CHAPTER 8 PRE-ENGINEERED STRUCTURES: BUILDINGS, K-SPANS, TOWERS, AND ANTENNAS
As a Steelworker, pre-engineered metal structures are a special interest to you; you are expected to assemble and disassemble them. Rigid-frame buildings, k-spans, steel towers, and antennas are some of the more commonly used structures, particularly at advanced bases overseas.
All pre-engineered structures, discussed in this text, are commercially designed structures, fabricated by civilian industry to conform to the specifications of the armed forces. The advantage of pre-engineered structures is that they are factory-built and designed to be erected in the shortest possible time. Each pre-engineered structure is shipped as a complete building kit including all the necessary materials and instructions to erect it.
Various types of pre-engineered structures are available from numerous manufacturers, such as Strand Corporation, Pasco, and Butler; however, all are similar because each is built to military specifications. It would not be practical to try and include all of the structures that each company fabricates; therefore, in this manual a description of the basic procedures for erecting and dismantling the 40-foot by 100-foot building is provided as an example.
This chapter introduces you to the design, the structure, and the procedures for the erection of the typical pre-engineered buildings (P.E.B.), the K-spans, the pre-engineered towers, and the antennas.
The basic pre-engineered metal building (fig. 8- 1) is 40 feet wide by 100 feet long. Although the unit length of the building is 100 feet, the length can be increased or decreased in multiples of 20 feet, which are called "20-foot bays." The true building length will be equal to the number of 20-foot bays plus 6 inches; each end bay is 20 feet 3 inches. The building is 14 feet high at the cave and 20 feet 8 inches at the ridge.
Pre-engineered buildings are ideal for use as repair shops or warehouses because they have a large, clear floor area without columns or other obstructions as well as straight sidewalls. This design allows floor-to-ceiling storage of material and wall-to-wall placement of machinery. The column-free interior also permits efficient shop layout and unhindered production flow.
After a building is up, it can be enlarged while in use by "bays", providing additional space under one roof. If desired, buildings can be erected side by side "in multiples." When a building is no longer needed it can be disassembled, stored, or moved to another location and re-erected because only bolted connections are used. There is no field riveting or welding. The rigid frame is strong. It is designed for
Figure 8-1.-Completed 40-foot by 100-foot by 14-foot pre-engineered building.
working loads of 20 pounds per square foot load, plus the dead load, and the load from a 70 mph wind.
The building can be easily modified to varying lengths and purposes by taking out or adding bays or by substituting various foundation and wall sections. A bay is the distance between two column centers or between the end wall and the first column center in from the end wall.
Formulas used to determine the number of bays, frames, and intermediate frames in a building are as follows: Length divided by 20= number of bays
Bays + 1 = total number of frames
Total number of frames -2 = number of intermediate frames PRE-ERECTION WORK
Extensive pre-erection work is required before you start the actual erection of a building. After the building site is located and laid out by the Engineering Aids, it will then be cleared and leveled by Equipment Operators. Batter boards are set up in pairs where each comer of the foundation is located. Builders fabricate the forms for concrete while Steelworkers are cutting, bending, tying, and placing reinforcing steel. If this particular building requires underslab utilities (that is, plumbing and electrical service), the Utilitiesman and Construction Electricians will also be on the jobsite. Last, all underslab work must be completed and pass all Quality Control inspections before concrete is placed and finished.
Most importantly (as far as ease of erection is concerned), before the concrete is placed, templates for the anchor bolts are attached to the forms, and the anchor bolts are inserted through the holes in each.
Next, the forms are tied to make sure they remain vertical. It must be stressed at this point that the proper placement of the anchor bolts is absolutely critical in the erection of a P.E.B. You will only have- a tolerance of plus or minus one eighth of an inch to work with. The threads of the bolts are greased, and the nuts are placed on them to protect the threads. Concrete is poured into the formwork and worked carefully_ into place around these bolts, so they will remain vertical and in place. Finally, according to the plans and specifications, the slab is poured.
While the foundation is being prepared, the crew leader will assign personnel/crews to perrform various types of preliminary work, such as uncrating and inventorying all material on the shipping list, bolting up rigid-frame assemblies, assembling door eaves, and glazing windows. Box 1 contains the erection manual, the drawings, and an inventory list and should be opened first. If all of the preliminary work is done correctly, the assembly and erection of the entire building is accomplished easily and quickly.
All material, except the sheeting, should be uncrated and laid out in an order] y manner, so the parts can be located easily. Do not uncrate the sheeting until you are ready to install it. When opening the crates, use care not to cause any undue damage to the lumber. This is important since the lumber can be used for sawhorses and various other items around the jobsite.
In most situations, after the building foundation has been prepared, building materials should be placed around the building site new the location where they will be used (fig. 8-2). This action provides the greatest accessibility during assembly.
Girts, purlins, cave struts, and brace rods should be equally divided along both sides of the foundation.
Figure 8-2.-Material layout
Panels and miscellaneous parts, which will not be used immediately, should be placed on each side of the foundation on pallets or skids and covered with tarps or a similar type of covering until needed. Parts, making up the rigid-frame assemblies, are laid out ready for assembly and in position for raising.
Care should always be used in unloading materials. Remember that damaged parts will cause delays in getting the job done. To avoid damage, lower the materials to the ground slowly and do not drop them.
Figure 8-3 will help you identify the structural members of the building and their location. Each part has a specific purpose and must be installed in the location called for to ensure a sound structure. NEVER OMIT ANY PART CALLED FOR ON THE DETAILED ERECTION DRAWINGS. Each of the members, parts, and accessories of the building is labeled by stencil, so it is not necessary to guess which one goes where. Refer to the erection plans to find the particular members you need as you work.