Perfil

Task 1
Review of Literature
Introduction
Stress-laminated deck superstructures consist of a series of lumber laminations that are placed
edgewise and are transversely compressed with high-strength prestressing bars to create large
structural assemblies. The concept for these bridge designs began in the 1970s as Ontario
highway officials developed new methods to rehabilitate nail-laminatedtimber deck bridges
(Taylor and Csagoly, 1979). In contrast to longitudinal glulam deck assemblies and
nail-laminated assemblies, which achieve load transfer among laminations by structural
adhesives or mechanical fasteners, the load transfer between laminations in stress-laminated
bridges is developed through compression and interlaminar friction. This interlaminar friction is
created by thehigh-strength steel stressing elements typically used in prestressed concrete. By
1983, design specifications were available for longitudinal stress-laminated timber deck designs
in Canada (Ontario Ministry of Transportation and Communication, 1983; Taylor, 1983).
Design specifications for these bridges became available in the U.S. in 1991 (AASHTO, 1991).
The early stress-laminated deck bridgedesigns had simple rectangular cross sections composed
of longitudinal sawn lumber laminations with transverse prestressing (i.e., slab type systems).
Early research on these bridge designs was conducted at the University of Wisconsin in
cooperation with the USDA Forest Service (Dimakis and Oliva, 1987; Oliva and Dimakis, 1986;
Oliva and Dimakis, 1988; Oliva et al., 1985). Construction ofthese types of bridges in the U.S.
began in 1989 with work conducted cooperatively between the USDA FPL and West Virginia
University (WVU). Fifteen of these bridges were built in West Virginia between 1989 and 1991,
with an emphasis placed on utilizing locally available hardwood lumber. Other bridges using
different lumber species were subsequently constructed at many locations around the U.S.These
designs proved relatively successful in short span applications and they were relatively cost
effective. However, their moment of inertia was limited by the size of the available sawn
lumber, which is generally 16 inches or less. Therefore, to achieve longer spans with
stress-laminating technology, new concepts were needed.
To meet this need for longer spans, researchers first developed astress-laminated T-beam type of
superstructure. The first such design was completed by researchers at WVU and the Barlow
Drive bridge was subsequently constructed in 1989 in Charleston, WV (Dickson, 1995; Dickson
and GangaRao, 1990). The system consisted of stress-laminated top flanges connected with
continuous webs. Flange material was sawn hardwood lumber while the webs could beconstructed of glulam beams, laminated veneer lumber (LVL), parallel-strand lumber, or other
non-wood structural products. The Barlow Drive bridge used LVL webs. The next stresslaminated T-beam bridge was not constructed until 1992 and then nine more such bridges were
installed in West Virginia with spans up to 119 ft.

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Due to the high cost of the T-beam bridge, researchers shifted their emphasisto a cellular or box
beam type of superstructure (Barger et al., 1993a, 1993b; Davis, 1992; GangaRao and Latheef,
1991; Lopez-Anido and GangaRao, 1993). The system consisted of stress-laminated top and
bottom flanges connected with continuous webs. The first Box-beam bridge was designed in
1990 and constructed in Morgantown, WV. After the first bridge was constructed, 26 more Boxbeam bridgeswere installed across West Virginia through 1994 with spans up to 104 ft. During
1992, other similar Box-beam bridges were constructed in South Dakota and New York as part
of the US Timber Bridge Initiative.
While this activity was occurring in the U.S., researchers in Australia also began experimenting
with the concepts of stress-laminated timber deck bridges (Crews, 1996; Crews and Walter,...