MWFRS Wall Pressure (ASCE 7 Ch. 27)
The lateral pressure the whole building resists, feeding the diaphragm and shear walls.
Example
You enter
- Windward velocity pressure qz (psf) 25.9
- Leeward velocity pressure qh (psf) 25.9
- Windward wall Cp 0.8
- Leeward wall Cp -0.5
- Gust-effect factor G 0.85
- Internal GCpi magnitude 0.18
You get
- Windward wall pressure 22.3 psf (pushing in)
- Leeward wall pressure -15.7 psf (suction)
- Net horizontal design pressure 28.6 psf
Details, formula, and sources
ASCE 7 Chapter 27 MWFRS p = q G Cp - qi (GCpi), G = 0.85 rigid, Cp +0.8 windward / -0.5 leeward. A 25.9 psf building carries +22.3 psf on the windward wall (pushing in) and -15.7 psf on the leeward (suction), for a 28.6 psf net horizontal design pressure - the internal pressure cancels in the net, so the story force is insensitive to enclosure while the walls are not. Enter qz/qh from wind-pressure. Walls only. A design aid, not the engineer of record's stamped design.
p_ww = qz G Cp_ww +/- qh GCpi (worst sign); p_lw = qh G Cp_lw +/- qh GCpi (worst sign); p_net = qz G Cp_ww - qh G Cp_lw (internal cancels).
The ASCE 7-22 Chapter 27 MWFRS design wall pressure p = q G Cp - qi (GCpi), with G = 0.85 (rigid), the wall Cp (+0.8 windward, -0.5 leeward for L/B <= 1), and GCpi = +/-0.18 (enclosed), by name.
ASCE 7 is available through the ASCE Library at ascelibrary.org; the Chapter 27 Directional-Procedure MWFRS provisions are public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: qz_psf, qh_psf, cp_ww, cp_lw, g_f, gcpi, p_ww_psf, p_lw_psf, p_net_psf
- Wall pressure p = q G Cp - qi (GCpi); q = qz windward, qh leeward; G = 0.85 rigidASCE 7-22 27.3.1
- Wall coefficients Cp = +0.8 windward, -0.5 leeward for a building with L/B <= 1ASCE 7-22 Fig. 27.3-1
- Net cancels internal the internal pressure acts equally outward on both walls, so the net horizontal pressure is the external differenceASCE 7-22 Ch. 27 commentary