Structural Steel, Estimating for the Painting Contractor
Article #5 of 7, It is helpful to know something about the description and terminology of the members that make up the different framing systems.
by Len Hijuelos
may not be of particular interest to some contractors, in that, except for industrial facilities, very often the structural steel framing of a building is either concealed from view or is simply left with the shop prime coat. There is, however, enough field painting of steel in the commercial field being performed to warrant inclusion in these articles.
Structural steel drawings, for some reason, seem to be even more of a mystery to many contractors than the architectural drawings. In reality, the format and the structure is the same. That is, the drawings are shown in plan view, usually referred to as “framing plans” (Exhibit One) elevations, sections, and details. Orientation is usually defined by column lines, that is, the columns are listed horizontally and vertically by a series of numbers and letters (Exhibit One).
There are four basic types of steel framing systems:
1. Steel beam construction
2. Steel beams and open web joists construction
3. Steel beam and truss construction
4. Rigid Frame construction.
It is helpful to know something about the description and terminology of the members that make up the different framing systems. Following is a brief description of the more commonly used members and their shapes. Exhibit Two shows the members we are discussing.
1. Steel beams shaped like an “l” are commonly referred to as I (eye) beams. This shape on structural drawings may be referred to as “W”, such as W 16 X 50, which means that the Web of the beam (see Exhibit Two) is 16 inches in depth and weighs 50 pounds per linear foot. Other designations for this particular type of member are M, S, or HP.
2. Channels are “C” or “Z” shaped members commonly used as purlins, girts or part of steel truss. “Z” shapes are generally used in rigid frame construction.
3. Angles are “L” shaped used as girts or part of a truss. Both channels and angles may be used in other support modes such as skylights or equipment framing.
4. Open web joists, also commonly known as bar joists, are open web members which are made up of various shapes such as channels, angles, rods or a combinations thereof. Joists may have various designations such HJ 12-4.5. The letters refer to the type of joist, the first number refers to the depth of the joist, the second number refers to the weight per linear foot.
5. Steel trusses are also open web members designed to carry a heavier load than joists. Normally made of a combination of channels and angles.
6. Rigid frames are a system in themselves, lightweight and originally designed for metal buildings. The frames itself is both beam and column in somewhat of a tapered “l” shape. “Z” channels are usually used as roof purlins, and angles or channels or usually used as girts to which the siding is fastened.
7. Metal roof decks (the underside of the roof) and siding comes in different configurations, from corrugated to pan, which can vary substantially depending on the configuration.
There are several different approaches used to arrive at prices for painting steel, such as square feet of floor space, by bays, by tonnage, etc. Any of these are inherently risky, the safest and most accurate method is to follow the same basic format used as in taking off any other part of the building, that is piece by piece. Again, a slow process, but accurate. Using the framing and section drawing shown in Exhibit One, using this method, we would arrive at the following quantities:
Roof Deck 6' x 20' = 720 square feet
W12 x 27 beams 2 @ 20'
2 @ 36' = 112 linear feet
HJ 12-4.5 joists 17 @ 20' = 340 linear feet
W12 x 40 columns 12 @ 20' = 240 linear feet
These numbers then have to be converted to square feet for pricing. The PDCA Estimating Guide provides excellent tables for the conversion of structural steel members. There are no tables provided for open web joists, the accepted practice is to use the length of the joist multiplied by the depth of the joist, doubled. Using the PDCA tables, these are the quantities we would use for pricing:
Roof Deck 36' x 20' x 1.5 = 1,080 square feet
W 12 x 27 beams 112 LF x 4.12 = 461 square feet
HJ 12 joists 340 LF x 2 = 680 square feet
W 12 x 40 columns 240 LF x 4.61 = 1,106 square feet
Total 3,326 square feet
The example we used in this article is obviously very simple, but by consistently using the same type of format, more complex structures become easier to deal with.
The next articles will address pricing structures.