For the purpose of inventing a new seismic retrofitting method for the reinforced high strength concrete (HSC) T-section beam using carbon fiber reinforced polymer (CFRP) sheet, three series, a total of twelve T-secti...For the purpose of inventing a new seismic retrofitting method for the reinforced high strength concrete (HSC) T-section beam using carbon fiber reinforced polymer (CFRP) sheet, three series, a total of twelve T-section beams with nine specimens confined by CFRP sheet in the plastic zone and three control beams were conducted up to failure under four-point bending test. The effectiveness of confining CFRP sheet on improving the flexural ductility of unstrengthened T-section beams was studied. The parameters such as the width and the thickness of CFRP sheet and the type of T-section were analyzed. The experimental results show that ductility and rotation capacity of plastic hinge can be improved by the confinement of CFRP sheet, and the ductility indices increase with the increment of width and thickness of CFRP sheet. A plastic rotation model considering the width of CFRP sheet and the effect of flange of T-section beam is proposed on the basis of the model of BAKER, and the test results show a good agreement with the perdicted results. The relevant construction suggestions for seismic retrofitting design of beam-slabs system in cast-in-place framework structure are presented.展开更多
Based on an extensive experimental program,the paper studies the behavior of HPFRCC under triaxial compression. The experimental parameters are lateral confining pressure and PVA fiber content by volume. The test resu...Based on an extensive experimental program,the paper studies the behavior of HPFRCC under triaxial compression. The experimental parameters are lateral confining pressure and PVA fiber content by volume. The test results indicate that ultimate strength and peak strain are significantly improved with the increases of confining pressure. The confining effect introduced by the fibers becomes minor in triaxial compression tests,where there is relatively high external confining pressure. The axial stress-strain curves with different confining pressure and different PVA fiber content by volume are obtained. Lateral confining pressure constraints the lateral expansion of HPFRCC,so there is a big plastic deformation with its ultimate strength improved. At lower confining pressure,PVA fiber content by volume has some effect on the decreased section of stress-strain curve. According to test results,the paper establishes formula of confining pressure with ultimate strength and axial peak strain respectively.展开更多
Uniaxial compression tests were conducted to characterize the main compressive performance of ultra high toughness cementitious composite （UHTCC） in terms of strength and toughness and to obtain its stress-strain re...Uniaxial compression tests were conducted to characterize the main compressive performance of ultra high toughness cementitious composite （UHTCC） in terms of strength and toughness and to obtain its stress-strain relationships. The compressive strength investigated ranges from 30 MPa to 60 MPa. Complete stress-strain curves were directly obtained, and the strength indexes, including uniaxial compressive strength, compressive strain at peak stress, elastic modulus and Poisson＇s ratio, were calculated. The comparisons between UHTCC and matrix were also carried out to understand the fiber effect on the compressive strength indexes. Three dimensionless toughness indexes were calculated, which either represent its relative improvement in energy absorption capacity because of fiber addition or provide an indication of its behavior relative to a rigid-plastic material. Moreover, two new toughness indexes, which were named as post-crack deformation energy and equivalent compressive strength, were proposed and calculated with the aim at linking up the compressive toughness of UHTCC with the existing design concept of concrete. The failure mode was also given. The study production provides material characteristics for the practical engineering application of UHTCC.展开更多
Experimental investigations into the compressive behavior of glass fiber reinforced polymer(GFRP)composite at high strain rates were carried out using a split Hopkinson pressure bar(SHPB)setup.The GFRP laminates were ...Experimental investigations into the compressive behavior of glass fiber reinforced polymer(GFRP)composite at high strain rates were carried out using a split Hopkinson pressure bar(SHPB)setup.The GFRP laminates were made from E-glass fibers and epoxy resins by vacuum assisted compression molding machine.The results of the compressive tests indicated that the mechanical behavior of the GFRP composite depends highly on the strain rate.The compressive peak stress,toughness and Young's modulus of the GFRP composite increased with the increase of strain rate,while the strain level at the initial stages of damage was shortened with the increase of strain rate.In addition,the dynamic deformation behavior and failure process of the specimens were observed directly by using a high-speed camera.Following the experiments,the fracture morphologies and damage modes were examined by scanning electron microscopy(SEM)to explore the possible failure mechanisms of the specimens.The results showed that multiple failure mechanisms appeared,such as matrix crack,fiber-matrix debonding,fiber failure and shear fracture.展开更多
