Sadeghian, Pedram

Permanent URI for this collectionhttps://hdl.handle.net/10222/73004

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Open Access
Slender RC Columns Strengthened with a Novel Hybrid Strengthening System of External Longitudinal and Transverse FRPs
(ASCE, 2021-10-01) Khorramian, Koosha; Sadeghian, Pedram
In this study, the performance of slender circular concrete columns strengthened with a novel hybrid system of longitudinally bonded prefabricated fiber-reinforced polymer (FRP) laminates and transverse FRP wrapping is investigated. The novelty of the hybrid system is to improve the load-carrying capacity of slender steel-reinforced concrete (RC) columns under eccentric axial compression by providing high modulus longitudinal carbon FRP (CFRP) laminates through enhancing the flexural stiffness of the slender column and to laterally support the longitudinal laminates by FRP wraps to prevent debonding and local buckling. A total of 6 large-scale circular slender RC columns with a diameter of 260 mm and a length of 3,048 mm were tested under combined axial and flexural loads. The results showed that, for the strengthening of the slender columns, the hybrid system is a more effective strengthening system than wrapping controlling second-order deformations due to the slenderness effect and enhancing the load-bearing capacity. Also, the performance of the system was further investigated using an analytical-numerical model considering the second-order deformations of the slender columns. The model considered nonlinearity in material and confinement effects plus the geometrical nonlinearity via an iterative second-order analysis. The model was verified against experimental data from the current study (hybrid system) and an independent study (wrapping system) and showed a good agreement with the test results. Then, a comprehensive parametric study was conducted to study the effect of various parameters including slenderness ratio, load eccentricity, longitudinal and transverse FRP reinforcement ratios, concrete strength, and column diameter on the performance of slender RC columns strengthened with the hybrid system. It was found that the hybrid strengthening system was more effective for RC columns with high slenderness ratios, high load eccentricities, and low concrete strength.
Open Access
New mechanics-based confinement model and stress–strain relationship for analysis and design of concrete columns wrapped with FRP composites
(Elsevier, 2021-10-01) Khorramian, Koosha; Sadeghian, Pedram
The analysis and design of concrete columns wrapped with fiber-reinforced polymer (FRP) composites require the mathematical equation of stress–strain relationship and the ultimate conditions (i.e., stress and strain) corresponding to the failure of FRP-confined concrete. The ultimate conditions of FRP-confined concrete were mostly developed using empirical methods based on regression analysis of test data obtained from the literature. There is a lack of mechanics-based formulations of the ultimate condition. In addition, from a practical design perspective, despite new advancements in the field of FRP confinement and the availability of sophisticated analysis-oriented and data-driven models, design guidelines and practicing engineers mainly need a single equation for the stress–strain relationship of confined concrete. Thus, in this study, a five-parameter William-Warnke plasticity model was utilized to find a new mechanics-based prediction of the ultimate condition of FRP-confined concrete using an updated database of 788 test data. Moreover, a new optimized stress–strain relationship based on the general expression of the Richard and Abbott equation was developed using 200 complete experimental stress–strain curves from 16 different independent studies. The proposed stress–strain relationship was presented in a single equation for the ease of application and its performance was verified against the experimental curves.
Open Access
Self-healing of Engineering Cementitious Composite with Crystalline Admixture Under Different Exposure Conditions
(Canadian Society for Civil Engineering, 2021-05-26) Mahmoodi, Sina; Sadeghian, Pedram
Self-healing mechanisms in concrete can promote healing of cracks with the material produced through the concrete itself. Engineered Cementitious Composites (ECC) is a special category of HighPerformance Fiber Reinforced Cementitious Composites (HPFRCC) that has been extensively investigated for self-healing purposes. Hydration of unhydrated binders in the matrix and precipitation of calcite were recognized as the two main mechanisms to cause self-healing in ECC. In addition, the high portions of fly ash and Polyvinyl Alcohol (PVA) fibers in the mixture improves the mechanism; however, small crack widths were reported to be healed in this material. The current experimental program aims at determining the extent of self-healing in large cracks by providing favorable conditions. Crystalline Admixture (CA) is also used as a self-healing promoter to increase the crack filling capacity. Three different exposure conditions of air dry, tap water, and sea water were tested using a water permeability (WP) test. The results indicate high sealing capacities in a short period for specimens made with CA and submerged in sea water.
