Papers by Keyword: Confinement

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Authors: Jian Chin Lim, Togay Ozbakkloglu
Abstract: This paper presents a study on the axial compressive behavior of fiber reinforced polymer (FRP)-confined high-strength concrete (HSC). A large experimental test database assembled from the published literature was used to investigate and quantify factors influencing the compressive behavior of FRP-confined HSC. The database consisted of 976 test data having unconfined concrete strength ranging from 6.2 to 169.7MPa. Based on the analysis results of the database, it was found that the threshold confinement stiffness increases significantly with an increase in concrete strength, which in turn adversely affects the strength enhancement of confined concrete. It was also observed that the hoop rupture strain of FRP shell decreases with an increase in concrete strength. Existing confinement models that are applicable to FRP-confined HSC were assessed using the database. Finally, a new simple design-oriented model for FRP-confined HSC developed on the basis of the database is presented.
Authors: Wen Bai Qiu, Yang Yue Ye Cao, Zhi Gang Jiang, Chao Mei Meng
Abstract: Cases of tunneling adjacent to existing structures are common nowadays in urban construction. The interaction between newly constructed tunnels and existing underground structures is an important issue, while the previous works mainly focused on the effect that constructing a new tunnel would have on existing structures. In this article, the effect that existing structures would have on newly constructed tunnels was come up with, and a model was proposed to analyze the confinement of existing structures to the tunnel surrounding rock. Discussions were carried out theoretically and numerically.
Authors: Giovanni Minafò, Marinella Fossetti, Maurizio Papia, Giuseppe Patti
Abstract: Reinforced concrete (RC) jacketing is becoming increasingly common among the different retrofit techniques for poor RC members, due to its economical and practical advantages. Experimental investigations in the literature have shown that the actual axial capacity of RC jacketed members can be substantially lower than that analytically evaluated by adapting the most common theoretical models for confined concrete. This fact can be explained by taking into account the presence of tensile stresses developing in the concrete, due to a mutual interaction between the inner core and the external jacket. This phenomenon is relevant especially in members where the concrete properties of the jacket are different with respect to those of the core, causing the premature failure of the external layer. This paper presents a simplified approach able to evaluate these effects. Circular RC jacketed sections are studied and a model is presented to predict the concrete softening effect. The section is modeled by joining circular hollow layers and circumferential and radial stresses are firstly calculated under the assumption of linear elastic behaviour and plane strain state. The model is extended in the non-linear range by adopting a secant constitutive law. Finally, comparisons are made with experimental data available in the literature, showing good agreement.
Authors: Gustavo Tumialan
Abstract: This article provides an overview of ACI 440.7R – Design Guide for Strengthening of Masonry with FRP Systems. ACI 440.7R was developed by the American Concrete Institute (ACI) Committee 440 and published in 2010. ACI 440.7R has recently revised to include new topics. This article provides an overview of the design methodologies recommended by ACI 440 for flexural and shear strengthening of masonry walls, confinement of masonry, and repair (“stitching”) of cracked masonry with FRP systems.
Authors: Togay Ozbakkloglu, Butje Alfonsius Louk Fanggi
Abstract: This paper reports on part of an ongoing experimental program at The University of Adelaide on FRP-concrete-steel composite columns. The results from eight FRP-concrete-steel double-skin columns (DSTCs) that were tested under constant axial compression are presented. The key parameters examined included diameter, thickness, and strength of inner steel tube. The results of the experimental study indicate that concrete in a DSTC system is confined effectively by FRP and steel tubes. The results also indicate that increasing the inner steel tube diameter leads to an increase in the ultimate axial strength and strain of DSTCs. No clear influence of the strength of inner steel tube is observed on the ultimate condition of concrete in DSTCs. These results are presented together with a discussion on the influence of the key parameters on the compressive behavior of DSTCs.
Authors: Thomas Vincent, Togay Ozbakkloglu
Abstract: It is well established that external confinement of concrete with fiber reinforced polymer (FRP) sheets results in significant improvements on the axial compressive behavior of concrete. This understanding has led to a large number of experimental studies being conducted over the last two decades. However, the majority of these studies have focused on normal strength concretes (NSC) with compressive strengths lower than 55 MPa, and studies on higher strength concretes have been very limited. This paper presents the results of an experimental study on the compressive behavior of FRP confined high- and ultra high-strength concrete (HSC and UHSC) with average compressive strengths of 65 and 100 MPa. A total of 29 specimens were tested under axial compression to investigate the influence of key parameters such as concrete strength and method of confinement. All specimens were cylindrical, confined with carbon FRP and were 305 mm in height and 152 mm in diameter. Results obtained from the laboratory testing were graphically presented in the form of axial stress-strain relationships and key experimental outcomes are discussed. The results of this experimental study indicate that above a certain confinement threshold, FRP-confined HSC and UHSC exhibit highly ductile behavior. The results also indicate that FRP-wrapped specimens perform similar to concrete-filled FRP tube (CFFT) specimens at ultimate condition, however notable differences are evident at the transition region when comparing stress-strain curves.
