This study is an experimental investigation pertaining to the creep behavior of slender pultruded fiber-reinforced polymeric (FRP) columns subjected to sustained concentric axial loading at elevated service temperatures. Six creep tests were performed on columns having a slenderness ratio of 49 at different combinations of axial load and temperature for a duration of at least 1,000 hours. The axial loads used represented 33%, 67%, and 90% of the critical buckling load for the column selected. For each load level, one test was performed at 22.8℃ (73℉) and one test was performed at 65.5℃ (150℉) Knife-edge end supports were utilized to simulate pinned-pinned boundary conditions. Midheight lateral deflection and axial shortening were recorded incrementally for the duration of the testing. Following termination of the creep tests, the columns were allowed to recover and tested for buckling strength. A semi-empirical model for long-term behavior of concentrically loaded FRP columns at elevated service temperatures is proposed based on experimental results.

No description available.

Fiber reinforced polymeric (FRP) composite materials are beginning to find use in construction and infrastructure applications. Composite members may potentially provide more durable replacements for steel and concrete in primary and secondary bridge structures, but the experience with composites in these applications is minimal. Recently, however, a number of groups in the United States have constructed short-span traffic bridges utilizing FRP members. These demonstration cases will facilitate the development of design guidelines and durability data for FRP materials. The Tom's Creek Bridge rehabilitation is one such project that utilizes a hybrid FRP composite beam in an actual field application. This thesis details much of the experimental work conducted in conjunction with the Tom's Creek Bridge rehabilitation. All of the composite beams used in the rehabilitation were first proof tested in four-point bending. A mock-up of the bridge was then constructed in the laboratory using the actual FRP beams and timber decking. The mock-up was tested in several static loading schemes to evaluate the bridge response under HS20 loading. The lab testing indicated a deflection criterion of nearly L/200; the actual field structure was stiffer at L/450. This was attributed to the difference in boundary conditions for the girders and timber panels. Finally, the bridge response was verified with an analytical model that treats the bridge structure as a wood beam resting upon discrete elastic springs. The model permits both bending and torsional stiffness in the composite beams, as well as shear deformation. A parametric study was conducted utilizing this model and a mechanics of laminated beam theory to provide recommendations for alternate bridge designs and modified composite beam designs. / Master of Science

Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / Pultruded fiber reinforced polymer (FRP) shapes are gaining popularity in the construction industry. Pultruded FRP profiles introduce a new world of construction that could prove to be a viable option to traditional structural materials. The use of pultruded FRP profiles in structures is discussed in this report. First a brief history of FRPs and their applications are addressed before explaining in detail the two main components of FRP; fibers and resin. The manufacturing process known as pultrusion and how two separate materials become one structural member is examined. As a result of pultrusion, engineers and designers can create structural profiles in customizable shapes, sizes, and strengths to suit any project and price. Theoretically, a pultruded FRP profile can be customized to different strengths within the geometrical and material bounds of the profile; however, many manufacturers publish data regarding mechanical and thermal properties along with allowable loads for their nominal profiles. Currently, there are no governing codes or guidelines for pultruded FRPs but there are design manuals and handbooks published by various committees and manufacturers so the design of pultruded FRP profiles is discussed. Ultimate and serviceability limit states are design concerns that engineers always deal with but concerns of heat or fire, chemical or corrosion, and moisture affect pultruded FRPs differently than steel or wood. Pultruded FRPs pose interesting design concerns because increased customizability and workability means the member can be tailored to meet the needs for that project but that would counter the benefit of mass-produced nominal sizes. A lack of uniform codes and standards inhibits the growth of the pultrusion industry in the United States but codes developed in Europe along with the development of specialized agencies and organizations could help gain a foothold. Lastly, a set of beams varying in length and load exhibit a side-by-side comparison to examine how pultruded FRPs match up next to traditional building materials. Although wood, steel, and reinforced concrete have been the preferred materials of construction, pultruded FRP structural shapes are gaining popularity for its economical and physical advantages, and advances in manufacturing and technology stand to usher in the widespread use of pultruded FRP profiles.

