Wind-resistant Design Of Structures Research Articles

Analysis of the Near-Ground Wind Field Characteristics during Typhoon Soulik

In 2013, during Typhoon Soulik, wind data were collected at various heights above the ground (15, 27, 53, 67, and 82 m) on the 550 kV 52# pole transmission tower in Ningde City, Fujian Province. The wind speed profile, turbulence intensity, gust factor, crest factor, and power spectrum were analyzed using 10 min interval wind speed records. The results show the following: (1) the average wind velocity of Typhoon Soulik varies in accordance with both the power law and the logarithmic law, but the Deaves–Harris model exhibits significant discrepancies; (2) the turbulence intensity in u, v, and w orientations decreases with the average wind velocity at each height. Exponential fitting is conducted on the strength of turbulence and gust factor profiles in each direction based on the standards of different countries, resulting in the derivation of empirical expressions; (3) the integral scale components of turbulence in u, v, and w orientations exhibit a positive correlation with both average wind velocity and height. The turbulence integral scale ratios in the longitudinal, transverse, and vertical directions at heights of 15, 53, and 82 m are 1:0.68:0.11, 1:0.67:0.27, and 1:0.67:0.30, respectively; (4) the Von Karman empirical spectrum and the modified Kaimal cross-spectrum model closely match the observed wind power spectrum of Typhoon Soulik. The presented results contribute to furthering references for wind-resistant design of structures in typhoon-prone areas and prevention of typhoon-related disasters.

Displacement estimation for a high-rise building during Super Typhoon Mangkhut based on field measurements and machine learning

Knowledge of displacement responses of high-rise buildings under harsh wind excitations is essential for their wind-resistant structural design. This paper develops a machine learning model named long short-term memory (LSTM) to estimate the displacements of a 420-m-high building during Super Typhoon Mangkhut based on available field measurements. The developed model is trained and validated using the field measurements on the building during typhoon events, and the performance of the model is assessed against several evaluation criteria. Then, the trained LSTM model is employed to estimate the displacements of the skyscraper during Mangkhut. The accuracy of the estimated displacements is validated in time and frequency domains. Moreover, the background and resonant components of the estimated displacements during the extreme windstorm are analyzed. This paper aims to provide valuable reference for the wind-resistant design of high-rise buildings in tropical cyclone-prone regions.

Computational Fluid Dynamics-Aided Simulation of Twisted Wind Flows in Boundary Layer Wind Tunnel

The twisted wind flow (TWF), referring to the phenomenon of wind direction varying with height, is a common feature of atmospheric boundary layer (ABL) winds, noticeably affecting the wind-resistant structural design and the wind environment assessment. The TWF can be effectively simulated by a guide vane system in wind tunnel tests, but the proper design and configuration of the guide vanes pose a major challenge as practical experience in using such devices is still limited in the literature. To address this issue, this study aims to propose an approach to determining the optimal wind tunnel setup for TWF simulations using a numerical wind tunnel, which is a replica of its physical counterpart, using computational fluid dynamics (CFD) techniques. By analyzing the mechanisms behind guide vanes for generating TWF based on CFD results, it was found that the design must take into account three key parameters, namely, (1) the distance from the vane system to the side wall, (2) the distance from the vane system to the model test region, and (3) the separation between the vanes. Following the optimal setup obtained from the numerical wind tunnel, TWF profiles matching both the power-law and Ekman spiral models, which, respectively, reflect the ABL and wind twist characteristics, were successfully generated in the actual wind tunnel. The findings of this study provide useful information for wind tunnel tests as well as for wind-resistant structural designs and wind environment assessment.

