Behaviour of FRP-to-concrete bonded joints

The bond behaviour between FRP (fibre-reinforced polymer) and concrete is a consideration in the design of FRP strengthening mechanisms for structurally deficient or functionally obsolete concrete structures. In the past, a number of empirical models and fracture mechanics based theoretical models have been proposed for determining the effective bond length and bond strength of FRP sheets/plates bonded to concrete. However, these methods have yielded large discrepancies in the predictions of effective bond length and bond strength. In this paper, the results of an experimental investigation into effective bond length and bond strength are presented. Comparison of experiments results with predictions from three empirical and three fracture mechanics based theoretical models shows that a recently proposed fracture mechanics based local-bond slip model provides a conservative prediction of the effective bond length and an accurate prediction of bond strengt

An investigation on the stiffness of timber sleepers for the design of fibre composite sleepers

This paper presents an experimental investigation on timber railway sleepers with a view to select a suitable stiffness and a modulus of elasticity for the design of a fibre composite railway sleeper. Eight full size timber sleepers were tested using a four point bending test arrangement. An overview of existing material for railway sleepers is also presented. Based on the tests, it is concluded that timber sleepers have significant variation in strength and stiffness as can be inferred from the modulus of elasticity (Esleeper) which ranged between approximately 9520 MPa and 27600 MPa. It is desirable to develop a concept fibre composite sleeper within a similar range of modulus of elasticity. Based on the statistical analysis, it is proposed to use the lower tail value that is 12000 MPa as design modulus of elasticity for the fibre composite railway sleeper

Flexural behaviour of structural fibre composite sandwich beams in flatwise and edgewise positions

The flexural behaviour of a new generation composite sandwich beams made up of glass fibre-reinforced polymer skins and modified phenolic core material was investigated. The composite sandwich beams were subjected to 4-point static bending test to determine their strength and failure mechanisms in the flatwise and the edgewise positions. The results of the experimental investigation showed that the composite sandwich beams tested in the edgewise position failed at a higher load with less deflection compared to specimens tested in the flatwise position. Under flexural loading, the composite sandwich beams in the edgewise position failed due to progressive failure of the skin while failure in the flatwise position is in a brittle manner due to either shear failure of the core or compressive failure of the skin followed by debonding between the skin and the core. The results of the analytical predictions and numerical simulations are in good agreement with the experimental results

Structural evaluation of concrete expanded polystyrene sandwich panels for slab applications

Sandwich panels are being extensively and increasingly used in building construction because they are light in weight, energy efficient, aesthetically attractive and can be easily handled and erected. This paper presents a structural evaluation of Concrete-Expanded Polystyrene (CEPS) sandwich panels for slab applications using finite element modeling approach. CEPS panels are made of expanded polystyrene foam sandwiched between concrete skins. The use of foam in the middle of sandwich panel reduces the weight of the structure and also acts as insulation against thermal, acoustics and vibration. Applying reinforced concrete skin to both sides of panel takes the advantages of the sandwich concept where the reinforced concrete skins take compressive and tensile loads resulting in higher stiffness and strength and the core transfers shear loads between the faces. This research uses structural software Strand7, which is based on finite element method, to predict the load deformation behaviour of the CEPS sandwich slab panels. Non linear static analysis was used in the numerical investigations. Predicted results were compared with the existing experimental results to validate the numerical approach used

Experimental investigation on the flexural behaviour of pultruded GFRP beams filled with different concrete strengths

Glass fibre reinforced polymer (GFRP) pultruded profiles are being increasingly used in the construction industry due to their numerous advantageous over the conventional materials. However, most pultruded GFRP sections fail prematurely without utilising their high tensile strength due to their thin-walled sections. As a result, several hybrid systems made out of GFRP profiles and concrete as a filler material have been proposed in order to enhance their structural performance. Most of these studies utilised high strength concrete wherein the additional cost does not justify the enhancement in the stiffness and strength of the infilled GFRP profiles. This paper presents an experimental investigation on the effect of the compressive strength of concrete infill on the flexural behaviour of beams with a view to determine a lower cost infill for GFRP profiles. Pultruded GFRP square beams (125 mm x125 mm x 6.5mm) were filled with concrete having 10, 37 and 43.5 MPa compressive strength and tested under static four-point bending. The results showed that the capacity of the filled beam sections increased by 100 to 141% than the hollow sections. However, the compressive strength of the concrete infill has no significant effect on the flexural behaviour of the beams. The increase in concrete compressive strength from 10 to 43.5 MPa increased the ultimate moment by only 19% but exhibited an almost same flexural stiffness indicating that a low strength concrete is a practical solution to fill the GFRP profile

