京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19236号 / 工博第4071号 / 新制||工||1628(附属図書館) / 32235 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 西脇 眞二, 教授 松原 厚, 准教授 小森 雅晴 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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<p> The thesis summarizes the experimental and analytical results of studies on the behavior of two FRP-encased steel-concrete composite columns under axial loading. Composite columns have been conventionally constructed using steel and concrete. This study utilizes FRP in combination with steel and concrete to manufacture composite columns with enhanced behavior. The first type of column is a concrete-encased steel column wrapped with epoxy-saturated glass and carbon fiber reinforced polymer (GFRP and CFRP) sheets in the transverse direction. The second type of composite column utilizes a GFRP tube that surrounds a steel I section column, which is subsequently filled with concrete. </p> <p> To the best of the author's knowledge, columns comprising FRP, steel and concrete in the shape of the proposed composite systems has not been reported on in the literature. This study includes two major phases. In the first phase, behavior of stub columns is investigated where stability effects are ignored and failure is governed by the loss of cross-sectional strength. In the second phase, influence of stability on the behavior of the proposed composite columns is studied by testing specimens with various slenderness ratios. </p> <p> To investigate the cross-sectional strength, a total of nine short (500 mm in height) composite column specimens were constructed and tested under axial compression. Five specimens were wrapped with FRP sheets and the remaining four were constructed using a GFRP tube. Experimental results showed significant enhancement in the behavior of the composite columns which was achieved due to confinement and composite action between the constituent materials. The compressive strength of the confined concrete core in the composite specimens constructed using FRP sheets and GFRP tube increased by a factor of 2.4 and 1.8, respectively. An analytical model was developed to predict crosssectional behavior of the proposed composited column. </p> <p> With the primary objective of investigating the influence of slenderness on the behavior of the composite columns, ten additional column specimens, ranging between 1,000 mm and 3,000 mm in height, were tested. Five specimens were constructed using FRP sheets and five constructed using the GFRP tube technique. It was found that the compressive strength of the confined concrete core in the longest tubular composite specimen was reduced to approximately 60% of that of the corresponding short specimen. No confinement was achieved in the longest FRP wrapped composite column specimen. </p> <p> Three bare steel columns, ranging between 500 mm and 3,000 mm in height, were also tested to facilitate comparison with the composite columns in terms of increased axial capacity, as well as stiffness and energy dissipation characteristics of the columns. The compressive strength, elastic axial stiffness and ultimate axial strain of the bare steel columns increased by a factor of up to 10, 6 and 3, respectively, in the composite columns constructed utilizing the concrete-filled GFRP tube. These factors were reduced to 5 .2, 2.5 and 2.6, respectively, in the concrete-encased steel columns wrapped with FRP jackets. </p> <p> Finally, an analytical model was developed to establish the capacity curves for the proposed composite columns accounting for slenderness effects. A simple design equation to predict the compressive strength of the tubular composite columns was proposed based on the capacity curve generated from the analytical model. Compressive capacity of the composite columns predicted using the proposed design equation showed favorable agreement with the experimental results. </p> / Thesis / Doctor of Philosophy (PhD)

This dissertation discusses topics related to the performance and long-term durability of glass-reinforced composites. The first portion of this dissertation describes work to assess the effect that post-curing has on widely used E-glass/vinyl-ester composites (E-glass/Derakane 510-A and E-glass/Derakane 8084). It is shown that post-curing can have significant positive effects on the initial material properties of glass-reinforced vinyl ester composites. Furthermore, the post-cure of 82ºC for four hours stabilizes the matrix, and as such reduces matrix-related material property evolution. By stopping or nearly stopping material property evolution due to matrix curing over time, the post-cure regime isolates and allows the study of other time-dependent effects, such as fatigue or hygrothermal degradation, and aids designers by establishing an unchanging base set of initial (undamaged) material design properties. The second portion of this dissertation discusses the effects that mean stress and R-ratio have on the fatigue performance of the same material. Qualitative and quantitative differences are seen in the performance as a function of the loading ratio. A residual strength based life prediction model developed at Virginia Tech is applied to the fatigue data, characterizing the material under constant-amplitude loading. Three curve-fitting parameters are then used along with the model to predict variable-amplitude fatigue lives, with remarkably good results. The final portion of the dissertation concerns the effect of hygrothermal and accelerated aging on glass-reinforced composites. A meta-study is performed on data from the literature, and a glass-degradation-based life-prediction model is applied to the data. It is seen that a static fatigue-based activation energy approach to residual strength can predict activation energies associated with glass-reinforced composite strength degradation in the case of glass-reinforced concrete quite well, predicting values of 80-100 kJ/mol, which are similar to those expected for glass dissolution via silica ring opening. The model may also hold some promise for doing the same for glass-reinforced polymer composites. / Ph. D.

