Allan Manalo

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.

Characterisation of recycled mixed plastic solid wastes: Coupon and full-scale investigation.

In Australia, the plastic solid waste (PSW) comprises 16% by weight of municipal solid waste but only about one-fourth are recycled. One of the best options to increase the recycling rate of mixed PSW is to convert them into products suitable for construction. However, a comprehensive understanding on the mechanical behaviour of mixed PSW under different loading conditions is important for their widespread use as a construction material. This study focuses on investigating the mechanical behaviour of recycled mixed PSW containing HDPE, LDPE and PP using coupon and full-scale specimens. From coupon test, the strength values were found to be 14.8, 19.8, 20, 5.6MPa in tension, compression, flexure and shear respectively, while the modulus of elasticity are 0.91, 1.03, 0.72GPa in tension, compression and flexure respectively. The coefficient of variance of the measured properties for coupon and fullscale specimens was less than 10% indicating that consistent material properties can be obtained for mixed PSW. More importantly, the strength properties of mixed PSW are comparable to softwood structural timber. The flexural behaviour of full-scale specimens was also predicted using fibre model analysis and finite element modelling. Comparison showed that using coupon specimens properties, the flexural behaviour of the full-scale specimens can be predicted reliably which can eliminate the costly and time consuming arrangements for full-scale experimental tests.

Bond stress-slip behavior: case of GFRP bars in geopolymer concrete

The use of geopolymer concrete reinforced with fiber-reinforced polymer (FRP) bars is anticipated to address the concerns on the usage of traditional reinforced concrete structures, such as the corrosion of internal steel reinforcement, costly repair and rehabilitation, and development of sustainable infrastructures. To gain wide acceptance in the construction market, the bond between geopolymer concrete and the FRP bar should be investigated first because it is a critical factor that influences the behavior of structures, specifically its strength and long-term durability. In this study, the bond performance of sand-coated glass fiber-reinforced polymer (GFRP) bars into geopolymer concrete with a compressive strength of 33 MPa was investigated under a direct pullout test. The effects of parameters such as bar diameter (12.7, 15.9, and 19.0 mm) and embedment length (5, 10, and 15 db, where db is the bar diameter) were evaluated. The results showed that the maximum average bond stress obtained is around 23 MPa. As GFRP bar diameter increases, the average bond stress decreases. Similarly, the average bond stress decreases as the bond length becomes longer. The specimens with shorter embedment length failed because of pullout of the bars, whereas those with longer embedment lengths failed because the concrete split. The results further revealed that the geopolymer concrete reinforced with GFRP bars have a bond strength similar to that of steel-reinforced geopolymer concrete. Finally, bond-slip models for the ascending branch up to maximum bond stress of the bond-slip curves for GFRP bars and geopolymer concrete were proposed.

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.

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.

Behaviour of hollow pultruded GFRP square beams with different shear span-to-depth ratios

It is important to determine accurately the elastic properties of fibre-reinforced polymer composites material, considering that their member design is often governed by deflection rather than strength. In this study, the elastic properties of the pultruded glass fibre-reinforced polymer square sections were evaluated firstly using full-scale with different shear span to depth (a/d) ratios and tested under static four-point bending. Back calculation and simultaneous methods were then employed to evaluate the flexural modulus and shear stiffness and were compared with the results of the coupon tests. Secondly, the full-scale beams were tested up to failure to determine their capacity and failure mechanisms. Finally, prediction equations describing the behaviour of the pultruded glass fibre-reinforced polymer square beams were proposed and compared with the experimental results. The results indicate that the back calculation method gives more reliable values of elastic properties of glass fibre-reinforced polymer profiles. In addition, the behaviour of the beams is strongly affected by the a/d ratios. The shear was found to have a significant contribution on the behaviour of beams with lower a/d ratios while the flexural stress played a major part for higher a/d ratios. The proposed equation, which accounts for the combined effect of the shear and flexural stresses, reasonably predicted the failure load of pultruded glass fibre-reinforced polymer square beams.

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.

Effects of diameter on the durability of glass-fiber-reinforced-polymer (GFRP) bars conditioned in alkaline solution

AbstractCurrent standards do not consider the diameter of glass fiber-reinforced polymer (GFRP) bars used as internal reinforcement in concrete structures to be a factor influencing bar durability....

Behavior of fiber-reinforced composite beams with mechanical joints

The fundamental behavior of the fiber-reinforced composite beams with mechanical joints was examined using coupon and full-scale specimens. The effect of applied bolt torque, the contribution of adhesive bonding, and the number and configuration of bolts on the load capacity and failure mode of the double-lap bolted joints were investigated. The results showed that at different levels of applied bolt torque (10, 15, 20 and 25 N-m), little friction resistance developed. A slight increase on the load capacity was however observed with increasing tightening torque. On the other hand, the mechanical joints using bolts accompanied by adhesive bonding provided resistance against slipping. The flexural behavior of full-scale fiber composite beams with joints at midspan connected with bolts alone and a combination of bolts and epoxy was further examined. The beams connected using bolts and epoxy exhibited the same strength and stiffness as the beams without joints while using bolts alone resulted to a beam with only 65% of the stiffness of those without joints. This showed that the combination of bolts and epoxy adhesives could provide a reliable connection method for fiber-reinforced composite beams.