This paper presents an investigation on the practicability and structural efficiency of prestressed CFRP strips with a gradient anchorage in the framework of a bridge
Advancements in optical imaging devices and computer vision algorithms allow the exploration of novel diagnostic techniques for use within engineering systems. A recent field of application lies in the adoption of such devices for non-contact vibrational response recordings of structures, allowing high spatial density measurements without the burden of heavy cabling associated with conventional technologies. This, however, is not a straightforward task due to the typically low-amplitude displacement response of structures under ambient operational conditions. A novel framework, namely Magnified Tracking (MT), is proposed herein to overcome this limitation through the synergistic use of two computer vision techniques. The recently proposed phase-based motion magnification (PBMM) framework, for amplifying motion in a video within a defined frequency band, is coupled with motion tracking by means of particle tracking velocimetry (PTV). An experimental campaign was conducted to validate a proof-of-concept, where the dynamic response of a shear frame was measured both by conventional sensors as well as a video camera setup, and cross-compared to prove the feasibility of the proposed non-contact approach. The methodology was explored both in 2D and 3D configurations, with PTV revealing a powerful tool for the measurement of perceptible motion. When MT is utilized for tracking “imperceptible” structural responses (i.e., below PTV sensitivity), via the use of PBMM around the resonant frequencies of the structure, the amplified motion reveals the operational deflection shapes, which are otherwise intractable. The modal results extracted from the magnified videos, using PTV, demonstrate MT to be a viable non-contact alternative for 3D modal identification with the benefit of a spatially dense measurement grid.
This paper presents recent experimental investigations on structural strengthening by means of (Carbon) Fiber Reinforced Cementitious Matrix (FRCM) in Switzerland. A first test series deals with full-scale reinforced concrete slabs strengthened with one or two composite reinforcement meshes embedded in a shotcrete layer. Static load tests up to failure show the efficiency of the strengthening in terms of increased yield and ultimate load compared to the reference specimen. Due to the initially necessary straightening of the textile, the contribution at lower deflection levels is limited. Only with advanced cracking and crack opening, the mesh develops its full contribution. Ultimate load is reached after a prompt relative slip of the mesh in the shotcrete. In the post-peak domain, failure by concrete crushing was observed. To study the residual tensile strength of the carbon reinforcement after exposure to high temperatures, various tensile tests on small rovings previously cut out of a composite mesh were performed. The specimens were heated to temperatures of 300 °C, 500 °C, 700 °C, and 1000 °C, kept at that level for 30 minutes, and finally cooled down to room temperature. The subsequent tensile tests performed at room temperature revealed a significant drop in the residual tensile strength for exposure temperature higher than 300 °C. A final test was performed on a reinforced concrete slab strip strengthened with a shotcrete layer including a composite mesh as tensile reinforcement. Under a constant service load, the slab was exposed to fire with a temperature rise according to a European standard curve (ETK) for two hours. The slab could withstand the applied loads for the full two hours, during which the composite mesh reached a temperature of about 440 °C. This observation is consistent with the results from tensile tests on filaments, clearly indicating a residual tensile strength after exposure at a similar temperature. The temperature in the internal steel reinforcement did not trespass a critical value of 500 °C as proposed by current design recommendations.
Externally Bonded Reinforcement (EBR) technique has been widely used for flexural strengthening of concrete structures by using carbon fiber-reinforced polymers (CFRP). EBR technique offers several structural advantages when the CFRP material is prestressed. This paper presents an experimental and numerical study on reinforced (RC) slabs strengthened in flexure with prestressed CFRP strips as a structural strengthening system. The strips are applied as an externally bonded reinforcement (EBR) and anchored with either a mechanical or a gradient anchorage. The former foresees metallic anchorage plates fixed to the concrete substrate, while the latter is based on an accelerated epoxy resin curing followed by a segment-wise prestress force decrease at the strip ends. Both anchorage systems, in combination with different CFRP strip geometries, were subjected to static loading tests. It could be demonstrated that the composite strip's performance is better exploited when prestressing is used, with slightly higher overall load carrying capacities for mechanical anchorages than for the gradient anchorage. The performed investigations by means of a cross-section analysis supported the experimental observation that in case a mechanical anchorage is used, progressive strip debonding changes the fully bonded configuration to an unbonded end-anchored system. The inclusion of defined debonding criteria for both the anchorage zones and free length between the anchorage regions allowed to precisely capture the ultimate loading forces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.