Wind Hazard Risk Assessment and Management for Structures

Chapter 2. Structural Components and Wind Directionality 26
failure at a single point in time, t ∗ , within the time domain [0, tL]. (This approach is in a
sense compatible with the characteristics of wind loads on low-rise structures, when dynamic
response amplification is insignificant.) The method approximates the probability of failure
as:
Pf ≈ P ∗ f = Prob{S(t∗ ) − R < 0}. (2.15)
The above equation would be equivalent to equation (2.13) if S(t ∗ ) = Smax. However,
finding t ∗ such that S(t ∗ ) = Smax requires evaluation of S(t) across the time domain [0, tL],
which is equivalent to the time-stepping method described above. To simplify the problem,
the effect of wind direction is assumed to be negligible so that t ∗ is selected as the time
point at which the wind speed is maximum, e.g. V (t ∗ ) = maxt V (t). Therefore,
2.4 Numerical Examples
2.4.1 Setup
Smax ≈ S ∗ = 1
2 ρV (t∗ ) 2 Cp(θ(t ∗ ) − γ). (2.16)
This section focuses on the building envelope of low-rise residences, which is the most vul-
nerable building component in tropical cyclones under wind pressure (National Institute of
Standards and Technology, 2006b). Four pressure coefficients of building envelope compo-
nents are selected to illustrate the difference in results between the two analysis methods;
these coefficients relate to:
1. Positive Wall Pressure;
2. Negative Wall Pressure;
3. External Pressure at Roof Corner;
4. External Pressure at Near-Edge Roof.