The concept of stay-in-place (SIP) structural formwork has the potential to simplify and accelerate the construction process to a great extent. Fibre-reinforced polymer (FRP) SIP structural formwork offers further potential benefits over existing formwork systems in terms of ease and speed of construction, improved site safety and reduced long-term maintenance in corrosive environments. However, it is not without its limitations, including primarily the possibility of a lack of ductility, which is a key concern regarding the use of FRP structural formwork in practice. This thesis presents the findings of an experimental and analytical investigation into a novel FRP SIP structural formwork system for a concrete slab with a particular emphasis on its ability to achieve a ductile behaviour. The proposed composite system consists of a moulded glass fibre-reinforced polymer (GFRP) grating adhesively bonded to square pultruded GFRP box sections. The grating is subsequently filled with concrete to form a concrete-FRP composite floor slab. Holes cut into the top flange of the box sections allow concrete studs to form at the grating/box-section interface. During casting, GFRP dowels are inserted into the holes to further mechanically connect the grating and box sections. An initial experimental investigation into using GFRP grating as confinement for concrete showed that a significant increase in ultimate strength and strain capacity could be achieved compared to unconfined concrete. This enhanced strain capacity in compression allows greater use of the FRP capacity in tension when used in a floor slab system. Further experimental investigation into developing ductility at the grating/box-section interface showed that the proposed shear connection exhibited elastic-‘plastic’ behaviour. This indicated the feasibility of achieving ductility through progressive and controlled longitudinal shear failure. Following these component tests on the concrete-filled grating and the shear connectors, a total of six (300 x 150 x 3000) mm slab specimens were designed and tested under five-point bending. It was found that the behaviour of all specimens was ductile in nature, demonstrating that the proposed progressive longitudinal shear failure was effective. A three-stage analytical model was developed to predict the load at which the onset of longitudinal shear failure occurred, the stiffness achieved during the post elastic behaviour and, finally, the deflection at which ultimate failure occurred. Close agreement was found between experimental results and the theory.

[pt] Este trabalho tem como objetivo investigar a influência de temperaturas elevadas no comportamento à flexão de compósitos poliméricos reforçados com fibra de vidro fabricados pelo processo de pultrusão. São analisados quatro diferentes compósitos constituídos por matrizes de resinas poliéster isoftálica, éster vinílica ou fenólica, reforçados por fibras de vidro tipo E dispostas na forma de rovings, manta de filamentos contínuos e véus. Fundamentos teóricos associados aos comportamentos mecânico e físico de materiais compósitos poliméricos reforçados com fibra de vidro são apresentados e os resultados de um programa experimental que envolveu ensaios à flexão, antes e após exposição às temperaturas de até 320 graus Celsius, análises da degradação dos materiais através de ensaios de termogravimetria e ensaios à tração, são reportados e analisados. As análises das propriedades mecânicas envolveram: estudo do módulo de elasticidade, tensão de ruptura e deformação. Os resultados mostraram que, apesar da degradação aparente, as propriedades mecânicas apresentaram melhoras em temperaturas próximas de 200 graus Celsius e não apresentaram significativas alterações após exposições até 320 graus Celsius. Os compósitos de matriz éster vinílica apresentaram as maiores resistências e o compósito de matriz fenólica se mostrou menos resistente e com comportamento mais frágil. Por fim, amostras dos materiais foram analisadas no microscópio eletrônico de varredura (MEV), antes e após a exposição à temperatura elevadas, com o objetivo de se verificar danos microestruturais em sua estrutura. / [en] This work aims to investigate the influence of high temperatures on the flexural behavior of pultruded glass fiber reinforced polymeric profiles made by the pultrusion process. Four different composites constituted by isophthalic polyester, ester vinilic or phenolic resins reinforced with E-glass fibers arranged in form of rovings, continuous filaments and veils are analyzed. Theories associated with the mechanical and physical behavior of glass fiber reinforced polymer composites are presented and the results of an experimental program involving bending tests, before and after exposure to temperatures up to 320 degrees Celsius, thermogravimetric material degradation analyzes and tensile tests, are reported and analyzed. The analysis of the mechanical properties involved: study of modulus of elasticity, tensile strength and strain. The results showed that, despite the apparent degradation, the mechanical properties showed improvements at temperatures close to 200 degrees Celsius and did not show significant changes after exposures up to 320 degrees Celsius. The composites of the vinyl ester matrix showed the highest strengths and the phenolic matrix composite showed lower resistant and fragile behavior. Finally, samples of the materials were analyzed in the scanning electron microscopy (SEM), before and after exposure to high temperatures, in order to verify microstructural damages in its structure.

[pt] O presente trabalho propõe um novo tipo de ligação entre perfis pultrudados que não exija furação do material, seja leve e fabricado por manufatura aditiva. Para isso, fez-se uma revisão do estado da arte no âmbito das ligações entre perfis de compósitos, abordando ligações parafusadas simples, cujos parafusos estão sujeitos apenas ao corte, bem como as ligações semirrígidas, que são menos contempladas pela literatura atual. Além disso, tratou-se do uso de otimização topológica em componentes mecânicos voltados à impressão 3D. Posteriormente, define-se a geometria básica do componente proposto e o respectivo modelo numérico adotado no processo de otimização topológica, expondo todas as condições de contorno, carregamento e otimização. A fim de verificar experimentalmente o comportamento do componente apresentado, ensaios momento-rotação foram realizados em três grupos, sendo um composto por exemplares com a geometria original básica e os demais por componentes otimizados (com e sem reforço). Por fim, foi observado que o caminho de fibras estabelecido foi coerente com as solicitações às quais o componente está submetido, haja vista a maior eficiência manifestada pelo aumento de resistência e rigidez por unidade de massa. A mesma constatação se aplica ao processo de otimização e ajuste. No mais, a utilização do reforço com fibras implicou numa maior repetibilidade na resposta mecânica da ligação. / [en] The current work proposes a new type of joint between pultruded profiles that does not require drilling, is lightweight and build by additive manufacturing. To accomplish that, a state of art review on pultruded profiles joints was carried, addressing simple bolted joints which have their bolts only subjected to shear, as well as semi-rigid joints. Besides, the use of topology optimization on 3D-printed mechanical components is also addressed. Posteriorly, the basic geometry of the proposed component is defined and its respective numeric model used within the topology optimization, presenting their boundary, load and optimization conditions. In order to experimentally verify the behaviour of the component, moment-rotation tests were carried in three groups, namely, the original geometry group, the simple optimized group and the reinforced optimized group. In the end, it was observed that the defined fibre path is consistent with the stresses acting within the component, regarding the greatest efficiency shown in terms of strength and stiffness per unit mass for the reinforced specimens. The same applies to the optimization and adjusting processes. Furthermore, the use of fibre reinforcement led to a greater repeatability of mechanical response.

