• Computers and Concrete
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• v.12 no.5
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• pp.585-612
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• 2013

The paper presents quasi-static numerical simulations of the behaviour of short reinforced concrete beams without shear reinforcement under mixed shear-tension failure using the FEM and four various constitutive continuum models for concrete. First, an isotropic elasto-plastic model with a Drucker-Prager criterion defined in compression and with a Rankine criterion defined in tension was used. Next, an anisotropic smeared crack and isotropic damage model were applied. Finally, an elasto-plastic-damage model was used. To ensure mesh-independent FE results, to describe strain localization in concrete and to capture a deterministic size effect, all models were enhanced in a softening regime by a characteristic length of micro-structure by means of a non-local theory. Bond-slip between concrete and reinforcement was considered. The numerical results were directly compared with the corresponding laboratory tests performed by Walraven and Lehwalter (1994). The advantages and disadvantages of enhanced models to model the reinforced concrete behaviour were outlined.

• Advances in Computational Design
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• v.2 no.2
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• pp.147-168
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• 2017

Over the past couple decades, externally bonded fiber reinforced polymer (FRP) composites have emerged as a repair and strengthening material for many concrete infrastructure applications. This paper presents an analytical investigation of the use of carbon FRP (CFRP) for a specific problem that occurs in concrete bridge girders wherein the girder ends are damaged by excessive exposure to deicing salts and numerous freezing/thawing cycles. A 3D finite element (FE) model of a full scale prestressed concrete (PC) I-girder is used to investigate the effect of damage to the cover concrete and stirrups in the end region of the girder. Parametric studies are performed using externally bonded CFRP shear laminates to determine the most effective repair schemes for the damaged end region under a short shear span-to-depth ratio. Experimental results on shear pull off tests of CFRP laminates that have undergone accelerated aging are used to calibrate a bond stress-slip model for the interface between the FRP and concrete substrate and approximate the reduced bond stress-slip properties associated with exposure to the environment that causes this type of end region damage. The results of these analyses indicate that this particular application of this material can be effective in recovering the original strength of PC bridge girders with damaged end regions, even after environmental aging.

• Computers and Concrete
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• v.26 no.2
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• pp.115-125
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• 2020

To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800℃ for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concrete-rebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

• Magazine of the Korea Concrete Institute
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• v.3 no.2
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• pp.115-121
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• 1991

Slippage of beam longitudinal reinforcement at beam-column connections is an important cause of damage to reinforced concrete frames under static and dynamic loads, This paper summarizes the results of an experimen¬tal study on the effects of confinements and compressive strength of concrete on the local bond stress-slip cha¬racteristics of deformed bars. I t is concluded from experimental results that, as far as the bond splittmg cracks are restrained by the vertical column reinforcement, confinement of concrete by transverse reinforcement has insignigicant direct effect on the local bond behavior. The ultimate bond strength, however, Increases pro¬portionally with the square root of concrete compressive strength. An empirical model was developed for local bond st ressslip relationslip of deformed bars in confined concrete of different compressive strengths.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.395-409
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• 2022

The presence of infill generally neglected in design despite the fact that infill contribution significantly increase the lateral stiffness and strength of the reinforced concrete frame structure. Several experimental studies and computational models have been proposed to capture the rational response of infill-frame interaction at global level. However, limited studies are available on explicit finite element modelling to study the local behavior due to high computation and convergence issues in numerical modelling. In the current study, the computational modelling of RC frames is done with various configurations of infill masonry in terms of types of blocks, lateral loading and reinforcement detailing employed with material nonlinearities, interface contact issues and bond-slip phenomenon particularly near the beam-column joints. To this end, extensive computational modelling of five variant characteristics test specimens extracted from the detailed experimental program available in literature and process through nonlinear static analysis in FEM code, ATENA generally used to capture the nonlinear response of reinforced concrete structures. Results are presented in terms of damage patterns and capacity curves by employing the finest possible detail provided in the experimental program. Comparative analysis shows that good correlation amongst the experimental and numerical simulated results both in terms of capacity and crack patterns.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.157-164
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• 1997

일반적으로 콘크리트와 철근간의 경계면을 나타내는 유한요소법에는 균열의 부근에서 발생하는 부착열화 현상을 고려하지 않고 있다. 이것은 균열 부근에서 과도한 부착을 초래하고 , 국소 변형과 균열의 진전에도 영향을 준다. 본 연구에서는 철근콘크리트 구조물의 균열부근에서 일어나는 부착거동의 변화를 고려한 비선형 부착응력-미끄럼 모델을 제안하였다. 철근과 콘크리트간의 경계면에는 링크요소를 이용하였고, 링크의 특성은 철근을 가로지르는 균열의 상태에 따라 변하도록 조정하였다. 균열의 형성상태를 정량화하고, 부착거동을 두 포락선 1) 균열로부터 충분히 떨어진 위치에서의 부착상태를 모델링한 외연포락선, 2)횡균열면에 있어서의 부착상태를 모델링한 내연포락선의 사이에 변이시키기 위하여 비국소적 손상도 개념을 도입하였다. 이 방법의 유효성을 알아보기 위하여 편재하중을 받는 T형 교각의 실험 및 해석결과를 제시하였다. 제안된 모델의 결과를 실험결과와 비교하여 본 모델의 유용성을 검증하였다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.271-278
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• 2019

