www.acronymfinder.com is a valuable resource for answering that sort of question. However, as none of the definitions listed there is appropriate, one might reasonably assume that the one given in #2 is not far off the mark. It is up to the original poster to place a new definition of <...frd...> there should the need arise.
The abbreviation <...IBR...> is listed, incidentally, with 38 possible meanings at the time of writing. Someone with sufficient talent to do the crossword puzzle in a national newspaper would have little difficulty in sorting out one that is appropriate, particularly with EN 12953, which is a standard, given as a clue.
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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
I don't know how it works in those two standards, but you could look for "braced and stayed surfaces". In any case, the number of possibilities and their calculations are too many to fit into forum-type replies.
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In vino veritas; in cervisia carmen; in aqua E. coli.
The inspector/surveyor from the company providing burst/collapse indemnity insurance cover for the vessel certainly can. The tool to use to unwrap the method is the telephone.
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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856