How do I calculate load on one truss?

Add dead, snow and other area loads, then multiply by truss spacing and span. Example: (0.35 + 1.8 + 0.15) kPa × 2 m × 6 m = 27.6 kN on one truss.

Does this calculator report allowable truss capacity?

No. The calculator reports applied load and preliminary forces, stresses and deflection from a linear 2D model. Final capacity must be checked to the governing design code, including buckling, connections, welds and out-of-plane behavior.

Steel Tube Roof Truss Calculator — Loads & Deflection

Build a gable, mono-pitch or arched rectangular-tube truss and calculate roof loads, reactions, member forces, deflection, tube mass and a cut schedule.

Symmetric truss with straight top chords and a ridge node.

Load on one truss27,6 kN

Tube with allowance25,06 m

Deflection · reference L/2506,07 mm · L/989

Preliminary pin-jointed model: review the result, then refine geometry, section and loads below.

Truss geometry and loading

Units

Roof pitchEnter an angle or rise per 12; ridge height stays synchronized.

10.4° · 2.2:12 · 18.3%

Pitch angle, degreesRise per 12

For a gable truss, pitch is measured over half the span. For mono-pitch, it uses the full span.

Span, mmBetween support nodes. Height at support, mm Ridge height, mmFrom the bottom chord to the ridge node. PanelsUse an even number for a symmetric gable truss. Deflection referenceChoose a comparison limit; this is not an automatically selected code limit. Number of trusses Material allowance, %

Tube section and procurement mass

One rectangular tube section is used for chords, diagonals and verticals. Lengths are measured along member centerlines.

Tube depth, mm Tube width, mm Wall thickness, mm

Load on one truss

Enter design values with the required load factors already applied. 1 kPa is approximately 20.9 psf.

Truss spacing, mTributary roof width carried by one truss. Dead load, kPaRoofing, purlins and self-weight. Snow load, kPaDesign load for the project location. Other load, kPaServices, maintenance and other loads.

Applied load on one truss 27,6 kN

per truss · applied load, not capacity

To establish allowable capacity, an engineer must also check every compression member, connection, weld and out-of-plane restraint.

Maximum node deflection6,07 mm

Maximum axial force26,1 kN

Maximum stress85,9 MPa

N / Euler Ncr35,2%

E = 200,000 MPa · pin joints · same section for every member

Critical model memberBottom chord · 1 000 mm

tension

Deflection versus selected reference6,07 mm of 24,00 mm · L/989

25% of reference

Weak-axis bucklingDiagonal · 1 133 mm · λ 93 · Ncr 69,3 kN

Euler idealization

compressiontensionlow forcethicker line means larger force

Area load2,30 kPa

Line load4,60 kN/m

Reaction at each support13,8 kN

Interior-node load4,60 kN

Equivalent Mmax20,7 kN·m

Chord-force estimate M/h23,0 kN

Members25

Tube length23,42 m

With allowance25,06 m

Tube mass55,9 kg

Mass with allowance59,8 kg

Send members to cut optimizer →

6 m steel-tube roof truss deflection example

For the six-panel gable example with a total applied load of 27.6 kN, the linear pin-jointed model gives 6.07 mm maximum vertical deflection, 26.1 kN maximum axial force and 85.9 MPa maximum stress. Change the section, geometry or loading and all three results update together.

How to calculate roof-truss load

Short answer: the load on one truss equals the sum of dead, snow and other area loads multiplied by truss spacing and span: P = (G + S + Q) × spacing × span.

Add the dead, snow and other area loads in kPa, multiply the sum by truss spacing, then multiply that line load by span. For 0.35 + 1.8 + 0.15 kPa, 2 m spacing and a 6 m span: p = 2.30 kPa, q = 4.60 kN/m, total load on one truss is 27.6 kN, and each support reaction for the symmetric layout is 13.8 kN.

The calculator distributes line load to the top nodes: each interior node receives one full panel load and each end node receives half a panel load. In arched mode, the top chord follows a circular arc through the ends and midspan; the schedule reports straight node-to-node chord lengths for fabrication.

Area loadsp = G + S + Q

Line loadq = p × spacing

ReactionR = qL / 2

Chord estimateN ≈ (qL² / 8) / h

This is a preliminary linear model, not a capacity certification. Deflection and axial forces come from a 2D pin-jointed stiffness model with the same section for every member. Compression members show force divided by the ideal weak-axis Euler buckling load using node-to-node effective length. Wind uplift, unbalanced snow, load combinations, code buckling factors, actual restraint, joint rigidity, welds and out-of-plane behavior are not included.

How to read N / Ncr. As the ratio approaches 100%, the compression member approaches ideal elastic buckling. This is not a code utilization ratio; real design strength is usually lower because of imperfections, eccentricity and restraint conditions.

How to read L/δ and the deflection reference. L/δ is span divided by calculated deflection; a larger number means a stiffer model. The selectable L/200–L/400 values are comparison references only. The required limit depends on use, roofing, load combinations and governing design code; the calculator does not select it automatically.

Reference basis: ASCE/SEI 7-22 — Minimum Design Loads; steel member and connection reference: ANSI/AISC 360-22 — Specification for Structural Steel Buildings.