• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1696-1701
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• 2007

This paper presents a micro-mechanical model of ductile fracture for the API X65 steel using the Gurson-Tvergaard-Needleman (GTN) model. Experimental tests and FE damage simulations using the GTN model are performed for smooth and notched tensile bars, from which the parameters in the GTN model are calibrated. As application, the developed GTN model is applied to simulate small-sized, single-edge-cracked tensile and bend bars, via three-dimensional FE damage analyses. Comparison of FE damage analysis results with experimental test data shows overall good agreements.

• International journal of steel structures
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• v.18 no.4
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• pp.1125-1138
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• 2018

During earthquakes, braces behave in complex manners because of the asymmetric response nature of their responses in tension and compression. Hollow structural sections (HSS) have been popularly used for braces due to their sectional efficiency in compression. The purpose of this study is to accurately simulate the cyclic behavior of rectangular HSS braces using a computationally efficient numerical model. A conceptually efficient and simple physical theory model is used as a basis model. To improve the accuracy of the model, cyclic beam growth and buckling load, as well as the incidences of local buckling and brace fracture are estimated using empirical equations obtained from regression analyses using test data on rectangular HSS braces. The accuracy of the proposed model is verified by comparing actual and simulated cyclic curves of brace specimens with various slenderness and width-to-thickness ratios.

• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.475-487
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• 2003

This study developed an analysis model of estimating fatigue damage using the linear elastic fracture mechanics method. Stress history occurring to an element when a truck passed over a bridge was defined as block loading and crack closure theory explaining load interaction effect was applied. Stress range frequency analysis considering dead load stress and crack opening was done. Probability of stress range frequency distribution was applied and the probability distribution parameters were estimated. The Monte Carlo simulation of generating the probability various of distribution was performed. The probability distribution of failure block numbers was obtained. With this the fatigue reliability of an element not occurring in failure could be calculated. The failure block number divided by average daily truck traffic remains the life of a day. Fatigue reliability analysis model was carried out for the welding member of cross beam flange and vertical stiffener of steel box bridge using the proposed model. Consequently, a 3.8% difference was observed between the remaining life in the peak analysis method and in the proposed analysis model. The proposed analysis model considered crack closure phase and crack retard.

• Structural Engineering and Mechanics
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• v.32 no.2
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• pp.251-267
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• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.400-410
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• 2019

In this study, the numerical code for the 3D nonlinear dynamic analysis of an SLWR (Steel Lazy Wave Riser) was developed using the lumped mass line model in a FORTRAN environment. Because the lumped mass line model is an explicit method, there is no matrix operation. Thus, the numerical algorithm is simple and fast. In the lumped mass line model, the equations of motion for the riser were derived by applying the various forces acting on each node of the line. The applied forces at the node of the riser consisted of the tension, shear force due to the bending moment, gravitational force, buoyancy force, riser/ground contact force, and hydrodynamic force based on the Morison equation. Time integration was carried out using a Runge-Kutta fourth-order method, which is known to be stable and accurate. To validate the accuracy of the developed numerical code, simulations using the commercial software OrcaFlex were carried out simultaneously and compared with the results of the developed numerical code. To understand the nonlinear dynamic characteristics of an SLWR, dynamic simulations of SLWRs excited at the hang-off point and of SLWRs in regular waves were carried out. From the results of these dynamic simulations, the displacements at the maximum bending moments at important points of the design, like the hang-off point, sagging point, hogging points, and touch-down point, were observed and analyzed.

• Steel and Composite Structures
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• v.29 no.6
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• pp.717-734
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• 2018

This paper presents the flexural performance of steel beam-to-column joints composed of hollow structural section beams and columns. A finite element (FE) model was developed incorporating geometrical and material nonlinearities to evaluate the behaviour of joints subjected to bending moments. The numerical outcomes were validated with experimental results and compared with EN1993-1-8. The demountability of the structure was discussed based on the tested specimen. A parametric analysis was carried out to investigate the effects of steel yield strength, end-plate thickness, beam thickness, column wall thickness, bolt diameter, number of bolts and location. Consequently, an analytical model was derived based on the component method to predict the moment-rotation relationships for the sub-assemblies with extended end-plates. The accuracy of the proposed model was calibrated by the experimental and numerical results. It is found that the FE model is fairly reliable to predict the initial stiffness and moment capacity of the joints, while EN1993-1-8 overestimates the initial stiffness extensively. The beam-to-column joints are shown to be demountable and reusable with a moment up to 53% of the ultimate moment capacity. The end-plate thickness and column wall thickness have a significant influence on the joint behaviour, and the layout of double bolt-rows in tension is recommended for joints with extended end-plates. The derived analytical model is capable of predicting the moment-rotation relationship of the structure.