Thermoset based composites are used increasingly in industry for light weight applications, mainly for aircraft, windmills and for automobiles. Fiber reinforced thermoset polymers show a number of advantages over conv...Thermoset based composites are used increasingly in industry for light weight applications, mainly for aircraft, windmills and for automobiles. Fiber reinforced thermoset polymers show a number of advantages over conventional materials, like metals, especially their better performance regarding their strength-to-weight ratio. However, composite recycling is a big issue, as there are almost no established recycling methods. The authors investigate the recyclability of polycyanurate homo- and copolymers with different recycling agents under different conditions. Also the influence of the recycling process on the most important reinforcement fibers, i.e. carbon-, glass-, aramid-, and natural-fiber is investigated. The authors find that: the recycling speed is not only dependent on the temperature, but also is significantly influenced by the particular recycling agents and the polycyanurate formulation. Hence, the stability against the recycling media can be adjusted over a broad range by adjusting the polymer composition. Furthermore, the authors find that the inorganic reinforcement fibers (carbon and glass) are almost unaffected by neither recycling agent at either temperature. Aramid-fibers degrade, depending on the particular recycling agent, from slightly up to extremely strong. This leaves one with the possibility to find a combination of matrix resin and recycling agent, which does not affect the aramid-fiber significantly. In the case of natural fibers, the dependence on the particular recycling media is very strong: some media do not affect the fiber significantly;others reduce the mechanical properties (tensile strength and elongation at break) significantly, and still others even improve both mechanical properties strongly. From the Recyclate, the authors synthesize and subsequently characterize a number of new polyurethane thermosets (foamed and solid samples) with different contents of recyclate, exhibiting Tg in the range of 60°C to 128°C.展开更多
基金Project(51121005) supported by the Science Fund for Creative Research Groups of the National Natural Science Foundation of ChinaProject(50878035) supported by the National Natural Science Foundation of China
文摘For the purpose of inventing a new seismic retrofitting method for the reinforced high strength concrete (HSC) T-section beam using carbon fiber reinforced polymer (CFRP) sheet, three series, a total of twelve T-section beams with nine specimens confined by CFRP sheet in the plastic zone and three control beams were conducted up to failure under four-point bending test. The effectiveness of confining CFRP sheet on improving the flexural ductility of unstrengthened T-section beams was studied. The parameters such as the width and the thickness of CFRP sheet and the type of T-section were analyzed. The experimental results show that ductility and rotation capacity of plastic hinge can be improved by the confinement of CFRP sheet, and the ductility indices increase with the increment of width and thickness of CFRP sheet. A plastic rotation model considering the width of CFRP sheet and the effect of flange of T-section beam is proposed on the basis of the model of BAKER, and the test results show a good agreement with the perdicted results. The relevant construction suggestions for seismic retrofitting design of beam-slabs system in cast-in-place framework structure are presented.
基金support from the youth science fund project of China (50908187)Henan provincial natural science research project ( 2010B560006 )Shanxi provinces youth fund project(2009JQ7013)
文摘Based on an extensive experimental program,the paper studies the behavior of HPFRCC under triaxial compression. The experimental parameters are lateral confining pressure and PVA fiber content by volume. The test results indicate that ultimate strength and peak strain are significantly improved with the increases of confining pressure. The confining effect introduced by the fibers becomes minor in triaxial compression tests,where there is relatively high external confining pressure. The axial stress-strain curves with different confining pressure and different PVA fiber content by volume are obtained. Lateral confining pressure constraints the lateral expansion of HPFRCC,so there is a big plastic deformation with its ultimate strength improved. At lower confining pressure,PVA fiber content by volume has some effect on the decreased section of stress-strain curve. According to test results,the paper establishes formula of confining pressure with ultimate strength and axial peak strain respectively.
