A load moving left to right across a through-type Pratt truss alters the force nature in any left-half diagonal member such that it will_______________?
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Answer: A. change from compression to tension
Explanation
Moving live loads alter shear force signs in diagonal members across the truss span. A change in internal shear sign directly reverses member stress from compression to tension. Left-half diagonals experience this specific stress reversal during forward load progression. Truss diagonals primarily resist internal shear forces generated by applied external loads. Pratt trusses feature diagonals sloping down toward the center under gravity loads. As wheel loads advance, shear forces in specific web members cross zero magnitude.
Bridge designers must design diagonal members for stress reversal fatigue conditions. Reversible stresses can cause joint slip or buckling in slender tension members. Proper analysis ensures railway and highway bridges safely support moving vehicles. Option B describes the opposite stress reversal behavior seen in right-half diagonals. Option C is wrong because diagonal forces do not remain exclusively compressive always. Option D is incorrect since moving loads definitely trigger compressive stress phases.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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