衢州学院本科毕业设计（论文）外文翻译(6)

8.4 TORSION AND SHEAR IN BEAMS WITHOUT WEB REINFORCEMENT It is evident that in superposition ; the shear stresses generated by torsion and shearing force are additive along one side and subtractive along the opposite side of a rectangular beam section .The critical diagonal tensile stresses that ensue are further affected by flexural tensile stresses in the concrete, because it is impossible to apply shearing forces without simultaneously inducing flexure. A fully rational theory for the interaction of shear and torsion in the presence of bending is not known to have yet been developed. For this reason reliance must be placed on empirical information derived from tests. By providing more than adequate flexural reinforcement, it is possible to experimentally study the failure criteria for combined shear and torsion. It is usual in such tests to keep the torsion to, shear ratio constant while the load is being increased to failure. However, in practice one action may occur first,imposing its own crack pattern before the other action becomes significant. For the time being, it is advisable to be conservative in the interpretation of test results.

Figure 8.10 plots the scatter obtained in typical combined torsion-shear tests. It also indicates that a circular interaction relationship (normalized for this particular group of tests) can be useful for design purposes, provided sufficiently low stress values for diagonal cracking by shear and torsion are chosen. For these beams,which contained no web reinforcement, the shear and torsional stresses which formed an approximate lower bound for the plotted experimental points, as computed from Eqs. 7.5 and 8.8, were found to be, respectively,

The circular interaction action relationship is the basis of the current ACI code provisions. 8.2

For convenience, the magnitude of the interaction shear and torsional forces carried by a cracked section at ultimate load can be expressed in terms-of nominal stress as

where

vt = induced nominal torsional stress carried by the concrete at ultimate, given by Eq. 8.8

vu = induced nominal shear stress carried by the concrete at ultimate given by Eq. 7.5

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