Добірка наукової літератури з теми "FRP tube"

This paper studies the impact performance of concrete filled FRP-steel tube which is a composed structure made by filling concrete into steel tube and wrapping outside with fiber reinforced polymer (FRP) sheet. Numerical simulations have been conducted to study the dynamic response of fixed-pined supported beams of concrete filled FRP-steel tubes. The finite element models of concrete filled FRP-steel tubes are established to analyse its lateral impact dynamic characteristics under different loading situations, with respective kinds of FRP and thicknesses of steel tubes. The impact force and displacement histories were recorded. Comparing to the traditional concrete filled steel tube structure, the concrete filled FRP-steel tube indicates a promising structure with more advantages in the mechanical and constructional performance. Especially with its higher loading-carrying capacity and better toughness, it is more adaptable for the structures subjected to accidental impact load. Analytical solution is compared with experimental result to show the correctness and the effectiveness of present study.

Hybrid double-tube concrete columns (hybrid DTCCs) are a novel form of hybrid columns that combine fiber-reinforced polymer (FRP) composites with two traditional construction materials (i.e., concrete and steel). Hybrid DTCCs consist of an outer FRP tube and an inner steel tube aligned concentrically, with the space between the two tubes and inside of the steel tube filled with concrete. The three materials (i.e., FRP, concrete, and steel) in hybrid DTCCs are combined optimally to deliver excellent performances, such as excellent ductility and remarkable corrosion resistance. Recently, hybrid DTCCs have received increasing research attention on their compressive behavior. Existing studies, however, are focused on hybrid DTCCs with fibers of the FRP tube oriented in the hoop direction or close to the hoop direction. Against this background, this paper presents a series of monotonic axial compression tests on hybrid DTCCs with a particular focus on the effect of fiber angles (i.e., the angle of the fiber orientations to the longitudinal axis of the FRP tube). Three types of fiber angles (i.e., ±45°, ±60°, or ±80°) and two FRP tube thicknesses (i.e., 4 mm and 8 mm) were employed in the present study. Experimental results show that the concrete in hybrid DTCCs is well confined by both the FRP tube and the steel tube, leading to excellent ductility; the confinement effect of the FRP tube increases with the increase of the absolute value of fiber angles, whereas the ultimate axial strain decreases with the increase of the absolute value of fiber angles. An existing analysis-oriented model, which considers the different confining states of the concrete between the two tubes and that inside of the steel tube, is verified using the present test results. The model is capable of providing accurate predictions for hybrid DTCCs with a ±80° FRP tube. For hybrid DTCCs with a ±45° or ±60° FRP tube, the model yields reasonable accurate predictions for the peak axial load but underestimates the ultimate axial strain consistently.

Three large-scale concrete-filled FRP-steel composite circular tubes and a control steel tube were tested to investigate flexural behavior. The effects of FRP and composite with different types of FRP with various ultimate strains were investigated. The study demonstrated the important effect of FRP, and showed that the load-displacement curves of FRP-steel composite tube beams could be divided into four stages: elastic stage, plastic stage, hardening stage and residual stage. An additional decline stage was gained for multi-fiber with different ultimate strains and steel composite tube concrete beams. FRP could increase the ultimate bearing capacity and bring the hardening stage after steel tube yielding, and a certain degree of stiffness would be achieved to avoid the “zero stiffness”. The composite of a variety of FRP could relax fracture failure for the FRP-steel composite steel concrete beams, realized the successive rupture of fiber in batches and changed the failure modes.

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 selected circular 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, manufacturing method of the tubes, and size of the CFFTs. Results indicate that concrete strength 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.

FRP-confined concrete filled steel tube may fully use the character of FRP-confined concrete and concrete filled steel tube. Based on the analysis of existing experimental data, the formula of ultimate bearing capacity of FRP-confined concrete filled steel tube is proposed. The mechanical behavior of FRP-confined concrete filled steel tube is mainly related to the equivalent confinement effect coefficient before the rupture of FRP. Based on the static equilibrium condition, the equivalent conversion section is adopted; taking as main parameter, the simplified stress-strain model of FRP-confined concrete filled steel tube is established. The predictions of the model agree well with test data.

An innovative beam concept made from hollow FRP tube with external flanges and filled with crumbed rubber concrete was investigated with respect to bending and shear. The performance of the rubberised-concrete-filled specimens was then compared with hollow and normal-concrete-filled tubes. A comparison between flanged and non-flanged hollow and concrete-filled tubes was also implemented. Moreover, finite element simulation was conducted to predict the fundamental behaviour of the beams. The results showed that concrete filling slightly improves bending performance but significantly enhances the shear properties of the beam. Adding 25% of crumb rubber in concrete marginally affects the bending and shear performance of the beam when compared with normal-concrete-filled tubes. Moreover, the stiffness-to-FRP weight ratio of a hollow externally flanged round tube is equivalent to that of a concrete-filled non-flanged round tube. The consideration of the pair-based contact surface between an FRP tube and infill concrete in linear finite element modelling predicted the failure loads within a 15% margin of difference.

In this research study, the performance of geopolymer concrete (GPC) in-filled fibre-reinforced polymer (FRP) composite (GPC-FRP) columns exposed to compressive loading is examined using the finite element (FE) analysis. The load–deflection behaviour is investigated by considering the impact of the strength of concrete, different fibre orientations and thicknesses of FRP tubes in terms of the diameter/thickness (D/t) ratio, surface friction in between the concrete and enclosing FRP tube, the lateral confinement and the axial stress distribution characteristics. The load-carrying capacity (LCC) of the GPC-FRP composite columns and cement concrete (CC) in-filled FRP composite (CC-FRP) columns is compared and the results imply that the LCC of the GPC-FRP composite columns is (0.9 to 2.04%) greater than the CC-FRP composite columns. The improvement in the LCC and lateral confining pressure of the GPC-FRP composite columns is observed as the thickness of the FRP tube increases. The LCC of the GPC-FRP composite columns with a D/t ratio of 30 was almost (12.70 to 14.23%) greater than the GPC-FRP composite columns with a D/t ratio of 50. The GPC-FRP composite columns with a fibre orientation in the axial and hoop directions (0°) exhibit (8.4 to 11.39%) better performance than the columns with any other orientations (30° and 53°). The LCC of the GPC-FRP composite columns with a coefficient of friction of 0.25 and 0.5 are quite comparable. The axial stress distribution in the GPC-FRP composite columns with different tube thicknesses is explored in this research. This FE model is validated with the experimental results obtained by Kim et al., (2015) and the load and deflection are predicted with the validation error of 6.5 and 6.1%, respectively.

