• Wind and Structures
• /
• 제7권5호
• /
• pp.345-357
• /
• 2004

In the 1990s, four strong typhoons hit the Kyushu area of Japan and inflicted severe damage on power transmission facilities, houses, and so on. Maximum gust speeds exceeding 60 m/s were recorded in central Kyushu. Although the wind speeds were very high, the gust factors were over 2.0. No meteorological stations are located in mountainous areas, creating a deficiency of meteorological station data in the area where the towers were damaged. Since 1995 the authors have operated a network for wind measurement, NeWMeK, that measures wind speed and direction, covering these mountainous areas, segmenting the Kyushu area into high density arrays. Maximum gusts exceeding 70 m/s were measured at several NeWMeK sites when Typhoon Bart (1999) approached. The gust factors varied widely in southerly winds. The mean wind speeds increased due to effects of the local terrain, thus further increasing gust speeds.

• Wind and Structures
• /
• 제8권4호
• /
• pp.251-268
• /
• 2005

This paper describes the work of the International Association for Wind Engineering Working Group E -Dynamic Response, one of the International Codification Working Groups set up at the Tenth International Conference on Wind Engineering in Copenhagen. Comparisons of gust loading factors and wind-induced responses of major codes and standards are first reviewed, and recent new proposals on 3-D gust loading factor techniques are introduced. Then, the combined effects of along-wind, crosswind and torsional wind load components are discussed, as well as the dynamic characteristics of buildings. Finally, the mathematical forms of along-wind velocity spectra for along-wind response calculation and codification of acceleration criteria are discussed.

• Wind and Structures
• /
• 제5권6호
• /
• pp.543-562
• /
• 2002

The main purpose of this study is to discuss the design wind loads for the structural frames of single-layer latticed domes with long spans. First, wind pressures are measured simultaneously at many points on dome models in a wind tunnel. Then, the dynamic response of several models is analyzed in the time domain, using the pressure data obtained from the wind tunnel experiment. The nodal displacements and the resultant member stresses are computed at each time step. The results indicate that the dome's dynamic response is generally dominated by such vibration modes that contribute to the static response significantly. Furthermore, the dynamic response is found to be almost quasi-static. Then, a series of quasi-static analyses, in which the inertia and damping terms are neglected, is made for a wide range of the dome's geometry. Based on the results, a discussion is made of the design wind load. It is found that a gust effect factor approach can be used for the load estimation. Finally, an empirical formula for the gust effect factor and a simple model of the pressure coefficient distribution are provided.

• Wind and Structures
• /
• 제12권3호
• /
• pp.239-257
• /
• 2009

This paper develops and discusses a method by which it is possible to evaluate the Equivalent Static Force (ESF) of wind in the case of long-span bridges. Attention is focused on the alongwind direction. The study herein carried out deals with the classical problems of determining the maximum effects due to the alongwind action and the corresponding ESFs. The mean value of the maximum alongwind displacement of the deck is firstly obtained both by the spectral analysis and the Gust Response Factor (GRF) technique. Successively, in order to derive the other wind-induced effects acting on the deck, the Gust Effect Factor (GEF) technique is extended to long-span bridges. By adopting the GRF technique, it is possible to define the ESF that applied on the structure produces the maximum alongwind displacement. Nevertheless the application of the ESF so obtained does not furnish the correct maximum values of other wind-induced effects acting on the deck such as bending moments or shears. Based on this observation, a new technique is proposed which allows to define an ESF able to simultaneously reproduce the maximum alongwind effects of the bridge deck. The proposed technique is based on the GEF and the POD techniques and represents a valid instrument of research for the understanding of the wind excitation mechanism.

• Wind and Structures
• /
• 제31권6호
• /
• pp.575-591
• /
• 2020

Wind load is typically considered as one of the governing design loads acting on a structure. Understanding its nature is essential in evaluation of its action on the structure. Many codes and standards are founded on state of the art knowledge and include step by step procedures to calculate wind loads for various types of structures. One of the most accepted means for calculating wind load is using Gust Load Factor or base bending Moment Gust Load Factor (MGLF), where codes are adjusted based on local data available. Although local data may differ, the general procedure is the same. In this paper, ASCE 7-16 (2017), which is used as the main reference in the U.S., and Korean Building Code (KBC 2016) are compared in evaluation of wind loads. The primary purpose of this paper is to provide insight on each code from a structural engineering perspective. Herein, discussion focuses on where the two codes are compatible and differ. In evaluating the action of wind loads on a building, knowledge of the dynamic properties of the structure is critical. For this study, the design of four figurative high-rise buildings with dual systems was analyzed.

• Wind and Structures
• /
• 제22권1호
• /
• pp.17-41
• /
• 2016

To address the uncertainty of the flight trajectories caused by the turbulence and gustiness of the wind field over the roof and in the wake of a building, a 3-D probabilistic trajectory model of flat-type wind-borne debris is developed in this study. The core of this methodology is a 6 degree-of-freedom deterministic model, derived from the governing equations of motion of the debris, and a Monte Carlo simulation engine used to account for the uncertainty resulting from vertical and lateral gust wind velocity components. The influence of several parameters, including initial wind speed, time step, gust sampling frequency, number of Monte Carlo simulations, and the extreme gust factor, on the accuracy of the proposed model is examined. For the purpose of validation and calibration, the simulated results from the 3-D probabilistic trajectory model are compared against the available wind tunnel test data. Results show that the maximum relative error between the simulated and wind tunnel test results of the average longitudinal position is about 20%, implying that the probabilistic model provides a reliable and effective means to predict the 3-D flight of the plate-type wind-borne debris.

