However, the roof still needs to be designed appropriately assuming the solar panels are removed or not present. The wind loads for solar panels do not have to be applied simultaneously with the component and cladding wind loads for the roof. See ASCE 7-16 for important details not included here. Example of ASCE 7-16 Figure 29.4-7 Excerpt for rooftop solar panel design wind loads. Further testing is currently underway for open structures, and these results will hopefully be included in future editions of the Standard.įigure 5. Thus, these provisions are not applicable to open structures because the flow of the wind over the roof of enclosed structures and open structures varies significantly.
Each of these provisions was developed from wind tunnel testing for enclosed structures. One method applies specifically to a low-sloped roof (less than 7 degrees) ( Figure 5) and the second method applies to any roof slope where solar panels are installed parallel to the roof. There are two methods provided in the new Standard. Previously, designers commonly attempted to use a combination of the component and cladding provisions and other provisions in the Standard to determine these loads, often resulting in unconservative designs. These provisions give guidance to the users of ASCE 7 that has been missing in the past. New additions to the Standard are provisions for determining wind loads on solar panels on buildings. This means that if a cooling tower is located on an administration building (Risk Category II) of a hospital but serves the surgery building (Risk Category IV) of the hospital, the wind loads determined for the cooling tower would be based on the Risk Category IV wind speed map. One new clarification is that the basic design wind speed for the determination of the wind loads on this equipment needs to correspond to the Risk Category of the building or facility to which the equipment provides a necessary service. This limitation was removed in ASCE 7-16, and thus the provisions apply to rooftop equipment on buildings of all heights. The provisions contained within ASCE 7-10 for determining the wind loads on rooftop equipment on buildings is limited to buildings with a mean roof height h ≤ 60 feet. Table 26.9-1 – ASCE 7-16 ground elevation factor. For example, in Denver, CO, the “Mile High City,” the ground elevation factor, K e, is 0.82 which translates to an 18% reduction in design wind pressures. The adjustment can be substantial for locations that are located at higher elevations. This factor provides a simple and convenient way to adjust the velocity pressure in the wind pressure calculations for the reduced mass density of air at the building site. This reduction was provided in the Commentary of previous editions of the Standard however, it is being brought into the body of the Standard to facilitate its use. The new K e factor adjusts the velocity pressure to account for the reduced mass density of air as height above sea level increases (see Table).
Not many users of the Standard utilize the Serviceability Wind Speed Maps contained in the Commentary of Appendix C, but these four maps (10, 25, 50 & 100-year MRI) are updated to be consistent with the new wind speed maps in the body of the Standard. Example of ASCE 7-16 Risk Category II Hawaii effective wind speed map. These new maps better represent the regional variations in the extreme wind climate across the United States.įigure 4. To meet the requirements of Chapter 1 of the Standard, a new map is added for Risk Category IV buildings and other structures ( Figure 3). The most significant reduction in wind speeds occurs in the Western states, which decreased approximately 15% from ASCE 7-10 ( Figures 1 and 2). The wind speeds in the northern Great Plains region remain approximately the same as in ASCE 7-10. Consequently, wind speeds generally decrease across the country, except along the hurricane coastline from Texas to North Carolina. Also, a small revision was made to the hurricane wind speeds in the Northeast region of the country based upon updated hurricane models. This separation was between thunderstorm and non-thunderstorm events. This study focused on the non-hurricane areas of the country and used a new procedure that separated the available data by windstorm type and accounted for changes in the site exposure characteristics at the recording anemometers. Basic Wind Speed MapsĪn updated study of the wind data from over 1,000 weather recording stations across the country was completed during this last cycle. See ACSE 7-10 for important details not included here. Example of ASCE 7-10 Risk Category II Basic Wind Speed Map.