• 국제초고층학회논문집
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• 제7권4호
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• pp.343-362
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• 2018

A simplified spring connection modelling approach for steel flush endplate beam-to-column connections in fire has been developed to enable realistic behaviour of connections to be incorporated into full-scale frame analyses at elevated temperature. Due to its simplicity and reliability, the proposed approach permits full-scale high-temperature frame analysis to be conducted without high computational cost. The proposed simplified spring connection modelling approach has been used to investigate the influence of connection ductility (both axial and rotational) on frame behaviour in fire. 2D steel and 3D composite frames with a range of beam spans were modelled to aid the understanding of the differences in frame response in fire where the beam-to-column connections have different axial and rotational ductility assumptions. The modelling results highlight that adopting the conventional rigid or pinned connection assumptions does not permit the axial forces acting on the connections to be accurately predicted, since the axial ductility of the connection is completely neglected when the rotational ductility is either fully restrained or free. By accounting for realistic axial and rotational ductilities of beam-to-column connections, the frame response in fire can be predicted more accurately, which is advantageous in performance-based structural fire engineering design.

• Structural Engineering and Mechanics
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• 제81권1호
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• pp.1-9
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• 2022

Due to the frequency and magnitude of some loads produced by gusts of turbulent wind, building floors can develop lateral displacements and significant accelerations which can produce strong inertial forces on structural, non-structural elements and occupants. A device that can help to reduce the floor accelerations is the well-known Tuned Mass Damper (TMD); however, nowadays there is no enough information about its capacity in order to dissipate energy of turbulent wind loads. For this reason, in this paper different buildings with and without TMD are modeled and dynamically analyzed under simulated wind loads in order to study the reduction of peak floor accelerations. The results indicate that peak floor accelerations can be reduced up to 40% when TMD are incorporated in the buildings, which demonstrated that the Tuned Mass Damper is an efficient device to reduce the wind effects on tall buildings.

• 국제초고층학회논문집
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• 제1권4호
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• pp.311-332
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• 2012

Earthquake response of mid-rise to high-rise buildings provided with friction dampers is investigated. The steel buildings are modelled as shear-type structures and the investigation involved modelling of the structures of varying heights ranging from five storeys to twenty storeys, in steps of five storeys, subjected to real earthquake ground motions. Three basic types of structures considered in the study are: moment resisting frame (MRF), braced frame (BF), and friction damper frame (FDF). Mathematical modelling of the friction dampers involved simulation of the two distinct phases namely, the stick phase and the slip phase. Dynamic time history analyses are carried out to study the variation of the top floor acceleration, top floor displacement, storey shear, and base-shear. Further, energy plots are obtained to investigate the energy dissipation by the friction dampers. It is seen that substantial earthquake response reduction is achieved with the provision of the friction dampers in the mid-rise and high-rise buildings. The provision of the friction dampers always reduces the base-shear. It is also seen from the fast Fourier transform (FFT) of the top floor acceleration that there is substantial reduction in the peak response; however, the higher frequency content in the response has increased. For the structures considered, the top floor displacements are lesser in the FDF than in the MRF; however, the top floor displacements are marginally larger in the FDF than in the BF.

• KIEAE Journal
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• 제7권4호
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• pp.147-152
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• 2007

Numerous non-destructive tests(NDT) to assess the safety of real structures have been developed. System identification(SI) techniques using dynamic responses and behaviors of structural systems become an outstanding issue of researchers. However the conventional SI techniques are identified to be non-practical to the complex and tall buildings, due to limitation of the availability of an accurate data that is magnitude or location of external loads. In most SI approaches, the information on input loading and output responses must be known. In many cases, measuring the input information may take most of the resources, and it is very difficult to accurately measure the input information during actual vibrations of practical importance, e.g., earthquakes, winds, micro seismic tremors, and mechanical vibration. However, the desirability and application potential of SI to real structures could be highly improved if an algorithm is available that can estimate structural parameters based on the response data alone without the input information. Thus a technique to estimate structural properties of building without input measurement data and using limited response is essential in structural health monitoring. In this study, shaking table tests on three-story plane frame steel structures were performed. Out-put only model analysis on the measured data was performed, and the dynamic properties were inverse analyzed using least square method in time domain. In results damage detection was performed in each member level, which was performed at story level in conventional SI techniques of frequency domain.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.79-83
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• 2000

