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SEISMIC ISOLATION: WHY, WHERE, WHEN

Seismic isolation is coming out from its pioneer period and now it is on the way to become a popular system for the seismic protection of ordinary structures. The criteria concerning the architectural morphology, the selection of the structural configurations and other design options of seismic isolated buildings shall be discussed to popularise its use, to improve the effectiveness of ordinary applications, to cut down the construction costs and to open the way to new and wide applications. Moreover, the experts should emphasise the higher reliability of the design procedures commonly used for fixed-base structures, when applied to isolated structures. The target is to avoid that new applications are discouraged by unnecessary and complex analyses required by specific codes. Taking the opportunity of some demonstrative initiatives promoted by the local Government of the Umbria Region after the seismic ''swarm'' that struck central Italy in 1997 and 1998, this papers deals with practical topics concerning the application of seismic isolation to ordinary residential and commercial buildings.

 ALBERTO PARDUCCI

Introduction

 

This paper deals with practical considerations and problems concerning the usual design practice, when seismic isolation is applied to design ordinary buildings. Seismic isolation is coming out of its pioneer period and now it is on the way to become a construction technique widely used for seismic protection of many structures in all the seismic areas in the world. Besides the results of theoretical and experimental research, the real effectiveness of seismic isolation was clearly shown by the performance of the isolated buildings recently struck by severe earthquakes. These performances were clearly shown by the records of the real response of the buildings shaken by the earthquakes of Los Angeles in California [1] and Kobe in Japan [2,3,4]. Till now, seismic isolation has been generally applied to protect important or demonstrative buildings, whose design was carried out by structural engineers expert in this field. Due to its excellent performance, we can now foresee that seismic isolation will be soon extended to design and construct a large number of buildings. Therefore, an important target is to make the applications of seismic isolation easy to perform, so that it becomes a current practice in architectural and structural design. The harmonisation of the architectural morphology of the buildings with the specific performance of the isolating systems is an important aspect that has not enough taken into account in order to guarantee the effectiveness and to reduce the cost of the ordinary applications. The architectural design can be a critical aspect to enlarge and popularise the use of seismic isolation. Therefore, it is important to involve the architects in practical and theoretical discussions in this topic.

Complementary aspects of seismic isolation

At the present stage of the studies, we have to underline how seismic isolation can be effectively applied in the current design of ordinary buildings. The experts should be engaged in order to popularise its use. This aspect is more important than to illustrate the results of further theoretic or experimental research or to show how seismic isolation has been applied to special structures. We must also underline that, in addition to the reduction of structural stresses (current target of the design practice), there are other aspects that make seismic isolation suitable and profitable for the construction of ordinary buildings in seismic zones. The base isolation is a simple way to reduce the horizontal accelerations transmitted to floors or to other structural elements. This is an important factor seldom taken into the right consideration. Generally, this aspect is disregarded in the design practice, since it is not considered by the design specifications. On the contrary, the reduction of seismic accelerations is a very important aspect of the seismic design, because it avoids damages of non-structural elements and of the objects inside the buildings. Another significant aspect is this: the common design procedures and the numerical calculations are more reliable and effective when they are applied to seismic isolated rather than to fixed-base structures. This matter will be examined closer. Finally, it should be underlined how the seismic performance of the isolated structures mainly depends on the selection of a suitable architectural morphology. It is known that there is a strong correlation between seismic performance and architectural configuration [9]. All the reports always emphasise this aspect when they illustrate the damages due to real earthquakes [1,2,3]. This correlation is stronger when seismic isolation is applied. Both engineers and architects should be involved to optimise this critical point.

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Ultimo aggiornamento: 14/05/2010 02:10

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