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Doubly Reinforcing Cementitious Beams with Instrumented Hollow Carbon Fiber Tendons
Abstract
Surface mounted strain gages are used to characterize the behavior of polymer-enhanced cementitious beams designed to withstand reverse loadings. These unique composite structures are doubly reinforced with hollow carbon fiber (graphite) tendons equipped with strain gages and the study includes section design, materials considerations, structural testing, and finite element analysis. The primary purpose of strain gage integration is to insure that the stress in the materials remains within the elastic range so that damage does not occur. A finite element model is developed to characterize the structural response in the elastic range and a hybrid approach is suggested in which displacement, strain, and stress can be obtained with a single strain gage. The ability to characterize structural performance beyond the elastic range is also demonstrated by analyzing data obtained from displacement-controlled tests.
Unidirectional fiber composites produced by pultrusion have good mechanical properties. We conducted compression experiments to investigate the factors that influenced the compression of pultruded unidirectional carbon fiber-reinforced plastics (CFRPs) under static axial loads. The CFRPS were composed of carbon fiber or carbon fiber cloth as reinforcement material, resin, ceramic, metal, cement, carbon or rubber as matrix. The modulus and compressive strength were measured. The experimental data were compared with the theoretical values obtained from the rule of mixtures. Moreover, the effects of the components, dispersion, interface states, and other factors on the compressive mechanical behaviors of the composites were studied. Scanning electron microscopy revealed the microstructure and fracture of the material. The results showed that the modulus and compressive strength of the CFRPs with a higher carbon fiber modulus decreased with the modulus and resin strength. The compressive modulus and compressive strength of CFRPs with the same resin increased with the modulus and strength of the carbon fibers. Upon increasing the modulus and strength of the carbon fibers, the compressive modulus and compressive strength of the CFRPs decreased with the modulus and strength of the resin. Moreover, glass fiber-reinforced plastics (GFRPs) were used to compare the difference between CFRPs, C/GFRP, and GFRP. The relationship between the the microstructure and promperties of these composites was systematically revealed. These research results are valuable for the design and synthesis of low-cost pultruded unidirectional fiber composites with excellent mechanical properties.
This study focuses on the development of a lightweight, high-performance cementitious composite material reinforced with Poly(vinyl alcohol) (PVA) fiber. The material which contains Poly(vinyl butyral) (PVB) as the sole aggregate has a low average density of 1548 kg/m3 and a compressive strength of about 40 MPa. The flexural strength, impact resistance, and fracture toughness are also evaluated and are found to be improved in comparison to those of lightweight concrete. The addition of PVA fiber further improves ductility, fracture toughness and impact resistance. The increase in fracture toughness was found to be linear with increasing fiber volume fraction. Comparisons are made with a lightweight concrete of equal density, and a normal-weight concrete. A model based on fiber bridging mechanics and the rule of mixtures is developed to characterize the fracture toughness, and a good correlation is obtained for the materials tested when experimental results are compared to those predicted by the model.
This paper describes how experimental modal analysis was used to study the dynamic behavior (natural frequencies, mode shapes, and damping) of two racing canoes fabricated from a new class of Graphite Reinforced Silica/Polymer Matrix Composite (GRSPMC) materials. Student teams from the University of Alabama in Huntsville (UAH) built the boats for the 2001 and 2003 American Society of Civil Engineer's (ASCE) National Concrete Canoe Competitions. In 2001, the students relied on the large difference in stiffness between the constituents in their boat's composite section to drive the internal stress from a flexible cementitious matrix to three layers of relatively stiff reinforcement. They placed materials symmetrically to form an adaptive section optimized to resist stress reversals and strategically positioned fiber layers to tune the modal response. In 2003, rule changes necessitated varying the constituents in the cementitious matrix and the team rotated fibers in one of the reinforcing layers to enhance their canoe's dynamic performance.
