An unexpected brittle failure of connections and of members occurred during the last earthquakes of Northridge and Kobe. For this reason a heightened awareness developed in the international scientific community, particularly in the earthquake prone countries of the Mediterranean and Eastern Europe, of the urgent need to investigate this topic. The contents of this volume result from a European project dealing with the 'Reliability of moment resistant connections of steel frames in seismic areas' (RECOS), developed between 1997 and 1999 within the INCO-Copernicus joint research projects of the 4th Framework Program. The 30 month project focused on five key areas: *Analysis and syntheses of research results, including code provisos, in relation with the evidence of the Northridge and Kobe earthquakes; *Identification and evaluation through experimental means of the structural performance of beam-to-column connections under cyclic loading; *Setting up of sophisticated models for interpreting the connection response; *Numerical study on the connection influence on the seismic response of steel buildings; *Assessment of new criteria for selecting the behaviour factor for different structural schemes and definition of the corresponding range of validity in relation of the connection typologies.

This is a review of developments in the behaviour and design of steel structures in seismic areas. The proceedings look at the analytical and experimental research on the seismic response of steel structures, and cover topics such as global behaviour and codification, design and application.

The catastrophic earthquakes of the last decades (Mexico City, 1985; Loma Prieta, 1989; Northridge, 1994; Kobe, 1995) have seriously undermined there putation of steel structures, which in the past represented the most suitable solution for seismic resistant structures. Even if in very few cases, the performance of steel joints and members was unexpectedly bad, showing that it was due to some lacks in the current design concept. As a consequence of the lessons learned from the above dramatic events, many progress has been recently achieved in the conception, design and construction, by introducing the new deals of the performance based design, including the differentiation of earthquaketypes and considering all factor influencing the steel structure behaviour under strong ground motions. In this scenario, the aim of the book is to transfer the most recent achievements into practical rules for a safe design of seismic resistant steel structures. The seven Chapters cover the basic principles and design criteria for seismic resistant steel structures, which are applied to the main structural typologies, like moment resistant frames, braced frames and composite structures with particular reference to connections and details.

With the gradual development of rules for designing against instability the idea emerged, in London, in 1974 to hold an International Colloquium treating every aspect of structural instability of steel structures. There have been 17 International Colloquia Stability Sessions around the world, starting with the first one in Paris in 1972, until with the last one in Nagoya in 1997. In Nagoya it was decided to continue the series of travelling colloquia by launching the Sixth Colloquium in September 1999 with the First Session to be held at the "Politehnica" University of Timişoara, România, which will be followed by another in the year 2000 at the Gediminas Technical University in Vilnius, Lithuania, a third one during SSRC's Year 2000 Annual Meeting in the US, and a fourth one in Australia or New Zealand. At present important research projects are in progress around the world, like SAC Joint Venture Project in USA, INCO-COPERNICUS "RECOS" in Europe and others, which are devoted to improve and develop new methods for the safety design of steel structures in seismic zones. Special attention is paid in Europe, USA and Japan to improve the design codes and detailing of seismic resistant steel structures. This was the reason to organise the Session of Nagoya as "Stability and Ductility of Steel Structures" Colloquium. Romania is also a strong seismic territory and therefore, the topic of the Timişoara Session covered both stability and ductility problems. The technical programme of the SDSS'99 Colloquium in Timişoara has been split into nine working sessions.

A detailed presentation of the major role played by correctly designed and fabricated joints in the safe and reliable response of steel, composite and timber structures. The typology/morphology of connections is discussed for both conventional pinned and rigid joints and semi-rigid types. All relevant topics are comprehensively surveyed: definitions, classification, and influence of joint behaviour on overall structural response. Also presented are the application of the component method, the notion of rotational capacity, the local ductility of different types of earthquake-resistant structural joints as determined in cyclic experiments, numerical techniques for the realistic simulation of joint response, simple and moment-resistant structural connections. Readership: An incomparable resource for engineers who analyze and design steel, composite and timber structures; researchers and graduate students in the same areas.