Absent a grade stamp or other documentation, it is difficult to determine such values by paper means (and risky since there were several grades produced). About a year ago, I had to determine the values for (44) 7x29-1/4 x 58'-0" GLBs over a water reservoir for a potential photo voltaic project. Jeff Linville of AITC ( www.aitc-glulam.org
) was very helpful. He provided me with the pertinent grading rules and we esentially did our own regrading from a floating platform. We were more interested in expected current values to determine actual capacity rather than the legacy values offered in the code. Although our GLBs had a Fb = 2,600 psi (per available drawings) under the rules in effect when they were produced (1960), under current rules about 1/3 of the GLBs did not meet the tension lamination requirements for Fb=2,600 psi under today's rules and we downgraded them to what would be expected under today's rules.
You may be interested in an article by Robert Powell in Structure Magazine, February 2004, "From Experience" column that discusses determing GLB stresses although he is talking about older ones than you asked about. The link is:
Bill Cain, S.E.
From: Sharon <sharon(--nospam--at)arconengineers.com>
Sent: Fri, 10 Feb 2006 10:38:37 -0800
Subject: 1976 UBC GLULAM
Does someone have a source for GLB design values for a 1979 building?