Compressive behavior of concrete-filled FRP tube columns: Assessment of critical column parameters

A comprehensive experimental program has been underway at the Structures Laboratory of the University of Adelaide to investigate the behavior of concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) under concentric compression. This paper presents the results from a group of 92 selected circular, square, and rectangular CFFTs and discusses the influence of the critical column parameters on the compressive behavior of CFFTs. These parameters include concrete strength, amount and type of FRP tube material, manufacture method of the tubes, and size and shape of the CFFTs. In addition to conventional FRP tubes, new types of tubes with integrated internal FRP reinforcement have been designed and tested. Results indicate that concrete strength, cross-sectional shape, and the amount and type of tube material significantly affect the behavior of CFFTs. The manufacture method of FRP tube also has some, but less significant, influence on the behavior of CFFTs. The influence of specimen size has been found to be small. No apparent difference has been found between the compressive behaviors of circular CFFTs and companion FRP-wrapped cylinders. The results also indicate that newly developed square and rectangular CFFTs, with internal FRP reinforcement, exhibit significantly improved behavior over conventional CFFTs. © 2013 Elsevier Ltd.Togay Ozbakkalogl

Seismic behaviour of reinforced concrete frames in Australia

Many intra-tectonic plate regions are considered to have low to moderate seismic risk. However, devastating earthquakes can occur in these regions and result in high consequences in terms of casualties and damage. This paper presents an experimental and analytical investigation to understand the seismic capacity of typically detailed Australian reinforced concrete (RC) frames. The experimental programme included a series of progressively increasing earthquake simulator tests, using base motion with design spectrum similar to that for firm soil sites in Australian design code. The analytical study consisted of inelastic time-history analyses of 3-, 5- and 12-storey RC frames with ground acceleration patterns based on artificially generated earthquake data for Boston region (on the east coast of the US). The main objectives of this research were (1) to investigate the behaviour of non-seismically designed RC frames under a 500 year return period (YRP) earthquake and (2) to determine the different magnitudes of earthquake (YRP) that are likely to cause excessive structural and nonstructural damage or collapse of gravity-load-designed (GLD) RC frames. The performance of the frames was analysed in relation to the drift limits, base shear, ductility and overstrength.J. Kashyap, M. Griffith & T. Ozbakkalogluhttp://www.aees.org.au/Proceedings/2008_Index.pd

Influence of concrete strength and confinement method on axial compressive behavior of FRP confined high- and ultra high-strength concrete

This paper presents an experimental investigation on the effect of concrete compressive strength and confinement method on confined high and ultra high-strength concrete (HSC and UHSC) specimens. A total of 55 fiber reinforced polymer (FRP) confined concrete specimens were tested under monotonic axial compression. All specimens were cylinders with 152 mm diameter and 305 mm height and confined by carbon FRP (CFRP). Three different concrete mixes were examined, with average compressive strengths of 35, 65 and 100 MPa. The effect of the confinement method was also examined with FRP-wrapped specimens compared to FRP tube-encased specimens. Axial and lateral behavior was recorded to observe the axial stress-strain relationship and lateral strain behavior for concentric compression. Ultimate axial and lateral conditions are tabulated and the complete stress-strain curves have been provided. The experimental results presented in this paper provide a performance comparison between FRP-confined conventional normal-strength concrete (NSC) and the lesser understood area of FRP-confined HSC and UHSC. The results of this experimental study clearly indicate that above a certain confinement threshold, FRP-confined HSC and UHSC exhibits highly ductile behavior, however for the same normalized confinement pressures, axial performance of FRP-confined concrete reduces as concrete strength increases. The results also indicate that ultimate conditions of FRP-wrapped specimens are similar to those confined by FRP tubes, however a performance difference is evident at the transition region. The performance of 10 existing stress-strain models were assessed against the experimental datasets and the performance of these models discussed. The results of this model assessment revealed the need for further development for stress-strain models developed specifically for FRP-confined HSC or UHSC. © 2013 Elsevier Ltd. All rights reserved.Thomas Vincent, Togay Ozbakkalogl

Signature of structure failure using asymmetric and broadening factors of brillouin spectrum

Copyright © 2005 IEEEWe introduce a novel data analysis approach based on the extraction of peak strain, asymmetric and broadening factors of the Brillouin spectrum measured with the distributed Brillouin sensor (DBS). Such an approach provides simultaneously global and local strains, describing the status of the structure, at the contrary of average strain measurements. These results are confirmed by a trial on a composite column subjected to vertical and bending loads. This demonstrates that the DBS is a powerful tool to give the signature of the structure failure and then to identify early problems in structures that none of existing point sensors can detect.Fabien Ravet, Xiaoyi Bao, Togay Ozbakkaloglu, and Murat Saatciogl

