Behaviour of composite sandwich panels bonded with epoxy polymer matrix for railway sleepers

The Australian railway industry spends millions of dollars every year in replacing poor condition railway sleepers in order to maintain the track quality and ensure a safe track operation. It is estimated that more than 2.5 million timber sleepers per year are required for railway track maintenance. Over the last decade, it has been increasingly difficult to get suitable quality hardwood to keep up with the demand for railway maintenance. Moreover, the global environmental impact due to felling huge number of trees for manufacturing timber sleepers is a major concern. In recent years, significant efforts have been provided towards the development of polymer composite sleeper alternatives to replace deteriorating timber sleepers. Despite their potential, the uptake of polymer composite sleepers has been extremely limited because of the high production cost of these technologies. An improved understanding of composite sleeper technology such that improved designs and effective material usage needs to be developed to reduce the overall cost of production. This study focused on investigating the behaviour of a fibre composite railway sleeper manufactured from composite sandwich panels and the panels are bonded together with epoxy polymer matrix. An intensive characterisation of the epoxy polymer matrix and composite sandwich panels was conducted to determine the effective usage of these materials for railway sleepers. The effect of resin-to-filler ratio on the thermal, physical, mechanical and durability properties of the epoxy polymer matrix were evaluated. Filler materials composed of fire retardant filler, hollow microsphere and fly ash were increased from 0% to 60% in the epoxy based matrix. The results showed that epoxy-based polymer mixes containing 30% to 50% fillers by volume provided a good balance of thermal, physical, mechanical, and durability properties suitable for coating the composite railway sleepers. The capacity of single composite sandwich beam in resisting bending and shear forces were then determined by testing them in horizontal and vertical orientations and with a shear span-to-depth ratio varying between 0.5 and 12. The results showed that the horizontal sandwich beams performed better under bending while vertical sandwich beams were more effective in resisting shear. It was also found that the beam orientation has more influence on the load carrying capacity and stiffness properties than changing the shear span-to-depth ratio. The structural integrity and composite action between the sandwich panels and epoxy polymer matrix were investigated. The effects of binder properties, bond length, bond thickness and bond width were investigated to evaluate the bond behaviour of a composite sandwich panel and epoxy polymer matrix. The results indicated that the bond thickness has the greatest influence on the bond strength followed by the properties of polymer matrix, bond length and bond width. A bond thickness of 5 mm, bond length of 70 mm and using polymer matrix with 40% filler and 60% resin (by volume) can eliminate failure in the glue line and promote failure in the sandwich panels. Using these bond parameters, full-scale layered sandwich beams were manufactured and their structural behaviour was evaluated under four-point bending and asymmetrical beam shear tests. Results showed that the binding of sandwich panels using epoxy polymer matrix can prevent the wrinkling and buckling of the fibre composite skins as well as the indentation in the phenolic core. This concept increased the bending and the shear strength of the vertically oriented beams by as much as 25% and 100%, respectively, compared to single sandwich beams. Using the same amount of material, the vertically layered beams exhibited similar bending strength and 50% higher shear strength but only 7% lower effective modulus of elasticity compared to horizontally layered beams. More importantly, the layered sandwich beams were found to have strength and stiffness similar to the hardwood timber. The optimal design of layered sandwich beams for railway sleepers and the performance evaluation under static loads were conducted as the last study. The optimal shape of sleeper under quasi-static load was obtained using topology optimisation. The optimal sleeper shape requires only 50% volume of materials compared to a rectangular timber sleeper. Moreover, the rail seat and centre bending moments, shear strength, screw holding capacity, and electrical resistance of optimised composite sleeper are higher than the traditional hardwood timber and exceed considerably the performance requirements for a railway sleeper. The handling, installing and fastening system of this composite sleeper were similar to timber and require the same equipment and machineries. A total of 50 sleepers have been installed on a trial basis in the Southern line rail track at Nobby, Queensland, which are performing very well and are expected to outperform its design life. An in-depth understanding of the behaviour of a new type of composite sleepers made from layered sandwich panels bonded by epoxy polymer matrix was the significant outcome of this study. The experimental data, simplified theoretical models and finite element simulations derived from this study can be used as important tools for a safe design of composite railway sleepers. The optimal sleeper shape proposed in this study can provide a cost-effective alternative to timber sleepers in a mainline track to decrease railway track maintenance, and provide a totally recyclable and sustainable sleeper technology

Effect of beam-column joint stiffness on the design of beams

The infrastructure should be design in such a way that ensures safe, serviceable, durable and economic construction. For the beam design, the joints between beam and column is traditionally considered a rigid connection which actually not fully rigid and therefore accounted an extra moment leading to structural over-design and subsequently higher cost of beam construction. This paper proposed a theoretical model for moment and deflection considering the actual stiffness of beam-column joint rather than traditional concept of rigid connection. A concentrated moving load is applied on the beam with three different support conditions such as fixed both end, simply supported and propped cantilever. This proposed model is then verified theoretically considering known boundary conditions. Results showed that the proposed theoretical model for moment and deflection of beam perfectly captured the existing beam equations with that specific support conditions and the cost of the beam construction can be reduced due to considering the actual beam-column joint stiffness

