Thanks for your thoughts. There is some truth in what you say as small deflection theory can not be used. You may be interested in viewing all of the comments made on this subject including those received after writing to the Institution of Structural Engineers. These are at:- [URL]http://home.btconnect.com/cadoss[/URL] Further comments would be appreciated. Regards Martin Double CADOSS Email: [email][/email] Web Site: [URL]http://home.btconnect.com/cadoss[/URL]