L 
0.25   L (5.1) o AI where Lo  unreduced live load, lb / ft2 (see Table 5.1a) AI  influence area, or floor area over which the influence surface for structural effects is significantly different from zero  area of four surrounding bays for an interior column, plus similar area from supported floors above, if any  area of two adjoining bays for an interior girder or for an edge column, plus similar areas from supported floors above, if any  area of one bay for an edge girder or for a corner column, plus similar areas from supported floors above, if any The reduced live load L, however, should not be less than 0.5Lo for members supporting one floor or 0.4Lo for members supporting two or ore floors. Roofs used for promenades should be designed for a minimum life load of 60 lb/ft2, and those used for gardens or assembly, for 100 lb / ft2. Ordinary roofs should be designed for a minimum live load L, lb/ft2, computed from where R1  1.2  0.001At but not less than 0.6 or more than 1.0 At  tributary area, ft2, for structural member being designed R2  1.2  0.05r but not less than 0.6 or more than 1.0 r  rise of roof in 12 in for a pitched roof or 32 times the ratio of rise to span for an arch or dome This minimum live load need not be combined with snow load for design of a roof but should be designed for the larger of the two. Subgrade Pressures. Walls below grade should be designed for lateral soil pressures and the hydrostatic pressure of subgrade water, plus the load from surcharges at ground level. Design pressures should take into account the reduced weight of soil because of buoyancy when water is present. In design of floors at or below grade, uplift due to hydrostatic pressures on the underside should be considered. Wind Loads. Horizontal pressures produced by wind are assumed to act normal to the faces of buildings for design purposes and may be directed toward the interior of the buildings or outward (Arts. 3.2.1 and 3.2.2). These forces are called velocity pressures because they are primarily a function of the velocity of the wind striking the buildings. Building codes usually permit wind pressures to be either calculated or determined by tests on models of buildings and terrain if the tests meet specified requirements (see Art. 3.2.2). Codes also specify procedures for calculating wind loads, such as the following: Velocity pressures due to wind to be used in building design vary with type of terrain, distance above ground level, importance of building, likelihood of hurricanes, and basic wind speed recorded near the building site. The wind pressures are assumed to act normal to the building facades. The basic wind speed used in design is the fastest-mile wind speed recorded at a height of 10 m (32.8 ft) above open, level terrain with a 50-year mean recurrence

NA
c (9.136) s 0.5y where A
area of that part of the cross section between the flexural tension face and centroid of gross section Nc
tensile force in the concrete under actual dead load plus live load y
yield strength of bonded reinforcement, but not more than 60,000 psi In the negative moment regions of two-way flat plates at column supports, the minimum amount of bonded reinforcement provided in the top of the slab in each direction should be A
0.00075A (9.137) s c where Ac
larger gross cross-sectional area of the slab-beam strips of the two orthogonal equivalent frames intersecting at a column of a two-way flat plate The Code requires the bonded reinforcement computed by Eq. (9.137) to be distributed between lines that are 1.5h outside opposite faces of the column support, and that at least four bars be provided in each direction spaced not over 12 in, where h is the depth of the flat plate. Requirements are included in the Code for minimum lengths and extensions of the bonded reinforcement computed by Eqs. (9.135), (9.136) and (9.137). Grouting of Tendons. When posttensioned tendons are to be bonded, a cement grout is usually injected under pressure (80 to 100 psi) into the space between the tendon and the sheathing material of the duct. The grout can be inserted in holes in the anchorage heads and cones, or through buried pipes. To ensure filling of the space, the grout can be injected under pressure at one end of the member until it is forced out the other end. For long members, it can be injected at each end until it is forced out a vent between the ends. Grout provides bond between the posttensioning tendons and the concrete member and protects the tendons against corrosion. Members should be above 35F in temperature at the time of grouting. This minimum temperature should be maintained until field-cured 2-in cubes of grout reach a minimum compressive strength of 800 psi. Tendon Sheaths. Ducts for grouted or unbonded tendons should be mortar-tight and nonreactive with concrete, tendons, or filler material. To facilitate injection of the grout, the duct should be at least 1/4 in larger than the diameter of a single posttensioning tendon. For multiple strand, bar or wire tendons, the duct should have an internal area at least twice the gross area of the prestressing steel. TABLE 9.29 Minimum Concrete Cover in in Prestressed Members Concrete cast against and permanently exposed to earth 3 Concrete exposed to earth or weather: Wall panels, slabs, and joists 1

diameter, in 1/2 2.1 Any 15 5 21/4 21/2 28/10 21/2 3/4 3 Any 15 8 32/10 31/2 4 31/2 1 3.7 Any 15 8 4 41/2 5 41/2 30 30 00 14 R 1/2 11/2 5.3 Any 15 10 56/10 61/4 7 61/4 TABLE 15.3 Protection of Three-Phase 208-V Motors and Circuits (Continued) Size and class of motor Horsepower Ampere rating Class Branch circuit protection* Maximum size fuse permitted by the code Timedelaycartridge or lowpeak fuse that can be used Motor-running protection Size of time-delay-cartridge or low-peak fuse Ordinary service Heavy service Maximum size motor All other motors Size of fused switch or fuse holder Maximum size switch that can be used Size that can be used with time-delaycartridge or lowpeak fuses Minimum size of starter: size Minimum size and type of wire: or Minimum size of conduit: diameter, in TABLE 15.3 Protection of Three-Phase 208-V Motors and Circuits (Continued) Size and class of motor Horsepower Ampere rating Class Branch circuit