Numerical Evaluation of Splitting Performance of Prestressed Concrete Prisms With Larger Diameter Prestressing Wires

2019 ◽  
Author(s):  
Moochul Shin ◽  
Hailing Yu
Keyword(s):  
Prestressed Concrete ◽  
Structural Damage ◽  
Numerical Study ◽  
Experimental Studies ◽  
Concrete Cover ◽  
Small Scale ◽  
Slip Model ◽  
Cohesive Elements ◽  
Bond Slip ◽  
Pull Out

This numerical study focuses on evaluating the structural performance of prestressed concrete prisms with larger diameter (0.315 in) prestressing wires. More commonly used prestressing wires are the 0.209 in (5.32 mm) diameter wires for prestressed concrete crossties. However, there has been an interest to adopt larger diameter prestressing wires in order to provide higher prestress forces with the aim of mitigating the structural damage of prestressed concrete crossties. Previous experimental studies demonstrated that small-scale pretensioned concrete prisms had excellent correlation in bonding performance of concrete ties pretensioned with 0.209 in (5.32 mm) wires or three- or seven-wire strands. Using a finite element (FE) modeling approach, this study investigates the effects of 8 mm diameter prestressing wires on the splitting/bursting performance of prisms at the onset of de-tensioning of the wires. The studied parameters include geometrical/mechanical parameters such as thickness of the concrete cover, spacing between the wires, level of prestress forces, and concrete release strength in compression. Cohesive elements with a newly developed nonlinear bond-slip model are assigned to the interface between the prestressing wires and the surrounding concrete. The parameters for the bond-slip model are calibrated based on a simple pull-out test on concrete cylinders with the 0.315 in (8 mm) diameter wires. The simulation results are compared with the predicted splitting performance of prisms pretensioned with 0.209 in (5.32 mm) wires or seven-wire strands. Based on the FE analysis results, recommendations are made on the minimum concrete cover thickness and wire spacing required to achieve acceptable splitting/bursting performance in prestressed concrete prisms.

scholarly journals A theoretical verification of the integral fluctuation theorem for accelerated colloidal systems in the long-time limit

2021 ◽  
Author(s):  
Yash Lokare
Keyword(s):  
Steady State ◽  
Time Scales ◽  
Numerical Study ◽  
Quantitative Description ◽  
Experimental Studies ◽  
Fluctuation Theorem ◽  
Nonequilibrium Steady States ◽  
Small Scale ◽  
Colloidal Systems ◽  
Long Time

A quantitative description of the violation of the second law of thermodynamics in relatively small classical systems and over short time scales comes from the fluctuation-dissipation theorem. It has been well established both theoretically and experimentally, the validity of the fluctuation theorem to small scale systems that are disturbed from their initial equilibrium states. Some experimental studies in the past have also explored the validity of the fluctuation theorem to nonequilibrium steady states at long time scales in the asymptotic limit. To this end, a theoretical and/or purely numerical model of the integral fluctuation theorem has been presented. An approximate general expression for the dissipation function has been derived for accelerated colloidal systems trapped/confined in power-law traps. Thereafter, a colloidal particle trapped in a harmonic potential (generated by an accelerating one-dimensional optical trap) and undergoing Brownian motion has been considered for the numerical study. A toy model of a quartic potential trap in addition to the harmonic trap has also been considered for the numerical study. The results presented herein show that the integral fluctuation theorem applies not only to equilibrium steady state distributions but also to nonequilibrium steady state distributions of colloidal systems in accelerated frames of reference over long time scales.

On the analysis of the integral fluctuation theorem for accelerated colloidal systems in the long-time limit

2021 ◽  
Author(s):  
Yash Lokare
Keyword(s):  
Steady State ◽  
Time Scales ◽  
Numerical Study ◽  
Quantitative Description ◽  
Experimental Studies ◽  
Fluctuation Theorem ◽  
Nonequilibrium Steady States ◽  
Small Scale ◽  
Colloidal Systems ◽  
Long Time

