| 種別 | paper |
| 主題 | Microscopic Experimental Observation of Concrete |
| 副題 | |
| 筆頭著者 | Junichiro NIWA（Nagoya University） |
| 連名者1 | Ahmed M. FARAHAT（Graduate School of Nagoya University） |
| 連名者2 | Kouji YAMADA（Student of Nagoya University） |
| 連名者3 | |
| 連名者4 | |
| 連名者5 | |
| キーワード | |
| 巻 | 14 |
| 号 | 2 |
| 先頭ページ | 1041 |
| 末尾ページ | 1046 |
| 年度 | 1992 |
| 要旨 | INTRODUCTION The idea of defining the inelastic behavior of different materials, independent of planes of different orientations within the material has a long history. For metals, in the slip theory of plasticity, the stresses acting on various slip planes are assumed to be the resolved components of the applied macroscopic stress tensor, while the plastic strains on the slip planes are not the resolved components of the macroscopic strain tensor. For concrete, in the microplane models, the strains on various planes are assumed to be resolved components of the macroscopic strain tensor while the stresses on these planes are not resolved components of the macroscopic stress tensor. However, because of the lack of microscopic experimental data, the material is assumed to be either statically or kinematically constrained. On the other hand, the authors believe that the real stress and strain fields at the microlevel are highly scattered and nonsmooth. Therefore, the effect of the nonuniform stress or strain distribution at the microlevel should be considered. Recently, although some investigators tried to consider the nonuniformity of strain distribution in concrete, a more precise distribution of microstrains seems necessary. In the current study, an experimental work is conducted to observe the real distribution of the microstrains in concrete. For this purpose, five specimens are examined. In these specimens, coarse aggregates are simulated by rounded steel cylinders of 3.2 cm diameter and 5.0 cm height, embedded in mortar. The rounded steel cylinders are used to provide an idealized smooth surface for measuring system. Finally, the effects of mortar strength, specimen size and measuring procedure(i.e. gauge length) on the distribution of the microstrains are investigated. CONCLUSIONS In this study, an experimental work has been conducted microscopically for concrete. The first objective of the experiment is to observe the distribution of the microstrains at the contact. The second objective is to check whether concrete material is kinematically constrained or not. The effects of specimen size, strength of mortar, and gauge length on the strain distribution are investigated. It is observed that the microstrains are highly scattered, nonsmooth and cannot be predicted by a simple rule. It is recommended that the shorter gauge length should be used to measure the microstrains because it measures only the strains of mortar, while the measurements by the longer one is affected by the strains of the coarse aggregates. Also, it is noticed that minor differences of the microstrains are obtained with the use of different mortar strengths. Moreover, although a small variation of specimen sizes is used, an obvious difference of the microstrains is noticed. This is due to the fact that from the microscopic point of view, the behavior of the microstructure is greatly influenced by the quantity and the distribution of coarse aggregates. In addition, the crack patterns of all specimens are presented. It is observed that most of the cracks start either at the boundary of steel cylinders or in the thin layers of mortar located at the contacts. To have a general relationship between both the microscopic and macroscopic strains, a more comprehensive experimental work must be conducted on the microlevel. Moreover, the effect of mortar thickness at the contacts and the roughness of steel cylinders to consider the irregularity of aggregates on the microstrains should be observed. The authors are investigating the influence of these parameters and analytical proceedings show that these parameters have considerable bearing on the actual response. |
| PDFファイル名 | 014-01-2180.pdf |