A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . are diagonaland in the direction which would be expected from the theory of diagonaltension. A typical crack due to diagonal tension is shown in Fig. 139, page 444- Such cracks as these can be due only to a combination of the shearingstress with the horizontal tensile stress, whose resultant forms diagonal ?The above principle may be expressed bv the equation vy 2t = vjj> —, which solved for vv bwill give formula (28). 444 A TREATISE ON CONCRETE tension. It is tl
A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . are diagonaland in the direction which would be expected from the theory of diagonaltension. A typical crack due to diagonal tension is shown in Fig. 139, page 444- Such cracks as these can be due only to a combination of the shearingstress with the horizontal tensile stress, whose resultant forms diagonal ?The above principle may be expressed bv the equation vy 2t = vjj> —, which solved for vv bwill give formula (28). 444 A TREATISE ON CONCRETE tension. It is tliis diagonal tension wliich must be sustained in a reinforcedconcrete beam by the area of concrete or by bent up rods and stirrups, asindicated in paragraphs which follow. Tests by Prof. Talbot* and Prof. Witheyf indicate that for 1:2:4concrete the first diagonal crack in a beam without stirrups or inclined rein-forcement is apt to occur when the maximum shear is from 100 to 200pounds per square inch. Since failure by diagonal tension is sudden, it isadvisable to provide a high factor of safety. In a beam with diagonal. Fig. 139.—Beam under Load at University of Illinois Cracked byDiagonal Tension. {See p. 443.) tension reinforcement, the first diagonal crack occurs at a period but slightlylater than in a beam with horizontal rods alone, but in this case it is verysmall and not dangerous if the steel is designed to take the stress. However,it is desirable that there should be always a sufficient area of concrete, evenwhen reinforced, to prevent the diagonal tension from exceeding the crack-ing point in the concrete. * Bulletin No. 12, University of Illinois, 1907. ?{? Bulletin of University of Wisconsin, Vol. 4, No. 2, 1907. REINFORCED CONCRETE DESIGN 445 REINFORCEMENT TO PREVENT DIAGONAL CRACKS IN BEAMS The failure of a beam from diagonal tension is more sudden than fromordinary tension or compression, and therefore must be guarded againsteven more carefully. Formerly when
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