A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . nthe algebraic work. 578 A TREATISE ON CONCRETE 11. Determine the moment,thrust, and eccentricity, and if desired theshear at the center points, i, 2, 3, etc., of the divisions, and enter in a tableas shown below. The moment is computed from formulas (19) and (20)on page 554, the values of whose terms have already been found by items7 and 8. The thrust and shear may be scaled from the force polygon. Forexample, at section i on folding Fig. 181 the thrust line is dra
A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . nthe algebraic work. 578 A TREATISE ON CONCRETE 11. Determine the moment,thrust, and eccentricity, and if desired theshear at the center points, i, 2, 3, etc., of the divisions, and enter in a tableas shown below. The moment is computed from formulas (19) and (20)on page 554, the values of whose terms have already been found by items7 and 8. The thrust and shear may be scaled from the force polygon. Forexample, at section i on folding Fig. 181 the thrust line is dra^vn parallelto the tangent to the axis at i, and the shear Hne at right angles to the thrustline. The eccentricities, e, of the sections i, 2, 3, etc., are computed bydividing the moment on the section (see page 561) by the thrust for thatsection just scaled. For positive moments and therefore positive values ofe, the line of thrust lies above the arch axis. 12. Compute the thrust and moment at the crown due to variation intemperature by formulas (25) and (26), page 556, the moments on the Table 2. Final Moments and Thrusts. Thrusts in lb. Moments in ft. lb. Shear in arch design is small and need not be computed. various sections by formula (27), page 557, and the thrusts and shears byresolving the crown thrust into tangential and radial components, as shownin the small force polygon in the diagram. A rise in temperature of 20 degrees Fahr., and of the same amount,is sufficient even in the northern part of the United States for arches withfilled spandrels. For the arch shown on folding Fig. 181 the crown thrust H^, due totemperature, is a tension of 2545 lbs., and z. compression of equal crown moment M^is + 2900 ft. lb. and — 2900ft. lb. 13. The effect of rib shortening due to the thrust is comparatively necessary to compute it, use formula (31) and (32), page 558. (See P-576.) For the problem here shown the thrust at crown due to this cause is
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