As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective ...As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective solution is to use externally bonded fiber-reinforced polymer(FRP)sheets;however,limited research has been done on aged PC beams using the FRP,especially for beams with unbonded prestressing strands(UPC beams).Therefore,this research investigates the flexural strengthening efficacy of external FRP sheets on aged UPC beams with unbonded tendons.Aging minimally affected the failure modes of UPC beams,with nonstrengthened beams showing flexural failure via rebar yielding and concrete crushing,and FRP-strengthened beams failing due to FRP debonding and tensile reinforcement yielding,though tendons in the aged beams did not yield due to prestress losses,unlike the new beams.The U-wrap anchor curbed widespread debonding,leading to tensile reinforcement yielding and FRP rupture.Aging hastened crack growth and stiffness loss,increasing deflections and reducing load resistance,but FRP reinforcement mitigated these effects,enhancing cracking resistance by 14%over the unstrengthened aged beams and 7%over the new beams while boosting ultimate resistance by 9%above the non-strengthened new beams.Compared to the new FRP-strengthened beams,the aged counterparts had lower cracking resistance,stiffness and capacity—showing 20%higher deflections,7–9%lower serviceability loads,7%–17%reduced ultimate strength and 17%less deformability—due to prestress losses and premature FRP debonding.展开更多
This paper presents analytical and numerical models to predict the behavior of unbonded flexible risers under torsion.The analytical model takes local bending and torsion of tensile armor wires into consideration,and ...This paper presents analytical and numerical models to predict the behavior of unbonded flexible risers under torsion.The analytical model takes local bending and torsion of tensile armor wires into consideration,and equilibrium equations of forces and displacements of layers are deduced.The numerical model includes lay angle,cross-sectional profiles of carcass,pressure armor layer and contact between layers.Abaqus/Explicit quasi-static simulation and mass scaling are adopted to avoid convergence problem and excessive computation time caused by geometric and contact nonlinearities.Results show that local bending and torsion of helical strips may have great influence on torsional stiffness,but stress related to bending and torsion is negligible;the presentation of anti-friction tapes may have great influence both on torsional stiffness and stress;hysteresis of torsion-twist relationship under cyclic loading is obtained by numerical model,which cannot be predicted by analytical model because of the ignorance of friction between layers.展开更多
This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the syste...This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the system, particularly in the critical touchdown zone, the traditional method is insufficient for accurately evaluating the fatigue life of these risers. The main challenge lies in the transposition from global to local analyses, which is a key stage for the fatigue analysis of flexible pipes owing to their complex structure. The new enhanced approach derives a multi-layer stress-decomposition method to meet this challenge. In this study, a numerical model validated experimentally is used to demonstrate the accuracy of the stress-decomposition method. And a numerical case is studied to validate the proposed approach. The results demonstrate that the multi-layer stress-decomposition method is accurate, and the fatigue lives of the metallic layers predicted by the enhanced multi-layer analysis approach are rational. The proposed fatigue-analysis approach provides a practical and reasonable method for predicting fatigue life in the design of unbonded flexible risers.展开更多
A helical wire is a critical component of an unbounded flexible riser prone to fatigue failure. The helical wire has been the focus of much research work in recent years because of the complex multilayer construction ...A helical wire is a critical component of an unbounded flexible riser prone to fatigue failure. The helical wire has been the focus of much research work in recent years because of the complex multilayer construction of the flexible riser. The present study establishes an analytical model for the axisymmetric and bending analyses of an unbonded flexible riser. The interlayer contact under axisymmetric loads in this model is modeled by setting radial dummy springs between adjacent layers. The contact pressure is constant during the bending response and applied to determine the slipping friction force per unit helical wire. The model tracks the axial stress around the angular position at each time step to calculate the axial force gradient, then compares the axial force gradient with the slipping friction force to judge the helical wire slipping region, which would be applied to determine the bending stiffness for the next time step. The proposed model is verified against the experimental data in the literature. The bending moment-curvature relationship under irregular response is also qualitatively discussed. The stress at the critical point of the helical wire is investigated based on the model by considering the local flexure. The results indicate that the present model can well simulate the bending stiffness variation during irregular response, which has significant effect on the stress of helical wire.展开更多