The corrosion of reinforcements embedded in concrete causes severe deterioration in reinforced concrete structures. As a countermeasure, epoxy coated reinforcements are used to prevent corrosion of reinforcements. When epoxy coated bars are used, the resistance of corrosion is excellent, but epoxy coating on the bars have a disadvantage of reduction in bond capacity comparing to that of normal bars. Therefore, it is necessary to confirm the bond performance of epoxy coated reinforcements through experimental and analytical methods. Bond behaviors of epoxy coated bars for various diameters of 13 and 19mm and thicknesses of cover concrete of 3 types(ratio of cover to bar diameter) are examined. As the diameters of the epoxy coated bars increase, the difference of bond strength between epoxy coated and uncoated bars also increases and damage patterns showed pull out failure. In addition, finite element analysis was performed based on the bond-slip relationship obtained by direct pullout test and compared with the flexural test results. It is considered that flexural member test is more useful than pullout test for simulating the behavior of actual structure.

• Computers and Concrete
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• v.20 no.3
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• pp.351-360
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• 2017

This paper presents an efficient membrane finite element for the cyclic inelastic response analysis of RC structures under complex plane stress states including shear. The model strikes a balance between accuracy and numerical efficiency to meet the challenge of shear wall simulations in earthquake engineering practice. The concrete material model at the integration points of the finite element is based on damage plasticity with two damage parameters. All reinforcing bars with the same orientation are represented by an embedded orthotropic steel layer based on uniaxial stress-strain relation, so that the dowel and bond-slip effect of the reinforcing steel are presently neglected in the interest of computational efficiency. The model is validated with significant experimental results of the cyclic response of RC panels with uniform stress states.

• Computers and Concrete
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• v.22 no.2
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• pp.167-182
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• 2018

The modeling of loss of bond between reinforcing bars (rebars) and concrete due to corrosion is useful in studying the behavior and prediction of residual load bearing capacity of corroded reinforced concrete (RC) members. In the present work, first the possibility of using different methods to simulate the rebars-concrete bonding, which is used in three-dimensional (3D) finite element (FE) modeling of corroded RC beams, was explored. The cohesive surface interaction method was found to be most suitable for simulating the bond between rebars and concrete. Secondly, using the cohesive surface interaction approach, the 3D FE modeling of the behavior of non-corroded and corroded RC beams was carried out in an ABAQUS environment. Experimental data, reported in literature, were used to validate the models. Then using the developed models, a parametric study was conducted to examine the effects of some parameters, such as degree and location of the corrosion, on the behavior and residual capacity of the corroded beams. The results obtained from the parametric analysis using the developed model showed that corrosion in top compression rebars has very small effect on the flexural behaviors of beams with small flexural reinforcement ratio that is less than the maximum ratio specified in ACI-318-14 (singly RC beam). In addition, the reduction of steel yield strength in tension reinforcement due to corrosion is the main source of reducing the load bearing capacity of corroded RC beams. The most critical corrosion-induced damage is the complete loss of bond between rebars and the concrete as it causes sudden failure and the beam acts as un-reinforced beam.

• Advances in Computational Design
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• v.8 no.2
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• pp.97-112
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• 2023

The Finite Element (FE) modeling of Reinforced Concrete (RC) under seismic loading has a sensitive impact in terms of getting good contribution compared to experimental results. Several idealized model types for simulating the nonlinear response have been developed based on the plasticity distribution alone the model. The Continuum Models are the most used category of modeling, to understand the seismic behavior of structural elements in terms of their components, cracking patterns, hysteretic response, and failure mechanisms. However, the material modeling, contact and nonlinear analysis strategy are highly complex due to the joint operation of concrete and steel. This paper presents a numerical simulation of a chosen RC column under monotonic and cyclic loading using the FE Abaqus, to assessthe hysteretic response and failure mechanisms in the RC columns, where the perfect bonding option is used for the contact between concrete and steel. While results of the numerical study under cyclic loading compared to experimental tests might be unsuccessful due to the lack of bond-slip modeling. The monotonic loading shows a good estimation of the envelope response and deformation components. In addition, this work further demonstrates the advantage and efficiency of the damage distributions since the obtained damage distributions fit the expected results.