• Structural Engineering and Mechanics
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• v.18 no.5
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• pp.541-563
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• 2004

For reaching large inelastic deformations without a substantial loss in strength, the potential plastic hinge regions of the reinforced concrete structural members should be confined by adequate transverse reinforcement. Therefore, simple and realistic representation of confined concrete behaviour is needed for inelastic analysis of reinforced concrete structures. In this study, a trilinear stress-strain model is proposed for the axial behaviour of confined concrete. The model is based on experimental work that was carried out on nearly full size specimens. During the interpretation of experimental data, the buckling and strain hardening of the longitudinal reinforcement are also taken into account. The proposed model is used for predicting the stress-strain relationships of confined concrete specimens tested by other researchers. Although the proposed model is simpler than most of the available models, the comparisons between the predicted results and experimental data indicate that it can represent the stress-strain relationship of confined concrete quite realistically.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.7-8
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• 2009

In this research, comparison and analysis were performed to understand how the cover thickness influences the equation for calculating the amount of confining reinforcement for reinforced concrete columns. And, also, an equation for calculating the amount of confining reinforcement was proposed for reasonable seismic design. In addition, appropriateness and safety of the proposed equation were examined based on the various experimental results performed at home and abroad.

• Computers and Concrete
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• v.12 no.4
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• pp.443-498
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• 2013

A detailed finite element modeling is presented for the simulation of the nonlinear behavior of reinforced concrete structures which manages to predict the nonlinear behavior of four different experimental setups with computational efficiency, robustness and accuracy. The proposed modeling method uses 8-node hexahedral isoparametric elements for the discretization of concrete. Steel rebars may have any orientation inside the solid concrete elements allowing the simulation of longitudinal as well as transverse reinforcement. Concrete cracking is treated with the smeared crack approach, while steel reinforcement is modeled with the natural beam-column flexibility-based element that takes into consideration shear and bending stiffness. The performance of the proposed modeling is demonstrated by comparing the numerical predictions with existing experimental and numerical results in the literature as well as with those of a commercial code. The results show that the proposed refined simulation predicts accurately the nonlinear inelastic behavior of reinforced concrete structures achieving numerical robustness and computational efficiency.

• Smart Structures and Systems
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• v.25 no.6
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• pp.669-678
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• 2020

This paper focuses on the free vibration analysis of axially functionally graded (FG) Euler-Bernoulli beams. The material properties of the beams are assumed to obey the linear law distribution. The complexities in solving differential equation of transverse vibration of composite beams which limit the analytical solution to some special cases are overcome using the Differential Transformation Method (DTM). Natural frequencies and corresponding normalized mode shapes are calculated. Validation targets are experimental data or finite element results. Different parameters such as reinforcement distribution, ratio of the reinforcement Young's modulus to the matrix Young's modulus and ratio of the reinforcement density to the matrix density are taken into investigation. The delivered results prove the capability and the robustness of the applied method. The studied parameters are demonstrated to be very crucial for the normalized natural frequencies and mode shapes.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.430-439
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• 2002

The development of reinforcing steel is required in reinforced concrete structures. The standard hooks that have been widely used for the tensile development in the beam-column joints tend to create difficulties of construction such as steel congestion as the member cross sections are becoming smaller due to the use of higher strength concrete and higher grade steel. Using the reinforcing bars with end mechanical anchoring device (headed reinforcement) provides potential economies in construction such as reduction in development lengths, simplified details, and improved responses to cyclic loadings. In this paper, the pullout strengths and behaviors of the headed reinforcement were experimentally studied. In 33 pullout tests performed using D25 deformed reinforcing bars, the test parameters were embedment depth, edge distance, head size, and the use of transverse reinforcement. The pullout strengths determined from tests closely agreed with the pullout strengths predicted using the CCD method. The pullout strengths increased with increasing embedment depths nd edge distances. The strengths tend to increase with the use of larger heads. From the experimental program where the effect of the transverse reinforcement was examined, a modification factor to the CCD was suggested to represent the effect of such reinforcement that is installed across the concrete failure plane on the pullout strengths.

