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On April 25, 2015, a Mw 7.8 earthquake struck the Gorkha district of Kathmandu, Nepal. In Patan, vibrational characteristics of a 300-year-old two-story masonry building near Patan Durbar Square had been measured prior the Gorkha earthquake. In the inspection of the building after the Gorkha earthquake, several new cracks were found. The vibrational characteristics of the building were measured again, and it was found that the natural frequencies after the earthquake were smaller than those before the earthquake, indicating the reduction of the stiffness. Finite element models of the structure representing pre- and post-earthquake conditions are established so that the natural frequencies match the pre- and post-earthquake measurements and the structural damage is identified based on the stiffness reduction. Finally, the dynamic analysis of the finite element model of the building in the pre-earthquake condition using the observed ground motion record during the Gorkha earthquake as the input is conducted, and the structural response of the building during the Gorkha earthquake is discussed.

eformability for failure analysis of masonry structures. Many people in developing countries live in masonry structures. In earlier DEM schemes, a structure is modeled as an assembly of rigid elements, but element deformability cannot be considered. The deformation of a structure can be modeled by overlapping between elements, but Poisson’s effect cannot be modeled. However, bricks used in developing countries can readily be deformed due to their low stiffness. Therefore, it is preferable to also consider element deformability in the DEM. In the new DEM, each element is divided into two parts: an inner part that considers deformation of the element itself, and an outer part that deals with contact between elements. Deformation of a structure can be modeled by overlapping between elements and deformation of the elements themselves. The validity of the method is confirmed through a comparison of the elastic deformation with a finite element model. It was found that the original DEM and the proposed method show different failure patterns of seismic behavior due to Poisson’s effect.

Medium pressure gas pipelines sustained severe buckling damage during the 2007 Niigata-ken Chuetsu earthquake. We investigated relationship between damage to the gas pipeline and the ground with irregular interface at Kashiwazaki city in Niigata prefecture. Axial strain of the ground have a great influence on pipelines, therefore, we calculated the ground strain parallel to the pipeline by using Aki-Larner Method, which can solve the ground response for arbitrary input ground motion. The ground strain obtained is in good agreement with the value of experimental data at which the buckling begins to occur.

This study deals with a damage detection method using a time reversal technique which does not require reference data at an intact state but only data at a current state to detect damages. The method assumes linear damages such as notches or holes, and is applicable to damped structures. A tone burst force is firstly input to a structure at one point A and the acceleration response is measured at the other point B. Then the time-reversed acceleration response is input at point B as a force and the acceleration response is measured at point A. This response is then time-reversed and is defined as "reconstructed wave". Damage existence and location can be detected simply from the waveform of the reconstructed wave. Numerical analysis was carried out on a plate structure with and without a rib, and the effectiveness of the method is verified.

We conducted seismic evaluations of a traditional wooden building using three-dimensional earthquake response analyses. The building is registered as one of the "Historic Monuments of Ancient Kyoto", UNESCO World Heritage Site, and is located in a region of strong earthquake motion from a scenario earthquake. The structure is an invaluable asset, but it is at risk of damage resulting from earthquake. Our numerical estimation was based on a dynamic interaction analysis between the building and the surrounding ground because it was located on the slope of a hill with complicated geophysical features. We also conducted a dynamic non-interaction analysis of the structure for a comparison with the aforementioned interaction model. Boring explorations and geotechnical tests were conducted before the assessment in order to investigate the ground foundation. We included the surrounding ground for a more realistic analysis because the seismic estimation for a model consisting only of the main structure differs significantly from that of the structure-ground coupling model. The results showed that the main wooden building was at risk of partial damage as it exceeded the safety limits prescribed for a scenario earthquake, and would collapse in the case of double the amplitude of the scenario earthquake. Language: en

The process of failure propagation of masonry buildings during earthquakes is simulated using a refined version of the distinct element method that simulates three-dimensional elastic, failure, and collapse behaviors of structures. Models with a flat roof and models with a vault roof are considered, and their failure propagation mechanisms are examined. The influence of the direction of the input ground motion on failure propagation is also investigated. Moreover, the effectiveness of three reinforcement measures is compared. One measure is increasing the mortar strength, the second is increasing the thickness of the bearing walls, and the third is introducing wooden columns and beams. Among these measures, increasing the mortar strength is found to be the most effective. Increasing the thickness of the bearing walls and introducing wooden columns and beams are found to be effective only if the roof has sufficient integrity since the collapse of the roof depends on the integrity of the bearing walls and the roof itself.

