Understanding Truss Reactions
Truss reactions are the support forces that keep a frame in balance. They are found before member forces are calculated. A truss may look complex, yet its outside balance is simple. The whole structure must satisfy horizontal force balance, vertical force balance, and moment balance. This calculator uses those three checks.
Why Reaction Calculations Matter
Correct reactions protect every later step. If a reaction is wrong, each joint result can be wrong. Designers use reactions to size bearings, plates, anchors, and foundations. Students use them before the method of joints or sections. The tool also shows the moment arm for each load. That makes the example easier to audit.
Loads Accepted by the Tool
The form accepts point loads, distributed loads, angled loads, and applied couples. A distributed load is converted into one equivalent point load at its centroid. An angled load is resolved into horizontal and vertical components. Applied clockwise moments are added directly to the moment equation. These options cover many classroom truss reaction examples.
Assumptions Used
The calculator treats the truss as a planar determinate structure. One support should restrain horizontal movement. Two vertical reactions are solved from equilibrium. Members are assumed pin connected. Their internal forces are not needed for support reactions. Loads are applied at known x positions. Units stay consistent throughout the page.
Reading the Results
The result area lists Ax, Ay, and By. It also reports total load sums and balance residuals. Small residuals near zero confirm the equations. A negative reaction is not an error. It means the support force acts opposite to the selected direction. Large residuals usually mean bad input, copied headers, or mixed units.
Good Modeling Habits
Use the same length unit everywhere. Enter downward loads as positive values. Put upward loads as negative values. Enter rightward horizontal loads as positive values. Check support spacing before calculating. Review the example table first. Then replace the values with your own truss data. Export the report when you need a record.
When to Be Careful
A truss with two horizontal restraints may be indeterminate. This page can share the horizontal reaction for review only. Use stiffness analysis when restraint stiffness matters in final design and code checks instead.