• Wind and Structures
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• v.37 no.6
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• pp.445-460
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• 2023

Accurate estimation of modal parameters (i.e., natural frequency, damping ratio) of tall buildings is of great importance to their structural design, structural health monitoring, vibration control, and state assessment. Based on the combination of variational mode decomposition, smoothed discrete energy separation algorithm-1, and Half-cycle energy operator (VMD-SH), this paper presents a method for structural modal parameter estimation. The variational mode decomposition is proved to be effective and reliable for decomposing the mixed-signal with low frequencies and damping ratios, and the validity of both smoothed discrete energy separation algorithm-1 and Half-cycle energy operator in the modal identification of a single modal system is verified. By incorporating these techniques, the VMD-SH method is able to accurately identify and extract the various modes present in a signal, providing improved insights into its underlying structure and behavior. Subsequently, a numerical study of a four-story frame structure is conducted using the Newmark-β method, and it is found that the relative errors of natural frequency and damping ratio estimated by the presented method are much smaller than those by traditional methods, validating the effectiveness and accuracy of the combined method for the modal identification of the multi-modal system. Furthermore, the presented method is employed to estimate modal parameters of a full-scale tall building utilizing acceleration responses. The identified results verify the applicability and accuracy of the presented VMD-SH method in field measurements. The study demonstrates the effectiveness and robustness of the proposed VMD-SH method in accurately estimating modal parameters of tall buildings from acceleration response data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.4
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• pp.401-408
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• 2015

Conventional model updating methods for the structures have used global structural responses which are modal parameters obtained through vibration measurements. Although models updated by modal parameters estimate global structural responses accurately, they have difficulties to predict local responses for safety assesment of structural members. The safety of structural members in the structures has been evaluated through the stress estimation based on strain measurements. Thus, this study additionally uses measured strain responses of structural members to perform model updating besides modal parameters. In the proposed method, the objective functions are set to the differences of the global and local responses obtained from updated model and measurement and those functions are minimized by NSGA-II, one of the multi-objective optimization techniques. The strain responses predicted from updated model are used for safety assessment of the steel frame structures. The proposed method are verified by numerical and experimental studies through the impact hammer tests for a steel frame specimen.

• Structural Engineering and Mechanics
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• v.40 no.4
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• pp.453-469
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• 2011

A one-story, wooden-frame, intermediate-bay model with Dou-Gon designed according to the Building Standards of the Song Dynasty (A.D.960-1279), was tested on a unidirectional shaking table. The main objectives of this experimental study were to investigate the seismic performance of Chinese historic wooden structure under various base input intensities. El Centro wave (N-S), Taft wave and Lanzhou wave were selected as input excitations. 27 seismic geophones were instrumented to measure the real-time displacement, velocity and acceleration respectively. Dynamic characteristics, failure mode and hysteretic energy dissipation performance of the model are analyzed. Test results indicate that the nature period and damping ratio of the model increase with the increasing magnitude of earthquake excitation. The nature period of the model is within 0.5~0.6 s, the damping ratio is 3~4%. The maximum acceleration dynamic magnification factor is less than 1 and decreases as the input seismic power increases. The frictional slippage of Dou-Gon layers (corbel brackets) between beams and plates dissipates a certain amount of seismic energy, and so does the slippage between posts and plinths. The mortise-tenon joint of the timber frame dissipates most of the seismic energy. Therefore, it plays a significant part in shock absorption and isolation.

• Journal of Korean Society of Steel Construction
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• v.15 no.4 s.65
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• pp.379-388
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• 2003

The response of single story buildings and other case studies were investigated to observe trends and develop a better understanding of the impact of some design parameters on the seismic response of Concentrically Braced Frames (CBF). While many parameters are known to influence the behavior of braced frames, the focus of this study was mostly on quantifying energy dissipation in compression and its effectiveness on seismic performance. Based on dynamic analyses of single story braced frame and case studies, a bracing member designed with bigger R and larger KL/r was found to result in lower normalized cumulative energy ratio in both cases.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.261-271
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• 2015

Steel concentrically braced frame is an efficient system that can acquire resistance against the lateral force of buildings with the least amount of quantity. In this study is intended to proceed on the research of schemes for reinforcement by supplementing previously installed H-formed brace with non-welded cold-formed plastic stiffening materials restricting the flexure and buckling and acquire a consistent strength on the tensile and compressive force. As for the measures of supplementing previously-installed inverted V-formed braced frame, stiffening materials in the previous studies were converted to weak-axial supplementing materials to suggest a specific scheme evaluating the structural function through an experiment of members, interpretation of members, and frame-focused experiment. Reinforced brace satisfied the requirement to be prevent AISC brace from being ruptured due to imbalanced strength in the beam.

