Glossary · Steel structures
Thin-walled cold-formed C-profile
A bent steel section with thin walls that buckles locally before yielding; it is designed to DSTU-N B EN 1993-1-3:2012.
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Definition
Most ground-mount PV trusses are built from 41×41 C-channel, 1.4–2.5 mm thick, the lipped "solar" mounting profile. Such a section loses local stability of its walls and stability of its cross-section shape before the steel reaches yield. DBN V.2.6-198:2014 (cl. 3.22) defines thin-walled cold-formed structures in exactly these terms.
Change 1 to DBN V.2.6-198:2014 added a direct limit to section 1: the norms do not apply to the design of thin-walled steel structures of cold-formed profiles. So the C-profile is designed to DSTU-N B EN 1993-1-3:2012, the Ukrainian edition of EN 1993-1-3:2006, together with EN 1993-1-5:2006 for effective widths and EN 1993-1-1:2005 for the buckling curves. Closed tubes 42×42×2, 60×60×2 and the like are not thin-walled in the sense of cl. 3.22 and stay under DBN V.2.6-198:2014.
In practice the compression and bending resistance of a C-profile is noticeably lower than the gross section suggests, because part of the walls drops out of action. A check on the gross section with rules for ordinary rolled steel overstates the margin. Perforation adds to this: factory slots weaken the section and change how the bolted node works.
Why it matters for PV. A ground-mount truss works against wind uplift and snow, and its members are long and light. Our audit of 2026-10-05 found that the old approach did not check the C-profile truss members at all, and that the rafter is also in bending because the rails do not sit at the nodes. So a check on the gross section under the rules for rolled steel does not fit. If a truss fails, the simplest steps are a thicker profile or shorter spans between nodes; the Solispec constructor recalculates both at once.
How Solispec applies it
The Solispec engine checks every C-profile member of the truss (base, legs, rafters, braces, rails) to DSTU-N B EN 1993-1-3:2012: effective section, buckling under compression and bending, distortional buckling, bolt bearing. The γM factors are the EN recommended ones, since we did not obtain the national annex, and the report says so. For tubes the engine switches to DBN V.2.6-198:2014.
Norms and clauses
- DSTU-N B EN 1993-1-3:2012
- DBN V.2.6-198:2014, Change 1, section 1; cl. 3.22
- EN 1993-1-5:2006, cl. 4.4
- EN 1993-1-1:2005, cl. 6.3
Related terms
- Effective cross-sectionThe part of a thin-walled section that still carries compression after its walls buckle locally; computed per EN 1993-1-5 and EN 1993-1-3.
- Profile perforation and bolts in slotsFactory slotted holes of a mounting C-profile; bolts go into the slots without drilling, and the maker confirms a slotted bolt’s resistance.
- Buckling reduction factor φ (χ)A factor that reduces a compressed member’s resistance for flexural buckling: φ in DBN V.2.6-198, χ in Eurocode 3.
- Steel partial factors γM and γmFactors that divide the characteristic steel resistance: γ_M per Eurocode for C-profiles, γ_m per DBN V.2.6-198 for tubes.
- DSTU-N B EN 1993-1-3:2012: designing C-profiles for PV mountingNorms explained
- DBN V.2.6-198:2014 “Steel structures”: tubes in PV framesNorms explained
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.