• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.73-82
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• 2022

The study presents a three-dimensional approach to simulate the nonlinear behavior of a 72 m long Ultra High Performance Fiber Reinforced Concrete (UHPFRC) pre-stressed box girder for a pedestrian bridge in Busan, South Korea. The concrete damage plasticity (CDP) model is adopted to model the non-linear behavior of the UHPFRC material, in which the material properties are obtained from uniaxial compressive and tensile tests. The simulation model based on the proposed stress-strain curve is validated by the results of four-point bending model tests of a 50 m UHPFRC pre-stressed box girder. The results from the simulation models agree with the experimental observations and predict the flexural behavior of the 50 m UHPFRC pre-stressed box girder accurately. Afterward, the validated model is utilized to investigate the flexural behavior of the 72 m UHPFRC pre-stressed box girder. Here, the load-deflection curve, stress status of the girder at various load levels, and connection details is analyzed. The load-deflection curve is also compared with design load to demonstrate the great benefit of the slender UHPFRC box girder. The obtained results demonstrate the applicability of the nonlinear finite element method as an appropriate option to analyze the flexural behavior of pre-stressed long-span girders.

• Structural Engineering and Mechanics
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• v.88 no.1
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• pp.67-81
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• 2023

The reinforced concrete (RC) structures might need strengthening or upgradation due to adverse environmental conditions, design defects, modification requirements, and to prolong the expected lifespan. The RC beams have been efficiently strengthened using the near surface mounted (NSM) approach over the externally bonded reinforcing (EBR) system. In this study, the performance of RC beam elements strengthened with NSM-steel rebars was investigated using an experimental program and nonlinear finite element modeling (FEM). Nine medium-sized, rectangular cross-section RC beams total in number made up for the experimental evaluation. The beams strengthened with varying percentages of NSM reinforcement, and the number of grooves was assessed in four-point bending experiments up to failure. Based on the experimental evaluation, the load-displacement response, crack features, and failure modes of the strengthened beams were recorded and considered. According to the experimental findings, NSM steel greatly improved the flexural strength (up to about 84%) and stiffness of RC beams. The flexural response of the tested beams was simulated using a 3D non-linear finite element (FE) model. The findings of the experiments and the numerical analysis showed good agreement. The effect of the NSM groove and reinforcement on the structural response was then assessed parametrically.

• Structural Engineering and Mechanics
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• v.92 no.2
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• pp.133-147
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• 2024

Composite beams of steel and concrete strengthened with fiber-reinforced polymers (FRP) may exhibit considerably enhanced flexural behaviour, but the combination of three materials with different characteristics and the various possible failure mechanisms that may govern performance make their analysis quite demanding. Previous studies provided significant insights into this problem and several methods were proposed for calculating flexural stiffness and strength, but these studies are restricted to the single member level of a simply supported composite beam section. However, the problem considerably changes when the beam is part of a frame system due to the degree of continuity provided by the surrounding structure, which represents the most common situation in practice. This paper explores the behaviour of semi-continuous FRP-strengthened composite beams, by considering the response characteristics of their end connections and their effects on overall performance. A novel analytical model is derived, which enables a step-by-step representation of the nonlinear relationship between an incremental mid-span design bending moment and corresponding connection rotations. After verification against finite element analyses, a parametric study is conducted which shows that the substantially increased bending moment resistance of FRP-strengthened composite beams can hardly be fully utilized due to a deficiency of corresponding large deformation capacity available in the connections. The extent to which the presence FRP strengthening can be exploited to enhance the beam flexural response depends on the interplay between various structural parameters, including the connection rotation capacity, the beam span, and the FRP modulus of elasticity and ultimate strength.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.4
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• pp.45-54
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• 2011

A simple model for reinforced concrete shear walls with boundary elements is proposed, which is a macro-model composed of spring elements representing flexure and shear behaviors. The flexural behaviour is represented by vertical springs at the wall ends, where the moment strength and rotational capacity of the wall are based on section analysis. The shear behaviour is represented by a horizontal spring at the wall center, where the key parameters for the shear behavior are based on the flexural behaviour since the shear walls with boundary elements are governed by the flexure. The proposed model was prepared with the results of hysteretic tests of the shear walls, and then the reliability of the hysteretic rule and variables was investigated by nonlinear dynamic analyses. Using parametric study with nonlinear dynamic analyses, the effect of the variables on demand and capacity, which are major parameters in seismic performance evaluation, are investigated. Results show that the measured and calculated shear forces versus the shear distortion relationships are slightly different, but the global response is well simulated. Furthermore, the demand and capacity are also changed in a similar way to the change in the major parameters so that the proposed model may be appropriate for reinforced concrete shear walls with boundary elements.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.3 s.22
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• pp.29-35
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• 2006

Fiber element method in earthquake response analysis of bridges is used to represents a realistic flexural deformation according to nonlinear behavior of beam-column section. Nonlinear pseudo-static analysis of two column bent using fiber element is accomplished and failure mechanism of the plastic hinge region is studied. Load-displacement curve obtained by nonlinear pseudo-static analysis can be applicable to earthquake response analysis by capacity spectrum method. The nonlinear time history analysis of a full bridge model using fiber element experienced by the ground motion corresponding to the target response spectrum is accomplished. The result of time history analysis is similar to that of capacity spectrum method.

