Steel partial factors γ_M and γ_m

The design resistance of steel is lower than the characteristic one: it is divided by a material partial factor. PV trusses involve two such systems, because the C-profile and the tube are designed to different norms.

For a C-profile under DSTU-N B EN 1993-1-3:2012 the factors are γ_M0 (section resistance), γ_M1 (member buckling) and γ_M2 (connections, including bolt bearing). The EN recommended values are γ_M0 = 1.0, γ_M1 = 1.0, γ_M2 = 1.25. The national annex may change them; we did not obtain its text, so Solispec labels these as EN recommended values, not checked against the NA.

For a tube under DBN V.2.6-198:2014 the design resistance is R_y = R_yn / γ_m, with γ_m = 1.050 for "other rolled sections and tubes" (Table 7.2), since the specific tube standard is usually unknown in a project. The service condition factor γ_c = 1.0. Example: steel with R_yn = 245 MPa gives R_y = 245 / 1.05 ≈ 233 MPa.

Material factors should not be confused with load factors: γ_fm for snow and wind under DBN V.1.2-2:2006 sit on the other side of the inequality.

What follows from this. For a C-profile, the section and buckling checks at γ_M0 = γ_M1 = 1.0 rest directly on the steel's yield strength, so the steel grade and actual wall thickness count directly. Bolted nodes are checked with γ_M2 = 1.25. For a tube under the DBN the margin sits in γ_m. If the national annex of DSTU-N B EN 1993-1-3:2012 sets other values, the check results change in proportion, which is why Solispec states in the report which factors it used. The engine does not apply the responsibility factor γ_n in the tube checks.

The Solispec engine uses γ_M0 = γ_M1 = 1.0 and γ_M2 = 1.25 in the C-profile checks and writes "EN recommended, NA not checked" in the report. For tubes it uses γ_m = 1.05 and γ_c = 1.0 per DBN V.2.6-198:2014.

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