is mostly noise-free and anomalies-free, yet still presents a newly diagnosed hitch that needs addressing in future research.

The contribution of concrete to the tensile stiffness (tension stiffening) of a reinforced concrete (RC) member is a key governing factor for structural serviceability analyses. However, among the current tension stiffening models, few consider the effect brought forth by concrete shrinkage, and none studies take account of the effect for very long-term shrinkage. The present work intends to tackle this exact issue by testing multiple RC tensile elements (with different bar diameters and reinforcement ratios) after a five-year shrinking time period. The experimental deformative and tension stiffening responses were subjected to a mathematical process of shrinkage removal aimed at assessing its effect on the former. The results showed shrinkage distinctly lowered the cracking load of the RC members and caused an apparent tension stiffening reduction. Furthermore, both of these effects were exacerbated in the members with higher reinforcement ratios. The experimental and shrinkage-free behaviors of the RC elements were finally compared to the values predicted by the CEB-fib Model Code 2010 and the Euro Code 2. Interestingly, as a consequence of the long-term shrinkage, the codes expressed a smaller relative error when compared to the shrinkage-free curves versus the experimental ones.

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A bond mechanism at the reinforcement-concrete interface is one of the key sources of the comprehensive functioning of reinforced concrete (RC) structures. In order to apprehend the bond mechanism, the study on bond stress and slip relation (henceforth referred as bond-slip) is necessary. On this subject, experimental and numerical investigations were performed on short RC tensile specimens. A double pull-out test with pre-installed electrical strain gauge sensors inside the modified embedded rebar was performed in the experimental part. Numerically, a three dimensional rib scale model was designed and finite element analysis was performed. The compatibility and reliability of the numerical model was verified by comparing its strain result with an experimentally obtained one. Afterwards, based on stress transfer approach, the bond-slip relations were calculated from the extracted strain results. The maximum disparity between experimental and numerical investigation was found as 19.5% in case of strain data and 7% for the bond-slip relation at the highest load level (110 kN). Moreover, the bond-slip curves at different load levels were compared with the bond-slip model established in CEB-fib Model Code 2010 (MC2010). Overall, in the present study, strain monitoring through the experimental tool and finite element modelling have accomplished a broader picture of the bond mechanism at the reinforcement-concrete interface through their bond-slip relationship.

The bond and slip between concrete and the reinforcement bars, cover a key role in the inter-material force transfer of Reinforced Concrete (RC) structures. In light of the lack of tools able to thoroughly inspect the inner workings of RC structures and to extract reliable bond stress values, modern bond stress–slip (Bond–slip) models are often inaccurate and in contradiction with each other. Considering the recent surge of novel hyper-performant strain sampling tools (Distributed Sensing for example), their application for the creation of novel and physically accurate Bond–slip models is just a matter of time. This being said, one of the main reasons behind the modern coexistence of multiple inaccurate and at times contradictory Bond–slip models is the absence of a tool that has allowed researchers to rapidly corroborate and calibrate their newly created models. To this end, the present article proposes such a Bond–slip validation tool for RC elements. This one is designed to extract reinforcement strain profiles at any given load level on the grounds of a specific bond–slip law and geometrical inputs. Said profile is then compared against an experimentally extracted one based on specimens with identical geometrical features. The performance of the validation tool is demonstrated through an application to six existing bond–slip models. Granted the proposal of validation tools is paramount for the future of the discussion on bond–slip modelling, stress-transfer analyses and serviceability of RC structures, the here proposed validation tool is a first significant step in that direction.