Cyclic behavior of reinforced concrete members strengthened by smart cover

Today, rehabilitation and retrofitting of concrete structures are accomplished through various techniques. One of the most widely used methods involves the implementation of Fiber Reinforced Polymers (FRPs). FRP-based techniques offer several proven advantages, such as high strength-to-weight ratios, corrosion resistance, and ease of application. However, these methods also have notable drawbacks, including the reduction of ductility in reinforced elements. This reduction in ductility can compromise the structural performance under extreme loading conditions, such as seismic events. Therefore, it is crucial to select a suitable retrofitting method that not only strengthens the structure but also preserves or enhances the ductility of reinforced elements, and improves their functional efficiency under various loading scenarios.
In this paper, a novel approach using smart plates composed of elastomer and Shape Memory Alloy (SMA) is proposed for the rehabilitation of concrete elements subjected to cyclic loading. Smart plates consist of two primary components: shape memory alloy wires embedded within an elastomer matrix. The elastomer was chosen as a ductile substrate to hold the SMA wires in place, as it can undergo substantial deformation without losing its integrity. This combination ensures that the behavior of the smart coatings is predominantly governed by the properties of the SMA wires, which exhibit unique characteristics such as superelasticity and shape memory effects. The integration of these two ductile materials results in a highly adaptable and ductile strengthening system. This system can be easily attached to the concrete surface, with the SMA wires anchored in grooves at their ends to ensure effective load transfer.
To evaluate the performance of columns strengthened with smart plates, two concrete column specimens of the same height but with different dimensions, reinforcement details, and resistance properties were numerically analyzed using OpenSees software. OpenSees is a powerful computational tool capable of simulating the behavior of various structural systems and materials. The numerical models were first validated against available experimental data to ensure accuracy. The fiber method was employed for modeling, with the concrete02 material model used to define the concrete properties. This model accounts for the tensile behavior of concrete in a linear manner, and its parameters were calculated using the Mander model. For the steel reinforcement, the steel02 material model was adopted.
The study investigated the influence of several parameters, including the percentage of SMA wires within the elastomer matrix. Additionally, due to the temperature-dependent behavior of SMA, the modeling was conducted at different temperatures to assess its impact on performance. The results were compared using key parameters such as effective stiffness, effective damping, energy dissipation, and hysteresis behavior.
Main findings of this research can be mentioned as follows:


The use of smart plates does not reduce the ductility of reinforced specimens, making them a viable alternative to traditional FRP-based methods.
The application of smart plates in strengthening reinforced concrete columns increased the initial force required to initiate plastic deformation in the specimens.
Increasing the percentage of SMA wires relative to the elastomer matrix enhanced energy dissipation and hardness in the specimens.
The use of SMA wires at elevated temperatures significantly increased the load-bearing capacity of the elements and produced a distinctive flag-shaped hysteresis curve, indicative of improved energy absorption and self-centering capabilities.


The findings of this study highlight the potential of smart plates as an innovative solution for the retrofitting of concrete structures. Unlike conventional methods, smart plates offer a unique combination of strength, ductility, and adaptability, making them particularly suitable for structures in seismic-prone regions. The ability of SMA wires to recover their original shape after deformation, coupled with the elastomer's capacity to accommodate large strains, ensures that the strengthened elements can withstand cyclic loading without experiencing brittle failure.