Special Issues Between Adjacent Buildings With Different Heights and the Peculiar Vrancea Earthquakes

Abstract eng:
The earthquake risk in Romania is one of the highest in Europe and the seismic hazard for almost half of the country, including its capital, is determined by the Vrancea seismic region. The strongest Vrancea earthquake ever known is generally accepted to be the October 26, 1802 seismic event (M G-R = 7.5). The Vrancea earthquake with the highest seismic magnitude in the 20th century was the November 10, 1940 seismic event (M G-R = 7.4). The most destructive earthquake of the last century was the one that occurred on March 4, 1977 (M G-R = 7.2; M W = 7.5). All the above mentioned strong seismic motions have severely affected Bucharest, Romania’s capital city, where the buildings that are subject of this paper are situated. Two major events have changed the concept of building design in Romania: the first strong ground motion record obtained during the on March 4, 1977 earthquake, which revealed long period motions in Bucharest, much different from those currently adopted in the design codes based on Southern California recordings, and the change of the political regime in Romania which led to the integration of the country in the European Union. In the period between 1990÷2016 high-rise buildings were built very close to the existing old, low-rise buildings, some of them of heritage value. Up-to-date, studies on soil-structure interaction are in general restricted for a single foundation on elastic half space medium. A very few theoretical studies for adjacent buildings founded at different depths using several structural models of analysis were performed and some of the obtained results will be presented in brief. Wave propagation in layered subsoil with two adjacent foundations at different depths is very complicated. The purpose of this paper is to present the relevant aspects of an instrumental investigation carried out at the site of two adjacent buildings with different heights, structural systems and foundation levels, under ambient vibrations, and to extend the findings in the case of the peculiar strong motion generated by the Vrancea seismic source. The instrumental study has aroused major interest as, on one hand, there were no instrumental investigations for such tall buildings ever performed in Romania and, on the other hand, high-rise buildings with several basements haven’t been until then the subject of a responsibly conducted research. A point of view on the possibility that a high-rise building has a negative influence on the neighboring low-rise constructions during strong future earthquakes is also presented. The instrumental investigations carried out simultaneously inside and outside the high-rise building revealed the fact that between the bulb of pressure of its foundation structure and the area of influence of the nearest shallow foundation of the low-rise building there can be no significant interaction. It was arrived to the conclusion that there will not be any notable influence of the foundation medium and of the structural physical base of the investigated high-rise building on the foundation medium and on the foundation structure of the adjacent low-rise building, during future strong ground motions.

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