Hybrid FRP-concrete-steel double-skin tubular columns (hybrid DSTCs) are a novel form of hollow columns consisting of an outer FRP tube, an inner steel tube, and an annular layer of concrete between the two tubes. Due to the effective confinement of the two tubes, the concrete in hybrid DSTCs is well confined, leading to excellent ductility and strength enhancement. Hybrid DSTCs also have excellent corrosion resistence due to the effective protection of the outer FRP tube. However, existing studies mainly focused on hybrid DSTCs with a circular cross-section. When subjecting to different loads in the two horizontal directions, elliptical columns are preferred as they can provide different bending stiffness and moment capacity around two axes of symmetry without significantly reducing the confining effect of the FRP tube. This paper extends the existing work on circular DSTCs to elliptical DSTCs with a particular focus on four issues: the effect of elliptical aspect ratio (i.e., the ratio of the major axis to the minor axis of the outer elliptical cross-section), the effect of the FRP tube thickness, the effect of void area ratio (i.e., the ratio of the area of concrete void to the area of the outer elliptical section), and the effect of the cross-section of the inner steel tube (i.e., both rectangular and elliptical steel tubes were used). Experimental results show that, the averaged peak stress of the confined concrete in elliptical DSTCs increases with the increase in the elliptical aspect ratio, whereas the elliptical aspect ratio has no obvious effect on the ultimate axial strain; the cross-section shape of the inner steel tube has significant effect on the axial stress-strain behavior of the confined concrete in elliptical DSTCs; elliptical DSTCs with an elliptical steel tube exhibit much better ductility and strength enhancement than those specimens with a rectangular steel tube. A simple stress-strain model of confined concrete was proposed for elliptical DSTCs to account for the effects of the elliptical aspect ratio, the inner void, and the shape of the inner steel tube, which can provide reasonably accurate but conservative predictions.

Penelitian ini bertujuan untuk menguji sejauhmana FRP tube yang terbuat dari Carbon Fiber Sheet efektif digunakan sebagai material perkuatan kolom beton ringan pada saat kolom tersebut dibebani secara tekan sentris. Sejumlah delapan buah silinder beton ringan dengan ukuran diameter 150 mm dan tinggi 300 mm dicetak dan dites hingga hancur. Kedelapan silinder tersebut terdiri dari dua buah silinder tanpa perkuatan, empat buah silinder dengan perkuatan menggunakan FRP tube, dan dua buah silinder dengan perkuatan menggunakan FRP wrapping. Hasil penelitian ini tidak dapat menunjukan sejauhmana FRP tube maupun wrapping efektif digunakan untuk memperkuat beton ringan karena benda uji miring. Walaupun demikian, tampak bahwa FRP tube dengan 3 lapis sangat efektif untuk memperkuat beton ringan Karena itu, untuk mengatasi masalah kemiringan pada benda uji yang diperkuat dengan FRP tube, perlu digunakan bekesting pada saat pengecoran.

In order to facilitate the actual design of the project, we study force performance of FRP tube steel-reinforced concrete columns under axial load. By five FRP tube steel reinforced concrete structures of axial compression, explore the damage characteristics and the force characteristics of the combination of column, and study parameters on performance of the force combination of column such as FRP tube wall thickness, fiber winding angle and loading mode etc. The capacity of combination column increases with the larger of the FRP tube wall thickness; and increases with the smaller of the FRP fiber winding angle; loaded in different ways lead to different capacities. Using superposition method Study and deduce a more reasonable axial compressive bearing capacity formula of FRP tube steel reinforced concrete structure. Theoretical calculation results match well with experimental results.

Recent terrorist attacks on critical infrastructures using car bombs have heightened awareness on the needs for blast resistance of structures. Blast design of civilian buildings has not been a common practice in structural design. For this reason, there is now an urgent need to mitigate the potentially devastating effects of blast shock waves on existing structures. The current research project, the results of which are reported in this dissertation, aims to expand knowledge on blast resistance of reinforced concrete building columns, while developing a technology and design procedure for protecting critical buildings columns against the damaging effects of impulsive blast loads through the use of externally applied fibre-reinforced polymer (FRP) jackets of different material architecture. The research project has a significant experimental component, with analytical verifications. A total of thirty two reinforced concrete columns were experimentally investigated under the effects of simulated blast loads using the University of Ottawa Shock Tube. Column dimensions were 150 mm x 150 mm in cross section and 2438 mm in length. Each concrete column was reinforced longitudinally with four 10M rebars which were tied laterally with 6.3 mm closed steel hoops, spaced at 37.5 mm and 100 mm c/c, representing seismic and non-seismic column details, respectively. The experimental research had two phases. Phase-I (sub-study) included blast tests of eight as-built, seismically detailed columns. The behaviour of these columns was explored under single and multiple blast shots, with and without the application of pre-blast axial loads. Phase-II (main-study) included column tests of different carbon FRP (CFRP) designs to investigate the significance of the use of different CFRP column jacket designs on dynamic response of twenty four seismic and non-seismic RC columns. Analytical investigation was conducted to assess and verify the significance of experimentally investigated parameters on column response. These included the use of Single-Degree-of-Freedom (SDOF) dynamic inelastic analysis, generation of dynamic resistance functions, the effects of variable axial loads, different plastic hinge lengths and the influence of secondary moments (P- moments) on column behaviour. The results indicate that the loading history has effects on column response, with multiple shots reducing column stiffness, and affecting dynamic response of columns relative to single blast shots of equivalent magnitude. The effect of concrete strength within the normal-strength concrete range is to increase strength and decrease deformations. Columns with CFRP jackets have considerable improvements in column deformability, with additional increases in column strength. The CFRP laminate design influences performance, with jackets having fibres in ±45o orientation especially improving column ductility and increasing plastic hinge lengths, thereby permitting redistribution of stresses and dissipating blast energy. Axial gravity loads vary during blast loads and can affect column strength. It was shown that SDOF dynamic inelastic analysis does capture key structural performance parameters in blast analysis. The consideration of experimentally observed parameters in column analysis; including the influence of CFRP design and associated change in plastic hinge length, variable axial load during response, and secondary moment (P- moments) result in significant improvements in the accuracy of blast analysis. The experimental results and the suggested improvements to the SDOF analysis technique can be used to implement a performance-based design approach recommended as part of the current research project for design of CFRP protection systems for concrete columns.This research project was conducted jointly by the National Research Council Canada (NRC) and the University of Ottawa.

