Dynamic Multiaxial Strength Criterion for Concrete Based on Strain Rate–Dependent Strength Parameters

The majority of existing studies on the strain rate effect of concrete have concentrated on the dynamic uniaxial strength or a narrow range of strain rates. However, concrete material always works under a multiaxial stress state and suffers from loads with different strain rates. This paper presents a method to describe the dynamic multiaxial strength of concrete at all strain rates. The advantages of the nonlinear unified strength criterion (NUSC) are that this factor can reasonably describe the static strength behavior of concrete under a multiaxial stress state. In addition, the dynamic uniaxial S criterion can express the actual dynamic uniaxial strength at all strain rates. A nonlinear dynamic multiaxial strength criterion is developed based on the strain rate–dependent strength parameters of the NUSC, in which the strain rate–dependent strength parameters are derived from the S criterion. The obtained strength criterion consists of a series of continuous smooth convex surfaces in the principal stress space, which extends outward with increasing strain rate. In addition, the strength curve gradually changes from a curved triangle to a von Mises circle with increasing strain rate in the deviatoric plane. The proposed criterion is verified via its application to extensive experimental data from multiaxial dynamic tests in the literature, and the results demonstrate that the proposed criterion can reasonably describe the multiaxial strength and reflect the ultimate dynamic strength of concrete.