Continuous, two equal spans UDL
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About this case
How to analyze a continuous beam with two equal spans
This page pre-loads a two-span continuous beam: pins at A, B, C; each span length L; uniform load w on both spans. Edit L, w, section or material directly. Results update instantly.
Textbook values: reactions R_A = R_C = 3wL/8, R_B = 10wL/8; hogging moment over B: M = wL²/8; maximum sagging moment in each span: M = 9wL²/128 at x = 5L/8 from the outer support; deflection ≈ 0.0054 wL⁴/EI per span.
What to watch for with continuous beams
The interior support B carries 1.25× the total load of one span (10/8 vs 8/8 for a simple support), and the hogging moment over B (wL²/8) is larger in magnitude than the midspan moment of a simply supported beam (wL²/8 vs wL²/8 — equal here, but for unequal spans the interior moment dominates).
The midspan positive moment (9wL²/128 ≈ 0.07 wL²) is smaller than the simply supported midspan moment (wL²/8 = 0.125 wL²) because the continuity restrains the deflection. This is why continuous beams are more efficient: lower midspan moment for the same span.
Common mistakes with continuous beams
Analysing a continuous beam as a series of simply supported spans misses the hogging moment over the interior support — the connection and top flange bracing there are critical. Assuming the interior support reaction is just wL (it's 1.25 wL here, and can be higher with unequal spans). Forgetting that support settlement at an interior support significantly redistributes moments — the calculator supports prescribed settlement to study this.