Abstract A quantitative description of the violation of the second law of thermodynamics in relatively small classical systems and over short time scales comes from the fluctuation-dissipation theorem. It has been well established both theoretically and experimentally, the validity of the fluctuation theorem to small scale systems that are disturbed from their initial equilibrium states. Some experimental studies in the past have also explored the validity of the fluctuation theorem to nonequilibrium steady states at long time scales in the asymptotic limit. To this end, a theoretical and/or purely numerical model of the integral fluctuation theorem has been presented. An approximate general expression for the dissipation function has been derived for accelerated colloidal systems trapped/confined in power-law traps. Thereafter, a colloidal particle trapped in a harmonic potential (generated by an accelerating one-dimensional optical trap) and undergoing Brownian motion has been considered for the numerical study. A toy model of a quartic potential trap in addition to the harmonic trap has also been considered for the numerical study. The results presented herein show that the integral fluctuation theorem applies not only to equilibrium steady state distributions but also to nonequilibrium steady state distributions of colloidal systems in accelerated frames of reference over long time scales.

Bond Properties of Plain Steel Bar in Concrete with Machine-Made Sand

2013 ◽  
Vol 438-439 ◽  
pp. 20-24
Author(s):  
Feng Lan Li ◽  
Ke Fei Yu ◽  
Xin Xin Ding ◽  
Chang Ming Li
Keyword(s):  
Bond Strength ◽  
Experimental Studies ◽  
Bond Stress ◽  
Test Method ◽  
Bond Properties ◽  
Bond Slip ◽  
Ordinary Concrete ◽  
Strength Grade ◽  
Pull Out ◽  
Steel Bar

To meet the requirement of machine-made sand application in concrete structures, it is necessary to understand the bond properties of steel bar with machine-made sand concrete (MSC). Therefore, the experimental studies were carried out on the bond of plain steel bar with MSC by the central pull-out test method. Three specimens were cast as one group, 6 groups were tested considering the changes of strength grade of MSC and ordinary concrete. The bond-slip curves were measured and analyzed. The results show that the bond slip begins at the tensile side and transfers gradually to the free end before the entire slip turns up along the interface of plain steel bar and surrounded concrete, the largest average bond stress, i. e. the bond strength of plain steel bar corresponds to the initial entire slip of plain steel bar. With the increasing strength grade of MSC and ordinary concrete, the difference of slip at tensile side and free end becomes greater. Comparing that only appears in ordinary concrete with higher strength, the larger slips turn up while the bond stress reaches the largest for the plain steel bar in MSC. Larger scatter of bond strength is between specimens in the same group. Some plain steel bars yields with the beginning of entire slip along the interface.

scholarly journals Experimental Study on Bond-Slip Behavior of Bamboo Bolt-Modified Slurry Interface under Pull-Out Load

2018 ◽  
Vol 2018 ◽  
pp. 1-23 ◽  
Author(s):  
Wei Lu ◽  
Dong Zhao ◽  
Xiao-fei Mao ◽  
Yu Ai
Keyword(s):  
Axial Direction ◽  
Impact Factors ◽  
Slip Model ◽  
Distribution Law ◽  
Bond Slip ◽  
Pull Out ◽  
Control Interface ◽  
Bolt Diameter ◽  
Interface Bond

This paper presents an analysis of bamboo bolt-modified slurry interfaces based on 26 in situ axial pull-out tests intended to highlight the mechanical behavior of interface under a fracture mode. Three impact factors are analyzed: anchorage length, bolt diameter, and bolt hole diameter, using the same materials of bamboo and modified slurry. The result shows that the interface between the bamboo bolt and anchoring agent is the control interface of an anchorage system, and the local behavior of the interface involves four stages: elastic, soften, friction, and decoupling. Distribution law and change trend of slippage, stress, and strain of anchoring interface along with the axial direction of an anchor bolt were analyzed. The result shows that there is effective anchoring length limit in this kind of interface, and that the complete decoupling phenomenon should not be neglected. Through a comparative analysis of the existing bond-slip model and interface bond-slip curve, and considering the correspondence of the strain-slip curve and trilinear bond-slip model simultaneously, a modified trilinear bond-slip model has been proposed. The friction section of this model is limited, and shearing stress in the complete decoupling section is zero.

