免费桁架内力计算器
计算桁架各杆件的轴向内力。
Bottom Chord Force (tension)
90.0 kN
Bottom Chord Force (tension) vs Total Applied Load (W)
公式
## 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.
计算示例
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
常见问题
Is this exact for all truss types?
This gives a close approximation for parallel-chord trusses under uniform load. For exact forces in each member, use the method of joints or method of sections with the actual geometry.
How do I find diagonal member forces?
Diagonal forces depend on the shear at each panel point. Near the supports where shear is highest, diagonal forces are largest. Use the method of sections cutting through the diagonal of interest.
What affects truss efficiency?
Deeper trusses have lower chord forces for the same span and load, reducing material usage. However, deeper trusses require longer diagonal members and more vertical clearance.
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