Open Access
Analytical Investigation of Concrete Beam Reinforced with GFRP Rebars Under Low Axial Loading
(Canadian Society for Civil Engineering, 2021-05-26) Velkumar, Senthil Kumar; Sadeghian, Pedram
The main objective of the research presented in this paper was to perform the analytical study to investigate the flexural capacity of the concrete beam reinforced longitudinally and laterally with glass fiber-reinforced polymers (GFRP) bars subjected to low axial compressive load. If the GFRP beam is subjected to compression due to any accidental wind or seismic load, ignoring compression during this condition might not be conservative. To characterize the flexural capacity of the beam under low axial loading – the study was performed considering the specimen with a cross-sectional size of 300 x 400 mm with a concrete grade of 40 MPa and reinforcement ratio of 4%. The analytical model was developed using PTC MATHCAD Prime to carry out the analysis for the sand coated GFRP reinforced concrete beam. From the analytical study results of a beam, the interaction diagram showed that the ultimate bending resistance of the beam decreases with the application of lower load in the range of 5 to 10 % of its axial capacity. Further with the analytical model, a parametric study was performed to investigate the effect of reinforcement ratio, concrete strength, and axial load. As part of this ongoing research, an experimental investigation is further carried out at Dalhousie University to verify the analytical study by testing the full scale GFRP concrete beam under Four-point bending with low axial compressive loads applied at both ends of the beam. During the time of the conference presentation, there will be more test data available to endorse the analytical behavior of the GFRP reinforced concrete beam presented in this paper.
Open Access
Shear and Bending Behaviour of Short-span Steel-reinforced Concrete-filled FRP Tubes with ±55◦ Fiber Orientation
(Canadian Society for Civil Engineering, 2021-05-26) Roy, Subharajit; Sadeghian, Pedram
In this study, steel-reinforced concrete-filled ±55◦ glass-fiber-reinforced-polymer (GFRP) tubes (CFFT) are examined under monotonic loading to understand their shear behaviour. A total of three test specimens with three different nominal pressure ratings (50, 100 and 150 Psi) were tested under three point bending. The pressure ratings are associated with the tube wall thickness. The shear span to depth ratio (a/D) was adopted as 1 for this study. The applied load for each test was measured using a 1.5MN load cell. The deflection at mid-span and the bond-slip measured with the help of a string potentiometer and linear potentiometers. The strains at the compression and tension regions were measured using strain gauges with a gauge length of 6mm. The test results show that the increase in the ultimate strength of the concrete-filled GFRP tubes was due to the increase in the wall thickness. All specimens failed in flexure: initial stretching of the tensile fibers with minor compression fracture development at the top and ultimately failed due to fracture at the tension fibers at mid-span. No significant amount of slip between concrete core, GFRP tube and steel reinforcement were recorded, which shows that the superior compositeness between the components of the test specimens. The importance of this study is to improve the understanding of shear and flexural behaviour of the CFFTs with ±55◦ fiber orientation.
