FE Exam Review 69 – Influence Line for Member U2U3 in a Truss (Which Diagram Is Correct?) In this FE Civil Exam structural analysis problem, we identify which influence line diagram correctly represents the axial force in truss member U2U3 as a point load moves across the span. We review how influence lines behave for internal truss members and how the maximum effect occurs when the load passes directly over or near the member. You will learn: What influence lines represent and why they matter How to locate the critical influence zone for the member How to evaluate diagram shapes for maximum internal force How to quickly eliminate incorrect influence line options on the FE Why the correct answer is: B This type of conceptual structural analysis question shows up often — easy win if you understand member influence behavior! Correct Answer: B ⏱ TIMESTAMPS – Spread Across 6:30 Minutes 00:00 – Problem Statement & Load Path Overview 00:22 – What Influence Lines Represent 00:48 – Internal Force vs. Reaction/Moment Influence Lines 01:15 – Locating Truss Member U2U3 and Critical Panel 01:42 – How Load Position Affects Axial Force 02:05 – Where Maximum Influence Occurs 02:32 – Checking Each Influence Line Option 03:00 – Why Option A Is Incorrect 03:26 – Why Option C & D Are Not Logical 03:52 – Why Option B Matches Maximum Effect 04:18 – Understanding the Negative Sign (-1.0) 04:45 – Fast Elimination Strategy for Exam 05:15 – FE Tip: Tension vs Compression in ILD Signs 05:55 – Final Answer & Key Takeaways 06:20 – Next Truss Influence Line Challenge Preview 06:30 – End Screen Alright guys, we’re walking a tightrope — but instead of a rope, it’s a TRUSS MEMBER! Imagine you’re this heavy point load jumping from joint to joint — BOOM! Where you land = how much pain U2U3 feels 😂 We just gotta find that one spot where U2U3 screams the loudest — and that’s Option B! Let’s hit that jackpot answer! 💥 Influence lines show the force in a member as a point load moves across a structure. To find the correct diagram for U2U3, we look for the shape that gives the largest response when the load is directly above or near the member. U2U3 lies near midspan, so the influence line should reach its maximum magnitude there. Option B provides the strongest effect at that location, so that is the correct influence line for this member. 🧠 Step-by-Step Summary (Shown On Screen) 1️⃣ Influence lines show force response due to a point load 2️⃣ Maximum influence happens when the load is directly over the member 3️⃣ Diagrams should show a peak or dip at this position 4️⃣ Option B matches the behavior → Correct Answer: B 📚 Books Recommended FE Civil Practice Exam (NCEES): FE Civil Practice (PPI): FE Civil Practice Problems (PPI): TI-36X Pro: 🔖 HASHTAGS #FECivil #StructuralAnalysis #InfluenceLines #TrussAnalysis #civilengineer #FEExamPrep #AverageCivilEngineerPE #usa #InternalsForces #FETips #EngineerLife