Integration gives the slope at any point of the cable w x y  o (5.205) H A second integration yields the parabolic equation for the cable shape w x2 y  o (5.206) The distance from the low point C to the left support L is l Hh a  (5.207) 2 w l o where l  span, or horizontal distance between supports L and R  a  b h  vertical distance between supports The distance from the low point C to the right support R is l Hh b  (5.208) 2 w l o When supports are not at the same level, the horizontal component of cable tension H may be computed from w l 2 h w l 2 H  o

   o (5.209) h2 R 2 L R 8 where L  vertical distance from C to L R  vertical distance from C to R  sag of cable measured vertically from chord LR midway between supports (at x  Hh/wo l ) As indicated in Fig. 5.100b, h   y (5.210) L 2 M where yM  Hh2/2wo l 2. The minus sign should be used in Eq. (5.209) when low point C is between supports. If the vertex of the parabola is not between L and R, the plus sign should be used. The vertical components of the reactions at the supports can be computed from w l Hh w l Hh V  w a  o  V  w b  o  (5.211) L o 2 l R o 2 l Tension at any point is T  H2  w2x2 (5.212) o Length of parabolic arc RC is 2 2 b wb H wb 1 w o o o3 L  1 
  sinh  b 
 b     (5.213) RC  2 KH 2w H 6 H o Length of parabolic are LC is 2 2 a wa H wa 1 w o o o3 L  1 
  sinh  a 
 a     (5.214) LC  2 H 2w H 6 H o When supports are at the same level, L  R  , h  0, and a  b  l/2. The horizontal component of cable tension H may be computed from

landing sill should be at least 1/2 in where side door guides are used and 3/4 in where corner guides are used, but not more than 11/2 in. Maximum clearance between the loading side of the car platform and the hoistway enclosure generally is 5 in but may be as much as 71/2 in when vertically sliding hoistway doors are used. Clearance between a car and its counterweight should be at least 1 in. Between the counterweight and other components, the clearance should be at least 3/4 in. In multiple hoistways, a minimum of 2-in clearance should be provided between moving equipment. A car consists basically of a platform for transporting passengers and goods. The platform is raised or lowered by wire ropes or a hydraulic piston or plunger. The car is required to be completely enclosed. Car enclosures of sheet metal or plywood are common; some decorative elevators are enclosed in laminated glass. To provide access to the car, openings protected by doors are provided in one or two of the car walls. In addition, the platform and the car enclosures are supported on a structural steel frame (Fig. 16.12). For electric elevators, the wire ropes that move the car are attached to the frame or threaded around sheaves connected to it. For hydraulic elevators, the frame is seated on the piston. The frame also supports the upper and lower wheels that roll along the vertical guide rails in the hoistway (Fig. 16.13). In addition, car frames of electric elevators carry safety devices that stop an overspeeding elevator mechanically. Design, construction, and installation of elevator cars should meet the requirements of the National Standard Safety Code for Elevators, Dumbwaiters, Escalators and Moving Walks, ANSI A17.1. 16.8.1 Door Controls Car doors may be horizontally or vertically sliding. They usually are power operated. For safety, they should be equipped with devices that prevent them from opening while the car is moving or is outside the landing zones, the space 18 in above and below a landing. Also, ANSI A17.1 requires safety devices that will keep the car from moving while the doors are open. The Americans with Disabilities Act requires specific door-open dwell times in response to car and landing

Solid-sawn 1025 Glulam 10100 Continuous span: Solid-sawn 1025 Glulam 1050 Glulam arches: Three-hinged: Gothic 40100 Tudor 40120 A-frame 20100 Three-centered 40250 Parabolic 40250 Radial 40250 Two-hinged Radial 50200 Parabolic 50200 Roof trusses: Flat or parallel chord 25100 Triangular or pitched 25100 Bowstring 50200 Domes 200500 Simple-span floor beams: Solid sawn 620 Glulam 1040 Continuous floor beams 1040 Roof sheathing and decking: 1-in sheathing 14 2-in sheathing 610 3-in roof deck 815 4-in roof deck 1220 * Not applicable. Use standard details wherever possible. Avoid specially designed and manufactured connecting hardware. Use as simple and as few joints as possible. Place splices, when required, in areas of lowest stress. Do not locate splices where bending moments are large, thus avoiding design, installation, and fabrication difficulties. Avoid unnecessary variations in cross section of members along their length. Use identical member designs repeatedly throughout a structure, whenever practicable. Keep the number of different arrangements to a minimum. Specify required design stresses to permit the widest range of products that can be used for a given design situation. Use wood products pressure treated with preservatives where service conditions dictate. Such treatment need not be used where decay or insect attack hazards do not exist. Fire-retardant treatments may be used to meet a specific flamespread rating for interior finish, but are not necessary for large-cross-sectional members that are widely spaced and have a natural resistance to fire because of their relatively large size. Instead of long, simple spans, consider using continuous or suspended spans or simple spans with overhangs. Select an appearance grade best suited to the project. Do not specify the highest quality appearance grade available for all members if it is not required. Table 10.2 may be used as a general guide to typical ranges of spans for roof and main floor framing members (excluding repetitive member joist and rafter applications). Dressed sizes of sawn lumber are given in the grading rules of agencies that formulate and maintain such rules and in Table 10.3. The nominal and dressed sizes are developed in accordance with the American Softwood Lumber Standard, Voluntary Product Standard PS 20-94. These sizes are generally available, but it is good practice to consult suppliers before specifying sizes not commonly used to find out what sizes are on hand or can be readily secured. The supplement to the National Design Specification
for Wood Construction published by the American Forest & Paper Association (formerly the National Forest Products Association) presents tables of section properties of standard dressed sawn lumber and glulam timber. Standard finished sizes of structural glulam timber should be used to the extent that conditions permit. These standard finished sizes are based on lumber sizes given in Voluntary Product Standard PS 20-94. Other finished sizes may be used to meet the size requirements of a design, or to meet other special requirements. For the manufacture of glulam nominal 2-in-thick lumber, surfaced to 13/8 in or 11/2 in before gluing, is used to laminate straight members and curved members having radii of curvature within the bending-radius limitations for the species. Nominal 1-in-thick lumber, surfaced to 3/4 in before gluing, may be used for laminating TABLE 10.3 Nominal and Minimum Dressed Sizes of Sawn Lumber