Major seismic events around the world along with the aging and deterioration of infrastructures keep increasing the need for repair/strengthening and rehabilitation of existing bridges. Seismic repairing and strengthening are an area that has seen major developments due to the availability of robust numerical simulation frameworks, large experimental facilities, structural health monitoring techniques, development of advanced materials and construction techniques, seismic fragility assessment of retrofitted infrastructures, and sophisticated performance-based seismic design and assessment methodologies. Despite the progress, there are many challenges yet to be addressed. The main objective of this session is to present results from recent research studies (experimental/numerical/analytical) and practical examples of existing bridge retrofit and repair. This session will provide a forum for practicing engineers and researchers to share and discuss the various issues related to design and construction issues of seismic repair/retrofit/strengthening of bridges at the element and system level.
(1) Discuss the new experimental and numerical approaches for the rehabilitation of concrete bridges with seismic isolation and energy dissipating devices;
(2) Summarize new design guidelines adopted by several codes and standards for seismic repair/strengthening of bridges;
(3) Highlight the advances in different cement-based composites for repair and rehabilitation of bridges;
(4) Present findings from large scale experimental testing of retrofitted bridge components.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Precast Bridge Columns with Replaceable Components for Quick Repair
Presented By: Mostafa Tazarv
Affiliation: South Dakota State University
Description: Reinforced concrete (RC) columns, which are usually the main source of energy dissipation and ductility in bridges, are widely used in seismic regions of the nation. Even though current bridge design specifications ensure collapse prevention, damage of bents is expected in extreme events. Minor damage such as cover spalling may be repaired. Nevertheless, more severe damages such as buckled reinforcement and core concrete failure of RC bents cannot be easily repaired, which usually result in bridge total replacement. A new detailing has been developed for RC bridge bents in which all components are precast to accelerate construction and the damage is limited to exposed reinforcement to minimize bridge repair time and cost. The seismic performance of the proposed repairable precast connection was investigated through testing of three half-scale bridge columns under slow cyclic loading. A conventional cast-in-place column (CIP) was also tested as the benchmark model. The precast columns were tested at least twice to practice the repairability by replacing the exposed BRR. The presentation discusses the repairable detailing and highlights the key findings of the experimental study.
Seismic Performance of Retrofitted Bridge Column Under Major and Several Aftershocks
Presented By: Saif Aldabagh
Affiliation: University of British Columbia
Description: Glass fiber-reinforced polymer (GFRP) with low tensile strength (hereafter referred to as low-grade GFRP) is a cost-effective alternative to other types of GFRP with higher tensile strength. This paper investigates the prospect of retrofitting deficient and repairing damaged circular concrete columns with low-grade GFRP jackets. Two identical one-third scale models of a seismically deficient prototype bridge pier were constructed and tested under constant axial compression and quasi-static reversed cyclic loading. The first column was tested twice, first under “as-built” condition and second under repaired conditions. The second column was retrofitted prior to testing. The repaired and retrofitted columns were characterized with enhanced flexural, ductility, and energy dissipation capacities when compared to the deficient column; and were stable up to 6.9% drift. The applicability of the provisions of the Seismic Retrofitting Manual for Highway Structures of the Federal Highway Administration to low-grade GFRP retrofit was assessed.
Full-Scale Evaluation of a Repair Measure of Earthquake Damaged Bridge Column
Presented By: A K M Golam Murtuz
Affiliation: Portland State University
Description: The Cascadia Subduction Zone (CSZ) earthquake is expected to damage the existing bridges in the Pacific Northwest and spread geographically throughout the region. A rapid repair method to restore mobility along the lifeline route should be implemented quickly as part of the earthquake damaged bridge repair and replacement. A repair method incorporating semi-permanent installation is being developed anticipating the need for such quick measures. The presentation will outline the development of the repair methodology, analytical design approach and results from a full-scale cyclic test validating the performance for seismically substandard concrete bridge substructure. Seismically substandard bridges in the region will undergo damage ranging from concrete core crushing to reinforcement bar buckling/fracture following CSZ earthquake. While the conventional repair methods are effective in restoring the strength in the damaged zones, often lead to higher stiffness and strength that would likely result in shifting the failure to other part of the structure under future earthquake or aftershock demands. The proposed repair methodology uses the capacity design principles to protect the reminder of the bridge into future earthquake and eradicates the need for establishing rebar continuity resulting in less labor-intensive repair method. The adopted concept is to utilize U-shaped metallic plates as externally attached ductile fuses to be anchored with the non-damaged part of the column and hence bypassing the damaged zone to restore the lateral capacity. The damaged zone can then be repaired with strips of fiber reinforced polymer (FRP) sheets to provide lateral confinement preventing any further damage to the core concrete.
