(1) General. All signs shall be designed and constructed to resist wind and seismic forces as specified in this chapter and the International Building Code (IBC). All bracing systems shall be designed and constructed to transfer lateral forces to the foundations. For signs on buildings, the dead and lateral loads shall be transmitted through the structural frame of the building to the ground in such a manner as not to overstress any of the elements thereof.
The overturning moment produced from lateral forces shall in no case exceed two-thirds of the dead-load resisting moment. Uplift due to overturning shall be adequately resisted by proper anchorage to the ground or to the structural frame of the building. The weight of earth superimposed over footings may be used in determining the dead-load resisting moment. Such earth shall be carefully placed and thoroughly compacted.
(2) Wind Loads. For the purpose of design, wind pressure shall be taken upon the gross area of the vertical projection of all signs at not less than 15 pounds per square foot for those portions less than 50 feet above the ground.
In calculating wind pressure on cylindrical or spherical signs or sign structures, this pressure shall be assured to act on six-tenths of the projected area. In all open frame signs, the area used in computing wind pressure shall be one and one-half times the net area of the framing members exposed to the wind.
(3) Seismic Loads. Signs and sign structures shall be designed and constructed to resist seismic forces as specified in the building code.
(4) Combined Loads. Wind and seismic loads need not be combined in the design of signs or sign structures; only that loading producing the larger stresses need be used.
Vertical design loads shall be assumed to be acting simultaneously with the wind or seismic loads.
(5) Allowable Stresses. The design of wood, concrete, or steel members shall conform to the requirements of the building code. Loads, both vertical and horizontal, exerted on the soil shall not produce stresses exceeding those specified in the building code.
The working stresses for wind or seismic loads combined with dead loads may be increased as specified in the building code.
The working stresses of wire rope and its fastenings shall not exceed 25 percent of the ultimate strength of the rope or fasteners.