ASTM E1886-19

5.1 Structural design of exterior windows, curtain walls, doors, and impact protective systems is typically based on positive and negative design pressure(s). Design pressures based on wind speeds with a mean recurrence interval (usually 25 to 100 years) that relates to desired levels of structural reliability and are appropriate for the type and importance of the building 5.1.1 Many factors affect the actual loading on building surfaces during a severe windstorm, including varying wind direction, duration of the wind event, height above ground, building shape, terrain, surrounding structures, and other factors 5.1.2 Windows, doors, and curtain walls are building envelope components often subject to damage in windstorms. The damage caused by windborne debris during windstorms goes beyond failure of building envelope components such as windows, doors, and curtain walls. Breaching of the envelope exposes a building's contents to the damaging effects of continued wind and rain 5.1.3 The commentary to ANSI/ASCE 7-93 discusses internal pressure coefficients and the increased value to be used in designing envelopes with “openings” as follows:

Thus, there are two options in designing buildings for windstorms with windborne debris: buildings designed with “openings” (partially enclosed buildings) to withstand the higher pressures noted in the commentary to ANSI/ASCE 7-93 and, alternatively, building envelope components designed so they are not likely to be breached in a windstorm when impacted by windborne debris. The latter approach reduces the likelihood of exposing the building contents to the weather.

5.2 In this test method, a test specimen is first subjected to specified missile impact(s) followed by the application of a specified number of cycles of positive and negative static pressure differential (8). The assembly must satisfy the pass/fail criteria established by the specifying authority, which may allow damage such as deformation, deflection, or glass breakage.

5.3 The windborne debris generated during a severe windstorm varies greatly, depending upon windspeed, height above the ground, terrain, surrounding structures, and other sources of debris 5.4 To determine design wind loads, averaged wind speeds are translated into air pressure differences. Superimposed on the averaged winds are gusts whose aggregation, for short periods of time (ranging from fractions of seconds to a few seconds) may move at considerably higher speeds than the averaged winds. Wind pressures related to building design, wind intensity versus duration, frequency of occurrence, and other factors are considered.