Open Access
Reliability-Based Evaluation of the Stiffness Reduction Factor for Slender GFRP Reinforced Concrete Columns
(Canadian Society for Civil Engineering, 2021-05-26) Khorramian, Koosha; Oudah, Fadi; Sadeghian, Pedram
The stiffness of concrete columns is adjusted by a factor referred to as the stiffness reduction factor or the stability resistance factor when utilizing the simplified second-order moment magnification method for designing slender reinforced concrete (RC) columns. The stiffness reduction factor of 0.75 in ACI 318, CSA A23.3, and CSA S6 was calibrated for steel-RC columns using reliability analysis to account for the variability in concrete strength, steel strength, and applied loads. The upcoming ACI 440 code adopts the same stiffness reduction factor for the design of slender glass fiber-reinforced polymer (GFRP) RC columns when using the moment magnification method. The structural reliability of slender GFRP-RC columns designed using a stiffness reduction factor of 0.75 was not evaluated despite the difference in the GFRP statistical parameters and stiffness characteristics as compared with conventional steel. The objective of this research is to conduct a reliability analysis of slender GFRP-RC columns to evaluate the reliability index associated with the use of the stiffness reduction factor and provide recommendations regarding the optimum value of the factor to meet code target safety limits. Monte Carlo simulation is used to conduct the reliability analysis. Statistical input parameters (distribution type, bias ratio, and coefficient of variation) of GFRP based on an extensive experimental database are utilized in the study. The proposed research presents a necessary step toward quantifying the safety associated with the design provisions proposed in upcoming ACI 440 code.
Open Access
Second-order Analysis of Slender GFRP Reinforced Concrete Columns Using Artificial Neural Network
(Canadian Society for Civil Engineering, 2021-05-26) Khorramian, Koosha; Sadeghian, Pedram; Oudah, Fadi
Analysis of slender concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars is required for design and optimization purposes. Finite element, finite difference, and analytical-numerical tools were developed in literature to accurately predict the response of slender columns reinforced with GFRP bars. The primary challenge with using these tools is the high computational cost required to accurately predict the response of the slender columns due to the material and geometric nonlinearities. Design codes and standards provide a simplified second-order analysis method, called the moment magnification method, to avoid the high computational cost associated with conducting complex nonlinear second-order analyses. The accuracy of the moment magnification method is often compromised when used in analyzing slender elements. Therefore, there is a need for developing efficient and accurate methods of analyzing slender columns, particularly when a large number of analyses is required (e.g., reliability analysis and optimization applications). The objective of this study is to propose an efficient regression-based method to predict the second-order effects on GFRP reinforced concrete (RC) columns by utilizing the artificial neural network (ANN) approach. Nonlinear finite-difference analysis of slender GFRP-RC columns was utilized to generate a training dataset including multiple eccentricity ratios, slenderness ratios, reinforcement ratios, section aspect ratios, and material properties to train the ANN. Preliminary results indicate an average error of less than 1 kN for the second-order analysis based on the trained ANN model. Preliminary reliability analysis of slender GFRP-RC columns indicates that using the developed ANN method yields a significant reduction in the computational cost as compared with existing finite difference methods.
Open Access
Three-point Bending of Sandwich Beams with FRP Facing and PP Honeycomb Core
(Canadian Society for Civil Engineering, 2021-05-26) Kassab, Raghad; Sadeghian, Pedram
In this study, two sets of sandwich beams were tested in three-point bending. The sandwich panels were fabricated in a wet layup process. The facing component was made of either polyethylene terephthalate (PET) fiber-reinforced polymer (FRP), or glass fiber reinforced polymer (GFRP). The facing thickness was 3 mm for both PET FRP and GFRP. Polypropylene (PP) in honeycomb structure form, with a density of 80 kg/m3, was used as the core component among all tested beams. The sandwich beam dimensions were consistent at 1,200 mm length, 78 mm width, and 82 mm height. While testing each sandwich beam, the applied load, overall beam deflection, and facing strain were captured at mid-span. The resulting data were processed to produce load-deflection, moment-curvature, and load-strain diagrams. At peak load, bond failure between the walls of the cylindrical tubes within the honeycomb structure occurred; therefore, the failure mode for all tested sandwich beams was attributed to shear failure. The load-deflection relation was nonlinear in both sets, which was derived from the thermoplastic component (PET FRP facing and/or PP core). A nonlinear analytical model was developed and compared to the experimental testing data. The method used for experimental testing and analytical modelling was outlined in this study. The experimental matrix, testing results, and analytical model indicated that the nonlinearity of the sandwich beam's load-deflection relation stems from the facing and core components. In contrast, the nonlinearity of moment-curvature and load-strain relation stems solely from the facing component.
