5.19.2 Design Spectral Response Accelerations Ground motion accelerations, represented by response spectra and coefficients derived from these spectra, shall be determined in accordance with the general procedure or the site-specific procedure. The later procedure shall be used for structures on sites classified as Site Class F. General Procedure for Determining Maximum Considered Earthquake and Design Spectral Response Accelerations. The maximum considered earthquake spectral response accelerations maps only provide values for Site Class B at short TABLE 5.12 Plan Structural Irregularities Irregularities Irregularity type and description Seismic Design Category application 1a Torsional irregularityto be considered when diaphragms are not flexible D, E, and F Torsional irregularity shall be considered to exist when the maximum story drift, computed including accidental torsion, at one end of the structure transverse to an axis is more than 1.2 times the average of the story drifts at the two ends of the structure

Control of Building Height. Zoning places limitations on building dimensions to limit population density and to protect the rights of occupants of existing buildings to light, air, and esthetic surroundings. Various zoning ordinances achieve these objectives in a variety of ways, including establishment of a specific maximum height or number of stories, limitation of height in accordance with street width, setting minimums for distances of buildings from lot lines, or relating total floor area in a building to the lot area or to the area of the lot occupied by a building. Applications of some of these limitations are illustrated in Fig. 1.11. Figure 1.11a shows a case where zoning prohibits buildings from exceeding 12 stories or 150 ft in height. Figure 1.11b illustrates a case where zoning relates building height to street width. In this case, for the specific street width, zoning permits a building to be erected along the lot boundary to a height of six stories or 85 ft. Greater heights are permitted, however, so long as the building does not penetrate sky-exposure planes. For the case shown in Fig. 1.11b, these planes start at the lot line at the 85-ft height and incline inward at a slope of 3:1. Some zoning codes will permit the upper part of the building to penetrate the planes if the floor area of the tower at any level does not exceed 40% of the lot area and the ratio of floor area to lot area (floor-area ratio) of the whole building does not exceed 15. To maximize the floor area in the building and maintain verticality of exterior walls, designers usually set back the upper parts of a building in a series of steps (Fig.

d 4(sec   1) The section modulus of the corrugated sheet may be computed from d  t The radius of gyration, in, is given by I and the tangent length-depth ratio is m sin  K d 1  cos  2 (See Fig. 8.19f.) ExampleCorrugated Sheet Properties. Consider a corrugated sheet with a 6-in pitch, 2-in depth, inside radius R of 11/8 in, and thickness t of 0.135 in. The mean radius r is then 1.125  0.135/2
1.192 in; q
r /d
1.192/2
0.596 in, and K
p/d
6/2
3. From Fig. 8.19e, angle  is found to be nearly 45
. For p/d
3 and 
45
, Fig. 8.19b, c, d, and f indicate that C5
0.14, C6
0.145 
1.24, and m/d
0.93. Section properties per inch of corrugated width are then computed as follows: From Eq. (8.49), A
1.24  1  0.135
0.167 in2 From Eq. (8.50), I
0.14  1(0.135)3  0.145  1(2)20.135
0.0786 in4 From Eq. (8.51), 2  0.0786 S

0.0736 in3 From Eq. (8.52),

0.686 in 0.167 and from Eq. (8.53), m
0.93  2
1.86 in I, S, and A for corrugated sheets with widths b are obtained by multiplying the per-inch values by b. Unit Stresses. The allowable unit bending stress Fr , ksi, at extreme fibers of corrugated sections of carbon or low-alloy steel may be taken as 0.6Fy, if r / t does not exceed 1650/Fy . For 1650/Fy  r / t  6500/Fy , F
331t / r  0.399F (8.54) r y where Fy
specified minimum yield point of the steel, ksi. Section properties of corrugated sheets with cross sections composed of flat elements may be computed with the linear method given in Art. 8.4, by combining properties of the various elements as given in Table 8.4. (See also Sectional Properties of Corrugated Sheets Determined by Formula, Civil Engineering, February Metric sheeting, the cross section of which is shown in Fig. 8.20, has a corrugationlike conformation with locking side edges. It has a laying width of 500 mm or 0.5 m (192/3 in), and is available in thicknesses of 5, 7, 8, 10, and 12 ga. Sheets are installed vertically in soil with edges of successive units interlocking. For additional corrosion protection, metric sheeting may be ordered galvanized after continuous cold forming in lengths of 4 to 40 ft. FIGURE 8.20 Steel metric sheeting. Applications include checkdams, core walls, wingwalls, trench walls, excavations, low retaining walls, ditch checks, jetties and lagoon baffles. The sheeting often can be put into soft ground with the aid of a backhoe, although for harder subgrades, conventional drop, vibratory, or diesel hammers applied to a light driving head make emplacement easier. The tight metal-to-metal interlock at the edges of metric sheeting contains soil and controls water movement. Table 8.15 lists its structural properties.