• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.591-596
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• 1999

Current design methods as well as the majority of the previous researches for shear strength of the reinforced concrete are based on empirical method. There is a need to propose the rational models based on analytical approach. This paper presents the modified strut-and-tie model for reinforced concrete columns, under axial compression, shear, and flexural moment, considering tensile strength of concrete. Using this model, the strength and the failure mode of R/C columns are investigated, and the proposed models are compared with test data available in the literature.

• Earthquakes and Structures
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• v.25 no.3
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• pp.177-186
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• 2023

Reinforced concrete frames with a masonry infill panel is a structural typology frequently used worldwide. In seismic cases, the interaction between the masonry infill and the RC frames constitutes one of the most complex subjects in earthquake engineering. In this work, an enhancement of an existing numerical model is proposed to improve the estimation of lateral strength and stiffness of masonry-infilled frame structures and predict their probable failure modes. The proposed improvement is based on attributing corrective coefficients to the shear strength of each diagonal shear spring of the macro element, which simulates the masonry infill. The improved numerical model is validated by comparing the results with those of the original numerical model and with experimental results available in the literature. The enhanced macro element model can be used as a powerful, accessible tool for assessing the capacity and stiffness of masonry-infilled frame structures and predicting their probable failure modes.

• Steel and Composite Structures
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• v.36 no.5
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• pp.587-602
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• 2020

In recent years, the composite columns have been widely used in the structures. These columns are mainly used to construct the structures with a large span and high floor height. Concrete filled tubes (CFTs) are a type of composite column, which are popular nowadays due to their numerous benefits. The purpose of this study is to investigate such frames at elevated temperatures. The method used in this research is based on section 2.2 of Eurocode 4. First, for the verification purpose, a comparison was made between the experimental results and the numerical model of the concrete filled tube. Then a composite frame was analyzed under fire temperature with different parameters. The results showed that the failure time decreased with increasing the friction of different models. Moreover, investigation of the concrete moisture content revealed that an increase in the concrete moisture content from 3% to 10% led to extended failure time for different models. For instance, in the second frame model, the failure time has increased up to 8%.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.99-107
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• 2022

Existing reinforced concrete building structures constructed before 1988 have seismically-deficient reinforcing details, which can lead to the premature failure of the columns and beam-column joints. The premature failure was resulted from the inadequate bonding performance between the reinforcing bars and surrounding concrete on the main structural elements. This paper aims to quantify the bond-slip effect on the dynamic responses of reinforced concrete frame models using finite element analyses. The bond-slip behavior was modeled using an one-dimensional slide line model in LS-DYNA. The bond-slip models were varied with the bonding conditions and failure modes, and implemented to the well-validated finite element models. The dynamic responses of the frame models with the several bonding conditions were compared to the validated models reproducing the actual behavior. It verifies that the bond-slip effects significantly affected the dynamic responses of the reinforced concrete building structures.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.468-473
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• 1998

The objective of this paper is to develop a consistent algorithm for the finite element analysis for behavior of concrete under cyclic loading using viscoplastic-damage model. For modeling the behavior of concrete under cyclic loading, consistent algorithms of rate-dependent viscoplastic-damage are employed with a Willam-Warnke 5-parameter failure criterion which can consider the softening behavior of concrete and consistent tangent moduli are derived. Using finite element program implemented with the developed algorithms, the algorithms are verified and the behaviors of concrete under cylic loading are simulated and compared with experimental data.

• Korean Journal of Agricultural Science
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• v.47 no.1
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• pp.163-171
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• 2020

In this study, a large laboratory model experiment was conducted with the aim of developing an embankment reinforcement method to prevent overtopping, which is the main cause for the failure of agricultural reservoirs. The model experiment was carried out with concrete and asphalt as a permanent reinforcement method and with geomembrane as the emergency method at a deteriorated homogeneous reservoir. Under the non-reinforced conditions, the pattern of the failure appeared in several scour directions from the downstream slope as the overtopping began, and the width and depth of the erosion were magnified as it gradually moved to the dam crest. Under the conditions reinforced with asphalt and concrete, the overtopping was stabilized. In the case of the concrete reinforcement, it was found that the slope of the riprap boundary exhibited downward erosion by the current; thus, it was necessary to construct an extension up to the riprap joint of the upstream and downstream sides to prevent the expansion of the failure. Under the conditions reinforced with the geomembrane sheet, the overtopping was stabilized, and no seepage was found that required the emergency reinforcement method. Asphalt, concrete, and geomembrane sheet reinforcements have been shown to be capable of delaying failure for about 1 hour and 40 minutes compared to the non-reinforcement conditions. The reinforcement method is considered to be a very effective method to prevent disasters during overtopping. The pore water pressure can be used as useful data to predict the risk of failure at an embankment.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.187-192
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• 1995