Copula-based estimation of directional extreme wind speeds: Application for wind-resistant structural design

Accurate probabilistic modelling of wind loads has important implications to the wind-resistant design of structures. Whereas, most previous studies merely concerned the statistical analysis of wind speed, while the effect of wind direction was usually neglected in the wind load modelling. This paper thereby proposes a novel copula-based approach to construct the joint distribution of wind speed and direction for determining the directional extreme wind speed. Based on the wind records at six typical sites in Hong Kong, a series of parametric and nonparametric copula models are applied to model the joint probability density function (JPDF) of wind speed and direction. The goodness-of-fit test indicates that the Bernstein copula is the best model to describe the correlation between variables. Furthermore, by applying the superior copula model, directional extreme wind speeds with a 10-year return period at the six selected sites are determined on basis of the conditional probability theory. The results show that the estimated extreme wind speeds vary obviously among different directions. And, the estimated directional extreme wind speed may be unreliable in some directions when ignoring the joint effect of wind speed and direction in wind load modelling. Notably, the presented method is an effective and practical tool to estimate the directional extreme wind speed with a certain return period. This paper aims to provide useful reference for the wind-resistant design in tropical cyclone-prone regions.

A Mesoscale CFD Simulation Study of Basic Wind Pressure in Complex Terrain—A Case Study of Taizhou City

The basic wind pressure or the reference wind pressure for structural design varies greatly across complex terrain. Since only a few meteorological stations can provide adequate extreme wind speed records, it is very difficult to appropriately determine the basic wind pressure for a specific site without a long history of meteorological records. To solve this problem, a mesoscale CFD model was developed and optimized based on geographic information data for Taizhou and suitable turbulence models were selected for CFD simulation. The mean extreme wind speed and the corresponding direction at five main weather stations with long observation histories in Taizhou were used as the verification conditions to perform the CFD simulation of the extreme wind field. The maximum wind speeds of the rural areas, cities, and streets of Taizhou were obtained from the results of the mesoscale CFD simulations. Then, the 50-year return period reference wind pressures were calculated and could be used for the wind-resistant structural design of buildings for sites without a long history of meteorological records. The reliability of the results was verified by comparing the simulation results with the observation data at five main stations with a long history.

Wind-resistant optimal design of tall buildings based on improved genetic algorithm

Modern tall buildings are likely sensitive to wind excitations due to their increasing height and structural flexibility. Proper or optimal wind-resistant structural design of such high-rise buildings is required or sometimes necessary to meet the requirement of safety and serviceability. Combining a genetic algorithm (GA) with improved penalty function and calculation method for equivalent static wind loads (ESWLs), this paper presents an optimal procedure for the wind-resistant design of tall buildings, which aims to minimize the total weight of the designed building subject to the constraints of top acceleration and lateral drifts. A penalty function is utilized to deal with the implicit expressed constraints of optimization. The ESWLs can be instantaneously updated due to the change of structural dynamic properties during the optimal design process. A 60-story rectangular reinforced concrete frame structure with the same geometric shape of the CAARC standard tall building is adopted to verify the feasibility of the presented method. The example demonstrates that the proposed optimal design procedure is an effective tool for the wind-resistant optimal design of tall buildings.

Analysis of typhoon wind hazard in Shenzhen City by Monte-Carlo Simulation

As one of the most serious natural disasters, many typhoons affect southeastern China every year. Taking Shenzhen, a coastal city in southeast China as an example, we employed a Monte-Carlo simulation to generate a large number of virtual typhoons for wind hazard analysis. By analyzing 67-year historical typhoons data from 1949 to 2015 using the Best Track Dataset for Tropical Cyclones over the Western North Pacific recorded by the Shanghai Typhoon Institute, China Meteorological Administration (CMA-STI), typhoon characteristic parameters were extracted and optimal statistical distributions established for the parameters in relation to Shenzhen. We employed the Monte-Carlo method to sample each distribution to generate the characteristic parameters of virtual typhoons. In addition, the Yan Meng (YM) wind field model was introduced, and the sensitivity of the YM model to several parameters discussed. Using the YM wind field model, extreme wind speeds were extracted from the virtual typhoons. The extreme wind speeds for different return periods were predicted and compared with the current structural code to provide improved wind load information for wind-resistant structural design.