• Wind and Structures
• /
• 제31권2호
• /
• pp.85-102
• /
• 2020

Accurate load evaluation is essential in any performance-based design. Design wind speeds and associated wind loads are well defined for synoptic boundary layer winds but not for thunderstorms. The method presented in the current study represents a new approach to obtain design wind speeds associated with thunderstorms and their gust fronts using historical data and Monte Carlo simulations. The method consists of the following steps (i) developing a numerical model for thunderstorm downdrafts (i.e. downbursts) to account for storm translation and outflow dissipation, (ii) utilizing the model to characterize previous events and (iii) extrapolating the limited wind speed data to cover life-span of structures. The numerical model relies on a previously generated CFD wind field, which is validated using six documented thunderstorm events. The model suggests that 10 parameters are required to describe the characteristics of an event. The model is then utilized to analyze wind records obtained at Lubbock Preston Smith International Airport (KLBB) meteorological station to identify the thunderstorm parameters for this location, obtain their probability distributions, and utilized in the Monte Carlo simulation of thunderstorm gust front events for many thousands of years for the purpose of estimating design wind speeds. The analysis suggests a potential underestimation of design wind speeds when neglecting thunderstorm gust fronts, which is common practice in analyzing historical wind records. When compared to the design wind speed for a 700-year MRI in ASCE 7-10 and ASCE 7-16, the estimated wind speeds from the simulation were 10% and 11.5% higher, respectively.

• 한국농림기상학회지
• /
• 제26권2호
• /
• pp.115-125
• /
• 2024

바람은 농업환경에 주요한 영향을 주는 기상요소이며, 강풍은 낙과, 시설물 파괴 등의 피해를 일으킨다. 본 연구는 LENS에 물리모델을 적용해서 농경지에 활용될 수 있는 저고도 풍속예측을 진행하였다. 물리모델은 LOG, POW가 사용되었고 지표 변수에 대해서는 환경부지표와 MODIS 지표를 따로 적용하였다. 농촌진흥청에서 운영하는 2022년도 3 m 고도의 바람 및 강풍 자료를 수집하고 검증을 진행하였고 결과를 산점도, 상관계수, RMSE, NRMSE, TS로 나타내었다. 풍속비교 4가지 방법의 결과에서 모델이 관측보다 더 크게 예측하고 있음을 확인할 수 있었다. 강풍 기준 값이 3 m s^-1 일 때, TS 가 약 0.65 정도로 나타났다. 결과는 RMSE와 NRMSE에서는 LOG_L, LOG_M, POW_L, POW_M 순으로 좋게 나타났고 상관계수와 TS에서는 역순으로 좋게 나타났다. 이러한 결과는 정해진 강풍 기준을 추가하여, 농경지 바람 및 강풍확률예측 연구에 도움이 될 것으로 기대된다.

• 한국공간구조학회논문집
• /
• 제6권1호
• /
• pp.83-90
• /
• 2006

Gust Factor법은 구조물의 등가정적 풍하중을 평가하는 일반적인 방법으로 구조물의 최대 응답시의 풍하중의 분포가 평균풍하중의 분포와 동일한 형상을 가진다는 가정하에 적용한다. 그러나 대스팬 구조물의 경우 평균 풍하중의 형상과 변동 풍하중의 형상이 다를 수 있어 1차모드뿐 아니라 고차모드의 영향을 고려하여 구조물의 풍응답과 풍하중을 산정하여야 한다. 본 논문에서는 등가정적 풍하중을 산정하기 위하여 현재 사용되고 있는 Gust Factor 법 (GF법), Load-response-correlation법 (LRC법)에 대해 고찰하고, Advanced Conditional Sampling 법 (ACS법)을 제안하였다. ACS법은 최대하중효과를 나타내는 순간에 선택된 풍압분포와 구조물의 동적거동에 의해 발생한 관성력을 합성하여 등가정적풍하중을 산정하는 방법이다. 최대하중 효과는 풍동실험에서 얻어진 풍압데이터를 이용하여 시간이력해석으로 평가한다. 제안된 ACS법과 기존의 GF법 및 LRC법을 지붕 구조물에 적용하여 등가정적 풍하중을 산출하고 이를 상호 비교 분석함으로써 ACS법의 유효성을 검증하고자 한다.

• 대기
• /
• 제16권3호
• /
• pp.169-185
• /
• 2006

We have investigated the wind speed variations over the leeward region when the strong wind blows. In this study we employ Envi-met numerical model to simulate the effect of surface boundary conditions. This model is applied for three cases which are characterized by land use and terrain height. The base case having natural geographical condition shows the weakest wind speed around lee side of Chunsudae. The others which remove the vegetation and cut off the terrain above 20 m ASL represent the stronger wind speed than base case. The main factor of this result is the surface friction. The distinct variation of wind is found at offshore area between Chunsudae and the southern part of village, but the northern part where is apart from Chunsudae shows a small variation of wind pattern. The weakening of wind speed around residential area is a maximum of 4~10 m/s when the wind blows in the village as strong as 55 m/s. The gust wind speed is weakened about 7~17 m/s in this case if the coefficient of gust wind adapted as 1.75.