Non-linear cyclic performance of stainless steel reinforced concrete materials and components

Abstract

The deterioration of reinforced concrete structures is primarily caused by the corrosion of reinforcing bar (rebar) initiated by chloride ingress from de-icing salts or seawater exposure in coastal environments. This degradation compromises the structural performance, shortens service life and results in substantial economic costs. Stainless steel rebars present a promising alternative to conventional carbon steel rebars due to their superior corrosion resistance, enhancing durability and resilience of reinforced concrete structures.

Current design standards for concrete structures reinforced with stainless steel rebar are largely adapted from those developed for carbon steel rebars and do not specifically account for the distinct mechanical behaviour of stainless steel rebars. Stainless steels exhibit a nonlinear stress-strain response with high ultimate-to-yield strength ratios and superior ductility, which influence the composite behaviour and failure modes of stainless steel reinforced concrete structures. Considering the lack of experimental data and validated constitutive models capable of accurately simulating stainless steel rebars under various loading conditions, this thesis investigated the response of stainless steel rebars and reinforced concrete components subjected to static, cyclic and fatigue loading.

An extensive experimental programme was conducted to characterise the mechanical behaviour of stainless steel rebars under monotonic, cyclic and fatigue loading. A total of 10 tensile, 49 compressive, 25 cyclic and 125 low-cycle high-amplitude fatigue tests were performed. Three stainless steel rebar types were investigated: 12 mm diameter cold-rolled austenitic EN 1.4301, 12 mm diameter hot-rolled austenitic EN 1.4301 and 16 mm diameter hot-rolled lean-duplex EN 1.4482. B500C carbon steel rebars of the same diameters were also tested for comparison. The results demonstrated that stainless steel rebars exhibit superior strain hardening, more gradual post-peak softening and greater energy dissipation under cyclic loading. Fatigue tests revealed enhanced fatigue performance in hot-rolled stainless steel rebars, particularly at lower slenderness ratios, while cold-rolled stainless steel exhibited reduced fatigue life. Strain-life models were calibrated to predict the fatigue life. Uniaxial material models for use in a distributed plasticity approach via fibre sections, adopted in modelling software such as OpenSees, were developed for stainless steel rebars and calibrated using experimental results for application in reinforced concrete structural models.

At component level, the tension stiffening behaviour of stainless steel rebars was investigated, where it was shown that the response of stainless steel rebars differ from that of carbon steel rebars due to the differences in the material stress-strain responses. The codified tension stiffening models, including the crack width and crack spacing provisions, were assessed in detail and implications of the results were discussed. An improved modified tension stiffening model for stainless steel rebars is presented, incorporating the Ramberg–Osgood stress–strain relationship. Large-scale lateral cyclic tests on concrete columns reinforced with stainless steel and carbon steel rebars were carried out. The results demonstrated that stainless steel reinforced concrete columns had improved lateral load resistance, energy dissipation and drift capacity. In addition, numerical models of reinforced concrete columns were developed in OpenSees and validated against the experimentally measured load-drift responses, providing a validated modelling approach for simulation of these components.

The findings of this research highlight the need for revised design provisions that reflect the material properties of stainless steel rebars. The experimental and numerical results in this study provide a foundation for optimising stainless steel reinforced concrete design, contributing to more durable and resilient structures.

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Identifiers

ORCID for Sheida Afshan: orcid.org/0000-0003-1048-2931

ORCID for John Preston: orcid.org/0000-0002-6866-049X

ORCID for Simon Blainey: orcid.org/0000-0003-4249-8110

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