種別 | Paper |
主題 | DIFFERENT METHODS TO DETERMINE FRACTURE ENERGY AND STRAIN SOFTENING OF CONCRETE |
副題 | |
筆頭著者 | Keitetsu ROKUGO |
連名者1 | Folker H. WITTMANN |
連名者2 | Pieter E. ROELFSTRA |
連名者3 | Eugen BRUHWILER |
連名者4 | |
連名者5 | |
キーワード | |
巻 | 9 |
号 | 2 |
先頭ページ | 663 |
末尾ページ | 668 |
年度 | 1987 |
要旨 | 1. INTRODUCTION The whole failure process as expressed by complete load-displacement diagram has gained interest for huge and important concrete structures such as prestressed pressure vessels, tanks for liquified natural gas, large dams, etc. In order to describe the failure behaviour of concrete in a realistic way, concepts of Fracture Mechanics must be introduced in numerical analysis. The fictitious crack model [1,2] and the blunt crack model [3] have been developed based on the fracture energy concept. RILEM Technical Committee 50-FMC has proposed a recommendation [4], which specifies a method for the determination of the fracture energy G_{F} of concrete by means of three-point bending tests on notched beams. It has been shown that not only the G_{F}-value but also the shape of the strain-softening diagram [2,6] is needed for the application in computerized structural analysis [5]. The current status of Fracture Mechanics of concrete is reported in ref. [6]. In this contribution, the fracture energy and the strain-softening diagram of concrete as determined by means of the newly proposed wedge splitting test [11] are presented. These test results are compared with those obtained from the three-point bending test [7] suggested by RILEM recommendation and from the compact tension (CT) test [8]. The effect of the ligament length and the geometry of the specimens on the fracture energy are investigated. Load-displacement curves are numerically predicted with the assumption of a bilinear softening-diagram, and are compared with experimental curves. The G_{F}-value as obtained from the calculated strain-softening diagram is compared with the G_{F}-value determined from the load-displacement curve. 5. CONCLUSIONS (1) The fracture energy and the strain-softening diagram of concrete can be determined by means of the wedge splitting test as well as the CT-test. (2) The fracture energy G_{F} of concrete depends on the ligament length of the specimen. The results indicate that G_{F} increases with increasing ligament length up to certain limit, then G_{F} seems to remain constant. For the concretes tested in this project the limit is about 300mm. (3) G_{F}-values as obtained by the three different testing methods agree well for similar ligament length. It can be concluded that no strong influence of the geometry of specimens on G_{F} exists. (4) With the assumption of a bilinear strain-softening diagram, load-displacement curves can be calculated by means of FE-analysis and lead to a good agreement with the experimentally determined curves. For the cube specimen and the CT-specimen, the G_{F}-values as obtained from the calculated strain-softening diagram correspond well to the G_{F}-values determined directly from the load-displacement curve. |
PDFファイル名 | 009-01-2114.pdf |