Cross ply laminates of (02,902)s configuration having AS4 graphite fibers in three epoxy resins of different toughness: 3501-6, Tactix® 556 and Tactix® 695, have been tested to determine their transverse cracking behavior and the associated mechanical response under longitudinal tensile loading. The test data are analyzed using Talreja's con tinuum damage model [1-3]. The material constants needed in the model to predict the in- plane stiffness changes are determined. The measured Poisson's ratio, which shows signifi cant change, is compared with the prediction of the model. The constants for the three materials are found to increase with the increase in their fracture toughness.
The rehabilitation, repair, and strengthening of concrete structures has increased worldwide with a growing number of systems employing externally applied fiber-reinforced polymer (FRP) composites. However, the service life and effectiveness of FRP repair and strengthening techniques when applied to concrete in corrosive marine environments is still not well understood. This paper presents the results of an experimental study on the corrosion performance of embedded steel reinforcement in cylindrical reinforced concrete specimens with 13 different surface treatment options. Samples were subjected to an impressed current and a high salinity solution. Test variables included the type of epoxy, wrap fiber orientation, and the number of wrap layers. Samples were evaluated for corrosion activity by monitoring corrosion potentials and impressed current flow levels, and by examining reinforcement mass loss and concrete chloride content among samples. Test results indicated that FRP wrapped specimens had prolonged test life, decreased reinforcement mass loss, and reduced concrete chloride content. The performance of wrapped specimens was superior to that of either control samples or those coated only with epoxy. Epoxy type had a significant effect on the performance of samples regarding their resistance to corrosion. It was concluded that carbon FRP wraps were able to confine concrete, slowing deterioration from cracking and spalling and inhibiting the passage of salt water.
This paper describes how Strategically Tuned Absolutely Resilient Structures (STARS) are being designed for energy transfer and morphing applications based on the strength, stiffness, and the position of the component materials in the composite section. The discussion ranges from on-line health monitoring and smart diagnostics/prognostics strategies developed to improve the readiness and performance of STARS to integrated sensors and structural information systems designed to keep the stress in the reinforcement below yield and prevent cracks from propagating through the surrounding matrix.
In this paper we describe how finite element and experimental modal analyses can be used to characterize the dynamic behavior
of plates made from a new class of graphite reinforced silica/polymer matrix composite (GRSPMC) materials. An agreement is
obtained between both methods, and the results show that GRSPMC materials can be modeled and tested using tools similar to
those applied to the study of classical composite laminates.
This paper discusses the design considerations used to produce a new generation of structurally efficient, reinforced concrete composite panels capable of resisting the dangerous stresses produced by reverse bending. The panels rely on a lightweight, polymer modified concrete mix designed to be structurally compatible with a multilayered reinforcement scheme. The design is based on both material compliance and strength, making the strategy different from that taken by conventional reinforced concrete designers.
I MECHANICS: Kinematics / Dynamics / Rigid Bodies / Micromechanics / Gravitation and the Theory of Relativity / Mechanics of Continuous Media / Nonlinear Dynamics, Chaos, and Fractals / Tables on Mechanics II VIBRATIONS AND WAVES: Vibrations / Waves / Acoustics / Optics / Tables on Vibrations, Waves, Acoustics, and Optics III ELECTRICITY: Charges and Currents / Electric and Magnetic Field / Applications in Electrical Engineering / Current Conduction in Liquids, Gases, and Vacuum / Plasma Physics / Tables on Electricity IV THERMODYNAMICS: Equilibrium and State Variables / Heat, Conversion of Energy, and Changes of State / Phase Transitions, Reactions, and Equalizing of Heat / Tables on Thermodynamics V QUANTUM PHYSICS: Photons, Electromagnetic Radiation, and Light Quanta / Matter Waves--Wave Mechanics of Particles / Atomic and Molecular Physics / Elementary Particle Physics--Standard Model / Nuclear Physics / Solid State Physics / Tables in Quantum Physics VI APPENDIX: Measurements and Measurement Errors / Vector Calculus / Differential and Integral Calculus / Tables on SI Units
This paper discusses the research, development, and design considerations used to produce a Structural Information System
(SIS) capable of characterizing the behavior of an adaptive reinforced concrete structure designed to withstand reverse loadings.
