Wind Components and Cladding Pressure (ASCE 7 Ch. 30)
The local envelope pressure wind-pressure cannot make.
Example
You enter
- Basic wind speed V (mph) 115
- Exposure coefficient Kz (mean roof ht) 0.9
- External coefficient GCp (signed, zone) -1.8
- Topographic factor Kzt 1
- Directionality factor Kd 0.85
- Ground-elevation factor Ke 1
- Internal GCpi magnitude 0.18
You get
- Velocity pressure qh 25.9 psf
- P a (psf) -51.3
- Governing design pressure -51.3 psf
Details, formula, and sources
ASCE 7 Chapter 30 C&C design pressure p = qh [(GCp) - (GCpi)], where qh = 0.00256 Kz Kzt Kd Ke V^2 and GCpi = +/-0.18 (enclosed). A 115 mph Exposure C building draws qh 25.9 psf, and a roof corner (Zone 3, GCp = -1.8) sees -51.3 psf of suction - roughly double the field, the number a corner fastener and its spacing are designed for. GCp comes from the Ch. 30 zone figures (enter it). Local cladding pressure, not the whole-building MWFRS. A design aid, not the engineer of record's stamped design.
qh = 0.00256 Kz Kzt Kd Ke V^2; p_a = qh (GCp - GCpi); p_b = qh (GCp + GCpi); governing = the larger magnitude of p_a, p_b.
The ASCE 7-22 Chapter 30 components-and-cladding design pressure p = qh [(GCp) - (GCpi)], with the velocity pressure qh = 0.00256 Kz Kzt Kd Ke V^2 (Kd = 0.85, V in mph) and GCpi = +/-0.18 for an enclosed building, by name; GCp is read from the Chapter 30 zone figures.
ASCE 7 is available through the ASCE Library at ascelibrary.org; the Chapter 30 C&C provisions and the 0.00256 velocity-pressure constant are public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: v_mph, kz, gcp, kzt, kd, ke, gcpi, qh_psf, p_a_psf, p_gov_psf
- Velocity pressure qh = 0.00256 Kz Kzt Kd Ke V^2 at mean roof height (Kd = 0.85, V in mph)ASCE 7-22 26.10
- Design pressure p = qh (GCp - GCpi); both internal signs evaluated, the larger magnitude governsASCE 7-22 30.3
- GCp read from the Chapter 30 zone figures by roof/wall zone and effective wind area (entered)ASCE 7-22 Ch. 30 figures