GNDT: Pubblicazioni - Segnalazioni

Preface

Developments in computational structural dynamics coupled with technological innovations, field investigations in the aftermath of destructive earthquakes and subsequent research efforts have resulted in an enormous accumulation of knowledge on earthquake engineering problems. These developments have taken place from the second half of last century up to the present time. Unfortunately, the current state of practice lags far behind the state of knowledge and this gap needs to be filled if a substantial reduction of seismic risk is to be achieved. The five chapters of this book address this problem from different but convergent directions.

In the first chapter the earthquake problem is reviewed and its main objectives are stated. In particular the most reliable innovative approaches in earthquake engineering are described and the need for their application in engineering practice is emphasised. The impediments to their application and the conditions for their efficient use are also outlined. Amongst the conceptual and technological innovations considered are Performance Based Earthquake Engineering, Seismic Isolation Systems, Passive, Active and Hybrid Seismic Protection Systems.

The second chapter addresses the concept of "Damage Controlled Structures" or "Damage Tolerant Structures" introduced in the United States and in Japan after the Northridge (1994) and Kobe (1995) earthquakes. The basic idea behind this innovation is the separation of the structural system into two independent parts: one is the elastic primary structure designed to withstand the vertical service load; the other is the energy dissipation system designed to resist the lateral earthquake load. The primary structure can remain elastic even under severe earthquakes while the energy dissipation devices take care of most of the energy imparted to the overall structural system by the seismic excitation. In the third chapter the problem is addressed of the evaluation of the seismic resistance and vulnerability of reinforced concrete buildings not designed to resist the seismic action. This is a relevant problem in many urban and rural areas in earthquake prone regions where seismic regulations were not enforced at the time of construction either because seismic alertness had faded after relatively long periods of seismic quiescence or because of severe economic depression after long wars. The evaluation of the seismic vulnerability of single or groups of buildings in residential areas may be of paramount importance in policy decision-making concerning seismic rehabilitation. The problem is addressed through a case study, which applies recently adopted procedures and some new ones specifically developed for the purpose.

The fourth chapter addresses the theme of seismic risk to historical and monumental masonry buildings. Because of their peculiar architectural properties, these buildings need specific procedures for the assessment of their vulnerability, which are substantially different from those available for ordinary buildings. Particular aspects of the seismic hazard that reflect the response behaviour of these structures also need to be considered. The problem is dealt with specifically with reference to church buildings and bell towers adopting ad hoc models for the nonlinear dynamic analyses used in the vulnerability assessments. Specific measures of the seismic hazard based on significant characteristics of the ground motion are also developed for the structural types considered.

The fifth and final chapter considers a long seismic sequence that struck two adjacent regions in Central Italy from September 1997 to April 1998.The analysis is particularly relevant because of the damage imparted by several moderate seismic events to historic town centres, housing, notable monuments, and works of art. The characteristics of the seismic sequence are investigated in terms of released energy, magnitude, macro-seismic effects and seismic history of the affected area. The ground motion characteristics are analysed from a large set of acceleration records including significant samples of site effects. The study is concluded with the analysis of the damage to the existing constructions.

The topics considered in the five chapters of this book embrace a wide spectrum of problems in earthquake engineering and provide an extensive view of modern seismic engineering. The book should prove helpful in closing the gap that was mentioned initially and should be useful to research students, professional engineers, government officials and public policy makers. I wish to take this opportunity to thank all the authors for their dedication in producing this significant work, especially Professor Vitelmo V. Bertero, who has enthusiastically dedicated his life to the advancement of earthquake engineering.

Giuseppe Oliveto - (Catania, Italy 2002)