The research presented in this dissertation furthers the state of the art for reliability-based design of composite structures subjected to high cycle variable amplitude (spectrum) fatigue loads. The focus is on fatigue analyses for axially loaded fiber reinforced polymer (FRP) composites that contain a significant proportion of fibers in the loading direction and thus have fiber-direction dominated failure. The four papers presented in this dissertation describe the logical progression used to develop an improved reliability-based methodology for fatigue-critical design. Throughout the analysis extensive experimental fatigue data on several material systems was used to verify the assumptions and suggest the path forward. A comparison of 12 fatigue model approaches from the literature showed that a simple linear residual strength approach (Broutman and Sahu) provides an improvement in fatigue life prediction compared to the Palmgren-Miner rule, while more complex residual strength models did not consistently improve on Broutman and Sahu. Evaluation of the effect of load history randomness on fatigue life was made using experimental results for spectra in terms of the first order autocorrelation of the stress events. For approximately reversed Rayleigh distributed fatigue loading, load sequence was not critical in the material behavior. Based on observations of empirical data and evaluation of the micro-mechanics deterioration and failure phenomena of FRP composites under fatigue loading, a new residual strength model for the tension and compression under any load history was proposed. Then this model was implemented in a stochastic framework and a method was proposed to enable calculation of the load and resistance factor design (LRFD) parameters for realistic reliabilities with relatively few computations. The proposed approach has significant advantages over traditional lifetime-damage-sum-based reliability analysis and provides a significant step toward enabling more accurate reliability-based design with composite materials. / Ph. D.

