Showing papers by "Rami A. Hawileh published in 2020"

Flexural Strengthening of Reinforced Concrete Beams with Externally Bonded Hybrid Systems

Abstract: Carbon fiber reinforced polymers (FRP) have been used widely as Externally Bonded Reinforcing (EBR) materials for strengthening and retrofitting of RC structural members, both in flexure and shear. The use of high strength Galvanized Steel Mesh (GSM) strengthening material has recently gained wide acceptance as well. Both CFRP and GSM have many advantages and some shortcomings. One of their major shortcoming is the lack of ductility. Recently developed Aluminum Alloys (AA) has high ductility and some desirable features that may overcome some of the shortcomings of GSM and CFRP laminates. The major aim of this research is to develop a hybrid ductile strengthening system by combining AA plates with GSM and CFRP laminates to strengthen RC beams in flexure. An experimental program that includes tensile test of six coupon specimens and five flexure tests of beam specimens were conducted. The test results showed the effect of hybrid combination on both strength and ductility of the tested beams and that the newly proposed hybrid systems are promising in improving the flexural behaviour in terms of strength and ductility. The tested hybrid coupons of AA with high density steel mesh (SMH) and AA with CFRP showed an increase in the strain capacity by 6.52 and 4.55 times, respectively compared to that of GSM and CFRP alone. The flexural capacity of the beams strengthened with hybrid laminate increased by around 28% over the control beam, while the beam strengthened with hybrid GSM and AA (SMH+AA) laminate showed an ultimate deflection equivalent to 98.5% of the un-strengthened control beam. The failure modes of the tested beams included debonding and delamination and they were influenced by the type of hybrid system used.

Shear strengthening of reinforced concrete T-beams using CFRP laminates anchored with bent CFRP splay anchors

Abstract: Strengthening of reinforced concrete (RC) structures via external bonded fiber-reinforced polymer (EB-FRP) systems has been widely documented and used. This form of retrofitting has proven to be effective in enhancing flexural and shear capacity of RC beams. However, it is limited due to premature debonding of the FRP laminates prior to utilizing the laminates strength, and typically results in brittle member failure. To overcome this issue, studies have shown that proper anchorage systems mitigate debonding and enables the achievement of higher strengthening levels. Out of the many anchorage systems researched, FRP splay anchors have proven to be effective in enhancing member’s capacity by delaying the laminates debonding. However, the literature is lacking adequate information on the effect of splay anchors on the performance externally strengthened RC beams in shear. Accordingly, five shear deficient RC T-beams specimens were cast and strengthened with CFRP U-wrapped laminates and anchored with CFRP anchors. The parameter investigated in this study is the anchor dowel diameter. Three dowel diameters were tested: 12 mm, 14 mm, and 16 mm. The performance of the anchored U-wrapped specimens in terms of failure modes, load-deflection responses, shear strength, strain in CFRP laminates, and ductility is compared to that of unstrengthened and unanchored strengthened control specimens. Test results showed that CFRP anchors delayed debonding of the U-wraps, improved the shear strength of unanchored U-wraps, and significantly enhanced the ductility of the beam specimens. In addition, it was concluded that anchoring CFRP laminates with CFRP anchors highly utilized the strain attained in CFRP laminates. No clear trend was observed between anchor diameter and ultimate load-carrying capacity of the specimens. Based on the results of this study, anchor dowel diameter of 14 mm was found optimum for an anchor embedment depth of 85 mm.

Experimental and Analytical Investigations of the Use of Groove-Epoxy Anchorage System for Shear Strengthening of RC Beams Using CFRP Laminates.

