Modeling Creep of Short Fiber Reinforced Concrete

短纤维混凝土的徐变建模

• 批准号: 422068083
• 负责人: Dr.-Ing. Johanna Eisenträger
• 金额: --
• 依托单位: School of Civil and Environmental Engineering
• 依托单位国家: 德国
• 项目类别: Research Fellowships
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/422068083?language=en
• 关键词: Modeling; Creep; Short; Fiber; Reinforced

As a modern and versatile material, short fiber reinforced concrete (FRC) is nowadays used in many applications, such as tunnel linings or marine structures. To increase the mechanical properties such as the ductility and to reduce crack propagation, the brittle concrete is mixed with short fibers, which results in a complex microstructure, including the concrete matrix, coarse aggregates, and fibers. Under constant long-term loads, creep occurs both in pure concrete as well as in FRC, thus the deformation increases with time.Although creep in FRC is a highly nonlinear process, up to now, only linear approaches for viscoelasticity have been proposed for this material. Furthermore, these models are restricted to uniaxial stress and deformation states. Additionally, the presented models for creep in FRC idealize microstructural features of this material, such as the shape and distribution of fibers and aggregates. To conclude, to date there is no viable approach which takes the complex microstructure into account. So far, numerical models are based on simplifying assumptions resulting in a limited ability to describe physical processes. Therefore, this project aims at developing a new numerical framework for creep of FRC under consideration of the real microstructural components. The procedure is based on computed tomography (CT) scans of FRC specimens, which have been cut from large-scale floor slabs. For the numerical simulation, the scaled boundary finite element method is used in conjunction with the octree algorithm, which allows for an automatized and efficient mesh generation based on the CT data. Thus, the proposed numerical model reflects precisely the real microstructure of FRC.In addition to the numerical framework, a new constitutive model for nonlinear creep of FRC is developed. Thereby, separate constitutive equations are formulated for the concrete matrix, the aggregates, and the fibers. While the mechanical behavior of the aggregates and the fibers can be modelled within the framework of elasticity, a new nonlinear model is developed to account for the inelastic deformations of concrete subjected to multiaxial stress and deformation states. The material parameters are determined based on creep tests on pure concrete, and the constitutive model is implemented into the numerical framework. In order to validate the proposed numerical tool, creep tests are conducted on FRC specimens, such that the resulting experimental data can be compared to the numerical simulation results.Consequently, this project presents a new simulation methodology for creep of FRC, while considering the complex microstructure of this material with high precision. Furthermore, a new nonlinear constitutive model is included into this framework, in order to account for creep deformations of FRC under multiaxial stress and deformation states. This provides the basis for a realistic estimation of the effect of long-term loading on FRC components.

作为一种现代且通用的材料，如今在许多应用中使用了短纤维钢筋混凝土（FRC），例如隧道衬里或海洋结构。为了增加机械性能，例如延展性和减少裂纹繁殖，脆性混凝土与短纤维混合，从而导致复杂的微结构，包括混凝土基质，粗骨料和纤维。在恒定的长期载荷下，蠕变既出现在纯混凝土和FRC中，因此变形随时间增加。尽管FRC中的蠕变是一个高度非线性的过程，直到现在，只有为此材料提出了粘弹性的线性方法。此外，这些模型仅限于单轴应力和变形状态。另外，提出的FRC中蠕变模型理想化了该材料的微观结构特征，例如纤维和聚集体的形状和分布。总而言之，迄今为止，还没有可行的方法来考虑复杂的微观结构。到目前为止，数值模型基于简化的假设，导致描述物理过程的能力有限。因此，该项目旨在开发一个新的数值框架，以考虑实际的微观结构组件的考虑。该过程基于对FRC标本的计算机断层扫描（CT）扫描，这些扫描已从大规模的地板板上切割。对于数值模拟，将缩放的边界有限元方法与OCTREE算法结合使用，该方法允许基于CT数据自动且有效的网格生成。因此，提出的数值模型精确地反映了frc的实际微观结构。在数值框架中，开发了一种新的非线性蠕变的本构模型。因此，为混凝土基质，聚集体和纤维制定了单独的本构方程。虽然可以在弹性框架内建模聚集体和纤维的机械行为，但开发了一种新的非线性模型，以说明遭受多轴应力和变形状态的混凝土的非弹性变形。材料参数是根据纯混凝土上的蠕变测试确定的，并且本构模型被实现到数值框架中。为了验证所提出的数值工具，对FRC样品进行了蠕变测试，以便可以将所得的实验数据与数值模拟结果进行比较。结果，该项目对FRC的蠕变进行了新的模拟方法，同时考虑了具有高精度的该材料的复杂微结构。此外，该框架中包括一个新的非线性本构模型，以说明在多轴应力和变形状态下FRC的蠕变变形。这为对长期负载对FRC组件的影响进行现实估计提供了基础。

项目成果

Discrete modeling of fiber reinforced composites using the scaled boundary finite element method

• DOI: 10.1016/j.compstruct.2019.111744
• 发表时间: 2020-03-01
• 期刊: COMPOSITE STRUCTURES
• 影响因子: 6.3
• 作者: Zhang, J.;Eisentrager, J.;Song, C.
• 通讯作者: Song, C.

Analytical model predicting the concrete tensile stress development in the restrained shrinkage ring test

• DOI: 10.1016/j.conbuildmat.2021.124930
• 发表时间: 2021-11
• 期刊: Construction and Building Materials
• 影响因子: 7.4
• 作者: Yingda Zhang;Sumaiya Afroz;Q. D. Nguyen;Taehwan Kim;J. Eisenträger;A. Castel;Tengfei Xu

An SBFEM Approach for Rate-Dependent Inelasticity with Application to Image-Based Analysis

• DOI: 10.1016/j.ijmecsci.2020.105778
• 发表时间: 2020-09
• 期刊: International Journal of Mechanical Sciences
• 影响因子: 7.3
• 作者: J. Eisenträger;Junqi Zhang;Chongmin Song;S. Eisenträger