Mechanism of fatigue crack growth in concrete : observation and modeling | |
| Author | Shin, Hak Chul |
| Call Number | AIT Thesis no.ST-90-17 |
| Subject(s) | Concrete--Fatigue Concrete--Cracking |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | Fatigue crack growth in concrete is studied experimentally and theoretically with a main object to identify its governing mechanism. It has been clarified that Dugdale-Barenblatt-type model with tension-softening relation describes fracture of concrete under monotonic load. Tension-softening relation represents material behavior governing fracture phenomena. In the present study, the tension-softening behavior of concrete under cyclic tensile load is considered to be responsible for the fatigue crack growth. Tension-softening behavior of concrete under cyclic tensile load has several characteristics. One of the features is the residual opening displacement in unloaded state which resist to close crack faces resulting in tensile stress at the crack tip. The residual opening displacement is evaluated analytically to examine the possibility of crack growth due to residual opening displacement. It is shown that the residual opening displacement creates tensile stress at the crack tip, but it is not large enough to extend the crack. Another feature of cyclic tension-softening behavior is the stress degradation in reloading. The opening displacement and transmitted stress in reloading process is almost proportional with a reduced slope. The maximum stress in reloading decreases to about 85% of the stress before unloading. This stress degradation may be responsible for crack extension. An analytical model is proposed with the stress degradation in reloading. The model predicts crack extension at each load cycles. The amount of crack extension decreases with. increasing loading cycles, and crack growth stops after several cycles. -iii- With increasing load the crack growth rate increases, and the number of cycles before the crack growth arrest increases. When the load is large and close to the maximum load for monotonic fracture, the crack growth becomes unstable after several cycles. Low-cycle fatigue crack growth tests are carried out where the distribution of crack opening displacement is measured by laser speckle method. Amount of crack extension at each load cycle is evaluated from measured distribution of crack opening displacement. Experimental results are compared with analytical predictions by the proposed model. The agreement between the experimental result and analytical prediction of crack extension length is satisfactory. The proposed analytical model predicts arrest of crack extension after several cycles when the load level is low. This tendency seems to agree with observed phenomena. It is concluded that the mechanism of fatigue crack growth in concrete is the degradation of stress in reloading process. The proposed model provides theoretical prediction of fatigue crack growth under different conditions. |
| Year | 1990 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Horii, Hideyuki |
| Examination Committee(s) | Ueda, Tamon ;Pichai Nimityongskul |
| Scholarship Donor(s) | The Government of Japan |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1990 |