Abstract: Recently, fiber-reinforced polymer (FRP) composite materials have been used in the field of civil engineering constructions especially in corrosive environments. They can be used as internal reinforcement for beams, slabs, and pavements, or as external reinforcement for rehabilitation and strengthening different structures. One of their innovative applications is the concrete-filled FRP tubes (CFFTs) which are becoming an alternative for different structural members such as piles, columns, bridge girders, and bridge piers due to their high performance and durability. In such integrated systems, the FRP tubes act as stay-in-place forms, protective jackets for the embedded concrete and steel, and as external reinforcement in the primary and secondary direction of the structural member. Extensive research was developed on CFFTs as columns, but comparatively limited research was carried out on CFFTs as beams especially those with rectangular sections. The circular sections exhibit magnificent confinement efficiency in case of columns. However, the rectangular sections have higher moment of inertia and flexural stiffness to resist the applied loads and deformations in case of beams. Moreover, the construction and architectural requirements prefer the rectangular section of beams, rather than the circular beams, due to its stability during installation and its workability during connecting to other structural members like slabs and columns. Also, CFFTs that are completely filled with concrete are not optimal for applications governed by pure bending, because the excess weight of the cracked concrete below the neutral axis may increase the transportation and installation cost. This dissertation presents experimental and theoretical investigations on the flexural behaviour of rectangular CFFT beams with steel rebar. These hybrid FRP-concrete-steel tubular rectangular beams contain outer rectangular filament-wound glass-FRP (GFRP) tubes to increase the sectional moment of inertia, to provide flexural and shear reinforcement, and to protect the inner structural elements (concrete and steel) against corrosion. The outer tubes were fully-or-partially filled with concrete and were reinforced with steel rebar at the tension side only. Inner hollow circular or square filament-wound GFRP tubes, shifted toward the tension zone, were provided inside the CFFT beam to eliminate the excess weight of the cracked concrete at the tension side, to confine actively the concrete at the compression side and to act as reinforcement at the tension side. The surfaces of tubes adjacent to concrete were roughened by sand coating to fulfill the full composite action of such hybrid section. Several test variables were chosen to investigate the effect of the outer and inner tubes thickness, fibers laminates, and shape on the flexural behaviour of such hybrid CFFT beams. To fulfil the objectives of the study, twenty-four full-scale beam specimens, 3200 mm long and 305×406 mm2 cross section, were tested under a four-point bending load. These specimens include eight fully-CFFT beams with wide range of tube thickness of 3.4 mm to 14.2 mm, fourteen partially-CFFT beams with different outer and inner tubes configurations, and two conventional steel-reinforced concrete (RC) beams as control specimens. The results indicate outstanding performance of the rectangular fully and partially-CFFT beams in terms of strength-to-weight ratio and ductility compared to the RC beams. The fully-CFFT beams with small tube thickness failed in tension by axial rupture of fibers at the tension side. While, the fully-CFFT beams with big tube thickness failed in compression by outward buckling of the outer tube compression flange with warning signs. The results indicate also that the flexural strength of the fully-CFFT beams was ascending nonlinearly with increasing the tubes thickness until a certain optimum limit. This limit was evaluated to define under-and-over-reinforced CFFT sections, and consequently to define the tension and compression failure of fully-CFFT beams, respectively. The inner hollow tubes act positively in reinforcing the partially-CFFT beams and confining the concrete core at the compression side. The strength-to-weight ratio of the partially-CFFT beams attained higher values than that of the corresponding fully-CFFT beams. Generally, the partially-CFFT beams failed gradually in compression due to outward buckling of the outer tube compression flange with signs of confining the concrete core at the compression side. The inner circular voids pronounced better performance than the square inner voids, however they have the same cross sectional area and fiber laminates. Theoretical section analysis based on strain compatibility/equilibrium has been developed to predict the moment-curvature response of the fully-CFFT section addressing the confinement and tension stiffening of concrete. The analytical results match well the experimental results in terms of moment, deflection, strains, and neutral axis responses. In addition, analytical investigation was conducted to examine the validity of the North American design codes provisions for predicting the deflection response of fully and partially-CFFT beams. Based on these investigations, a new power and assumptions were proposed to Branson’s equation to predict well the effective moment of inertia of the CFFT section. These assumptions consider the effect of the GFRP tube strength, thickness and configuration, in addition to the steel reinforcement ratio. The proposed equations predict well the deflection in the pre-yielding and post-yielding stages of the hybrid FRP-concrete-steel CFFT rectangular beams.
