Abstract
The outline of the failure stress conditions of concrete has been gradually clearified experimentally; neither the mohrenvelope type ctiteron, nor octahedral stress type criterion can explain the exact experimental results. The authors tried to create a new failure criterion, which solves the above contradictions and conforms to the microcracking phenomenon before failure. In the proposed "Phased Plane-moment Fracture Hypothesis", the plane distribution of σ-|τ| conditions is eveluated by Mp(k) curve, defined by the next equation, [numerical formula] The σ-|τ| stress plane is assumed "stress leveled" by a family of Griffith parabolas and the stress level is indicated by the parameter k of the following equation, [numerical formula] Where K_1 means |σ_c|/10. The σ-|τ| stress plane is also assumed "phased" by the phase angle θ=(tan)^<-1>(|τ|/σ). In the (4) eq., P(θ) means some monotonous decreasing function of θ, corresponding to crack-propagation difficulty and failure-standing tendency in high compressive range; in this paper P(θ)=cos^4(θ/2)/sin(θ/2) is assumed. (t-k) term represents the crack-propagation length dependency upon stress level. f(θ, t) d θ dt gives the differential plane quantity of (θ, k=t) expressed as "plane-distribution" (See Fig. 3〜Fig. 7). The proposed failure criterion is that Mp(k_0) reaches a constant value when concrete of the same quality fractures under any stress combination (σ_1, σ_2, σ_3) with similar test procedure. The substitution of k_0 into k in the (2) eq. gives crack-propagation stress condition, which conforms to visual microcrackong phenomenon before failures.