The SIS consists of a collection of surface mounted and embedded sensors connected to a portable computer. The composite structure
is reinforced with hollow carbon fiber tendons equipped with embedded strain gages and the work includes theoretical arguments,
polymer concrete mix design, concrete testing, reinforcement selection and placement, sensor selection and placement, and
structural testing and analysis. The primary objective is to insure that the stress in the materials remains within the elastic
range so that damage does not occur. A finite element model is developed to accurately characterize the structural response
in the elastic range and a hybrid approach is suggested in which displacement, strain, and stress can be obtained with a rudimentary
SIS consisting of a single embedded sensor. The ability to characterize failure, once it occurs, is also demonstrated by analyzing
data obtained from displacement-controlled tests. Results indicate that splices in the tendons and slippage between the tendons
and the concrete help to prevent sudden failure and allow the structure to withstand relatively high service loads despite
appreciable deformation.
In 2001, the concrete canoe team at the University of Alabama in Huntsville fabricated the Survivor boat by placing cementitious mixture over three layers of graphite. This was done to form an adaptive section optimized to resist stress reversals and tune the modal response. Following completion of the canoe, finite element and experimental tests were conducted to determine dynamic response. For this purpose, the structure was suspended in a free-hanging configuration. Modal parameters were determined via standard impact hammer tests. Results show that the standard impact hammer test can be used to test PEGRCC structures, and that these structures can be analyzed using finite element models developed based on the classical laminated plate theory.
The impact resistance of polypropylene fibre-reinforced concrete (FRC) was investigated using the repeated drop-weight impact test recommended by ACI Committee 544. The results were analysed based on a statistical approach. The variation in results was examined within the same batch and between different batches. Statistical parameters were compared with reported variations in impact resistance of concrete composites reinforced with other types of fibres such as carbon and steel fibres. Statistical analysis indicated that the results obtained from this test had large variations and it is necessary to increase the number of replications to at least 40 specimens per concrete mix to assure an error below 10%. It is concluded that this test with its current procedures and recommendations should not be considered as a reliable impact test. This study has highlighted the need for modifying this test in such a way as to increase its accuracy and reduce the large variation in results.
This study focuses on the development of a lightweight high-performance cementitious composite material which is reinforced with poly(vinyl alcohol) (PVA) fiber and contains poly(vinyl butyral) (PVB) as the sole aggregate. Mechanical properties such as compressive and flexural strengths, impact resistance, and fracture toughness are evaluated. PVB composite produces low average density concrete of 1548 kg/m3 (96.6 pcf) and a compressive strength of about 40 MPa (5800 psi). The addition of PVA fiber improves ductility, fracture toughness and impact resistance with fiber volume fractions. In general, the increase in fracture toughness is found to be linear with increasing fiber volume fraction, whereas the increase associated with the impact resistance is non-linear. A model based on fiber bridging mechanics and the rule of mixtures is developed to characterize fracture toughness. Comparisons are made with a lightweight concrete having equal density, and a normal-weight concrete. A good correlation is obtained for the materials tested when experimental results are compared to those predicted by the developed model.
