Title PSAD 25 Influence Lines - Trusses.pdf ✅

2. Draw the influence line for the force in member CJ. SOLUTION: Influence Line for Support Reaction at A: Method of Sections: When Unit Load is at Joint C: tan θ = 6 4 θ = 56.3099° When Unit Load is at Joint C, RA = 4 6 ∑Fvertical = 0 CJ sin 56.3099 + 1 = 4 6 CJ = −0.4006 (compression) When Unit Load is at Joint D: When Unit Load is at Joint D, RA = 3 6
∑Fvertical = 0 CJ sin 56.3099 = 3 6 CJ = 0.6009 (tension) Influence Line for Member CJ: Recall Influence Line for Diagonal Members: 3. Draw the influence line for the force in member IJ. SOLUTION: Influence Line for Support Reaction at A: Method of Sections: When Unit Load is at Joint C: