268 research outputs found

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

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    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

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

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    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

    Evaluation of the flexural strength and serviceability of geopolymer concrete beams reinforced with glass-fibre-reinforced polymer (GFRP) bars

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    Geopolymer concrete reinforced with glass-fibre-reinforced polymer (GFRP) bars can provide a construction system with high durability, high sustainability, and adequate strength. Few studies deal with the combined use of these materials, and this has been the key motivation of this undertaking. In this study, the flexural strength and serviceability performance of the geopolymer concrete beams reinforced with GFRP bars were evaluated under a four-point static bending test. The parameters investigated were nominal bar diameter, reinforcement ratio, and anchorage system. Based on the experimental results, the bar diameter had no significant effect on the flexural performance of the beams. Generally, the serviceability performance of a beam is enhanced when the reinforcement ratio increases. The mechanical interlock and friction forces provided by the sand coating was adequate to secure an effective bond between the GFRP bars and the geopolymer concrete. Generally, the ACI 4401.R-06 and CSA S806-12 prediction equations underestimate the beam strength. The bending-moment capacity of the tested beams was higher than that of FRP-reinforced concrete beams from the previous studies

    Behaviour of concentrically loaded geopolymer-concrete circular columns reinforced longitudinally and transversely with GFRP bars

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    The behavior of concentrically loaded geopolymer-concrete circular columns reinforced longitudinally and transversely with glass–fiber-reinforced-polymer (GFRP) bars was investigated. Six full-scale short columns (L/r = 8) were cast: one column without transverse reinforcement; three columns with circular hoops spaced at 50 mm, 100 mm, and 200 mm on centers; and two columns with spirals spaced at 50 mm and 100 mm on centers. In addition, two slender columns (L/r = 16) transversely reinforced with hoops and spirals both spaced at 100 mm on centers were fabricated. Based on the experimental results, the GFRP bars contributed an average of 7.6% to the overall capacity of the tested columns. The hoop- and spiral-confined slender columns failed at a load equal to 66% and 82%, respectively, of the strength of their counterpart short columns. Irrespective of the tie configuration, the columns with higher volumetric ratios showed better compressive behavior than those with lower volumetric ratios. The ductility and confinement efficiency of the spiral-confined columns were higher than that of their counterpart hoop-confined columns. The tested columns yielded relatively superior compression performance compared to OPC-based concrete columns reinforced with GFRP bars and ties. Further studies dealing with the behavior and slenderness limit in GFRP-reinforced geopolymer concrete slender columns are recommended to increase its uptake in the construction industry

    Seismic Vulnerability Assessment of Priority Cultural Heritage Structures in the Philippines

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    At the end of 2013 two catastrophic events occurred in the Philippines: the M 7.2 earthquake in Bohol and the strongest ever recorded Typhoon Haiyan, causing destruction across the islands of Cebu, Bohol and the Visayas region. These events raised the need to carry out a multi-hazard risk assessment of heritage buildings, many of which were irretrievably lost in the disasters. Philippines’ Department of Tourism engaged ARS Progetti S.P.A., Rome, Italy, and the Center for Conservation of Cultural Property and Environment in the Tropics (CCCPET), University of Sto. Tomas, Manila, to undertake the “Assessment of the Multi-Hazard Vulnerability of Priority Cultural Heritage Structures in the Philippines”, with experts from University College London, UK, and De La Salle University. The main objective of the project was to reduce the vulnerability of cultural heritage structures to multiple natural hazards, including earthquake, typhoon, flood, by: (i) prioritizing of specific structures based on hazard maps and historical records; (ii) assessing their vulnerability; and (iii) recommending options to mitigate the impacts on them. The paper presents the methodology introduced to determine the seismic risk these heritage buildings are exposed to. All the selected cultural heritage structures are under the jurisdiction of the National Museum Commission of Philippines and of the National Commission for Culture and Arts

    Comparison of the shear behaviour of geopolymer concrete beams with GFRP and steel transverse reinforcements

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    This study presents a comparison of the shear behaviour of geopolymer concrete beams transversely reinforced with glass fiber-reinforced polymer (GFRP) and steel bars. Two full-scale beams with GFRP and steel stirrups spaced at 150 mm on-center were fabricated and tested up to failure using the four-point static bending test. Another beam without web reinforcements was also cast to determine the shear contribution of the geopolymer concrete. All the beams were provided with the same amount of flexural reinforcements. The beams were supported over a 1200 mm clear span with 450 mm shear span on each side. The shear span-to-depth ratio of the beams was 1.8. Based on the test results, the provision of GFRP stirrups almost doubled the shear capacity of the beam without web reinforcements. Comparable load-deflection response, shear strength, deflection capacity, and strain readings were observed between the beams with GFRP and steel stirrups. The two beams yielded similar crack pattern; however, wider cracks were developed in the former beam owing to the lower elastic modulus of GFRP bar compared with steel bar. Furthermore, both beams failed in shear, classified as a diagonal strut compression failure; however, the failure of the beam with GFRP stirrups was induced by the stirrup’s lap splice failure while steel yielding caused the failure of beam with steel stirrups. This had led to a more brittle final failure of the former beam compared with the latter beam