Fiber reinforced polymer (FRP) is a composite material made of fibers that carry tensile loads embedded in a polymeric matrix. Externally bonded FRP retrofits of reinforced concrete elements provide an efficient, economical, and accepted method of mitigating deficiencies related to seismic and blast loads, as well as addressing corrosion-related issues. FRPs retrofits are widely regarded as cost effective as the cost associated with retrofit installation and facility down-time are usually less than similar retrofit systems. Besides issues of bond and anchorage between the FRP and the substrate, the main disadvantage of FRP materials is that they behave in a brittle, linear elastic manner. As a result, strengthening concrete structures with FRP may introduce new and undesirable behaviors that are mitigated by design codes through strict strain limits. Because FRP is designed for very low strain levels to prevent brittle rupture and unpredictable debonding, buildings and bridges are strengthened in such a way that restricts their energy dissipation capacity at the ultimate limit state. This runs counter to the structural design philosophy of new buildings where the design objective is to develop significant plastic deformation to dissipate energy. An ideal composite material for infrastructure strengthening is one that combines the ease of application of FRP rehabilitation systems with the ability of ductile metals to yield under relatively large strains to provide energy dissipation and ensure ductile behavior. Known as a fiber metal laminate (FML), the aerospace industry has successfully developed a composite consisting of thin metal sheets alternatively bonded to epoxy saturated fiber fabric that is widely used to construct aircraft fuselages and wings. Unlike FRP, FML composites possess a well-defined yield point and exhibit inelastic behavior. However, aerospace grade FML composites cannot directly be applied to building and bridges because they: (i) were developed for low-stress fatigue resistance rather than performance near ultimate stress; (ii) are precisely manufactured to unnecessarily tight tolerances by civil construction standards; and (iii) are not economical compared with current FRP strengthening techniques. Therefore, developing a multifunctional civil engineering composite material based on FML theory would unlock opportunities related to plastic design, energy dissipation, and other mechanisms not currently possible with FRP. This dissertation presents a comprehensive study on the use FML jackets to enhance the strength and ductility of concrete cylinders. The confinement effect and failure mechanisms of FML confined concrete were analyzed for a range of experimental parameters, including the effect of the number of layers, the fiber orientation, and fabric architecture of the FML jackets. The experimental program was divided into two phases. The first phase consisted of a series of uniaxial tension coupon tests to investigate how the stacking arrangement of various E-glass fabrics and aluminum sheets could be tuned to control the yield strength, post-yield stiffness, and ductility characteristics of the FML lay-ups. Mechanical roughening of aluminum sheets and the addition of a bond enhancement agent to the resin system was found to enhance the interlayer bonding and splice capacity of metal and fiber layers. The results demonstrated that FML coupons with [±45°] glass fabrics exhibited pseudo-elastic-plastic stress-strain response, while coupons with [0°] and [0°/90°] fabrics exhibited strain hardening after yielding of aluminum layers. Furthermore, the ratio of the relative contribution of composite layers to the total elastic stiffness of the FML composites was found to be a good indicator of the mechanical properties and shape of the uniaxial stress-strain response of the FML lay-ups. An analytical model based on the Rule of Mixtures (ROM) was used to predict the tensile behavior of the FML coupons. The second phase consisted of axial compression testing of concrete cylinders confined by FML jackets to investigate the influence of various lay-up schemes on the strength and ductility of the confined concrete. Cylinders jacketed with FML showed a significant increase in their strength and ductility. The degree of strain-softening response, maximum strength, peak strain, ultimate deformation, and energy dissipation capacity of the FML confined concrete was found to be controlled by the pseudo-ductile stress-strain response of the FML jackets. FML lay-ups which exhibited strain hardening uniaxial behavior tended to produce greater enhancements in confined concrete strength and steeper strain softening response than FML lay-ups which exhibited pseudo-elastic-plastic uniaxial behavior. Furthermore, FML confined concrete showed improved performance, compared to FRP confined concrete, in terms of confined concrete behavior and failure mode. Finally, the project also demonstrated that an in-situ, hand lay-up preparation procedure for FML jackets provided a level of performance and construction tolerance suitable for use in civil infrastructure applications. Although the results of this study encourage the use of FML as a viable substitute to FRP for retrofitting deficient concrete members, further research is recommended on large-scale columns to verify the feasibility of this innovative retrofit technique. / Doctor of Philosophy / Glass fiber fabrics infused with epoxy resin can be wrapped around concrete cylinders to create a form of confinement jacket that enhances the strength and ductility of the concrete. The cured fiber reinforced polymer (FRP) composite will resist the lateral expansion of the cylinder when it is subject to axial compression. The resistance action works in the form of an external confining pressure developed by jacket and applied to the surface of the cylinder. The increase in confinement pressure is proportional to the lateral expansion of the cylinder which creates hoop strains in the jacket material. The FRP jacket will rupture suddenly when the jacket reaches its ultimate strain capacity, causing the confined cylinder to fail in an explosive manner. FRP composites are often used to repair and strengthen structures suffering from performance deficiencies. However, the brittle mode of failure of FRP is undesirable because it can occur suddenly and without warning. An ideal composite for infrastructure strengthening applications is one that combines the ease of application of FRP rehabilitation systems with the ability of ductile metals to yield under large strains to provide energy dissipation and ensure ductile behavior. The objective of this research was to investigate the strength and ductility of concrete cylinders confined by fiber metal laminates (FML), a composite material consisting of thin aluminum sheets alternatively bonded to layers of glass fiber fabrics. Axial compression testing of concrete cylinders confined by FML jackets was performed to investigate the influence of various FML lay-up schemes on the strength and ductility of the confined cylinders. Concrete cylinders jacketed with FML showed a significant increase in strength and ductility. FML lay-ups which exhibited strain hardening uniaxial behavior tended to produce greater enhancements in confined concrete strength and steeper strain softening response than FML lay-ups which exhibited pseudo-elastic-plastic uniaxial behavior. Furthermore, FML confined concrete showed improved performance, compared to FRP confined concrete, in terms of confined concrete behavior and failure mode. Although the results of this study encourage the use of FML as a viable substitute to FRP for retrofitting deficient concrete members, further research is recommended on large-scale columns to verify the feasibility of this innovative retrofit technique.

This thesis investigates the repair of impact-damaged prestressed concrete bridge girders with strand splices and fabric-reinforced cementitious matrix systems, specifically for repair of structural damage to the underside of an overpass bridge girder due to an overheight vehicle collision. Collision damage to bridges can range from minor to catastrophic, potentially requiring repair or replacement of a bridge girder. This thesis investigates the performance of two different types of repair methods for flexural applications: strand splice repair, which is a traditional repair method that is often utilized, and fabric-reinforced cementitious matrix repair, which is a relatively new repair method. The overarching goal of this project was to provide guidance for assessment and potential repair of impact-damaged girders. Prestressed concrete girders were tested to failure in flexure in this research. After a control test to establish a baseline for comparison, five tests were performed involving damaging a girder, repairing it using one of the repair methods, and testing it to failure. These tests showed that both strand splice repairs and fabric-reinforced cementitious matrix repairs can adequately restore the strength of an impact-damaged girder when up to 10% of the prestressing strands are severed. Combined repairs can also be a viable option if more than 10% of the prestressing strands are severed, though as the damage gets more severe, girder replacement becomes a more attractive option. / Master of Science

