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Sunday, 20 October 2013

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Mechanical Walkin Interviews - 10:11
Part 2

What Public Domain Documents are Available for Further Study?

A building project may be broadly divided into two major phases, the design phase and the construction phase. First, the architect conceives the building, ship, or aircraft in his or her mind, then sets down the concept on paper in the form of presentation drawings, which are usually drawn in perspective by using pictorial drawing techniques. Next, the architect and the engineer work together to decide upon materials and construction methods. The engineer determines the loads the supporting structural members will carry and the strength each member must have to bear the loads. He or she also designs the mechanical systems of the structure, such as heating, lighting, and plumbing systems. The end result is the preparation of architectural and engineering design sketches that will guide the draftsmen who prepare the construction drawings. These construction drawings, plus the specifications, are the chief sources of information for the supervisors and craftsmen who carry out the construction. 

General plans contain information on the size, material, and makeup of all main members of the structure, their relative position and method of connection, as well as the attachment of other parts of the structure. The number of general plan drawings supplied is determined by such factors as the size and nature of the structure, and the complexity of operations. General plans consist of plan views, elevations, and sections of the structure and its various parts. The amount of information required determines the number and location of sections and elevations.
Fabrication drawings, or shop drawings, contain necessary information on the size, shape, material, and provisions for connections and attachments for each member. This information is in enough detail to permit ordering the material for the member concerned and its fabrication in the shop or yard. Component parts of the members are shown in the fabrication drawing, as well as dimensions and assembly marks.
Erection drawings, or erection diagrams, show the location and position of the various members in the finished structure. They are especially useful to personnel performing the erection in the field. For instance, the erection drawings supply the approximate weight of heavy pieces, the number of pieces, and other helpful data.
The term falsework refers to temporary supports of timber or steel that sometimes are required in the erection of difficult or important structures. When falsework is required on an elaborate scale, drawings similar to the general and detail drawings already described may be provided to guide construction. For simple falsework, field sketches may be all that is needed.
Construction drawings are those in which as much construction information as possible is presented graphically, or by means of pictures. Most construction drawings consist of orthographic views. General drawings consist of plans and elevations drawn on relatively small scale. Detail drawings consist of sections and details drawn on a relatively large scale; we will discuss detail drawing in greater depth later in this chapter. A plan view is a view of an object or area as it would appear if projected onto a horizontal plane passed through or held above the object area. The most common construction plans are plot plans (also called site plans), foundation plans, floor plans, and framing plans. We will discuss each of them in the following paragraphs. A plot plan shows the contours, boundaries, roads, utilities, trees, structures, and other significant physical features about structures on their sites. The locations of the proposed structures are indicated by appropriate outlines or floor plans. As an example, a plot may locate the comers of a proposed structure at a given distance from a reference or base line. Since the reference or base line can be located at the site, the plot plan provides essential data for those who will lay out the building lines. The plot also can have contour lines that show the elevations of existing and proposed earth surfaces, and can provide essential data for the graders and excavators.  A foundation plan (fig. 7-9) is a plan view of a structure projected on a imaginary horizontal plane passing through at the level of the tops of the foundations. Framing plans show the dimension numbers and arrangement of structural members in wood-frame construction.  A wall framing plan provides information for the studs, corner posts, bracing, sills, plates, and other structural members in the walls. Since it is a view on a vertical plane, a wall framing plan is not a plan in the strict technical sense. However, the practice of calling it a plan has become a general custom. A roof framing plan gives similar information with regard to the rafters, ridge, purlins, and other structural members in the roof. A utility plan is a floor plan that shows the layout of heating, electrical, plumbing, or other utility systems. Utility plans are used primarily by the ratings responsible for the utilities, and are equally important to the builder. Most utility installations require that openings be left in walls, floors, and roofs for the admission or installation of utility features. The builder who is placing a concrete foundation wall must study the utility plans to determine the number, sizes, and locations of openings he or she must leave for utilities.
Elevations show the front, rear, and sides of a structure projected on vertical planes parallel to the planes of the sides. Elevations give you a number of important vertical dimensions, such as the perpendicular distance from the finish floor to the top of the rafter plate and from the finish floor to the tops of door and window finished openings. They also show the locations and characters of doors and windows. However, the dimensions of window sashes and dimensions and character of lintels are usually set forth in a window schedule.
A section view is a view of a cross section. The term is confined to views of cross sections cut by vertical planes. A floor plan or foundation plan, cut by a horizontal plane, is a section as well as a plan view, but it is seldom called a section. The most important sections are the wall sections.  Starting at the bottom, you learn that the footing will be concrete, 1 foot 8 inches wide and 10 inches high. The vertical distance to the bottom of the footing below FIN GRADE (finished grade, or the level of the finished earth surface around the house) varies-meaning that it will depend on the soil-bearing capacity at the particular site. The foundation wall will consist of 12-inch concrete masonry units (CMU) centered on the footing. Twelve-inch blocks will extend up to an unspecified distance below grade, where a 4-inch brick facing (dimension indicated in the mid-wall section) begins. Above the line of the bottom of the facing, it is obvious that 8-inch instead of 12-inch blocks will be used in the foundation wall. The building wall above grade will consist of a 4-inch brick facing tier, backed by a backing tier of 4-inch cinder blocks. The floor joists consist of 2 by 8s placed 16 inches OC and will be anchored on 2 by 4 sills bolted on the top of the foundation wall. Every third joist will be additionally secured by a 2 by 1/4 strap anchor embedded in the cinder block backing tier of the building wall.  Flooring will consist of a wood finished floor on a wood subfloor. Inside walls will be finished with plaster on lath (except on masonry, which would be with or without lath as 7-16 directed). A minimum of 2 vertical feet of crawl space will extend below the bottoms of the floor joists. The middle wall section gives similar information for a similar building constructed with wood-frame walls and a double-hung window. The third wall section gives you similar information for a similar building constructed with a steel frame, a casement window, and a concrete floor finished with asphalt tile.
Detail drawings are on a larger scale than general drawings, and they show features not appearing at all, or appearing on too small a scale, in general drawings. The wall sections are details as well as sections, since they are drawn on a considerably larger scale than the plans and elevations. Framing details at doors, windows, and cornices, which are the most common types of details, are nearly always shown in sections. Details are included whenever the information given in the plans, elevations, and wall sections is not sufficiently “detailed” to guide the craftsmen on the job.
The construction drawings contain as much information about a structure as can be presented graphically. A lot of information can be presented this way, but there is more information that the construction craftsman must have that is not adaptable to the graphic form of presentation. Information of this kind includes quality criteria for materials (for example, maximum amounts of aggregate per sack of cement), specified standards of workmanship, prescribed construction methods, and so on. When there is a discrepancy between the drawings and the specifications, always use the specifications as authority. This kind of information is presented in a list of written specifications, familiarly known as the specs. A list of specifications usually begins with a section on general conditions. This section starts with a general description of the building, including type of foundation, types of windows, character of framing, utilities to be installed, and so on. A list of definitions of terms used in the specs comes next, followed by certain routine declarations of responsibility and certain conditions to be maintained on the job.
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