Three-member joint equilibrium

Symmetric triangular truss

Inputs

Support spanLHorizontal distance between the two lower pin supports.

Apex risehVertical apex distance above the lower chord.

Declared vertical apex loadPDownward static load at the apex joint only.

Each diagonal member length

2.5

Left vertical support reaction

Right vertical support reaction

Each diagonal axial compression magnitude

7.5

Bottom-chord axial tension magnitude

4.5

ΣFy = 0; RA = RB = P/2; Ndiagonal = (P/2)/sin θ; Nbottom = Ndiagonal cos θ

A first-pass number, not a code check, certification, or approval. Read the method and its limits below. What this is and is not.

Calculation snapshot

Formula version 1.0.0

Each diagonal member length	2.5 m
Left vertical support reaction	6 kN
Right vertical support reaction	6 kN
Each diagonal axial compression magnitude	7.5 kN
Bottom-chord axial tension magnitude	4.5 kN

ΣFy = 0 · RA = RB = P/2 · Ndiagonal = (P/2)/sin θ · Nbottom = Ndiagonal cos θ

Engineering Statics method of joints: https://engineeringstatics.org/method-of-joints.html

This printout is a record of displayed inputs and deterministic formula output. It is not an approval, certification, or engineering conclusion.

Method

Calculate static reactions and axial member forces for a symmetric, pin-jointed triangular truss with one vertical apex load.

ΣFy = 0; RA = RB = P/2; Ndiagonal = (P/2)/sin θ; Nbottom = Ndiagonal cos θ

When

Don’t

This is a symmetric three-member, pin-jointed, two-force-member equilibrium model with one vertical apex load. It excludes arbitrary truss topology, joint rigidity, member sizing, buckling, deflection, connection design, stability, code checks, and approval.