GRAIN REFINEMENT IN BEARING STEELS USING A DOUBLE-QUENCHING HEAT-TREATMENT PROCESS

이광오,홍석기,강영기,윤희재,강성수 한국자동차공학회 2009 International journal of automotive technology Vol.10 No.6

A double-quenching (D/Q) process is proposed for heat-treating high carbon-chromium bearing steels to improve the fatigue properties through refinement of the microstructure. The new heat treatment method has two steps: The first step is a nitrocarburizing process that results in high surface hardness and lowers the transformation temperature. The second step is the same as in the conventional quenching process but can be conducted at a considerably lower temperature than in conventional quenching. The microstructure in the material that is caused by the D/Q heat treatment is much finer than in the conventional Q/T (quenching and tempering) process. In order to quantify the performance of the proposed heattreatment process, various mechanical property tests are carried out. The rolling contact fatigue life of double-quenched bearing steels was eight times higher than in bearing steels that were treated by conventional Q/T. A double-quenching (D/Q) process is proposed for heat-treating high carbon-chromium bearing steels to improve the fatigue properties through refinement of the microstructure. The new heat treatment method has two steps: The first step is a nitrocarburizing process that results in high surface hardness and lowers the transformation temperature. The second step is the same as in the conventional quenching process but can be conducted at a considerably lower temperature than in conventional quenching. The microstructure in the material that is caused by the D/Q heat treatment is much finer than in the conventional Q/T (quenching and tempering) process. In order to quantify the performance of the proposed heattreatment process, various mechanical property tests are carried out. The rolling contact fatigue life of double-quenched bearing steels was eight times higher than in bearing steels that were treated by conventional Q/T.

Dynamic punching shear tests of flat slab-column joints with 5D steel fibers

Yezid A. Alvarado,Benjamín Torres,Manuel Buitrago,Daniel M. Ruiz,Sergio Y. Torres,Ramón A. Álvarez 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.3

This study aimed to analyze the dynamic punching shear performance of slab-column joints under cyclic loads with the use of double-hooked end (5D) steel fibers. Structural systems such as slab-column joints are widely found in infrastructures. The susceptibility to collapse of such structures when submitted to seismic loads is highly dependent on the structural performance of the slab-column connections. For this reason, the punching capacity of reinforced concrete (RC) structures has been the subject of a great number of studies. Steel fibers are used to achieve a certain degree of ductility under seismic loads. In this context, 5D steel hooked fibers provide high levels of fiber anchoring, tensile strength and ductility. However, only limited research has been carried out on the performance under cyclic loads of concrete structural members containing steel fibers. This study covers this gap with experimental testing of five different full-scale subassemblies of RC slab-column joints: one without punching reinforcement, one with conventional punching reinforcement and three with 5D steel fibers. The subassemblies were tested under cyclic loading, which consisted of applying increasing lateral displacement cycles, such as in seismic situations, with a constant axial load on the column. This set of cycles was repeated for increasing axial loads on the column until failure. The results showed that 5D steel fiber subassemblies: i) had a greater capacity to dissipate energy, ii) improved punching shear strength and stiffness degradation under cyclic loads; and iii) increased cyclic loading capacity.

Analytical and Experimental Studies on All-Steel Buckling Restrained Brace with Double Steel Tubes

Jinhe Gao,Jiahuan Xi,Jiajun Ding,Yuwen Xu,Junwen Zhu,Yi Chang 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.1

This study proposes a new type of all-steel buckling restrained brace with double steel tubes composed of an inner round steel tube and an outer square steel tube, the inner core adopting a cruciform section and an H-section. These two types of cross-sectional inner cores have larger cross-sectional stiff ness than round bars and better meet the requirement that inner core should be easy to yield but not easy to buckle. In this study, a theoretical design method for designing the proposed BRB in a simplifi ed and optimal way is presented. The assembly scheme, constraint system, and overall structure are defi ned. The quasi-static tests of two brace specimens under a cyclic load are carried out to verify the brace's mechanical performance, axial strain distribution, and energy dissipation capacity. These results show that, relying on these two types of cross-sections, the hysteresis curves of all-steel buckling restrained braces with double-steel tubes are overall in good shape and stable. In addition, its energy dissipation performance is stable without any widespread instability phenomena. Also, the inner core has a stable plastic deformation capacity even after yielding, based on the comparative analysis of axial strain response of each components. Both specimens can meet the requirements of seismic design.