The scrap tire rubber pad(STRP)made by natural or synthetic rubber and high strength reinforcing cords exhibits substantial vertical stiffness and horizontal flexibility,and these properties can be regarded as suitabl...The scrap tire rubber pad(STRP)made by natural or synthetic rubber and high strength reinforcing cords exhibits substantial vertical stiffness and horizontal flexibility,and these properties can be regarded as suitable for seismic isolators for structures.The use of environmentally burdensome scrap tires as STRP isolators might be convenient as an efficient and low-cost solution for the implementation of aseismic design philosophy for low-to-medium rise buildings,especially in developing countries.Finite element analyses of unbonded square and strip-shaped STRP isolators subjected to a combination of axial and lateral loads are conducted to investigate its lateral deformation performance under seismic loading.The rubber of the isolator is modelled with Mooney-Rivlin hyperelastic and Prony viscoelastic materials,including the Mullins material damage effect.The influence of the length-to-width ratio and bearing height on the isolator performance is assessed in terms of the force-displacement relationship,horizontal stiffness,damping,and isolation periods.It is shown that the dependence of stiffness on the length-to-width ratio is significant in the longitudinal direction and minor in the transverse direction.The STRP isolators following the proposed design criteria are shown to satisfy the performance requirement at different levels of seismic demand specified by the ASCE/SEI 7-2010 seismic provisions.展开更多
This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA mod...This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.展开更多
Owing to nonlinear contact problems with slip and friction, a lot of limiting assumptions are made when developing analytical models to simulate the behavior of an unbonded flexible riser. Meanwhile, in order to avoid...Owing to nonlinear contact problems with slip and friction, a lot of limiting assumptions are made when developing analytical models to simulate the behavior of an unbonded flexible riser. Meanwhile, in order to avoid convergence problems and excessive calculating time associated with running the detailed finite element （FE） model of an unbonded flexible riser, interlocked carcass and zeta layers with complicated cross section shapes are replaced by simple geometrical shapes （e.g. hollow cylindrical shell） with equivalent orthotropic materials. But the simplified model does not imply the stresses equivalence of these two layers. To solve these problems, based on ABAQUS/Explicit, a numerical method that is suitable for the detailed FE model is proposed. In consideration of interaction among all component layers, the axial stiffness of an eight-layer unbonded flexible riser subjected to axial tension is predicted. Compared with analytical and experimental results, it is shown that the proposed numerical method not only has high accuracy but also can substantially reduce the calculating time. In addition, the impact of the lay angle of helical tendons on axial stiffness is discussed.展开更多
Since the assumption of plane sections cannot be applied to the strain of unbonded tendons in prestressed concrete beams subjected to loadings,a moment-curvature nonlinear analysis method is used to develop analytical...Since the assumption of plane sections cannot be applied to the strain of unbonded tendons in prestressed concrete beams subjected to loadings,a moment-curvature nonlinear analysis method is used to develop analytical programs from stress increases in unbonded tendons at the ultimate limit state.Based on the results of model testing and simulation analysis,equations are proposed to predict the stress increase in tendons at the ultimate state in simple or continuous beams of partially prestressed concrete,considering the loading type,non-prestressed reinforcement index βp,prestressing reinforcement index βs,and span-depth ratio L/h as the basic parameters.Results of 380 beams studied here and test results for 35 simple beams obtained by the China Academy of Building Research were compared with those from prediction equations given in codes and other previous studies.The comparison reveals that the values predicted by the proposed equations agree well with experimental results.展开更多
A coupled element modeling method is proposed for global dynamic analyses of unbonded flexible risers.Owing to the multi-layer structure of unbonded flexible risers, the global-dynamic-analysis method applied to the s...A coupled element modeling method is proposed for global dynamic analyses of unbonded flexible risers.Owing to the multi-layer structure of unbonded flexible risers, the global-dynamic-analysis method applied to the steel rigid risers is insufficient for flexible risers. The main challenges lie in the enormous difference between the anti-tension and anti-binding capacity of unbonded flexible risers which results in serious ill-conditional calculation in global dynamic analysis. In order to solve this problem, the coupled element modeling approach was proposed in this study. A time domain fatigue analysis was applied to illustrate the necessity of the proposed approach.A dynamic benchmark case is used to demonstrate the accuracy of the coupled element method respectively.Subsequently the validated coupling element method is employed to conduct the global dynamic analyses for a free hanging flexible riser. The results demonstrate that the proposed approach can give the accurate global dynamic response under the guidance of the fatigue failure mode for unbonded flexible riser. The parametric influence analyses also provide a practical and effective way for predicting the global dynamic response.展开更多
