Page 541 - Forensic Structural Engineering Handbook

TIMBER STRUCTURES 14.31

5 ft

L = 46 ft

FIGURE 14.10 Truss profile. Rainier Beach Library, Seattle, Washington.

A branch of the Seattle Public Library system was constructed in 1980, framed with
timber roof trusses. Parallel chord trusses were designed using glulam chords and webs
and connected with bolted steel plates. Truss span is 46 ft, and overall truss depth is
5 ft (see Fig. 14.10). Chords are continuous, and web-to-chord connections were ana-
lyzed as pinned. Member sizing and bolt capacity were adequate for the primary load-
ing condition.
1
The web-to-chord connections consisted of welded 3-in × / 4-in steel fin plates on
each side of truss following the profile of truss members. All connectors were 1-in bolts.
The welded truss connection plates created partial fixity at truss joints. When the truss
deflected under loading and nodal joints rotated, the multiple bolts in a row resisted that
rotation by creation of moment couples in the glulam truss members, inducing a force
perpendicular to grain and thereby stressing the glulam member in cross-grain tension
(see Fig. 14.11).

7'-8"

4" 4" 4" 4" 4" 28" 4" 3" 3" 4"
1
5 / ' × 9" Glulam
8
8 1 / 2
4"
Failure
5 1 / 8 ' × 6" Glulam
4" 4" 4"
plane
5'-0" c L Column Glulam
5 1 / 8 ' × 6"

4"
7 3 / 4
1
5 / ' × 7 / " Glulam
1
8 2 4" 4" 4"
1'-2 1 / 2 "

FIGURE 14.11 Truss heel detail. Failure occurred at outer diagonal web. Rainier Beach Library, Seattle,
Washington.