• Computers and Concrete
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• v.6 no.4
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• pp.319-341
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• 2009

A new formulation based on lumped plasticity and inelastic hinges is presented in this paper for nonlinear analysis of Reinforced Concrete (RC) frame structures. Inelastic hinge behaviour is described using the principles of Continuum Damage Mechanics (CDM). Member formulation contains provisions to model stiffness degradation due to cracking of concrete and yielding of reinforcing steel. Depending on its nature, cracking is classified as concentrated or distributed. Concentrated cracking is accounted through a damage variable and its growth is defined based on strain energy principles. Presence of distributed flexural cracks in a member is taken care of by modelling it as non-prismatic. Plasticity theory supported by effective stress concept of CDM is applied to describe the post-yield response. Nonlinear quasi-static analysis is carried out on a RC column and a wide two-storey RC frame to verify the formulation. The column is subjected to constant axial load and monotonic lateral load while the frame is subjected to only lateral load. Computed results are compared with those due to experiments or other numerical methods to validate the performance of the formulation and also to highlight the contribution of distributed cracking on global response.

• Steel and Composite Structures
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• v.18 no.1
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• pp.213-233
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• 2015

A nonlinear finite element analysis (FEA) model is presented for simulating the behaviour of recycled aggregate concrete-filled steel tube (RACFST) beam-columns subjected to constant axial compressive load and cyclically increasing flexural loading. The FEA model was developed based on ABAQUS software package and a displacement-based approach was used. The proposed engineering stress versus engineering strain relationship of core concrete with the effect of recycled coarse aggregate (RCA) replacement ratio was adopted in the FEA model. The predicted results of the FEA model were compared with the experimental results of several RACFST as well as the corresponding concrete-filled steel tube (CFST) beam-columns under cyclic loading reported in the literature. The comparison results indicated that the proposed FEA model was capable of predicting the load versus deformation relationship, lateral bearing capacity and failure pattern of RACFST beam-columns with an acceptable accuracy. A parametric study was further carried out to investigate the effect of typical parameters on the mechanism of RACFST beam-columns subjected to cyclic loading.

• Computers and Concrete
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• v.24 no.6
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• pp.561-570
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• 2019

Understanding the realistic behavior of concrete up to failure under different loading conditions within the framework of damage mechanics and plasticity would lead to an enhanced design of concrete structures. In the present investigation, QR (Quick Response) code based random speckle pattern is used as a non-contact sensor, which is an innovative approach in the field of digital image correlation (DIC). A four-point bending test was performed on RC beams of size 1800 mm × 150 mm × 200 mm. Image processing was done using an open source Ncorr algorithm for the results obtained using random speckle pattern and QR code based random speckle pattern. Load-deflection curves of RC beams were plotted for the results obtained using both contact and non-contact (DIC) sensors, and further, Moment (M)-Curvature (κ) relationship of RC beams was developed. The loading curves obtained were used as input data for material model parameters in finite element analysis. In finite element method (FEM) based software, concrete damage plasticity (CDP) constitutive model is used to predict the realistic nonlinear quasi-static flexural behavior of RC beams for monotonic loading condition. The results obtained using QR code based DIC are observed to be on par with conventional results and FEM results.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.541-546
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• 1998

The use of steel fibers in conventional reinforced concrete increases the strength and ductility under various loading conditions. In order to examine the possibility of the use of these combinations achieving required strength and ductility of a reinforced concrete beam, a refined optimization procedure based on nonlinear layered finite element method and nonlinear programming technique is developed in this study. Six design variables-beam width and depth, fiber volume fraction, amounts of tensile and compressive rebars, and stirrup, and stirrup spacing-are considered. The developed model can be used as a tool in determining the economical use of steel fibers in designing the reinforced steel fibrous concrete beam.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.175-182
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• 1998

An analytical study to trace the nonlinear structural behavior of composite beams is undertaken to include the nonlinear material properties of steel sheeting, reinforcing steel bar and concrete. To trace Moment-curvature relations, sectioning analysis method and two simple formulas are developed. A simple power model which has been originally used to expect the flexural capacity of the beam to column connections is proposed and the second formula is composed of two experimental functions to express the Moment-curvature relation in the elastic and plastic range separately. The load-deflection behavior of the beams has been simulated by the step-by-step numerical integration method and is compared with the test results available.