• Journal of the Korea Concrete Institute
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• v.11 no.6
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• pp.101-112
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• 1999

Structural walls have been mostly used for the design of reinforced concrete buildings in seismic areas because they play a role as an efficient bracing system and offer great potential for lateral load resistance and drift control. The lateral resistance system for the earthquake load should be designed to have enough ductility and stable hysteretic response in the critical regions where plastic deformation occurred beyond yielding. The behavior of the reinforced concrete element to experience large deformation in the critical areas by a major earthquake is affected by the performance of the confined core concrete. Thus, the confinement of concrete by suitable arrangements of transverse reinforcement results in a significant increase in both the strength and ductility of compressed concrete. This paper reports the experimental results of reinforced concrete structural walls for wall-type apartment structure under axial loads and cyclic reversal of lateral loads with different confinement of the boundary elements. The results show that confinement of the boundary element by open 'U'-bar and cross tie is effective. The shear strength capacity is not increased by the confinement but deformation capacity is improve.

• Structural Engineering and Mechanics
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• v.47 no.2
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• pp.247-263
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• 2013

It is evident that torsional resistance of a reinforced concrete (RC) member is attributed to both concrete and steel reinforcement. However, recent structural design codes neglect the contribution of concrete because of cracking. This paper reports on the results of an experimental and numerical investigation into the torsional capacity of concrete beams reinforced only by longitudinal rebars without transverse reinforcement. The experimental investigation involves six specimens tested under pure torsion. Each specimen was made using a cast-in-place concrete with different amounts of longitudinal reinforcements. To create the torsional moment, an eccentric load was applied at the end of the beam whereas the other end was fixed against twist, vertical, and transverse displacement. The experimental results were also compared with the results obtained from the nonlinear finite element analysis performed in ANSYS. The outcomes showed a good agreement between experimental and numerical investigation, indicating the capability of numerical analysis in predicting the torsional capacity of RC beams. Both experimental and numerical results showed a considerable torsional post-cracking resistance in high twist angle in test specimen. This post-cracking resistance is neglected in torsional design of RC members. This strength could be considered in the design of RC members subjected to torsion forces, leading to a more economical and precise design.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.3 s.43
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• pp.69-75
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• 2005

In this paper, the comparative performance of repaired RC columns using steel and CFRP is presented. Also, the effect of transverse reinforcement ratio on the behavior of the steel and the CFRP repairing is investigated. Monotonic and cyclic load tests are conducted on nine RC column specimens with different repairing strategies and transverse reinforcement ratios to compare the load-displacement curves and the hysteretic behaviors. From the tests, it is observed that both steel and CFRP jacket repairings can significantly increase the displacement ductility and the ultimate load capacity of damaged columns.

• Earthquakes and Structures
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• v.18 no.1
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• pp.15-25
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• 2020

The seismic behaviour of reinforced concrete (RC) columns made from high-strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength stirrups (HSSs) and three with normal-strength stirrups (NSSs), were tested under a combination of high axial and reversed cyclic loads. The effects of stirrup strength and the ratio of transverse reinforcement on the cracking patterns, hysteretic response, strength, stiffness, ductility, energy dissipation and strain of transverse reinforcement were studied. The results indicate that good seismic behaviour of an RC column subjected to high axial compression can be obtained by using a well-shaped stirrup. Stirrup strength had little effect on the lateral bearing capacity. However, the ductility was significantly modified by improving the stirrup strength. When loaded with a large lateral displacement, the strength reduction of NSS specimens was more severe than that of those with HSSs, and increasing the stirrup strength had little effect on the stiffness reduction. The ductility and energy dissipation of specimens with HSSs were superior to those with NSSs. When the ultimate displacement was reached, the core concrete could be effectively restrained by HSSs.

• Earthquakes and Structures
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• v.7 no.5
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• pp.843-859
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• 2014

In the present study, the seismic performance of structural walls with boundary elements confined by conventional tie hoops and steel fiber concrete (SFC) was investigated. Cyclic lateral loading tests on four wall specimens under constant axial load were performed. The primary test parameters considered were the spacing of boundary element transverse reinforcement and the use of steel fiber concrete. Test results showed that the wall specimen with boundary elements complying with ACI 318-11 21.9.6 failed at a high drift ratio of 4.5% due to concrete crushing and re-bar buckling. For the specimens where SFC was selectively used in the plastic hinge region, the spalling and crushing of concrete were substantially alleviated. However, sliding shear failure occurred at the interface of SFC and plain concrete at a moderate drift ratio of 3.0% as tensile plastic strains of longitudinal bars were accumulated during cyclic loading. The behaviors of wall specimens were examined through nonlinear section analysis adopting the stress-strain relationships of confined concrete and SFC.