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Reliability-based design of infrastructure requires the probabilistic assessment of jointly occurring natural hazards. As infrastructure design practices evolve, it is important that multiple hazards be considered--for example, wind and storm surge in a hurricane, an earthquake generating a tsunami, or strong winds and high temperatures leading to wildfires. These jointly occurring hazards in some cases can be more devastating than a single hazard. This paper describes the assessment of two jointly occurring hazards: wind and ice. For locations in the United States, wind and ice [e.g., freezing rain (FR)] are hazards whose properties are of interest for the design of transmission lines and other energy infrastructure (e.g., wind turbines). Using archived meteorological data from measurement stations in the Midwest, occurrences of icing conditions and the wind speeds that accompany them were identified and input into a simple ice accretion model. Observations from wind speed and ice thickness were fit to probability distributions, and simulations using these distributions were constructed. These simulations were then compared with the observed data and with existing prescribed treatments of these two hazards in design loading guidelines, such as ASCE 7. It is shown that the ASCE 7 method is overly conservative when considering joint hazards. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to discuss issues associated with ASCE 7-10 standard methods for determining wind loads on buildings and other structures that warrant comment, correction, or improvement. The assessment is intended to serve as a resource in the development of a new version of the ASCE 7 standard and to stimulate a wider participation in that development by the structural engineering community. Issues discussed in the paper include: wind speeds in nonhurricane regions; alternative analytical methods for determining wind loads and wind effects on main wind force resisting systems and components and/or cladding; aerodynamic pressure coefficients; pressures on rooftop equipment; component and cladding pressures on arched roofs; and the wind tunnel procedure. It is noted that the ASCE 49 standard essentially covers wind tunnel testing, rather than the wind tunnel procedure, of which wind tunnel testing is only a part. [ABSTRACT FROM AUTHOR]

Over the past decade, numerous field campaigns and laboratory experiments have examined air-sea momentum exchange in the deep ocean. These studies have changed the understanding of drag coefficient behavior in hurricane force winds, with a general consensus that a limiting value is reached. Near the shore, wave conditions are markedly different than in deep water because of wave shoaling and breaking processes, but only very limited data exist to assess drag coefficient behavior. Yet, knowledge of the wind stress in this region is critical for storm surge forecasting, evaluating the low-level wind field across the coastal transition zone, and informing the wind load standard along the hurricane-prone coastline. During Hurricane Ike (2008), a Texas Tech University StickNet platform obtained wind measurements in marine exposure with a fetch across the Houston ship channel. These data were used to estimate drag coefficient dependence on wind speed. Wave conditions in the ship channel and surge level at the StickNet location were simulated using the Simulating Waves Nearshore Model coupled to the Advanced Circulation Model. The simulated waves were indicative of a fetch-limited condition with maximum significant wave heights reaching 1.5 m and peak periods of 4 s. A maximum surge depth of 0.6 m inundated the StickNet. Similar to deep water studies, findings indicate that the drag coefficient reaches a limiting value at wind speeds near hurricane force. However, at wind speeds below hurricane force, the drag coefficient is higher than that of deep water datasets, particularly at the slowest wind speeds. [ABSTRACT FROM AUTHOR]

This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering. [ABSTRACT FROM AUTHOR]

Abstract: Traffic-signal-support structures with cantilevered mast arms are known to exhibit large-amplitude vibrations under certain wind conditions. Previous investigations of the problematic vibrations have primarily focused on the aerodynamics of the signal heads of various configurations. Based on full-scale measurement of a traffic-signal-support structure, the role of the cantilevered mast arm in the aeroelastic vibrations is studied. Contrary to previous reports that the vibrations are due to galloping of the traffic signals, this study reveals that the aeroelastic interaction between the wind and the mast arm is critical in the excitation mechanism of the vibrations. Two types of excitation mechanisms, vortex-shedding at low wind speeds and buffeting at high wind speeds, were identified. [Copyright &y& Elsevier]

Abstract: This paper presents a follow-up study to our earlier work on comparing approaches to determine topographic effects in four major wind load codes. These codes are further evaluated and compared with earlier studies as well as new tests undertaken in the Texas Tech University boundary layer wind tunnel. Wind tunnel experiments with a model scale of 1:1000 were carried out to evaluate the wind speed-up effects of two main types of topography: escarpments and symmetrical ridges. Of particular interest were effects of ground surface roughness and the upwind slope of the two topographic features on wind speed-up and the space limits for speed-up applications around the crest of topography. Experimental results show that the surface roughness has significant speed-up effects for ridges rather than for escarpments. The results also indicate that wind load codes tend to be unconservative in specifying the minimum and maximum upwind slope as well as the spatial extent around the crest for application of speed-up factors. [Copyright &y& Elsevier]

Abstract: This paper describes a study of topographic effects on gust wind speed. Four major wind-loading codes are reviewed and a combined terrain/height and topographic multiplier for each code is derived. Detailed comparisons of topographic effects between codes are presented. Specific examples employing different codes along with meticulous analyses are given to illustrate recommendations for code revisions and for future research. [Copyright &y& Elsevier]