Industry or Facility Approach. Industry in this case refers to the specific commercial or industrial use for which a project is intended. For example, a client who wishes to build a factory usually is more concerned with the application to which the factory will be put than with the details of its construction, such as bricks, mortar, joists, and rafters. The client is interested in the specific activities that will be carried out and the space that will be needed. When information about these activities has been obtained, the designers convert this information into a total building design, including work spaces, corridors, stairways, restrooms, and airconditioning equipment. After this has been done, the estimator uses the design to prepare an estimate. Discipline or Trade Approach. This takes the point of view of the contractor rather than the client. The job is broken into disciplines, or trades, of the workers who will perform the construction. The estimate is arrived at by summing the projected cost of each discipline, such as structural steel; concrete; electrical; heating, ventilating, and air conditioning (HVAC); and plumbing. 19.2.1 Types of Estimates Typical types of estimates are as follows: feasibility, order of magnitude, preliminary, baseline, definitive, fixed price, and claims and changes. These do not represent rigid categories. There is some overlap from one type to another. All the types can be prepared with an industry or discipline approach, or sometimes a combination of them. Feasibility Estimates. These give a rough approximation to the cost of the project and usually enable the building owner to determine whether to proceed with construction. The estimate is made before design starts and may not be based on a specific design for the project under consideration. For example, for a power plant, the estimate may involve only a determination of the energy density of the fuel; the altitude of the plant, which determines the amount of oxygen in the air and hence the efficiency of combustion; the number of megawatts to be produced; and the length of the transmission line to the grid. The feasibility estimate is inexpensive and can be made quickly. Not very accurate, it does not take into account creative solutions, new techniques, and unique costs. It can be prepared by the owner, the lender, or the designer. Order-of-Magnitude Estimates. These are more detailed than feasibility estimates, because more information is available. For example, a site for the building may have been selected and a schematic design, including sketches of the proposed structure and a plot of its location on the site, may have been developed. Like the feasibility estimate, the order-of-magnitude estimate is inexpensive to prepare. Generally made by the designer, it is prepared after about 1% of the design has been



0.0031(w/ t) (8.9) where E
29,500 ksi for steel. Substitution of  in Eq. (8.7) yields b/w
. Moreover, when   0.673, b
w and when   0.673, b
w. Figure 8.7b shows a nest of curves for the relationship of b/ t to w/ t for stiffened elements for w/ t between 0 and 500 with between 10 and 90 ksi. In beam deflection determinations requiring use of the moment of inertia of the cross section, the allowable stress is used to calculate the effective width of a FIGURE 8.6 Schematic diagrams showing effective widths for unstiffened and stiffened elements, intermediate stiffeners, beam webs, and edge stiffeners. FIGURE 8.7 Curves relate effective-width ratio b / t to flat-width ratio w/ t at various stresses for (a) unstiffened elements and (b) stiffened elements. stiffened element in a cold-formed steel member loaded as a beam. However, in beam strength determinations requiring use of the section modulus of the cross section, 1.67 is the stress to be used in Eq. (8.9) to calculate the effective width of the stiffened element and provide a margin of safety. In determination of the safe loads for a cold-formed steel section used as a column, effective width for a stiffened element must be determined for a nominal buckling stress, Fn, to ensure an adequate margin of safety. Since effective widths are proportional to k, the effective width of a stiffened element is 4.00/0.43
3.05 times as large as that of an unstiffened element at applicable combinations of and w/ t. Thus, stiffened elements offer greater strength and economy. Single Intermediate Stiffener. For uniformly compressed stiffened elements with a single intermediate stiffener, as shown in Fig. 8.6c, calculations for required moment of inertia Ia of the stiffener are based on a parameter S.

F
Ma
a (3.2) g where F
force, lb M
mass accelerated a
acceleration of the mass, ft / s2 W
weight of building component accelerated, lb g
acceleration due to gravity
32.2 ft / s2 3.3.2 Seismic Scales For study of the behavior of buildings in past earthquakes and application of the information collected to contemporary aseismic design, it is useful to have some quantitative means for comparing earthquake severity. Two scales, the Modified Mercalli and the Richter, are commonly used in the United States. The Modified Mercalli scale compares earthquake intensity by assigning values to human perceptions of the severity of oscillations and extent of damage to buildings. The scale has 12 divisions. The severer the reported oscillations and damage, the higher is the number assigned to the earthquake intensity (Table 3.1). The Richter scale assigns numbers M to earthquake intensity in accordance with the amount of energy released, as measured by the maximum amplitude of ground