Abstract: Reinforced concrete (RC) beams strengthened in shear with carbon fiber reinforced polymer (CFRP) laminates as externally bonded reinforcement (EBR) usually fail due to debonding. This paper presents an experimental and analytical investigation on the use of groove-epoxy as an anchorage system for CFRP plates and sheets bonded on both sides of shear deficient RC beams. The aim of this study is to assess the effectiveness of using groove-epoxy in enhancing the shear capacity of RC beams. Nine rectangular RC beams were strengthened with CFRP plates and sheets with groove-epoxy anchorage systems of different groove widths and tested under four point bending. It is observed that the RC beams strengthened with the groove-epoxy anchorage system showed an increase in the shear-strength over the unstrengthened control beam up to 112 and 141% for plates and sheets, respectively. Also, the increase of shear-strength contribution of the groove-epoxy system to that of CFRP without grooves ranged between 30–190% for CFRP plates and between 40–100% for CFRP sheets. Generally, the contributions of groove-epoxy on shear-strength decreased with the increase of groove width. Moreover, shear strength prediction models, based on modifications of the ACI440.2R-17 shear model, were developed by incorporating groove factors as a modifier to the FRP shear-strength contribution. The developed models predicted the experimental shear-strength of the tested RC beams with a good level of accuracy, with an average mean absolute percent error (MAPE) = 3.31% and 6.68%, normalized mean square error (NMSE) = 0.072, 0.523, and coefficient of determination R2 = 0.964, 0.691, for plates and sheets, respectively.

Experimental Investigation and Modeling of the Thermal Effect on the Mechanical Properties of Polyethylene-Terephthalate FRP Laminates

Abstract: Recent advancements in material sciences have led to the development of new fiber-reinforced polymer (FRP) systems that, unlike traditional FRPs, are specifically tailored to have large fra...

Use of Bore-Epoxy Anchorage System with CFRP Sheets for Shear Strengthening of RC Beams

Abstract: Shear failure in reinforced concrete (RC) beams is brittle and undesirable type of failure. This paper investigates the use of bore-epoxy as an anchorage technique for CFRP sheets used as externally bonded shear strengthening reinforcement. Five shear deficient RC beams were cast, one was used as a control (C), one was strengthened with two side CFRP sheets as EBR without anchorage and used as a second control or reference beam (S-EBR) and the remaining three were strengthened using two side CFRP sheets as EBR with bore-epoxy anchorage of different bore diameters (15 mm, 25 mm, 35 mm). The RC beam specimens were tested under four point bending. Load-deflection and load-strain values were recorded. The results showed that the bore-epoxy anchorage system delayed the CFRP sheets de-bonding and increased the shear capacity of the tested specimens by up to 10% compared to the S-EBR control beam and by up to 56% compared to the unstrengthen control beam. The load-deflection curves showed a considerable increase (up to 63.5%) in the deflection of the RC beams strengthened with bore-epoxy anchorage compared to the control beam resulting in a more ductile failure. The failure modes of the tested RC beams varied with the strengthening and the anchorage system used, but they were predominately delamination for the beams strengthened with externally bonded CFRP sheets on bore-epoxy anchorages.

Effect of U-wrap anchors on the strength and ductility of externally bonded RC beams with mortar bonded GSM sheets

Abstract: Strengthening of deficient reinforced concrete (RC) structures had been one of the major concerns of researchers over the past few decades. Thus, new materials are being discovered to ease the process of externally strengthening RC structures. One of the various strengthening materials is Galvanized Steel Mesh (GSM) that is available in different cord densities. High and low cord-density GSM sheets can be externally bonded to RC structures using epoxy adhesives, while only low cord-density GSM sheets can be externally bonded with cement Mortar. In this experimental study, low cord-density GSM sheets (3.15 cords/cm) were bonded with cement mortar to the soffit of RC beams surfaces. A total of four RC beams were cast, three of which were externally strengthened in flexure with GSM sheets and bonded with mortar and the remaining beam was kept as a control un-strengthened specimen. In order to avoid the brittle delamination failure mode, one of the strengthened specimens was anchored with end U-Wrap carbon-fiber reinforced polymer (CFRP) sheets, while the other strengthened specimen was anchored with intermediate U-Wrap CFRP sheets, and the remaining third strengthened specimen was not anchored, to serve as a control strengthened specimen. All specimens were subjected to four-point loading test and the load-deflection response curve of each specimen was recorded. It was observed that flexural strengthening using GSM sheets increased the ultimate-load capacity of strengthened specimens by a range of 41.8 to 51.4 %, when compared to control un-strengthened specimen. While, no strength increase was observed when comparing anchored strengthened specimens to non-anchored strengthened specimens. However, the ductility of end anchored specimens increased by 142.1 and 270% when compared to control and non-anchored specimens, respectively. In addition, the ductility of intermediate anchored specimens increased by 134.1 and 257.3 % when compared to control and non-anchored specimens, respectively. Thus, it can be concluded that GSM laminates if properly anchored can enhance the strength and ductility of RC beams in flexure.

