Steel Tube Truss Calculator
About Steel Tube Truss Calculation
This calculator performs a geometric calculation of a steel tube truss made from rectangular hollow section steel for a canopy, awning, or other light metal structure. It determines the shape of the outer chord, the lengths of individual members, and the truss subdivision into verticals and diagonals. The calculation is suitable for mono-pitch and double-pitch layouts and helps estimate tube cutting lengths before fabrication.
The result is based on the entered geometry in millimetres and on uniform span subdivision according to the number of verticals. The calculator determines only the truss member dimensions, not its load-bearing capacity, stability, or section selection under load.
Reference points and recommendations
How the outer chord geometry is built
Basic layout. The calculation uses the truss length A in mm and two heights H1 and H2 in mm. The bottom chord is assumed to be straight. The top chord is built as a straight line between the specified heights.
Mono-pitch truss. For a mono-pitch layout, the height difference across the full span is ΔH = |H1 - H2|. The length of the sloping top chord is determined using the Pythagorean theorem:
L = √(A2 + ΔH2)
In this layout, the bottom chord length is A.
Double-pitch truss. For a double-pitch layout, the span is divided into two equal parts of A / 2. Each half of the top chord is calculated separately using the height difference ΔH = |H1 - H2|:
L1/2 = √((A / 2)2 + ΔH2)
The total top chord length is taken as 2 x L1/2. The bottom chord is also taken as length A.
How the vertical positions are determined
Subdivision into panels. If n verticals are specified, the span is divided into n + 1 equal panels. The spacing between adjacent nodes along the truss length is calculated as follows:
p = A / (n + 1)
Vertical coordinates. Each vertical is placed at a subdivision node. Its length equals the distance between the bottom and top chord at that point. Since the top chord is a straight line, the height of each vertical is found by linear interpolation between the end heights. For a double-pitch truss, interpolation is performed separately for the left and right half, so the members become mirror-symmetrical.
Practical meaning. With the same number of panels, the calculator keeps identical node spacing along the span. Because of this, vertical lengths usually differ if the top chord is sloped.
How diagonals are calculated
Diagonal construction. If the diagonal option is enabled, diagonal members are built between adjacent truss nodes according to the selected panel pattern. For each diagonal, the actual coordinates of its two ends are used, and the length is determined as the distance between these points:
Ld = √((Δx)2 + (Δy)2)
Result logic. Since the panel height changes along the truss length, diagonals in different zones can have different lengths. In a double-pitch layout, identical members on the left and right side repeat in mirror form.
How the final values are formed
Member lengths. The calculator separately determines the lengths of chords, verticals, and diagonals in mm. The members are then grouped by type so the user can see which parts need to be fabricated and in what quantity.
Selection of the final value. If the truss is symmetrical, the total for symmetrical members is taken with repetition on the second side included. If diagonals are disabled, only the outer frame and verticals are included in the result. This means the final result depends not on one condition alone, but on the combination of truss type, number of panels, and the presence of diagonals.
Section size. The entered hollow section size is given in mm and is used for geometric display and member positioning in the scheme. Since wall thickness, steel grade, and design load are not entered, this parameter alone cannot determine the structural capacity of the truss.
Engineering references and standards context
Geometric verification. For a real structure, after obtaining the member lengths, the load-bearing capacity, deflection, chord stability, and joint behaviour are usually checked separately. In Europe, such checks are carried out using EN 1990 Eurocode. Basis of structural design, EN 1991 Eurocode 1. Actions on structures, and EN 1993-1-1 Eurocode 3. Design of steel structures. General rules and rules for buildings.
Fabrication. For welded and assembled steel trusses, designers also refer to EN 1090-2 Execution of steel structures and aluminium structures. Technical requirements for steel structures. This is important for assigning tolerances, joint requirements, and fabrication control.
Practical reference. This type of calculator is especially useful at the layout and cutting stage, when the goal is to obtain tube lengths quickly and understand the overall geometry. For a final design decision, these data are not sufficient without a load-based structural check.
FAQs
Can this calculator be used to select the truss section?
No. This hollow section truss calculator determines geometry and member lengths, but it does not select the section based on strength. Section selection requires loads, wall thickness, steel grade, support conditions, and verification according to Eurocode 3.
Why are the vertical lengths different from each other?
This is normal for a mono-pitch or double-pitch truss with a sloping top chord. Since the top chord changes height along the span, the distance between the chords at each panel is different. That is why the truss calculator shows different vertical lengths at different nodes.
What affects the diagonal length the most?
The main factors are panel spacing and truss height. The greater the distance between nodes and the greater the truss depth, the longer the diagonals. In a double-pitch layout, diagonal lengths also depend on the panel position relative to the centre.
Why does the calculation not include metal weight and load capacity?
That cannot be determined from the external hollow section size alone. Wall thickness, steel properties, connections, combinations of snow and wind load, and member stability checks are also required. Because of this, this online truss calculation is intended primarily for geometry and cutting lengths.
Is this calculation suitable for a canopy truss?
Yes, it is useful for a preliminary canopy truss layout. It allows you to estimate chord, vertical, and diagonal lengths quickly and prepare cut members. However, before fabrication, the canopy truss should preferably also be checked for snow, wind, and service loads.