Thiru Aravinthan

Flexural Behavior of Two-Span Continuous Prestressed Concrete Girders with Highly Eccentric External Tendons

[Abstract]: It is generally known that the flexural strength of beams prestressed with external tendons is comparatively lower than that of members with internal bonded tendons. One possible method of enhancing the flexural strength of such beams is to place the tendons at high eccentricity. To obtain an insight into the flexural behavior of beams with highly eccentric tendons, an experimental investigation is conducted on single-span and two-span continuous beams. The test variables include external tendon profile, loading pattern on each span, casting method, and confinement reinforcements. It is found that continuous girders with linearly transformed tendon profiles exhibit the same flexural behavior irrespective of tendon layout. The presence of confinement reinforcement enhances the ductility behavior but does not increase the ultimate flexural strength. The degree of moment redistribution is affected by the tendon layout and the loading pattern on each span. The results of the experimental investigation are discussed in this paper.

State-of-the-art review on FRP sandwich systems for lightweight civil infrastructure

AbstractFiber-reinforced polymer (FRP) sandwich systems as primary load-bearing elements are relatively new concepts in lightweight civil infrastructure. These systems offer a combination of light weight, high strength, thermal insulation for some types, and service-life benefits. Recent developments and applications have demonstrated that these composite systems have emerged as a cost-effective alternative, especially when each material component is appropriately designed. Still, some issues and challenges need to be addressed if FRP systems are to gain widespread use in civil infrastructure. This paper provides an overview of the state-of-the-art research, development, and applications of FRP sandwich systems. It also identifies the challenges and future opportunities for the broad use of these advanced systems in civil engineering and construction.

Behavior of Full-Scale Railway Turnout Sleepers from Glue-Laminated Fiber Composite Sandwich Structures

An experimental study on the flexural and shear behavior of the full-scale glue-laminated composite sandwich beams in three different layouts was conducted to evaluate the suitability of this construction system for railway turnout sleepers. The building block of this innovative beam is a novel composite sandwich structure made up of glass fiber composite skins and modified phenolic core material that has been specifically developed for civil engineering applications. The sandwich beam is produced by gluing layers of fiber composite sandwich structure together in flatwise (horizontal) and in edgewise (vertical) orientations. The glued sandwich beams with edgewise laminations presented appropriate strength and stiffness for replacement turnout timber sleeper. The mechanical properties of these glue-laminated sandwich beams are comparable with the existing timber turnout sleepers, demonstrating that the innovative composite sandwich beam is a viable alternative sleeper material for railway turnouts. From this study, it is concluded that the glue-laminated composite sandwich structures have the potential to be used for replacement railway turnout sleepers. An enhanced understanding of the behavior of fiber composite sandwich structures for potential civil engineering applications is also an outcome of this investigation.

Thermo-mechanical properties of epoxidized hemp oil-based bioresins and biocomposites

Novel epoxidized hemp oil-based biocomposites containing jute fibre reinforcement were produced at the Centre of Excellence in Engineered Fibre Composites (CEEFC) owing to the need to develop new types of biobased materials. Mechanical properties (tensile, flexural, Charpy impact and interlaminar shear), thermo-mechanical properties (glass transition temperature, storage modulus and crosslink density) and moisture-absorption properties (saturation moisture level and diffusion coefficient) were investigated and compared with samples containing commercially produced epoxidized soybean oil and a synthetic bisphenol A diglycidyl ether-based epoxy control, R246TX cured with a blend of triethylenetetramine and isophorone diamine. Scanning electron microscopy was also performed to investigate the fibre–matrix interface. Epoxidized hemp oil-based samples were found to have marginally superior mechanical, dynamic mechanical and similar water-absorption properties in comparison to samples made with epoxidized soybean oil bioresin; however, both sample types were limited to bioresin concentrations below 30%. Synthetic epoxy-based samples exhibited the highest mechanical, dynamic mechanical and lowest water-absorption properties of all investigated samples. This study has also determined that epoxidized hemp oil-based bioresins when applied to jute fibre-reinforced biocomposites can compete with commercially produced epoxidized soybean oil in biocomposite applications.

Composite Behaviour of a Hybrid FRP Bridge Girder and Concrete Deck

This paper involves experimental investigation onto the composite behaviour of a hybrid FRP bridge girder with an overlying concrete deck. Two types of shear connections were investigated: epoxy resin adhesives alone and epoxy resin combined with steel u-bolts. The results showed that the steel u-bolts combined with epoxy resin provided a more effective connection; hence a full-size specimen was prepared based on this result. Four-point bending test was carried out to determine the behaviour of a full-scale composite hybrid FRP girder and concrete deck. The composite action resulted to a higher stiffness and strength with the hybrid FRP girder exhibiting higher tensile strain before final failure. There was a significant decrease in the compressive strain in the top flange of the FRP girder thereby preventing the sudden failure of the beam. The composite beam failed due to crushing of the concrete followed by shear failure in the top flange and web of the FRP girder.