Résumé: Les matériaux composites en polymère renforcé de fibres (PRF) ont récemment été utilisés dans le domaine des constructions de génie civil, en particulier dans les environnements corrosifs. Elles peuvent être utilisées comme une armature interne pour des poutres, dalles et les trottoirs, ou comme une armature externe pour la réhabilitation et le renforcement de différentes structures. L'une de leurs applications novatrices est les tubes de polymères renforcés de fibres remplis de béton (TPFRB ) qui sont en train de devenir une alternative pour divers éléments structuraux tels que les pieux, les colonnes, les poutres et les piliers de ponts en raison de leur haute performance et durabilité. Dans de tels systèmes intégrés, les tubes PRF agissent comme un coffrage permanent, une chemise protectrice pour le béton et l'acier encastrés, et comme une armature externe dans les directions longitudinale et transversale de l'élément structural. La recherche a été concentrée sur les TPRFB comme des colonnes, mais très peu de recherche a été effectué les TPRFB comme des poutres particulièrement celles à section rectangulaire. La section circulaire présente une efficacité de confinement efficace en cas de colonnes. Toutefois, la section rectangulaire a un moment d'inertie plus élevé et une rigidité flexionnelle plus efficace pour résister les charges appliquées et les déformations dans le cas des poutres. Par ailleurs, les travaux de construction et les exigences architecturales préfèrent la section rectangulaire des poutres, plutôt que les poutres circulaires, en raison de sa stabilité pendant l'installation et sa maniabilité lors de la connexion à d'autres membres structuraux comme les dalles et les colonnes. En outre, les poutres TPRFB qui sont complètement remplis de béton ne sont pas optimales pour les applications contrôlées par la flexion pure, puisque le béton fissuré en dessous de l'axe neutre ne contribue pas à la résistance et augmente le poids propre et les coûts de transport et d'installation. Cette thèse présente des études théoriques et expérimentales sur le comportement en flexion de poutres rectangulaires (TPRFB) en béton armé. Ces poutres rectangulaires tubulaires hybrides en PRF-béton-acier sont composées de tubes rectangulaires externes fabriquées par enroulement filamentaire. Ces tubes fournissent un renforcement de flexion et de cisaillement; et protègent le béton armé contre la corrosion. Les poutres peuvent être soient entièrement ou partiellement remplies de béton. Des tubes intérieurs ( de section circulaires ou carrés) en polymères renforcés de fibres de verre (PRFV) sont positionnés dans la zone tendue de la poutre afin de réduire le poids et d’éliminer le béton fissuré en traction. Pour augmenter l'action composite de la section hybride, les surfaces des tubes adjacents au béton ont été rendues rugueuses par enrobage de sable. Plusieurs variables ont été choisis pour étudier l'effet de l’épaisseur des tubes extérieurs et intérieurs, les laminés de fibres, et la forme sur le comportement en flexion de ces poutres hybrides (TPRFB). Pour atteindre les objectifs de l’étude, vingt-quatre échantillons de poutre pleine grandeur, ayant une longueur de 3200 mm et une section transversale de 305×406 mm2, ont été testés sous une flexion à quatre points. Ces échantillons comprennent huit poutres de TPRFB entièrement remplis avec une large gamme d'épaisseur du tube externe de 3.4 mm à 14.2 mm, quatorze poutres de TPRFB partiellement remplis avec différentes configurations de tubes extérieurs et intérieurs, et deux poutres en béton armé conventionnel, comme échantillons de référence. Les résultats indiquent une performance exceptionnelle des poutres rectangulaires de TPRFB entièrement et partiellement remplies en termes du rapport de la résistance sur la masse et de la ductilité par rapport aux poutres en béton armé conventionnel. Les poutres de TPRFB entièrement remplies avec un tube de petite épaisseur ont rompu de façon moins ductile en tension par rupture axiale des fibres. Les poutres de TPRFB entièrement remplies et ayant une grande épaisseur ont rompu de façon ductile en compression par flambage local vers l’extérieur des parois en compression du tube externe. Les résultats indiquent également que la résistance à la flexion des poutres de TPRFB entièrement remplies augmente d’une façon non linéaire avec l'augmentation de l'épaisseur des tubes jusqu'à une certaine limite optimale. Cette limite a été évaluée pour définir les sections TPRFB sous-armées et surarmées et, par conséquent, pour définir la rupture en tension et en compression des poutres de TPRFB entièrement remplies, respectivement. Les tubes creux intérieurs agissent positivement dans le renforcement des poutres de TPRFB partiellement remplies et en confinant le noyau de béton du côté en compression. En général, les poutres de TPRFB partiellement remplies ont rompu en compression par flambage local vers l'extérieur des parois en compression du tube externe. Les vides circulaires intérieurs ont montré une meilleure performance que les vides carrés intérieurs, bien qu’ils aient la même superficie de la section transversale et le même taux de PRF. Une analyse théorique basée sur la compatibilité des déformations d’une section en flexion a été développée pour prédire la réponse moment-courbure de la poutre TPRFB en tenant compte des pourcentages de confinement externe et interne. Les résultats analytiques et les résultats expérimentaux s’accordent en termes de moment, flèche, déformations, et positions de l'axe neutre. En outre, une étude analytique a été menée afin d'examiner la validité des codes de conception nord-américains pour prédire la réponse en flexion des poutres TPRFB. En se basant sur les résultats de ces études, de nouvelles équations ont été proposées pour mieux prédire le moment effectif d'inertie de la section et une nouvelle procédure de conception pour prédire les capacités ultimes. Ces équations considèrent l'effet de la résistance des tubes en PRFV externe et interne que le taux d’armature en acier. En outre, ils prédisent bien la flèche dans les phases avant et après la limite élastique des poutres rectangulaires hybrides à haute performance.

