Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . 478 MECHANICS OF ENGINEERING. per sq. inch) = J ± J ± d is obtained for any sectionto compute a proper thickness of web, spacing of rivets,etc. 388 The Arch-Truss, or braced arch. An open-worktruss, if of homogeneous design from end to end, may betreated as a beam of constant section and constant momentof inertia, and if curved, like the St. Louis Bridge and theCoblenz Bridge (see § 378, Class D), may be trea
Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . 478 MECHANICS OF ENGINEERING. per sq. inch) = J ± J ± d is obtained for any sectionto compute a proper thickness of web, spacing of rivets,etc. 388 The Arch-Truss, or braced arch. An open-worktruss, if of homogeneous design from end to end, may betreated as a beam of constant section and constant momentof inertia, and if curved, like the St. Louis Bridge and theCoblenz Bridge (see § 378, Class D), may be treated as anarch-rib.* The moment of inertia may be taken as 2 2^-iV 2; where FY is the sectional area of one of the pieces (I to thecurved axis midway between them, Fig. 437, and h = dis-tance between them. l^v^O. Fig. 438. Fig. 437. Treating this curved axis as an arch-rib, in the usualway (see preceding articles), we obtain the spec, equil. its force diagram for given loading. Any plane ~| tothe rib-axis, where it crosses the middle m of a web-member, cuts three pieces, A, B and 0, the total com- *The St Louis Bridge is not strictly of constant moment of inertia, being somewhatstrengthened near each pier ARCH-RIBS. 479 pressions (or tensions) in which are thus found : For thepoint ra, of rib-axis, there is a certain moment = Hz, athrust = Th, and a shear = J, obtained as previously ex-plained. We may then write P sin ft = J (1) and thus determine whether P is a tension or compres-sion ; then putting P+P ± P cos fi = Th . . . 2(in which P is taken with a plus sign if a compression, andminus if tension); and {Pr-P)\=Hz (3) A we compute F and P, which are assumed to be both com-pressions here, /? is the angle between the web memberand the tangent to rib-axis at ra, the middle of the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectenginee, bookyear1888
