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Seismic Repair/Retrofit/Strengthening of Bridges at the Element or System Level, Part 1 of 2

Sunday, October 17, 2021  10:00 AM - 12:00 PM

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, and sophisticated performance-based seismic design and assessment methodologies. Despite the progress, there are many challenges yet to be addressed. With the increase in transportation demand and more stringent seismic performance requirements, bridge retrofit, and repair is an important task for engineers and researchers. Bridge retrofits usually involve functional upgrades (such as deck widening) and seismic upgrades (such as strengthening seismic load path). The effects of the two upgrades are usually coupled and need to be analyzed. Therefore, more sophisticated analysis and customized solution is needed. While providing structural upgrade solutions to seismic issues, engineers also need to reduce the interruption to the traffic as much as possible.
Learning Objectives:
(1) Highlight ongoing research studies on the performance of repaired/retrofitted bridges under extreme events
2. Present recent findings regarding the behavior of retrofitted concrete bridges under axial and combined flexure/lateral loads or environmental loads (corrosion, freeze-thaw cycles, high-temperature differential, freeze-thaw cycles, and ice load impact)
3. Discuss the new experimental and numerical approaches for the rehabilitation of concrete bridges with seismic isolation.

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.


Seismic Retrofit and Quick Repair Technique for Bridge Columns Through Transverse Prestressing

Presented By: Murat Saatcioglu
Affiliation: University of Ottawa
Description: Reinforced concrete bridge columns built prior to the enactment of seismic design and detailing requirements of modern codes of practice suffer significant damage in the event of a strong earthquake. The column damage can be primarily due to three design deficiencies: i) insufficient shear strength, ii) lack of concrete confinement and iii) improper splicing of longitudinal reinforcement in the potential hinge region. These bridges benefit from seismic retrofitting. An innovative bridge retrofit technology was developed at the University of Ottawa, consisting of transverse prestressing to overcome all three deficiencies. Tests of large-scale bridge columns with circular and square cross-sections, having a sectional dimension of 500 mm and a shear span of either 1.5 m or 2.0 m, were tested to develop the technology. A design procedure was developed for all three deficiencies. The retrofit technology is shown to be effective as a quick repair technique after damaging earthquakes, as it induces active lateral pressure, controlling/partially closing diagonal cracks while increasing lateral clamping force against bar slip and concrete confinement. The objective of the research program reported in the paper is to present the results of experimental research and the design procedure for the seismic retrofit and quick repair technique.


Shape Memory Alloy Based Dampers used for Seismic Retrofit of Continuous Bridges with Unequal Height Piers

Presented By: Nailiang Xiang
Affiliation: Nagoya Institute of Technology
Description: Continuous bridges with unequal height piers are highly vulnerable to seismic hazards with the shorter (stiffer) piers prone to suffer severe damages due to the unbalanced inertia force distributions among the unequal piers. One of the common retrofit measures for such irregular bridges is that flexible devices like rubber bearings or metallic steel dampers are inserted at the shorter piers to mitigate the seismic forces imposed on piers, while simultaneously, share a certain amount of force with the taller piers. However, such devices can hardly show both recentering and energy dissipation characteristics that have been proved to be very important factors for seismic damage mitigation of structures. This study investigates the possibility of using shape memory alloy (SMA)-based dampers for seismic retrofit of unequal height continuous bridges. First, a static pushover analysis is conducted on the bridges with and without SMA retrofit measures, to reveal the progressive damage mechanism and sequences of different structural components. The design parameters of the SMA dampers can be adjusted accordingly to obtain a satisfactory damage development pattern. After that, nonlinear incremental dynamic analysis (IDA) as well as probabilistic fragility analysis is then performed to verify the results from the static analysis. The results indicate that SMA dampers can not only well balance the seismic forces between the unequal piers to lead to a uniform damage across the piers, but also show high effectiveness in seismic resilience enhancement by minimizing the post-earthquake residual displacements of the bridges.


