Exposed to Earth or weather Castin- place concrete Precast concrete Prestressed concrete Not exposed to weather or in contact with ground Castin- place concrete Precast concrete Prestressed concrete 3, 4, and 5 11/2 11/4 11/2 11/2 5/8 11/2 6 through 11 2 11/2 11/2 11/2 db* 11/2 14 and 18 2 2 11/2 11/2 11/2 11/2 Stirrups Same as above for each size 3/8 1 * db
nominal bar diameter, in. Generally, any vertical member whose length and height are both much larger than the thickness may be treated as a wall. Walls subjected to vertical loads are called bearing walls. Walls subjected to no loads other than their own weight, such as panel or enclosure walls, are called nonbearing walls. Walls with a primary function of resisting lateral loads are called shear walls. They also may serve as bearing walls. See Art. 9.89. Reinforced concrete bearing walls may be designed as eccentrically loaded columns or by an empirical method given in the ACI 318 Building Code. The empirical method may be used when the resultant of the applied load falls within the middle third of the wall thickness. This method gives the capacity of the walls as 2 kL P  P
0.55
A 1   c  (9.82) u nw cg 32h

The tensile stress t parallel to the grain should be computed for the net section area. This stress should not exceed the design value for tension parallel to grain Ft. Designs that induce tensile stress perpendicular to the grain should be avoided. The reason for this is that wood is weaker and more variable in tension perpendicular to the grain than in other properties. Furthermore, these tensile properties have not been extensively evaluated and published values are not readily available. When tension perpendicular to grain cannot be avoided, mechanical reinforcement sufficient to resist the stresses may be required. An example of a construction that induces critical tensile stress perpendicular to grain is a load supported from a beam from a point below the neutral axis. This practice should be avoided for medium to heavy loads. When a bending moment and an axial force act on a section of a structural member, the effects of the combined stresses must be provided for in design of the member. 10.10.1 Bending and Axial Tension Members subjected to combined bending and axial tension should be proportioned to satisfy the interaction equations, Eqs. (10.26) and (10.27). t b   1 (10.26)

Accordingly, a means of egress is a continuous, unobstructed path for evacuees from any point in a building to a public way. Its three parts are: Exit accessthat portion that leads to an entrance to an exit Exitthe portion that is separated from all other building spaces by construction or equipment required to provide a protected path to the exit discharge Exit dischargethe portion that connects the termination of an exit to a public way Means of egress may be provided by exterior and interior doors and enclosed horizontal and vertical passageways, including stairs and escalators. (Elevators and exterior fire escapes are not generally recognized as reliable means of egress in a fire.) Exit access includes the space from which evacuation starts and passageways and doors that must be traversed to reach an exit. Types of Exits. Building codes generally recognize the following as acceptable exits when they meet the codes safety requirements: Corridorsenclosed horizontal or slightly inclined public passageways, which lead from interior spaces toward an exit discharge. Minimum floor-to-ceiling height permitted is generally 80 in. Minimum width depends on type of occupancy and passageway (Table 3.7 and Art. 3.5.11). Codes may require subdivision of corridors into lengths not exceeding 300 ft for educational buildings and 150 ft for institutional buildings. Subdivision should be accomplished with noncombustible partitions incorporating smokestop doors. In addition, codes may require the corridor enclosures to have a fire rating of 1 or 2 hr. Exit passagewayshorizontal extensions of vertical passageways. Minimum floor-to-ceiling height is the same as for corridors. Width should be at least that of the vertical passageways. Codes may require passageway enclosures to have a 2-hr fire rating. A street-floor lobby may serve as an exit passageway if it is sufficiently wide to accommodate the probable number of evacuees from all contributing spaces at the lobby level. Exit doorsdoors providing access to streets or to stairs or exit passageways. Those at stairs or passageways should have a fire rating of at least 3/4 hr. Horizontal exitpassageway to a refuge area. The exit may be a fire door through a wall with a 2-hr fire rating, a balcony providing a path around a fire barrier, or a bridge or tunnel between two buildings. Doors in fire barriers with 3- or 4-hr fire ratings should have a 11/2-hr rated door on each face of the fire division. Walls permitted to have a lower fire rating may incorporate a single door with a rating of at least 11/2 hr. Balconies, bridges, and tunnels should be at least as wide as the doors providing access to them, and enclosures or sides of these passageways should have a fire rating of 2 hr or more. Exterior-wall openings, below or within 30 ft of an open bridge or balcony, should have at least 3/4-hr fire protection. Interior stairsstairs that are inside a building and that serve as an exit. Except in one-story or two-story low-hazard buildings, such stairs should be built of noncombustible materials. Stairway enclosures generally should have a 2-hr fire rating. Building codes, however, may exempt low dwellings from this requirement. Exterior stairsstairs that are open to the outdoors and that serve as an exit to ground level. Height of such stairs is often limited to 75 ft or six stories. The stairs should be protected by a fire-resistant roof and should be built of noncombustible materials. Wall openings within 10 ft of the stairs should have 3/4-hr fire