• Structural Engineering and Mechanics
• /
• 제18권1호
• /
• pp.21-40
• /
• 2004

In this paper, we modify the L-L model (Li et al. 2003) and extend the application of this model to concrete confined by both steel reinforcement and CFRP. Thirty-six concrete cylinders with a dimension of ${\varphi}30{\times}60$ cm were tested to verify the effectiveness of the proposed model. The experimental test results show that different types of steel reinforcement have a great effect on the compressive strength of concrete cylinders confined by steel reinforcement, but the different types of steel reinforcement have very little effect on concrete cylinders confined by both steel reinforcement and CFRP. Compared with the stress-strain curves of confined concrete cylinders, we can conclude that the proposed model can provide more effective prediction than others models.

• Earthquakes and Structures
• /
• 제7권5호
• /
• pp.705-718
• /
• 2014

This paper presents an analytical model for determining the transverse reinforcement required for reinforced concrete exterior beam-column joints subjected to reversed cyclic loading. Although the joint aspect ratio can affect joint shear strength, current design codes do not consider its effects in calculating joint shear strength and the necessary amount of transverse reinforcement. This study re-evaluated previous exterior beam-column joint tests collected from 11 references and showed that the joint shear strength decreases as the joint aspect ratio increases. An analytical model was developed, to quantify the transverse reinforcement required to secure safe load flows in exterior beam-column joints. Comparisons with a database of exterior beam-column joint tests from published literature validated the model. The required sectional ratios of horizontal transverse reinforcement calculated by the proposed model were compared with those specified in ACI 352R-02. More transverse reinforcement is required as the joint aspect ratio increases, or as the ratio of vertical reinforcement decreases; however, ACI 352R-02 specifies a constant transverse reinforcement, regardless of the joint aspect ratio. This reevaluation of test data and the results of the analytical model demonstrate a need for new criteria that take the effects of joint aspect ratio into account in exterior joint design.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.804-807
• /
• 2002

In general, the reinforcement of a structure is performed with cylinders. In this study, it is attempted to analyze the circular reinforcement with fins. And the maximum stress and deflection is investigated fur the circular reinforcement between two plates. The shape of models are : one which has only circular reinforcements of different diameters and one which has circular reinforcements with fins and one which has fin of same length and circular cylinders of different diameters. And in each model, there are two kinds; one is with upper and lower plates and the other with none. The results shows that the maximum stress is less in the model of circular reinforcement with fins than that in the model without fins. And the maximum stress of a model without upper and lower plate is less than that of a model with plates.

• Earthquakes and Structures
• /
• 제22권1호
• /
• pp.39-51
• /
• 2022

The axial compression behavior of nine self-compacting concrete columns confined with CFRP-PVC spirals was studied. Three parameters of spiral reinforcement spacing, spiral reinforcement diameter and height diameter ratio were studied. The test results show that the CFRP strip and PVC tube are destroyed first, and the spiral reinforcement and longitudinal reinforcement yield. The results show that with the increase of spiral reinforcement spacing, the peak bearing capacity decreases, but the ductility increases; with the increase of spiral reinforcement diameter, the peak bearing capacity increases, but has little effect on ductility, and the specimen with the ratio of height to diameter of 7.5 has the best mechanical properties. According to the reasonable constitutive relation of material, the finite element model of axial compression is established. Based on the verified finite element model, the stress mechanism is revealed. Finally, the composite constraint model and bearing capacity calculation method are proposed.

• 한국전자통신학회논문지
• /
• 제16권1호
• /
• pp.95-100
• /
• 2021

본 논문에서는 수중 건설 로봇을 제어하기 위한 모델 기반 메타 강화 학습 방법을 제안한다. 모델 기반 메타 강화 학습은 실제 응용 프로그램의 최근 경험을 사용하여 모델을 빠르게 업데이트한다. 다음으로, 대상 위치에 도달하기 위해 매니퓰레이터의 제어 입력을 계산하는 모델 예측 제어로 모델을 전송한다. MuJoCo 및 Gazebo를 사용하여 모델 기반 메타 강화 학습을 위한 시뮬레이션 환경을 구축하였으며 수중 건설 로봇의 실제 제어 환경에서의 모델 불확실성을 포함하여 제안한 방법을 검증하였다.