Four types of experiments were performed to check the similitude of member behavior between prototype and 1/10 scale models:(1) Test of slender columns with P- effect, (2)Test of short columns with and without confinement steel, (3)Test of simple beams without stirrups, and (4)T-beam test. Based on the results of experiments, the conclusions were made as follows : (1) The P- effect of slender columns can be almost exactly represented by 1/10 acale model. (2)The effect of confinement on short columns by the hoop steel can also roughly simulated by 1/10 scale model. (3)The failure modes of simple beams models were the yielding of tension steel followed by large diagonal tension cracking+compressive concrete failure. (4)The behaviors of prototype and 1/10 scale model in T-beams appear very similar.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.914-921
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• 2006

To describe the effect of the numerous and various oriented microcracks on the compressive and tensile concrete behaviors, the directional nonlocality is defined. The plasticity model using multiple failure criteria is developed for RC planar members in tension-compression. The crack damages are defined in the pre-determined reference orientations, and then the total crack damage is calculated by integrating multi-oriented crack damages. To describe the effect of directional nonlocality on the anisotropic tensile damage, based on the existing test results, the nonlocal damage factor is defined in each reference orientation. The reduced compressive strength in the cracked concrete is defined by the multi-oriented crack damages defined as excluding the tensile normal plastic strain from the compressive equivalent plastic strain. The proposed model is implemented to finite element analysis, and it is verified by comparisons with various existing panel test results.

• Journal of Ocean Engineering and Technology
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• v.21 no.6
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• pp.7-15
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• 2007

A mechanical model was developed to predict the behavior of point-loaded RC slender beams (a/d > 2.5) without stirrups. It is commonly accepted by most researchers that a diagonal tension crack plays a predominant role in the failure mode of these beams, but the failure mechanism of these members is still debatable. In this paper, it was assumed that diagonal tension failure was triggered by the concrete cover splitting due to the dowel action at the initial location of diagonal tension cracks, which propagate from flexural cracks. When concrete cover splitting occurred, the shape of a diagonal tension crack was simultaneously developed, which can be determined from the principal tensile stress trajectory. This fictitious crack rotates onto the crack tip with load increase. During the rotation, all forces acting on the crack (i.e, dowel force of longitudinal bars, vertical component of concrete tensile force, shear force by aggregate interlock, shear force in compression zone) were calculated by considering the kinematical conditions such as crack width or sliding. These forces except for the shear force in the compression zone were uncoupled with respect to crack width and sliding by the proposed constitutive relations for friction along the crack. Uncoupling the shear forces along the crack was aimed at distinguishing each force from the total shear force and clarifying the failure mechanism of RC slender beams without stirrups. In addition, a proposed method deriving the dowel force of longitudinal bars made it possible to predict the secondary shear failure. The proposed model can be used to predict not only the entire behavior of point-loaded RC slender shear beams, but also the ultimate shear strength. The experiments used to validate the proposed model are reported in a companion paper.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.198-203
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• 1995

The objective of this study is to provide the information on the techniques of manufacturing and experiment in small scale modeling of precast concrete(P.C.)large panel structures. The adopted scale was 1/5th 4types of experiments were performed : material tests for model concrete and model reinforcement, compressive test of horizontal joint, shear test of vertical joint and cyclic static test of 2-story subassemblage structure. Based on the experimental results, the following conclusions are drawn: (1)Model concrete may have in general larger compressive strength than expected. (2) Model reinforcement can show less ductility if the annealing processes were performed without using vaccuum tube. (3) Failure modes of horizontal and vertical joints were almost same for both prototype and model. But the strength of model appears to be higher than required by similitude law. (4)Hysteretic behavior of 1/5 scale subassemblage model can be made quite similar to prototype's if the ductility of model reinforcement and compressive strength of model concrete could be representative of those of prototype.