PSI - Issue 11

Antonio Bossio et al. / Procedia Structural Integrity 11 (2018) 394–401 Author name / Structural Integrity Procedia 00 (2018) 000–000

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non-destructive testing, especially the latter when dealing with heritage building stock. The scientific support is provided by laboratory experimental tests on real scale specimens of members affected by current induced and long term natural corrosion. This knowledge allows to estimate the loss in performance in terms of shear and combined axial load and bending (not only in terms of strength, but of ductility, too), as corrosion is not only simple steel bar cross section reduction, but also loss of bond, concrete cover, etc. where external transverse reinforcement is more affected than internal counterpart. In this sense usually shear is more critical than bending, not only for its well known brittleness, but also because stirrups are less thick and corrode earlier. Ductility and strength play a different role in static and seismic vulnerability of structure, and push over analyses have been performed on structures subjected not only to different degrees of corrosion, but also configuration of corrosion (a facade only, up to a complete generalized corrosion occurring in bare frames without any infill wall). The indexes to evaluate seismic vulnerability have been the PGA and return periods, the latter easily related to the timing of corrosion development. After the evaluation of the actual state of a structure, a potential solution has been also explored in terms of retrofit with HPC (High Performance Concrete), that has high compressive strength, but particularly high tensile strength. By means of replacing the concrete cover (usually spalled out at corrosion levels impacting on structural capacity) it is possible to gain significant enhancements of shear and bending capacity. It is worth noting that the contribution of the jacket has been included in the evaluation only as confinement, i.e. transverse reinforcement, hence the axial capacity of HPC has been neglected, both for bending and axial load. Similarly deliberately no additional steel bars as longitudinal reinforcement or stirrups, have been added, so that shear was mainly resisted transversally by HPC jacket. Even if at high levels of corrosion it is not always possible to regain the initial non-corroded strength, and this should be taken into account for static vulnerability if the thickness of the HPC jackets is not larger than concrete cover initial dimensions, the significant gain in terms of ductility, by means of HPC confinement, allows to reduce dramatically the seismic vulnerability of such structures. 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