• Computational Structural Engineering
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• v.8 no.4
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• pp.117-127
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• 1995

The objective of this research is to investigate the effectiveness of rotating orthotropic axes model in analyzing reinforced concrete planar members under cyclic as well as monotonic loading. The structural members to be addressed are moderately reinforced beams, columns, beam-column joints, and shear walls, whose failure occurs due to compressive crushing after extensive crack propagation, The rotating orthotropic axes model which is usually used for monotonic loading is developed for cyclic loading. With the existing cyclic material models of reinforcing steel and bond-slip, this material model is used for the finite element analysis. For monotonic loading, the analytical results of the rotating orthotropic axes model are compared with reinforced concrete beams which have brittle failure. For Shear wall members under cyclic loading, the analyses are compared with the experiments for the ultimate load capacity, nonlinear deformation, and pinching effect due to crack opening and closing.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.403-408
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• 2003

The objective of this study is to understand the variables affected the confinement for the transverse reinforcement of the reinforced concrete structural walls with the T-shaped cross section subjected to cyclic lateral loads. The structural performance of T-shaped walls was advanced by the transverse reinforcement which restrained the concrete subjected to compressive stress. If the arrangement of transverse reinforcement was not suitable for the confinement, T-shaped walls happened the brittle failure by web crushing or bucking of vertical reinforcement at the compression zone. It is necessary to confine transverse reinforcement in order to prevent the these failure. But the location of neutral axis and the magnitude of ultimate strain vary according to the section shape, a ratio of axial load, a ratio of wall cross sectional area to the floor-plan area, an aspect ratio and the reinforcement ratio. Therefore, the objective of this research is to grasp the location of neutral axis and the range which needs for the confinement of transverse reinforcement through the results of the sectional analysis which varies the ratio of axial load and the ratio of vertical reinforcement.

• Steel and Composite Structures
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• v.26 no.3
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• pp.347-360
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• 2018

The aim of this paper is to evaluate the accuracy and reliability of the available bond-slip laws which are being used for the numerical modeling of Fiber Reinforced Polymer (FRP)/concrete interfaces. For this purpose, a set of Reinforced Concrete (RC) beams retrofitted with external FRP were modeled using the 3D nonlinear Finite Element (FE) approach. All considered RC beams have been previously tested and the corresponding experimental data are available in the literature. The failure modes of these beams are concrete crushing, steel yielding and FRP debonding. Through comparison of the numerical and experimental results, the effectiveness of each FRP/concrete bond-slip model for the prediction of the structural behavior of externally retrofitted RC beams is assessed. The sensitivity of the numerical results against different modeling considerations of the concrete constitutive behavior and bond-slip laws has also been evaluated. The results show that the maximum allowable stress of FRP/concrete interface has an important role in the accurate prediction of the FRP debonding failure.

• Steel and Composite Structures
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• v.35 no.2
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• pp.237-247
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• 2020

Shear connectors are essential elements in the design of steel-concrete composite systems. These connectors are utilized to prevent the occurrence of potential slips at the interface of steel and concrete. The two types of shear connectors which have been recently employed in construction projects are C- and L-shaped connectors. In the current study, the behavior of C and L-shaped angle shear connectors is investigated experimentally. For this purpose, eight push-out tests were composed and subjected to monotonic loading. The load-slip curves and failure modes have been determined. Also, the shear strength of the connectors has been compared with previously developed relationships. Two failure modes of shear connectors were observed: 1) concrete crushing-splitting and 2) shear connector fracture. It was found that the L-shaped connectors have less shear strength compared to C-shaped connectors, and decreasing the angle leg size increases the shear strength of the C-shaped connectors, but decreases the relative ductility and strength of L-shaped connectors.

• Steel and Composite Structures
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• v.47 no.3
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• pp.405-421
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• 2023

An experimental study on six axially-loaded composite short columns with different thicknesses of steel tube and that of the concrete plate was carried out. Compared to the mechanical behavior of component specimens under axially compressed, the failure modes, compression deformation, and strain process were obtained. The two main parameters that have a significant enhancement to cross-sectional strength were also analyzed. The failure of an axially loaded UHPC-CFST short column is due to the crushing of the UHPC plate, while the CFST member does reach its maximum resistance. A reduction coefficient K'c, related to the confinement coefficient, is introduced to account for the contribution of CFST members to the ultimate load-carrying capacity of the UHPC-CFST composite short columns. Based on the regression analysis of the relationship between the confinement index ξ and the value of fcc/fc, a unified formula for estimating the axial compressive strength of CFST short columns was proposed, combined with the experimental results in this research, and an equation for reliably predicting the strength of UHPC-CFST composite short columns under axial compression were also proposed.