Open Access
Tensile Properties of PET FRP with Bio-resin Polymer
(Canadian Society for Civil Engineering, 2021-05-26) Kassab, Raghad; Sadeghian, Pedram
This study analyses the mechanical behaviour of polyethylene terephthalate fiber-reinforced polymer (PET FRP) made with a bio-resin polymer matrix. The utilized bio-resin is furfuryl alcohol mixed with phthaloyl dichloride catalyst; this selection of resin type, catalyst type, catalyst dose, and curing time was made based on previous investigations. A sheet of PET FRP composite was fabricated following the wet lay-up method. The composite sheet was cut into six coupons (three in the longitudinal direction and three in the transverse direction). The coupons were then tested in uniaxial tension, and the stress-strain relationship was extracted. The stress-strain relationship of the bio-resin PET FRP was found to be nonlinear and consisted of three main stages of linear curves. The elastic modulus at each stage was derived along with the coupon's average yielding stress and ultimate strength. By deriving and presenting the mechanical performance of this newly developed FRP, this study aims to determine whether the composite could be a potentially sustainable alternative to conventionally used FRPs. The two sets of tested coupons had equal strain capacity–which is four times the strain capacity of glass fiber-reinforced (GFRP) composite. Conversely, longitudinally cut coupons had double the strength capacity of transversely cut coupons.
Open Access
Hybrid system of longitudinal CFRP laminates and GFRP wraps for strengthening of existing circular concrete columns
(Elsevier, 2021-05-15) Khorramian, Koosha; Sadeghian, Pedram
This paper presents an investigation on the behavior of a strengthening system of longitudinal premanufactured carbon fiber-reinforced polymer (CFRP) laminates and transverse glass FRP (GFRP) wrapping for strengthening of concrete columns (here after is called a hybrid system). The idea behind using the longitudinal CFRP strips was to enhance the system by increasing the flexural stiffness of the column which is effective for the strengthening of slender columns and eccentrically loaded columns where additional flexural stiffness is required for buckling control. The study was conducted experimentally in two phases under monotonic loads. Phase I was conducted on small-scale concrete specimens to characterize the hybrid system and phase II was conducted to verify the effectiveness of the hybrid system for the strengthening of large-scale slender concrete columns. In phase I, it was observed that by applying GFRP wraps on longitudinal CFRPs, the failure mode of CFRP laminates changed from buckling/debonding to crushing to achieve the full capacity of the system. However, as expected, test results in phase I showed that the usage of wrapping without longitudinal CFRP laminates was more effective than the proposed hybrid system for the strengthening of small scale concrete columns subjected to pure axial loading. For slender columns in phase II, the hybrid system enhanced the wrapping system by adding 52%, 105%, and 94% gain for axial capacity, flexural capacity, and lateral displacement at peak load, respectively, by altering the load–deflection curve of the slender columns to achieve a higher performance level.
Open Access
Post-impact residual strength and resilience of sandwich panels with natural fiber composite faces
(Elsevier, 2011-06-01) Betts, Dillon; Sadeghian, Pedram; Fam, Amir
In this paper, the post-impact residual flexural behavior of sandwich panels with flax fiber-reinforced polymer (FFRP) faces and polyisocyanurate (PIR) foam cores is investigated experimentally. The faces were manufactured using a wet lay-up procedure with a balanced bidirectional 2x2 twill flax fiber fabric and a bio-based epoxy with a bio-content of 30%. Each specimen was 1200 mm long x 75 mm wide x 80 mm thick. The main parameters in the study were the face thickness (one, two or three FFRP layers, representing core-to-skin thickness ratios of approximately 54, 28 and 20) and core density (32, 64 or 96 kg/m3); a total of nine combinations. In this study, 27 specimens (three specimens for each combination) were tested under impact loads and the surviving specimens were tested under monotonic three-point bending. Each of the three identical specimens was tested under different impact condition, namely 100%, 75% and 50% of the energy resistance of an intact specimen, with the last two impacted 50 times. The results of the post-impact residual flexural tests were compared to three-point bending tests of intact specimens. The beams demonstrated remarkable resilience in that the impact events did not have a negative effect on their flexural strength or stiffness. In fact, those tested at higher energy levels exhibited a slight increase in strength after impacts. This shows their suitability for use in infrastructure applications such as building cladding panels, flooring and roofing as they retain their strength and stiffness even after multiple impacts.