A group of researchers, engineers, and government transportation officials have teamed up to design two bridges with simply-supported FRP composite structural beams. The Toms Creek Bridge, located in Blacksburg, Virginia, has been in service for six years. Meanwhile, the Route 601 Bridge, located in Sugar Grove, Virginia, has been in service for two years. Researchers have conducted load tests at both bridges to determine if their performance has changed during their respective service lives. The key design parameters under consideration are: deflection, wheel load distribution, and dynamic load allowance. The results from the latest tests in 2003 yield little, yet statistically significant, changes in these key factors for both bridges. Most differences appear to be largely temperature related, although the reason behind this effect is unclear. For the Toms Creek Bridge, the largest average values from the 2003 tests are 440 me for service strain, 0.43 in. (L/484) for service deflection, 0.08 (S/11.1) for wheel load distribution, and 0.64 for dynamic load allowance. The values for the Route 601 Bridge are 220 me, 0.38 in. (L/1230), 0.34 (S/10.2), and 0.14 for the same corresponding paramters. The recommended design values for the dynamic load allowance in both bridges have been revised upwards to 1.35 and 0.50 for the Toms Creek Bridge and Route 601 Bridge, respectively, to account for variability in the data. With these increased factors, the largest strain in the toms Creek Bridge and Route 601 Bridge would be less than 13% and 12%, respectively, of ultimate strain. Therefore, the two bridges continue to provide a large factor of safety against failure. / Master of Science

As fiber reinforced polymer (FRP) structures find application in highway bridge structures, methodologies for describing their long-term performance under service loading will be a necessity for designers. The designer of FRP bridge structures is faced with out-of-plane damage and delamination at ply interfaces. The damage most often occurs between hybrid plys and dominates the life time response of a thick section FRP structure. The focus of this work is on the performance of the 20.3 cm (8 in) pultruded, hybrid double web I-beam structural shape. Experimental four-point bend fatigue results indicate that overall stiffness reduction of the structure is controlled by the degradation of the tensile flange. The loss of stiffness in the tensile flange results in the redistribution of the stresses and strains, until the initiation of failure by delamination in the compression flange. These observations become the basis of the assumptions used to develop an analytical life prediction model. In the model, the tensile flange stiffness is reduced based on coupon test data, and is used to determine the overall strength reduction of the beam in accordance the residual strength life prediction methodology. Delamination initiation is based on the out-of-plane stress sz at the free edge. The stresses are calculated using two different approximations, the Primitive Delamination Model and the Minimization of Complementary Energy. The model successfully describes the onset of delamination prior to fiber failure and suggests that out-of-plane failure controls the life of the structure. / Master of Science

Fiber-reinforced polymeric (FRP) composites are being considered for structural members in bridge construction as lighter, more durable alternatives to steel and concrete. Extensive testing and analysis of a pultruded, hybrid double web beam (DWB) developed for use in bridge construction has been conducted at Virginia Tech. A primary purpose of this testing is the development of a structural design guide for the DWB, which includes stiffness and strength data. The design manual also includes design allowables determined through a statistical analysis of test data. Static testing of the beams, including failure tests, has been conducted in order to determine such beam properties as bending modulus, shear stiffness, failure mode, and ultimate capacity. Measuring and calculating the shear stiffness has proven to be an area of particular interest and difficulty. Shear stiffness is calculated using Timoshenko beam theory which combines the shear stiffness and shear area together along with a shear correction factor, k, which accounts for the nonuniform distribution of shear stress/strain through the cross-section of a structure. There are several methods for determining shear stiffness, kGA, in the laboratory, including a direct method and a multi-span slope method. Herein lays the difficulty as it has been found that varying methods produces significantly different results. One of the objectives of current research is to determine reasons for the differences in results, to identify which method is most accurate in determining kGA, and also to examine other parameters affecting the determination of kGA that may further aid the understanding of this property. This document will outline the development of the design guide, the philosophy for the selection of allowables and review and discuss the challenges of interpreting laboratory data to develop a complete understanding of shear effects in large FRP structural members. / Master of Science