Design wind pressure, large openings, 100 yr

Assumptions (not all data are given). Basic wind speed is not stated, so $V_b = 47$ m/s is assumed. Building: dimension over 50 m, so Class C; height 15 m. Terrain: open with scattered obstructions 1.5 to 10 m high, so Category 2. Design life 100 years. Large openings (more than 20% of wall area).

Step 1: Design wind speed

• $k_1$: for a life of 100 years and $V_b = 47$ m/s, Table 1 gives $k_1 = 1.07$.
• $k_2$: Category 2, Class C, at 15 m: interpolating between 10 m (0.93) and 15 m (0.97): $k_2 = 0.970$, i.e. $0.97$ (Table 2).
• $k_3$ (Appendix C): hill height $Z = 160$ m, slope 1 vertical to 3 horizontal, $\theta = \tan^{-1}(1/3) = 18.4^\circ > 17^\circ$, so $C = 0.36$ and $L_e = Z/0.3 = 533$ m. The building is on the downward (leeward) slope at 100 m above the base, i.e. 60 m below the crest, so the horizontal distance from the crest is $X = 60\times3 = 180$ m downwind: $X/L_e = 0.337$; $H/L_e = 15/533 = 0.028$. From Fig. 15, $s \approx 0.65$ (read from the chart; approximate). $k_3 = 1 + Cs = 1 + 0.36\times0.65 = 1.234$ (within the limit 1.36).

$$\begin{aligned} V_z &= V_bk_1k_2k_3 = 47\times1.07\times0.97\times1.234 = 60.2\ \text{m/s} \\ p_z &= 0.6V_z^2 = 0.6\times60.2^2 = 2174\ \text{N/m}^2 = 2.17\ \text{kN/m}^2 \end{aligned}$$

Step 2: Net pressure with large openings

For openings above 20% of the wall area, $C_{pi} = \pm0.7$ (cl. 6.2.3.2). Taking the external coefficients of a rectangular clad building (Table 4, $h/w < 1/2$, wind 0°): windward wall $C_{pe} = +0.7$, leeward wall $-0.5$.

Answer

Design wind speed $V_z = 60.2$ m/s; design wind pressure $p_z \approx 2174$ N/m² ($\approx 2.17$ kN/m²). The largest net pressure on the walls is $1.4p_z \approx 3.04$ kN/m² (inward on the windward wall with the internal suction case) and the largest net suction is $1.2p_z \approx 2.61$ kN/m².