Son Bunka, Li Ganggang, Luo Zhiwei, Sun Yuping
Graduate School of System Informatics, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan.
Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan.
Materials (Basel). 2024 Nov 28;17(23):5850. doi: 10.3390/ma17235850.
The objective of this paper is to develop assessment models to quantitatively evaluate the seismic damage caused to resilient concrete columns intended for buildings located in strong-earthquake-prone regions such as Japan and China. The proposed damage assessment models are based on the fractal analysis of crack patterns on the surface of damaged concrete columns and expressed in the form of a fractal dimension (FD) versus transient drift ratio relationship. To calibrate the proposed damage assessment models, a total of eighty images of crack patterns for eight concrete columns were utilized. All the columns were reinforced by weakly bonded ultra-high-strength (WBUHS) rebars and tested under reversed cyclic loading. The experimental variables covered the shear span ratio of the column, the concrete strength, the axial load ratio, and the amount of steel in the WBUHS rebars. A box-counting algorithm was adopted to calculate or derive the FD of the crack pattern corresponding to each transient drift ratio. The test results reveal that the FD is an efficient image-based quantitative indicator of seismic damage degree for resilient concrete columns and correlates strongly with the transient drift ratio and is subjected to the influence of the shear span ratio. The influence of the other experimental variables on the derived FDs is, if any, little. Based on the test results, a linear equation was developed to define the relationships between the FD and transient drift ratio, and a multi-linear equation was formulated to relate the transient drift ratio to the residual drift ratio, an important index adopted in current design guidelines to measure the repairability of damaged concrete structures. To further verify the efficiency of the drift ratio-based FD in seismic damage assessment, the correlation between the FD and relative stiffness loss (RSL), an indicator used to measure the overall damage degree of concrete structures, was also examined. The driven FD exhibited very strong correlation with RSL, and an empirical equation was developed to reliably assess the overall seismic damage degree of resilient concrete columns with an FD.
本文的目的是开发评估模型，以定量评估对位于日本和中国等地震多发地区的建筑用韧性混凝土柱造成的地震损伤。所提出的损伤评估模型基于受损混凝土柱表面裂缝模式的分形分析，并以分形维数（FD）与瞬态位移比关系的形式表示。为了校准所提出的损伤评估模型，总共使用了八根混凝土柱的八十张裂缝模式图像。所有柱子均采用弱粘结超高强度（WBUHS）钢筋加固，并在反复循环加载下进行测试。实验变量包括柱的剪跨比、混凝土强度、轴压比以及WBUHS钢筋中的含钢量。采用盒计数算法来计算或推导对应于每个瞬态位移比的裂缝模式的FD。试验结果表明，FD是韧性混凝土柱地震损伤程度的一种基于图像的有效定量指标，与瞬态位移比密切相关，并受剪跨比的影响。其他实验变量对推导得到的FD的影响（如果有的话）很小。基于试验结果，建立了一个线性方程来定义FD与瞬态位移比之间的关系，并制定了一个多线性方程来将瞬态位移比与残余位移比联系起来，残余位移比是当前设计指南中用于衡量受损混凝土结构可修复性的一个重要指标。为了进一步验证基于位移比的FD在地震损伤评估中的有效性，还研究了FD与相对刚度损失（RSL）之间的相关性，RSL是用于衡量混凝土结构整体损伤程度的一个指标。推导得到的FD与RSL表现出非常强的相关性，并建立了一个经验方程，以通过FD可靠地评估韧性混凝土柱的整体地震损伤程度。
