• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.105-112
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• 2015

A shared tuned mass damper (STMD) was proposed in previous research for reduction of dynamic responses of the adjacent buildings subjected to earthquake loads. A single STMD can provide similar control performance in comparison with two traditional TMDs. In previous research, a passive damper was used to connect the STMD with adjacent buildings. In this study, a smart magnetorheological (MR) damper was used instead of a passive damper to compose an adaptive smart STMD (ASTMD). Control performance of the ASTMD was investigated by numerical analyses. For this purpose, two 8-story buildings were used as example structures. Multi-input multi-output (MIMO) fuzzy logic controller (FLC) was used to control the command voltages sent to two MR dampers. The MIMO FLC was optimized by a multi-objective genetic algorithm. Numerical analyses showed that the ASTMD can effectively control dynamic responses of adjacent buildings subjected to earthquake excitations in comparison with a passive STMD.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.253-261
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• 1998

The buckling length of exterior beam-columns of the first floor in moment resisting steel frames with weak beams is uncertain when plastic hinges occur at the ends of weak beams due to seismic loads. The objective of this study is to investigate the buckling strength of concrete-filled tubular beam-columns and to suggest the reduced buckling length of them to apply to the beam-column design code. The exterior beam-columns are modelized with horizontal displacement restraint springs. Their strength and reduced buckling length are evaluated by numerical analysis.

• Steel and Composite Structures
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• v.5 no.6
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• pp.459-484
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• 2005

In recent years, the use of steel tube confined concrete (STCC) columns has been the interests of many structural engineers. The present study is an attempt to study the monotonic and cyclic behaviours of STCC columns. For the monotonic behaviours, a series of tests on STCC stub columns (twenty one), and beam-columns (twenty) were carried out. The main parameters varied in the tests are: (1) column section types, circular and square; (2) tube diameter (or width) to thickness ratio, from 40 to 162, and (3) load eccentricity ratio (e/r), from 0 to 0.5. For the cyclic behaviours, the test parameters included the sectional types and the axial load level (n). Twelve STCC column specimens, including 6 specimens with circular sections and 6 specimens with square sections were tested under constant axial load and cyclically increasing flexural loading. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes. It was found that STCC columns exhibit very high levels of energy dissipation and ductility, particularly when subjected to high axial loads. Generally, the energy dissipation ability of the columns with circular sections was much higher than those of the specimens with square sections. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes such as AIJ-1997, AISCLRFD- 1994, BS5400-1979 and EC4-1994.

• International Journal of Concrete Structures and Materials
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• v.11 no.1
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• pp.161-169
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• 2017

Flat slab systems are vastly used in multi-story buildings because of their savings in story height and construction time, as well as for their flexibility in architectural remodeling. However, they frequently suffer brittle punching-shear failure around columns, especially when subjected to lateral loads. Therefore, seismic codes labeled flat slabs as non-ductile systems. This research goal is investigating some construction alternatives to enhance flat slab ductility and deformability. The alternatives are: adding different types of punching-shear reinforcement, using discreet fibers in concrete mixes, and increasing thickness of slab around columns. The experimental study included preparation and testing of seven half-scale interior slab-column connections up to failure. The first specimen is considered a reference, the second two specimens made of concrete mixes with different volumetric ratios of polymer fibers. Another three specimens reinforced with different types of punching-shear reinforcement, and the last specimen constructed with drop panel of inverted pyramidal shape. It is found that using the inverted pyramid-shape drop panel of specimen, increases the punching-shear capacity, and the initial and the post-cracking stiffnesses. The initial elastic stiffnesses are different for all specimens especially for the slab with closed stirrups where it is experienced the highest initial stiffness compared to the reference slab.

• Structural Engineering and Mechanics
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• v.39 no.5
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• pp.621-642
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• 2011

Passive tuned mass dampers (TMDs) efficiently suppress vibrations induced by quasi-stationary dynamic inputs, such as winds, sea waves or traffic loads, but may prove of little use against pulse-like excitations, such as near-field (NF) ground motions. The extent of such impairment is however controversial, partly due to the different evaluation criteria adopted within the literature, partly to the limited number of seismic records used in most investigations. In this study, three classical techniques and two new variants for designing a TMD on an SDOF structure are tested under 338 NF records from the PEER NGA database, including 156 records with forward-directivity features. Percentile response reduction spectra are introduced to statistically assess TMD performance, and TMD robustness is verified through Monte Carlo simulations. The methodology is extended to a variety of MDOF bending-type and shear-type frames, and simulated on a case study building structure recently constructed in Central Italy.Results offer an interesting insight into the performance of TMDs against NF earthquakes, ultimately showing that, if properly designed and sufficiently massive, TMDs are effective and robust even in the face of pulse-like ground motions. The two newly proposed design techniques are shown to generally outperform the classical ones.

