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

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

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

Applications of Fiber Reinforced Polymer Composites

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

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

Axial compressive behavior of square and rectangular high-strength concrete-filled FRP tubes

This paper presents results of an experimental study on the behavior of square and rectangular high-strength concrete (HSC)-filled fiber-reinforced polymer (FRP) tubes (HSCFFT) under concentric compression. The effects of the tube thickness, sectional aspect ratio, and corner radius on the axial compressive behavior of concrete-filled FRP tubes (CFFT) were investigated experimentally through the tests of 24 CFFTs that were manufactured using unidirectional carbon fiber sheets and high-strength concrete with 78 MPa average compressive strength. As the first experimental investigation on the axial compressive behavior of square and rectangular HSCFFTs, the results of the study reported in this paper allow a number of significant conclusions to be drawn. First and foremost, test results indicate that sufficiently confined square and rectangular HSCFFTs can exhibit highly ductile behavior. The results also indicate that confinement effectiveness of FRP tubes increases with an increase in corner radius and decreases with an increase in sectional aspect ratio. It is also observed and discussed that HSCFFTs having tubes of low confinement effectiveness may experience a significant strength loss at the point of transition on their stress-strain curves. Furthermore, it is found that the behavior of HSCFFTs at this region differ from that of normal-strength CFFTs and that it is more sensitive to the effectiveness of a confining tube. Examination of the test results have also lead to a number of important observations on the influence of the key confinement parameters on the development and distribution of the hoop strains on the tubes of CFFTs, which are presented and discussed in the paper. © 2013 American Society of Civil Engineers.Togay Ozbakkalogl

Revealing the dependence of the physiochemical and mechanical properties of cement composites on graphene oxide concentration

This paper presents a comprehensive study to evaluate the influence of graphene oxide (GO) concentration on the physiochemical and mechanical properties of cement mortar composites. Scanning electron micrographs (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) characterizations were performed to understand the correlation between physicochemical and observed axial tension and compression properties of GO–cement mortar composites. The results show considerable concentration dependence, with the optimum concentration of 0.1% GO that increases the tensile and compressive strength of the composite by 37.5% and 77.7%, respectively. These results are explained by the stronger bonding of calcium silicate hydrate (C–S–H) components in the cement matrix in the presence of GO sheets and the dependence of their dispersions and possible aggregation.Aliakbar Gholampour, Meisam Valizadeh Kiamahalleh, Diana N. H. Tran, Togay Ozbakkaloglu and Dusan Losi

Behavior of FRP-confined normal- and high-strength concrete under cyclic axial compression

An important application of fiber-reinforced polymer (FRP) composites is as a confining material for concrete, both in the seismic retrofit of existing reinforced concrete columns and in the construction of concrete-filled FRP tubes as earthquake-resistant columns in new construction. The reliable design of these structural members against earthquake-induced forces necessitates a clear understanding of the stress-strain behavior of FRP-confined concrete under load cycles. This paper presents the results of an experimental study on the behavior of FRP-confined normal- and high-strength concrete under axial compression. A total of 24 aramid and carbon FRP-confined concrete cylinders with different concrete strengths and FRP jacket thicknesses were tested under monotonic and cyclic loading. Examination of the test results has led to a number of significant conclusions in regards to both the trend and ultimate condition of the axial stress-strain behavior of FRP-confined concrete. These results are presented, and a discussion is provided on the influence of the main test parameters in the observed behaviors. The results are also compared with two existing cyclic axial stress-strain models for FRP-confined concrete. © 2012 American Society of Civil Engineers.Togay Ozbakkaloglu and Emre Aki

Flexural Rigidity Evaluation of Seismic Performance of Hollow-Core Composite Bridge Columns

This paper investigates experimentally the seismic behavior of two hollow-core fiber-reinforced polymer-concrete-steel HC-FCS columns under cyclic loading as a cantilever. The typical precast HC-FCS member consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The FRP tube provides continuous confinement for the concrete wall along the height of the column. Five large-scale HC-FCS columns were investigated during this study to estimate the effective flexural (which is an important factor to define the buckling capacity and deflection of such columns) and the effective structural stiffness of the composite columns. These columns have the same geometric properties; the only difference was in the thickness of the inner circular steel tubes and the steel tube embedded length into the footing. A three-dimensional numerical model has been developed using LS_DYNA software for modeling this large scale HC-FCS columns. The nonlinear FE models were designed and validated against experimental results gathered from HC-FCS columns tested under cyclic lateral loading and used to evaluate the effective stiffness’s results. The estimated effective stiffness results that obtained from the experimental work were compared with the FE results. This study revealed that the effective flexural and the effective structural stiffness for the HC-FCS columns need more investigation to be addressed in the standard codes. Since the embedded hollow core steel tube socket connections cannot reach the fully fixed end condition to act as a cantilever member subjected to a lateral load with a fully fixed end condition. Moreover, the effective stiffness results were found to be highly sensitive to the steel tube embedded length and slightly to the unconfined concrete strength