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1. Performance assessment of prestressed concrete bridge girders using fiber optic sensors and artificial neural networks

   https://doi.org/10.1080/15732479.2020.1759658  

   Khandel, Omid; Soliman, Mohamed; Floyd, Royce W.; Murray, Cameron D. (May 2020, Structure and Infrastructure Engineering)

   null (Ed.)

   Structural health monitoring (SHM) activities are essential for achieving a realistic characterisation of bridge structural performance levels throughout the service life. These activities can help detect structural damage before the potential occurrence of component- or system-level structural failures. In addition to their application at discrete times, SHM systems can also be installed to provide long-term accurate and reliable data continuously throughout the entire service life of a bridge. Owing to their superior accuracy and long-term durability compared to traditional strain gages, fiber optic sensors are ideal in extracting accurate real-time strain and temperature data of bridge components. This paper presents a statistical damage detection and localisation approach to evaluate the performance of prestressed concrete bridge girders using fiber Bragg grating sensors. The presented approach employs Artificial Neural Networks to establish a relationship between the strain profiles recorded at different sensor locations across the investigated girder. The approach is capable of detecting and localising the presence of damage at the sensor location without requiring detailed loading information; accordingly, it can be suitable for long-term monitoring activities under normal traffic loads. Experimental laboratory data obtained from the structural testing of a large-scale prestressed concrete bridge girder is used to illustrate the approach. 

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2. New directions for reinforced concrete coastal structures

   https://doi.org/10.1186/s43065-021-00015-4  

   Nolan, Steven; Rossini, Marco; Knight, Chase; Nanni, Antonio (December 2021, Journal of Infrastructure Preservation and Resilience)

   null (Ed.)

   Abstract Within the last century, coastal structures for infrastructure applications have traditionally been constructed with timber, structural steel, and/or steel-reinforced/prestressed concrete. Given asset owners’ desires for increased service-life; reduced maintenance, repair and rehabilitation; liability; resilience; and sustainability, it has become clear that traditional construction materials cannot reliably meet these challenges without periodic and costly intervention. Fiber-Reinforced Polymer (FRP) composites have been successfully utilized for durable bridge applications for several decades, demonstrating their ability to provide reduced maintenance costs, extend service life, and significantly increase design durability. This paper explores a representative sample of these applications, related specifically to internal reinforcement for concrete structures in both passive (RC) and pre-tensioned (PC) applications, and contrasts them with the time-dependent effect and cost of corrosion in transportation infrastructure. Recent development of authoritative design guidelines within the US and international engineering communities is summarized and a examples of RC/PC verses FRP-RC/PC presented to show the sustainable (economic and environmental) advantage of composite structures in the coastal environment. 

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3. Long-term behavior of precast, prestressed concrete sandwich panels reinforced with carbon-fiber-reinforced polymer shear grid

   https://doi.org/10.15554/pcij66.5-01  

   Nafadi, M.K.; Lucier, G.; Yaman, T.S.; Gleich, H.; Rizkalla, S. (September 2021, PCI journal)

   This paper documents the testing of six 20 ft × 4 ft × 8 in. (6.1 m × 1.2 m × 203.2 mm) precast, prestressed concrete sandwich panels constructed with continuous rigid insulation and a carbon-fiber-reinforced polymer grid shear transfer mechanism. All panels were identical except for foam type and were cast together on the same prestressing bed. Three of the six panels were fabricated with expanded polystyrene (EPS) foam insulation, and the remaining three panels were fabricated using sandblasted extruded polystyrene (XPS) foam. For each group of three panels, one was tested to failure as a control and two others were cycled 2 million times to 45% of their design ultimate load before failure testing. The tested EPS panels all failed when the applied lateral load was greater than or equal to 100 lb/ft2 (4.79 kPa), which is 2.35 times their design load of 42.5 lb/ft2 (2.03 kPa). The tested XPS panels all failed at the equivalent of 175 lb/ft2 (8.38 kPa) of applied lateral pressure, which is more than 4.0 times their design load of 42.5 lb/ft2. All four panels subjected to fatigue survived 2 million reverse-cyclic lateral load cycles without any visible signs of degradation. 

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4. Shear behavior of reinforced concrete beams with GFRP needles as coarse aggregate partial replacement: Full-scale experiments

   X.F. Nie, B. Fu (September 2019, Advances in Engineering Materials, Structures and Systems: Innovations, Mechanics and Applications)

   Fiber reinforced polymer (FRP) waste is becoming an environmental concern due to the widespread use and non-biodegradable nature of FRP composites. Cutting FRP waste into discrete reinforce-ments (referred to as “needles” hereafter) as coarse aggregate in concrete has been suggested as a possible solution to FRP waste recycling. It has previously been observed in small specimens that FRP needles increase the tensile strength and energy absorption capacity of concrete. This paper presents an experimental investiga-tion into the effect of GFRP needles as coarse aggregate partial replacement in concrete on shear behavior of full-scale reinforced concrete (RC) beams. A total of 10 RC beams without steel stirrups in the critical zone were tested under four-point bending. The volume replacement ratio of the coarse aggregate and the surface type of GFRP needles were chosen as the test parameters. GFRP needles, with either smooth or helically wrapped surfaces, were added to the concrete mix to replace 5% or 10% of coarse aggregate by volume, respectively. All test beams failed in shear in a brittle manner with the ductility being slightly enhanced by the partial replace-ment of coarse aggregate using GFRP needles. An enhancement of 8%-10% in the load carrying capacity was observed in beams with helically wrapped needles, while beams with smooth needles showed a reduction in the load carrying capacity. 

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5. A study on Residual Drift and Concrete Strains in Unbonded Post-Tensioned Precast Rocking Walls

   Sharma, Sumedh; Aaleti, Sriram (June 2019, Proceedings of the ... Canadian Conference on Earthquake Engineering)

   Modern seismic resistant design has been focusing on development of cost effective structural systems which experience minimal damage during an earthquake. Unbonded post-tensioned precast concrete walls provide a suitable solution due to their self-centering behavior and their ability to undergo large nonlinear deformation with minimal damage. Several experimental and analytical investigation focusing on lateral load resisting behavior of unbonded post-tensioned precast walls has been carried out in the past two decades. These investigations have primarily focused on lateral load resistance, self-centering capacity, energy dissipation and extent of damage in confined concrete region of the wall system. Past experimental results have shown that self-centering capacity of the wall system decreases at higher lateral drifts. Particularly, rocking walls with higher energy dissipation capacity, sustain considerable residual displacement. This residual displacement in the wall system may affect the ability of the entire structure to re-center. Though increasing initial prestressing force helps in reducing residual drift, it also subjects concrete to increased axial compressive stress which may lead to premature strength degradation of confined concrete in rocking corners. Accurate prediction of expected concrete strains in confined regions during increasing drift cycle is critical in design of such wall systems. Simplified design procedures available in literature assume different values for plastic hinge length to estimate critical concrete strain values. The results from the experimental tests available in literature were analyzed, to understand the effects of energy dissipating elements on residual drift and to examine the accuracy of simplified design procedures in predicting critical concrete strain. Based on the findings, recommendations are made on design of energy dissipating elements and plastic hinge length for unbonded post-tensioned precast rocking walls. 

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