Distributed sensing for serviceability analysis of reinforced concrete structures

Mattia Francesco Bado

Doctoral dissertation

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The present doctoral thesis is set on introducing a novel manner of tackling the serviceability analyses of Reinforced Concrete (RC) structures.

Classical approaches have either considered a perfect interaction between steel and concrete or a simplified constant bond relation. Either way, due to the lack of tools that could accurately assess the strains inside RC structures, they adopted theoretical, empirical or numerical solutions to define the analyses’ parameters. Modern research, instead, advocates the use of the stress transfer approach which suggests an interaction between the rebars and its surrounding concrete in the form of a force transfer (bond stress). The latter provides a realistic reflection of the behavioral nature of RC, of its bond-slip mechanisms, of the effect of tension stiffening and of the crack development. Still, the issue of accurately investigating the strains inside of a RC structure persists.

With the introduction of Distributed Optical Fiber Sensors (DOFS), accurate, completely-distributed, experimentally measured strain profiles of the RC structure’s constitutive materials are finally possible. DOFS finally fills the gap that ever-present instrumental gap holding back the reliability of RC structure serviceability models. The current thesis displays how to marry the potential of DOFS with the one of the stress transfer for the models’ substantiation, integration and/or provision of data for the formulation of new ones.

In order to achieve such, the author performed multiple DOFS-powered experimental campaigns on RC tensile members subjected to both double pull-out testing and simple concrete shrinkage. During testing the rebar strain profiles were continuously (250 Hz) and distributedly (every 0.6 mm) sampled. On the ground of the experimental data, the stress-transfer analysis constituting parameters were extracted i.e., concrete-steel bond stress and slip. A new correlation between steel bond stress and reinforcement ratio was discovered and constituted the bod of novel bond stress law. The latter was then integrated in a revisited version of the Strain Compliance crack spacing Model whose predicting capabilities was demonstrated to be extensively superior to the ones of the present day model codes, namely fib Model Code 2010 and Euro Code 2. DOFS was also employed for the assessment of the effect of concrete shrinkage on the residual performance of RC members. In particular, a new tension-stiffening law that accounts for the effect of concrete shrinkage was introduced and substantiated thanks to the DOFS-monitoring of concrete shrinkage-induced strains on embedded steel rebars.

In conclusion, this thesis demonstrates the potential of DOFS to elevate the serviceability analyses of RC structures either substantiating the present day models or presenting valid substitutes to them.

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DOI: https://doi.org/10.20334/2021-027-M

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148 p.
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