Observations of typhoon effects on a high-rise building and verification of wind tunnel predictions

This paper presents the analysis results of 18-h-long field measurement data collected at a 420-m-high building and four meteorological stations in Hong Kong during the passage of Typhoon Usagi (1319) which was the most intense tropical cyclone that attacked Hong Kong in 2013. In this paper, the wind characteristics during Typhoon Usagi over five different sites in Hong Kong are presented and discussed; the modal parameters of the monitored high-rise building are estimated by a probabilistic approach in a Bayesian framework (i.e., Bayesian spectral density approach) and a deterministic method (i.e., Random decrement technique), respectively; the serviceability of the high-rise building under typhoon condition is evaluated against four comfort criteria. Furthermore, the wind tunnel predictions of structural dynamic responses of the monitored building are validated by the field measurements. The goal of this study is to further the understanding of the effects of wind on high-rise buildings so as to provide useful information for the wind-resistant structural design in tropical cyclone-prone regions.

Reconstruction of radial parametric pressure field near ground surface of landing typhoons in Northwest Pacific Ocean

The radial distribution of environmental pressure near the ground surface during typhoons is an initial input condition for height-resolving typhoon modeling widely used as a practical and relatively accurate method for rapid assessment of typhoon-induced natural hazards and wind-resistant design of structures. The radius to maximum wind speed Rmax and radial pressure distribution parameter βs, (usually named the Holland power exponent of atmospheric pressure) are two key pressure field parameters that fundamentally determine the parametric typhoon pressure field and collocated wind velocity field. Observations from the Joint Typhoon Warning Center (JTWC) show that Rmax follows a lognormal distribution and has strong correlation with central pressure difference Δps and typhoon center latitude ψ. However, it is still hard to satisfactorily reproduce the landing typhoon environmental pressure. By employing near-ground environmental pressure data involving several hundreds of meteorological stations distributed in coastline regions of the Northwest Pacific Ocean, evolution of typical environmental pressures during four strong typhoons, Khanun (0515), Wipha (0713), Krosa (0716) and Morakot (0908), have been recorded in Southeast China. Finally, a novel technique for modeling the radial surface pressure model is proposed utilizing an appropriate model for radius to maximum winds Rmax. The variation characteristics for directions, landfall states and probability distributions of βs are compared and discussed, and then probability correlations among βs and Rmax, Δps, ψ are fitted and validated, showing that the statistical correlation function model is obviously different from former formulations and is more suitable for rebuilding a wind velocity field, especially near the ground surface after typhoon landfalls along the southeast coastlines of China, which are typhoon-prone hazard regions during moving typhoons.

Characteristics of Wind Load on Spatial Structures with Typical Shapes due to Aerodynamic Geometrical Parameters and Terrain Type

The characteristics of wind load on large‐span roofs are complicated by their unique geometrical configurations and strong dependence on aerodynamic geometrical parameters and terrain type. However, there is rarely comprehensive research for characteristics of wind load on spatial structures due to aerodynamic geometrical parameters of roofs and terrain type. In this study, first, the effects of geometrical parameters of roofs and terrain type on the wind pressure distribution based on the data obtained from the existing wind tunnel tests were summarized. Then, the wind loads of full‐scale structures were predicted by CFD, and the efficiency of numerical results was further verified by the available wind tunnel tests on spatial structures. Finally, with comparative analyses of the wind pressure distribution of the roofs predicted by CFD under different cases, the effects of shape ratios, especially rise‐span ratio, height‐span ratio, length‐span ratio, and so on, and terrain type on the wind pressure field of typical spatial structures were presented. It can be beneficial to wind‐resistant design of structures and can be provided as reference for aerodynamic design optimum of span spatial structures.

Fluctuating wind pressure distribution around full-scale cooling towers

At present, external wind pressure description around cooling towers in various loading Codes is based on full-scale measurement data. The data has been collected during 1960s–1990s for hyperbolic cooling towers with heights of about 90m~120m, and focus has been usually on the average wind pressure distribution. In fact, modern cooling towers taller than 165m show sensitivity to wind-induced effects under strong wind excitation. The performance of these flexible structures is closely related to the fluctuating wind action in the atmospheric boundary layer. Modeling of these features is underscored by the difficulty in matching supercritical Reynolds number in boundary layer wind tunnels. Accordingly, it has been difficult to accurately establish a relationship between fluctuating pressures on the surface of a cooling tower to inflow conditions. This has caused a bottleneck for enhancements in the state of wind resistant structural design of larger cooling towers. In view of this difficulty, high Reynolds number flows were simulated in the wind tunnel using scaled model with a combination of surface roughness elements to establish a relationship between the inflow turbulence intensity and pressure fluctuations. This was supplemented by a validation using data from long-term measurements of wind pressure around a 166.68m cooling tower. Wind tunnel experiments were in a general agreement with full-scale observations which offered a relationship between the fluctuating wind pressure distribution and the incoming turbulence intensity at supercritical Reynolds number conditions (Re≥4×10E7).