In consideration that behavior of curvature ductility of interior support directly influences the degree of moment modification of unbonded prestressed concrete (UPC) continuous structures, constitutive relationships ...In consideration that behavior of curvature ductility of interior support directly influences the degree of moment modification of unbonded prestressed concrete (UPC) continuous structures, constitutive relationships of concrete, non-prestressed reinforcement and prestressed reinforcement used for nonlinear analysis are given. Through simulation analysis on simple beams subjected to single loading at the middle of the span, the law of factors influencing curvature ductility, such as global reinforcing index, prestressing degree, effective prestress, strength of concrete and grade of non-prestressed reinforcement are explored. Based on these researches, calculating formula of curvature ductility coefficient of UPC beams is established, which provides basic data for further research on plastic design of UPC indeterminate structures.展开更多
A study on fatigue behavior of unbonded partially prestressed concrete beams is presented. Model tests have been carried out in static loading and cyclic compressive loading on 15 beams with flexure. The ratios of the...A study on fatigue behavior of unbonded partially prestressed concrete beams is presented. Model tests have been carried out in static loading and cyclic compressive loading on 15 beams with flexure. The ratios of the lower limit to the upper limit of fatigue load are 0.5 and 0.3 respectively, and the frequencies of cyclic loading are 8 Hz and 4.5 Hz respectively. The experimental results of the strains of the concrete and steel bars, the deflection of test beams, and the crack width of normal section are analyzed. According to statistics and analysis of test results, the corresponding calculation models are developed and presented.展开更多
Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models ...Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models for unbonded flexible pipes.Then the mechanical property of the unbonded flexible pipe under tension,torsion and bending load has been analyzed and compared via ABAQUS software on the basis of three created models.The research shows that different modeling methods of flexible pipes make a great difference in the results.Especially,modeling simplifications of the carcass and pressure armor have a great impact on the accuracy of the results.Model 3,in which the carcass is simulated by spiral isot ropic shell and other layers are Simula ted by solid element,possesses good adaptability,which has been proved by comparing the experiment data and other models.This paper can offer a reference for the FE modeling methods,selection and mechanical property analysis of unbonded flexible pipe.展开更多
Unbonded post-tensioned(PT)concrete systems are widely used in safety-critical structures,yet model-ing practices for prestress implementation and tendon-concrete interaction remain inconsistent.This study investigate...Unbonded post-tensioned(PT)concrete systems are widely used in safety-critical structures,yet model-ing practices for prestress implementation and tendon-concrete interaction remain inconsistent.This study investigates the effects of sheath(duct)implementation and confinement assumptions through nonlinear finite element analysis.Four modeling cases were defined,consisting of an explicit sheath without tendon-concrete confinement(S)and three no-sheath variants with different confinement levels(X,N,A).One-way beams and two-way panels were analyzed,and panel blast responses were validated against experimental results.In both beams and panels,average initial stress levels were similar across models,through local stress concentrations appeared when the sheath was modeled.Under blast loading,these local effects became critical,and the sheath-implemented model reproduced experimental behavior most accurately,whereas non-implemented models deviated.Reduced blast intensity diminished the differences among models,thereby reaffirming that sheath-induced localization and damage propagation are critical factors.These findings highlight the importance of explicit sheath implementation for realistic numerical assessment of unbonded PT structures under extreme loads.展开更多
Unbonded flexible risers exhibit complex structures.Different structural layers can withstand axial loads and exhibit different degrees of coupled deformation.Based on the different material properties and structural ...Unbonded flexible risers exhibit complex structures.Different structural layers can withstand axial loads and exhibit different degrees of coupled deformation.Based on the different material properties and structural forms of each layer of an unbonded flexible riser,the structural layers are divided into three types:cylindrical,steel helical,and polymer helical layers.This study establishes a theoretical model of flexible risers under axial loads based on the law of conservation of energy and the geometry of de-formation,and deduces theoretical expressions for the axial load and axial stiffness of flexible risers.MATLAB was used to compile calculation programs to calculate the cross-sectional mechanical properties of flexible risers under axial tensile and compressive loads and to compare the calculation results with the experimental results and the results of other researchers to verify the reliability of the theoretical derivation and calculation programs.By further calculating the cross-sectional force distribution of each structural layer of the flexible risers under axial tensile loads,it is clarified that the tensile armor layer is the main component that can withstand axial tensile loads.A sensitivity analysis of the helix angle and number of helical strips of the tensile armor layer on the tensile properties of flexible risers was con-ducted;the results show that the helix angle had a more obvious influence on the tensile properties of flexible risers.The results of this study can provide a reference for the structural design and optimization of flexible risers.展开更多
