Wind Hazard Risk Assessment and Management for Structures

Chapter 2. Structural Components and Wind Directionality 14
time within individual strong-wind events.
Currently, two methods are commonly used in different tropical cyclone damage esti-
mation models. The first considers the effect of varying wind directionality during a strong
wind event and the second does not. In the first, the time-stepping method, employed in
damage estimation models such as the HAZUS-MH model, the structural loading is eval-
uated at a series of time steps, e.g. at 10-minute interval, for both wind speed and wind
direction (Vickery et al., 2006a,b). The second method, the point-in-time method, used
in other models, including the Florida Public Hurricane Loss Projection Model, evaluates
the wind load only at the maximum wind speed during the tropical cyclone event (and
the corresponding wind direction at the maximum wind speed) (Gurley et al., 2006; Li
and Ellingwood, 2006). If the two methods are applied to the same quasi-static wind load
model (used by both HAZUS-MH and the Florida Public Hurricane Loss Projection Model,
since fatigue and dynamic loading are generally not considered), the difference in results is
attributable to the variation in wind direction over time.
The flowchart in Figure 2.1 summarizes the simplified loss estimation framework adopted
in this study. In what follows, we examine and quantify the effect of varying wind direc-
tionality on low-rise structural damage estimation, illustrating the methodology through
numerical examples. In the first part of this chapter, we present an efficient probabilistic
model to generate wind speed and wind direction time series in tropical cyclones. These
are used, in the second part, to calculate wind loads and analyze the reliability of some
representative structural components of low-rise structures.