Assessment of Effect of Strain Amplitude and Strain Ratio on Energy Dissipation Using Machine Learning

Abstract: In this study Artificial Neural Networks (ANN) as a machine learning technique is used to predict and assess the effect of strain amplitude and strain ratio on energy dissipated in steel reinforcing bars in reinforced concrete members. The steel reinforcement bars were experimentally tested and were subjected to variable strain amplitudes beyond yield. The developed machine learning model, which is based on Back-Propagation ANN, accurately predicted the experimentally measured dissipated energy. The developed model is then used to deeply assess the effect of a range of strain amplitudes and strain ratios in the amount of energy dissipated at the first cycle, in an average of selected number of cycles and in all cycles, all at different levels of low-cycle fatigue loading of the reinforcement bars. It is concluded that the developed machine learning model can accurately predict the hysteresis energy dissipated in steel bars subjected to low-cycle fatigue load and more importantly it is a viable machine learning tool for deep assessment of the tested specimens with several parameter values that were not covered by the experimental program, but within the domain bounded by the maximum and minimum values of the training data. Based on the prediction and the deep assessment results, several conclusions were drawn.

Behavior of RC Beams externally strengthened with GSM & CFRP sheets

Abstract: This paper examines the behavior of reinforced concrete beams strengthened in flexure with galvanized steel mesh (GSM) sheets and carbon fiber reinforced polymers (CFRP) sheets. A total of three RC beams specimens were examined under a four-point loading test. One beam was strengthened with GSM sheets, another was strengthened with a CFRP sheet with about the same reinforcement ratio to GSM specimen, and the final beam was set aside unstrengthened as a control specimen for comparison. The ultimate load and deflection, and the load-deflection curves for all the tested specimens were recorded. The reported test results revealed that the GSM strengthened specimen increased its ultimate load-carrying capacity by 58% when compared to the control specimen. In addition, the CFRP strengthened specimen ultimate load-carrying capacity increased by 47% when compared to the same control specimen. Thus, the RC beam strengthened with GSM sheets has a larger load-carrying capacity than that of RC beam strengthened with CFRP sheet. Thus, it could be concluded that GSM laminates are a good substitute for CFRP laminates.

Bond stress and behavior of interface between untreated aluminum alloy surface and concrete

Abstract: This paper explores the viability of using aluminum alloy (AA) plates as an externally bonded reinforcement (EBR) material that could overcome some of the shortcomings of the prevailing steel and FRP materials and provides new advantages. A total of 32 prisms with different concrete strengths have been prepared as single shear test specimens with AA plates bonded to the prisms at different lengths using epoxy adhesive. Single shear tests were conducted on the prism specimens until failure. Load-extension and load-strain values were recorded. Bond stress and bond slip values were calculated. Test results have shown that plain untreated AA surface is susceptible to premature debonding; however treating the AA surface, by roughening it, increases its bond strength and ultimate load capacity considerably. Generally, the ultimate load and maximum bond stress increased with the increase of the bonded length and concrete strength, on the average, for the AA roughened surface compared to the AA plain untreated surface, by up to 457%, 327%, respectively. It is also observed that the modes of failure were influenced by the changes in the bonded length, concrete strength and AA surface treatment.