Investigation of the Effect of Incomplete Droplet Prevaporization on NOx Emissions in LDI Combustion Systems

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Christian H. Beck ◽  
Rainer Koch ◽  
Hans-Jörg Bauer
Keyword(s):  
Reaction Zone ◽  
Liquid Fuel ◽  
Laser Doppler Anemometry ◽  
Numerical Study ◽  
Experimental Studies ◽  
Peak Temperature ◽  
Small Scale ◽  
Nitric Oxides ◽  
Transition Range ◽  
Combustion Systems

The influence of incomplete liquid fuel prevaporization on the emissions of nitric oxides in a swirl stabilized model gas turbine combustor is investigated experimentally and numerically. The design of the model combustor enables the variation of the degree of prevaporization. This is achieved by using two liquid fuel injectors. One injector is located far upstream of the combustor and generates a fully prevaporized and premixed air fuel mixture. The second injector is located at the combustor inlet. Consequently, the liquid fuel mass flow split between the two injectors determines the fraction of nonprevaporized fuel present in the reaction zone. The NO∕NO2 measurements were performed with a chemoluminescence analyzer. In accordance to the findings of other researchers, the present experimental study revealed that the influence of prevaporization on nitric oxide emissions is of significance for practical applications. The experimental studies were accompanied by numerical studies of partially prevaporized lean combustion in an abstracted configuration. The purpose of this numerical study is to gain a detailed understanding of the influence of droplet slip on droplet flame position and peak temperature. The droplet slip velocity was found to have a significant impact on the peak temperature of the droplet flame and, therefore, NO formation rates within the droplet flame. The combustion system used for the experimental investigation was characterized regarding droplet slip velocities with an extended laser Doppler anemometry technique. The comparison between numerical and experimental results shows that the droplet slip velocities in the macroscopic reaction zone are within the transition range from an envelope to a wake flame. It is concluded that small-scale mixing effects play a significant role in the formation of nitric oxides in spray combustion systems with incomplete prevaporization.

scholarly journals A Theoretical Analysis of the Integral Fluctuation Theorem for Accelerated Colloidal Systems in the Long-Time Limit

2021 ◽  
Author(s):  
Yash Lokare
Keyword(s):  
Steady State ◽  
Time Scales ◽  
Numerical Study ◽  
Quantitative Description ◽  
Experimental Studies ◽  
Fluctuation Theorem ◽  
Nonequilibrium Steady States ◽  
Small Scale ◽  
Colloidal Systems ◽  
Long Time

A quantitative description of the second law of thermodynamics in relatively small classical systems and over short time scales comes from the fluctuation-dissipation theorem. It has been well established both theoretically and experimentally, the validity of the fluctuation theorem to small scale systems that are disturbed from their initial equilibrium states. Some experimental studies in the past have also explored the validity of the fluctuation theorem to nonequilibrium steady states at long time scales in the asymptotic limit. To this end, a theoretical and/or purely numerical model of the integral fluctuation theorem has been presented. An approximate general expression for the dissipation function has been derived for accelerated colloidal systems trapped/confined in power-law traps. Thereafter, a colloidal particle trapped in a harmonic potential (generated by an accelerating one-dimensional optical trap) and undergoing Brownian motion has been considered for the numerical study. A toy model of a quartic potential trap in addition to the harmonic trap has also been considered for the numerical study. The results presented herein show that the integral fluctuation theorem applies not only to equilibrium steady state distributions but also to nonequilibrium steady state distributions of ideal colloidal systems in accelerated frames of reference over long time scales.

Experimental Study on Bond-Slip between Steel Bar and Recycled Aggregate Concrete

2011 ◽  
Vol 250-253 ◽  
pp. 1651-1656 ◽  
Author(s):  
Qing Feng Huang ◽  
Da Fu Wang
Keyword(s):  
Concrete Strength ◽  
Concrete Cover ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Aggregate Concrete ◽  
Bond Slip ◽  
Pull Out ◽  
Steel Bar ◽  
Cover Thickness

By a static and repeated pull-out experiment between steel bar and recycled aggregate concrete, and bond-slip curves between recycled concrete with different recycled coarse aggregate(RCA) replacement percentages were recorded. Based on the analysis of the experimental results, replacement percentages of recycled concrete, cover thickness, anchorage length, concrete strength and loading method was investigated. At last, the bond-slip constitutive relation was also discussed.

