Master of Science / Department of Architectural Engineering and Construction Science / Sutton F. Stephens / Trusses have been a common structural system for hundreds of years. The design and
analysis of trusses evolved over time to its current state. Most manual truss analyses use the
methods of joints and sections under idealized conditions. These ideal conditions, including
pinned connections, cause discrepancies between the ideal truss being analyzed and the actual
truss being constructed. The discrepancies include joint rigidity, connection eccentricity, and
transverse loading. These cause secondary stresses, which induce bending moment into the truss
members due to the chord’s continuity. Secondary stresses are most severe in continuous
compression chord members. In these members, secondary stresses should be addressed to
determine if they are severe and should be included in the truss design, or if idealized analysis
will suffice.
This report aims to determine the variables that affect the magnitude of secondary
stresses in continuous compression chords due to chord continuity. The variables considered are
chord stiffness, truss depth, and chord efficiency. Pratt trusses with WT chords were analyzed
using the commercial analysis software RISA 3D. Pinned and continuous chord trusses were
compared using the interaction value for each chord member. The results were used to
determine how these variables affect secondary stresses and how secondary stresses can be
predicted. Evaluation criteria were examined to determine the severity of secondary stresses.
These criteria examine the radius of gyration, moment of inertia, depth, and section moduli of the
chord members, and the moment of inertia of the truss for determination of secondary stress
severity.
The results of the studies show that secondary stresses increase with increasing member
stiffness, decreasing member efficiency, and decreasing truss depth. The necessity for secondary
stress consideration can be determined most accurately using the radius of gyration criterion
(L/r[subscript]x < 50) for the compression chord.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/1399 |
| Date | January 1900 |
| Creators | Smith, Megan C. |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Report |
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