Unbonded concrete overlay(UBCO) is the most used pavement rehabilitation technique across United States with an overall usage of 47% amongst all the rehabilitation methods.It is aimed to improve the performance of any...Unbonded concrete overlay(UBCO) is the most used pavement rehabilitation technique across United States with an overall usage of 47% amongst all the rehabilitation methods.It is aimed to improve the performance of any deteriorated/cracked jointed plain concrete pavement(JPCP).Unbonded JPCP overlay involves placement of a separation layer of hot mix asphalt(HMA),which acts as a stress relief layer between the existing concrete pavement and the overlay.There are numerous factors that affect the design and performance of UBCOs and out of these,existing pavement condition or the severity of damage of existing pavement is a prime factor.The severity of damage is described by the distressed elastic modulus thus,accurate determination of the distressed elastic modulus of the existing concrete pavement is essential for predicting the accurate performance of the unbonded overlay.This study focuses on analyzing the impact of distressed modulus by conducting simulations in the AASHTOWare pavement ME design software version 2.3 and evaluating the predicted performance of JPCP overlay for two different climatic regions.The results indicated that the distressed modulus of existing concrete pavement affects the performance of the overlay with regards to transverse cracking,joint faulting and pavement roughness.Transverse cracking is the most affected performance parameter with a change of 0.27% 2.31% with a unit change in distressed modulus.The impact of climatic conditions on the performance of unbonded overlay was also observed.The adverse effects of distressed modulus can be minimized by reducing the joint spacing or increasing the overlay slab thickness.展开更多
基金support by the Ministry of Education and Training of Vietnam for this research,under grant no.B2023-MBS-02.
文摘As prestressed concrete(PC)structures age,long-termeffects,e.g.,creep,shrinkage,and prestress losses,compromise their structural performance.Strengthening these aged PC beams has become a crucial matter.One effective solution is to use externally bonded fiber-reinforced polymer(FRP)sheets;however,limited research has been done on aged PC beams using the FRP,especially for beams with unbonded prestressing strands(UPC beams).Therefore,this research investigates the flexural strengthening efficacy of external FRP sheets on aged UPC beams with unbonded tendons.Aging minimally affected the failure modes of UPC beams,with nonstrengthened beams showing flexural failure via rebar yielding and concrete crushing,and FRP-strengthened beams failing due to FRP debonding and tensile reinforcement yielding,though tendons in the aged beams did not yield due to prestress losses,unlike the new beams.The U-wrap anchor curbed widespread debonding,leading to tensile reinforcement yielding and FRP rupture.Aging hastened crack growth and stiffness loss,increasing deflections and reducing load resistance,but FRP reinforcement mitigated these effects,enhancing cracking resistance by 14%over the unstrengthened aged beams and 7%over the new beams while boosting ultimate resistance by 9%above the non-strengthened new beams.Compared to the new FRP-strengthened beams,the aged counterparts had lower cracking resistance,stiffness and capacity—showing 20%higher deflections,7–9%lower serviceability loads,7%–17%reduced ultimate strength and 17%less deformability—due to prestress losses and premature FRP debonding.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51579146 and 51490674)Shanghai Municipal Natural Science Foundation(Grant No.15ZR1423500)Shanghai Rising-Star Program(Grant No.16QA1402300)
文摘This paper presents analytical and numerical models to predict the behavior of unbonded flexible risers under torsion.The analytical model takes local bending and torsion of tensile armor wires into consideration,and equilibrium equations of forces and displacements of layers are deduced.The numerical model includes lay angle,cross-sectional profiles of carcass,pressure armor layer and contact between layers.Abaqus/Explicit quasi-static simulation and mass scaling are adopted to avoid convergence problem and excessive computation time caused by geometric and contact nonlinearities.Results show that local bending and torsion of helical strips may have great influence on torsional stiffness,but stress related to bending and torsion is negligible;the presentation of anti-friction tapes may have great influence both on torsional stiffness and stress;hysteresis of torsion-twist relationship under cyclic loading is obtained by numerical model,which cannot be predicted by analytical model because of the ignorance of friction between layers.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51009093 and 51379005)
文摘This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the system, particularly in the critical touchdown zone, the traditional method is insufficient for accurately evaluating the fatigue life of these risers. The main challenge lies in the transposition from global to local analyses, which is a key stage for the fatigue analysis of flexible pipes owing to their complex structure. The new enhanced approach derives a multi-layer stress-decomposition method to meet this challenge. In this study, a numerical model validated experimentally is used to demonstrate the accuracy of the stress-decomposition method. And a numerical case is studied to validate the proposed approach. The results demonstrate that the multi-layer stress-decomposition method is accurate, and the fatigue lives of the metallic layers predicted by the enhanced multi-layer analysis approach are rational. The proposed fatigue-analysis approach provides a practical and reasonable method for predicting fatigue life in the design of unbonded flexible risers.
