• Wind and Structures
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• v.31 no.5
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• pp.381-392
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• 2020

Despite that the failure of sign structure may not have disastrous consequence, its sheer number still ensures the need for rigorous safety standard to regulate their maintenance and construction. During its service life, a sign structure is subject to extensive wind load, sometimes well over its permissible design load. A fragility analysis of a sign structure offers a tool for rational decision making and safety evaluation by using a probabilistic framework to consider the various sources of uncertainty that affect its performance. Wind fragility analysis was used to determine the performance of sign structure based on the performance of its connection components. In this study, basic wind fragility concepts and data required to support the fragility analysis of the sign structure such as sign panel's parameters, connection component's parameters, as well as wind load parameters were presented. Fragility and compound fragility analysis showed disparity between connection component. Additionally, reinforcement of the connection system was introduced as an example of the utilization of wind fragility results in the retrofit decision making.

• Wind and Structures
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• v.9 no.3
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• pp.217-230
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• 2006

This paper describes a procedure to develop fragility curves for woodframe structures subjected to lateral wind loads. The fragilities are cast in terms of horizontal displacement criteria (maximum drift at the top of the shearwalls). The procedure is illustrated through the development of fragility curves for one and two-story residential woodframe buildings in high wind regions. The structures were analyzed using a monotonic pushover analysis to develop the relationship between displacement and base shear. The base shear values were then transformed to equivalent nominal wind speeds using information on the geometry of the baseline buildings and the wind load equations (and associated parameters) in ASCE 7-02. Displacement vs. equivalent nominal wind speed curves were used to determine the critical wind direction, and Monte Carlo simulation was used along with wind load parameter statistics provided by Ellingwood and Tekie (1999) to construct displacement vs. wind speed curves. Wind speeds corresponding to a presumed limit displacement were used to construct fragility curves. Since the fragilities were fit well using a lognormal CDF and had similar logarithmic standard deviations (${\xi}$), a quick analysis to develop approximate fragilities is possible, and this also is illustrated. Finally, a compound fragility curve, defined as a weighted combination of individual fragilities, is developed.

• Wind and Structures
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• v.27 no.3
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• pp.199-211
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• 2018

This paper deals with wind fragility and risk analysis of high rise buildings subjected to stochastic wind load. Conventionally, such problems are dealt in full Monte Carlo Simulation framework, which requires extensive computational time. Thus, to make the procedure computationally efficient, application of metamodelling technique in fragility analysis is explored in the present study. Since, accuracy by the conventional Least Squares Method (LSM) based metamodelling is often challenged, an efficient Moving Least Squares Method based adaptive metamodelling technique is proposed for wind fragility analysis. In doing so, artificial time history of wind load is generated by three wind field models: i.e., a simple one based on alongwind component of wind speed; a more detailed one considering coherence and wind directionality effect, and a third one considering nonstationary effect of mean wind. The results show that the proposed approach is more accurate than the conventional LSM based metamodelling approach when compared to full simulation approach as reference. At the same time, the proposed approach drastically reduces computational time in comparison to the full simulation approach. The results by the three wind field models are compared. The importance of non-linear structural analysis in fragility evaluation has been also demonstrated.

• Wind and Structures
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• v.32 no.5
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• pp.405-421
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• 2021

To gain insight into the wind-induced safety concerns associated with attached tower cranes during the construction of super-tall buildings, a 606 m level frame-core tube super-tall building is selected to investigate the wind-induced vibration response and fragility of an outer-attached tower crane at all stages of construction. The wind velocity time history samples are artificially generated and used to perform dynamic response analyses of the crane to observe the effects of wind velocity and wind direction under its working and non-working resting state. The adverse effects of the relative displacement response at different connection supports are also identified. The wind-resistant fragility curves of the crane are obtained by introducing the concept of incremental dynamic analysis. The results from the investigation indicate that a large relative displacement between the supports can substantially amplify the response of the crane at high levels. Such an effect becomes more serious when the lifting arm is perpendicular to the plane of the connection supports. The flexibility of super-tall buildings should be considered in the design of outer-attached tower cranes, especially for anchorage systems. Fragility analysis can be used to specify the maximum appropriate height of the tower crane for each performance level.

