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Structural Steel Designers Handbook Part 14

Tham khảo tài liệu 'structural steel designers handbook part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 14.66 SECTION FOURTEEN FIGURE 14.45 Section for brace between arch ribs. Width-Thickness Ratios 2-in top plate 7 i6-vertical plate Actual b 1 18 0.5 36 185 0.438 42.3 Allowable b 1 126.5 vja 39 45 max 158 vja 48.7 50 max The brace section is satisfactory. 14.11.6 Rib Bracing The plan of the structural carbon steel bracing used for the arch rib is shown in Fig. 14.18. Figure 14.45 shows the section used for a brace in the first panel of bracing. Rib bracing is designed to carry its own weight wind on ribs and rib bracing and an assumed buckling shear from compression of the ribs. Loads on the first-panel brace are given in Table 14.10 and section properties are computed in Table 14.11. The maximum bending stress produced by total load is _ 1120 X 12 134.5 X 12 - 1284 652 10.5 2.5 13.0 ksi TABLE 14.10 Loads on Brace Between Arch Ribs P kips Mx ft-kips My ft-kips Dead load . 1120 67.5 Wind 58.7 . 67.0 Buckling 266.0 Total 324.7 1120 134.5 ARCH BRIDGES 14.67 TABLE 14.11 Properties of Rib Brace Axis x-x Axis y-y Section A dx Io Ad. - Ix x dy Io Ady2 Iy PL 2 47 X 3 8 35.2 . . . 6490 . . . 6 490 12.19 . 5230 5230 PL 2 24 X 7 s 42.0 23.56 . . . 23 300 23 300 . 2020 . 2020 4 WT 6 X 13 15.3 8.00 35 979 1014 7.14 47 780 827 92.5 30 804 8077 Radius of gyration rx V30 804 92.5 18.2 in r. ry V8 077 92.5 9.34 in Unsupported length 58.7 ft Effective length factor K 0.75 truss-type member connections Slenderness ratio KL rx 0.75 X 58.7 X 12 18.2 29.0 Slenderness ratio KL ry 0.75 X 58.7 X 12 9.34 56.6 Section modulus S 30 804 24 1284 in3 Sy 8 077 12.38 652 in3 The total axial stress is fa 324.7 92.5 3.5 ksi For combined stresses with wind allowable stresses may be increased 25 . Axial and bending loads are evaluated for combined stresses with Eq. 14.11 with Cm 1. F ex 2 29 000 160.5 ksi F ey 2 29 000 42.1 ksi 2.12 56.6 2 . s Fa 16.98 - 0.00053 56.6 2 15.3 ksi Fb 20.0 ksi 3.5 __1.0 X 10.5 _1.0 X 2.5_ 1.25 X 15.3 1 - 3.5 160.5 20.0 X 1.25 1 - 3.5 42.1 20.0 X