基金Supported by the Natural Science Foundation of Jiangsu Province under Grant No. BK20160557, and the General Program for Colleges and Universities in Jiangsu Province under Grant No. 16KJD570001
文摘A helical wire is a critical component of an unbounded flexible riser prone to fatigue failure. The helical wire has been the focus of much research work in recent years because of the complex multilayer construction of the flexible riser. The present study establishes an analytical model for the axisymmetric and bending analyses of an unbonded flexible riser. The interlayer contact under axisymmetric loads in this model is modeled by setting radial dummy springs between adjacent layers. The contact pressure is constant during the bending response and applied to determine the slipping friction force per unit helical wire. The model tracks the axial stress around the angular position at each time step to calculate the axial force gradient, then compares the axial force gradient with the slipping friction force to judge the helical wire slipping region, which would be applied to determine the bending stiffness for the next time step. The proposed model is verified against the experimental data in the literature. The bending moment-curvature relationship under irregular response is also qualitatively discussed. The stress at the critical point of the helical wire is investigated based on the model by considering the local flexure. The results indicate that the present model can well simulate the bending stiffness variation during irregular response, which has significant effect on the stress of helical wire.
文摘The scrap tire rubber pad(STRP)made by natural or synthetic rubber and high strength reinforcing cords exhibits substantial vertical stiffness and horizontal flexibility,and these properties can be regarded as suitable for seismic isolators for structures.The use of environmentally burdensome scrap tires as STRP isolators might be convenient as an efficient and low-cost solution for the implementation of aseismic design philosophy for low-to-medium rise buildings,especially in developing countries.Finite element analyses of unbonded square and strip-shaped STRP isolators subjected to a combination of axial and lateral loads are conducted to investigate its lateral deformation performance under seismic loading.The rubber of the isolator is modelled with Mooney-Rivlin hyperelastic and Prony viscoelastic materials,including the Mullins material damage effect.The influence of the length-to-width ratio and bearing height on the isolator performance is assessed in terms of the force-displacement relationship,horizontal stiffness,damping,and isolation periods.It is shown that the dependence of stiffness on the length-to-width ratio is significant in the longitudinal direction and minor in the transverse direction.The STRP isolators following the proposed design criteria are shown to satisfy the performance requirement at different levels of seismic demand specified by the ASCE/SEI 7-2010 seismic provisions.
文摘This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.
基金financially supported by the Fund of State Key Laboratory of Ocean Engineering(Grant No.GKZD010059-6)
文摘Owing to nonlinear contact problems with slip and friction, a lot of limiting assumptions are made when developing analytical models to simulate the behavior of an unbonded flexible riser. Meanwhile, in order to avoid convergence problems and excessive calculating time associated with running the detailed finite element （FE） model of an unbonded flexible riser, interlocked carcass and zeta layers with complicated cross section shapes are replaced by simple geometrical shapes （e.g. hollow cylindrical shell） with equivalent orthotropic materials. But the simplified model does not imply the stresses equivalence of these two layers. To solve these problems, based on ABAQUS/Explicit, a numerical method that is suitable for the detailed FE model is proposed. In consideration of interaction among all component layers, the axial stiffness of an eight-layer unbonded flexible riser subjected to axial tension is predicted. Compared with analytical and experimental results, it is shown that the proposed numerical method not only has high accuracy but also can substantially reduce the calculating time. In addition, the impact of the lay angle of helical tendons on axial stiffness is discussed.
