• Corrosion Science and Technology
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• v.4 no.3
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• pp.100-107
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• 2005

Reinforcing steel bars in reinforced concrete structures are protected from corrosion by passive film on the steel surface inside concrete with high alkalinity. However, when the passive film breaks down due to chloride ion ingressed into the RC structures, a corrosion initiates at the surface of steel bars. Then, internal pressure by volume expansion of corrosion products in reinforcing bars induces cracking and spalling of cover concrete, which reduces not only durability performance but also structural performance in RC structures. In this paper, a service life prediction of RC structures is carried out by using a micro-mechanics based corrosion model. The corrosion model is composed of a chloride penetration model to evaluate the initiation of corrosion and an electric corrosion cell model and an oxygen diffusion model to evaluate the rate and the accumulated amounts of corrosion. Then, a corrosion cracking model is combined to the models to evaluate critical amount of corrosion product for initiation cracking in cover concrete. By implementing the models into a finite element analysis program, a time and space dependent corrosion analysis and a service life prediction of RC structures due to chloride attack are simulated and the results of the analysis are compared with test results. The effect of crack width on the corrosion and the service life of the RC structures are analyzed and discussed.

• Computers and Concrete
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• v.4 no.2
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• pp.135-156
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• 2007

Three 3D nonlinear finite-element models are developed to study the behavior of concrete beams and plates with and without external reinforcement by fibre-reinforced plastic (FRP). All three models are formulated based upon the 3D theory of elasticity. The stress model is modified from the element developed by Ramtekkar, et al. (2002) to incorporate material nonlinearity in the formulation. Both transverse stress and displacement components are used as nodal degrees-of-freedom to ensure the continuity of both stress and displacement components between the elements. The displacement model uses only displacement components as nodal degrees-of-freedom. The transition model has both stress and displacement components as nodal degrees-of-freedom on one surface, and only displacement components as nodal degrees-of-freedom on the opposite surface. The transition model serves as a connector between the stress and the displacement models. The developed models are validated by comparing the results of the analyses with an existing experimental result. Parametric studies of the effects of the externally reinforced FRP on the load capacity of reinforced concrete (RC) beams and concrete plates are performed to demonstrate the practicality and the efficiency of the proposed models.

• Computers and Concrete
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• v.19 no.5
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• pp.545-553
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• 2017

In the authors' previous study, an axial force-flexural moment (P-M) interaction curve model was proposed to evaluate fire-resisting performances of reinforced concrete (RC) column members. The proposed method appeared to properly consider the axial and flexural strength degradations including the secondary moment effects in RC columns due to fire damage. However, the detailed P-M interaction curve model proposed in the authors' previous study requires somewhat complex computational procedures and iterative calculations, which makes it difficult to be used for practical design in its current form. Thus, the aim of this study was to develop a simplified P-M interaction curve model of RC columns exposed to fire considering the effects of fire damage on the material performances and magnitudes of secondary moments. The simplified P-M interaction model proposed in this study was verified using 66 column fire test results collected from literature, and the verification results showed that the proposed simplified method can provide an adequate analysis accuracy of the failure loads and fire-resisting times of the RC column specimens.

• Journal of the Korean Society of Safety
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• v.26 no.2
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• pp.62-69
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• 2011

This paper presents a new simple two-dimensional frame finite element able to accurately estimate the load-carrying capacity of reinforced concrete beams flexurally strengthened externally bonded fiber reinforced polymer (FRP) strips and plates. The proposed analysis model considers distributed plasticity with layer-discretization of the cross-sections and the bond-slip behavior of epoxy layer. The proposed model is used to predict the load-carrying capacity and the applied load-midspan deflection response of RC beams subjected to bending loading. Numerical simulations and experimental measurements are compared based on numerous tests available in the literature and published by different authors. The numerically simulated response agree remarkably well with the corresponding experimental results. Thus, the proposed model is suitable for efficient and accurate modeling and analysis of flexural strengthening of RC beams with externally bonded FRP sheets/plates and for practical use in design-oriented parametric studies.

• Earthquakes and Structures
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• v.14 no.3
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• pp.187-201
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• 2018

The paper describes a modified cyclic bar model including bond-slip phenomena between steel reinforcing bars and surrounding concrete. The model is focused on plain bar and is useful, for its simplicity, for the seismic analyses of RC structures with plain bars and insufficient constructive details, such as in the case of '60s -'70s Mediterranean buildings. The model is based on an imposed exponential displacements field along the bar including both steel deformation and slip; through the adoption of equilibrium and compatibility equations a stress-slip law can be deducted and simply applied, with opportune operations, to RC numerical models. This study aims to update and complete the original monotonic model published by the authors, solving some numerical inconsistencies and, mostly, introducing the cyclic formulation. The first aim is achieved replacing the imposed linear displacement field along the bar with an exponential too, while the cyclic behaviour is described through a formulation based on the results of parametric analyses concerning a large range of steel and concrete properties and geometric configurations. Validations of the proposed model with experimental results available in the current literature confirm its accuracy and the reduced computational burden, highlighting its suitability in performing nonlinear analyses of RC structures.