A revised empirical model and CFD simulations for 3D axisymmetric steady-state flows of downbursts and impinging jets

It has been recognized that downburst wind accounts for a high proportion in annual extreme winds. Although real downburst wind characteristics are complicated and far from fully understood, simplified analytical and empirical models are useful tools in wind-resistant design of structures in areas where extreme winds are dominated by downbursts. This paper aims to establish a simple empirical model with improved accuracy for 3D axisymmetric steady-state velocity fields of downbursts and impinging jets. The original OBV model (Oseguera and Bowles, 1988; Vicroy, 1991) considers the boundary layer effects by shaping functions only and the development of boundary layer is regarded as a linear variation. However, the boundary layer thickness of downbursts and impinging jets grows nonlinearly. The revised model developed in this paper integrates the nonlinear effects by incorporating varying characteristic lengths into the velocity shaping functions and adds external shaping functions for intensity scalars. Besides, based on in-depth analysis of the intrinsic properties of the shaping functions, a simple vertical shaping function of radial velocity and a modification to radial shaping function of radial velocity are proposed to improve the simplicity and accuracy of the model. A detailed 3D CFD simulation study using Reynolds Stress Model (RSM) is performed for the fitting and verification of the revised model. Compared with the original OBV model, the revised model yields more accurate steady-state flow fields especially for radial velocity profiles.

Predictability of unsteady two-dimensional k− ε model on the aerodynamic instabilities of some rectangular prisms

It is well known that a bluff body cross-section exhibits various kinds of aerodynamic instabilities such as vortex-induced vibration, galloping and torsional flutter. Since these cross-sections are used in long-span bridges and tall buildings, it is important to predict their occurrence in wind resistant structural design. In this paper, the authors make a series of comparisons of unsteady wind forces, unsteady pressure distributions and free vibration responses between previously conducted studies and an unsteady two-dimensional k– ε model for rectangular cross-sections with cross-sectional ratios of 2 and 4 in a smooth uniform flow in order to verify computational predictability of aerodynamic instabilities. As a result, the computation successfully predicted the onset velocities and responses of these aerodynamic instabilities for these cross-sectional ratios, which are common to tall buildings and long bridges.

Actual ground-exposure determination and its influences in structural analysis and design

Wind exposure categories are currently used to account for the influences of different ground roughness in wind profile that is fundamentally important to wind-resistant structural analysis and design. Since each classified exposure covers a relatively large spectrum of ground roughness with constant indices such as exponent α, this results in uncertain wind-resistant structural analysis and design for structures in each and every categorized exposure. More importantly, such an uncertainty is not only quantitative but also qualitative in terms of aerodynamic instability assessment and economic loss estimation. This study proposes a method to determine the actual wind exposure and estimates its influences in wind-resistant structural analysis and design. In particular, this paper first provides a review of wind exposure categories and illustrates the shortcomings of its use in structural analysis and design. It then introduces a method to determine the actual ground exposure. The method generates formulae for the actual ground roughness exponent on the basis of measured data from both wind-tunnel and full-scale experiments, of ground roughness-induced wind energy dissipation analysis, as well as of current Chinese and other countries’ loading codes. Through examples of hypothetical and practical engineering projects, this study finally investigates the influences of the actual ground roughness exponent on wind-induced structural responses and economic loss estimation, as well as on wind-resistant structural design.

Tornado Risks and Design Wind Speed

An analytical method of assessing tornado risks is presented whereby the probability of a tornado striking a given point with a maximum wind speed exceeding a prescribed value can be evaluated. An illustrative example of the application of this method to structural design is given. The results indicate that in design of structures with stringent safety requirements, tornadoes present much higher risks than ordinary winds in areas with high tornado frequency. Thus under these circumstances, effects of tornadoes are really the controlling factors in wind-resistant design of structures.