Rapid Repair of Reinforced Concrete Columns Using Plastic Hinge Relocation

Presented By: Taylor Brodbeck
Affiliation: North Carolina State University
Description: Bridges subjected to extreme damage have usually been considered unrepairable and requiring replacement. However, recent studies have shown that a repair technique, called plastic hinge relocation, is capable of restoring the column to its original force and displacement capacities. In this repair, the original plastic hinge is strengthened so that should another large earthquake occur, damage will form above the repair in a previously undamaged section, ensuring a predictable and ductile response. The aim of this research is to improve the constructability and performance of the plastic hinge relocation repair using a steel jacket. Experimental tests were conducted on RC columns subjected to reverse cyclic loading which were repaired and re-tested. To reduce the construction time of the repair, reinforcing bars and couplers were pre-embedded in the footing allowing for additional reinforcing steel to be coupled in place at the time of the repair. The steel jacket utilized a bolted connection which simplified construction and was shown to be a suitable alternative to welding when designed as a slip-critical connection. Previous research has shown that the repair’s response is weakened when bars which fracture in the original plastic hinge debond from the repair. In these tests, anchorage of the fractured bars was improved by increasing the confining pressures by using a larger jacket thickness and bond conditions were improved by replacing the cracked concrete around the fractured bars. This enhanced the seismic resilience of the repaired column, evident by an increase in dissipation of energy and reduction in strength degradation.


Proposed Shear Design Equation and Reliability Analysis for Shear-Critical RC Beams Strengthened with Inorganic Composites

Presented By: Tadesse Wakjira
Affiliation: The University of British Columbia
Description: Inorganic matrix-based composites; particularly, fabric-reinforced cementitious matrix (FRCM) and steel reinforced grout (SRG) have shown to be effective in strengthening reinforced concrete (RC) beam deficient in shear. However, accurate determination of the shear capacity of FRCM/SRG-strengthened beams remains a challenge, which limits the practical application of FRCM/SRG composites. Thus, this study is aimed to propose a simple and rational shear design equation for FRCM/SRG-strengthened RC beams accounting for the contribution of concrete in compression, internal shear reinforcement, and the strengthening system. The prediction capability of the proposed equation was validated against an existing experimental database of FRCM/SRG-strengthened RC beams. Moreover, the comparison of the proposed and existing code equation revealed a superior performance of the proposed equation in predicting the shear capacity of the beams. Finally, a reliability analysis is conducted to calibrate a strength reduction factor to achieve a target reliability index of 3.5, and a design example is provided using the calibrated resistance reduction factor.


Rapid Repair of Hollow-Core FRP-Concrete-Steel Columns

Presented By: Mohamed ElGawady
Affiliation: Missouri S&T
Description: This paper develops a quick repair technique in 6 hours of a new accelerated bridge construction system of hollow-core fiber reinforced polymer (FRP)-concrete-steel columns (HC-FCS). This HC-FCS column consists of a concrete wall sandwiched between an outer FRP tube and an inner steel tube. The steel tube works as a longitudinal and transverse reinforcement and the FRP tube confines the sandwiched concrete. The FRP tube protects the steel tube from corrosion because the FRP tube has no corrosion. This system offers several benefits: including reduced construction time, minimal traffic disruptions, reduced life-cycle costs, improved construction quality, and improved safety. The HC-FCS columns reduce the columns’ weight which reduces the seismic loading, the transportation costs, and the need to cranes of high capacity. Two large scale columns were tested under static cyclic lateral loading with a constant axial load. One of these columns was a conventional reinforced concrete (RC) column and the other was the HC-FCS column. The RC column failed by rebar rupture and the HC-FCS column failed by FRP rupture. The flexural strength of the HC-FCS column was 123% of that of the RC column. The HC-FCS column was repaired and retested under the same loading of the virgin column. The HC-FCS column was repaired by FRP wrapping using quake bond epoxy and grout injection. The repaired column achieved 95% of the virgin column’s flexural strength and 61% of the virgin column’s stiffness. However, the repaired column achieved 117% of the RC column’s strength and 70% of the RC column’s stiffness.


Multi-Column Bridge Bent Considering Different Jacketing Options

Presented By: Abu Chowdhury
Affiliation: University of British Columbia
Description: In this research, detailed finite element models of as built and retrofitted multicolumn bents have been developed and validated against available experimental results. Four different jacketing techniques such as, carbon fiber reinforced polymer (CFRP), steel, engineering cementitious composite (ECC), and concrete have been considered in this study. Multi-column bents were retrofitted according to CSA S6-19. Using the validated numerical models, performance-based damage states are developed for the retrofitted bridge bents. This study will aid engineers to obtain material strain limits for retrofitted bridge currently unavailable in design codes/standards.

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