• Earthquakes and Structures
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• v.7 no.5
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• pp.691-704
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• 2014

Reinforced concrete (RC) shear walls are commonly used for building structures to resist seismic loading. While the RC shear walls can have a high load-carrying capacity, they tend to fail in a brittle mode under shear, accompanied by forming large diagonal cracks and bond splitting between concrete and steel reinforcement. Improving seismic performance of shear walls has remained a challenge for researchers all over the world. Engineered Cementitious Composite (ECC), featuring incredible ductility under tension, can be a promising material to replace concrete in shear walls with improved performance. Currently, the application of ECC to large structures is limited due to the lack of the proper constitutive models especially under shear. In this paper, a new Cyclic Softening Membrane Model for reinforced ECC is proposed. The model was built upon the Cyclic Softening Membrane Model for reinforced concrete by (Hsu and Mo 2010). The model was then implemented in the OpenSees program to perform analysis on several cases of shear walls under seismic loading. The seismic response of reinforced ECC compared with RC shear walls under monotonic and cyclic loading, their difference in pinching effect and energy dissipation capacity were studied. The modeling results revealed that reinforced ECC shear walls can have superior seismic performance to traditional RC shear walls.

• Computers and Concrete
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• v.33 no.3
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• pp.285-299
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• 2024

Recently, many engineering computations have realized their digital transformation to Machine Learning (ML)-based systems. Predicting the behavior of a structure, which is mainly computed with structural analysis software, is an essential step before construction for efficient structural analysis. Especially in the seismic-based design procedure of the structures, predicting the lateral load capacity of reinforced concrete (RC) columns is a vital factor. In this study, a novel ML-based model is proposed to predict the maximum lateral load capacity of RC columns under varying axial loads or cyclic loadings. The proposed model is generated with a Deep Neural Network (DNN) and compared with traditional ML techniques as well as a popular commercial structural analysis software. In the design and test phases of the proposed model, 319 columns with rectangular and square cross-sections are incorporated. In this study, 33 parameters are used to predict the maximum lateral load capacity of each RC column. While some traditional ML techniques perform better prediction than the compared commercial software, the proposed DNN model provides the best prediction results within the analysis. The experimental results reveal the fact that the performance of the proposed DNN model can definitely be used for other engineering purposes as well.

• Journal of Industrial Technology
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• v.24 no.A
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• pp.179-184
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• 2004

Each year, new technological advancements for repair-purpose are being introduced to overlay the old deterioration of RC bridge deck at highway by latex-modified concrete. The days may come when this old problem will be successfully resolved. While the experimental works and researches are very active at both laboratory and field, only a few theoretical studies were performed on interfacial problems, especially on stress distribution and concentration of RC beam overlayed by latex-modified concrete. The repaired and strengthened structures would induce a premature failure due to the stress concentration at the adhesive layer of different material before the design expected failure. This paper investigated and proposed an analytical model for predicting interfacial shear and normal stresses of RC beam repair-purpose overlayed by latex-modified concrete. This would be used for predicting interfacial stresses and preventing premature failure at interfaces. This study modified Smith-Teng method for applying to cementitious repairing material, which was based on a direct governing equation and linear-elastic approach for interfacial normal and shear stresses. The proposed theoretical model was verified using commercial FEA program, LUSAS, in terms of interfacial stresses predicted by the proposed model and calculated by LUSAS.

• Computers and Concrete
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• v.19 no.5
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• pp.537-544
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• 2017

The strength and deformational capacity of slender reinforced concrete (RC) columns greatly rely on their slenderness ratios, while an additional secondary moment (i.e., the $P-{\delta}$ effect) can be induced especially when the RC column members are exposed to fire. To evaluate the fire-resisting performances of RC columns, this study proposed an axial force-flexural moment (i.e., P-M) interaction curve model, which can reflect the fire-induced slenderness effects and the nonlinearity of building materials considering the level of stress and the magnitude of temperature. The P-M interaction model proposed in this study was verified in detail by comparing with the fire test results of RC column specimens reported in literature. The verification results showed that the proposed model can properly evaluate the fire-resisting performances of RC column members.

• Earthquakes and Structures
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• v.18 no.5
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• pp.555-565
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• 2020

The main objective of seismic codes is to prevent structural collapse and ensure life safety. Collapse probability of a structure is usually assessed by making a series of analytical model assumptions. This paper investigates the effect of finite element modeling (FEM) assumptions on the estimated collapse capacity of a reinforced concrete (RC) frame building and points out the modeling limitations. Widely used element formulations and hysteresis models are considered in the analysis. A full-scale, three-story RC frame building was utilized as the experimental model. Alternative finite element models are established by adopting a range of different modeling strategies. Using each model, the collapse capacity of the structure is evaluated via Incremental Dynamic Analysis (IDA). Results indicate that the analytically estimated collapse capacities are significantly sensitive to the utilized modeling approaches. Furthermore, results also show that models that represent stiffness degradation lead to a better correlation between the actual and analytical responses. Results of this study are expected to be useful for in developing proper models for assessing the collapse probability of RC frame structures.