• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.263-281
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• 2017

Global optimization that considers the processes at integrated steel mills is more important than the local optimization to improve the efficiency of a single process. Research utilizing mathematical models at integrated steel mills predominantly focus on solving problems solely for a specific process or focusing on what techniques are applied to. However, it is important to define the problems that must be solved at the steelworks, identify the objectives and constraints that can be modeled, and selection of methodologies that can be applied to the problems. The purpose of this study is to investigate the problems in improving efficiency at integrated steel mills from the viewpoint of production & operations management. We review the research have been conducted in order to solve those problems. We classified the research into 6 categories and suggested future research direction based on the global optimization. It is expected that research themes for improving the efficiency at integrated steel mills will be derived.

• Computers and Concrete
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• v.22 no.3
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• pp.279-289
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• 2018

Shear walls are one of the important structural elements for bearing loads imposed on buildings due to winds and earthquakes. Composite shear walls with high lateral resistance, and high energy dissipation capacity are considered as a lateral load system in such buildings. In this paper, a composite shear wall consisting of steel faceplates, infill concrete and tie bars which tied steel faceplates together, and concrete filled steel tubular (CFST) as boundary columns, was modeled numerically. Test results were compared with the existing experimental results in order to validate the proposed numerical model. Then, the effects of some parameters on the behavior of the composite shear wall were studied; so, the diameter and spacing of tie bars, thickness and compressive strength of infill concrete, thickness of steel faceplates, and the effect of strengthening the bottom region of the wall were considered. The seismic behavior of the modeled composite shear wall was evaluated in terms of stiffness, ductility, lateral strength, and energy dissipation capacity. The results of the study showed that the diameter of tie bars had a trivial effect on the performance of the composite shear wall, but increasing the tie bars spacing decreased ductility. Studying the effect of infill concrete thickness, concrete compressive strength, and thickness of steel faceplates also showed that the main role of infill concrete was to prevent buckling of steel faceplates. Also, by strengthening the bottom region of the wall, as long as the strengthened part did not provide a support performance for the upper part, the behavior of the composite shear wall was improved; otherwise, ductility of the wall could be reduced severely.

• Steel and Composite Structures
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• v.34 no.5
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• pp.625-641
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• 2020

The realistic modeling of the beam-column semi-rigid connection in steel frames attracted the attention of many researchers in the past for the seismic analysis of semi-rigid frames. Comparatively less studies have been made to investigate the behavior of steel frames with semi-rigid connections under different types of earthquake. Herein, the seismic behavior of semi-rigid steel frames is investigated under both far and near-field earthquakes. The semi-rigid connection is modeled by the multilinear plastic link element consisting of rotational springs. The kinematic hysteresis model is used to define the dynamic behavior of the rotational spring, describing the nonlinearity of the semi-rigid connection as defined in SAP2000. The nonlinear time history analysis (NTHA) is performed to obtain response time histories of the frame under scaled earthquakes at three PGA levels denoting the low, medium and high-level earthquakes. The other important parameters varied are the stiffness and strength parameters of the connections, defining the degree of semi-rigidity. For studying the behavior of the semi-rigid frame, a large number of seismic demand parameters are considered. The benchmark for comparison is taken as those of the corresponding rigid frame. Two different frames, namely, a five-story frame and a ten-story frame are considered as the numerical examples. It is shown that semi-rigid frames prove to be effective and beneficial in resisting the seismic forces for near-field earthquakes (PGA ≈ 0.2g), especially in reducing the base shear to a considerable extent for the moderate level of earthquake. Further, the semi-rigid frame with a relatively weaker beam and less connection stiffness may withstand a moderately strong earthquake without having much damage in the beams.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.385-395
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• 2011

The flexural strength of composite HSB hybrid I-girders under positive moment is investigated by the moment-curvature analysis method to evaluate the applicability of the current AASHTO LRFD design specification to such girders. The hybrid girders are assumed to have the top flange and the web fabricated from HSB600 steel and the bottom flange made of HSB800 steel. More than 6,200-composite I-girder sections that satisfy the section proportion limits of AASHTOL RFD specifications are generatedby the random sampling technique to consider a statistically meaningful wide range of section properties. The flexural capacities of the sections are calculated by the nonlinear moment-curvature analysis in which the HSB600 and HSB800 steels are modeled as an elastoplastic, strain-hardening material and the concrete as CEB-FIP model. The effects of ductility ratio and compressive strength of concrete slab on the flexural strength of composite hybrid girders make of HSB steels are analyzed. Numerical results indicated that the current AASHTO-LRFD equation can be used to calculate the flexural strength of composite hybrid girders fabricated from HSB steel.