• Wind and Structures
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• v.31 no.1
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• pp.59-73
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• 2020

Wind fragility analysis (WFA) of concrete chimney is often executed disregarding temperature effects. But combined wind and temperature effect is the most critical limit state to define the safety of a chimney. Hence, in this study, WFA of a 70 m tall RC chimney for combined wind and temperature effects is explored. The wind force time-history is generated by spectral representation method. The safety of chimney is assessed considering limit states of stress failure in concrete and steel. A moving-least-squares method based dual response surface method (DRSM) procedure is proposed in WFA to alleviate huge computational time requirement by the conventional direct Monte Carlo simulation (MCS) approach. The DRSM captures the record-to-record variation of wind force time-histories and uncertainty in system parameters. The proposed DRSM approach yields fragility curves which are in close conformity with the most accurate direct MCS approach within substantially less computational time. In this regard, the error by the single-level RSM and least-squares method based DRSM can be easily noted. The WFA results indicate that over temperature difference of 150℃, the temperature stress is so pronounced that the probability of failure is very high even at 30 m/s wind speed. However, below 100℃, wind governs the design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.107-113
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• 2007

This study presents fragility curves for the wind fragility analysis of a six-span extradosed bridge. The loads and corresponding load combinations are calculated using domestic design codes. Random variables are utilized to considering the uncertainties of the input variables for wind loads. The fragility curve is represented as a log-normal distribution function, in which two parameters are estimated by the maximum likelihood method. The results show that the extradosed bridge is safe to suffer static wind forces.

• Journal of Wetlands Research
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• v.21 no.4
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• pp.298-304
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• 2019

In this paper, the analytical method to derive wind fragility for urban street tree in Korea was shown. Monte Carlo Simulation method was used to determine the probability of failure for urban street tree. This probability result was used to determine wind fragility parameters for four types of tree based on the study of street tree species in urban area in Daegu, Korea. Wind fragility for street tree was presented in terms of median capacity and standard deviation of the natural logarithm of the capacity. Results showed that the dominant factor affecting the probability of failure of tree under wind load was their diameter. Moreover, amongst the four types of tree chosen, the tree with height 7m and diameter 35cm had the lowest probability of failure under wind loading, whereas the tree with height 8m and diameter 30cm could resist the least wind loading. The median failure wind speed for urban street tree with height 7m were 43.8m/s and 50.6m/s for diameter 30cm and 35cm, respectively. Also, for tree with height 8m, their median failure wind speeds were 38.7m/s and 45.4m/s for tree with diameter 30cm and 35cm, respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.236-243
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• 2013

Offshore wind turbines has to be proved against accidental events such as ship collision. In this study, ship collision fragility analysis of offshore wind turbine is done. Dynamic collision analysis is accomplished by considering soil foundation interaction and fluid structure interaction. Uncertainties due to ship weight and speed, angle are also considered. By analyzing dynamic response of offshore wind turbine, fragility curves are obtained for different damage levels. They can be used for restricting boat speed around the wind turbine and allowable size of the boat for inspection and for other purposes. Results of the fragility, it was confirmed fragility of collision speed of bulk ship of 30,000DWT and 850ton barge ship.

• Wind and Structures
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• v.21 no.5
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• pp.461-487
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• 2015

In recent years, the Graphics Processing Unit (GPU) has become a competitive computing technology in comparison with the standard Central Processing Unit (CPU) technology due to reduced unit cost, energy and computing time. This paper describes the derivation and implementation of GPU-based algorithms for the analysis of wind loading uncertainty on high-rise systems, in line with the research field of probability-based wind engineering. The study begins by presenting an application of the GPU technology to basic linear algebra problems to demonstrate advantages and limitations. Subsequently, Monte-Carlo integration and synthetic generation of wind turbulence are examined. Finally, the GPU architecture is used for the dynamic analysis of three high-rise structural systems under uncertain wind loads. In the first example the fragility analysis of a single degree-of-freedom structure is illustrated. Since fragility analysis employs sampling-based Monte Carlo simulation, it is feasible to distribute the evaluation of different random parameters among different GPU threads and to compute the results in parallel. In the second case the fragility analysis is carried out on a continuum structure, i.e., a tall building, in which double integration is required to evaluate the generalized turbulent wind load and the dynamic response in the frequency domain. The third example examines the computation of the generalized coupled wind load and response on a tall building in both along-wind and cross-wind directions. It is concluded that the GPU can perform computational tasks on average 10 times faster than the CPU.

• Journal of Ocean Engineering and Technology
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• v.27 no.4
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• pp.98-106
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• 2013

Seismic fragility curves for an offshore wind-turbine structure were obtained. The dynamic response of an offshore wind turbine was analyzed by considering the nonlinear behavior of layered soil and the added mass effect due to seawater. A pile-soil interaction effect was considered by using nonlinear p-y, t-z curves. In the analysis, the amplification effect of ground acceleration through layered soil was considered by applying ground motion to each of the soil layers. The vertical variation in ground motion was found by one-dimensional free-field analysis of ground soils. Fragility curves were determined by damage levels in terms of tower stress and nacelle displacements that were found from static pushover analysis of the wind-turbine structure.