Mechanical and durability properties of high-strength concrete containing steel and polypropylene fibers

Damage characterization of laminated composites has been thoroughly studied the last decades where researchers developed several damage models, and in combination with experimental evidence, contributed to better understanding of the structural behavior of these structures. Experimental techniques played an essential role on this progress and among the techniques that were utilized, acoustic emission (AE) was extensively used due to its advantages for in-situ damage monitoring with high sensitivity and its capability to inspect continuously a relatively large area. This paper presents a comprehensive review on the use of AE for damage characterization in laminated composites. The review is divided into two sections; the first section discusses the literature for damage diagnostics and it is presented in three subsections: damage initiation detection, damage type identification and damage localization, while the second section is devoted to damage prognostics and it focuses on the remaining useful life (RUL) and residual strength prediction of composite structures using AE data. In every section, efforts have been made to analyze the most relevant literature, discuss in a critical manner the results and conclusions, and identify possibilities for future work.

Damage characterization of laminated composites using acoustic emission: A review

Flexural behavior and serviceability performance of 24 full-scale concrete beams reinforced with carbon-, glass-, and aramid-fiber-reinforced-polymer (FRP) bars are investigated. The beams were 3,300 mm long with a rectangular cross section of 200 mm in width and 300 mm in depth. Sixteen beams were reinforced with carbon-FRP bars, four beams were reinforced with glass-FRP bars, two beams were reinforced with aramid-FRP bars, and two were reinforced with steel, serving as control specimens. Two types of FRP bars with different surface textures were considered: sand-coated bars and ribbed-deformed bars. The beams were tested to failure in four-point bending over a clear span of 2,750 mm. The test results are reported in terms of deflection, crack-width, strains in concrete and reinforcement, flexural capacity, and mode of failure. The experimental results were compared to the available design codes.

Evaluation of Flexural Behavior and Serviceability Performance of Concrete Beams Reinforced with FRP Bars

Reinforcing concrete with a combination of steel and glass fiber-reinforced polymer (GFRP) bars promises favorable strength, serviceability, and durability. To verify its promise and to support design of concrete structures with this hybrid type of reinforcement, we have experimentally and theoretically investigated the load-deflection behavior of concrete beams reinforced with hybrid GFRP and steel bars. Eight beams, including two control beams reinforced with only steel or only GFRP bars, were tested. The amount of reinforcement and the ratio of GFRP to steel were the main parameters investigated. Hybrid GFRP/steel-reinforced concrete beams with normal effective reinforcement ratios exhibited good ductility, serviceability, and load carrying capacity. Comparisons between the experimental results and the predictions from theoretical analysis showed that the models we adopted could adequately predict the load carrying capacity, deflection, and crack width of hybrid GFRP/steel-reinforced concrete beams.

Flexural Behavior of Concrete Beams Reinforced with Hybrid (GFRP and Steel) Bars

Fibre-reinforced polymers (FRPs) are an accepted material by structural engineers for the strengthening of structural elements. With increasing environmental concerns, further emphasis is being placed on the use of sustainable construction materials such as timber. This paper describes an experimental programme which examines the reinforcement in flexure of low-grade glued laminated timber (glulam) with a commercially attractive recyclable FRP. Unreinforced glulam beams, FRP plate reinforced glulam beams, unreinforced glulam beams incorporating an additional sacrificial lamination and FRP plate reinforced glulam beams, which had a sacrificial lamination bonded beneath the FRP plate, were fabricated and tested in flexure. The unreinforced glulam demonstrated linear elastic behaviour and exhibited brittle tensile-flexural failures in comparison to the pseudo-ductile behaviour of the reinforced beams. The addition of reasonable reinforcement percentages strategically located in the tension zone resulted in moderate enhancements in the stiffness while more significant improvements in the ultimate moment capacity were obtained. Strain profiles illustrated that increased utilisation of the compression strength of the timber is obtained when FRP reinforcement is included.

