Toward the definition of equivalent damage parameters for the assessment of corroded RC structures

Abstract

The effects of reinforcement corrosion need to be included in the assessment of existing Reinforced Concrete structures for a reliable evaluation of the structural performances over time and a correct choice of the renovation strategy. The DEMSA protocol proposes straightforward tools available to professional engineers, enabling the calibration of equivalent damage parameters able to describe corrosion effects starting from environmental easy-measurable conditions. Guidance to implement the equivalent damage parameters describing corrosion effects at a sectional level in the structural analyses is provided. Then, a simplified approach to model the corrosion attack distribution along the bar length is proposed. Finally, nonlinear static analyses are carried out on reference RC frames subjected to different corrosion patterns by adopting fiber modeling technique, to show how the equivalent damage parameters allow detecting the impact of corrosion effects on the structural performances, in terms of internal actions distribution, reduction of stiffness, strength, and ductility.

DEMSA Protocol: Deterioration Effect Modelling for Structural Assessment of RC Buildings

“…Then, other data from the literature ('M' for Martinez and Andrade, 2009 [22] and 'R' for RILEM, 1996 [23]) were considered to reduce the proposed ranges by adapting to the scenarios' classification the conditions in which they were defined [12]. Values indicated with 'E' in Table 6 were finally estimated by Casprini [12,24] through analyses of corroded bars extracted from existing structures, for which a scenario and an aggressiveness class were identified, and aggressiveness conditions were measured. Finally, some values (named 'REF' in Table 6) are here identified and proposed as the representative values to be adopted for the setting of the equivalent damage parameters, considering all the former data from the literature.…”

“…A more refined analytical model should account also for the distribution of the maximum corrosion attack along the bar length. A simplified analytical model aimed at estimating the ductility reduction of the bare bar featuring a single equivalent defect of a certain length with a maximum attack was proposed by the authors in Casprini et al, 2021 [41]; then, since, in existing structures, the corrosion attack distribution on bars is highly variable, and the attack distribution along the bar length is not predictable, it may be useful to relate typical configurations of the natural corrosion patterns to such an equivalent single defect, in order to estimate the residual elongation capacity with the proposed model [12].…”

“…As for the corrosion pattern of the school building, the worst condition for Scenario S2O is assumed as detailed in Section 3.2 (T c = 50 years, Model 1 for bar average cross-section reduction, v avg = 10 µm/year, R p = 7), while for the car park in Scenario S2H, an intermediate condition is assumed (T c = 43 years, Model 1 for bar average cross-section reduction, v avg = 30 µm/year, R p = 5). A simplified method (further detailed in Casprini et al [41]) is here adopted to model an uneven corrosion attack pattern by means of a simplified one: the average attack ('avg') is modelled in the whole corroded elements, except for a portion where the maximum attack ('max') is introduced. This portion is defined as a single 'equivalent defect', which is characterised by a chosen length, associated with the scenario of interest and the aggressiveness of the attack (in this case, 15 cm for the school and 40 cm for the car park).…”