Free vibration analysis of laminated composite plates based on FSDT using one-dimensional IRBFN method

This paper presents a new effective radial basis function (RBF) collocation technique for the free vibration analysis of laminated composite plates using the first order shear deformation theory (FSDT). The plates, which can be rectangular or non-rectangular, are simply discretised by means of Cartesian grids. Instead of using conventional differentiated RBF networks, one-dimensional integrated RBF networks (1D-IRBFN) are employed on grid lines to approximate the field variables. A number of examples concerning various thickness-to-span ratios, material properties and boundary conditions are considered. Results obtained are compared with the exact solutions and numerical results by other techniques in the literature to investigate the performance of the proposed method

Floodway Design Process Revisted

Floodways are small road structures that are meant to be overtopped by floodwater during a flood event with relatively low average recurrence interval and expected to be in complete functional stage after the flood water recedes. The severity of 2011 and 2013 flood events in Queensland damaged the floodways in the state causing a huge impact mainly to the rural community during the recovery and rehabilitation stage. Therefore, the resilience of these small critical road structures is of great importance for the survival, safety and recovery stages during such events. Using a case study region in Lockyer Valley Regional Council area, the authors found that majority of the structural damage was caused due to the heavy impact load from the boulders/logs that came with the flood water. Another aspect reviewed was the damage sustained by floodway aprons due to excessive debris loading. This is of particular concern since aprons are the most expensive component of a floodway to repair or replace. Since floodways encounter many forces throughout their service life thorough review and investigation of current design standards are required in order to improve floodway resilience. In an attempt to develop a floodway design process, this paper focusses on the analysis of two types of floodways and reports the procedure used to develop design charts. Detailed finite element analysis is demonstrated by using one type of floodway. Finally, the contribution that resulted from the structural analysis is linked with the current floodway design guide

Analysis of retrofitted corroded steel pipes using internally bonded FRP composite repair systems

Steel pipelines play an important role in the oil and gas industry. Hence corrosion of the steel pipe systems during its service life is a critical issue for the industry. Fibre reinforced composites offer solutions with broad applicability and efficiency for the internal repair of these corroded pipelines. Understanding the behaviour of internal composite repair systems against different internal pressure regimes is an important aspect in the development of a repair system. This study develops the analyses of internal composite bonded repair systems for long steel pipes with an axisymmetric defect, based on Lame’s equation. Various levels of bonding between the steel and composite are studied. Fully bonded optimum internal composite repair thicknesses are determined using biaxial carbon and glass fibre composites for different levels of corrosions, using the Von Mises yielding and Tsai-Hill failure criterion approaches. Two case studies are illustrated using the design nomographs. The analysis technique used was found to be accurate when compared with finite element modelling results

A multiscale coarse grained model for simulating mechanical responses of plant food tissues

Plant food materials are highly sensitive to the external mechanical responses. Simulation of the material behaviour under mechanical loading is important in many engineering applications. Several researchers have used tissue based (macroscale) and cellular based (microscale) numerical models to assess the plant material behaviour. In doing so, generally, finite element modelling and meshfree based discretization strategies are commonly used and the latter has been proven to be more flexible, accurate and more robust in numerical simulations. This study aims to develop a coarse grained (CG) model for a cellular system of plant food tissue in microscale. The basic idea here is to maintain the accuracy given by the cellular scale while minimizing the computational cost for the simulations. The developed model accounts for the deformation of a coarse grained system under an external mechanical load. In order to represent the viscoelastic behaviour of a plant food material, we use a spring damper system connected to coarse grained beads. The model predictions show a satisfactory agreement with the morphological changes given by the cellular model. This developed CG model has laid a solid foundation for the further development of the multiscale model for the plant tissue

A new high-order nine-point stencil, based on integrated-RBF approximations, for the first biharmonic equation

This paper is concerned with the development of a new compact 9-point stencil, based on integrated-radial-basis-function (IRBF) approximations, for the discretisation of the first biharmonic equation in two dimensions. Derivatives of not only the first order but also the second order and higher are included in the approximations on the stencil. These nodal derivative values, except for the boundary values of the derivative, are directly derived from nodal variable values along the grid lines rather than from the biharmonic equation, and they are updated through iteration. With these features, the double boundary conditions are imposed in a proper way. The biharmonic equation is enforced at grid points near the boundary without any special treatments. More importantly, they enable the IRBF solution to be highly accurate and not influenced by the RBF width. There is no need for searching the optimal value of the RBF width. The proposed stencil can be used to solve the biharmonic problem defined on a rectangular/non-rectangular domain. A fast convergence rate with respect to grid refinement (up to ten) is achieved