Compressive strength, flat, min, psi Avg of 5 Individual Water absorption, 5-hr boil, max% Avg of 5 Individual Saturation* coefficient, max% Avg of 5 Individual SWSevere weathering 3000 2500 17.0 20.0 0.78 0.80 MWModerate weathering 2500 2200 22.0 25.0 0.88 0.90 NWNo exposure 1500 1250 No limit No limit No limit No limit * Ratio of 24-hr cold absorption to 5-hr boil absorption. usually by the amount of the width of the mortar joint. Current specification requirements for strength and absorption of building brick are given in Table 4.8 (see ASTM C652, C62, and C216). Strength and absorption of brick from different producers vary widely. Thermal expansion of brick may range from 0.0000017 per
F for fire-clay brick to 0.0000069 per
F for surface-clay brick. Wetting tests of brick indicated expansions varying from 0.0005 to 0.025%. The thermal conductivity of dry brick as measured by several investigators ranges from 1.29 to 3.79 Btu/ (hr)(ft3)(
F)(in). The values are increased by wetting. Structural clay tiles are hollow burned-clay masonry units with parallel cells. Such units have multitude of uses: as a facing tile for interior and exterior unplastered walls, partitions, or columns; as load-bearing tile in masonry constructions designed to carry superimposed loads; as partition tile for interior partitions carrying no superimposed load; as fireproofing tile for protection of structural members against fire; as furring tile for lining the inside of exterior walls; as floor tile in floor and roof construction; and as header tiles, which are designed to provide recesses for header units in brick or stone-faced walls. Units are available with the following ranges in nominal dimensions: 8 to 16 in in length, 4 in for facing tile to 12 in for load-bearing tile in height, and 2 in for facing tile to 12 in for load-bearing tile in

where A is the cross-sectional area, in2, and L the length of bar, in. This equation indicates that, for a given unit stress, energy absorption of a member may be improved by increasing its length or area. Sharp changes in cross section should be avoided, however, because of associated high stress concentrations. Also, uneven distribution of stress in a member due to changes in section should be avoided. For example, if part of a member is given twice the diameter of another part, the stress under axial load in the larger portion is one-fourth that in the smaller. Since the energy absorbed is proportional to the square of the stress, the energy taken per unit of volume by the larger portion is therefore only one-sixteenth that absorbed by the smaller. So despite the increase in volume caused by doubling of the diameter, the larger portion absorbs much less energy than the smaller. Thus, energy absorption would be larger with a uniform stress distribution throughout the length

FIGURE 16.11 Arrangements of spiral escalators: (a) at main entrance or center of a building; (b) in a corner. An elevator is a hoisting and lowering mechanism equipped with a car or platform that moves along guides in a shaft, or hoistway, in a substantially vertical direction and that transports passengers or goods, or both, between two or more floors of a building. Passenger elevators are designed primarily to carry persons. Hospital elevators are also passenger elevators but employ special cars, suitable in size and shape for transportation of patients in stretchers or standard hospital beds and of attendants accompanying them. Freight elevators carry freight, which may be accompanied only by an operator and persons necessary for loading and unloading it. Elevators are desirable in all multistory buildings for movement of passengers and freight. They may be required by local building codes for any buildings over two stories high or for transportation of disabled persons. Elevators, however, are not usually accepted as a means of egress, because no cohesive strategy has been established to assure proper operation of elevators in an emergency. Most codes require automatic evacuation of all elevators if fire or smoke is detected on a served floor. These elevators can later be recaptured by emergency personnel. Nevertheless, elevators are vital for firefighting in a high-rise building. Also, they can be used for emergency evacuation of building occupants who cannot use the building stairs. The height of modern buildings makes it mandatory that elevators be included in emergency planning for fire or other disaster. Most elevators are the roped electric or hydraulic type. For the roped electric elevator, the car is suspended from wire ropes and counterbalanced by a counterweight that mirrors the operation of the elevator. The electric elevator is moved via an electrically powered machine that drives a hardened steel traction sheave over which the wire ropes are suspended (Fig. 16.12a and b). Electric elevators are used exclusively in tall buildings and many low buildings (Art. 16.9). Hydraulic elevator cars (Fig. 16.12c) are raised and lowered by an oil pumping system, which actuates a plunger or piston (Art. 16.10). They are frequently used for passenger elevators serving up to four or five floors and for low-rise freight service. Their low performance when compared to electric-type elevators means that they cannot be substituted on a one-for-one basis and provide equivalent service. Where passenger-moving capability is paramount, the hydraulic elevator cannot compete with the electric