• Steel and Composite Structures
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• v.21 no.3
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• pp.517-536
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• 2016

Thick steel plate is commonly found with mega steel structures but its properties have not been fully explored. Grade Q345GJ-C steel plate with thickness ranging from 60 mm to 120 mm are studied in this paper. Both the static and cyclic performance of material in different directions (horizontal and through-thickness directions) and locations (outer surface, 1/4 thickness and mid-depth) are experimentally obtained. The accumulative damage during cyclic loading is also calculated by using bilinear mixed hardening (BMH) constitutive relationship together with the Lemaitre's damage model. Results show that the static properties are better at the outer surface of thick steel plates than those at mid-depth. Properties in through-thickness direction are similar to those at mid-depth in the horizontal direction. The cyclic performance at different locations of a given plate is similar within the range of strain amplitude studied. However, when damage parameters identified from monotonic tensile tests are included in the numerical simulation of cyclic loading tests, damage is found accumulating faster at mid-depth than close to outer surface.

• Steel and Composite Structures
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• v.34 no.4
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• pp.561-580
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• 2020

Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. In the second part of this paper, a complex nonlinear numerical model for the tested BRBs was developed in the finite element environment Abaqus. The calibration of the numerical model was performed at both component (material models: steel, concrete, unbonding material) and member levels (loading, geometrical imperfections). Geometrically and materially nonlinear analyses including imperfections were performed on buckling restrained braces models under cyclic loading. The calibrated models were further used to perform a parametric study aiming at assessing the influence of the strength of the buckling restraining mechanism, concrete class of the infill material, mechanical properties of steel used for the core, self-weight loading, and frame effect on the cyclic response of buckling restrained braces.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.3
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• pp.54-60
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• 2003

Fatigue strength of offshore structures or ship structures is significantly decreased due to corrosive environment condition such as sea water and/or coal, crude oil of cargoes, compared to that of on shore structures. In corrosive environment, fatigue strength of structures also depends on characteristics of weld material heat affected zone(HAZ). In this research work, rotary bending fatigue tests of parent material and HAZ of TMCP steel were performed in order to investigate the initiation and propagation of cracks both in air and in NaCl solution. Comparison of fatigue strength In relation with the salinity of NaCl were carried out as well. According to the test results weld material or HAZ of TMCP steel showed higher fatigue strength than that of the parent material. The fatigue strength of TMCP steel decreases drastically in NaCl solution compared to that of in air environment. In particular, more reduced fatigue strength is observed in 1% NaCl solution than in 3% NaCl solution.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1161-1176
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• 2015

The connection between a column and a beam is of particular importance to ensure the safety of civil engineering structures, such as high-rise buildings and bridges. While the connector must bear sufficient force for load transmission, increase of its ductility, toughness and damping may greatly enhance the overall safety of the structures. In this work, a composite beam-column connector is proposed and analyzed with the finite element method, including effects of elasticity, linear viscoelasticity, plasticity, as well as geometric nonlinearity. The composite connector consists of three parts: (1) soft steel; (2) polymer; and (3) conventional steel to be connected to beam and column. It is found that even in the linear range, the energy dissipation capacity of the composite connector is largely enhanced by the polymer material. Since the soft steel exhibits low yield stress and high ductility, hence under large deformation the soft steel has the plastic deformation to give rise to unique energy dissipation. With suitable geometric design, the connector may be tuned to exhibit different strengths and energy dissipation capabilities for real-world applications.

• Archives of Metallurgy and Materials
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• v.66 no.4
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• pp.1049-1054
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• 2021

In this study, stainless steel 316L and Inconel 625 alloy powders were additively manufactured by using directed energy deposition process. And heat treatment effect on hardness and microstructures of the bonded stainless steel 316L/Inconel 625 sample was investigated. The microstructures shows there are no secondary phases and big inclusions near interfacial region between stainless steel 316L and Inconel 625 except several small cracks. The results of TEM and Vickers Hardness show the interfacial area have a few tens of micrometers in thickness. Interestingly, as the heat treatment temperature increases, the cracks in the stainless steel region does not change in morphology while both hardness values of stainless steel 316L and Inconel 625 decrease. These results can be used for designing pipes and valves with surface treatment of Inconel material based on stainless steel 316L material using the directed energy deposition.