• Structural Engineering and Mechanics
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• v.44 no.6
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• pp.763-774
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• 2012

Reinforced concrete frame structures with masonry infill walls constitute the significant portion of the building stock in Turkey. Therefore it is very important to understand the behavior of masonry infill frame structures under earthquake loads. This study presents an experimental work performed on reinforced concrete (RC) frames with different types of masonry infills, namely standard and locked bricks. Earthquake effects are induced on the RC frames by quasi-static tests. Results obtained from different frames are compared with each other through various stiffness, strength, and energy related parameters. It is shown that locked bricks may prove useful in decreasing the problems related to horizontal and vertical irregularities defined in building codes. Moreover tests show that locked brick infills maintain their integrity up to very high drift levels, showing that they may have a potential in reducing injuries and fatalities related to falling hazards during severe ground shakings.

• Earthquakes and Structures
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• v.7 no.5
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• pp.891-906
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• 2014

The purpose of this study is to propose a modification factor to reflect the lateral stiffness modification when a step is located in flat plates. Reinforced concrete slabs with steps have different structural characteristics that are demonstrated by a series of structural experiment and nonlinear analyses. The corner at the step is weak and flexible, and the associated rotational stiffness degradation at the corner of the step is identified through analyses of 6 types of models using a nonlinear finite element program. Then a systematic analysis of stiffness changes is performed using a linear finite element procedure along with rotational springs. The lateral stiffness of reinforced concrete flat plates with steps is mainly affected by the step length, location, thickness and height. Therefore, a single modification factor for each of these variables is obtained, while other variables are constrained. When multiple variables are considered, each single modification factor is multiplied by the other. Such a method is verified by a comparative analysis. Finally, a complex modification factor can be applied to the existing effective slab width.

• Structural Engineering and Mechanics
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• v.66 no.1
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• pp.1-14
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• 2018

Column is usually floating on the stone base directly with or without positioning tenon in traditional Chinese timber structure. Vertical load originated by the heavy upper structure would induce large friction force and compression force between interfaces of column foot and stone base. This study focused on the mechanical behaviors of column foot joint with consideration of the influence of vertical load. Mechanism of column rocking and stress state of column foot has been explored by theoretical analysis. A nonlinear finite element model of column foot joint has been built and verified using the full-scale test. The verified model is then used to investigate the mechanical behaviors of the joint subjected to cyclic loading with different static vertical loads. Column rocking mechanism and stress distributions of column foot were studied in detail, showing good agreement with the theoretical analysis. Mechanical behaviors of column foot joint and the effects of the vertical load on the seismic behavior of column foot were studied. Result showed that compression stress, restoring moment and stiffness increased with the increase of vertical load. An appropriate vertical load originated by the heavy upper structure would produce certain restoring moment and reset the rocking columns, ensuring the stability of the whole frame.

• Computational Structural Engineering
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• v.10 no.2
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• pp.243-254
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• 1997

When dynamic loads such as mechanical load, wind load, and seismic load, which causing a vibration, acts on the body of the 3-D framework resting on soil foundation, it is required to consider the dynamic behavior of soil-space framework interation system. Thus, this study presents the 3-dimensional soil-interaction system analyzed by finite element method using 4-node plate elements with flexibility, 2-node beam elements, and 8-node brick elements for the purpose of idealizing an actual structure into a geometric shape. The objective of this study is the formulation of the equation for a dynamic motion and the development of the finite element program which can analyze the dynamic behavior of soil-space framework interaction system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.659-665
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• 2010

The finite element method(FEM) is proven to be an effective approximate method of structural analysis if proper element types and meshes are chosen, and recently, the method is often applied to solve complex dynamic and nonlinear problems. A properly chosen element type and mesh yields reliable results for dynamic finite element structural analysis. However, dynamic behavior of a structure may include unpredictably large strains in some parts of the structure, and using the initial mesh throughout the duration of a dynamic analysis may include some elements to go through strains beyond the elements' reliable limits. Thus, the finite element mesh for a dynamic analysis must be dynamically adaptive, and considering the rapid process of analysis in real time, the dynamically adaptive finite element mesh generating schemes must be computationally efficient. In this paper, a computationally efficient dynamically adaptive finite element mesh generation scheme for dynamic analyses of structures is described. The concept of representative strain value is used for error estimates and the refinements of meshes use combinations of the h-method(node movement) and the r-method(element division). The shape coefficient for element mesh is used to correct overly distorted elements. The validity of the scheme is shown through a cantilever beam example under a concentrated load with varying values. The example shows reasonable accuracy and efficient computing time. Furthermore, the study shows the potential for the scheme's effective use in complex structural dynamic problems such as those under seismic or erratic wind loads.