Composite confinement systems for RC column repair and construction under seismic loads: Concept, characterization and performance

This study aims at developing, characterizing and validating an integrated composite confinement system of conventional jackets for: (1) repair and retrofit of existing bridge columns; and (2) construction of new bridge columns, subjected to earthquake excitations. A new composite steel confinement jacket was proposed by combining a thin steel sheet and prestressing strands as a hybrid jacket, incorporating active and passive confining pressure on damaged RC columns. Both experimental and analytical studies were conducted to understand the performance and effectiveness of the proposed repair method. The experimental study involved two 1/2-scale lap-spliced deficient RC bridge columns originally tested to failure under reversed cyclic loading. The proposed jacket was designed and implemented to repair the damaged columns to achieve the required performance level after repair intervention for service and ultimate limit states. Experimental results indicated that both repaired columns exceeded the strength and ductility of their as-built columns. The stiffness of the second column designed for ultimate limit state was completely restored. Analytical studies and collapse analyses on the seismic performance of post-mainshock repaired bridges subjected to mainshock-aftershock sequences demonstrated the efficacy of the proposed technique under severe mainshock-severe aftershock attacks. Another new composite confinement system of a fiber reinforced polymer (FRP) sheet wrapped around a polyvinyl chloride (PVC) tube with energy dissipation medium in between was developed for new bridge columns construction. This composite system is essentially a FRP-confined concrete-filled PVC tube, featuring exceptional durability properties of PVC materials in addition to high strength of the FRP fabrics. Experimental tests under uniaxial compression and flexural loading were undertaken to establish the representative stress-strain behavior of confined concrete filled PVC tubes (CCFPT). Experimental studies clearly demonstrated that the CCFPT system outperforms conventional FRP jacket. The intermediate energy dissipation medium is critical to make the post-peak behavior more ductile. Analytical studies were conducted and equations were derived for the prediction of the ultimate strength and strain of a CCFPT system --Abstract, page iv

Collapse Vulnerability and Fragility Analysis of Substandard RC Bridges Rehabilitated with Different Repair Jackets under Post-Mainshock Cascading Events

Past earthquakes have signaled the increased collapse vulnerability of mainshock-damaged bridge piers and urgent need of repair interventions prior to subsequent cascading hazard events, such as aftershocks, triggered by the mainshock (MS). The overarching goal of this study is to quantify the collapse vulnerability of mainshock-damaged substandard RC bridge piers rehabilitated with different repair jackets (FRP, conventional thick steel and hybrid jacket) under aftershock (AS) attacks of various intensities. The efficacy of repair jackets on post-MS resilience of repaired bridges is quantified for a prototype two-span single-column bridge bent with lap-splice deficiency at column-footing interface. Extensive number of incremental dynamic time history analyses on numerical finite element bridge models with deteriorating properties under back-to-back MS-AS sequences were utilized to evaluate the efficacy of different repair jackets on the post-repair behavior of RC bridges subjected to AS attacks. Results indicate the dramatic impact of repair jacket application on post-MS resilience of damaged bridge piers—up to 45.5 % increase of structural collapse capacity—subjected to aftershocks of multiple intensities. Besides, the efficacy of repair jackets is found to be proportionate to the intensity of AS attacks. Moreover, the steel jacket exhibited to be the most vulnerable repair intervention compared to CFRP, irrespective of the seismic sequence (severe MS-severe or moderate AS) or earthquake type (near-fault or far-fault)

Hybrid Jacketing for Rapid Repair of Seismically Damaged Reinforced Concrete Columns

This study proposes hybrid jacketing for rapid repair of seismically damaged concrete columns for bridge safety. The hybrid jacketing for a reinforced concrete (RC) column is composed of a thin cold-formed steel sheet wrapped around the column and its outside prestressing strands. Although the prestressing strands can prevent buckling of the confining steel sheet, the steel sheet can in turn prevent the prestressing strands from cutting into the concrete. The hybrid jacketing concept was validated with testing of a large-scale RC column with lap splice deficiency typical of pre-1970 bridge constructions in the Central United States. Results from the original and repaired columns were compared for hysteresis loops, strength, stiffness, ductility, and energy dissipation. The hybrid jacketing proved to be effective in restoring structural behavior of the damaged column to prevent bridge collapse. Such a cost-effective solution can be implemented at bridge sites in hours. Design equations to establish the lateral force-displacement relationship of the tested column to design the hybrid jacket are derived in detail