基金Funded by the Key Program of National Natural Science Foundation of China( No.50438010)the Research & Application of Key Technology for the South-North Water Transfer Project Construction in China ( JGZXJJ2006-13)
文摘Uniaxial compression tests were conducted to characterize the main compressive performance of ultra high toughness cementitious composite （UHTCC） in terms of strength and toughness and to obtain its stress-strain relationships. The compressive strength investigated ranges from 30 MPa to 60 MPa. Complete stress-strain curves were directly obtained, and the strength indexes, including uniaxial compressive strength, compressive strain at peak stress, elastic modulus and Poisson＇s ratio, were calculated. The comparisons between UHTCC and matrix were also carried out to understand the fiber effect on the compressive strength indexes. Three dimensionless toughness indexes were calculated, which either represent its relative improvement in energy absorption capacity because of fiber addition or provide an indication of its behavior relative to a rigid-plastic material. Moreover, two new toughness indexes, which were named as post-crack deformation energy and equivalent compressive strength, were proposed and calculated with the aim at linking up the compressive toughness of UHTCC with the existing design concept of concrete. The failure mode was also given. The study production provides material characteristics for the practical engineering application of UHTCC.
基金Supported by the Ministerial Level Key Task Project of China(MS201507A0132)
文摘Experimental investigations into the compressive behavior of glass fiber reinforced polymer(GFRP)composite at high strain rates were carried out using a split Hopkinson pressure bar(SHPB)setup.The GFRP laminates were made from E-glass fibers and epoxy resins by vacuum assisted compression molding machine.The results of the compressive tests indicated that the mechanical behavior of the GFRP composite depends highly on the strain rate.The compressive peak stress,toughness and Young's modulus of the GFRP composite increased with the increase of strain rate,while the strain level at the initial stages of damage was shortened with the increase of strain rate.In addition,the dynamic deformation behavior and failure process of the specimens were observed directly by using a high-speed camera.Following the experiments,the fracture morphologies and damage modes were examined by scanning electron microscopy(SEM)to explore the possible failure mechanisms of the specimens.The results showed that multiple failure mechanisms appeared,such as matrix crack,fiber-matrix debonding,fiber failure and shear fracture.
文摘Thermoset based composites are used increasingly in industry for light weight applications, mainly for aircraft, windmills and for automobiles. Fiber reinforced thermoset polymers show a number of advantages over conventional materials, like metals, especially their better performance regarding their strength-to-weight ratio. However, composite recycling is a big issue, as there are almost no established recycling methods. The authors investigate the recyclability of polycyanurate homo- and copolymers with different recycling agents under different conditions. Also the influence of the recycling process on the most important reinforcement fibers, i.e. carbon-, glass-, aramid-, and natural-fiber is investigated. The authors find that: the recycling speed is not only dependent on the temperature, but also is significantly influenced by the particular recycling agents and the polycyanurate formulation. Hence, the stability against the recycling media can be adjusted over a broad range by adjusting the polymer composition. Furthermore, the authors find that the inorganic reinforcement fibers (carbon and glass) are almost unaffected by neither recycling agent at either temperature. Aramid-fibers degrade, depending on the particular recycling agent, from slightly up to extremely strong. This leaves one with the possibility to find a combination of matrix resin and recycling agent, which does not affect the aramid-fiber significantly. In the case of natural fibers, the dependence on the particular recycling media is very strong: some media do not affect the fiber significantly;others reduce the mechanical properties (tensile strength and elongation at break) significantly, and still others even improve both mechanical properties strongly. From the Recyclate, the authors synthesize and subsequently characterize a number of new polyurethane thermosets (foamed and solid samples) with different contents of recyclate, exhibiting Tg in the range of 60°C to 128°C.
