Madan B. Karkee

Earthquake risk to Inca's historical constructions in Machupicchu

The citadel of Machupicchu is probably the most famous Inca heritage site in Peru. Considering the seismically active region, this research is an attempt to perform a seismic risk analysis of the heritage structures at Machupicchu. A systematic approach is adopted for this purpose. Characteristic seismicity of the region, where these historical constructions are located, is discussed based on the seismic hazard analysis. Evaluation of the vulnerability of the structures under the prevalent earthquake hazard is another important aspect essential for risk analysis. As a first step to proper understanding of the seismic behavior of these heritage structures, typical elements of Inca construction are studied by simple analytical models to verify basic aspects of structural integrity. The possibility that peak ground acceleration corresponding to even relatively low hazard may produce instability in some structural components like gable walls was noted. In view of this preliminary result, attempt was made to identify the dynamic characteristics of typical buildings units from more detailed investigation. This forms part of the outcome from the field study program, which included microtremor measurement of free field as well as typical constructions, planned and undertaken by the authors. The results of the microtremor measurements are utilized to estimate the dynamic characteristics of the Inca stone structures. That is, the analytical results are compared with the measurements to calibrate the analytical model. Since microtremor measurements involve very small displacements, the characteristics of stones structures thus obtained correspond to elastic behavior applicable to small strain condition. Based on this scheme, an approach has been proposed to evaluate the seismic behavior and hence the seismic vulnerability of these structures. The procedure also permits identification of the probable mode of failure of the structures concerned.

Earthquake Resistance Of A Historical BrickBuilding In Akita Prefecture, Japan

During the Meiji period (by the end of the 19 th century) many brick masonry buildings were constructed in Japan. However, due to the lack of reinforcement, these structures collapsed during the great Kanto earthquake, which occurred in the year 1923. Since then, this type of structure is not used for buildings and only a few historical constructions remain from that era. In Akita Prefecture, in the northeastern part of Japan, some of these buildings have been declared as local culture heritages. One of them is located in Ani village and was constructed in 1879 to serve as the residence for a German engineer who was working for a local mining company. As an initial step to evaluate the seismic vulnerability of this historical building, dynamic characterization has been undertaken. For that purpose, measurements of the micro vibration of the building was planned and undertaken by the authors. For the analytical modeling, mechanical parameters were estimated from a series of laboratory tests on masonry brick units obtained from the stock that are conserved near the building under study. The results of the microtremor measurements are discussed in relation to the analytical procedure adopted to estimate the dynamic characteristics of this historical brick structure. The structure shows intricate modes of vibration that are reflected in the multiple peaks observed in the transfer functions of microtremor records. With the analytical simulation considering only the effect of the brick walls, the multiple predominant frequencies are obtained for a certain range. With this good agreement of the analytical procedure and the measurement results, the reliability of the employed methodology was verified.

Preliminary evaluation of the seismic vulnerability of the Inca's Coricancha temple complex in Cusco

Coricancha was probably the most important Inca temple complex dedicated primarily to Inti, the Sun god. At present, a small part of the Inca stonework is all that remains of the ancient complex. Most of the complex was demolished by Spaniard conquistadors in the 17 th century to make way for the construction of Catholic Church of Santo Domingo on this site, using part of the Inca construction as the foundation. This complex is a fine example of how Inca stonework had been incorporated into the structure of a colonial building. Major earthquakes have severely damaged the church, but the Inca stone walls, built out of huge, finely cut tightly-fitting blocks of stone, still stand as a testimony to Incas architectural skills and sophisticated stone masonry practice. In this complex, a series of microtremor measurements were carried out to estimate the dynamic characteristics of the structures and the ground. Measurements on buildings include the Incas masonry walls as well as the tower of the colonial church. Measurements to estimate the ground characteristics were performed in the inner yard and at the outer garden of the complex. In this paper, the results of the measurements and corresponding interpretations are discussed. It was found that the predominant period of vibration of the church tower is comparable to the predominant period of the ground, and therefore, the tower appears to be more vulnerable to earthquake occurrence because of the possible resonance phenomenon to be expected.

Seismic Behavior Of A Thatched House AtMinehama Village In Akita, Japan

Old traditional wooden constructions in Japan are declared as buildings of cultural interest and therefore efforts are made to preserve these kinds of buildings. In this study, a traditional wooden structure is investigated to determine its dynamic characteristics and evaluate its seismic performance. The structure corresponds to a framed wooden construction with traditional connections between columns and beams. In general, nails are not used in these joints, and instead, the beam is narrowed at each end to be inserted into a hole cut in the column. This joint is known as a mortise-tenon joint. The end narrowed member of the beam is called the tenon, and the hole in the column is called the mortise. The joints are wedged to lock them in place. The modeling of this joint becomes a challenge since it does not correspond to a rigid joint of a common frame or to a hinge. The stiffness of this joint varies from the hinge to the perfect rigid joint. Therefore, the model used in this study is called a half rigid joint where the moment rotation relationship is specified for each beam end. Then, the dynamic analysis is performed to obtain the modes of vibration, and the results are compared with those obtained by means of the microvibration measurements. In general, good agreement was obtained between both results.