• Journal of Korean Society of Steel Construction
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• v.23 no.5
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• pp.595-606
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• 2011

This study was conducted to investigate the seismic behavior of steel member resisting frames considering the relative stiffness of the connection and beams. Six-story steel moment frames were designed to study the seismic behavior. The connections were classified into Double Web-Angle connections (DWAs), Top- and Seat-angles with double Web-angles (TWSs), FEMA-Test Summary No. 28, Specimen ID: UCSD-6 (SAC), and Fully Restrained (FR). The rotational stiffness of the semi-rigid connections was estimated using the Three-Parameter Power Model adopted by Chen and Kishi. The relative stiffness, which is the ratio of the rotational stiffness of the connections to the stiffness of the beams, was used. Push-over, repeated loading, and time history analysis were performed for all the frames. The seismic behavior of each frame was analyzed with the story drift, plastic hinge rotation, and hysteretic energy distribution.

• Steel and Composite Structures
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• v.26 no.6
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• pp.719-731
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• 2018

Concrete filled steel tubular (CFST) laced columns have been widely used in high rise buildings in China. Compared to solid-web columns, this type of columns has a larger cross-section with less weight. In this paper, four concrete filled steel tubular laced columns consisting of 4 main steel-concrete tubes were tested under cyclic loading. Hysteresis and failure mechanisms were studied based on the results from the lateral cyclic loading tests. The influence of each design parameter on restoring forces was investigated, including axial compression ratio, slenderness ratio, and the size of lacing tubes. The test results show that all specimens fail in compression-bending-shear and/or compression-bending mode. Overall, the hysteresis curves appear in a full bow shape, indicating that the laced columns have a good seismic performance. The bearing capacity of the columns decreases with the increasing slenderness ratio, while increases with an increasing axial compression ratio. For the columns with a smaller axial compression ratio (< 0.3), their ductility is increased. Furthermore, with the increasing slenderness ratio, the yield displacement increases, the bending failure characteristic is more obvious, and the hysteretic loops become stouter. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.

• Advances in Computational Design
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• v.3 no.3
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• pp.233-267
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• 2018

Conventional seismic design of concentrically braced frame (CBF) structures suggests that the gusset plate connecting a steel brace to beams and/or columns should be designed as non-dissipative in earthquakes, while the steel brace members should be designed as dissipative elements. These design intentions lead to thicker and larger gusset plates in design on one hand and a potentially under-rated contribution of gusset plates in design, on the other hand. In contrast, research has shown that compact and thinner gusset plates designed in accordance with the elliptical clearance method rather than the conventional standard linear clearance method can enhance system ductility and energy dissipation capacity in concentrically braced steel frames. In order to assess the two design methods, six cyclic push-over tests on full scale models of concentric braced steel frame structures were conducted. Furthermore, a 3D finite element (FE) shell model, incorporating state-of-the-art tools and techniques in numerical simulation, was developed that successfully replicates the response of gusset plate and bracing members under fully reversed cyclic axial loading. Direct measurements from strain gauges applied to the physical models were used primarily to validate FE models, while comparisons of hysteresis load-displacement loops from physical and numerical models were used to highlight the overall performance of the FE models. The study shows the two design methods attain structural response as per the design intentions; however, the elliptical clearance method has a superiority over the standard linear method as a fact of improving detailing of the gusset plates, enhancing resisting capacity and improving deformability of a CBF structure. Considerations were proposed for improvement of guidelines for detailing gusset plates and bracing members in CBF structures.

