There is no nondestructive evaluation method capable of determining stresses in concrete structural members in situ. Here, we propose and evaluate a torsional-vibration testing technique that offers an approach to estimate the stress state in concrete specimens by means of characterizing the material nonlinearity. We axially load three prismatic specimens comprising different concrete mixtures and measure their torsional vibration frequencies during four loading cycles. The fundamental torsional frequency shows a positive correlation with applied compressive stress for both loading and unloading stages after correcting for the effects of non-uniform torsion, geometric nonlinearity and changing boundary conditions. To quantify this behavior, we define the nonlinear parameter $$\beta_{G}$$ β G to characterize the material nonlinearity (acoustoelasticity). The values of $$\beta_{G}$$ β G of the initial loading cycle are lower than those of the subsequent loading cycles. However, the latter values of our concrete mixtures are consistent and similar to the values computed from previously published results. An estimate of the $$\beta_{G}$$ β G parameter of a concrete structural member provides a pathway for nondestructive assessment of in situ compressive stress in the member.

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用于混凝土声弹性表征的扭振技术

没有能够在现场确定混凝土结构构件应力的无损评估方法。在这里，我们提出并评估了一种扭转振动测试技术，该技术提供了一种通过表征材料非线性来估计混凝土试样中应力状态的方法。我们对三个包含不同混凝土混合物的棱柱试样进行轴向加载，并在四个加载周期内测量它们的扭转振动频率。在校正非均匀扭转、几何非线性和不断变化的边界条件的影响后，基本扭转频率与加载和卸载阶段的应用压缩应力呈正相关。为了量化这种行为，我们定义非线性参数 $$\beta_{G}$$ β G 来表征材料的非线性（声弹性）。初始加载循环的$$\beta_{G}$$ β G 值低于后续加载循环的值。然而，我们的混凝土混合物的后一个值与先前公布的结果计算出的值一致且相似。对混凝土结构构件的 $$\beta_{G}$$ β G 参数的估计为构件中的原位压应力的无损评估提供了途径。