The application of fiber-reinforced polymer (FRP) jacketing for confinement may not always be feasible, particularly in cases where adjacent elements obstruct the structural member and prevent wrapping. To address this issue, the utilization of FRP laminate and spike anchors has been proven as an alternative solution. This study focuses on proposing a design methodology for this particular application. A stress-strain model was developed to assess the behavior of concrete prisms confined with FRP laminates and spike anchors under axial compression. The model adopts a bi-parabola stress-strain curve, with the coefficients derived from previously published experimental data on concrete prisms confined using this solution. The comparison between the analytical and tested stress-strain curves yielded a coefficient of determination (R2) averaging at 0.96, demonstrating the effectiveness of the bi-parabola model in describing the tested stress-strain responses.

With the aging and deterioration of infrastructure, the need for repair, strengthening, and rehabilitation of existing structures continues to increase. Climate change makes extending the service life of our infrastructure critical since any demolition and new construction will trigger substantial amounts of carbon emissions. Research related to repairing and strengthening existing infrastructure is seeing major developments as new green materials and technologies become available. Improved assessment and retrofit of deficient structures, and performance-based design of new structures are also in high demand. Despite the progress, there are many challenges yet to be addressed. The main objective of this Special Publication is to present results from recent research studies (experimental/numerical/analytical) on the retrofit and repair of structural elements along with the assessment, analysis, and design of structures. Several of these papers were presented at the ACI Fall Convention “Seismic Repair/Retrofit/Strengthening of Bridges at the Element or System Level: Parts 1 and 2.” The presented studies cover various aspects of structural retrofitting and strengthening techniques including the use of rubberized engineered cementitious composite for enhancing the properties of lightweight concrete elements, high-performance concrete jacketing to strengthen reinforced concrete piers/columns, and the behavior of fiber-reinforced-polymer-wrapped concrete cylinders under different environmental conditions. Additionally, the research explores the behavior of concrete-filled FRP tubes under axial compression, innovative bridge retrofit technologies, and retrofit techniques for deficient reinforced concrete columns. There is also a focus on evaluating the seismic response of retrofitted structures, designing guidelines for seismic retrofitting using tension-hardening fiber-reinforced concrete, strengthening unreinforced masonry walls with ferrocement overlays, and developing seismically resilient concrete piers reinforced with titanium alloy bars. The seismic response of a retrofitted curved bridge was also presented where elastomeric bearings of the as-built bridge were replaced by high damping rubber bearings as a part of the seismic retrofit. Recommendations for nonlinear finite element analysis of reinforced concrete columns under seismic loading are also presented to simulate their behavior up to collapse. Overall, the presented studies in this Special Publication demonstrate the potential of new materials, methods, and technologies to improve the performance of various structural elements under different loading conditions, including seismic and environmental loads. These studies are expected to help our practitioners and researchers not only develop more effective and sustainable methods for repairing and strengthening of structures but also improve their analysis and design skills.

This research investigates the High Performance Concrete (HPC) jacketing method to strengthen reinforced circular concrete piers/columns. Four different types of HPC jackets such as Self-Consolidating Concrete (SCC), Engineered Cementitious Composites (ECC) and two types of Ultra-High Performance Concrete (UHPC) with three jacket thicknesses of 25 mm, 38 mm and 51 mm, with same reinforcement configuration were used to strengthen reinforced SCC core piers and analyze behavior. Thirteen pier specimens were tested to failure under concentric axial load applied through the SCC core. Test results indicated performance enhancement of piers strengthened with UHPC and ECC jackets, which not only prevented brittle failure but also improved the ductility and energy absorbing capacity by achieving a superior ultimate axial load capacity increase by more than 90% with a jacket thickness of 33% of the core diameter. Existing Code and analytical equations with reduction factors can be used for predicting axial load capacity of the strengthened piers/columns but choice of equations should be based on types of jacket concrete to ensure safe design.

Tension-hardening fiber-reinforced concrete (THFRC) is characterized by ductile response in tension and a significant tensile strength that can be sustained to large levels of tensile strain. The strain ductility imparted by the dense network of fibers presents an opportunity in seismic design and retrofit, whereas the significant durability enabled by the low porosity of the cementitious matrix makes this class of materials ideal for bridge retrofits since they can mitigate many of the limitations of the existing approaches. However, no design provisions exist regarding the application of THFRC in seismic design and retrofit. A summary of a pertinent framework of design guidelines is presented, which are needed for determination of both seismic demands and criteria for performance-based design of THFRC based retrofits. To this end, stress-strain relationships are formulated considering the confinement effect imparted by the fiber reinforcement. Strain limits are established by reference to test data from various studies of THFRC.

Explosively formed projectiles (EFP) are one of the most severe explosive and impact loading threats for civil infrastructure and military vehicles. EFP warheads are commonly found in conventional anti-tank weapons. They are also regularly used by insurgent forces against armoured vehicles in conflict-affected countries. The energy of EFPs is significantly greater than that of large calibre ammunition, such that a threat is posed to the occupants of armoured vehicles both by perforation and spalling of the armour. This paper aims to present new experimental results of the hypervelocity impact of EFPs on reinforced concrete (RC) columns to demonstrate the vulnerability of infrastructure to EFP improvised explosive devices (EFP-IEDs). As a possible mitigation measure of threat against EFPs, an RC column was retrofitted with a steel-jacket. The ability of a steel-jacket to minimise RC column damage was evaluated where it was found to minimise damage to the RC column and contain concrete fragments. Threedimensional numerical simulations were performed to elucidate the different stages of EFP interaction with the RC columns. No previously published results on the EFP terminal ballistic performance of RC columns have been found in the open literature.