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.

In this study, the cyclic axial compressive behavior of newly proposed concrete-filled fiber-reinforced polymer (FRP) tubes (CFFT) was examined. Different types of FRP, including small rupture strain FRP (SRSFRP) and recyclable large rupture strain FRP (LRS-FRP), were used to reinforce the concrete columns. LRS-FRP is made of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) and has a high tensile rupture strain (usually greater than 5%), while SRS-FRP has a lower tensile rupture strain of 1-2%. A total of twelve CFFTs were tested to assess the strength, confinement ratio, ductility, ultimate strain, and energy dissipation of the columns. The results showed that the use of LRS-FRP led to improved ductility and ultimate strength in the confined concrete columns compared to the use of SRS-FRP. The study also compared the experimental results to existing analytical models available in the literature and proposed two new models for predicting the ultimate stress-strain behavior of hybrid LRS-FRP.

This paper presents the results of an extensive test program that was aimed at investigating the flexural behavior of rectangular concrete-filled glass fiber-reinforced-polymer (GFRP) tube (CFFT) beams post-tensioned (PT) with unbonded steel tendons. The tests intend to simulate a number of design parameters, which are mainly governed by flexural loading. All beams were tested under four-point bending over a simply supported span of 3,000 mm [1229 in.]. Four full-size beams with an identical rectangular cross-sectional of 305 mm × 406 mm [12.0 in. × 16.0 in.] were constructed. The investigated test parameters were the number of tendons (2 or 3) and concrete strength (40 or 65 MPa) [5.80 or 9.43 ksi]. Besides, a proposed design equation as an extension to AASHTO (2012) equation based on a regression analysis of the test results herein to predicate the flexural capacity is established. The test results show that the cracking loads and post-cracking stiffness can be improved by increasing the number of strands. However, increasing the number of strands shows a slight effect on the ultimate capacity. The flexural capacities of PT CFFTs can be enhanced by increasing the concrete compressive strength without affecting their overall ductility. The proposed model successfully predicts the ultimate moment capacity of the tested beams and other results from the literature with an average of 1.08±0.16 and a COV of 14.5%. However, due to the limited test results in the present study and, in the literature, additional tests on the flexural behavior of PT rectangular CFFT beams are needed to further validate the accuracy of the model.

Fiber-reinforced polymer (FRP) reinforcements for concrete structures and civil engineering applications have become one of the innovative and fast-growing technologies to stop the rapid degradation of conventional steel-reinforced concrete infrastructure. FRP reinforcements for construction can be divided into three main types: 1. External sheets or plates to rehabilitate and repair existing concrete and masonry structures, and in some cases steel and wood structures; 2. Internal FRP bars or tendons for new and existing reinforced concrete structures, and 3. FRP stay-in-place forms to be filled with unreinforced or reinforced concrete. A considerable and valuable development and application’s work has been accomplished during the last three decades, leading to the development of numerous design guidelines and codes around the world, making the FRP-reinforcement technology one of the fast-growing markets in the construction industry. During the ACI Concrete Convention, Fall 2021, four full sessions were sponsored and organized by ACI Committee 440. Session S1 was focused on the bond and durability of internal FRP bars; Session S2 on codes, design examples, and applications of FRP internal reinforcements; Session S3 on external FRP reinforcements; and Session S4 on new systems and applications of FRP reinforcements, such as CFFT post-tensioned beams, GFRP-reinforced concrete sandwich panels, FRP-reinforced masonry walls, CFFT under impact lateral loading, near-surface mounted FRP-bars, and GFRP-reinforced-UHPC bridge deck joints.

The development of rehabilitation strategies for reinforced concrete bridges is a significant concern for civil engineers. Bridges exposed to harsh environmental conditions and subjected to daily fatigue loading are vulnerable to corrosion and accelerated deterioration of their components. Previous studies and field applications have shown that bonding carbon fiber-reinforced polymer (CFRP) to the bridge element surface is an attractive solution for bridge strengthening. This paper aims at reviewing and evaluating the use of externally bonded CFRP for bridge rehabilitation. The article is structured in two main parts. The first part is an experimental and field survey on using CFRP as external reinforcement for concrete bridges. The second part focuses on evaluating the performance of the Original Champlain Bridge (OCB) edge girder strengthened with externally bonded CFRP under live load tests, which were performed by the developers of the bridge. The results of truckload tests on the edge girder of the OCB show that the rehabilitation technique using externally bonded CFRP sheets on the edge girder of the bridge was able to keep the shear strains constant and extend their service life for up to 10 years until deconstruction of the bridge.