• Structural Engineering and Mechanics
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• v.16 no.5
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• pp.613-625
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• 2003

This paper presents the lateral-torsional buckling (LTB) of beams or girders with continuous lateral support at top flange. Traditional moment gradient factors ($C_b$) given by AISC in LRFD Specification for Structural Steel Buildings and by AASHTO in LRFD Bridge Design Specifications were reviewed. Finite-element method buckling analyses of doubly symmetric I-shaped beams with continuous top bracing were conducted to develop new moment gradient factors. A uniformly distributed load was applied at midheight and either or both end moments were applied at the ends of beams. The proposed solutions are simple and accurate for use by engineers to determine the LTB resistance of beams.

• Steel and Composite Structures
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• v.1 no.1
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• pp.145-158
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• 2001

An experimental study was conducted to evaluate the effects of loading sequence and lateral bracing on the behavior of reduced beam section (RBS) steel moment frame connections. Four full-scale moment connections were cyclically tested-two with a standard loading history and the other two with a near-fault loading history. All specimens reached at least 0.03 radian of plastic rotation without brittle fracture of the beam flange groove welds. Two specimens tested with the nearfault loading protocol reached at least 0.05 radian of plastic rotation, and both experienced smaller buckling amplitudes at comparable drift levels. Energy dissipation capacities were insensitive to the types of loading protocol used. Adding a lateral bracing near the RBS region produced a higher plastic rotation; the strength degradation and buckling amplitude were reduced. A non-linear finite element analysis of a one-and-a-half-bay beam-column subassembly was also conducted to study the system restraint effect. The study showed that the axial restraint of the beam could significantly reduce the strength degradation and buckling amplitude at higher deformation levels.

• Steel and Composite Structures
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• v.24 no.2
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• pp.213-226
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• 2017

The behavior of building industry metal sheeting under shear forces has been extensively studied and equations have been developed to predict its shear stiffness. Building design engineers can make use of these equations to design a metal deck form bracing system. Bridge metal deck forms differ from building industry forms by both shape and connection detail. These two factors have implications for using these equations to predict the shear stiffness of deck form systems used in the bridge industry. The conventional eccentric connection of bridge metal deck forms reduces their shear stiffness dramatically. However, recent studies have shown that a simple modification to the connection detail can significantly increase the shear stiffness of bridge metal deck form panels. To the best of the author's knowledge currently there is not a design aid that can be used by bridge engineers to estimate the stiffness of bridge metal deck forms. Therefore, bridge engineers rely on previous test results to predict the stiffness of bridge metal deck forms in bracing applications. In an effort to provide a design aid for bridge design engineers to rely on bridge metal deck forms as a bracing source during construction, cantilever shear frame test results of bridge metal deck forms with and without edge stiffened panels have been compared with the SDI Diaphragm Design Manual and ECCS Diaphragm Stressed Skin Design Manual stiffness expressions used for building industry deck forms. The bridge metal deck form systems utilized in the tests consisted of sheets with thicknesses of 0.75 mm to 1.90 mm, heights of 50 mm to 75 mm and lengths of up to 2.7 m; which are representative of bridge metal deck forms frequently employed in steel bridge constructions. The results indicate that expressions provided in these manuals to predict the shear stiffness of building metal deck form panels can be used to estimate the shear stiffness of bridge metal deck form bracing systems with certain limitations. The SDI Diaphragm Design Manual expressions result in reasonable estimates for sheet thicknesses of 0.75 mm, 0.91 mm, and 1.21 mm and underestimate the shear stiffness of 1.52 and 1.90 mm thick bridge metal deck forms. Whereas, the ECCS Diaphragm Stressed Skin Design Manual expressions significantly underestimate the shear stiffness of bridge metal deck form systems for above mentioned deck thicknesses.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.10a
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• pp.281-288
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• 1999

This paper studied the efficiency of retrofitting of reinforced concrete structure which was not designed to endure an earthquake. The earthquake in Kobe Japan showed that there was a great possibility of having an earthquake even in big city and the damages were concentrated on mid or low story buildings which were not considered to be protected from an earthquake, . This experiment used reinforced concrete structure which restrained side-by-side displacement to test durability against an earthquake. This study deals with the structural performance of reinforced concrete frame structures strengthened with steel materials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.875-888
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• 2013

The researches have recently progressed toward the use of the superelastic shape memory alloys (SMAs) to develop new smart control systems that reduce permanent deformation occurring due to severe earthquake events and that automatically recover original configuration. The superelastic SMA materials are unique metallic alloys that can return to undeformed shape without additional heat treatments only after the removal of applied loads. Once the superelastic SMA materials are thus installed at the place where large deformations are likely to intensively occur, the structural system can make the best use of recentering capabilities. Therefore, this study is intended to propose new buckling-restrained braced frames (BRBFs) with superelastic SMA bracing systems. In order to verify the performance of such bracing systems, 6-story braced frame buildings were designed in accordance with the current design specifications and then nonlinear dynamic analyses were performed at 2D frame model by using seismic hazard ground motions. Based on the analysis results, BRBFs with innovative SMA bracing systems are compared to those with conventional steel bracing systems in terms of peak and residual inter-story drifts. Finally, the analysis results show that new SMA bracing systems are very effective to reduce the residual inter-story drifts.