반복 횡하중을 받는 복강판 패널의 구조성능에 대한 실험적 연구

정경수(Chung Kyung-Soo),정진안(Chung Jin-An),조봉호(Cho Bong-Ho),홍성걸(Hong Sung-Gul),정종현(Jung Jong-Hyun) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.2

Steel-plate shear walls offer several advantages to resist lateral forces such as wind and earthquakes. Particularly, the walls are lighter and more ductile as compared with reinforced concrete shear walls. When the walls are used in real construction field, the construction time can be decreased and the usable space can be extended. For the double skin steel panel developed by authors, static tests were conducted. The purposes of the tests are to (1) determine the panel resistance to lateral loading and to (2) examine the panel performance under fully reversed cycles of loading. The sizes of the test specimens are 0.85 by 2.4m, 0.55 by 2.4m, and 0.4 by 2.4m. The empirical formulae on the strength and stiffness of the double skin steel panel are proposed and verified on the basis of the experimental results. The results of the numerical analysis show a similar trend to the experimental results.

Study on Mechanical Properties of Press-Bending Members Based on Transmission Towers Diagonal Member Reinforcement In-Situ

Zhenke Xin,Huanhuan Wei,Yunhe Liu,Gang Liang 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.4

According to the reinforcement requirements of load-bearing members of existing transmission tower, a new type of in-situ reinforcement scheme for the angle steel T-shaped composite section is proposed. Through the compression test of 10 groups of members, the infl uence of slenderness ratio, the number of fi xtures, the number of bolt rows and other parameters on the failure mode and bearing performance of members was studied. A simulation model was established using ABAQUS software, the load-displacement curve, failure models and other aspects verify the reliability and validity of simulation results. The results show that when the slenderness ratio of member reaches a certain value, the ultimate bearing capacity of member reinforced with the reinforcement angle steel of same specifi cation and strength can be multiplied and increased several times, the slenderness ratio has little eff ect on the force transmission effi ciency of reinforcement angle steel. The number of bolt rows has a small eff ect on the ultimate bearing capacity of member, the increase rate of ultimate bearing capacity, the failure mode and the force transmission effi ciency of reinforcement angle steel, the infl uence of strength of reinforcement angle steel, the specifi cation of reinforcement angle steel on the ultimate bearing capacity, and the increase rate of ultimate bearing capacity of member obviously, the higher strength and specifi cation of reinforcement, the greater the ultimate bearing capacity of reinforced member, and the higher the rate of improvement of ultimate bearing capacity, the smaller the thickness of fi ller plate, that is the smaller the eccentricity, the higher force transmission effi ciency of reinforcement. The research results can provide experimental and theoretical basis for the reinforcement of tower structure and engineering design.

A Design Formula for Lateral Load Resistance of Concrete Filled Double-Steel-Plate Walls with Small Height-to-Length Ratio

Mojtaba Labibzadeh,Reza Hamidi 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.8

This study was designed to find an analytical formula for predicting the ultimate shear strength of a novel kind of complex steel-concrete shear walls known as double steel plate complex shear wall (DSCSW). The performance of these compound walls is now under research and no adequate design provisions are available. Three types of analytical formulae consisting of full shear yield, local and global shear elastic buckling were proposed and their precisions were investigated. To this end, a comprehensive 3D nonlinear finite element (FE) parametric analysis was performed. To carry out such parametric study, 120 FE models of DSCSWs were simulated and analyzed using ABAQUS package. All models were constructed according to an FE model of a test sample of DSCSW which had been constructed and tested in 2013 by Rafiei. The validity of that FE model was verified by comparing the simulation results with the experimental results. The variables considered in the parametric study were the profiled steel plate thickness, the compressive strength of infill concrete, the yield strength of the profiled steel plate and finally the number of the intermediate fasteners. At the end of this study, it was revealed that the full shear yield formula can provide a good estimation of the shear capacity of this type of shear walls when at least one row of the intermediate fasteners in the mid-height of the wall used for connecting the steel plates to the concrete panel.

