When a T form is used to provide needed compression area for an isolated beam, flange thickness should be at least one-half the web width, and flange width should not exceed 4 times the web width. When a T is formed by a beam cast integrally with a slab, only a portion of the slab is effective. For a symmetrical T-beam, the effective flange width should not exceed one-fourth the beam span, nor should the width of the overhang exceed 8 times the slab thickness nor one-half the clear distance to the next beam. For a beam having a flange on one side only, the effective flange width should not exceed one-twelfth the span, 6 times the slab thickness, nor one-half the clear distance to the next beam. The overhang of a T-beam should be designed to act as a cantilever. Spacing of the cantilever reinforcement should not exceed 18 in or 5 times the flange thickness. In computing the moment capacity of a T-beam, it may be treated as a singlyreinforced beam with overhanging concrete flanges (Fig. 9.15). The compression force on the web (rectangular beam) is C
0.85
b a (9.33) w cw where bw
width of web. The compression force on the overhangs is C
0.85
(b  b )h (9.34) c w where h
flange thickness and b
effective flange width of the T-beam. Forces equal in magnitude to these but opposite in direction stress the tension steel: T
A (9.35) w swy

7.11.1 Bracing Tall Buildings If the steel frame of the multistory building in Fig. 7.16a is subjected to lateral wind load, it will distort as shown in Fig. 7.16b, if the connections of columns and beams are of the standard type, for which rigidity (resistance to rotation) is nil. One can visualize this readily by assuming each joint is connected with a single pin. Naturally, the simplest method to prevent this distortion is to insert diagonal members triangles being inherently rigid, even if all the members forming the triangles are pin-connected. Braced Bents. Bracing of the type in Fig. 7.16c, called X bracing, is both efficient and economical. Unfortunately, X bracing is usually impracticable because of interference with doors, windows, and clearance between floor and ceiling. Usually, for office buildings large column-free areas are required. This offers flexibility of space use, with movable partitions. But about the only place for X bracing in this type of building is in the elevator shaft, fire tower, or wherever a windowless wall is required. As a result, additional bracing must be supplied by other methods. On the other hand, X bracing is used extensively for bracing industrial buildings of the

integrally with their supports should be taken as the clear span plus the depth of slab or beam but need not exceed the distance between centers of supports. For spans of continuous frames, spans should be taken as the distance between centers of supports. For solid or ribbed slabs with clear spans not exceeding 10 ft, if built integrally with their supports, spans may be taken as the clear distance between supports. If an elastic analysis is performed for continuous flexural members for each loading combination expected, calculated factored moments may be redistributed if the ratio  of tension-reinforcement area to effective concrete area or ratio of   
, where 
is the compression-reinforcement ratio, to the balanced-reinforcement ratio b, lie within the limits given in the ACI 318 Building Code. Positive factored moments should be increased by a percentage  and negative factored moments decreased by  to reflect the moment redistribution property of underreinforced concrete in flexure. When  or   
is not more than 0.5b, the percentage is