Authors: Y. X. Wang, Z. Y. Pan, B. E. Zhu, Y. Xiao, S. H. Guo
Abstract: Classical molecular dynamics simulation was used to investigate the structure, melting and mechanical properties of Au nanowires encapsulated in single-walled carbon nanotubes (SWCNT). A possibility of synthesizing controlled Au nanowires was firstly studied by encapsulating small clusters into CNTs with suitable diameters. The nanowires with multi-shell structure of cylindrical symmetry are predicted as a consequence of spontaneous and confined coalescence of gold clusters. The investigation of melting temperature and behavior of a gold nanowire with multi-shells in a carbon nanotube (CNT) showed that the melting temperature of the enclosed Au nanowire is lower than its bulk counterpart and higher than that observed for free-standing ones. Different from the melting behavior of freestanding Au nanowires, the melting of Au nanowires enclosed in CNTs with tube diameters (D) in the range of 1.08 nm < D < 2.09 nm investigated here was found to initiate from the center layers. Finally, the deformation behavior of the gold-filled single-walled carbon nanotube was simulated under axial compression. The results show that the buckling strength of the Au-filled carbon nanotube is increased compared with that of a hollow tube, and is similar to the case of filling with gases or fullerenes. The interactions between filling elements and the carbon wall help restrain the collapse of the tube. With Au-filling, the filled tube experiences an elastic-inelastic transition, somewhat like the behavior of metals, which is different from the cases when it is filled with gases or fullerenes, particularly for low filling density.
Authors: Zheng He, Jian Ping Jin
Abstract: Twenty-nine circular specimens in four groups were tested to investigate the effect of short-term preloading on axial compressive behavior of CFRP-confined concrete. The results indicate that short-term preloading generally put a slight positive effect on the axial resistance of pure axial compressive members. As the preloading stress level index increases, the elastic segments of the load-strain curves of confined plain specimens, with or without preloading, firstly increase and then decrease. The influence of short-term preloading on the load-strain responses of confined reinforced concrete specimens is found to be insignificant. The elastic stiffness of all confined specimens does not seem to be affected by the index, but it would be increased by the introduction of longitudinal reinforcement. The results also indicate that the ultimate expansion ratio of a confined concrete column is related to the index and confinement ratio. As the ratio of the index to confinement ratio increases, the ultimate expansion ratio firstly decreases slightly and then increases rapidly. The regressive expression has also revealed that the influence of short-term preloading could be ignored if a column is extremely heavily confined with CFRP materials.
Authors: Thomas Vincent, Togay Ozbakkloglu
Abstract: Concrete-filled FRP tubes (CFFTs) have received significant research attention over the last two decades. However, the experimental studies on the behavior of CFFTs filled with high- and ultra high-strength concretes (HSC and UHSC) remain very limited. This paper presents the results of an experimental study on the compressive behavior of circular HSC- and UHSC-filled fiber reinforced polymer (FRP) tubes (HSCFFTs and UHSCFFTs). A total of 24 aramid fiber made CFFTs were tested under uniaxial compression to investigate the influences of concrete strength, amount of confinement and manufacturing method of FRP tubes. The influence of tube manufacturing method was investigated with specimens manufactured with either automated filament winding or manual wet lay-up techniques. In this paper the experimentally recorded stress-strain relationships are presented graphically and key experimental outcomes discussed. The results indicate that the manufacturing method of the FRP tubes significantly influence the compressive behavior of CFFTs.
Authors: Thomas Vincent, Togay Ozbakkloglu
Abstract: This paper presents an experimental investigation into the axial strain measurement method of fiber reinforced polymer (FRP)-confined normal-and high-strength concrete (NSC and HSC). A total of 15 FRP-confined concrete specimens with circular cross-sections were tested under monotonic axial compression. Axial strain recordings were compared on specimens instrumented with three different measurement methods: axial strain gauges and full-and mid-height linear variable displacement transformers (LVDTs). The ultimate conditions are tabulated for each measurement method and key experimental outcomes discussed. The results indicate that axial strains of FRP-confined HSC are highly sensitive to the instrumentation arrangement and significant differences occur in the results obtained from different measurement methods.
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