Weena Lokuge

Vulnerability of floodways under extreme flood events

Floodways are commonly used in rural road networks due to the economic and environmental benefits offered as a low-cost and practical road crossing in flood-prone areas. They are designed with provision for submergence so that water flows over with minimum impediment to flow, at a probability given design flood. The floodway design process is traditionally governed by hydraulic aspects rather than structural aspects. Hydrological condition, availability of material, and familiarity of construction techniques are significant when selecting the floodway type. Nevertheless, extreme conditions can cause significant damage to floodways, as was evident from the 2011 and 2013 Queensland flood events, during which 58% of floodways in the Lockyer Valley Regional Council (LVRC) area in Queensland, Australia, which is the case study area of this paper, were damaged, causing huge economic lost at council and national level. This created a new track in research and development activities to assess vulnerability and to find methods for improving the resilience of floodways during extreme flood events. In line with this, the present study evaluates local design guidelines and damaged floodways to assess failure modes and severity of damage using a damage index (DI) method.

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.

Ductility enhancement of geopolymer concrete columns using fibre-reinforced polymer confinement

Geopolymer concrete is an environmentally friendly, green construction material. However, its use is constrained by its increased brittleness and lack of understanding of its behaviour under multi-axial loadings. Similar to ordinary portland cement concrete (OPC), the ductility of geopolymer concrete columns can be increased by lateral confinement and using fibre-reinforced polymers is one option in doing that. This research paper aims at investigating the effect of different confinements on the ductility of geopolymer concrete. Three different mixes with varying binder (fly ash and slag) and different curing conditions together with different levels of carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) confinement were investigated in this research paper. FRP confined normal strength geopolymer concrete shows similar stress–strain behaviour when compared to that of high-strength OPC concrete When compared with the same level of confinement, CFRP confined geopolymer concrete marginally outperforms GFRP confined geopolymer concrete in 28-day compressive strength. However, ductility levels with GFRP confinement are better than those with CFRP confinement.

Compressive strength characterization of polyester based fillers

This paper investigates the compressive properties of polyester based fillers with different proportions of resin, sand and fly ash. The research program aims at developing a polymer based filler for a glass fibre reinforced polymer (GFRP) tube to be used as a structural rehabilitation system. It has been initiated to improve fundamental understanding of this material and to provide the knowledge required for its broad utilization. In this development, sample trial mixes were considered based on several weight percentages of polyester resin, fly ash and sand. These weight percentages were selected after analyzing volumetric properties of sand. The effect of resin (binder), sand and fly ash contents on the compressive strength of polyester based fillers with respect to age is reported. It has been found that at the age of 7 days all the batches reached about 90% of the compressive modulus. The experimental compressive stress-strain curves reported here were compared with established analytical models for normal strength concrete.

AN OVERVIEW ON OIL CONTAMINATED SAND AND ITS ENGINEERING APPLICATIONS

Oil leakage is considered as one of the significant environmental issue worldwide, which affects the physical and chemical properties of the surrounding sand. A range of remediation methods for oil-contaminated sand was recommended but none are considered to be cost effective especially in developing countries. In order to find an alternative and cost-effective remediation method, the use of oil contaminated sand in engineering and construction has been considered. This paper reviews the main sources of oil contamination, the existing remediation methods and critically analysed several factors that affecting the properties of oil contaminated sand. Emerging applications of oil contaminated sand in engineering and construction are also presented.

Triaxial test results of high-strength concrete subjected to cyclic loading

High-strength concrete (HSC) has highly desirable structural engineering properties, which can lead to significant cost savings in heavily loaded concrete structures. However, its use is limited by a concern regarding an increased brittleness compared to normal strength concrete (NSC), especially under complex multi-axial loading conditions. The issue of ductility is extremely important in structures subjected to earthquake loading conditions. In order to determine the lateral confinement required for a given level of ductility, the relationship between axial stress and lateral strain of confined HSC needs to be established. This paper describes a testing programme carried out to obtain the relationships between axial stress, axial strain and lateral strain for HSC under cyclic loading and subjected to constant lateral confining pressures. Compressive strengths of concrete tested were 40, 60, 80 and 100 MPa. Uniform confining pressures applied were 4, 8 and 12 MPa. The experimental results are presented and the effects of cyclic loading and confinement on the constitutive behaviour of HSC are described.

