Among various alternatives developed for conventional reinforced concrete, ultra-high performance fiber-reinforced concrete (UHPFRC) is proven to provide superior mechanical properties, making it appropriate for impact-resistant structures. While several experimental tests have been conducted to determine the static and dynamic response of UHPFRC, the simulation of this important category of concrete materials, especially under impact loads, is still in need of extensive effort. To address this issue, the current study investigates how two widely-used concrete constitutive models, i.e., Continuous Surface Cap Model (CSCM) and Karagozian and Case Concrete (KCC), can be reliably employed for modeling UHPFRC subjected to low-velocity impact. Utilizing the available experimental test data, a rigorous calibration process has been developed in the current study for the two constitutive models, capturing the main strength parameters, damage evolution parameters, and strain rate effects. This process begins with single-element simulations performed under various stress paths to generate the information necessary for post-peak softening and confinement factors. The investigations with single-element simulations consist of four element sizes to study the mesh size sensitivity of both constitutive models. The study is then extended to examine the capabilities of the calibrated models in simulating the response of full-scale structural elements made with UHPFRC. For this purpose, the drop hammer tests are replicated on both plain and reinforced UHPFRC, and the performance of the two constitutive models is evaluated in comparison to the experimental tests. Specifically, this evaluation examines peak impact forces and displacements, considering various hourglass coefficients and drop hammer heights. Furthermore, a metamodel-based sensitivity analysis is conducted to quantify the effects of uncertainty inherent in the input parameters on the predicted impact response measures, in terms of force, displacement, and duration.

在为传统钢筋混凝土开发的各种替代方案中，超高性能纤维增强混凝土 (UHPFRC) 已被证明可提供卓越的机械性能，使其适用于抗冲击结构。虽然已经进行了几次实验测试来确定 UHPFRC 的静态和动态响应，但对这一重要类别的混凝土材料的模拟，尤其是在冲击载荷下，仍然需要大量的努力。为了解决这个问题，目前的研究调查了两种广泛使用的混凝土本构模型，即连续表面盖层模型 (CSCM) 和 Karagozian and Case Concrete (KCC)，如何可靠地用于模拟受到低速冲击的 UHPFRC。利用现有的实验测试数据，在当前的研究中，针对两个本构模型制定了严格的校准过程，捕获主要强度参数、损伤演化参数和应变率效应。该过程从在各种应力​​路径下执行的单元模拟开始，以生成峰值后软化和限制因素所需的信息。单元素模拟研究包括四种元素尺寸，用于研究两种本构模型的网格尺寸敏感性。然后扩展研究以检查校准模型在模拟由 UHPFRC 制成的全尺寸结构元件的响应的能力。为此，在普通和增强 UHPFRC 上重复落锤测试，并且与实验测试相比，评估了两个本构模型的性能。具体而言，该评估检查了峰值冲击力和位移，同时考虑了各种沙漏系数和落锤高度。此外，还进行了基于元模型的灵敏度分析，以量化输入参数中固有的不确定性对预测的冲击响应措施（在力、位移和持续时间方面）的影响。