Design, Construction and Load Testing of the Pat Daly Road Bridge in Washington County, MO, with Internal Glass Fiber Reinforced Polymers Reinforcement

The overarching goal of this project is to deploy and assess an innovative corrosion-free bridge construction technology for long-term performance of new and existing bridges. The research objective of this project is to conduct a comprehensive study (instrumentation, construction, both laboratory and field evaluation) of a rapidly constructed and durable, three-span bridge with cast-in-place cladding steel reinforced concrete substructure and precast concrete decks/girders reinforced with glass fiber reinforced polymers (GFRP). The bridge has one conventional concrete-girder span, one conventional steel-girder span, and one innovative concrete box-girder span. The conventional concrete and steel girders were used to demonstrate the effective use of corrosion-free bridge decks in deck replacement projects and, as benchmarks, to demonstrate the pros and cons of the innovative concrete box girders. The bridge was instrumented with embedded strain gauges to monitor the strains at critical locations during load testing. The collected data will allow the understanding of load distribution in various GFRP bars of the innovative concrete box girders and bridge deck slabs. Specifically, a full-scale concrete box girder and a full-scale concrete slab with internal GFRP reinforcement were tested in the Highbay Structures Laboratory at Missouri S&T to ensure that the test bridge components behaved as designed prior to the field construction. Furthermore, in-situ load tests of the completed bridge were conducted to demonstrate the load capacity and behavior of individual components and the bridge as a system. The field validated technology will have a longlasting value for future deck replacement projects of existing bridges and new constructions. It will provide a viable alternative to conventional bridge systems/materials for the improvement of our Nation\u27s deteriorating infrastructure

FRP-Confined Concrete Filled PVC Tubes: A New Design Concept for Ductile Column Construction in Seismic Regions

In their recent work Fakharifar and Chen (2016) [1] have introduced and validated a new ductile design concept of confined concrete-filled polyvinyl-chloride tubular (CCFPT) columns through experimental and analytical studies. Confinement was provided with the use of a polyvinyl-chloride (PVC) tube and fiber-reinforced polymer (FRP) wrappings or FRP with a sandwiched layer of foam to enhance impact energy reduction due to potential FRP rupture and PVC fracture. In the present paper, additional flexural tests on CCFPT columns were undertaken to further investigate the structural behavior of the proposed system for column construction in seismic regions. Axial and flexural behavior of CCFPT columns was investigated with compressive and flexural tests, respectively, and compared with those of their corresponding concrete-filled polyvinyl-chloride tubular (CFPT) and FRP-wrapped (FW) columns. Test results obtained from 152 x 305 mm (6 x 12 in.) stub columns under axial loads and 152 x 1524 mm (6 x 60 in.) flexural beams under four-point loads indicated that the CCFPT columns can significantly enhance strength over the CFPT columns and enhance ductility over the FW columns. The transverse confining pressure from FRP wrapping and the interface property between the FRP and PVC proved critical in CCFPT design. Furthermore, the idea of introducing a cushioning foam layer between FRP layers and PVC to lessen the brittleness of FRP rupture in seismic regions proved effective

Compressive Behavior of FRP-Confined Concrete-Filled PVC Tubular Columns

This paper presents a new composite confinement system of FRP wrap and PVC tube with and without an impact absorption medium (compressible foam) in between. The compressive behavior of the proposed FRP-confined concrete filled PVC tube (CCFPT) was investigated and compared with those of the concrete filled PVC tube (CFPT) and FRP-wrapped (FW) concrete cylinder. The effect of compressible foam on the post-peak behavior of the CCFPT specimen was explored. The applicability of seven existing FRP-confined stress-strain relationships to predict the ultimate strength and ductility enhancement of FW and CCFPT specimens was evaluated. A total of 14 FW, 5 CFPT, and 17 CCFPT specimens with 152 mm in diameter and 305 mm in height were tested under monotonically increasing axial loads in compression. The key parameters examined included the type and thickness of FRP wraps, the presence and thickness of compressible foam, and loading area. Test results indicated that, without compressible foam, the CCFPT cylinders resembled the FW cylinders in stress-strain relationships with brittle failures upon FRP rupture and immediately-followed PVC fracture due to sudden transfer in confining pressure. With compressible foam, the CCFPT cylinders can combine the strength of the FW cylinders and the ductility of the CFPT cylinders

