An experimental investigation into span length effect in composite CFS and timber-based flooring systems

Cold-formed steel (CFS) panelised built-offsite modern methods of construction offer economy of scale, high precision, reduction in construction waste and a more streamlined manufacturing and construction process, compared to traditional construction. Floors made with CFS joists and timber-based flooring systems, often jointed using screws and structural adhesives, have become increasingly popular. Nevertheless, the beneficial effect of the timber flooring on overall floor structural behaviour is often ignored in design due to limited understanding of CFS joist-timber board interaction and the effect of various influencing parameters. This article investigates, experimentally, the structural performance of such composite floors. This paper presents eighteen large scale bending tests of CFS composite floors and five pushout tests to investigate the effect of span length on composite action. The results demonstrate that a high degree of composite action can be achieved when both screws and adhesives are utilised, resulting in around 40% increase in flexural stiffness when compared to joist performance without boards. This can lead to a more efficient and sustainable design of CFS joisted floors. The results also show that further research is needed to extend existing design equations to cover short span lengths.European Commission Horizon 2020UK Research and Innovation, Innovate UK Knowledge Transfer Partnerships (KTP) programm

Constitutive model for rubberized concrete passively confined with FRP laminates

This article develops an analysis-oriented stress-strain model for rubberized concrete (RuC) passively confined with fiber reinforced polymer (FRP) composites. The model was calibrated using highly instrumented experiments on 38 cylinders with high rubber contents (60% replacement of the total aggregate volume) tested under uniaxial compression. Parameters investigated include cylinder size (100×200mm or 150×300mm; diameter×height), as well as amount (two, three, four or six layers) and type of external confinement (Carbon or Aramid FRP sheets). FRP-confined rubberized concrete (FRP CRuC) develops high confinement effectiveness (fcc/fco up to 11) and extremely high deformability (axial strains up to 6%). It is shown that existing stress-strain models for FRP-confined conventional concrete do not predict the behavior of such highly deformable FRP CRuC. Based on the results, this study develops a new analysis-oriented model that predicts accurately the behavior of such concrete. This article contributes towards developing advanced constitutive models for analysis/design of sustainable high-value FRP CRuC components that can develop high deformability

Optimisation of rubberised concrete with high rubber content: an experimental investigation

This article investigates experimentally the behaviour of rubberised concrete (RuC) with high rubber content so as to fully utilise the mechanical properties of vulcanised rubber. The fresh properties and short-term uniaxial compressive strength of 40 rubberised concrete mixes were assessed. The parameters examined included the volume (0–100%) and type of mineral aggregate replacement (fine or coarse), water or admixture contents, type of binder, rubber particle properties, and rubber surface pre-treatments. Microstructural analysis using a Scanning Electron Microscope (SEM) was used to investigate bond between rubber and concrete at the Interface Transition Zone (ITZ). This initial study led to the development of an “optimum” RuC mix, comprising mix parameters leading to the highest workability and strength at all rubber contents. Compared to a non-optimised concrete with 100% replacement of fine aggregates with rubber, the compressive strength of concrete with optimised binder material and moderate water/binder ratio was enhanced by up to 160% and the workability was improved significantly. The optimisation proposed in this study will lead to workable high rubber content RuC suitable for sustainable high-value applications

Development of Confined Rubberised Concrete for High Ductility Structural Applications

The global environmental and economic implications of the disposal of waste tyres have prompted research exploring valuable outlets for their components. Concrete is an inherently brittle material and can benefit from tyre rubber properties to achieve higher ductility and energy dissipation for special applications in locations of high deformation demands, such as coupling beams. Despite the prospective benefits, the use of rubber as partial mineral aggregate replacement negatively affects concrete workability and strength. Recent research has shown that the external confinement of RuC can benefit from its high lateral expansion and mitigate the drawbacks of RuC, leading to high strength. Nevertheless, the majority of this research is limited to low rubber contents, which restricts the deformability potential of confined rubberised concrete (CRuC). This research aims to advance the understanding on unconfined and FRP-confined RuC, developed with high rubber contents and optimised mix parameters, leading the way for new high-strength high-deformability concrete elements. More than forty RuC mixes were investigated experimentally to develop an understanding of the effect of rubber and various concrete mix parameters on RuC fresh properties and short-term compressive strength. An “optimum” RuC mix with adequate workability and strength at all rubber contents was developed for further study. The influence of rubber (content and type) on the stress-strain behaviour of the optimised RuC mix was investigated in a second parametric study involving more than 60 cylinders. The addition of rubber to concrete led to high lateral strains and premature failure, particularly at high rubber contents, which can be exploited to activate external confinement. The mix with high rubber content (60% total aggregate replacement) was identified as most suitable for study to maximise the deformability in RuC. The use of Aramid or Carbon FRP sheets as external confinement to high rubber contents RuC was examined experimentally under monotonic and cyclic uniaxial compression. This led to the development of constitutive models to accurately predict the performance of confined rubberised concrete (CRuC) subject to monotonic or cyclic loading. CRuC led to unprecedented axial strains (>6%) and compressive strength above 90 MPa, indicating high potential for its use in a variety of structural applications

Composites with recycled rubber aggregates : properties and opportunities in construction

