How a ground-mount truss for solar panels is checked
Loads, every member, the nodes, the supports and the geometry. Step by step — what to check before a truss goes into production, and how Solispec does it.
A ground-mount truss looks simple: a rafter, legs, a strut, a few braces. Yet it holds the panels under snow and wind for twenty years or more. A mistake in it does not show on the drawing — it shows in winter, after the first big storm. Below is the order of checks we follow at Solispec. It is useful when you calculate by hand, too.
1. Start with the loads, not the profile
The profile is chosen for the loads, not the other way round. In Ukraine the basis is ДБН В.1.2-2 "Loads and actions". For a truss, what matters is:
- snow — by region and by the return period you choose for the project;
- wind — by region, terrain type and the height of the panels;
- the self-weight of the panels and the structure.
Take the values for the site itself, not "by the oblast, roughly". From the site's coordinates, Solispec fills in the values of the nearest oblast centre (within 200 km), and you can replace them with your own. Terrain type changes wind a lot: an open field and a built-up area are different cases.
Check both combinations: with snow leading and with wind leading. Different sites are governed by different ones, and you cannot guess which in advance.
ДБН allows the force coefficient for inclined panels to be taken from EN 1991-1-4. Solispec does so, and warns separately when the tilt is outside the table.
2. Wind does not push at the centre
A common mistake is to spread wind evenly over the panel plane. In fact the resultant sits towards the windward edge (EN 1991-1-4, 7.3(6)). For the truss that means different forces in the rafter and the legs; for ballast, a different overturning moment. Check both wind directions: onto the panel face and uplift.
3. Check every member, not only the rail
The rail is the most visible part, but a truss can fail in the rafter or the strut. So you need a model of the whole truss — nodes, members, supports — and the force in each member.
Then each member is checked to the norm for its section:
- cold-formed C-profiles to EN 1993-1-3: effective section, distortional buckling, flexural-torsional buckling;
- tubes to ДБН В.2.6-198.
For slender members, stability governs rather than strength. Check both planes, each with its own buckling length: a member buckles where it is weakest.
4. The nodes are a check of their own
A truss is held by its bolts. For a bolted node in a thin-walled profile, EN 1993-1-3 asks for the bolt to be checked in bearing on the wall and in shear.
A perforated profile is a story of its own. The norm's table formula (EN 1993-1-3, Table 8.4) is written for round holes, and perforation means slots. The node is then outside the formula's scope, and its resistance is confirmed by the profile maker's data or by tests. The other way is to change the design: a node plate, or an unperforated profile in the truss.
5. Geometry: nothing through anything
A truss that passes every calculation can still fail to assemble on site. Two rules we keep:
- no profile passes through another — neither through a neighbouring member nor through a support;
- one hole, one bolt.
Solispec checks every pair of members for a clash and shows exactly which ones are in each other's way.
6. Supports: piles or ballast
A pile holds by the soil, so its capacity depends on the soil — confirm it on site with a trial installation. Ballast on the ground or a roof is checked per support line for three things:
- uplift by wind;
- overturning — with the off-centre wind resultant;
- sliding — governed by friction between the block and the base. If the friction value is not confirmed for your base, check it.
7. When it does not pass
A red result is no reason to "nudge the safety factor". The real options:
- a thicker profile wall;
- a shorter rafter span or an extra leg;
- a tube instead of a C-profile;
- fewer panels per row on one truss.
In Solispec a design that fails its checks cannot produce a PDF or a proposal. The report opens with a red block listing every critical item, so you see at once what to change.
In short
- Loads to ДБН В.1.2-2 first, both combinations.
- Wind as an off-centre resultant, in both directions.
- A model of the whole truss, each member to the norm for its section.
- Bolted nodes separately; perforation with care.
- Geometry without clashes, one hole one bolt.
- Supports: uplift, overturning, sliding.
The calculation is preliminary. A qualified engineer must check it before installation.