Analytical Study of Force–Displacement Behavior and Ductility of Self-centering Segmental Concrete Columns

Abstract In this study the behavior of unbonded post-tensioned segmental columns (UPTSCs) was investigated and expressions were proposed to estimate their ductility and neutral axis (NA) depth at ultimate strength. An analytical method was first employed to predict the lateral force–displacement, and its accuracy was verified against experimental results of eight columns. Two stages of parametric study were then performed to investigate the effect of different parameters on the behavior of such columns, including concrete compressive strength, axial stress ratio, diameter and height of the column, axial stress level, duct size, stress ratio of the PT bars, and thickness and ultimate tensile strain of fiber reinforced polymer wraps. It was found that the column’s aspect ratio and axial stress ratio were the most influential factors contributing to the ductility, and axial stress ratio and column diameter were the main factors contributing to the NA depth of self-centering columns. While at aspect ratios of less than ten, as the axial stress ratio increased, the ductility increased; at aspect ratios higher than ten, the ductility tended to decrease when the axial stress ratio increased. Using the results of parametric study, nonlinear multivariate regression analyses were performed and new expressions were developed to predict the ductility and NA depth of UPTSCs

Behavior and Strength of Passively Confined Concrete Filled Tubes

In this study, Confined Concrete Filled Tube (CCFT) is proposed and studied for the seismic design of reinforced concrete columns, exhibiting improved results in terms of stiffness, strength and ductility. Specifically, plastic instead of steel tubes were used to confine concrete in the Concrete Filled Tube (CFT) system since plastics are less expensive, lighter (approximately 1/6 of steel), retarding to fire effect, and immune to galvanic or electrolytic attack. Additional confinement to the CFT tubes was provided by an external Fiber Reinforced Polymer (FRP) layer. The use of the FRP layer can potentially delay and restrain local buckling of the plastic tube, which in turn mitigated undesirable failure modes, and enhanced ductility. Testes were carried out to better understand the composite action among FRP wrapping, tube, and concrete core. The efficacy of polymeric plastic tubes implemented in both CFT and CCFT specimens was demonstrated under uniaxial compressive tests. Uniaxial compressive tests results suggest that the use of such CCFT system, incorporating the FRP sheets and polymer plastic tubes, can dramatically increase the amount of energy absorbed and decrease the brittle failure, typically observed in the case of unconfined or poorly-confined concrete members. Due to the composite action among the FRP wrapping, plastic tube and concrete core, the CCFT specimens more significantly increased both strength and ductility of the composite columns

Innovative Hybrid Reinforcement Constituting Conventional Longitudinal Steel and FRP Stirrups for Improved Seismic Strength and Ductility of RC Structures

The use of fiber reinforced polymer (FRP) reinforcement is becoming increasingly attractive in construction of new structures. However, the inherent linear elastic behavior of FRP materials up to rupture is considered as a major drawback under seismic attacks when significant material inelasticity is required to dissipate the input energy through hysteretic cycles. Besides, cost considerations, including FRP material and construction of pre-fabricated FRP configurations, especially for stirrups, and probable damage to epoxy coated fibers when transported to the field are noticeable issues. The current research has proposed a novel economical hybrid reinforcement scheme for the next generation of infrastructures implementing on-site fabricated FRP stirrups comprised of FRP sheets. The hybrid reinforcement consists of conventional longitudinal steel reinforcement and FRP stirrups. The key feature of the proposed hybrid reinforcement is the enhanced strength and ductility owing to the considerable confining pressure provided by the FRP stirrups to the longitudinal steel reinforcement and core concrete. Reinforced concrete beam specimens and beamcolumn joint specimens were tested implementing the proposed hybrid reinforcement. The proposed hybrid reinforcement, when compared with conventional steel stirrups, is found to have higher strength, stiffness, and energy dissipation. Design methods, structural behavior, and applicability of the proposed hybrid reinforcement are discussed in detail in this paper