Structural Analysis of Trusses Flashcards
7 cards from real Civil Engineering PE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Structural Analysis of Trusses flashcards as text
In the analysis of a space (3D) truss, the determinacy condition is m + r = 3j. A space truss has 30 members, 6 reactions, and 12 joints. The truss is:
Answer: Statically determinate
For a 3D truss: m + r = 30 + 6 = 36 = 3j = 3(12) = 36, confirming the truss is statically determinate.
The influence line for the force in a diagonal tension member of a Pratt truss shows that the member carries tension when the live load is placed:
Answer: In the panel where the member is located and extending to one support
For a diagonal tension member in a Pratt truss, the critical live load position occupies the panel containing the member and extends to the nearest support.
A composite truss has steel top and bottom chords with timber web members. Under gravity loading, which chord is in compression?
Answer: Top chord
Under gravity (downward) loading, the top chord of a simply supported truss acts as a compression element, analogous to the top fiber of a beam.
For the Cremona (graphical) method of truss analysis, forces are found by:
Answer: Drawing a force polygon (Maxwell diagram) where member forces close the polygon at each joint
The Cremona/Maxwell diagram is a graphical force polygon technique where equilibrium at each joint is satisfied when the force polygon closes.
A truss bridge deck girder delivers concentrated loads only at panel points. This is a critical requirement because:
Answer: Loads applied between joints would cause bending in chord members, violating the two-force member assumption
Classical truss analysis assumes members are two-force members (axial only); loading between joints introduces bending moments that the analysis ignores.
In a Howe truss under gravity loading, the diagonal members are oriented such that they carry:
Answer: Compression
In a Howe truss, diagonals slope downward toward the center, causing them to carry compression under gravity loads (opposite of Pratt truss diagonals).
A redundant (statically indeterminate) truss requires which additional condition beyond equilibrium to solve member forces?
Answer: Compatibility of deformations (force-deformation relationships)
Statically indeterminate trusses cannot be solved by equilibrium alone; compatibility equations relating member deformations must also be satisfied.