As part of a multi-university research program funded by NSF, a comprehensive experimental and analytical study of seismic behavior of hybrid fiber reinforced polymer (FRP)-concrete column is presented in this dissertation. Experimental investigation includes cyclic tests of six large-scale concrete-filled FRP tube (CFFT) and RC columns followed by monotonic flexural tests, a nondestructive evaluation of damage using ultrasonic pulse velocity in between the two test sets and tension tests of sixty-five FRP coupons. Two analytical models using ANSYS and OpenSees were developed and favorably verified against both cyclic and monotonic flexural tests. The results of the two methods were compared. A parametric study was also carried out to investigate the effect of three main parameters on primary seismic response measures. The responses of typical CFFT columns to three representative earthquake records were also investigated. The study shows that only specimens with carbon FRP cracked, whereas specimens with glass or hybrid FRP did not show any visible cracks throughout cyclic tests. Further monotonic flexural tests showed that carbon specimens both experienced flexural cracks in tension and crumpling in compression. Glass or hybrid specimens, on the other hand, all showed local buckling of FRP tubes. Compared with conventional RC columns, CFFT column possesses higher flexural strength and energy dissipation with an extended plastic hinge region. Among all CFFT columns, the hybrid lay-up demonstrated the highest flexural strength and initial stiffness, mainly because of its high reinforcement index and FRP/concrete stiffness ratio, respectively. Moreover, at the same drift ratio, the hybrid lay-up was also considered as the best in term of energy dissipation. Specimens with glassfiber tubes, on the other hand, exhibited the highest ductility due to better flexibility of glass FRP composites. Furthermore, ductility of CFFTs showed a strong correlation with the rupture strain of FRP. Parametric study further showed that different FRP architecture and rebar types may lead to different failure modes for CFFT columns. Transient analysis of strong ground motions showed that the column with off-axis nonlinear filament-wound glass FRP tube exhibited a superior seismic performance to all other CFFTs. Moreover, higher FRP reinforcement ratios may lead to a brittle system failure, while a well-engineered FRP reinforcement configuration may significantly enhance the seismic performance of CFFT columns.

