InTrans / Aug 14, 2018
Performance of red oak and red maple glued-laminated bridges
A three year program to monitor the performance of a
red oak longitudinal girder, transverse deck gluedlaminated
(glulam) highway bridge is presented. The
results indicate that the predicted and observed live
load beam deflections agree to within 2% when the
stiffness of the individual beam laminations and ten
percent increase in beam stiffness due to composite
action between the deck panel and longitudinal girders
are incorporated into the design. Significant reflexive
cracking of the asphaltic wearing surface was observed
at the interface between each red oak deck panel. This
was attributed to the gap provided between each panel
during construction, to the placement of the waterproof
membrane directly over the creosote treated deck
panels, and to improper mating of the deck panels to
the beams during installation of the lag bolts. Long
term (three year) dead load deflection measurements
indicated that after approximately one year, dead load
deflections remained nearly constant for the interior
beams. Elevations of the lower surface of the two
exterior beams fluctuated considerably and varied
seasonally. There was no evidence of delamination of
the girders or deck panels after four years. However,
there was some evidence of delamination of the curbs
and to tops of rail posts. Preliminary observations of a
red maple glulam bridge, the design of which
addressed the three shortcomings of the red oak bridge,
suggest no delamination of the glulam components and
no reflexive cracking of the wearing surface after nine
months of service. Live load testing of the red maple
bridge is scheduled for the summer of 1996.