A sliding mode fuzzy control (SMFC) with disturbance estimator is applied to design a controller for the third generation benchmark problem on an wind-excited building. A distinctive feature in vibration control of large civil infrastructure is the existence of large disturbances, such as wind, earthquake, and sea wave forces. Those disturbances govern the behavior of the structure, however, they cannot be precisely measured, especially for the case of wind-induced vibration control. Since the structural accelerations are measured only at a limited number of locations without the measurement of the wind forces, the structure of the conventional control may have the feed-back loop only. General structure of the SMFC is composed of a compensation part and a convergent part. The compensation part prevents the system diverge, and the convergent part makes the system converge to the sliding surface. The compensation part uses not only the structural response measurement but also the disturbance measurement, so the SMFC has a feed-back loop and a feed-forward loop. To realize the virtual feed-forward loop for the wind-induced vibration control, disturbance estimation filter is introduced. the structure of the filter is constructed based on an auto regressive model for the stochastic wind force. This filter estimates the wind force at each time instance based on the measured structural responses and the stochastic information of the wind force. For the verification of the proposed algorithm, a numerical simulation is carried out on the benchmark problem of a wind-excited building. The results indicate that the present control algorithm is very efficient for reducing the wind-induced vibration and that the performance indices improve as the filter for wind force estimation is employed.

• 국제초고층학회논문집
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• 제7권2호
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• pp.145-151
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• 2018

Newly-designed high-rise buildings, both in China and abroad, have demonstrated new innovations from the creative concept to the creative method. from the creative concept to the creative method. At the same time, digital technology has enabled more design freedom in the vertical dimension. "Twisting" has gradually become the morphological choice of many city landmark buildings in recent years. The form seems more likely to be driven by the interaction of aesthetics and structural engineering. Environmental performance is often a secondary consideration; it is typically not simulated until the evaluation phase. Based on the research results of "DigitalFUTURE Shanghai 2017 Workshop - Wind Tunnel Visualization", an approach that can be employed by architects to design environmental-performance buildings during the early stages has been explored. The integration of a dynamic form-finding approach (DFFA) and programming transforms the complex relationship between architecture and environment into a dialogue of computer language and dynamic models. It allows the design to focus on the relationship between morphology and the surrounding environment, and is not limited to the envelope form itself. This new concept of DFFA in this research consists of three elements: 1) architectural form; 2) integration of wind tunnel and dynamic models; and 3) environmental response. The concept of wind tunnel testing integrated with a dynamic model fundamentally abandons the functional definition of the traditional static environment simulation analysis. Instead it is driven by integral environmental performance as the basic starting point of morphological generation.

• Earthquakes and Structures
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• 제15권6호
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• pp.639-654
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• 2018

Rocking motion have been used for achieving the 'resilient buildings' against earthquakes in recent studies. Low-rise buildings, unlike the tall ones, because of their small aspect ratio tend to slide rather than move in rocking mode. However, since rocking is more effective in seismic response reduction than sliding, it is desired to create rocking motion in low-rise buildings too. One way for this purpose is making the building's structure rock on its internal bay(s) by reducing the number of bays at the lower part of the building's skeleton, giving it a mushroom form. In this study 'mushroom skeleton' has been used for creating multi-story rocking regular steel buildings with square plan to rock on its one-by-one bay central lowest story. To show if this idea is effective, a set of mushroom buildings have been considered, and their seismic responses have been compared with those of their conventional counterparts, designed based on a conventional code. Also, a set of similar buildings with skeleton stronger than code requirement, to have immediate occupancy (IO) performance level, have been considered for comparison. Seismic responses, obtained by nonlinear time history analyses, using scaled three-dimensional accelerograms of selected earthquakes, show that by using appropriate 'mushroom skeleton' the seismic performance of buildings is upgraded to mostly IO level, while all of the conventional buildings experience collapse prevention (CP) level or beyond. The strong-skeleton buildings mostly present IO performance level as well, however, their base shear and absolute acceleration responses are much higher than the mushroom buildings.