基金Project supported by the National Natural Science Foundation of China (No.50178026)the New Century Excellent Talents in UniversityChangjiang Scholars Program of China (No.2009-37)
文摘Since the assumption of plane sections cannot be applied to the strain of unbonded tendons in prestressed concrete beams subjected to loadings,a moment-curvature nonlinear analysis method is used to develop analytical programs from stress increases in unbonded tendons at the ultimate limit state.Based on the results of model testing and simulation analysis,equations are proposed to predict the stress increase in tendons at the ultimate state in simple or continuous beams of partially prestressed concrete,considering the loading type,non-prestressed reinforcement index βp,prestressing reinforcement index βs,and span-depth ratio L/h as the basic parameters.Results of 380 beams studied here and test results for 35 simple beams obtained by the China Academy of Building Research were compared with those from prediction equations given in codes and other previous studies.The comparison reveals that the values predicted by the proposed equations agree well with experimental results.
基金the National Natural Science Foundation of China(Nos.51379005 and 51009093)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20120073120014)
文摘A coupled element modeling method is proposed for global dynamic analyses of unbonded flexible risers.Owing to the multi-layer structure of unbonded flexible risers, the global-dynamic-analysis method applied to the steel rigid risers is insufficient for flexible risers. The main challenges lie in the enormous difference between the anti-tension and anti-binding capacity of unbonded flexible risers which results in serious ill-conditional calculation in global dynamic analysis. In order to solve this problem, the coupled element modeling approach was proposed in this study. A time domain fatigue analysis was applied to illustrate the necessity of the proposed approach.A dynamic benchmark case is used to demonstrate the accuracy of the coupled element method respectively.Subsequently the validated coupling element method is employed to conduct the global dynamic analyses for a free hanging flexible riser. The results demonstrate that the proposed approach can give the accurate global dynamic response under the guidance of the fatigue failure mode for unbonded flexible riser. The parametric influence analyses also provide a practical and effective way for predicting the global dynamic response.
文摘In consideration that behavior of curvature ductility of interior support directly influences the degree of moment modification of unbonded prestressed concrete (UPC) continuous structures, constitutive relationships of concrete, non-prestressed reinforcement and prestressed reinforcement used for nonlinear analysis are given. Through simulation analysis on simple beams subjected to single loading at the middle of the span, the law of factors influencing curvature ductility, such as global reinforcing index, prestressing degree, effective prestress, strength of concrete and grade of non-prestressed reinforcement are explored. Based on these researches, calculating formula of curvature ductility coefficient of UPC beams is established, which provides basic data for further research on plastic design of UPC indeterminate structures.
文摘A study on fatigue behavior of unbonded partially prestressed concrete beams is presented. Model tests have been carried out in static loading and cyclic compressive loading on 15 beams with flexure. The ratios of the lower limit to the upper limit of fatigue load are 0.5 and 0.3 respectively, and the frequencies of cyclic loading are 8 Hz and 4.5 Hz respectively. The experimental results of the strains of the concrete and steel bars, the deflection of test beams, and the crack width of normal section are analyzed. According to statistics and analysis of test results, the corresponding calculation models are developed and presented.
基金the National Natural Science Foundation of China(Nos.11627802 and 51709118)the China Postdoctoral Science Foundation(No.2017M612669)+2 种基金the Science and Technology Program of Guangzhou(No.201804010482)the Fundamental Research Funds for the Central Universities of China(No.2017BQ089)the Fund of State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University(No.1708)
文摘Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models for unbonded flexible pipes.Then the mechanical property of the unbonded flexible pipe under tension,torsion and bending load has been analyzed and compared via ABAQUS software on the basis of three created models.The research shows that different modeling methods of flexible pipes make a great difference in the results.Especially,modeling simplifications of the carcass and pressure armor have a great impact on the accuracy of the results.Model 3,in which the carcass is simulated by spiral isot ropic shell and other layers are Simula ted by solid element,possesses good adaptability,which has been proved by comparing the experiment data and other models.This paper can offer a reference for the FE modeling methods,selection and mechanical property analysis of unbonded flexible pipe.