• Journal of Korean Association for Spatial Structures
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• v.7 no.3 s.25
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• pp.141-151
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• 2007

The appearance of many Glass Fiber Reinforced Plastic (GFRP) constructions look like ordinary steel construction, because GFRP has been imitated by the same way with the traditional steel's cross section as well as connection system. In terms of detachable connection, there was not enough appropriate option of GFRP connection, such as a traditional bolt connection for steel and wood structures. Most of all, from material characteristic of GFRP related to the deficient ductility, the shearstress principle of GFRP s not proper for the material property, which causes ineffective and not economic application of material. With this research problem, the innovative and detachable onnection system, which is more considered with appropriate material characteristic for FRP, is developed. Not only short time but also long time research with various connection variations is carried out.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.633-636
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• 2006

High-rise and large size buildings require high strength concrete and steel structure as a necessity. However, high strength concrete and steel structure are strong material but have a weakness to high temperature. Therefore, fire protection is a matter that must be considered very importantly in design for structure of high strength concrete and steel. Fire proof board that is existing method for fire proof has relatively low performance in fire protection emphasizes the need of new fire protection material due to the using of in numerable inflammables like plastics. The objective of this study is to understand the fire-resisting performance of newly developed fire protection material for building. This paper describes the results of fire tests using ISO curve that is fire protection regulation for buildings of the newly developed cementitious fire protection coating material applied concrete tunnel lining specimens.

• Steel and Composite Structures
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• v.18 no.6
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• pp.1517-1539
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• 2015

Eccentrically braced frames (EBFs) often use conventional steel with medium yield strength. This system requires structural members with large cross-sections for well seismic behavior, which leads to increased material costs. In eccentrically braced frames with high strength steel combination (HSS-EBFs), links use Q345 steel (specified nominal yield strength 345 MPa), braces use Q345 steel or high strength steel while other structural members use high strength steel (e.g., steel Q460 with the nominal yield strength of 460 MPa or steel Q690 with the nominal yield strength of 690 MPa). For this approach can result in reduced steel consumption and increased economic efficiency. Several finite element models of both HSS-EBFs and EBFs are established in this paper. Nonlinear hysteretic analyses and nonlinear time history analyses are conducted to compare seismic performance and economy of HSS-EBFs versus EBFs. Results indicate that the seismic performance of HSS-EBFs is slightly poorer than that of EBFs under the same design conditions, and HSS-EBFs satisfy seismic design codes and reduce material costs.

• Smart Structures and Systems
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• v.29 no.3
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• pp.445-455
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• 2022

Steel anchor bolts are installed in concrete using a variety of methods. One of the most common methods of anchor bolt installation is using epoxy resin as an infill material injected into the drilled hole to act as a bonding material between the steel bolt and the surrounding concrete. Typical design standards assume uniform stress distribution along the length of the anchor bolt accompanied with single crack leading to pull-out failure. Experimental evidence has shown that the steel anchor bolts fail owing to the multiple failure patterns, hence these design assumptions are not realistic. In this regard, the presented research work details the analytical model that takes into consideration multiple micro cracks in the infill material induced via impact loading. The impact loading from the Schmidt hammer is used to evaluate the bond condition bond condition of anchor bolt and the epoxy material. The added advantage of the presented analytical model is that it is able to take into account the various type of end conditions of the anchor bolts such as bent or U-shaped anchors. Through sensitivity analysis the optimum stiffness and shear strength properties of the epoxy infill material is achieved, which have shown to achieve lower displacement coupled with reduced damage to the surrounding concrete. The accuracy of the presented model is confirmed by comparing the simulated deformational responses with the experimental evidence. From the comparison it was found that the model was successful in simulating the experimental results. The proposed model can be adopted by professionals interested in predicting and controlling the deformational response of anchor bolts.

• Journal of Power System Engineering
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• v.8 no.3
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• pp.18-22
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• 2004

Boiler is one of the most important utilities providing steam to turbine in order to supply mechanical energy in thermal power plant. It is composed of thousands of tubes for high efficient heat transfer. The material for boiler tubes is used in such high temperature and pressure condition as $540^{\circ}C$, 22MPa. The boiler tube material is required to resist creep damage, fatigue cracking, and corrosion damages. 2.25%Cr-1Mo steel is used for conventional boiler tubes, and austenitenite stainless steel is used for higher temperature boiler tubes. But the temperature and pressure of steam in power plant became higher for high plant efficiency. So, the property of boiler tube material must be upgaded to fit the plant property. Several boiler tube material was developed to fit such conditions. X20CrMoV12.1 steel is also developed in 1980's and used for superheater and reheater tubes in supercritical boilers. The material has martensite microstructures which is difficult to evaluate the degradation. In this thesis, degrade the X20CrMoV12.1 steel at high temperatures in electric furnace, and evaluate hardness with Vickers hardness tester and strengths with Indentation tester.