    A New Design-Oriented Model of Glass Fiber-Reinforced Polymer-Reinforced Hollow Concrete Columns

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    Hollow concrete columns (HCCs) reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals are considered an effective design solution for bridge piers, electric poles, and ground piles because they use less material and maximize the strength-toweight ratio. HCC behavior is affected by critical design parameters such as inner-to-outer diameter ratio, reinforcement and volumetric ratios, and concrete compressive strength. This paper proposes a new design-oriented model based on the plasticity theory of concrete and considering the critical design parameters to accurately describe the compressive load-strain behavior of GFRP-reinforced HCCs under monotonic and concentric loading. The validity of the proposed model was evaluated against experimental test results for 14 full-scale hollow concrete columns reinforced with GFRP bars and spirals. The results demonstrated that the proposed design-oriented model was accurate and yielded a very good agreement with the axial compressive load behavior of GFRP-reinforced hollow concrete columns

    Hollow concrete columns: review of structural behavior and new designs using GFRP reinforcement

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    Hollow concrete columns (HCCs) reinforced with steel bars have been employed extensively for bridge piers, ground piles, and utility poles because they use fewer materials and offer higher structural efficiency compared to solid concrete columns with the same concrete area. Many experimental studies have been conducted to investigate the behavior of HCCs under different loading conditions and found that the structural performance of HCCs is critically affected by many design parameters. If not designed properly, HCCs exhibit brittle failure behavior, due to longitudinal bars buckling or the concrete wall failing in shear. In addition, the corrosion of steel bars has become an issue in reinforced-concrete structures. Therefore, this paper critically reviews the different design parameters that affect the performance of HCCs and identifies new opportunities for the safe design and effective use of this construction system. Moreover, the use of GFRP bars as reinforcement in hollow concrete columns is explored with the aim of developing a non-corroding and structurally reliable construction system

    Infrared and optical properties of pure and cobalt-doped LuNi_2B_2C

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    We present optical conductivity data for Lu(Ni1x_{1-x}Cox_x)2_2B2_2C over a wide range of frequencies and temperatures for x=0 and x=0.09. Both materials show evidence of being good Drude metals with the infrared data in reasonable agreement with dc resistivity measurements at low frequencies. An absorption threshold is seen at approximately 700 cm-1. In the cobalt-doped material we see a superconducting gap in the conductivity spectrum with an absorption onset at 24 +/- 2 cm-1 = 3.9$ +/- 0.4 k_BT_c suggestive of weak to moderately strong coupling. The pure material is in the clean limit and no gap can be seen. We discuss the data in terms of the electron-phonon interaction and find that it can be fit below 600 cm-1 with a plasma frequency of 3.3 eV and an electron-phonon coupling constant lambda_{tr}=0.33 using an alpha^{2}F(omega) spectrum fit to the resistivity.Comment: 10 pages with 10 embedded figures, submitted to PR

    Novel testing and characterization of GFRP bars in compression

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    Glass fibre reinforced polymer (GFRP) bars have now been increasingly used as longitudinal reinforcement in concrete columns. In column design and analysis, the contribution of GFRP bars to compression is often ignored or is estimated as a fraction of its tensile strength due to the limited understanding on their compressive behaviour. Moreover, there exists no standard test method to characterise the properties of GFRP bars in compression. This study implemented a novel test method to determine and characterise the compressive properties of high modulus GFRP bars. During the preparation of test specimens, hollow steel caps filled with cementitious grout were used to confine the top and bottom ends of the GFRP bars. The effects of the bar diameter (9.5, 15.9, and 19.1 mm) and the unbraced length-to-bar diameter ratio, Lu/db (2, 4, 8, and 16) were investigated on the compressive strength of the bars. The results showed that the increase in bar diameter increases the micro-fibre buckling and decreases the compressive-to-tensile strength ratio. Similarly, the failure mode changed from crushing to fibre buckling with the increase of Lu/db ratio. Simplified theoretical equations were proposed to reliably describe the compressive behaviour of GFRP bars with different bar diameters and Lu/db ratios