figure 4-44. The scaffold uprights are braced with diagonal members, and the working level is covered with a platform of planks. All bracing must form triangles, and the base of each column requires adequate footing plates for bearing area on the ground or deck. The steel scaffolding is usually erected by placing the two uprights on the ground or deck and inserting the diagonal members. The diagonal members have end fittings that permit rapid locking in position. In tiered scaffolding, figure 4-45, the first tier is set on steel bases on the ground, and a second tier is placed in the same manner on the first tier with the bottom of each upright locked to the top of the lower tier. A third and fourth upright can be placed on the ground level and locked to the first set with diagonal bracing. The scaffolding can be built as high as desired, but high scaffolding should be tied to the main structure. Where necessary, scaffolding can be mounted on casters for easy movement.

Prefabricated scaffolding comes in three categories: light, medium, and heavy duty. Light duty has nominal 2-inch-outside-diameter steel-tubing bearers. Posts are spaced no more than 6- to 10-feet apart. Light-duty scaffolding must be able to support 25-pound-per-square-foot loads.

Medium-duty scaffolding normally uses 2-inch-outside-diameter steel-tubing bearers. Posts should be spaced no more than 5- to 8-feet apart. If 2 1/2-inch-outside-diameter steel-tubing bearers are used, posts are be spaced 6- to 8-feet apart. Medium-duty scaffolding must be able to support 50-pound-per-square-foot loads.

Heavy-duty scaffolding should have bearers of 2-1/2-inch-outside-diameter steel tubing with the posts spaced not more than 6-feet to 6-feet 6-inches apart. This scaffolding must be able to support 75-pound-per-square-foot loads.

To find the load per square foot of a pile of materials on a platform, divide the total weight of the pile by the number of square feet of platform it covers.

BRACKET SCAFFOLDING

The bracket, or carpenter's scaffold (figure 4-46), is built of a triangular wood frame not less than 2- by 3-inch lumber or metal of equivalent strength. Each bracket is attached to the structure in one of four ways: a bolt (at least 5/8 inch) that extends through to the inside of the building wall; a metal stud

Figure 4-44. - Assembling prefabricated independent-pole scaffolding.

Figure 4-45. - Tiered scaffolding.