Major seismic events around the world, along with the aging and deterioration of civil infrastructure, continue to highlight the need for pre- and post-earthquake repair, strengthening, and rehabilitation of existing reinforced concrete (RC) structures (e.g., buildings and bridges). Significant advancements in seismic repair, strengthening, and retrofit techniques have been facilitated by the availability of large-scale testing facilities, structural health monitoring technologies, the development of advanced materials and construction methods, and sophisticated performance-based seismic design and assessment methodologies. Despite this progress, many challenges remain. For example, the accelerating deterioration of structural systems, increasing transportation demands, and more stringent seismic performance requirements have made bridge retrofit and repair critical tasks for engineers and researchers.
The main objective of this session is to present findings from recent research studies—experimental, numerical, and analytical—as well as practical examples of seismic repair and retrofit of RC structures. This session will provide a forum for practicing engineers and researchers to share and discuss various issues related to the design and construction of seismic repair, retrofit, and strengthening strategies for RC structures at both the element and system levels.
Learning Objectives:
(1) Highlight ongoing research studies on the performance of repaired and retrofitted of RC structures under extreme events;
(2) Present recent findings regarding the behavior of repaired and retrofitted RC structural components under axial and combined flexure, lateral loads or environmental loads;
(3) Discuss the new experimental and numerical approaches for the rehabilitation of concrete structures in seismic-prone areas;
(4)
Lateral Cyclic Behavior of Hybrid (GFRP–Steel) Reinforced Concrete Columns: Implications for Performance-Based Design
Presented By: Sherif Osman
Affiliation: University of British Columbia
Description: This study investigates the seismic performance of innovative reinforced concrete (RC) bridge piers incorporating double confinement and hybrid reinforcement systems, compared with conventional RC piers, under quasi-static cyclic loading. Two advanced configurations were examined: Hybrid Glass Fiber Reinforced Polymer–Steel RC Bridge Piers (HRCBPs), which utilize an external GFRP cage to protect inner steel reinforcement, and Double-Confined Steel (DCS) piers, featuring dual spiral layers to provide varying confinement zones within the concrete core. Large-scale specimens were tested following ACI 374.2R-13 protocols to evaluate drift ratio thresholds, lateral load capacity, stiffness degradation, strain distribution, and energy dissipation. Experimental results highlighted distinct material responses: GFRP’s linear-elastic behavior facilitated broad strain distribution, while steel exhibited nonlinear localized strain concentrations. HRCBPs showed enhanced corrosion resistance and reliable drift capacity, whereas DCS piers demonstrated superior ductility, confinement efficiency, and post-yield stiffness. Comparisons across hybrid and steel systems revealed unique hysteretic behaviors, plastic hinge development, and damage progression, with both systems surpassing conventional RC in seismic resilience. Performance-based damage states—ranging from minor to local collapse—were defined using engineering demand parameters such as strain, ductility, and displacement. Predictive models, including fiber-based simulations and moment-curvature analyses, validated experimental observations and generated practical design charts. Four distinct performance levels were established, aligning with CSA S6-19 and PBD frameworks. Overall, hybrid and double-confined systems offer promising alternatives to conventional RC piers by improving ductility, durability, and resilience, thereby advancing seismic design practices for critical infrastructure.
Retrofit and Repair of Reinforced Concrete Using Near-Surface-Mounted Titanium Bars.
Presented By: Scott Arnold
Affiliation: FYFE Co LLC
Description: Titanium alloys have been used extensively in the aerospace industry and have been recognized for their ability to provide a high strength-to-weight ratio. For over ten years, researchers have been validating the use of near-surface-mounted (NSM) titanium bars to provide strength and ductility to reinforced concrete bridge girders and columns. This titanium allow (Class 130, Ti-6Al-4V) is ideal to use as surface mounted reinforcement as it does not suffer from corrosion, it has a design yield strength of 130ksi and an ultimate elongation of over 10%. The bars can be bent and cut in the field and can be fully anchored with proper termination detailing. The testing has led to over twenty completed bridge projects and has now opened the possibility of strengthening building elements. Much like the externally bonded FRP industry started in aerospace, then moved to bridge strengthening and then eventually to building applications, the titanium NSM bars are progressing in the same way. The high strength and ductility of the bars provide potential strengthening solutions that linear elastic FRP systems lack. This talk will review the testing, the design fundamentals and the unique applications that near-surface-mounted titanium bars can provide.
