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Structural Steel Designers Handbook Part 12

Tham khảo tài liệu 'structural steel designers handbook part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 12.148 SECTION TWELVE be found by proportion from those previously calculated. Thus the moment at the support is 210 X 0.247 MLL----------00302------------172 ft-klps and the moment at midspan is 110 X 0.247 MLL --------0302----- 90 ft-kips . 3 2 Impact. For a 30-ft span impact is taken as 30 . At midspan M 0.30 X 90 27 ft-kips. At supports M 0.30 -172 -52 ft-kips. Total Floorbeam Moments. The design moments previously calculated are summarized in Table 12.78. Properties of Floorbeam Sections. For stress computations an effective width so of the deck plate is assumed to act as the top flange of member III. For determination of so the effective spacing of floorbeams Sf is taken equal to the actual spacing 180 in. The effective span le with the floorbeam ends considered fixed is taken as 0.7 X 30 X 12 252 in. Hence Sf le 180 252 0.715 From Table 4.6 for this ratio S- 0.53 and s 0.53 X 180 95 in sf Fig. 12.63 and c . The neutral axis of the floorbeam sections at midspan and supports can be located by taking moments of component areas about middepth of the web. This computation and those for moments of inertia and section moduli are given in Table 12.79. Floorbeam Stresses. These are determined for the total moments in Table 12.78 with the section properties given in Table 12.79. Calculations for the stresses at midspan and the supports are given in Table 12.80. Since the stresses are well within the allowable the floorbeam sections are satisfactory. TABLE 12.78 Moments ft-kips in Floorbeam with Orthotropic-Plate Flange Mdl MLL M Total M Midspan 104 90 27 221 Supports 0 -712 -52 -224 BEAM AND GIRDER BRIDGES 12.149 TABLE 12.79 Floorbeam Moments of Inertia and Section Moduli a At midspan Material A d Ad Ad2 Io I Deck 95 X 35.6 10.69 381 4 070 4 070 Web 21 X 3 8 7.9 290 290 Bottom flange 10 X 1 5.0 -10.75 -54 580 580 48.5 327 4 940 d 327 48.5 6.73 in -6.73 X 327 -2 210 Ina 2 730 Distance from neutral axis to Top of deck plate 10.50 0.375 - 6.73 4.15 in Bottom of