Free Truss Force Calculator
Estimate the axial force in the bottom chord of a parallel-chord Pratt truss under uniform loading.
Bottom Chord Force (tension)
90.0 kN
Bottom Chord Force (tension) vs Total Applied Load (W)
Truss Chord Forces
For a parallel-chord truss carrying uniform load, the midspan chord forces can be approximated from the equivalent beam moment.
Derivation
The midspan moment for equivalent simply supported beam: M = W L / 8.
The chord force equals the moment divided by the lever arm (truss depth): F_chord = W L / (8 h)
The bottom chord is in tension and the top chord is in compression with approximately equal magnitude at midspan.
Example Calculation
A 12 m span Pratt truss, 2 m deep, carrying a total load of 120 kN.
- 01Equivalent beam moment: M = 120 x 12 / 8 = 180 kN-m
- 02Chord force = 180 / 2 = 90 kN (tension in bottom chord)
- 03Support reaction = 120 / 2 = 60 kN
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