Creep information for sawn lumber exposed to constant and cyclic humid
ity environments previously published by the authors is supplemented b
y this study using glued laminated material of about the same size, te
sted on the same apparatus, and using the same general procedure. For
both sawn and glued laminated material, the relative creep was measure
d at about 55% of their average ultimate strength. Relative creep was
measured for specimens matched with respect to modulus of elasticity (
MOE) and exposed to a constant relative humidity (65 F and 65% RH) for
about 1,000 hours, and a cyclic relative humidity (65 F and 90% RH fo
r 82 hours followed by 65 F and 40% RH for 82 hours). This 164-hour cy
cle was repeated six times for about 1,000 hours of cyclic exposure. T
his is a more severe change in equilibrium moisture content of the env
ironment than is likely to occur in building structures. The result sh
owed relative creep of the glued laminated material increased by 40% t
o 72% as a result of cycling. One very low MOE pair showed an increase
of 167%. The increase for solid sawn lumber previously reported was 2
00% to 400% due to cycling. Results also showed that the ratio of rela
tive creep for cycled to constant humidity exposure did not change app
reciably as time under load was increased. These differences are attri
buted to permeability differences between glued laminated wood and saw
n lumber. The gluelines are believed to retard water vapor movement an
d reduce the moisture change rate and extremes of wood moisture conten
t in any given cycle.