A special one day Seminar was held at the Institution of Civil Engineers in London, organised by WIT with the collaboration of that Institution and the University of Catania in Italy.
The Seminar brought together a group of earthquake engineering experts from the USA, Italy and Japan who had recently published a book with WIT Press. The Co-Chairmen of the Meeting were Professor Giuseppe Oliveto of the University of Catania and Prof Carlos Brebbia from the Wessex Institute of Technology.
Carlos opened the Meeting by recalling how the idea of publishing the book and organising seminars in Italy and London originated during the 2nd International Conference on Earthquake Resistant Engineering Structures (ERES) held in Catania in 1999. Following that meeting, the main keynote speakers were invited to collaborate in a book which has recently been published with the same title as the Seminar, ie "Innovative Approaches to Earthquake Engineering".
The Seminar lectures followed the title of the different chapters and were presented by the main collaborators, ie:
- "Innovative Approaches to Earthquake Engineering" by V. Bertero from the University of California at Berkeley.
- "Design of Damage Controlled Structures" by A. Wada from Tokyo Institute of Technology.
- "Seismic Resistance and Vulnerability of Reinforced Concrete Buildings not Designed for Earthquake Action" by G. Oliveto, University of Catania.
- "Vulnerability of Historical and Monumental Buildings" by S. Casolo, Politecnico di Milano
- "Structural and Technological Implications of the 1997 Seismic Sequence in Umbria and Marche" by F. Mollaioli, University of Rome, La Sapienza.
Carlos Brebbia introduced Prof Vitelmo Bertero, the main speaker by recalling some anecdotes regarding personal views on an appreciation of Vitelmo's career. Carlos graduated from the same School of Engineering as Vitelmo, which is now part of the University of Rosario in Argentina. Although he started his research career working under a disciple of Vitelmo who was to finish also working at the University of California in Berkeley following one of the periodic political upheavals in Argentina, he was not able to meet Vitelmo until much later.
Furthermore, Carlos also carried out research under the well known Professor Jerry Connor of MIT, who was a PhD student at that Institute at the same time and in the same Department as Vitelmo. Jerry's assessment of Bertero was that he was extremely hard working, intelligent and committed. By then, Carlos had been offered the possibility of working under Vitelmo in Berkeley but for personal reasons decided first to carry out work at the University of Southampton in the UK and then at MIT under Jerry Connor.
After a few years, Carlos was appointed as Professor of Civil Engineering at the University of California, ie the same Institute as Bertero's but on a different Campus, Irvine rather than Berkeley.
Although Carlos visited Berkeley several times, he did not meet Vitelmo until 1999 when he was invited as the main keynote speaker at the ERES Conference in Catania, organised by WIT in cooperation with that University. Finally, Carlos was able to fulfil one of his lifelong ambitions, ie meet his famous mentor Prof Bertero.
Since then, a closer relationship has been established between Prof Bertero and WIT, resulting in the Seminar in London and the publication of the new book.
Prof Bertero's lecture discussed the concept of energy as relevant to earthquake engineering and the need to replace the conventional approach of adding rigidity to the structure for the innovative approach of making the structure more flexible. The idea is to avoid collapse by releasing the energy through plastic work and dampers and accept that the structure may need to be retrofitted after the event.
Prof Bertero also referred to base isolation in addition to the use of energy dissipation devices. This leads to innovative approaches resulting in reduced seismic risks. It is essential, in Prof Bertero's opinion, that the codes are rewritten to accept these new devices without the need for extensive and expensive tasks as required at present.
The existing codes tend to perpetuate the misunderstanding that a building designed and built to code will resist a severe earthquake ground motion without any damage. This has never been the case, as regretfully is always required after a major earthquake.
The trend is now to develop simple and reliable codes based on performance based design and construction procedures, originated several years ago.
Bertero was critical, however, of some of the new computer analysis carried out in California, including the idea of carrying out a "pushover" full non-linear analysis. The "pushover" is not a realistic simulation for earthquakes as their loads consist of a series of pulses and not a continuous static load. The effect of an earthquake is generally cumulative and it involves a series of cycles. This is why the importance of ductility becomes crucial to the survival of the structure.
Professor Akire Wada from the Tokyo Institute of Technology referred to the concept of Damage Controlled Structures using dampers in between columns and beams. He uses simple concepts with a straight forward relationship between the functional requirements and the design variables. The gravity design loads are applied for the analysis of the beams and columns system and the seismic design loads are used for the dampers. Damage controlled structures are also cheaper to retrofit after an earthquake.
The design prepared by Wada was tried in several buildings before Kobe Earthquake (1995) and the number has now increased after this earthquake as well as the one in Northridge (1994).
Professor Wada showed some case studies and a series of tests demonstrating that the system works well. Using the system, the maximum displacement and shearing for us can be reduced by between 40 and 80% by comparison with frames structures without dampers.
Prof Giuseppe Oliveto referred to the seismic resistance and vulnerability of reinforced concrete buildings. He described a case study, consisting of a 1970's building which was not designed to resist earthquake action. The structure has now been analysed including non-linear effects. The idea was just to subject the building to a push-over analysis, up to the collapse of the system. The structure went through three different phases, ie:
- Elastic behaviour
- Moderate plastic behaviour
- Strong plastic behaviour
A simplified way of investigating the problem has been devised based on energy considerations. The equivalence of work is employed to be able to simplify the problem and, in this way, finding an effective stiffness for the building.
The technique proposed produced larger collapse loads than those using the standard FEMA, which allows for a more refined procedure. The vulnerability of the structure depends on both its seismic resistance and the expected ground motion, the latter dependent on the seismic zone. Comparison of the new procedure with FEM method were presented during the lecture.
As expected, the performance of the building is better with the new procedure than with the FEMA conservative approach. The energy approach is more accurate and should be preferred. The method has been applied to the above described Reinforced Concrete Building.
The presentation by Prof Siro Casolo from the Politecnico di Milano investigated the Vulnerability of Historical Buildings and reported on the work done at the Institution on this important topic. Heritage Structures have their own peculiar type of seismic behaviour, resulting from the methods of construction and the materials used. An interesting case was the study of the collapsed Tower of Pavia in 1989 which was analysed using a histeretical rule for the masonry material of the tower proposed by Prof Binda of the same Politecnic.
The last lecture was on the Structural and Seismic implications of the 1997 Umbria and Marche earthquake. The chapter concentrates on the analysis of the date and, in particular, for strong ground motion. Another interesting effect is that which is due to local site effects and the amplification resulting from soft soils. The presentation ended with the analysis of damage characteristics and, in particular, that of historical buildings. The total damage of the 1997 earthquake was estimated at 3 billion US dollars and 26,000 houses in the area were condemned. More than 1,300 buildings were destroyed among the many historical constructions.
The Seminar closed with a general discussion involving all the lecturers.