Effect of skin-core debonding on the dynamic behaviour of GFRP composite beams

Composites are materials made by combining two individual materials where one material forms the matrix while the other provides the reinforcement. A novel composite sandwich made up of glass fibre reinforced polymer (GFRP) face sheets and modified phenolic core has been developed recently. Although perfect bond between the skin and the core is a common assumption, an important issue that needs to be considered in using a composite beam is the development of debonding between the skin and the core. Debonding may arise during fabrication or under service conditions, which causes changes to the dynamic behaviour in addition to the strength degradation. This paper focuses on the effect of debonding on dynamic characteristics of sandwich beams of different debonding sizes and end conditions. Strand7 software is used for 3D finite element simulation. Free vibration behaviour reported in the literature for composite beams will first be used to compare the analytical results with the fully bonded and debonded beams. Study is extended to depict the effect of debonding on free vibration behaviour of novel composite beams. It is revealed that the decrease in natural frequency with the increase in the extent of debonding is more dependent on the width of debonding across the beam than the length along the beam. It is also perceived that full width debonding leads to increased participation of twisting modes in comparison to half-width debonding in clamped-clamped end condition. End conditions of the beam are a governing factor dictating which modes are more affected.

Investigation of some fundamental properties of permeable concrete

This paper presents the outcomes from a laboratory based research study undertaken to evaluate the fundamental properties of permeable concrete, including compressive strength, global and local strain, elastic modulus (stiffness), porosity and permeability. Six permeable concrete mixtures were made with constant water - cement ratio of 0.34, using different aggregate sizes and sand percentages. The compressive strength range was 15-35 MPa, while the permeability varied between 1.5 to 5.5mm/s and the porosity varied between 25 to 35 %. Two testing methods were used to measure the strain and modulus of elasticity (MOE) of the permeable concrete namely, platen-to-platen method and strain gauge method. Considerable difference was found between the MOEs obtained by the two methods. The MOE determined using the platen-to-platen method consistently were lower in value, which has been attributed to the softness of the capping components, the interface between the specimens and the platen and overall machine compliance. The pore characteristics and their distribution were seen to have an influence on the material responses such as material stiffness and strain. A comparison drawn between the axial strain obtained by the strain gauge measurement and that deduced from the platen-to-platen measurement was undertaken to evaluate the strain homogeneity along with possible detection of the localization phenomena.

Fault tree analysis method for deterioration of timber bridges using an Australian case study

Purpose – Deterioration of timber bridges can often be related to a number of deficiencies in the bridge elements, connectors and/or as a result of been in aggressive environments which they are exposed to. The maintenance cost of timber bridges is affected significantly by a number of deterioration mechanisms which require a systematic approach for diagnosis and treatment. Evaluating the risk of failure of these bridges is of importance in bridge performance assessment and decision making to optimize rehabilitation options. The paper aims to discuss these issues. Design/methodology/approach – This paper identifies common causes for timber bridge deterioration and demonstrates an integrated approach based on fault tree analysis to obtain qualitative or quantitative estimation of the risk of failure of timber bridge sub-systems. Level 2 inspection report for a timber bridge in Queensland, Australia has been utilized as a case study in this research to identify the failure modes of the bridge. Findings – A ...

Laboratory Evaluation of the Stress-Strain relationship of Permeable Concrete

The authors conducted research aimed at developing a new type of permeable concrete material with enhanced structural strength. This paper presents and discusses the results of their investigation on the unaxial compressive stress-strain relationship of porous concrete made with two different mix designs with constant water to cement ratio. The concrete mixes were designed with a target compressive strength between 15-25 MPa and target porosity between 10-15% to study the effect of pore sizes on the stress-strain curve. The average pore space was increased by increasing the relative amount of large aggregate. The reduction in the relative amount of fine aggregate increased the average pore space and resulted in a reduction in mix stiffness and a marginal increase in ultimate strength.