Papers by Author: Takahiro Iwatate

Abstract: An urgent is needed on the preservation of Chinese architectural heritages, since environmental and time impacts have been abating their structural resistance capability. It is of great importance in protecting and rehabilitating the ancient architectural culture of China to study the structural characteristics of ancient Chinese timber architectures. As a typical example of ancient timber architectures-Yingxian Wooden Pagoda in west of Shanxi Prince, the dynamic characteristics and damage mechanics of the tower are investigated experimentally and numerically by micro tremor measurements and means of finite-element-method (FEM). The micro tremor measurements are conducted on the tower (each floor) and the surrounding ground. From the micro tremor observation data, the predominant frequency of the surface ground and natural frequency, vibration mode and the damage distribution characteristics of the tower were evaluated. Based on the experimental studies, the tower is created by a delicate finite element model. And in order to simulate the mortise and tenon joint---bucket arches in the structure, which is a combination of a series of timber structures, a special beam-element group is developed. Numerical simulation of the seismic response of the tower shows that the second and third floors of the tower would be damaged more seriously than other floors for their severe stresses when acted by seismic loading. The present analysis of the tower shows the same phenomena. The results provide basis for repairing and reinforcing the ancient timber tower.

Abstract: In practical engineering, the cracks are always mixed mode. The research on the mixed fracture criterion has an important significance in fracture mechanics and engineering. Stress state of the mixed mode cracks is complicated. A new unified strength theory considering the effects of all the three principal stresses is generalized into the fracture mechanics in this paper. The complex stress states are common characteristics between the mixed mode cracks and the unified strength theory. A unified fracture function criterion is established by using the unified strength theory in this paper. In the unified fracture function, the difference between tension and pressure and the effect of the intermediate principal stress σ₂ are considered. With the variation of α = σ_t/ σ_c and failure parameter b , a series of mixed mode crack criteria are formed, and can be applied for many materials. The J-integral is calculated through FEM. According to the relation between the result and the stress intensity factor, K_lc can be obtained. Then it is used in the unified fracture function. The unified fracture criterion is compared with those of other mixed mode criterions.

Abstract: The ground fissure is one of primary geological disasters in Xi’an, China. The extension pattern and deformation failure area near fissure are studied through the FEM of elastic-plastic fracture mechanics in this paper. The results show the crack extension is not completely tension crack, it is mixed mode when the confined aquifer was pumped. The extents of earth surface deformation and stress concentration of beyond plate are larger than that of the bottom one. It is consistent with observational results.