Information on passenger capacity of a moving walk or powered ramp should be obtained from the manufacturer. The capacity depends on treadway width and speed. Standard widths are 24, 32, and 40 in. With level entry and exit, ramp speeds generally are a maximum of 180 ft /min for slopes up to 8
and 140 ft /min for slopes between 8
and 15
. (Life Safety Code, National Fire Protection Association, Batterymarch Park, Quincy, MA 02269; American National Standard Safety Code for Elevators, Dumbwaiters, Escalators and Moving Walks, A17.1, and Making Buildings and FIGURE 16.2 Arrangement of straight stairs: (a) a single flight between floors; (b) a series of flights without change in direction; (c) parallel stairs; (d ) angle stairs; (e) scissors stairs. Facilities Accessible to and Usable by the Physically Handicapped, A117.1, American National Standards Institute, New York, NY 10018.) Less space is required for stairs than for ramps, because steeper slopes can be used. Maximum slope of stairs for comfort is estimated to be about 1 on 2 (27
), but this angle frequently is exceeded for practical reasons. Exterior stairs generally range in slope from 20
to 30
, interior stairs from 30
to 35
. 16.3.1 Types of Stairs Generally, stairs are of the following types: straight, circular, curved, or spiral, or

Fire-resistive rating 1 hour 2 hours 3 hours Normal weight concrete Top slab thickness* Siliceous aggregate 3.5 5.0 6.2 Carbonate aggregate 3.2 4.6 5.7 Structural lightweight concrete Top slab thickness* Sand-lightweight 2.7 3.8 4.6 Lightweight 2.5 3.6 4.4 *From Table 7-7-C-C in Uniform Building Code Std. 7-7 or Table 709.2.2.1 in Standard Building Code. TABLE 9.18 Minimum and Maximum Reinforcement for One-Way Concrete Slabs Slab thickness h, in Minimum reinforcement* Area As in2 / ft Bar size and spacing, in Weight psf Maximum reinforcement Area As in2 / ft Bar size and spacing, in Weight psf 4 0.086 No. 3 @ 12 0.38 0.552 No. 6 @ 91/2 1.90 41/2 0.097 No. 3 @ 131/2 0.33 0.648 No. 6 @ 8 2.25 5 0.108 No. 3 @ 12 0.38 0.744 No. 6 @ 7 2.58 51/2 0.119 No. 3 @ 11 0.41 0.840 No. 6 @ 6 3.00 6 0.130 No. 4 @ 18 0.45 0.924 No. 7 @ 71/2 3.27 61/2 0.140 No. 4 @ 17 0.49 1.020 No. 7 @ 7 3.50 7 0.151 No. 4 @ 151/2 0.52 1.104 No. 8 @ 81/2 3.77 71/2 0.162 No. 4 @ 141/2 0.55 1.200 No. 8 @ 71/2 4.27 8 0.173 No. 4 @ 131/2 0.59 1.284 No. 9 @ 9 4.53 81/2 0.184 No. 4 @ 13 0.62 1.380 No. 9 @ 81/2 4.80 9 0.194 No. 4 @ 12 0.67 1.476 No. 9 @ 8 5.10 *For Grade 60 reinforcement. Minimum area As 0.0018bh, where b
slab width and h
slab

Thickness, in Nominal Minimum dressed Dry* Green Face width, in Nominal Minimum dressed Dry* Green Boards 1 3/4 25/32 2 11/2 19/16 Dimension 2 11/2 19/16 2 11/2 19/16 Lumber 21/2 2 21/16 3 21/2 29/16 Timbers 5 and thicker 1/2 in less 5 and wider 1/2 in less * Dry lumber is defined as lumber seasoned to a moisture content of 19% or less. Green lumber is defined as lumber having a moisture content is excess of 19%. curved members when the bending radius is too tight to permit use of nominal 2- in-thick laminations. Other lamination thicknesses may be used to meet special curving requirements. Standard sizes and grades of structural panels are given in U.S. Product Standard PS 1-95 for Construction and Industrial Plywood and Performance Standard for Wood-Based Structural-Use Panels, Voluntary Product Standard, PS 2-92. See also Art. 10.12. Weight and Specific Gravity. Specific gravity is a reliable indicator of fiber content. Also, specific gravity and the strength and stiffness of solid wood or laminated products are interrelated. See Table 10.4 for weights and specific gravities of several commercial lumber species. TABLE 10.4 Weights and Specific Gravities of Commercial Lumber Species