Submitted on: 15 February 2001.
Revised on: 28 April 2001.
Accepted on: 10 May 2001.
___________________Ingegneria Sismica---PATRON EDITORE S R L
Submitted on: 28 April 2008.
Revised on: 05 August 2008.
Accepted on: 29 August 2008.
___________________Ingegneria Sismica---PATRON EDITORE S R L
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Submitted on: 25 July 2004.
Revised on: 27 October 2004.
Accepted on: 08 November 2004.
___________________Ingegneria Sismica---PATRON EDITORE S R L