In this study, we propose a method to consider deformability of elements for a failure analysis of masonry structures using the DEM. In the original DEM, the deformability of the structure can be modeled by overlapping between rigid elements, but Poisson's effect cannot be modeled. In the proposed method, an element is divided into two parts, an inner part to consider deformation of the element itself, and an outer part to deal with contact between elements. The stiffness of the inner part is modeled using the stiffness matrix of the finite element method. When two elements are continuous or in contact, springs are set between the elements and the spring constants are estimated based on the original DEM and the length of the outer part. The validity of the method is confirmed through the comparison of elastic deformation with the FEM. It is found that the original DEM and the proposed method show different failure patterns, and considering the deformability of element is found to be necessary.

Kathmandu Valley is a center of culture in Nepal. Unfortunately, a large number of historic buildings have been damaged due to earthquakes in Kathmandu over the centuries since it is located on the earthquake-prone zone. Especially, an earthquake which hit Kathmandu in 1934 had a magnitude over 8 and it destroyed most of the cultural heritage, such as temples, shrines and monuments. Jatapol is an old area in Kathmandu where many historic masonry residential buildings are built without special attention to earthquake. It is very important to leave those buildings for posterity. To take measures to save those buildings from earthquakes, it is necessary to evaluate their seismic risk. However, there exist no sufficient statistical data to evaluate the risk from the past earthquakes. With this background, this study aims to numerically evaluate seismic risk of buildings using the refined version of the DEM.

Saving human lives and cultural heritage from natural disasters is a key to earthquake-disaster mitigation strategies. Culturally valued structures built before earthquake codes and regulations emerged are often vulnerable to earthquake loads, but such structures must be comprehensively studied before applying mitigation measures. Microtremor measurements in Patan Durbar Square area, a World Heritage site, were investigated to determine dynamic properties of the soil at four locations and the predominant ground frequency calculated to be 2.07 Hz. Ambient vibration in an old masonry building was measured and vibration frequencies in different modes were detected using the Fourier spectrum, which found that the building has fundamental period in transverse direction. The building’s damping was estimated to be 5.2-6.4%.

We propose a dynamic analysismethod – a refined version of the DEM- that can simulate three-dimensional elastic, failure and collapse behaviors of structures. A structure is modeled as an assembly of rigid elements. Interaction between elements is modeled using multiple springs and multiple dashpots attached to surfaces of the elements. The elements are assumed to be rigid, but the method allows the simulation of structural deformation by permitting penetration between elements. There are two types of springs: one is a restoring spring to simulate elastic behavior before failure and the other is a contact spring for simulating contact and recontact between elements. A contact dashpot is also used to dissipate the energy of contact. Structural failure is modeled by replacing restoring springs with contact springs and dashpots. A method for determining spring constants is also proposed. The validity of the method is confirmed by the numerical simulation of masonry wall models. First, the elastic behavior induced by an impact force is calculated. It is found that the elastic behavior determined using the proposed method is in good agreement with that determined using the finite element method. Second, the seismic behaviors of masonry wall models with different laying patterns and a wall model with reinforcement are analyzed. It is found that the proposed method allows expression of the difference in behavior due to different laying patterns and reinforcement. The validity of the proposed method is thus confirmed. The proposed method is suitable for simulating seismic behavior of masonry structures.

The cultural property protection field is wide and varied, with the problem of natural disaster alone often being overlooked, especially in seismic hazard measures. Cultural property preservation field experts recognize that fire-prevention measures, for example, having focused on accidental fires and arson within shrine and temple precincts that have been ineffective in preventing fires from spreading to historical buildings during simultaneous fire outbreaks in surroundings of concern during earthquakes. In 2003, the Japanese government recognized the importance of cultural heritage disaster mitigation, and a National Committee was organized whose first report was released in 2004, leading, in turn, to the first national project for protecting cultural assets against natural disasters. The project focused on two 1,500-ton under-ground water storage tanks near Kiyomizudera and Sanneizaka. With a pressurized water sprinkler system and other fire control facilities, the facility is expected to be used to fight fires during earthquakes and to provide easy-to-use fire hydrants for other fires.