Open Access
Experimental and analytical investigations of the flexural behavior of hollow ±55° filament wound GFRP tubes
(Elsevier, 2021-02-01) Betts, Dillon; Sadeghian, Pedram; Fam, Amir
The behavior of ±55° filament wound glass fiber-reinforced polymer (GFRP) tubes under flexural loading was examined experimentally and analytically. A total of 15 tubes were tested under four-point bending. The main test parameter was the ratio of inner diameter (D) to wall thickness (t), (D/t) ratio. The inner diameters of the tubes were 76 and 203 mm, while their wall thicknesses varied from 1.7 to 6.7 mm, giving D/t ratios of 20–75. All tests exhibited a nonlinear load-deflection response and a similar failure mechanism, namely a progressive tensile weakening until a sudden compression failure occurs. The tests showed that the moment capacity of the tubes increased with both tube diameter and nominal pressure rating. The tubes also exhibited a prolonged post-peak behavior. An iterative cross-sectional analytical technique was developed to model both the moment-curvature and load-deflection behavior of the tubes. The model accounts for the potential failure due to local buckling as well as compression failure and was shown to accurately predict the behavior of the tubes. A parametric study was performed to find the moment capacity of tubes with ratios beyond the range tested and was used to establish a simple design equation for moment capacity.
Open Access
Experimental Investigation of Short and Slender Rectangular Concrete Columns Reinforced with GFRP Bars under Eccentric Axial Loads
(ASCE, 2020-12-01) Khorramian, Koosha; Sadeghian, Pedram
In this paper, the experimental behavior of short and slender concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars under eccentric compression loading is presented. A total of 10 large-scale concrete column specimens with a rectangular cross section (205 × 306 mm) were tested under a single curvature condition with equal load eccentricities at both ends of the column. Four slenderness ratios of 16.6, 21.5, 39.7, and 59.5 and two reinforcement ratios of 2.78% and 4.80% were considered. The results showed that no crushing of GFRP bars occurred prior to concrete spalling. The columns were able to sustain load, moment, and deformation after the concrete spalling up to the crushing of GFRP bars in compression. The latter was attributed to the contribution of GFRP bars in compression. An analytical model was also adopted to predict the behavior of the test specimens and to evaluate the effect of load eccentricities beyond the one considered in the experimental program. Also, the flexural stiffness and moment magnification factor obtained from the experimental program were compared with those calculated using equations from the literature. The results showed that most of the equations underestimated the flexural stiffness and the magnified moment.
Open Access
Axial Behavior of Innovative Sand-Coated GFRP Piles in Cohesionless Soil
(ASCE, 2020-10-01) Almallah, Ahmad; El Naggar, Hany; Sadeghian, Pedram
In pile construction, conventional pile materials such as concrete, steel, and wood are frequently subject to soil–substructure interaction durability problems due to corrosion and deterioration. Fiber-reinforced polymers (FRPs) provide a potential alternative to eliminate the durability problems of conventional materials. This paper describes the results of an experimental study on the effect of the interface on the behavior of glass FRP (GFRP) piles jacked into dense sand under axial loads. The aim of this study is to introduce an innovative GFRP piles in cohesionless soil through coating its surface with silica sand to enhance the pile interface behavior. The experimental program investigates seven small-scale GFRP piles with different surface roughness and a reference steel pile used as a control. The surface of five of the seven GFRP piles was coated with silica sand, and the performance of the GFRP piles was compared with that of the control steel pile. The results of the pile load tests were analyzed by using three different commonly used methods to determine the ultimate pile load capacities. The results showed that the innovative mechanism of coating GFRP piles with silica sand enhanced the interface friction of the GFRP piles in sand under axial loads and increased the ultimate pile load capacity in comparison with that of the control piles.