Replacement of Natural Sand with Expanded Vermiculite in Fly Ash-Based Geopolymer Mortars

Increasing the thermal insulation of building components to reduce the thermal energy loss of buildings has received significant attention. Owing to its porous structure, using expanded vermiculite as an alternative to natural river sand in the development of building materials would result in improvement of the thermal performance of buildings. This study investigates the properties of fly ash (FA)-based geopolymer mortars prepared with expanded vermiculite. The main aim of this study was to produce geopolymer mortar with lower thermal conductivity than conventional mortar for thermal insulation applications in buildings. A total of twelve batches of geopolymers were prepared for evaluating their different properties. The obtained results show that, at a given FA and expanded vermiculite content, the geopolymers prepared with a 10 molar NaOH solution exhibited a higher flowability, water absorption and porosity, as well as a lower dry unit weight, compressive strength, ultrasound pulse velocity and thermal conductivity compared with those prepared with a 15 molar NaOH solution. As is also shown, the geopolymers containing expanded vermiculite (15%) developed a lower flowability (~6%), dry unit weight (~6%), compressive strength (~7%), ultrasound pulse velocity (~6%) and thermal conductivity (~18%), as well as a higher apparent porosity (~6%) and water absorption (~9%) compared with those without expanded vermiculite at a given FA content and NaOH concentration. The findings of this study suggest that incorporating expanded vermiculite in FA-based geopolymer mortar can provide eco-friendly and lightweight building composites with improved sound and thermal insulation properties, contributing toward the reduction of the environmental effects of waste materials and conservation of natural sand

Applications of Fiber Reinforced Polymer Composites

2015-2016 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Factors influencing hoop rupture strains of FRP-confined concrete

It is now well understood that the hoop rupture strain of fiber reinforced polymer (FRP) jackets confining concrete is often lower than the ultimate tensile strain of the component fibers. A number of reasons for the lower hoop rupture strains in FRP have been identified; however, the relationships between the material properties of FRP-confined concrete and hoop ruptures strains are yet to be established. This paper presents the results of an experimental study into the factors influencing the hoop strain efficiency of FRP jackets. 24 FRP-confined concrete specimens were tested under axial compression. The results indicate that the hoop rupture strains of FRP jackets decrease with either an increase in the strength of the unconfined concrete or the elastic modulus of the fiber material. These observations were verified by additional results from a large FRP-confined concrete test database assembled from the published literature.</jats:p

Concrete-filled FRP tubes: Manufacture and testing of new forms designed for improved performance

This paper reports on the development and testing of three new concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) systems. These CFFT systems were designed to enhance the effectiveness of square and rectangular FRP tubes in confining concrete. In the design of the rectangular CFFTs two different enhancement techniques were considered; namely, corner strengthening and provision of an internal FRP panel. The technique used in the development of the square CFFT system involved the incorporation of four internal concrete-filled FRP cylinders as an integral part of the CFFT. The performance of these systems was investigated experimentally through axial compression tests of 10 unique CFFTs. The results of the experimental study indicate that the new CFFT systems presented in this paper offer significantly improved performance relative to conventional CFFTs with similar material and geometric properties. Examination of the test results have led to a number of significant conclusions with respect to the confinement effectiveness of each new CFFT system. These results are presented and a discussion is provided on the parameters that influenced the compressive behavior of these CFFT systems.Togay Ozbakkalogl

Development of Lateral Prestress in High-Strength Concrete-Filled FRP Tubes

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.This paper reports on an experimental investigation into the axial and lateral strain development of fiber reinforced polymer (FRP) confined high-strength concrete (HSC) with prestressed FRP shells. A total of 24 aramid FRP (AFRP)-confined concrete specimens were manufactured as concrete-filled FRP tubes (CFFTs) with instrumentation to measure the strain variations during application of prestress, removal of end constraints and progressive prestress losses. Prestressed CFFT specimens were prepared with three different dose rates of expansive mineral admixture to create a range of lateral prestress applied to AFRP tubes manufactured with sheet thicknesses of 0.2 or 0.3 mm/ply and referred to as lightly- or well-confined, respectively. In addition to these three levels of prestress, non-prestressed companion specimens were manufactured and tested to determine baseline performance. The experimental results from this study indicate that lateral prestressing of CFFTs manufactured with HSC can be achieved by varying the expansive mineral admixture dose rate with a lateral prestress of up to 7.3 MPa recorded in this study. Significant strain variations were measured during removal of the end constraints with up to 700 microstrain recorded in the axial direction. Finally, the measurement of prestress losses for the month following prestress application revealed minimal progressive losses, with only 250 and 100 με recorded for the axial and hoop strains, respectively