Analysis of hurricane pressure cycling following missile impact for residential structures

The research reported herein describes the approach used in the first ever direct simulation of the pressure cycles expected to be experienced by windows after being impacted by wind-borne debris in a hurricane. The approach uses wind tunnel measured time histories of pressures obtained from the Boundary Layer Wind Tunnel at the University of Western Ontario, coupled with a wind-borne debris impact model and simulated hurricanes. The modeling approach inherently takes into account the effects of changes in wind direction and wind speed as a hurricane passes by a site. The effect of storm duration is included through the use of very long time series of wind tunnel pressures coupled with the modeled hurricane wind speeds and directions. With information on the debris impact time within a given storm, we couple the simulated hurricane wind speeds with the wind tunnel measured time histories of wind induced pressures to derive the characteristics of the pressures experienced by a window after impact. Using these time series of pressures referenced to the design pressure as defined in ASCE-7-98, we performed an up-crossing analyses and pressure range analyses in order to develop the information needed for possible impact and pressure cycling test protocols. sults of the pressure cycle counting following impact clearly indicate that the requirements of the 1994 edition of the South Florida Building Code (SFBC) are extremely conservative with respect to the negative pressure cycle requirements, irrespective of the target design reliability and impact momentum required for glass breakage. The results also show that the number of pressure cycles expected to be experienced by a structure located in Miami, following the impact of debris with a momentum equal to that of the 9 lb two-by-four impacting at 50 fps is significantly less than required in the SFBC. The results indicate that the impact and pressure cycle requirements for windows and doors:(i) vary with location and the desired level of reliability. require impacting a window with a much lower momentum than currently specified in the SFBC, followed with the appropriate pressure cycling test, and finally impacting the window with a larger missile, with no pressure cycle tests after this final impact. protocol taking into account these two features would be much more realistic than the current SFBC requirements. The test would require the first impact to be consistent with the more common smaller debris generated in a hurricane, but would still provide for a system that provides protection from the relatively infrequent large missile impacts.