• Steel and Composite Structures
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• v.36 no.4
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• pp.383-398
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• 2020

This paper investigates the progressive collapse behavior of 3D steel-framed gravity buildings under fires with a cooling phase. The effect of fire protections and bracing systems on whether, how, and when a gravity building collapses is studied. It is found that whether a building collapses or not depends on the duration of the heating phase, and it may withstand a "short-hot" fire, but collapses under a mild fire or a "long-cool" fire. The collapse time can be conservatively determined by the time when the temperature of steel columns reaches a critical temperature of 550 ℃. It is also found that the application of a higher level of fire protection may prevent the collapse of a building, but may also lead to its collapse in the cooling phase due to the delayed temperature increment in the heated members. The tensile membrane action in a heated slab can be resisted by a tensile ring around its perimeter or by tensile yielding lines extended to the edge of the frame. It is recommended for practical design that hat bracing systems should be arranged on the whole top floor, and a combination of perimeter and internal vertical bracing systems be used to mitigate the fire-induced collapse of gravity buildings. It is also suggested that beam-to-column connections should be designed to resist high tensile forces (up to yielding force) during the cooling phase of a fire.

• Journal of Chest Surgery
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• v.53 no.5
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• pp.301-305
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• 2020

Background: Radiographic modalities have been commonly used to evaluate pectus carinatum (PC), and compressive orthotic bracing is the most widely accepted treatment method. The aim of this study was to determine the efficacy of 3-dimensional (3D) body surface scanning as an alternative modality for the evaluation of PC. Methods: The medical records of 63 patients with PC who were treated with compressive orthotic bracing therapy between July 2017 and February 2019 were retrospectively analyzed. Using both 2-view chest radiography (posteroanterior and lateral view) and 3D body scanning, the height of maximal protrusion of the chest wall was measured both before and after 2 weeks of bracing therapy. The difference between the pre- and post-treatment measurements was calculated for both modalities, and these differences were compared and analyzed. Results: Based on the comparison between the pre- and post-treatment radiographs, bracing therapy produced favorable outcomes in all patients (p<0.001). The measurements obtained via 3D scanning were strongly correlated with those obtained via chest radiography (r=0.60). Conclusion: Based on the findings of this study, 3D body surface scanning appears to be an effective, radiation-free, and simple method for the post-treatment follow-up evaluation of PC, and thus can be considered an alternative to radiography.

• Steel and Composite Structures
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• v.37 no.2
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• pp.175-191
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• 2020

In this article, for the first time, the seismic behavior of elliptic-braced moment resisting frame (ELBRF) is assessed through a laboratory program and numerical analyses of FEM specifically focused on the development of global- and local-type failure mechanisms. The ELBRF as a new lateral braced system, when installed in the middle bay of the frames in the facade of a building, not only causes no problem to the opening space of the facade, but also improves the structural behavior. Quantitative and qualitative investigations were pursued to find out how elliptic braces would affect the failure mechanism of ELBRF structures exposed to seismic action as a nonlinear process. To this aim, an experimental test of a ½ scale single-story single-bay ELBRF specimen under cyclic quasi-static loading was run and the results were compared with those for X-bracing, knee-bracing, K-bracing, and diamond-bracing systems in a story base model. Nonlinear FEM analyses were carried out to evaluate failure mechanism, yield order of components, distribution of plasticity, degradation of structural nonlinear stiffness, distribution of internal forces, and energy dissipation capacity. The test results indicated that the yield of elliptic braces would delay the failure mode of adjacent elliptic columns and thus, help tolerate a significant nonlinear deformation to the point of ultimate failure. Symmetrical behavior, high energy absorption, appropriate stiffness, and high ductility in comparison with the conventional systems are some of the advantages of the proposed system.

• Steel and Composite Structures
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• v.15 no.5
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• pp.539-566
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• 2013

This paper summarises the results of a numerical study on the non linear response of steel concentric braced frames under monotonic and cyclic loads, using force-based finite elements with section fibre discretisation. The first part of the study is addressed to analyse the single brace response. A parametric analysis was carried out and discussed to evaluate the accuracy of the model, examining the influence of the initial camber, the material modelling, the type of force-based element, the number of integration points and the number of fibers. The second part of the paper is concerned with the modelling issues of whole braced structures. The effectiveness of the modelling approach is verified against the nonlinear static and dynamic behaviour of different type of bracing configurations. The model sensitivity to brace-to-brace interaction and the capability of the model to mimic the response of complex bracing systems is analyzed. The influence of different approaches for modelling the inertia, the equivalent viscous damping and the brace hysteretic response on the overall structural response are also investigated. Finally, on the basis of the performed numerical study general modelling recommendations are proposed.

• Journal of the Korean Society of Safety
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• v.31 no.3
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• pp.68-74
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• 2016

This paper presents a new strengthening method of underground box structures against seismic loads for anti-seismic capacity improvement. A threaded steel member with pressure devices(so called 'Pre-flexed member system') is used to improve seismic capacity of the RC box structure. The pre-flexed member system is fixed the corner of opening after chemical anchor was installed by drilling hole on the box structure. The structural performance was evaluated analytically. Two bracing types of strengthening methods were used; conventional bracing method and I-bracing pressure system. For the performance evaluation, seismic analyses were performed on moment and shear resisting structures with and without strength member system. Numerical results confirmed that the proposed pre-flexed member system can enhance the seismic capacity of the underground RC box structures.