Effect of beam orientation on the static behaviour of phenolic core sandwich composites with different shear span-to-depth ratios

This study thoroughly investigated the flexural behaviour of phenolic cored sandwich beams with glass fibre composite skins in the horizontal and vertical positions. The beams have a shear span-to-depth ratio (a/d) varying between 0.5 and 12, and tested under 4-point static bending. Their failure load are then predicted theoretically. The results showed that changing the beam orientation from horizontal to vertical changes the failure mode from brittle to progressive. The sandwich beam’s high bending stiffness can be efficiently utilised by placing them vertically. The a/d ratio played a major role on the load capacity and failure mode. In both orientations, the load capacity decreased with the increased of a/d. The beam failed in shear, a combined shear and bending, and bending for a/d ≤ 2, 2 < a/d < 6, and a/d ≥ 6, respectively. These failure mechanisms can be correlated to the shear-to-bending stress ratio while the failure load can be reasonably predicted using the available theoretical models. The two-way analysis of variance showed that the beam orientation is a more influential parameter than the a/d ratio. From this study, the horizontal beams are preferable for flexural dominated structures while the vertical beams are desirable for shear dominated structures

Performance of an innovative composite railway sleeper

The high maintenance cost and scarcity of the hardwood timber promote alternative technologies for replacing the timber railway sleepers. The advantages of composites in high strength-to-weight ratio, durability, reliability, longer life and less maintenance are of great interest for their application in railway sleepers. This study investigated the performance of an innovative composite railway sleeper manufactured from sandwich panels and bonded with the epoxy polymer matrix. The performance including rail-seat vertical load, centre bending moment, shear strength, screw holding capacity and electrical resistance have been investigated and compared with the timber sleepers. Results showed that the new composite sleeper can maintain the minimum performance requirements and showed a very similar behaviour to the timber ones. This innovative composite technology could be a suitable replacement to the existing timber sleepers

Structural performance of heavy duty composite railway sleeper

Are composite materials a suitable alternative for heavy duty railway sleeper application

Design of epoxy resin based polymer concrete matrix for composite railway sleeper

A new type of railway sleeper made from composite materials is now being developed to replace deteriorating timber sleepers. To protect it from unfavorable environments and to increase the strength at rail-seat area, the sleeper is coated with epoxy based polymer concrete. This paper investigates the properties of the polymer concrete matrix with different percentages of epoxy resin binder and lightweight particulate filler. The mixing proportion of Particulate Filled Resin (PFR) was optimised while targeting a specific strength and workability. The content of epoxy resin was varied from 40 to 100% whereas the filler material ranged from 0 to 60%. The flexural performance of PFR was evaluated using three-point bending tests and the most suitable mix proportion is determined based on the experimental results

Bond behaviour of composite sandwich panel and epoxy polymer matrix

Fibre composite sandwich panel made up with glass fibre reinforced polymer skins and phenolic foam core can be glued or cast together to produce a large structural beam section. To ensure the structural integrity and composite action, the sandwich panels should be effectively bonded with polymer matrix. However, the bond behaviour between sandwich panel and polymer matrix is not well understood. This paper experimentally investigated the effect of epoxy polymer matrix properties, bond length, bond thickness, and bond width on the bond behaviour, and evaluated the optimal parameters for effective bonding. The experimental program was designed by Taguchi method to reduce the number of experiments. Results showed that the polymer matrix consist with 40% filler and 60% resin (by volume) is the optimal binder. A bond length of at least 70 mm and bond thickness of 5 mm were found effectively to utilise the strength of the composite sandwich panel. The bond width however has insignificant effect on the bond strength

Flexural behaviour of concrete slabs reinforced with GFRP bars and hollow composite reinforcing systems

Glass Fibre Reinforced Polymer (GFRP) bars are now attracting attention as an alternative reinforcement in concrete slabs because of their high resistance to corrosion that is a major problem for steel bars. Recentlyhollow concrete slab systems are being used to reduce the amount of concrete in the slab and to minimise the self-weight, but the internal holes makes them prone to shear failure and collapse. A hollow composite reinforcing system (CRS) with four flanges to improve the bond with concrete has recently been developed to stabilise the holes in concrete members. This study investigated the flexural behaviour of concrete slabs reinforced with GFRP bars and CRS. Four full-scale concrete slabs (solid slab reinforced with GFRP bars; hollow slab reinforced with GFRP bars; slab reinforced with GFRP bars and CRS; and slab reinforced with steel bars and CRS) were prepared and tested under four-point static bending to understand how this new construction system would perform. CRS is found to enhance the structural performance of hollow concrete slabs because it is more compatible with GFRP bars than steel bars due to their similar modulus of elasticity. A simplified Fibre Model Analysis (FMA) reliably predicted the capacity of hollow concrete slabs

Composite railway sleeper: a cost effective and eco-friendly alternative

Motivation • High maintenance cost • Huge CO2 emission • Early failure in the existing sleeper Conclusions: • Optimised shape reduces two-third volume of materials • Composite sleeper behaviour is comparable with timbe