Abstract : The construction industry is expressing great demand for innovative and durable structural members such as bridge decks and piers, piling, and poles. Many steel-reinforced concrete structures subjected to de-icing salts and marine environments require extensive and expensive maintenance. Fiber-reinforced polymers (FRPs) have recently gained wide acceptance as a viable construction material for repair, rehabilitation, or new construction of the aging infrastructures particularly those exposed to harsh environment conditions. The promising concept of concrete-filled FRP tube (CFFT) system, that may be further reinforced with steel or FRP bars, has raised great interest amongst researchers in the last decade. The CFFT technique has been used successfully in different concrete structure elements such as pier column and girder for bridges and also as fender piles in marine structures. The FRP tube acts as a stay-in-place structural formwork, a noncorrosive reinforcement for the concrete for flexure and shear, provides confinement to the concrete in compression, and the contained concrete is protected from intrusion of moisture with corrosive agents that could otherwise deteriorate the concrete core. Using FRP bars instead of conventional steel bars in the CFFT columns can provide a step forward to develop a promising totally corrosion-free new structural system. Nonetheless, the axial behaviour of FRP bars as longitudinal reinforcement in compression members has yet to be explored, especially for the CFFT columns. To date, most of the experimental investigations performed on FRP confined concrete columns have considered short, unreinforced, small-scale concrete cylinders, tested under concentric, monotonic, and axial load. The slenderness ratio, internal longitudinal reinforcement type (steel or FRP bars), and axial cyclic loading effects on the behaviour of FRP confined concrete long columns, however, have received only limited research attention. To address such knowledge gaps, this study aimed at investigating the behaviour of the CFFT long columns internally reinforced with steel or FRP bars tested under monotonic and cyclic axial loading. A total of ten reinforced concrete (RC) and CFFT columns were constructed and tested until failure. All columns had 1900-mm in height and 213-mm in diameter. The investigated parameters were: i) the effect of internal reinforcement type (steel, glass FRP (GFRP), or carbon FRP (CFRP)) and amount, ii) GFRP tube thicknesses, and iii) nature of loading (i.e. monotonic and cyclic). The effect of the different parameters on the axial behaviour of the tested columns is presented and discussed. The research work presented in this dissertation has resulted in one paper submitted to the Elsevier Journal of Engineering Structures (manuscript ID: ENGSTRUCT-D-15-01381) and one accepted conference paper submitted to the 5 th International Structural Specialty Conference (CSCE 2016), London, Ontario, June 1st - 4th, 2016. The experimental test results showed that the CFFT columns reinforced with GFRP bars exhibited similar responses compared to their counterparts reinforced with steel bars with no significant difference in terms of ultimate axial strength and strain capacities. The GFRP tubes provided significant confinement of the tested specimens attributing to shift the mode of failure from axially dominated material failure to flexural-dominated instability failure. The results also indicated that the plastic strains of the FRP-reinforced CFFT columns was linearly proportional to the envelop unloading strains (εun,env). The relationship depended little on level of confinement, but strongly on the longitudinal reinforcement amount and type, particularly when εun,env > 0.0035. On the other hand, an analytical investigation was conducted to examine the validity of the available design provisions for predicting the ultimate load capacity of tested columns. The results of the analysis were compared with the experimental values. It was found that the ACI 440.R1 (2015), CSA S806 (2012), and CSA S6-06 (2010) design provisions provided higher conservative results for the GFRP-reinforced control specimens than that of steel-reinforced specimen. This might be due to neglecting the contribution of the compressive resistance of the GFRP bars to the axial carrying capacity. Furthermore, for FRP-reinforced CFFT columns, the ACI 440.2R (2008), CSA S806 (2012), and CSA S6-06 (2010) provisions results over the experimental results were an average of 1.68±0.31, 1.57±0.18, and 1.72±0.35 with a COV of 18.4%, 11.3%, and 20.5%, respectively. By considering the confinement codes limits, the CSA S806 (2012) showed better correlation for the ultimate carrying capacity based on the average than the CSA S6-06 (2010) and ACI 440.2R (2008), particularly for specimens cast with tube Type B.
Résumé : L'industrie de la construction exprime une grande demande pour les structures innovantes et durables tels que les tabliers de ponts et les quais, les pieux et les poteaux. Plusieurs structures en béton armé sont soumises à des sels de déglaçage et à des environnements marins qui exigent un entretien coûteux. Les polymères renforcés de fibres (PRF) ont récemment été reconnus en tant que matériau de construction viable pour la réparation, la réhabilitation ou la construction de nouvelles infrastructures vieillissantes en particulier celles exposées à des conditions d'environnement sévères. Le concept prometteur du système de tube rempli de béton PRF (CFFT), qui peut être encore renforcé avec de l'acier ou des barres en PRF, a amorcé un grand intérêt parmi les chercheurs durant la dernière décennie. La technique CFFT a été utilisée avec succès dans les différents éléments de structure en béton tels que les colonnes et les poutres de ponts et aussi comme des pieux pour les structures marines. Le tube en PRF agit comme un coffrage structural sur place, un renforcement non corrosif pour le béton en flexion et au cisaillement en utilisant l'orientation des fibres multidirectionnelle, fournit un confinement au béton en compression, et le béton est protégé de toute intrusion d'humidité des agents corrosifs qui, autrement, pourraient détériorer le noyau de béton (ACI 440. R-07 (2007)). L’utilisation des barres de PRF au lieu de barres d'acier conventionnelles dans les colonnes CFFT peut fournir un pas en avant pour développer un nouveau système structurel. Néanmoins, le comportement axial des barres en PRF comme armatures longitudinales dans les membrures en compression n'a pas encore été exploré, en particulier pour les colonnes CFFT. À ce jour, la plupart des études expérimentales effectuées sur les colonnes en béton confinés de PRF, ont considéré des cylindres en béton, courts, à petite échelle non armés, et testés sous un charge concentrique, monotone, et axiale. Le rapport d'élancement, le renfort longitudinal interne (acier ou barres en PRF), et les effets du chargement axial cyclique sur le comportement des colonnes élancées de béton confinés et en PRF, ont connu une recherche limitée. Pour combler ce manque de connaissance, cette étude vise à étudier le comportement des colonnes élancées CFFT armé en acier ou en barres de PRF testées sous charges axiales monotones et cycliques. Un total de dix colonnes en béton armé (RC) et CFFT été fabriquées et testées jusqu'à la rupture. Toutes les colonnes ont 1900 mm de hauteur et 213 mm de diamètre. Les paramètres étudiés sont les suivants: i) l'effet de type de renforcement interne et la quantité de renforcement, ii) les épaisseurs de tubes PRV, et iii) le type de chargement (monotone et cyclique). L'effet des variables considérées sur le comportement axial des colonnes testées dans le travail expérimental est présenté et discuté. Le travail de recherche présenté dans cette analyse a fait l’objet d’un article scientifique soumis à Elsevier Journal of Engineering Structures (manuscrit ID: ENGSTRUCT-D-15-01381) et un article lors d’une conférence acceptée soumis à la 5ième International Structural Specialty Conference (CSCE 2016), London, Ontario, Juin 1er - 4ième, 2016. Les résultats des essais expérimentaux ont montré que les colonnes CFFT renforcées de barres en PRFV présentaient des réponses similaires par rapport à leurs homologues renforcées avec des barres d'acier sans différence significative en termes de capacité ultime de résistance axiale et de déformation. Les tubes en PRFV fournissent un confinement significatif des échantillons testés attribuant à changer le mode de rupture, c’est-à-dire d’une rupture des matériaux axialement à une rupture d’instabilité en flexion. En outre, l'augmentation de l'épaisseur du tube en PRFV de 2,9 à 6,4 mm améliore les rapports de résistance et de déformation de 25 % et 12 %, respectivement. Les résultats indiquent également que les déformations plastiques des colonnes renforcées de PRF sont linéairement proportionnelles aux enveloppes de tension de déchargement (εde,env). La relation dépend un peu du niveau de confinement, mais fortement de la quantité et du type de renfort longitudinal, en particulier lorsque εde,env > 0,0035. D'autre part, une investigation a été menée pour examiner la validité des dispositions de conception disponibles pour prédire la capacité de la charge ultime des colonnes testées. Les résultats de l'analyse ont été comparés avec les valeurs expérimentales. Il a été constaté que les prévisions de l'ACI 440.R1 (2015), CSA S806 (2012), et CSA S6-06 (2010) ont fourni des résultats conservateurs plus élevés pour les échantillons de contrôle en PRFV que celui de l'échantillon d'acier. Cela peut être dû à la négligence de la contribution de la résistance à la compression des barres de PRFV à la capacité de charge axiale. En outre, pour les colonnes de CFFT renforcées de PRF, les prévisions de l'ACI 440.2R (2008), du CSA S806 (2012), et du CSA S6-06 (2010) étaient de 1,68 ± 0,31, 1,57 ± 0,18 et 1,72 ± 0,35 avec un COV de 18,4 %, 11,3%, et 20,5%, respectivement. En considérant les limites des codes de confinement, le code CSA S806 (2012) a révélé les meilleures prévisions pour la capacité de charge ultime basée sur la moyenne que celui du code CSA S6-06 (2010) et de l’ACI 440.2R (2008), en particulier pour les échantillons réalisés avec des tubes de Type B.