A typical substandard reinforced concrete column-to-footing subassembly was damaged during a full-scale cyclic test under CSZ loading protocol.
Behavior of UHPFRC Strengthened Bridge Piers Under Lateral Impact Loads
Presented By: Gholamreza Gholipour
Affiliation: Lakehead University
Description: UHPFRC is one of the advanced high-strength concrete materials which demonstrates superior durability, strength and energy dissipation capacity against seismic and extreme loads. The impact performance of a UHPFRC-strengthened bridge pier is numerically investigated. The performance of the strengthened columns is assessed with the variations of different parameters including the thickness of UHPFRC jacket (tU), impact velocity (Vimp ), and axial load ratio (ALR). Since the full use of UHPFRC material for the whole cross- section of piers, can unreasonably increase the construction costs without any significant strength enhancement, exploring optimal levels for the thickness of UHPFRC jacket is as of interest. From sensitivity analysis of the damage index to tU, a thickness of 60 mm was recognized as the optimal level based on the behavioral trend of the UHPFRC-strengthened columns. That is, although tU had a marginal positive influence on the column impact resistance when it was beyond 60 mm, the application of a 60-mm-thickness UHPFRC jacket significantly increased the resistance of the column by reducing the damage index by 55% compared to conventional column. The columns with tU higher than 60 mm, endured low-level damage with an index of less than 0.2 when subjected to impact loads with velocities less than 10 m/s and the damage index was not highly sensitive to tU. Under impact loads with velocities higher than 10 m/s, a thickness of 60 mm was recognized as the optimal thickness of UHPFRC jacket for the column resistance. Also, an marginal positive effect of ALR on the impact resistance of the UHPFRC-strengthened columns.
Rehabilitation of a Concrete Multi-span Bridge using Seismic Isolation
Presented By: Mohammed Naimi
Description: The presentation will provide detailed example of a bridge in Vancouver that has been retrofitted with isolators. The bridge was seismically deficient and would not survive the design level earthquake. Detailed finite element simulation shows the seismic vulnerability of the existing bridge. The design of the retrofit using isolation devices will be presented. Later, the seismic simulation of the bridge after retrofit with the designed isolation devices will be performed, which clearly show that the bridge can even survive 2% in 50 years seismic event.
Performance-based Seismic Loss Assessment of Simply Supported Highway Bridges with Super Elastic SMA Reinforced Piers and Restraining Devices
Presented By: Shuai Li
Affiliation: The University of British Columbia
Description: The merit and effectiveness of a novel bridge system with super elastic (SE) shape memory alloy (SMA)-reinforced piers and restraining devices against destructive earthquakes have been validated, and promising results have been published; however, considering the high initial cost of SMA materials, the economic benefit of such a novel bridge has not been recognized yet. The objective of this study is to assess the main benefits of the novel bridge over the conventional bridge in terms of economic loss performance given different earthquake scenarios. Results revealed that the proposed novel bridge having SMA-reinforced piers equipped with SMA restrainers is less fragile at both the component and system levels compared to the prototype bridge. The novel bridge presents remarkable functionality and resilience with noticeable post-earthquake financial benefits (direct, indirect, and long-term losses). The results also showed much higher cost-benefit ratios of the proposed novel bridge under different earthquake scenarios.