Processing and characterization of 100% hemp-based biocomposites obtained by vacuum infusion

Novel biocomposites made of an acrylated epoxidized hemp oil based bioresin reinforced with random hemp fiber mat were manufactured by the vacuum infusion technique. Mechanical properties (tensile, flexural, Charpy impact and interlaminar shear), dynamic mechanical properties (glass transition temperature, storage modulus and crosslink density) and moisture absorption properties (saturation moisture level and diffusion coefficient) were investigated and compared with samples manufactured under the same conditions but using a commercial synthetic vinylester resin as the polymeric matrix. Results showed that the 100% biocomposites mechanical performance is comparable to that of the hybrid composites made with the synthetic resin. Moisture absorption tests showed that acrylated epoxidized hemp oil based samples displayed both higher diffusion coefficient and saturation moisture content; however, fiber reinforcement was the dominant transfer mechanism. Vinyl ester based samples were found to have higher storage modulus, glass transition temperature and crosslink density than acrylated epoxidized hemp oil samples.

A review on the characteristics of gomuti fibre and its composites with thermoset resins

Gomuti fibre is obtained from Arenga pinnata tree and is known with other names such as sugar-palm fibre, gomutu, ijuk, serat aren and black fibre. This article presents a review on the physical, mechanical, chemical and thermal properties of gomuti fibre in comparison with other common natural fibres. Furthermore, this article reviews the mechanical properties of gomuti fibre composites with thermoset polymer resins based on the existing published literature. It is observable that gomuti fibre has a close similarity to coir fibre in its physical and mechanical properties than the other natural fibres. It has the characteristics of lower density, strength and modulus, but higher elongation. The composites with gomuti fibre also exhibit properties similar to coir fibre composites.

Experimental Investigation of HFRP Composite Beams

This paper presents the development of composite beams using hybrid CFRP/GFRP (HFRP) I-beam and Normal Strength Concrete (NSC) slab and precast Ultra-High Performance fiber reinforced Concrete (UHPFRC) slab. UHPFRC has high strength and high ductility allowing for a reduction in the cross-sectional area and self weight of the beam. A number of full-scale flexural beam tests were conducted using different dimensions of slab and with/without epoxy bonding between the slab and HFRP I-beam. The test results suggested that the flexural stiffness of composite beams with bolted and bonded shear connection is higher than that with bolted-only shear connection. Delamination failure was not observed in the compressive flange of the HFRP I-beam and the high tensile strength of CFRP in the bottom flange was effectively utilized with the addition of the UHPFRC slab on the top flange.

Thermo-mechanical properties of acrylated epoxidized hemp oil based biocomposites

In this study, novel acrylated epoxidized hemp oil bioresin was used in the manufacturing of jute fibre reinforced biocomposites. The 100% biocomposite laminates were characterised in terms of mechanical properties (tensile, flexural, Charpy impact and interlaminar shear), thermo-mechanical properties (glass transition temperature, storage modulus and crosslink density) and water absorption properties (saturation moisture level and diffusion coefficient). Comparisons with the equivalent synthetic vinylester resin based jute fibre reinforced biocomposite panels were performed. Scanning electron microscopic analysis confirmed panel samples containing acrylated epoxidized hemp oil to display improved fibre–matrix interfacial adhesion compared with the vinylester resin based samples. Furthermore in terms of mechanical properties acrylated epoxidized hemp oil based biocomposites compared favourably with those manufactured from vinylester resin synthetic resin. Dynamic mechanical analysis found acrylated epoxidized hemp oil based biocomposites to have lower glass transition temperature, storage modulus and crosslink density than vinylester resin based samples. Increasing acrylated epoxidized hemp oil content resulted in a marginal increase in saturation moisture content and diffusion coefficient.

Mechanical properties characterization of the skin and core of a novel composite sandwich structure

This study has investigated the mechanical properties of the constituent materials of a novel structural composite sandwich panel developed for structural applications. Properly designed and carefully conducted experiments using coupon specimens following ISO and ASTM test standards were performed to characterize the flexural, tensile, compressive and shear properties of the fiber composite skins and the modified phenolic core of the composite sandwich structure. As a general behavior, the glass fiber composite skins behaved linearly elastic up to failure in both tension and compression with the tensile strength much higher than the compressive strength. The modified phenolic core behaved linearly elastic in tension but exhibited non-linear behavior in compression. The modified phenolic core material exhibited higher strength and modulus in shear and compression compared to the traditional core material systems. The improved mechanical properties of the core structure combined with the high-strength and lightweight glass fiber composite skins suggest a high potential of the novel composite sandwich panel for structural applications. Furthermore, the results of this study provide an understanding of the fundamental behavior of the constituent materials of a novel sandwich structure providing a base knowledge from which further research could continue.