Cooling, Evaporative. Cooling effect produced by evaporation of water, the required heat for the process being taken from the air. (This method is widely used in dry climates with low wet-bulb temperatures.) Cooling, Sensible. Cooling of a unit volume of air by a reduction in temperature only. Cooling Effect, Total. The difference in total heat in an airstream entering and leaving a refrigerant evaporator or cooling coil. Cooling Tower. A mechanical device used to cool water by evaporation in the outside air. Towers may be atmospheric or induced- or powered-draft type. Cooling Unit, Self-Contained. A complete air-conditioning assembly consisting of a compressor, evaporator, condenser, fan motor, and air filter ready for plugin to an electric power supply. Damper. A plate-type device used to regulate flow of air or gas in a pipe or duct. Defrosting. A process used for removing ice from a refrigerant coil. Degree Day. The product of 1 day (24 hr) and the number of degrees Fahrenheit the daily mean temperature is below 65
F. It is frequently used to determine heating-load efficiency and fuel consumption. Dehumidification. In air conditioning, the removal of water vapor from supply air by condensation of water vapor on the cold surface of a cooling coil. Diffuser (Register). Outlet for supply air into a space or zone. See also Grille

A common application of wall-bearing construction may be found in many single-family homes. A steel beam, usually 8 or 10 in deep, is used to carry the interior walls and floor loads across the basement with no intermediate supports, the ends of the beam being supported on the foundation walls. The relatively shallow beam depth affords maximum headroom for the span. In some cases, the spans may be so large that an intermediate support becomes necessary to minimize deflection. Usually a steel pipe column serves this purpose. Another example of wall-bearing framing is the member used to support masonry over windows, doors, and other openings in a wall. Such members, called lintels, may be a steel angle section (commonly used for brick walls in residences) FIGURE 7.6 Lintels supporting masonry. or, on longer spans and for heavier walls, a fabricated assembly. A variety of frequently used types is shown in Fig. 7.6. In types b, c, and e, a continuous plate is used to close the bottom, or soffit, of the lintel, and to join the load-carrying beams and channels into a single shipping unit. The gap between the toes of the channel flanges in type d may be covered by a door frame or window trim, to be installed later. Pipe and bolt separators are used to hold the two channels together to form a single member for handling. Bearing Plates. Because of low allowable pressures on masonry, bearing plates (sometimes called masonry plates) are usually required under the ends of all beams that rest on masonry walls, as illustrated in Fig. 7.7. Even when the pressure on the wall under a member is such that an area no greater than the contact portion of the member itself is required, wall plates are sometimes prescribed, if the member is of such weight that it must be set by the steel erector. The plates, shipped loose and in advance of steel erection, are then set by the mason to provide a satisfactory seat at the proper elevation. Anchors. The beams are usually anchored to the masonry. Government anchors, as illustrated in Fig. 7.7, are generally preferred. Nonresidential Uses. Another common application for the wall-bearing system is in one-story commercial and light industrial-type construction. The masonry side walls support the roof system, which may be rolled beams, open-web joists, or light FIGURE 7.7 Wall-bearing beam. trusses. Clear spans of moderate size are usually economical, but for longer spans (probably over 40 ft), wall thickness and size of buttresses (pilasters) must be built to certain specified minimum proportions commensurate with the spana requirement of building codes to assure stability. Therefore, the economical aspect should be carefully investigated. It may cost less to introduce steel columns and keep wall size to the minimum permissable. On the other hand, it may be feasible to reduce the span by introducing intermediate columns and still retain the wall-bearing system for the outer end reactions. Planning for Erection. One disadvantage of wall-bearing construction needs emphasizing: Before steel can be set by the ironworkers, the masonry must be built up to the proper elevation to receive it. When these elevations vary, as is the case at the end of a pitched or arched roof, then it may be necessary to proceed in alternate stages, progress of erection being interrupted by the work that must be performed by the masons, and vice versa. The necessary timing to avoid delays is seldom obtained. A few columns or an additional rigid frame at the end of a building may cost less than using trades to fit an intermittent and expensive schedule. Remember, too, that labor-union regulations may prevent the trades from handling any material other than that belonging to their own craft. An economical rule may well be: Lay out the work so that the erector and ironworkers can place and connect all the steelwork in one continuous operation. (F. S. Merritt and R. Brockenbrough, Structural Steel Designers Handbook, 2d ed., McGraw-Hill Publishing Company, New York.) In skeleton framing all the gravity loadings of the structure, including the walls are supported by the steel framework. Such walls are termed nonbearing or curtain walls. This system made the skyscraper possible. Steel, being so much stronger FIGURE 7.8 Typical beam-and-column steel framing, shown in plan. FIGURE 7.9 Typical steel spandrel beams. than all forms of masonry, is capable of sustaining far greater load in a given space, thus obstructing less of the floor area in performing its function. With columns properly spaced to provide support for the beams spanning between them, there is no limit to the floor and roof area that can be constructed with this type of framing, merely by duplicating the details for a single bay. Erected tier upon tier, this type of framing can be built to any desired height. Fabricators refer to this type of construction as beam and column. A typical arrangement is illustrated

For a beam of this material, the following assumptions will also be made: 1. Plane sections remain plane, strains thus being proportional to distance from the neutral axis. 2. Properties of the material in tension are the same as those in compression. 3. Its fibers behave the same in flexure as in tension. 4. Deformations remain small. Strain distribution across the cross section of a rectangular beam, based on these assumptions, is shown in Fig. 5.80a. At the yield point, the unit strain is y and the curvature y, as indicated in (1). In (2), the strain has increased several times, but the section still remains plane. Finally, at failure, (3), the strains are very large and nearly constant across upper and lower halves of the section. Corresponding stress distributions are shown in Fig. 5.80b. At the yield point, (1), stresses vary linearly and the maximum if y . With increase in load, more and more fibers reach the yield point, and the stress distribution becomes nearly constant, as indicated in (2). Finally, at failure, (3), the stresses are constant across the top and bottom parts of the section and equal to the yield-point stress. The resisting moment at failure for a rectangular beam can be computed from the stress diagram for stage 3. If b is the width of the member and d its depth, then the ultimate moment for a rectangular beam is