Dependency of pitting corrosion spatial variability on crack pattern of prestressed concrete members

Many existing reinforced concrete (RC) and prestressed concrete (PC) bridges all over the world are affected by corrosion deterioration of reinforcements. Therefore, the assessment of the re-sidual life of corroded structures and infrastructures results strategic to plan maintenance activi-ties and to limit sudden collapses, traffic disruptions and fatalities. The lack of consolidated methods for assessing the residual capacity of corroded PC members in engineering practice is related to the limited experimental and numerical researches available in the scientific literature. Indeed, limited works investigate the uncertainties in the correlation between the damage induced by corrosion and the structural resistance. The main novelty of the present study consists in the measurement-based correlation between the pitting corrosion spatial variability in prestressing strands and the crack pattern in PC members, caused by spalling of cover or splitting cracking of concrete. To this aim, the present study investigates several prestressing strands retrieved from six 10-years-old naturally corroded PC beams subjected to chloride ions attack during their ser-vice lifetime. Firstly, the surface defects of each analysed PC beam were mapped and the corre-sponding position of each retrieved sample was reported. Secondly, 3D-models of corroded strands were developed and the GOM Inspect software was adopted to measure the penetration depth of each scanned pit. Finally, useful correlations were derived for relevant variables such as the maximum penetration depth and the number of pits per meter. In this regards, two different groups were identified consisting of strands (i) retrieved and (ii) not retrieved from zones of PC beams characterised by the presence of splitting cracking. The results show that cracking of concrete play a fundamental role in the corrosion spatial variability of prestressing strand

A simplified stress–strain relationship for the mechanical behavior of corroded prestressing strands: The SCPS-model

This article presents a simplified stress–strain relationship for the definition of the mechanical behavior of prestressing strands subjected to chloride-induced corrosion, named SCPS-model (Simplified Model for Corroded Prestressing Strands). The constitutive law adopts the equivalent spring model, that reproduces the overall behavior of a corroded strand by summing the contributions of each wire, assumed as a spring working in parallel to the others. The SCPS-model is designed for the application in the daily engineering practice; to this aim, it is based on a single input parameter that is the maximum penetration depth of the most corroded wire. Following a detailed description of the model formulation and parameters, the article shows the validation of the stress–strain relationship through several comparisons with experimental tensile test outcomes coming from scientific literature. Finally, a statistical analysis of the dimensionless ratio of experimental and analytical results in terms of ultimate corroded strength and strain is carried out to demonstrate the effectiveness of the SCPS-model. Concluding, the accurate and safe side prediction of the residual mechanical behavior of corroded prestressing strands is proposed using the SCPS-model

Anchorage and laps of plain surface bars in R.C. structures

Current codes of practice, mainly devoted to new structures, do not include information and approaches relevant to old material and products. At the same time, old codes are not applicable since they are not reliability-based. The increasing need for assessment and renovation of existing constructions yields the necessity to develop new approaches for old materials and products that are consistent with the requirements of current codes. In this scenario, the aim of this article is to develop a new semi-empirical formulation for anchorage and lap strength of plain surface bars of R.C. structures that is also consistent with the reliability-based approach included in the forthcoming second generation of Eurocodes. To this aim, by using a reference test database, a novel step-by-step procedure is proposed for the statistical evaluation and optimization of the contribution of each parameter affecting anchorage and lap strength. Moreover, the probabilistic calibration of the proposed expressions is performed and equations for design anchorage and lap strength are proposed. These equations have the same format as that, for ribbed bars, included in the latest draft of the second-generation Eurocode 2. Finally, the proposed formulations are compared with those of previous studies and earlier codes