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. In addition, engineers must adopt efficient and cost-effective repair and strengthening methods to enhance the seismic resilience of existing RC buildings.
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.
Tailored Approaches to Concrete Bridge Seismic Retrofit Strategies
Presented By: Katrin Habel
Affiliation: Associated Engineering Ltd
Description: Many bridges in Western Canada, built in the 1950s to 1970s, are inadequately detailed to resist the current seismic hazard and ongoing deterioration. This presentation discusses the shortcomings and retrofit strategies for seismically deficient concrete bridges in British Columbia, via case studies of recent projects. The first case study demonstrates the retrofit approach for a 214 m long four-span concrete girder I-bridge with vulnerable half-joints and piers up to 60 m tall. Built in 1970 on a provincial highway, to prevent loss-of-span and achieve performance targets, the retrofit changed the structural articulation, reduced the bridge’s seismic displacements, and increased the ductility of critical structural elements. Next is a 77 m long five-span curved concrete I-girder bridge, built in 1977 on a municipal road where the seismic retrofit included making the deck continuous, replacing bearings, installing shear keys and abutment bumper plates, and installing sleeving to protect vulnerable deeply buried pier columns. The final case study describes the widening and retrofit of a 78 m long four-span multi-cell box girder bridge built in 2004 spanning a provincial highway. The widening required rethinking of the seismic detailing including foundation strengthening of intermediate supports with micropiles, pier column infills and steel collars, extending existing MSE abutment walls and modifying the structure articulation. The presentation describes the tailored performance-based approach used for each structure, explains the rationale, performance expectations agreed with the owner, and describes the integration of seismic retrofit with rehabilitation needs to provide optimum value.
Advancing Performance-Based Design of FRP Retrofit for Existing RC Structures
Presented By: Hector Garcia Matamoros
Affiliation: UC Berkeley
Description: Sophisticated performance-based engineering (PBE) frameworks are widely available for existing reinforced concrete (RC) structures. However, current retrofit design methods using externally bonded fiber-reinforced polymer (FRP) systems remain predominantly prescriptive and are not explicitly linked to performance objectives. A primary limitation is the lack of validated nonlinear modeling parameters for FRP-retrofitted components, which constrains their integration into performance-based engineering practice. This study seeks to advance the application of PBE principles to the design of FRP seismic retrofits. For deformation-controlled actions, FRP strengthening can be designed using a displacement-based approach, supported by ASCE 41-type nonlinear modeling parameters and acceptance criteria. Conversely, force-controlled actions can follow a strength-based design approach. The study presents nonlinear modeling parameters and acceptance criteria for FRP-jacketed RC columns, as well as a shear strength equation for FRP-retrofitted beam-column joints calibrated using experimental databases. A case study on displacement-based design of FRP sheets for a splice-deficient RC column is presented.
Sustainability of FRP-retrofitted Concrete Columns for Seismic Resistance
Presented By: Shamim Sheikh
Affiliation: University of Toronto
Description: The annual damage caused by the corrosion of steel in all its forms is estimated at 3.2% of the global GDP which amounts to over $3 trillion. A substantial part of this loss is in infrastructure. In this research, the fibre-reinforced polymers (FRP) are being investigated as an alternative to steel in reinforced concrete. Based on this research, a major application of external FRP was carried out to retrofit a highway bridge that was severely damaged due to steel corrosion. The main feature of the repair technique developed in the lab and used in the field is that the contaminated concrete and the corroded steel are not removed and the columns are built back to their original shapes using either non-shrink or expansive cement grouts. This is followed by the application of GFRP wraps a few days later. Monitoring of the retrofitted structure was carried out by measuring strain at various locations and the corrosion activity. This presentation will include selected results from the large dataset of tests on lab columns and field monitoring. This includes load-deformation responses of columns under axial load and under quasi static earthquake loads in addition to the change in corrosion potential over 9 years. The lab columns’ diameter varied between 356 mm and 500 mm while the field columns were larger than 1 meter in diameter. Several years after the retrofit, the repaired columns of the bridge are performing extremely well without showing any sign of deterioration or distress. The corrosion potential and the risk of corrosion have reduced to low levels from their initial high levels. The proposed procedure is significantly more efficient with respect to the cost and time for repair compared to the traditional methods and provides much longer service life.
Lateral Cyclic Behavior of Repaired Conventional and Hybrid (GFRP–Steel) Double-Layer RC Bridge Piers
Presented By: Sherif Osman
Affiliation: University of British Columbia
Description: This study examined the seismic response of a large-scale bridge pier subjected to repeated lateral cyclic loading. The bridge pier incorporated a hybrid reinforcement system consisting of steel and Glass Fibre-Reinforced Polymer (GFRP) arranged in two concentric layers, each providing both longitudinal and transverse reinforcement to enhance corrosion resistance, structural durability, and service life relative to conventional steel-reinforced concrete piers. The seismic performance was assessed through cyclic loading tests, during which the hybrid (GFRP-Steel) double-layer column exhibited ductility and load-carrying capacity comparable to those of a traditional steel-reinforced pier up to failure. After the initial loading phase, the damaged specimens were repaired using FRP wraps and re-tested under the same loading protocol to evaluate post-repair seismic behavior. In total, four large-scale specimens were tested as part of this experimental program. Enhanced structural integrity and energy dissipation underscore the effectiveness of advanced repair strategies in mitigating seismic vulnerability.