基金supported by the Nuclear Safety Research Program through the Korea Foundation of Nuclear Safety(KoFONS)using the financial resource granted by the Nuclear Safety and Security Commission(NSSC)of the Republic of Korea[RS-2025-02310881]the Korea Institute of Energy Technology Evaluation and Planning[KETEP]grant funded by the Ministry of Trade,Industry and Energy(MOTIE)[RS-2025-25447272].
文摘Unbonded post-tensioned(PT)concrete systems are widely used in safety-critical structures,yet model-ing practices for prestress implementation and tendon-concrete interaction remain inconsistent.This study investigates the effects of sheath(duct)implementation and confinement assumptions through nonlinear finite element analysis.Four modeling cases were defined,consisting of an explicit sheath without tendon-concrete confinement(S)and three no-sheath variants with different confinement levels(X,N,A).One-way beams and two-way panels were analyzed,and panel blast responses were validated against experimental results.In both beams and panels,average initial stress levels were similar across models,through local stress concentrations appeared when the sheath was modeled.Under blast loading,these local effects became critical,and the sheath-implemented model reproduced experimental behavior most accurately,whereas non-implemented models deviated.Reduced blast intensity diminished the differences among models,thereby reaffirming that sheath-induced localization and damage propagation are critical factors.These findings highlight the importance of explicit sheath implementation for realistic numerical assessment of unbonded PT structures under extreme loads.
基金supported by the National Natural Science Foun-dation of China(U1906233)the Major Basic Research Project of Shandong Province(2019JZZY010801)+2 种基金the Natural Science Foundation of Shandong Province(Grant No.ZR2022ME184)the National Natural Science Foundation of China(Grant No.51609222)the Opening Fund of the State Key Laboratory of Ocean Engineering(Shanghai Jiao Tong University)(Grant No.1511).
文摘Unbonded flexible risers exhibit complex structures.Different structural layers can withstand axial loads and exhibit different degrees of coupled deformation.Based on the different material properties and structural forms of each layer of an unbonded flexible riser,the structural layers are divided into three types:cylindrical,steel helical,and polymer helical layers.This study establishes a theoretical model of flexible risers under axial loads based on the law of conservation of energy and the geometry of de-formation,and deduces theoretical expressions for the axial load and axial stiffness of flexible risers.MATLAB was used to compile calculation programs to calculate the cross-sectional mechanical properties of flexible risers under axial tensile and compressive loads and to compare the calculation results with the experimental results and the results of other researchers to verify the reliability of the theoretical derivation and calculation programs.By further calculating the cross-sectional force distribution of each structural layer of the flexible risers under axial tensile loads,it is clarified that the tensile armor layer is the main component that can withstand axial tensile loads.A sensitivity analysis of the helix angle and number of helical strips of the tensile armor layer on the tensile properties of flexible risers was con-ducted;the results show that the helix angle had a more obvious influence on the tensile properties of flexible risers.The results of this study can provide a reference for the structural design and optimization of flexible risers.
文摘Unbonded concrete overlay(UBCO) is the most used pavement rehabilitation technique across United States with an overall usage of 47% amongst all the rehabilitation methods.It is aimed to improve the performance of any deteriorated/cracked jointed plain concrete pavement(JPCP).Unbonded JPCP overlay involves placement of a separation layer of hot mix asphalt(HMA),which acts as a stress relief layer between the existing concrete pavement and the overlay.There are numerous factors that affect the design and performance of UBCOs and out of these,existing pavement condition or the severity of damage of existing pavement is a prime factor.The severity of damage is described by the distressed elastic modulus thus,accurate determination of the distressed elastic modulus of the existing concrete pavement is essential for predicting the accurate performance of the unbonded overlay.This study focuses on analyzing the impact of distressed modulus by conducting simulations in the AASHTOWare pavement ME design software version 2.3 and evaluating the predicted performance of JPCP overlay for two different climatic regions.The results indicated that the distressed modulus of existing concrete pavement affects the performance of the overlay with regards to transverse cracking,joint faulting and pavement roughness.Transverse cracking is the most affected performance parameter with a change of 0.27% 2.31% with a unit change in distressed modulus.The impact of climatic conditions on the performance of unbonded overlay was also observed.The adverse effects of distressed modulus can be minimized by reducing the joint spacing or increasing the overlay slab thickness.