Low-grade glued laminated timber reinforced with FRP plate

Repair and rehabilitation of infrastructure is becoming increasingly important for bridges due to material deterioration and limited capacity to accommodate current load levels. An experimental program was undertaken to study the flexural behavior of creosote-treated sawn Douglas fir timber beams strengthened with glass fiber-reinforced polymer (GFRP) bars. Twenty-two half-scale and four full-scale timber beams strengthened with GFRP were tested to failure. The percent reinforcement ratios were between 0.27 and 0.82%. Additional unreinforced timber beams were tested as control specimens. The results have shown that using the proposed experimental technique changed the failure mode from brittle tension to compression failure, and flexural strength increased by 18 to 46%. Research findings indicate the use of near-surface GFRP bars overcomes the effect of local defects in the timber and enhances the bending strength of the members. Based on the experimental results, an analytical model is proposed to predict the flexural capacity of both unreinforced and GFRP-reinforced timber beams. The article also reviews implementation of the proposed technique for strengthening a timber bridge near Winnipeg, Manitoba, Canada.

Timber Beams Strengthened with GFRP Bars: Development and Applications

The design of fiber-reinforced polymer reinforced concrete (FRP-RC) is typically governed by serviceability limit state requirements rather than ultimate limit state requirements as conventional reinforced concrete is. Thus, a method is needed that can predict the expected service load deflections of fiber-reinforced polymer (FRP) reinforced members with a reasonably high degree of accuracy. Nine methods of deflection calculation, including methods used in ACI 440.1R-03, and a proposed new formula in the next issue of this design guide, CSA S806-02 and ISIS M03-01, are compared to the experimental deflection of 197 beams and slabs tested by other investigators. These members are reinforced with aramid FRP, glass FRP, or carbon FRP bars, have different reinforcement ratios, geometric and material properties. All members were tested under monotonically applied load in four point bending configuration. The objective of the analysis in this paper is to determine a method of deflection calculation for FRP RC m...

Critical Review of Deflection Formulas for FRP-RC Members

An experimental program was conducted at the University of Manitoba to test salvaged timber stringers strengthened with glass fiber-reinforced polymer (GFRP) laminates. A total of 20 creosote-treated Douglas Fir beams with dimensions of 130×330×4,500  mm were tested in three-point bending. Two groups were studied to examine the effect of GFRP reinforcement on the stiffness increase of the beams. The first group of 10 samples were reinforced with GFRP laminates on the tension side only (Group T), whereas the other group of 10 samples was reinforced with GFRP laminates alongside both tension and compression zones (Group TC). This study found that the strengthening with GFRP laminates, on average, increased the strength and the stiffness of the beams, respectively, by 36 and 3% for Group T and by 31 and 3.5% for Group TC. An analysis of a database of fiber-reinforced polymer (FRP)–strengthened timber beams tested by other researchers facilitated further study on the effect of FRP on the behavior of t...

Flexural Stiffness and Strength of GFRP-Reinforced Timber Beams

Fiber reinforced polymer (FRP) rods are used for pre-stressing and reinforcing in civil engineering applications. Damage in FRP rods can lead to sudden brittle failure, therefore, a reliable method that provides indicators of damage progression and potential failure in FRP rods is highly desirable. Acoustic emission (AE) signal analysis has been used for damage detection and monitoring of FRP materials. In this study, a new AE event detection algorithm, utilizing the root mean square envelope of AE signal, is applied to AE data to isolate each AE event separately, even when AE events are nearly coincident. A fuzzy c-means (FCM) clustering algorithm is used to classify these isolated AE events into 3 clusters. Scanning electron microscopy images of FRP rod cross-sections also show 3 types of damage. The hypothesis in this study is that each cluster represents a damage mechanism. The number of events in each cluster is monitored versus the percent of the ultimate load. The ratio of the number of AE events in one of the FCM clusters to the number of AE events in another FCM cluster was useful for providing an indication of when the stress levels have reached the point where the loads may cause the FRP rod to fail. The results of applying this parameter to four FRP rods show a significant slope change (factor of 10) in this ratio at around 40% and 60% of the ultimate load for glass FRP rods and carbon FRP rods, respectively. This method may prove useful in damage progression and failure prediction of the FRP rods in prefabricated structures where pre-stressed FRP is used and in field monitoring of FRP materials.

https://iopscience.iop.org/article/10.1088/1361-665X/aa6e43/pdf

Dagmar Svecova

Papers

Timber Beams Strengthened with GFRP Bars: Development and Applications

Critical Review of Deflection Formulas for FRP-RC Members

Flexural Stiffness and Strength of GFRP-Reinforced Timber Beams

On acoustic emission for damage detection and failure prediction in fiber reinforced polymer rods using pattern recognition analysis

Factors affecting bond between precast concrete and cast in place ultra high performance concrete (UHPC)