A comprehensive finite element analysis at the mesoscopic level has been conducted into the complex topic of size effect coupling dynamic strain-rates. Taking the lightweight aggregate concrete (LWAC) dumbbell-shaped samples as the object of numerical investigation, the influence of strain-rate (with the range of 10⁻⁵/s ∼ 100/s) on direct-tensile failure of LWAC (including different lightweight aggregate volume fractions $V_{\mathrm{agg}}$ = 40%, 30% and 20%) was discussed. Subsequently, the structure size of LWAC samples was further expanded (width W = 100, 200 and 300 mm) and the dynamic size effect on direct-tensile strength was investigated. Numerical results show that both the direct-tensile strength and its corresponding size effect of LWAC exhibit a strain-rate dependent behaviour. The increasing strain-rate can gradually weaken the size effect of LWAC and direct-tensile strength would be independent to the structure size as the strain-rate reaches the critical strain-rate. The increasing lightweight aggregate volume fraction can reduce direct-tensile strength. Furthermore, a dynamic size effect model establishing the direct link between the strain-rate effect and size effect was proposed, which can quantitatively predict the dynamic direct-tensile strength of LWAC.

对尺寸效应耦合动态应变率的复杂主题进行了细观层面的综合有限元分析。以轻骨料混凝土（LWAC）哑铃形试样为数值研究对象，应变率（范围为10 ^-5 /s ∼ 100/s）对LWAC（包括不同轻骨料体积分数${伏}_{\mathrm{聚合}}$ = 40%、30% 和 20%）进行了讨论。随后，LWAC样品的结构尺寸进一步扩大（宽度W = 100、200 和 300 毫米），并研究了动态尺寸对直接拉伸强度的影响。数值结果表明，LWAC 的直接拉伸强度及其相应的尺寸效应都表现出应变率相关的行为。随着应变率达到临界应变率，应变率的增加会逐渐减弱 LWAC 的尺寸效应，直接拉伸强度将与结构尺寸无关。增加轻骨料体积分数会降低直接抗拉强度。此外，提出了建立应变率效应和尺寸效应之间直接联系的动态尺寸效应模型，该模型可以定量预测LWAC的动态直接拉伸强度。