13-52-310 Minimum wind design pressures – Buildings and portions thereof and other structures.

   (a)   Buildings and Portions Thereof. All buildings, cladding and components shall be designed and constructed to resist a horizontal wind pressure on all surfaces exposed to the wind, allowing for wind in any direction, in accordance with Table 13-52-310 as set out in this section. Other structures shall be designed and constructed to comply with the applicable provisions of this section. Reductions in wind pressure due to neighboring structures and terrain shall not be considered. The height is to be measured above the average level of the ground adjacent to the building or structure. Wind pressures shall vary linearly between pressures established in Table 13-52-310 as follows:

Table 13-52-310
Minimum Design Wind Pressures – Buildings and Portions Thereof

Height – Feet	Column (A) Main Wind Force Resisting System Wind Pressure (pounds per square foot)	Column (B) Wind Pressure – Components/Cladding (pounds per square foot)
		Other Than Corner	Corner
200 or less	20	25	30
300	21	27	32
400	25	32	38
500	28	35	41
600	31	39	45
700	33	42	49
800	36	45	54
900	39	49	58
1,000	42	53	63

 

   Notes For Table 13-52-310:

   1.   The value set forth in Column (A) shall apply to the structural wind-force resisting system. Examples include two or three dimensional rigid and braced frames, roof and floor diaphragms, trusses and shear walls.

   2.   The values set forth in Column (B) shall apply to components and cladding of enclosed structures that are either directly loaded by the wind or receive wind load as relatively close locations and that transfer these loads to the main wind-force resisting system. Examples include curtain walls, exterior glass windows and panels, purlins, girts and studs. The pressures indicated may act inward or outward.

   3.   The corner pressures set forth in Column (B) shall apply at each corner of the building for a distance equal to ten percent of the least building width or 0.50 height above grade, whichever is smaller.

   4.   The pressure exposure category distribution for design of components and cladding in Column (B) are similar to A.N.S.I. A58.1-1982 Figure 3, pages 38 and 39 and Figure 4, page 40. “Other than Corners” refers to Zone 4, Figure 3 and to Zone 5, Figure 4. “Corner” refers to Zone 5, Figure 3 and to Zones 6 and 7b combined in Figure 4. The pressures are considered acting toward and away from the surfaces and may signify plus and minus signs, respectively.

   (b)   Roof Structures Over Enclosed Building Or Other Structures. All main roof framing structures shall be designed and constructed for the following pressures:

      1.   Flat roofs: an outward pressure acting normal to the surface equal to 75 percent of those established in Table 13-52-310, Column (A) for the corresponding mean height of the roof and applied to the entire roof area.

      2.   Sloped roof, slope equal to or less than 30 degrees: an outward pressure acting normal to the surface equal to 100 percent on the windward side and 75 percent on the leeward side of those established in Table 13-52-310, Column (A) for the corresponding mean height of the roof.

      3.   Sloped roofs, slope greater than 30 degrees: an inward pressure acting normal to the surface equal to 100 percent on the windward side and an outward pressure acting normal to the surface equal to 75 percent on the leeward side of those established in Table 13-52-310, Column (A) for the corresponding mean height of the roof.

      4.   Overhanging eaves and cornices: an upward or downward pressure acting normal to the surface equal to 200 percent of those established in Table 13-52-310, as set out in this section, column (A) for the corresponding height of the eave or cornice.

      5.   Roofing sheathing and membranes: an outward pressure acting normal to the surface equal to the pressures set forth in Section 13-52-310 b.1, b.2 and b.3 except within an area at the edge of the roof equal to ten percent of the width of the structure parallel to the wind direction being considered, outward pressure equal to 200 percent of those established in Table 13-52-310, Column (A) as set out in this section, for the corresponding mean height of the roof.

   (c)   Monoslope Roofs Over Unenclosed Buildings.

      1.   Slope less than ten degrees: shall be designed and constructed to withstand an inward or outward pressure acting normal to the surface equal to 100 percent of those established in Table 13-52-310, Column (A).

      2.   Slope greater than ten degrees shall be designed and constructed to withstand an inward or outward pressure acting normal to the surface equal to 150 percent of those established in Table 13-52-310, Column (A).

   (d)   Projecting Elements. All companies, balconies and parapets shall be designed and constructed to withstand wind pressures in any direction equal to 200 percent of those established in Table 13-52-310, Column (A) as set out in this section.

   (e)   Flagpoles. All flagpoles shall be designed to resist a wind pressure of one and one-half pounds per square foot of flag area applied at the top of the pole and an additional pressure of 50 pounds per square foot on the vertical projection of the pole.

   (f)   Signs, Tanks, Towers and Chimneys.

      1.   Signs. All signs and outdoor display structures shall be designed and constructed to withstand wind pressure applied to the projected exposed area allowing for wind in any direction in accordance with the following:

         (a)   Solid Signs. 30 psf up to a height of 100 feet. Above 100 feet, add 0.025 lb. per foot of additional height.

         (b)   Open Signs. increase wind pressure established for solid signs by one-third. Signs in which the projected area exposed to wind consists of 70 percent or more of the gross area as determined by the over-all dimensions shall be classed as solid signs; those in which the projected exposed area is derived from open letters, figures, strips and structural framing members, the aggregate total area of which is less than 70 percent of the gross area so determined, shall be classed as open signs.

      2.   Tanks, Solid Towers and Chimneys. Tanks, solid towers, chimneys and similar structures shall be designed and constructed to withstand pressures established in Table 13-52-310, Column (A) as set out in this section applied to the projected area multiplied by the following factors:

 

Shape in Horizontal Cross Section	Factor
Square or rectangular
H/D less than 7	1.0
H/D greater than 7	1.4
Polygonal – all values of H/D	1.0
Round – all values of H/D	0.7
Where:    H = height of structure    D = diameter of least horizontal dimension

 

      3.   Antenna towers and antenna supporting structures shall comply with the requirements of this Code and with “Structural Standard for Steel Antenna Towers and Antenna Supporting Structures” EIA Standard RS-222-C March 1976, published by Electronic Industries Association Engineering Department, Washington, D.C.

      4.   The increase in the basic allowable unit stresses permitted for wind loads per Section 13-52-300 c, shall not apply to structures considered in Section 13-52-310 f.

(Prior code § 68-4.2; Added Coun. J. 11-29-89, p. 8387)