Open Access
Numerical Modeling of the Lateral Behavior of Concrete-Filled FRP Tube Piles in Sand
(ASCE, 2020-08-01) Jafarian Abyaneh, Mostafa; El Naggar, Hany; Sadeghian, Pedram
In this study, a numerical model is developed to study concrete-filled FRP tube (CFFT) pile behavior and interactions with foundation soil under lateral loading. The model, based on nonlinear finite element analysis (NFEA) and the disturbed state concept (DSC), considers material and geometrical nonlinearity as well as the interface of soil with fiber-reinforced polymer (FRP). Furthermore, the structural and geotechnical performance of the interface of soil and CFFT pile is studied by utilizing 3D finite element models (FEMs) of full-scale field tests conducted during the construction of a highway bridge on Route 40 in Virginia. Based on deflection along the length of the pile, the model results are in good agreement with the experimental data. To investigate the effects of various parameters on the behavior of CFFT piles and local buckling, a parametric study was also performed on different geometrical and material properties, including the pile diameter to length ratio, FRP tube thickness, concrete strength, and soil properties. It was found that the surrounding soil and length to diameter ratio exerted the most noticeable influence, followed by concrete strength. The FRP thickness had the least impact on the results.
Open Access
1g model tests of vertically loaded GFRP piles
(Canadian Geotechnical Society (CGS), 2019-09-29) Almallah, Ahmad; El Naggar, Hany; Sadeghian, Pedram
The conventional piling materials (i.e., concrete, steel, wood) are more likely to have durability problems (i.e., corrosion, degradation, deterioration) in harsh environments and offshore construction. Fiber-reinforced polymer (FRP) was found to be a potential alternative to the conventional materials due to its high corrosion resistance which results in higher durability and longer life span. In Geotechnical engineering, more data is required to adopt this new composite material in the piling industry. This paper presents a small-scale experimental study on Glass FRP (GFRP) pile under axial loads and the results were compared to a steel reference pile. The results showed a slightly better performance for GFRP pile under axial loads compared to steel pile due to its higher friction resistance in sand.
Open Access
Simplified Material Model for Concrete Containing High-Content of Tire-Derived Coarse Aggregate under Compression Loading
(NRC Press, 2020-07-31) El Naggar, Abdelmoneim; El Naggar, Hany; Sadeghian, Pedram
The flexible properties of the shredded rubber tires give rubberized concrete desirable properties such as lower relative density, and better dampening ability, higher toughness, and improved deformability resulting in an enhanced dynamic performance. Limited work has been done in modeling these effects. In this study, natural coarse aggregates in concrete mixes were replaced by volume by shredded tires up to 100% replacement ratios following 10% increments. Compression tests were conducted to investigate the effects shredded tires on the mechanical properties of concrete. As expected, the results showed a decrease in the compressive strength and the elastic modulus of the concrete as the replacement ratio increase. Due to compatibility, strain at peak values increased and the integrity of the concrete after failure was enhanced. Models describing the effects shredded tires have on the mechanical properties of the concrete were developed and validated against experimental data from various researchers.
Open Access
Recycled gypsum powder from waste drywalls combined with fly ash for partial cement replacement in concrete
(Elsevier, 2020-07-18) Hansen, Sarah; Sadeghian, Pedram
Recent developments towards sustainable infrastructure have motivated more environmentally conscious construction practices. The concrete industry is known to have a large carbon footprint, which can be decreased by reducing the amount of cement required, thereby reducing the demand for virgin material production and its associated carbon emissions. Excessive waste accumulation is another notable environmental issue, and gypsum drywall is a major source of construction and demolition waste, typically disposed of unsustainably in landfills. To assess the recycling potential of gypsum waste in concrete, this research utilized gypsum in quantities above those typically considered to partially replace cement. This experimental study was conducted to investigate the mechanical performance of concrete with recycled gypsum powder (hereafter called gypsum) combined with fly ash as supplementary cementing materials. A total of 15 different concrete mixes were prepared containing 0, 5, 10, 15, and 20% gypsum and 0, 25 and 50% fly ash as partial replacement for cement. Superplasticizer was used to regulate the mixture consistency, as adding gypsum was found to dehydrate the mix. Nine identical specimens per mix were cast into 200 mm x 100 mm cylindrical molds, and three of each were tested for compressive strength after curing in a moist room for 7, 28 and 90 days. The study revealed that using only gypsum as a partial cement replacement was disadvantageous to strength, however combining fly ash and gypsum was beneficial at later ages. After 90 days, all mixes containing 50% fly ash revealed that additional gypsum did not have negative effects on the compressive strength. The presented research suggests that the novel application of recycled gypsum in concrete is achievable from a structural perspective, and including fly ash is essential. In order to be considered a practical alternative to traditional concrete, further investigation is recommended.