Bond-Slip Relation of Plain Steel Bar in Concrete with Machine-Made Sand

2012 ◽  
Vol 238 ◽  
pp. 142-146 ◽  
Author(s):  
Shun Bo Zhao ◽  
Xin Xin Ding ◽  
Chang Yong Li
Keyword(s):  
Constitutive Relations ◽  
Concrete Strength ◽  
Experimental Studies ◽  
Test Method ◽  
Group 14 ◽  
Bond Slip ◽  
Pull Out ◽  
Steel Bar ◽  
Characteristic Values ◽  
Powder Content

To meet the requirement of machine-made sand application in concrete structures, experimental studies were carried out on the bond of plain steel bar with Machine-made Sand Concrete (MSC) by the central pull-out test method. Three specimens were cast as one group, 14 groups were tested considering the influence of concrete strength, bond length and stone powder content in machine-made sand. Based on the experimental research, the characteristic values of bond-slip curve such as the initial-slip and ultimate bond stresses with corresponding slips are statistically analyzed, the bond-slip constitutive relations between plain steel bar and MSC were obtained.

scholarly journals Numerical study of the self-centering prestressed concrete pier with external energy dissipators

2019 ◽  
Vol 275 ◽  
pp. 02013
Author(s):  
Lianglong Song ◽  
Xin Shi ◽  
Tong Guo ◽  
Wenqian Zheng
Keyword(s):  
Energy Dissipation ◽  
Prestressed Concrete ◽  
Structural Damage ◽  
Numerical Study ◽  
Basalt Fiber ◽  
Interface Energy ◽  
The Self ◽  
Fe Model ◽  
External Energy ◽  
Energy Dissipators

A novel self-centering prestressed concrete (SCPC) pier with external energy dissipators (EDs) has been recently proposed to minimize the structural damage and residual deformations, and enhance the corrosion-resistant capability. In the SCPC pier with external EDs, internal post-tensioned basalt fiber-reinforced polymer (BFRP) tendons are used to provide the self-centering ability, and the energy dissipation is realized through the external aluminum bars. Previous cyclic load tests of 1/3-scaled specimens showed that the SCPC pier with external EDs had desirable self-centering and energy dissipation capacities. In this study, a three-dimensional finite element (FE) model is developed using the ANSYS software. The FE model can capture the complex behavior of the proposed pier, such as gap opening/closing at the pier-foundation interface, energy dissipation of EDs, and self-centering capacity. Good agreement is observed between the numerical and experimental results, demonstrating the accuracy of the developed FE model. This will enable the parametric studies on the seismic performance of the SCPC pier with external EDs in the future.

Numerical Simulation of the Interfacial Behaviour of Grouted Rockbolts in Tunnel Support Based on a Tri-Linear Bond-Slip Model

2012 ◽  
Vol 446-449 ◽  
pp. 1769-1774 ◽  
Author(s):  
Fei Fan Ren ◽  
Zhen Jun Yang ◽  
Chao Xu
Keyword(s):  
Interfacial Shear Stress ◽  
Material Model ◽  
Control Parameters ◽  
Slip Model ◽  
Interfacial Behavior ◽  
Cohesive Elements ◽  
Tunnel Support ◽  
Bond Slip ◽  
Interfacial Behaviour ◽  
Linear Material

Grouted rockbolts are widely used in tunneling excavation. However, the rockbolt design is still basically empirical, the mechanical behavior of grouted rockbolts, especially the interfacial behavior, has never been studied systematically. First of all, a tri-linear bond slip model is proposed for modeling the rockbolt interfacial behavior. Then analytical solutions to grouted rockbolt are presented on the basis of a tri-linear bond-slip model. Finally, a numerical model using Abaqus program to simulate the tunnel rockbolt is proposed. This model uses cohesive elements to simulate debonding along the anchorage interfaces, meanwhile, tabular damage variable is obtained on the basis of the damage evolution law in order to correspond with the tri-linear material model. The developed model was validated by monitored data. It was found that the model was capable of predicting accurately the interfacial shear stress distribution, load on the bolt as well as the rock movements. Therefore, this model can be used to optimize the control parameters of grouted rockbolts.

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