• Wind and Structures
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• 제19권3호
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• pp.339-352
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• 2014

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards, and in wind engineering generally. Although various proposed definitions are discussed, the 'moving average' gust duration has been widely accepted internationally. The commonly-specified gust duration of 3-seconds, however, is shown to have a significant effect on the high-frequency end of the spectrum of turbulence, and may not be ideally suited for wind engineering purposes. The effective gust durations measured by commonly-used anemometer types are discussed; these are typically considerably shorter than the 'standard' duration of 3 seconds. Using stationary random process theory, the paper gives expected peak factors, $g_u$, as a function of the non-dimensional parameter ($T/{\tau}$), where T is the sample, or reference, time, and ${\tau}$ is the gust duration, and a non-dimensional mean wind speed, $\bar{U}.T/L_u$, where $\bar{U}$ is a mean wind speed, and $L_u$ is the integral length scale of turbulence. The commonly-used Durst relationship, relating gusts of various durations, is shown to correspond to a particular value of turbulence intensity $I_u$, of 16.5%, and is therefore applicable to particular terrain and height situations, and hence should not be applied universally. The effective frontal areas associated with peak gusts of various durations are discussed; this indicates that a gust of 3 seconds has an equivalent frontal area equal to that of a tall building. Finally a generalized gust response factor format, accounting for fluctuating and resonant along-wind loading of structures, applicable to any code is presented.

• 국제초고층학회논문집
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• 제1권3호
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• pp.181-194
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• 2012

Chile is characterized by the largest seismicity in the world which produces strong earthquakes every $83{\pm}9years$ in the Central part of Chile, where it is located Santiago, the capital of Chile. The short interval between large earthquakes magnitude 8.5 has conditioned the Chilean seismic design practice to achieve almost operational performance level, despite the fact that the Chilean Code declares a scope of life safe performance level. Several Indexes have been widely used throughout the years in Chile to evaluate the structural characteristics of concrete buildings, with the intent to find a correlation between general structural conception and successful seismic performance. The Indexes presented are related only to global response of buildings under earthquake loads and not to the behavior or design of individual elements. A correlation between displacement demand and seismic structural damage is presented, using the index $H_o/T$ and the concrete compressive strain ${\varepsilon}_c$. Also the Chilean seismic design codes pre and post 2010 Maule earthquake are reviewed and the practice in seismic design vs Performance Based Design is presented. Performance Based Design procedures are not included in the Chilean seismic design code for buildings, nevertheless the earthquake experience has shown that the response of the Chilean buildings has been close to operational. This can be attributed to the fact that the drift of most engineered buildings designed in accordance with the Chilean practice falls below 0.5%. It is also known by experience that for frequent and even occasional earthquakes, buildings responded elastically and thus with "fully operational" performance. Taking the above into account, it can be said that, although the "basic objective" of the Chilean code is similar to the SEAOC VISION2000 criteria, the actual performance for normal buildings is closer to the "Essential/Hazardous objective".

• Smart Structures and Systems
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• 제18권6호
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• pp.1251-1267
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• 2016

In this paper, Simple Adaptive Control (SAC) is used to enhance the seismic response of nonlinear tall buildings based on acceleration feedback. Semi-active MR dampers are employed as control actuator due to their reliability and well-known dynamic models. Acceleration feedback is used because of availability, cost-efficiency and reliable measurements of acceleration sensors. However, using acceleration feedback in the control loop causes the structure not to apparently meet some requirements of the SAC algorithm. In addition to defining an appropriate SAC reference model and using inherently stable MR dampers, a modification in the original structure of the SAC is proposed in order to improve its adaptability to the situation in which the plant does not satisfy the algorithm's stability requirements. To investigate the performance of the developed control system, a numerical study is conducted on the benchmark 20-story nonlinear building and the responses of the SAC-controlled structure are compared to an $H_2/LQG$ clipped-optimal controller under the effect of different seismic excitations. As indicated by the results, SAC controller effectively reduces the story drifts and hence the seismically-induced damage throughout the structural members despite its simplicity, independence of structural parameters and while using fewer number of dampers in contrast with the $H_2/LQG$ clipped-optimal controller.