Enabling Resilient Structures with Repeated Post-Tensioning Using Novel Iron Shape Memory Alloy System
Date
2023-09-19
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Abstract
The degradation of reinforced concrete (RC) structures like bridge girders is concerning and emphasizes the need to invest in sustainable design practices. A proactive maintenance program employing an incremental post-tensioning (IP) technique should increase the service life of structures by inhibiting the ingress of moisture and harmful environmental agents which contribute to their degradation. IP is achieved using the shape memory effect of iron shape memory alloy (Fe-SMA) which recovers deformations (representing a period of degradation) from preloaded beams. Eight beams were tested in a four-point bending configuration to validate the Fe-SMA prestress-strengthening system (FPSS). The deformation from varying preload amounts and subsequent recovery of those deformations from activating the FPSS were investigated to validate the capability of the system and demonstrate how the proactive maintenance approach enables structural resiliency. The beams were constructed of carbon nanofiber-infused, ultra-high-performance, fibre-reinforced concrete (CNF-UHPFRC), which couples the benefits of IP with the exceptional mechanical properties and contribution from the steel fibres and CNF. The IP beam had comparable flexural performance as that of the beam preloaded to 45% (beam ID PS30) of the reference load (68 kN, yield load of the beam strengthened with a non-activated Fe-SMA strip), even though it experienced a larger preload (75% of the reference load). Also, the results of beam IP showed structural resiliency in terms of crack widths and deflections. The midspan deflection at 45% of the reference load (representing a service load on the girder) for PS30 and beam PS60 (preloaded to 90% of the reference load) was 7.20 and 5.09 mm, respectively while it was 4.93 mm for the IP Beam. The bottom crack widths at 90% of the reference load (60 kN) for PS30 and PS60 were 0.61 and 0.79 mm, respectively while it was 0.5 mm for the IP beam. The yield loads for PS30 and PS60 were 70.85 and 76.11 kN, respectively, while it was 71.98 kN for the IP beam. The ultimate loads for PS30 and PS60 were 72.78 and 77.64 kN, respectively, while it was 72.75 kN for the IP beam. IP experienced a less ductile failure than PS60.
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Citation
Forrest, B. T. (2023). Enabling resilient structures with repeated post-tensioning using novel iron shape memory alloy system (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.