Numerical investigation on the response of circular double-skin concrete-filled steel tubular slender columns subjected to biaxial bending

Awni Abu-Shamah,Rabab Allouzi 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.5

Recently, Concrete-filled double skin steel tubular (CFDST) columns have proven an exceptional structural resistance in terms of strength, stiffness, and ductility. However, the resistance of these column members can be severely affected by the type of loading in which bending stresses increase in direct proportion with axial load and eccentricity value. This paper presents a non-linear finite element based modeling approach that studies the behavior of slender CFDST columns under biaxial loading. Finite element models were calibrated based on the outcomes of experimental work done by other researchers. Results from simulations of slender CFDST columns under axial loading eccentric in one direction showed good agreement with the experimental response. The calibrated models are expanded to a total of thirty models that studies the behavior of slender CFDST columns under combined compression and biaxial bending. The influences of parameters that are usually found in practice are taken into consideration in this paper, namely, eccentricity-to-diameter (e/D) ratios, slenderness ratios, diameter-to-thickness (D/t) ratios, and steel contribution ratios. Finally, an analytical study based on current code provisions is conducted. It is concluded that South African national standards (2011) provided the most accurate results contrasted with the Eurocode 4 (2004) and American Institute of Steel Construction (2016) that are found to be conservative. Accordingly, correction factors are proposed to the current design guidelines to provide more satisfactory results.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

Jingfeng Wang,Lei Guo 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.2

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Evaluation of the Impact Resistance of Steel–Aluminum Laminated Target Plates with Isoplanar Density

Deng Yunfei,Wang Zhongshan 한국강구조학회 2024 International Journal of Steel Structures Vol.24 No.3

The research aims to investigate the impact resistance of steel-aluminum laminated target plates, which is crucial for the design of high-performance anti-invasion structures. Previous studies have presented confl icting views on the protective performance of steel-aluminum laminated target plates, highlighting the need to clarify the infl uence of structural parameters on their protection capabilities. To address this, two groups of steel and aluminum plates with similar strengths and large diff erences in strengths were selected and tested. The ballistic limits characteristics of these double-layered plates were analyzed under diff erent projectile nose shapes. Additionally, a 3D fi nite element model was established using ABAQUS/ Explicit software, after the validity of the model was verifi ed, the infl uence of the arrangement order of the steel and aluminum on the impact resistance was numerically simulated. The results show that the strength of the steel and aluminum plate materials is the key factor infl uencing the order of the best impact resistance of the target plate, and the shape of the projectile's nose and the thickness of the target plate don't have much infl uence on the order of the best impact resistance, which is also proved by the simulation results of the isoplanar density (same surface density). This study is instructive for the design and application of steel-aluminum laminated target plate structures with protective ends.

An enhanced simulated annealing algorithm for topology optimization of steel double-layer grid structures

Mostafa Mashayekhi,Hamzeh Ghasemi Techno-Press 2024 Advances in computational design Vol.9 No.2

Stochastic optimization methods have been extensively studied for structural optimization in recent decades. In this study, a novel algorithm named the CA-SA method, is proposed for topology optimization of steel double-layer grid structures. The CA-SA method is a hybridized algorithm combining the Simulated Annealing (SA) algorithm and the Cellular Automata (CA) method. In the CA-SA method, during the initial iterations of the SA algorithm, some of the preliminary designs obtained by SA are placed in the cells of the CA. In each successive iteration, a cell is randomly chosen from the CA. Then, the "local leader" (LL) is determined by selecting the best design from the chosen cell and its neighboring ones. This LL then serves as the leader for modifying the SA algorithm. To evaluate the performance of the proposed CA-SA algorithm, two square-on-square steel double-layer grid structures are considered, with discrete cross-sectional areas. These numerical examples demonstrate the superiority of the CA-SA method over SA, and other meta-heuristic algorithms reported in the literature in the topology optimization of large-scale skeletal structures.