• Journal of Navigation and Port Research
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• v.38 no.3
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• pp.269-275
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• 2014

In this study, the adsorption efficiency of mixed heavy metals in aqueous solution was investigated using steel slag. Moreover, heavy-metal stabilization treatment of contaminated marine sediment was achieved using steel slag as stabilizing agents. Heavy metal adsorption was characterized using Freundlich and Langmuir equations. The equilibrium adsorption data were fitted well to the Langmuir model in steel slag. The adsorption uptake of heavy metals were higher in the order of $Pb^{2+}$ > $Cd^{2+}$ > $Cu^{2+}$ > $Zn^{2+}$ > $Ni^{2+}$. The steel slage was applied for a wet-curing duration of 150 days. From the sequential extraction results, the exchangeable, carbonate, and oxides fractions of Ni, Zn, Cu, Pb, and Cd in sediment decreased by 13.0%, 6.0%, 1.3%, 17.0%, and 50.0%, respectively.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.1
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• pp.59-66
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• 1993

Ring Sector Plate Supported by Elastic Beam Although all the reinforced concrete circular ring sector plates are elastically supported, it is conventional to simplify their supporting conditions as fixed or simply-supported ones assuming that their supporting beam has infinite stiffness. However, in order to obtain a precise solution, it should be required to consider the stiffness of their supporting beam. As a methodological improvement to the precise analysis, "Reinforced Concrete Model" previously developed by the author was applied to the structural analysis of the reinforced concrete circular ring sector plates with elastically supported beam. The results of analysis in the cases under various conditions of open angle, steel ratio, relative stiffness(EI/DL) between plate and supporting beam were summarized as follows ; 1.Although the effect of relative stiffness between plate and supporting beam varies depending on the magnitude of open angle, in general, it shows the largest when not more than 5.0 and negligible when not less than 10.0. Therefore, it would be considered as fixed supporting condition :in the case of its open angle of 0$^{\circ}$rectangular plates), its stiffness ratio being not less than 10.0 and in the other case of its open angle of 30$^{\circ}$, its stiffness ratio being not less than 5.0. 2.In the rectangular plates, the effect of steel ratio is considerable in no supporting condition, but neglible in the supporting condition. So, the effect of steel ratio should be negligible in the case of the elastically supported circular ring sector plates. 3.However, the effect of steel ratio is much more considerable in the case of the fixed supported circular plates, especially, when steel ratio being not more than 1.0% and stiffness ratio being smaller. So, the effect of steel ratio should be considered in the analysis of reinforced concreate circular ring sector plates with fixed conditions. 4.The effect of open angle is greater in the case of without-supporting beam conditions. However, in the other case of with-supporting beam conditions, the effect is a little bit when open angle of not more than 300 and negligible when open angle of not more than 30$^{\circ}$.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.5
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• pp.151-159
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• 2000

Dynamic loading of structures often causes excursions of stresses will into the inelastic range and the influence of geometry changes on the response is also significant in may cases. In general , the shell structures designed according to quasi-Static analysis may collapse under condition of dynamic loading. Therefore, for a more realistic prediction on the lad carrying capacity of these shell. both material and geometric nonlinear effects should be considered. In this study , the material nonlinearity effect on the dynamic response is formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a Total Lagrangian formulation. the reinforcing bars are modeled by the equivalent steel layer at the location of reinforcements, and Von Mises yield criteria is adopted for the steel layer behavior. Also, Drucker-Prager yield criteria is applied for the behavior of concrete. the shape imperfection of dome is assumed as 'dimple type' which can be expressed Wd1=Wd0(1-(r-a)m)n while the shape imperfection of wall is assumed as sinusoidal curve which is Wwi =Wwo sin(n $\pi$y/l). In numerical test, three cases of shape imperfection of 0.0 -5.0cm(opposite direction to loading ; inner shape imperfection)and 5cm (direction to loading : outward shape imperfection) and thickness of steel layer determined by steel ratio of 0,3, and 5% were analyzed. The effect of shape imperfection and steel ratio and behavior characteristics of perfect shape shell and imperfect shape shell are identified through analysis of above mentioned numerical test. Dynamic behaviors of dome and wall according toe combination of shape imperfection and steel ratio are also discussed in this paper.