Additional devices are needed for power-operated doors to reopen the car and hoistway doors when they start to close on a passenger or other object. The National Elevator Industry standard, Suggested Minimum Passenger Elevator Requirements for the Handicapped, recommends that the devices be capable of sensing a person or object in the path of a closing door, without requiring contact for activation, at a nominal 5 and 29 in above the floor. Also, the doors should be kept open for at least 20 s after reopening. Still other devices should be installed for other safety reasons, for example, to prevent car and hoistway doors from closing and the car from moving when it is overloaded. 16.8.2 Car Equipment The interior of the car should be ventilated and illuminated with at least two electric lamps. Lighting provided at the landing edge of the car platform should be at least 5 fc for passenger elevators and 2.5 fc for freight elevators. In addition, an emergency electric-lighting power source should be installed, to operate immediately after failure of the normal power source. For a period of at least 4 h, this system should maintain at least 0.2 fc at a level 4 ft above the car floor and about 1 ft in front of a car station. The car must also house an approved communication device consistent with rules outlined in the Americans with Disabilities Act. The communication device provides a means for two-way communication with persons outside the hoistway. To be available for use by persons in wheelchairs, an alarm button should be installed in the car. When pressed, this button should sound an alarm outside the hoistway, and an emergency stop switch should be installed about 35 in above the platform. The height of the highest push button or of a telephone should not exceed 48 in. A handrail should be provided about 32 in above the floor along the rear car

FIGURE 12.1 Built-up roofing over two layers of preformed insulation board. Three plies of asphalt-impregnated glass-fiber felt, embedded in a continuous application of hot asphalt, overlay a base sheet adhered with asphalt to the insulation. Aggregate surfacing, about 3/8 in in diameter, is spread in the top flood coat of asphalt. (NRCA Roofing and Waterproofing Manual.) FIGURE 12.2 Protected-membrane roof with aggregate and insulation placed over, instead of under, the built-up membrane. Bitumen may be asphalt or coal tar. Roofing asphalt is a derivative of petroleum. It is described in ASTM Standard D312, which includes specifications for Types I, II, III, and IV. Each type has a different softening-point range, which should be considered by the specifier when specifying the type of asphalt to be used. Coal tar, described in ASTM D450, is a derivative of the production of coke from coal. Type I is referred to as old-style pitch. Type II is used for below-grade waterproofing. Type III, or coal-tar bitumen, was developed to be less of an irritant during application than Type I; however, Type III is no longer produced. Felts are sheet materials used to reinforce waterproofing and roofing membranes. The predominant type of felt used is glass fiber although organic felts are still commonly used in the construction of coal-tar systems. Polyester is an alternative type of felt. Asbestos felts were used in the past but are no longer produced in the

Single shear occurs when opposing forces act on a fastener as shown in Fig. 7.39a, tending to slide on their contact surfaces. The body of the fastener resists this tendency; a state of shear then exists over the cross-sectional area of the fastener. Double-shear takes place whenever three or more plates act on a fastener as illustrated in Fig. 7.40b. There are two or more parallel shearing surfaces (one on each side of the middle plate in Fig. 7.40b). Accordingly, the shear strength of the fastener is measured by its ability to resist two or more single shears. Bearing on Base Metal. This is a factor to consider; but calculation of bearing stresses in most joints is useful only as an index of efficiency of the net section of tension members. Edge Distances. The AISC Specification for Structural Steel for Buildings, ASD and LRFD, recommends minimum edge distances, center of hole to edge of connected part, as given in Table 7.28. In addition, the edge distance, in, when in the direction of force should not be less than 2P/Fut for ASD or P/Fut for LRFD, where p is the force, kips, transmitted by one fastener to the part for which the edge distance is applicable;   0.75; Fu is the specified minimum tensile strength of the part (not the fastener), ksi; and t is the thickness of the part, in. A special rule applies to beams with framed connections that are usually designed for the shear due to beam reactions. The edge distance for the beam web, with standard-size holes, should be not less than 2PR /Fut for ASD or PR /Fut for TABLE 7.28 Minimum Edge Distance for Punched, Reamed, or