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.

Lower-cost manufacturing methods have increased the anticipation for economical mass production of vehicles manufactured from composite materials. One of the potential applications of composite materials in vehicles is in energy-absorbing components such as hollow shells and struts (these components may be in the form of circular cylindrical shells, square and rectangular tubes, conical shells, and frusta). However, constructions which result in brittle fracture of the composite tubes in the form of circumferential or longitudinal corner crack propagation may lead to unstable collapse failure mode and concomitant very low energy absorption. As a result, metal-composite hollow tubes have been developed that combine the benefits of stable ductile collapse of the metal (which can absorb crushing energy in a controlled manner) and the high strength-to-weight ratio of the composites. The relative and absolute thicknesses of metal or FRP section has a substantial effect on energy absorption of the hybrid tubes. In particular, likelihood of delamination occurrence raises with increase in FRP thickness. This can reduce the energy absorption capability of the metal-FRP hybrid tubes. Additionally, adding a very thick FRP section may result in a global buckling failure mode (rather than local folding). Until now, there are no studies specifically addressing the effect of FRP thickness on energy absorption of hybrid tubes. In this study, the effects of fiber orientation and FRP thickness (the number of layers) on the energy absorption of S2-glass/epoxy-304 stainless steel square tubes were experimentally investigated. In addition, a new geometrical trigger was demonstrated which has positive effects on the collapse modes, delamination in the FRP, and the crush load efficiency of the hybrid tube. To complete this study, a new methodology including the combination of experimental results, numerical modeling, and a multi-objective optimization process was introduced to obtain the best combination of design variables for hybrid metal-composite tubes for crashworthiness applications. The experimental results for the S2 glass/epoxy-304 stainless steel square tubes with different configurations tested under quasi-static compression loading were used to validate numerical models implemented in LS-DYNA software. The models were able to capture progressive failure mechanisms of the hybrid tubes. In addition, the effects of the design variables on the energy absorption and failure modes of the hybrid tubes were explained. Subsequently, the results from the numerical models were used to obtain optimum crashworthiness functions. The load efficiency factor (the ratio of mean crushing load to maximum load) and ratio between the difference of mean crushing load of hybrid and metal tube and thickness of the FRP section were introduced as objective functions. To connect the variables and the functions, back-propagation artificial neural networks (ANN) were used. The Non-dominated Sorting Genetic Algorithm–II (NSGAII) was applied to the constructed ANNs to obtain optimal results. The results were presented in the form of Pareto frontiers to help designers choose optimized configurations based on their manufacturing limitations. Such restrictions may include, but are not limited to, cost (related to the number of layers), laminate architecture (fiber orientation and stacking sequence) which can be constrained by the manufacturing techniques (i.e. filament winding) and thickness (as an example of physical constraints).
Ph. D.

Corrosion of steel reinforcement causes continual degradation to the worldwide infrastructures and it has prompted the need for challenges to those involved with reinforced concrete structures. Recently, the use of fibre-reinforced polymers (FRP) tubes as structurally integrated stay-in-place forms for concrete members, such as beams, columns, bridge piers, piles and fender piles has emerged as an innovative solution to the corrosion problem. In such integrated systems, the FRP tubes may act as a permanent form, often as a protective jacket for concrete, and especially as external reinforcement in the primary and secondary directions such as for confinement. Furthermore, the use of concrete-filled FRP tubes (CFFT) technique is predicated on performance attributes linked to their high strength-to-weight ratios, expand the service life of structures, enhance corrosion resistance, and potentially high durability. This dissertation evaluates the axial and flexural performances of reinforced CFFT through experimental and analytical investigations. The details description and the findings of the investigations are presented through seven articles. To fulfill the objectives of this research, an experimental program has been designed including pure compression tests (33 specimens), axial-eccentric load tests (4 specimens) and pure flexure tests (10 specimens). Experimental investigations of the behaviour of CFFT have generally been carried out without using internal longitudinal reinforcement. The CFFT system of this study consists basically of filament-wound glass FRP tubes filled with concrete and reinforced internally with steel or FRP bars. Five types of new FRP tubes have been used with different thicknesses and two different diameters, 152 and 213 mm. Pure compression tests have been conducted on 40 specimens with a total height ranging from 305 mm to 1520 mm. One of the main objectives of testing these specimens is to evaluate the design equations of the North American codes and design guidelines to predict the ultimate load capacities of reinforced and unreinforced short CFFT columns. In addition, the effect of three parameters and their interactions on the buckling behaviour were investigated for these specimens; namely, the FRP tube thickness, concrete compressive strength, and slenderness ratio. The effect of eccentric load on the behaviour of four CFFT specimens of diameters 152mm and long 912mm, has been evaluated using four different eccentricity values (15, 30, 45 and 60 mm). Based on the finding of experimental and theoretical investigation for the CFFT columns, a new confinement model is proposed for the confined concrete compressive strength of the CFFT cylinders. Also, the design equations are modified to accurately predict the ultimate and yield loads capacities of internally reinforced and unreinforced short CFFT columns. In addition, the theoretical analysis was utilized to correlate the slenderness ratio of the CFFT columns to various material characteristics and geometric properties of the FRP tubes and concrete. It was found that a slenderness ratio of 12 gave a safe value for the design purposes. However a more precise formula for the slenderness ratio was proposed to control the buckling mode of failure. Pure flexural tests have been conducted on 10 RCFFT and RC beams of a total length 2000 mm with constant diameter 213 mm. The test variables were the type of internal reinforcements (steel or GFRP bars), the FRP tube thickness, concrete compressive strength and the type of transverse reinforcements (spiral steel or FRP tubes). The influence of the considered variables on the flexural behaviour of the tested RCFFT beams is presented. A simplified analytical method is developed to predict the yield and resisting moments corresponding to the failure modes of the tested RCFFT beams. The analysis was conducted according to the equations derived from linear elastic analysis. This analysis was found to be acceptable for predicting the ultimate and yield moments capacities of the FRP or steel-RCFFT beams. In addition, an analytical investigation to examine the validity of the available design provisions for predicting the load-deflection response of CFFT is conducted. The effective moments of inertia of the tested beams are analyzed using the different available code, manuals and design guidelines equations. The results of the analysis are compared with the experimental values. It has been found that the predicted tension stiffening for steel or FRP-RCFFT beams using the conventional equations (steel or FRP-RC member) is underestimated and hence the predicted deflections are overestimated. Based on the experimental data obtained in this study, new proposed equations and a modified expression for the effective moment of inertia of a simply supported CFFT beams reinforced with steel or GFRP bars are introduced.