El Prado Museum in Madrid has been recently submitted to a refurbishment of its roof which from been made with the traditional tiles has been changed to the use of modern waterproofing layers covered with a metallic lead finishing. Due to an unexpected damp patch that produced leaking in the hall in which Las Meninas by Velázquez was exhibited, the authors were commissioned by the Ministry of Education and Culture to study the suitability of the roof and its waterproofing properties. The study led to suggestions of modifications in the design of the roof layers, which are out of the scope of present paper. In present paper are given the behaviour of the sensors embedded in two specific areas of the roof. The sensors installed were of: temperature, relative humidity, measurement of local strain and detection of liquid water. The liquid water sensors reveal that some water is withheld in the layer just below the thermal insulation material, although it is standing. The results of over four years of readings show that the temperature attenuates over distance away from the outermost layer, where the readings are very high in summer, due to it consists of lead. During the colder seasons, in turn, the temperature in the inner layers of the roof is higher than in the outer layers. The strain recorded follows the logical evolution of temperature with no abnormal behaviour being detected. Some of relative humidity sensors had measuring problems due to water condensing on them. In summary however, if the behaviour in this area is extrapolated to the rest of the roof, it can be considered to perform correctly as intended. No more leaking events have been detected from the design modifications were incorporated to the existing roof.
Poly(vinyl butyral) (PVB) which has many special engineering aggregate properties such as super lightweight, physical toughness, adhesion to a variety of surfaces and energy-absorbing characteristics is utilized as the sole aggregate in this study to develop a novel cementitious composite reinforced with Poly(vinyl alcohol) (PVA) fiber. Impact energy absorption capacity is evaluated based on the Charpy impact test. The results show that PVB composite material has lower density but higher impact energy absorption capability compared with conventional lightweight concrete and regular concrete. The addition of PVA fiber improves the impact resistance with fiber volume fractions. The remarkable change in the interfacial bond strength contributed by the non-covalent bond such as hydrogen bond and ether interactions at the interfaces between fiber, aggregate and matrix contributes to the improvement of the impact resistant capacity. A model based on fiber bridging mechanics and the rule of mixtures is developed to characterize the impact energy. A good correlation was obtained for the materials tested when experimental results are compared to those predicted by the developed model.
Strategically embedding graphite meshes in a compliant cementitious matrix produces a composite material with relatively high tension and compressive properties as compared to steel-reinforced structures fabricated from a standard concrete mix. Although these composite systems are somewhat similar, the methods used to analyze steel-reinforced composites often fail to characterize the behavior of their more advanced graphite-reinforced counterparts. This Technical Memorandum describes some of the analytical methods being developed to determine the deflections and stresses in graphite-reinforced cementitious composites. It is initially demonstrated that the standard transform section method fails to provide accurate results when the elastic moduli ratio exceeds 20. An alternate approach is formulated by using the rule of mixtures to determine a set of effective material properties for the composite. Tensile tests are conducted on composite samples to verify this approach. When the effective material properties are used to characterize the deflections of composite beams subjected to pure bending, an excellent agreement is obtained. Laminated composite plate theory is investigated as a means for analyzing even more complex composites, consisting of multiple graphite layers oriented in different directions. In this case, composite beams are analyzed using the laminated composite plate theory with material properties established from tensile tests. Then, finite element modeling is used to verify the results. Considering the complexity of the samples, a very good agreement is obtained.
Model EDS-12 V vibrating wire sister bar strain meter
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Development of instrumented tendons for embedment in a structural information system. Master's Thesis, Department of Mechanical and Aerospace Engineering, University of Alabama in Huntsville 19 Design of a structural information system (SIS) for strategically tuned absolutely resilient structures
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Bommu RK (2010) Development of instrumented tendons for embedment in a structural information system. Master's Thesis, Department of Mechanical and Aerospace Engineering, University of Alabama in Huntsville 19. Biszick KR (2010) Design of a structural information system (SIS) for strategically tuned absolutely resilient structures (STARS).
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Ballistic testing of STARS
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Instrumented rebar and sister bar, Model IRHP and IRCL. Data sheet available on the web at: http:// www. roctest-group. com/ sites
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Matrix design for strategically tuned absolutely resilient structures (STARS)
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Development of instrumented tendons for embedment in a structural information system
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Model EDS-12 V vibrating wire sister bar strain meter
- Encardio-Rite Electronics