How many control spans should be used in a sag section consisting of seven spans?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (B)

Control spans provide fixed boundary conditions for how the line behaves in a sag section. They’re the end spans used to anchor and stabilize tension and angle so the interior spans can develop a predictable sag profile as temperature or loading changes. For a sag section consisting of seven spans, placing a control span at each end gives symmetrical, stable ends and keeps the interior spans from becoming difficult to manage. This two-span boundary setup is the standard way to control the overall sag without adding unnecessary complexity, so two control spans are used.