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

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.

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.