This paper examines the seismic performance of Japanese traditional wooden structures considering stiffness and strength aging changes in old structural members. In strength and embedding testing done to evaluate the strength properties of old structural members, results showed that zelkova has a Young's modulus similar or larger than new members. In non-linear earthquake response analysis for a Kiyomizudera model based on test results, maximum angle response of columns was decreased reflecting old zelkova stiffness and strength.

3次元個別要素法を用いた動的解析では,剛体要素の並進運動と回転運動の方程式をそれぞれ解く必要がある.並進運動の方程式は2階の微分方程式であり,安定性,精度,実装の容易さの点で好ましいとされるLeap-frog法が時間積分手法としてよく用いられている.一方,回転運動のEulerの運動方程式は1階の微分方程式であり,どのような時間積分手法を採用するのが良いかについては,あまり研究がなされていない.本研究では,Eulerの運動方程式をLeap-frog法に基づいて積分する手法を提案した.提案手法による計算結果を,Euler法と既往のLeap-frog法に基づく計算結果と比較することにより,安定性,計算時間,精度の点で提案手法が優れていることを示した.

1Post Doctoral Fellow, Ritsumeikan Global Innovation Research Organization, Ritsumeikan University, Japan (603-8341, Kyoto City, Kita-ku, Komatsubara, Kitamachi 58) 2Professor, Department of Urban Management, Kyoto University, Japan (615-8540, Kyoto City, Nishikyou-ku, Kyoto University-Katsura Campus) 3Professor, Ritsumeikan Global Innovation Research Organization, Ritsumeikan University, Japan (603-8341, Kyoto City, Kita-ku, Komatsubara, Kitamachi 58) 4Assistant Professor, Department of Civil and Earth Resources Engineering, Kyoto University, Japan (615-8540, Kyoto City, Nishikyou-ku, Kyoto University-Katsura Campus) 5Professor, Department of Civil Engineering, Institute of Engineering, Tribhuvan University, Nepal (Pulchowk Campus, Lalitpur)

本研究は、滋賀県の大学キャンパスを対象にして、緊急地震速報を活用した想定東南海地震に対する地震対策について検討したものである。まず、東南海地震時における地表での加速度波形を1 次元非線形応答解析により求め、揺れの大きさと震源からの主要動到達時間について検討した。その結果、対象場所における揺れは震度5 弱で1 分ほど続き、直前対策行動可能時間は約30 秒であることがわかった。また、主要動までの猶予時間30 秒に対する学生の意識調査、キャンパス内での危険箇所調査、避難実験による避難時間調査などを実施し、大学キャンパス内の緊急地震速報に対する地震対策方法を提案した。

本研究では、経年変化が清水寺本堂の耐震性能にどのような影響を与えるか検討を行った。劣化が起こりやすく、清水寺本堂の耐震性能に大きな影響を与えることが予想される柱脚部と柱貫接合部に劣化を仮定し、耐震性能評価を行った。また、清水寺本堂の主要構造部材はケヤキであるが、ケヤキは構造材となってから年が経つにつれて材自体の強度が低下するという研究報告がある。この経年による材自体の強度低下を考慮した耐震性能評価も行った。荷重増分解析の結果、経年変化を考慮することで清水寺本堂の保有水平耐力が低下した。特に、柱貫接合部の劣化が激しいと仮定した場合においては、保有水平耐力は健全時の70%程度になり危険であることがわかった。非線形地震応答解析の結果、柱脚部より柱貫接合部の劣化の方が清水寺本堂の耐震性能に与える影響は大きいことがわかった。さらに、懸造部の柱貫接合部の劣化が本堂部の耐震性能に与える影響は小さいことがわかった。清水寺本堂は建立されてから約400 年経過しており、このことからケヤキのヤング係数を低下させて非線形地震応答解析を行った結果、応答変位の最大値が大きくなったが倒壊に至るほどではなかった。

本研究では, 柱脚の軸力変動が木造建築物全体の耐震性能に及ぼす影響を検討した.柱が浮き上がることをも考慮した柱脚鉛直バネと, 摩擦による柱脚水平バネとを連成させた解析モデルを作成し地震応答解析を行った.入力地震波は想定花折地震動である.柱脚の浮き上がり柱脚部の水平方向変位に対する抵抗がなくなることを考慮したシミュレーションを行った.その結果, 柱頭の最大応答変位に柱の軸力変動が与える影響は小さいが, 柱の軸力変動を考慮することにより柱脚の残留変位, 柱のせん断力及び横架材の軸力の増加が生じることがわかった.