• Steel and Composite Structures
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• v.35 no.3
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• pp.305-325
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• 2020

Beams of steel frame-tube structures (SFTSs) typically have span-to-depth ratios of less than five. This makes a flexural beam unsuitable for such an application because the plastic hinges at the beam-ends cannot be adequately developed. This leads to lower ductility and energy dissipation capacities of SFTSs. To address this, SFTSs with bolted web-connected replaceable shear links (SFTS-BWSLs) are proposed. In this structural system, a web-connected replaceable shear link with a back-to-back double channel section is placed at the mid-length of the deep beam to act as a ductile fuse. This allows energy from earthquakes to be dissipated through link shear deformation. SFTS and SFTS-BWSL buildings were examined in this study. Several sub-structures were selected from each designed building and finite element models were established to study their respective hysteretic performance. The seismic behavior of each designed building was observed through static and dynamic analyses. The results indicate that the SFTS-BWSL and SFTS have similar initial lateral stiffness and shear leg properties. The SFTS-BWSL had lower strength, but higher ductility and energy dissipation capacities. Compared to the SFTS, the SFTS-BWSL had lower interstory drift, base shear force, and story shear force during earthquakes. This design approach could concentrate plasticity on the shear link while maintaining the residual interstory drift at less than 0.5%. The SFTS-BWSL is a reliable resistant system that can be repaired by replacing shear links damaged due to earthquakes.

• Design & Manufacturing
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• v.10 no.1
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• pp.41-45
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• 2016

Electrical equipment in factories, buildings, etc. with the development of the industry has become a large capacity. By the development, electric load also become diversified and there is also highly functional requirements being electrical equipment. Particularly in the small and medium-sized circuit breakers, tend to preferentially consider the economy stands out and improvements in safety, ease of mounting and connection through the modularity of the basic dimensions compact and cost to block expansion of the scope of the development of capacity, etc. The product having a competitive has been strongly required. In order to implement the circuit breakers of breaking capacity and compact at the same time taking into account the economic development of this technology applied to the current-limiting mechanism is essential budget or the current limiting mechanism is currently available mechanisms applicable to small and medium-sized frame (frame) can not do it. In this paper, at the same time satisfying the economic efficiency, by minimizing the load force of the moving contactor (moving contactor) to be applied to small and medium frame other hand to secure the economical efficiency without using high speed contact parting acceleration of the moving contactor conventional current-limiting mechanism, and to develop a current-limiting mechanism that can be satisfied with the same or higher performance to meet the needs of the market.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.1 s.20
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• pp.9-16
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• 2006

The moment resisting frame has been well-known as it had very excellent seismic performance, and it has been widely used and constructed in the design of a lot of buildings. However, the moment resisting frame system did not exert the seismic performance during the earthquake in Northridge and Kobe sufficiently, and it produced the crack or brittle fracture on the joint. this study was to ]m tests with the full-scale test subject as parameters of existence of H-beam web high tensile bolt shearing joint and reinforcement of H-flange rib. This researcher was to anticipate the decrease of number of high tensile bolts and the improvement of workability through the double shear joint by the experiment, and improve the seismic performance through the reinforcement of rib plate. In addition, this study was to prevent the brittle fracture by the stress concentration through the non scallop.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.405-415
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• 2011

For the safe seismic design of buildings, it is necessary to predict the plastic deformation demands of the members as well as the story drift ratio. In the present study, a simple method of estimating the beam plastic rotation was developed for special-moment-resisting steel frame structures designed with strong column-weak beam behavior. The proposed method uses elastic analysis rather than nonlinear analysis, which is difficult to use in practice. The beam plastic rotation was directly calculated based on the results of the elastic analysis, addressing the moment redistribution, the column and joint dimensions, the movement of the plastic hinge, the panel zone deformation, the gravity load, and the strain-hardening behavior. In addition, the rocking effect of the braced frame or core wall on the beam plastic rotation was addressed. For verification, the proposed method was applied to a six-story special-moment frame designed with strong column-weak beam behavior. The predicted plastic rotations of the beams were compared with those that were determined via nonlinear analysis. The beam plastic rotations that were predicted using the proposed method correlated well with those that were determined from the nonlinear pushover analysis.

• Journal of the Korean Wood Science and Technology
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• v.45 no.2
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• pp.147-158
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• 2017

Among the energy consumption in building, the heating energy takes the largest part. Therefore, it is important to minimize the heat energy loss in building for the reduction of overall energy use in construction. The most important points for the minimization of energy loss in building are insulation and airtightness. Especially, in wood houses, airtightness is very important for energy saving as well as increase of durability. However, the researches on airtightness of wood buildings have been started recently and are very deficient especially in Korea. In this study, air leakage properties and airtightness performance were evaluated for light-frame wood houses built in Daejeon and Chungnam area. Total 7 houses were evaluated, among which four houses (Case 1 to Case 4) were in the construction stage before interior finish and the other three houses (Case 5 to Case 7) were after completion of construction work. The tests for airtightness were conducted by pressurization-depressurization method, and the factors included in the measurements includes air leakage rate at 50 Pa (CMH50), air change rate at 50 Pa (ACH50), equivalent leakage area (EqLA) and EqLA per floor area. As a result of this study, key air leakage points in wood houses were found to be the gaps between floor and wall, the holes for wiring and plumbing, the double glasses windows and the entrance doors. The average value of ACH50 for the houses after completion of construction work was $3.5h^{-1}$ that was similar to Europe standard ($3.0h^{-1}$). ACH50 was proportional to EqLA per floor area but inversely proportional to the internal volume, the net floor area and the area of window.