Vulcanised rubber is extensively used in many industrial sectors due to its good physical, mechanical and dynamic properties, as well as excellent durability, outstanding abrasive resistance and relatively low cost. Unfortunately, most post-consumer rubber-derived products are still discarded as waste, buried in landfills or incinerated. Such materials require many years to degrade naturally due to i) their complex cross-linked composition, and ii) the additives used during manufacturing to extend the lifespan of rubber. Extensive research has investigated the use of end-of-life rubber as binder (e.g. elastomers, bitumen), or as conglomerates (cement, gypsums) to produce innovative composites in construction. To improve the properties of composites made with recycled rubber, the surface of rubber has been treated with different costly processes to improve the Interfacial Transition Zone (ITZ). However, the results available in the literature are inconsistent and many technical and practical aspects remain unsolved, thus preventing the cost-effective use of rubber in the construction industry. This study provides a comprehensive review on rubber properties and surface treatments of rubber recycled from post-consumer components so as to identify potential applications in composites for construction. It is concluded that an understanding of the chemical, physical and mechanical properties of rubber, as well as a proper characterisation, are necessary to take full advantage of this high quality material. Future research needs in the field are also suggested

Composite behaviour of cold-formed steel-timber floors

This article investigates, experimentally, the structural performance of lightweight cold-formed steel (CFS) - timber board composite flooring systems. Fifteen full-scale bending tests and twelve companion pushout connection tests were performed. The effect of connection detail (comprising self-drilling screws with or without a structural adhesive) on structural per-formance is examined. The results of this research demonstrate that the use of a polyurethane adhesive, in conjunction with screws, leads to a significant increase in connection slip modulus and a higher degree of composite action in the floors, resulting in up to 40% increase in flex-ural stiffness, when compared to joists designed individually. The experimental results are then compared to predictions from relevant existing analytical models

A new cyclic model for FRP ‐confined rubberized concrete

This article proposes a new constitutive model for the cyclic behavior of rubberized concrete confined with fiber-reinforced polymer (FRP) sheets. The model is calibrated with experimental results from 18 confined rubberized concrete (CRuC) cylinders tested in cyclic compression. The cylinders had 60% total aggregate volume replacement with recycled tyre rubber. Parameters investigated include the type of confining material (Carbon or Aramid FRP) and number of layers (two, three, or four). The results indicate that using FRP confinement leads to a strong (up to 100 MPa) and highly deformable (axial strains up to 7%) rubberized concrete that can be used in structural applications. The proposed constitutive model predicts accurately the material response under cyclic loading and can thus be used for design/analysis of highly deformable components made of FRP CRuC. This article contributes toward the development of advanced constitutive models for FRP CRuC, thus promoting the wider use of recycled materials in construction industry

Comportamiento en compresión axial del hormigón con caucho sin confinamiento y confinado con FRP

Esta investigación se desarollón el el marco de dos proyectos de investigación europeos: 1. Seismic-resistant Highly Deformable Structures (SHDS) bajo el programa Horizonte 2020 Marie Sklodowska-Curie ref n° 658248. 2. Anagennisi bajo el 7º programa marco ref n° 603722This article investigates the use of externally bonded Fibre Reinforced Polymer (FRP) jackets to develop a novel high-strength, highly-deformable FRP Confined Rubberised Concrete (CRuC). Sixty rubberised concrete (RuC) cylinders were tested in axial compression. The cylinders were produced using recycled tyre rubber to replace i) 0–100% fine or coarse aggregate volume or ii) a replacement of 40% or 60% of the total aggregate volume. Six cylinders of the latter mix were then confined with either two or three layers of Aramid FRP sheets. The results indicate that the use of high rubber contents in concrete lead to premature microcracking and lateral expansion, the latter of which can be used to activate the FRP confinement earlier and achieve higher confinement effectiveness. The CRuC cylinders reached compressive strengths of up to 75 MPa and unprecedented ultimate axial strains up to 5%, i.e. about fourteen times larger than those of normal concrete (0.35%). Such novel high-strength, highly-deformable CRuC is of great value to engineers and can be used for structural applications where large deformability is required.Department of Civil and Structural Engineering. The University of Sheffiel

Behaviour of unconfined and FRP-confined rubberised concrete in axial compression

This article investigates the use of externally bonded Fibre Reinforced Polymer (FRP) jackets to develop a novel high-strength, highly-deformable FRP Confined Rubberised Concrete (CRuC). Sixty rubberised concrete (RuC) cylinders were tested in axial compression. The cylinders were produced using recycled tyre rubber to replace i) 0–100% fine or coarse aggregate volume or ii) a replacement of 40% or 60% of the total aggregate volume. Six cylinders of the latter mix were then confined with either two or three layers of Aramid FRP sheets. The results indicate that the use of high rubber contents in concrete lead to premature microcracking and lateral expansion, the latter of which can be used to activate the FRP confinement earlier and achieve higher confinement effectiveness. The CRuC cylinders reached compressive strengths of up to 75 MPa and unprecedented ultimate axial strains up to 5%, i.e. about fourteen times larger than those of normal concrete (0.35%). Such novel high-strength, highly-deformable CRuC is of great value to engineers and can be used for structural applications where large deformability is required