CHAPTER 2 DRAWINGS AND SPECIFICATIONS

By this time in your Navy career, you have probably worked as a crewmember on various building projects. You probably did your tasks without thinking much about what it takes to lay out structures so they will conform to their location, size, shape, and other building features. In this chapter, you will learn how to extract these types of information from drawings and specifications. You will also be shown how to draw, read, and work from simple shop drawings and sketches.

We provide helpful references throughout the chapter. You are encouraged to study these, as required, for additional information on the topics discussed.

DESIGN OF STRUCTURAL MEMBERS LEARNING OBJECTIVE: Upon completing this section, you should be able to identify the different types of structural members.

From the Builder's standpoint, building designs and construction methods depend on many factors. No two building projects can be treated alike. However, the factors usually considered before a structure is designed are its geographical location and the availability of construction materials.

It is easy to see why geographical location is important to the design of a structure, especially its main parts. When located in a temperate zone, for example, the roof of a structure must be sturdy enough not to collapse under the weight of snow and ice. Also, the foundation walls have to extend below the frost line to guard against the effects of freezing and thawing. In the tropics, a structure should have a low-pitch roof and be built on a concrete slab or have shallow foundation walls.

Likewise, the availability of construction materials can influence the design of a structure. This happens when certain building materials are scarce in a geographical location and the cost of shipping them is prohibitive. In such a case, particularly overseas, the structure is likely to be built with materials purchased locally. In turn, this can affect the way construction materials are used-it means working with foreign drawings and metric units of weights and measures.

By comparing the designs of the two structures shown in figures 2-1 and 2-2, you can see that each is designed according to its function. For example, light-frame construction is usually found in residential buildings where a number of small rooms are desired. Concrete masonry and steel construction is used for warehouse-type facilities where large open spaces are needed. You should study these figures carefully and learn the terminology. Depending on the use of the structure, you may use any combination of structural members.

DEAD AND LIVE LOADS

The main parts of a structure are the load-bearing members. These support and transfer the loads on the structure while remaining equal to each other. The places where members are connected to other members are called joints. The sum total of the load supported by the structural members at a particular instant is equal to the total dead load plus the total live load.

The total dead load is the total weight of the structure, which gradually increases as the structure rises and remains constant once it is completed. The total live load is the total weight of movable objects (such as people, furniture, and bridge traffic) the structure happens to be supporting at a particular instant.

The live loads in a structure are transmitted through the various load-bearing structural members to the ultimate support of the earth. Immediate or direct support for the live loads is first provided by horizontal members. The horizontal members are, in turn, supported by vertical members. Finally, the vertical members are supported by foundations or footings, which are supported by the earth. Look at figure 2-1, which illustrates both horizontal and vertical members of a typical light-frame structure. The weight of the roof material is distributed over the top supporting members and transferred through all joining members to the soil.

Figure 2-1.-Typical light-frame construction.

Figure 2-2.-Typical concrete masonry and steel structure.

The ability of the earth to support a load is called its soil-bearing capacity. This varies considerably with different types of soil. A soil of a given bearing capacity bears a heavier load on a wide foundation or footing than on a narrow one.

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