• Computers and Concrete
• /
• 제22권3호
• /
• pp.305-317
• /
• 2018

Steel reinforced Engineered Cementitious Composite (ECC) components have been proposed for seismic structural applications, for example in coupling beams, infill panels, joints, columns, and flexural members. The development of strain in the steel reinforcement of cementitious components has been shown to vary based on both the steel reinforcement ratio and the applied deformation history. Strain in the steel reinforcement of reinforced ECC components is an important structural response metric because ultimate failure is often by fracture of the steel reinforcement. A recently proposed bond-slip model has been successfully calibrated to cyclically tested reinforced ECC beams wherein the deformation history contained monotonically increasing cycles. This paper reports simulations of two-dimensional finite element models of reinforced ECC beams to determine the appropriateness and significance of altering a phenomenological bond-slip model based on the applied deformation history. The numerical simulations with various values of post-peak bond-slip softening stiffness are compared to experimental results. Varying the post-peak bond-slip softening stiffness had little effect on the cracking patterns and hysteretic response of the reinforced ECC flexural models tested, which consisted of two different steel reinforcement ratios subjected to two different deformation histories. Varying the post-peak bond-slip softening stiffness did, however, affect the magnitude of strain and the length of reinforcing bar that strain-hardened. Overall, a numerical model with a constant bond-slip model represented well various responses in reinforced ECC beams with multiple steel reinforcement ratios subjected to different deformation histories.

• Computers and Concrete
• /
• 제20권2호
• /
• pp.215-227
• /
• 2017

A finite element model (FEM) for predicting early-age behavior of reinforced concrete (RC) bridge deck slabs with fiber-reinforced polymer (FRP) bars is presented. In this model, the shrinkage profile of concrete accounted for the effect of surrounding conditions including air flow. The results of the model were verified against the experimental test results, published by the authors. The model was verified for cracking pattern, crack width and spacing, and reinforcement strains in the vicinity of the crack using different types and ratios of longitudinal reinforcement. The FEM was able to predict the experimental results within 6 to 10% error. The verified model was utilized to conduct a parametric study investigating the effect of four key parameters including reinforcement spacing, concrete cover, FRP bar type, and concrete compressive strength on the behavior of FRP-RC bridge deck slabs subjected to restrained shrinkage at early-age. It is concluded that a reinforcement ratio of 0.45% carbon FRP (CFRP) can control the early-age crack width and reinforcement strain in CFRP-RC members subjected to restrained shrinkage. Also, the results indicate that changing the bond-slippage characteristics (sand-coated and ribbed bars) or concrete cover had an insignificant effect on the early-age crack behavior of FRP-RC bridge deck slabs subjected to shrinkage. However, reducing bar spacing and concrete strength resulted in a decrease in crack width and reinforcement strain.

• Structural Engineering and Mechanics
• /
• 제84권2호
• /
• pp.239-251
• /
• 2022

The use of lateral reinforcement in confined concrete columns can improve bearing capacity and deformability. The lateral responses of lateral reinforcement significantly influence the effective confining pressure on core concrete. However, lateral strain-axial strain model of concrete columns confined by lateral reinforcement has not received enough attention. In this paper, based on experimental results of 85 concrete columns confined by lateral reinforcement under axial compression, the effect of unconfined concrete compressive strength, volumetric ratio, lateral reinforcement yield strength, and confinement type on lateral strain-axial strain curves was investigated. Through parameter analysis, it indicated that with the same level of axial strain, the lateral strain slightly increased with the increase in the unconfined concrete compressive strength, but decreased with the increase in volumetric ratio significantly. The lateral reinforcement yield strength had slight influence on lateral strain-axial strain curves. At the same level of lateral strain, the axial strain of specimen with spiral was larger than that of specimen with stirrup. Furthermore, a lateral strain-axial strain model for concrete columns confined by lateral reinforcement under axial compression was proposed by introducing the effects of unconfined concrete compressive strength, volumetric ratio, confinement type and effective confining pressure, which showed good agreement with the experimental results.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 1998년도 추계학술대회 논문집
• /
• pp.96-102
• /
• 1998

The characteristics of roadbed are very important factors in the design of railways. Laboratory model tests were performed to investigate the effectiveness of geogrid placement in the subbase layers on reinforcement. Design parameters of reinforcement were determined through the laboratory model tests. The results indicated that geogrid reinforcement is increased the bearing capacity and reduced the settlement of railway foundation. The optimum length of geogrid reinforcement is about 4B. The effective depth of geogrid placement from the bottom of ballast is about 0.1B-0.2B depended on magnitude of applied load.

• 한국도로학회논문집
• /
• 제17권3호
• /
• pp.77-83
• /
• 2015

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.