Thesis (M.S. in civil engineering)--Washington State University, December 2009.
Title from PDF title page (viewed on Feb. 4, 2010). "Department of Civil Engineering." Includes bibliographical references (p. 134-135).

Il seguente elaborato di tesi nasce con lo scopo di valorizzare l’utilizzo di tubi cavi in materiale composito, principalmente in ambito offshore, poiché caratterizzati da un’elevata efficienza strutturale e soprattutto da un eccellente resistenza alla corrosione. In merito a questo, si fornisce un metodo alternativo atto a velocizzare e permettere la progettazione di essi senza l’utilizzo di un laborioso modello 3D agli elementi finiti. Lo studio effettuato, oltre ad ampliare la conoscenza sul comportamento dei tubolari, consiste nel calcolare i coefficienti della matrice di rigidezza tramite una semplice formulazione analitica. Quest’ultima, valida per la maggior parte degli schemi di laminazione, sfrutta il metodo di omogeneizzazione della sezione di Sun et al. e la formulazione di Eulero-Bernoulli per ottenere i coefficienti di rigidezza di un materiale isotropo. Si è constatato come attraverso il modello equivalente beam-frame 3D conseguito sia possibile ottenere valori dei coefficienti della matrice di rigidezza con errori minori del 5% rispetto a quelli definiti tramite il modello shell 3D agli elementi finiti. Per lo studio affrontato si sono considerati i laminati Cross-Ply, Angle-Ply, bilanciati e non, e laminati con configurazione particolare, ovvero, laminati con variazione angolare delle fibre tra gli strati molto piccola e laminati con materiali compositi fortemente ortotropi tali da generare valori di poisson negativi o molto elevati a seconda dello schema di laminazione. Si è cercato, infine, di dare una visione più concreta dell’argomento trattato illustrando un impiego plausibile, ovvero quello del ponteggio in ambito offshore. Grazie alla Gruppo Cosmi S.p.a. e alla Seico compositi S.r.l. è stato possibile effettuare un confronto a livello economico e gestionale tra i "tubi innocenti" tradizionali in acciaio e quelli in materiale composito valorizzando l’utilizzo di quest’ultimi.

In this study, the static and impact energy absorption characteristics and crushing mechanism based on precise cross-sectional observation of crush zone in two kinds of square FRP tube were investigated. The specific energy absorption value of unidirectional tube showed higher value than that of knitted fabric tube in both static and impact test. Energy absorption mechanism changed from central crack progressive mode with fiber fracture to delamination mode without fiber fracture for unidirectional tube, and from central creck progressive mode to collapse mode with large fragments of inner fronds for knitted fabric tube with the change in testing speed from static to impact.

During the evolutionary process of speciation in plants, naturally occurring barriers to reproduction have developed that affect the transfer of genes within and between related species. These barriers can occur at several different levels beginning with pollination-barriers and ending with hybrid-breakdown. The interaction between pollen and pistils presents one of the major barriers to intra- and inter-specific crosses and is the focus of this research project. Our long-term goal in this research proposal was defined to resolve questions on recognition and communication during pollen-pistil interactions in the extended tomato family. In this context, this work was initiated and planned to study the potential involvement of tomato pollen-specific receptor-like kinases (RLK's) in the interaction between pollen and pistils. By special permission from BARD the objectives of this research were extended to include studies on pollen-pistil interactions and pollination barriers in horticultural crops with an emphasis on citrus. Functional characterization of 2 pollen-specific RLK's from tomato was carried out. The data shows that both encode functional kinases that were active as recombinant proteins. One of the kinases was shown to accumulate mainly after pollen germination and to be phosphorylated in-vitro in pollen membranes as well as in-vivo. The presence of style extract resulted in dephosphorylation of the RLK, although no species specificity was observed. This data implies a role for at least one RLK in pollination events following pollen germination. However, a transgenic plant analysis of the RLK's comprising overexpression, dominant-negative and anti-sense constructs failed to provide answers on their role in pollination. While genetic effects on some of the plants were observed in both the Israeli and American labs, no clear functional answers were obtained. An alternative approach to addressing function was pursued by screening for an artificial ligand for the receptor domain using a peptide phage display library. An enriched peptide sequence was obtained and will be used to design a peptide-ligand to be tested for its effect o pollen germination and tube growth. Self-incompatibility (SI) in citrus was studied on 3 varieties of pummelo. SI was observed using fluorescence microscopy in each of the 3 varieties and compatibility relations between varieties was determined. An initial screen for an S-RNase SI mechanism yielded only a cDNA homologous to the group of S-like RNases, suggesting that SI results from an as yet unknown mechanism. 2D gel electrophoresis was applied to compare pollen and style profiles of different compatibility groups. A "polymorphic" protein band from style extracts was observed, isolated and micro-sequenced. Degenerate primers designed based on the peptide sequence date will be used to isolate the relevant genes i order to study their potential involvement in SI. A study on SI in the apple cultivar Top red was initiated. SI was found, as previously shown, to be complete thus requiring a compatible pollinator variety. A new S-RNase allele was discovered fro Top red styles and was found to be highly homologous to pear S-RNases, suggesting that evolution of these genes pre-dated speciation into apples and pears but not to other Rosaceae species. The new allele provides molecular-genetic tools to determine potential pollinators for the variety Top red as well as a tool to break-down SI in this important variety.