Experimental Investigation of Current Provisions for RC and FRP Retrofits for Non-ductile RC Structural Walls
Presented By: Ann Albright
Affiliation: Cal Poly
Description: Reinforced concrete (RC) structural walls are a common lateral force resisting system in regions of high seismicity. These regions may have older, non-ductile walls which are often shear critical, and may contain lap splices in the plastic hinge region. Retrofit strategies utilizing RC or fiber reinforced polymer (FRP) overlays have gained prominence as a seismic retrofit technique for non-compliant RC walls. The design of RC overlays is governed by the current ACI-318 code and the design of FRP seismic retrofit overlays is governed by a document of the ACI Committee 440. An experimental study was undertaken to evaluate the efficacy of current provisions for (1) shear-strengthening with RC overlay, (2) shear-strengthening with horizontal FRP overlay, (3) FRP flexural bar buckling prevention, and (3) FRP lap-splice slip prevention. The specimens were tested under a constant axial load and quasi-static lateral load with increasing displacement. The shear-strengthening retrofit was able to effectively delay diagonal tensile failure. The bar buckling retrofit resulted in unexpectedly high vertical reinforcement strains due to vertical strengthening through the FRP epoxy matrix and the vertical FRP anchor patches. The specimen with FRP overlays wrapped around a lap-splice region experienced strength degradation through bar rupture, eliminating the occurrence of lap-splice slip failure.
Lateral Cyclic Response of UHPC Confined Concrete Columns
Presented By: Stavroula Pantazopoulou
Affiliation: York University
Description: UHPC confinement provided by jacketing retrofits on RC Columns is an effective retrofit method both for durability and ductility enhancement for lateral load resistance. Experiments conducted by the authors, supplemented by published experimental evidence on RC columns jacketed by thin UHPC layers are examined collectively to establish the effectiveness of this solution in enhancing the strength and ductility of the encased member by suppressing undesirable modes of failure in lap splices or in the column web due to shear. Various UHPC jacket configurations are studied, either terminated above the critical section or penetrating into the support, including the use of bond breakers in the critical region to mitigate severe strain localization in primary embedded reinforcement. Performance limit states are proposed after consideration of the strain capacity of the UHPC-confined concrete. Design expressions are developed and evaluated, and detailed procedures are outlined for their implementation in bridge pier retrofitting. The results are supported by the database, providing a solid foundation for the broader application of UHPC in improving the lateral load resistance of bridge piers.
Moment Strengthening of Concrete Walls in Seismic Regions using CFRP
Presented By: Eduardo Leos
Affiliation: University of Texas At San Antonio
Description: Carbon fiber reinforced polymers (CFRP) are linear elastic until they fracture in a brittle manner. As such, applying CFRP for moment strengthening of concrete members in their hinge regions can pose the risk of reducing member ductility. On the other hand, CFRP fracture strain is on the order of 1%, which is several folds the yield strain of reinforcing bars. This indicates that properly detailed CFRP layouts, with fibers aligned in the longitudinal member direction, could allow reinforcing steel to yield and dissipate energy without pushing CFRP fibers beyond their fracture strains. An experimental program is under way with main objective to develop FRP detailing that can achieve moment strengthening of concrete walls in their hinge regions, while maintaining wall ductility. Results from full-scale wall tests exploring the effects of the amount of CFRP and CFRP anchorage details on moment strengthening are presented.