• Steel and Composite Structures
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• v.27 no.5
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• pp.537-543
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• 2018

Mechanical shear connectors are commonly used to transfer longitudinal shear forces across the steel-concrete interface in composite beams. Steel pipe as a new shear connector is proposed in this research and its performance to achieve composite strength is investigated. Experimental monotonic push-out tests were carried out for this connector. Then, a nonlinear finite element model of the push-out specimens is developed and verified against test results. Further, the finite element model is used to investigate the effects of pipe thickness, length and diameter on the shear strength of the connectors. The ultimate strengths of these connectors are reported and their respective failure modes are discussed. This paper comprises of the push-out tests of ten specimens on this shear connector in both the vertical and horizontal positions in different reinforced concretes. The results of experimental tests are given as load-deformation plots. It is concluded that the use of these connectors is very effective and economical in the medium shear demand range of 150-350 KN. The dominant failure modes observed were either failure of concrete block (crushing and splitting) or shear failure of pipe connector. It is shown that the horizontal pipe is not as effective as vertical pipe shear connector and is not recommended for practical use. It is shown that pipe connectors are more effective in transferring shear forces than channel and stud connectors. Moreover, based on the parametric study, a formula is presented to predict the pipe shear connectors' capacity.

• Journal of Korean Association for Spatial Structures
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• v.6 no.2 s.20
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• pp.53-60
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• 2006

The shear failure modes of reinforced concrete members using high-strength materials (high-strength concrete and high-strength steel) are different to those of reinforced concrete members using normal-strength materials. The reinforced concrete members using high-strength materials are inclined to fail due to concrete crushing before the shear reinforcing bar reaches its yield strength. This paper presents an evaluation equation to calculate the maximum shear reinforcement ratio based on the material stresses and strains when the reinforced concrete members fail in shear. The maximum shear reinforcement ratio calculated by the proposed equation increases as the compressive strength of concrete increases. Test results of 97 reinforced concrete members reported in the technical literatures are used to check the validity of the proposed equation. The comparison between the test results and the ratio calculated using the proposed equation indicated that the shear failure modes depended on the interaction between the amount of shear reinforcement and the compressive strength of concrete.

• Journal of the Korean Society for Railway
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• v.12 no.4
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• pp.590-596
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• 2009

In this study, the failure modes and energy absorption characteristics of four different kinds of circular tubes made of carbon, glass, Kevlar and carbon-Kevlar hybrid fibres composites with epoxy resin have been evaluated. To achieve these goals, compressive tests were conducted for the tubes under 10mm/min loading speed. Based on the test results, the carbon/epoxy tube showed the best energy absorption capability, while carbon-Kevlar/epoxy tubes were worst. In the failure mode during crushing, both of the carbon/epoxy tubes and the glass/epoxy tubes were crushed by brittle fracturing mode. The Kevlar/epoxy tubes were collapsed by local buckling mode like steel, while the carbon-Kevlar hybrid tubes were collapsed by mixed mode of local buckling and lamina bending.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.239-248
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• 2002

A constitutive model unifying plasticity and crack damage mode)s was developed to address the cyclic behavior of reinforced concrete planar members. The stress of concrete in tension-compression was conceptually defined by the sum of the compressive stress developed by the strut-action of concrete and the tensile stresses developed by tensile cracking. The plasticity model with multiple failure criteria was used to describe the isotropic damage of compressive crushing affected by the anisotropic damage of tensile cracking. The concepts of the multiple fixed crack damage model and the plastic flow model of tensile cracking were used to describe the tensile stress-strain relationship of multi-directional cracks. This unified model can describe the behavioral characteristics of reinforced concrete in cyclic tension-compression conditions, i.e. multiple tensile crack orientations, progressively rotating crack damage, and compressive crushing of concrete. The proposed constitutive model was implemented to finite element analysis, and it was verified by comparison with existing experimental results from reinforced concrete shear panels and walls under cyclic load conditions.

• Composites Research
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• v.22 no.4
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• pp.20-26
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• 2009

In the current study, thermoforming and compression analysis were carried out for the woven composite egg-box panel with the non-orthogonal constitutive material model, which is proposed by Xue et al. The material model is implemented in commercial engineering software, LS-DYNA, with a user subroutine. Directional properties in non-orthogonal coordinates are determinedusing the deformation gradient tensor and the material modulus matrix in local coordinate is updated at eaeh corresponding time step. After the implemented non-orthogonal constitutive model is verified by the bias extension test, the egg-box panel simulations are performed. The egg-box panel simulations are divided into two categories: thermoforming (draping) and crushing. The finite element model for crushing analysiscan be obtained using the displacement result of thermoforming process.