Open Access
Experimental and Analytical Behaviour of Sandwich Composites with Glass Fiber-reinforced Polymer Facings and Layered Fiber Mat Cores
(SAGE, 2020-07-06) MacDonnell, Lauren; Sadeghian, Pedram
This paper presents the results of experimental and analytical studies on the behaviour of sandwich beams fabricated with layered cores and glass fiber-reinforced polymer (GFRP) composite facings. The GFRP facings were fabricated using a unidirectional fiberglass fabric and epoxy resin, and the cores were fabricated using a thin non-woven continuous-strand polyester fiber mat with a thickness of 4.1 mm. A total of 30 sandwich beams with the width of 50 mm were prepared tested with five varying core configurations including cores made with one, two, or three layers of the fiber mat core and with or without the inclusion of intermediate GFRP layers. The specimens were tested up to failure under four-point bending at two different spans to characterize flexural and shear properties of the specimens. Two types of failure were observed, namely crushing of the compression facesheet and core shear. The load-deflection, load-strain, and moment-curvature behaviour were analyzed and using the results the flexural stiffness, shear stiffness, and core shear modulus were calculated. An analytical model was also developed to predict load-deflection behaviour and failure loading of sandwich specimens with varying core layouts. After verification, the analytical model was used for a parametric study of cases not considered in the experimental study, including additional GFRP and fiber mat core layers. It was shown that additional fiber mat core layers and the inclusion of intermediate GFRP layers can increase the strength and overall stiffness of a sandwich beam, while additional GFRP layers can only increase the overall stiffness of the system. The analytical model can be used to optimize the configuration of layered sandwich composites for cost effective rehabilitation techniques of culverts, pipelines, and other curved-shape structures where a thin, flexible core is needed to accommodate the curvature of the existing structure.
Open Access
Hybrid FRP Strengthening of Slender Steel Members for Buckling Control
(ASCE, 2020-10-01) Sadeghian, Pedram; MacEachern, Daina
In this paper, the structural properties and behaviour of slender steel members strengthened against buckling by a hybrid system of fibre-reinforced polymer (FRP) shells filled with self-consolidating grout (SCG), in the form of buckling restrained bracing (BRB), were investigated. The goal of the hybrid system is to increase the load carrying capacity of the slender member to reach the yielding load of the steel core through the addition of lateral support. A total of 36 small-scale specimens (27 strengthened specimens and 9 plain 25.4 mm×6.35 mm steel cores) were prepared and tested in compression. Strengthened specimens were prepared with three different FRP shell lengths (300, 600, and 900 mm) and three outer shell diameters (41, 53, and 65 mm). A lubricant was applied to the steel core to allow the steel core to carry the majority of the axial load independently. The contribution of each component of the hybrid system to the overall load carrying capacity was also calculated. The steel core was found to carry on average 86% of the load at yielding with the grout and FRP carrying only 13.5% and 0.5%, respectively. A simple linear elastic model was created to predict the failure mode of the hybrid system that can also be used to design an optimized system. The model accurately predicted the failure mode for all 27 reinforced specimens. Overall, provided the hybrid FRP strengthening system was sufficiently sized, the system was successful in changing the failure mode of the steel core from buckling to yielding.

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