• Steel and Composite Structures
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• v.42 no.5
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• pp.633-647
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• 2022

This paper presents the results from reliability analyses of the current Eurocode 4 (EN 1994-1-1) and AISC 360-16 design models for predicting the resistance of headed stud shear connectors within profiled steel sheeting, when the ribs are oriented transverse to the supporting beam. For comparison purposes, the performance of the alternative "Luxembourg" and "Stuttgart" model were also considered. From an initial database of 611 push-out tests, 269 cases were included in the study, which ensured that the results were valid over a wide range of geometrical and material properties. It was found that the current EN 1994-1-1 design rules deliver a corrected partial safety factor γ_M^* of around 2.0, which is significantly higher than the target value 1.25. Moreover, 179 tests fell within the domain of the concrete-related failure design equation. Notwithstanding this, the EN 1994-1-1 equations provide satisfactory results for re-entrant profiled sheeting. The AISC 360-16 design equation for steel failure covers 263 of the tests in the database and delivers 𝛾_M^*≈2.0. Conversely, whilst the alternative "Stuttgart" model provides an improvement over the current codes, only a corrected partial safety factor of 𝛾_M^*=1.47 is achieved. Finally, the alternative "Luxembourg" design model was found to deliver the required target value, with a corrected partial safety factor 𝛾_M^* between 1.21 and 1.28. Given the fact that the Luxembourg design model is the only model that achieved the target values required by EN 1990, it is recommended as a potential candidate for inclusion within the second generation of Eurocodes.

• Steel and Composite Structures
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• v.22 no.3
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• pp.497-520
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• 2016

The confined concrete stress-strain curves utilised in computational models of concrete-filled steel tubular (CFST) columns can have a significant influence on the accuracy of the predicted behaviour. A generic model is proposed for predicting the stress-strain behaviour of confined concrete in short circular, elliptical and octagonal CFST columns subjected to axial compression. The finite element (FE) analysis is carried out to simulate the concrete confining pressure in short circular, elliptical and octagonal CFST columns. The concrete confining pressure relies on the geometric and material parameters of CFST columns. The post-peak behaviour of the concrete stress-strain curve is determined using independent existing experimental results. The strength reduction factor is derived for predicting the descending part of the confined concrete behaviour. The fibre element model is developed for the analysis of circular, elliptical and octagonal CFST short columns under axial loading. The FE model and fibre element model accounting for the proposed concrete confined model is verified by comparing the computed results with experimental results. The ultimate axial strengths and complete axial load-strain curves obtained from the FE model and fibre element model agree reasonably well with experimental results. Parametric studies have been carried out to examine the effects of important parameters on the compressive behaviour of short circular, elliptical and octagonal CFST columns. The design model proposed by Liang and Fragomeni (2009) for short circular, elliptical and octagonal CFST columns is validated by comparing the predicted results with experimental results.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.1
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• pp.82-93
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• 2019

In this paper, the ductile fracture criteria for a marine structural steel (EH36) are presented and validated. The theoretical background of the recently developed Hosford-Coulomb (HC) fracture strain model and the DSSE fracture strain model which was developed to apply to the shell elements is described. In order to accurately estimate the flow stress in the large strain range up to the fracture, the material constants for the combined Swift-Voce constitutive equation were derived by the numerical analyses of the smooth and notched specimens made from the EH36 steel. As a result of applying the Swift-Voce flow stress to the other notched specimen model, a very accurate load - displacement curve could be derived. The material constants of the HC fracture strain and DSSE fracture strain models were independently calibrated based on the numerical analyses for the smooth and notch specimen tests. The user subroutine (VUMAT of Abaqus) was developed to verify the accuracy of the combined HC-DSSE fracture strain model. An asymmetric notch specimen was used as verification model. It was confirmed that the fracture of the asymmetric specimen can be accurately predicted when a very small solid elements are used together with the HC fracture strain model. On the other hand, the combined HC-DSSE fracture strain model can predict accurately the fracture of shell element model while the shell element size effect becomes less sensitive.

• Advances in concrete construction
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• v.8 no.3
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.