Takahiro Iwatate

Evaluation of Dynamic Behaviors and Damage Mechanism of Ancient Timber Architectures

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.

Imaging of caves in the ancient city wall of Xi'an

西安古城壁は，明代の1378年に完成したもので，当時の形がほぼ完全に保存されている中国で唯一の城壁である。現存する城壁としては世界的にみても最大級のものであり，また，城壁の西門（安定門）はシルクロードの起点としても知られていて歴史的文化遺産としての価値は極めて高い。城壁の外周は約14kmにおよび，高さは約12mである。断面は台形型で，上部の幅が12mから14m，下部の幅が15mから18mである。しかし，西安古城壁は，その内部に防空壕として掘削された総延長41kmにもおよぶ空洞が存在していることが知られている。特に城壁浅部に空洞が存在する地点では，陥没事故が生じるなどの被害が生じている。この歴史的文化遺産を保護するためには，空洞の分布を把握し対策を講じる必要がある。歴史的に極めて価値の高い構造物であるため，可能な限り非破壊での調査が望まれる。そこで，本研究では，城壁南門付近の100mの領域において地中レーダを用いた空洞探査を実施した。特に今回は陥没事故の原因とされている城壁浅部に存在する空洞の把握を目的とした。調査の結果，城壁浅部に空洞の存在を示唆する強い反射イベントが確認された。また，3次元マイグレーションを行った結果，空洞を3次元的に把握することができた。さらに，城壁表面のクラックの位置が，地中レーダにより検出された空洞位置や城壁内部の地盤状況とよく対応していることが明らかになり，歴史的文化遺産保護において重要な情報を得ることができた。

Application of the Unified Strength Theory in Analyzing Fracture Strength

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 = σt/ σc 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, Klc 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.

3-D Seismic Image beneath Hakone Volcano, Japan

Hakone volcano is located in the northern part of Izu peninsula. It is well known as inactive volcano and hot springs resort. But sometimes there are earthquake swarms. There was big earthquake swarm in April 2001. Total number of earthquakes was 15,816 during April to October. The cause of this activity is not yet solved. Explosion observation was carried out and 3-D velocity structure was estimated using explosions and micro earthquakes hybrid inversion method to know where magma exists or not. Not only micro earthquakes but also explosions were used, so the high resolution subsurface image and velocity value can be obtained with good accuracy. As results, we can find some faults as lines of hypocenter beneath Hakone volcano, and there is no results that suggests existence of magma. So it is considered that the cause of swarm earthquakes activity that occurred on 2001, was not activity of magma.