Externally bonding of fibre-reinforced polymer (FRP) strips or sheets has become a popular strengthening method for reinforced concrete structures over the last two decades. For most such strengthened concrete beams and slabs, the failure is at or near the FRP-concrete interface due to FRP debonding. The objective of this thesis is to develop a deeper understanding of the debonding behaviour of the FRP-concrete interface through mesoscale finite element simulation. Central to the investigation is the use of the concrete damaged plasticity (CDP) model for modelling the concrete. The FRP is treated as an elastic material. The numerical simulation is focused on the single shear test of FRP-concrete bonded joints. This problem is known to be highly nonlinear and has many difficulties in achieving a converged solution using the standard static loading procedures. A dynamic loading procedure is applied in this research and various parameters such as time step, loading rate etc. are investigated. In particular, the effect of the damping ratio is investigated in depth and an appropriate selection is recommended for solving such problems. It has been identified that the concrete damage model can have a significant effect on the numerical predictions in the present problem. Various concrete empirical damage models are assessed using cyclic test data and simulation of the single shear test of the FRP-concrete bonded joint and it is proposed that the Birtel and Mark’s (2006) model is the most appropriate one for use in the present problem. Subsequently, the effects of other aspects of the concrete behaviour on the FRP-concrete bond behaviour are investigated. These include the tensile fracture energy, compression strain energy and different concrete compression stress-strain models. These leads to the conclusion that the CEBFIP1990 model is the most appropriate one for the problem. An important issue for recognition is that the actual behaviour of the FRP-concrete bonded joints is three dimensional (3D), but most numerical simulations have treated the problem as two dimensional (2D) which has a number of imitations. True 3D simulation is however very expensive computationally and impractical. This study proposes a simple procedure for modelling the joint in 2D with the 3D behaviour properly considered. Numerical results show that the proposed method can successfully overcome the limitations of the traditional 2D simulation method. The above established FE model is then applied to simulate a large number of test specimens. The bond stress-slip relationship is extracted from the mesoscale FE simulation results. An alternative model is proposed based on these results which is shown to be advantageous compared with existing models. This new model provides the basis for further investigation of debonding failures in FRP strengthened concrete structures in the future.

Essa dissertação trata da modelagem física de filamentos de fibras visando adequá-las a aplicações em equipamentos de enrolamento filamentar - filament winding. No decorrer do trabalho é abordada a criação do subsistema para condução e posicionamento dos fios que compõem as bobinas - rovings. São feitas análises por elementos finitos e realizados testes de bancada com os componentes mecânicos visando validar o subsistema como parte integrante das máquinas de filament winding. É estudada a forma de impregnação dos fios, a tensão e o grau de espalhamento dos fios no decorrer da sua passagem pelo sistema, o qual é composto por um conjunto de polias, um tracionador e um enrolador desses fios. / This dissertation deals with the use of fiber reinforcements, in order to improve its appliance in filament winding machines. Throughout this work it is created a mechanism system to remodel the fiber filaments from rovings to the part that is been produced. Finite element analyses and experimental tests are performed to validate the system as part of the filament winding machines. Its is studied the impregnation characteristics, the tensioning and the spreading of the fibers along the designed system, which is composed by a set of pulleys and tensioners. The system is built and satisfactory results are obtained. The results obtained as well as proposals to improve the system are presented and the results discussed.

Essa dissertação trata da modelagem física de filamentos de fibras visando adequá-las a aplicações em equipamentos de enrolamento filamentar - filament winding. No decorrer do trabalho é abordada a criação do subsistema para condução e posicionamento dos fios que compõem as bobinas - rovings. São feitas análises por elementos finitos e realizados testes de bancada com os componentes mecânicos visando validar o subsistema como parte integrante das máquinas de filament winding. É estudada a forma de impregnação dos fios, a tensão e o grau de espalhamento dos fios no decorrer da sua passagem pelo sistema, o qual é composto por um conjunto de polias, um tracionador e um enrolador desses fios. / This dissertation deals with the use of fiber reinforcements, in order to improve its appliance in filament winding machines. Throughout this work it is created a mechanism system to remodel the fiber filaments from rovings to the part that is been produced. Finite element analyses and experimental tests are performed to validate the system as part of the filament winding machines. Its is studied the impregnation characteristics, the tensioning and the spreading of the fibers along the designed system, which is composed by a set of pulleys and tensioners. The system is built and satisfactory results are obtained. The results obtained as well as proposals to improve the system are presented and the results discussed.