UNI EN 1090-2 Execution Class

How to determine the execution class of the structures as required by UNI 1090-2

As it is known from July 1, 2014, the implementation of the "CE" marking of steel and aluminum structural elements used in buildings (UNI EN 1090-1: 2011) has become mandatory.

The standard provides a unique approach to the realization of any type of structure, whether it be large civil engineering works such as the construction of stadiums, hospitals, major infrastructure of strategic importance, such as bridges on national and international routes (eg bridge over Bosporus or the new containment system of Chernobyl), to the simple metal constructions for the construction of canopies, stairs, or simple components for the static consolidation of buildings, the standard applies to serial production and not, to differentiate the technical requirements according to the complexity of the components, four execution classes, with more stringent technical requirements, have been introduced from class 1 for the so-called simple works with moderate risks related to possible collages or failures to class 4, which refers to particularly complex structures with important safety implications!

Why is it important to rely on certified companies in the execution class at least EXC-3?

he execution class of a steel (or aluminum) structure can easily be determined by combining the essential parameters divided by the Concentration Class (CC or Consequence Class) and POTENTIAL RISKS (SC or Service Categories and PCs or Production Categories)

Definition of classes of consequences: (CC Consequences Class).

Consequences Class Descriptions Examples of buildings and civil engineering works
CC3 High consequences for loss of lives, or very serious consequences in economic, social or environmental terms
  • Steep sports facilities
  • Public buildings where the consequences of collapse are high (eg concert halls)
  • Railways
  • Bridges
  • etc ...
CC2 Average consequences for loss of human life, considerable consequences in economic, social or environmental terms
  • Residential and office buildings
  • Public buildings where the consequences of collapse are average (eg office building)
  • Industrial Buildings
CC1 Low Impact on Human Losses, with Moderate or Negligible Economic, Social or Environmental Repercussions
  • Agricultural constructions, where no one usually enters (eg greenhouses)
  • Warehouses for non-hazardous substances and in which staff access is absolutely limited
 CC1=LOW             CC2=STANDARD             CC3=HIGH

Definitions of Services Class: (SC Service Categories).

Categoria Parametri
  • Structures and components designed only for quasi static actions;
  • Structures and components whose connections are designed for earthquake action in regions with low seismicity and DCL ductility class;
  • Structures and components designed for crankshafts / mechanical cranes (class S0);
  • Structure and components designed for fatigue resistance according to EN 1993 (eg road and rail bridges, cranes, class carriages S1 to S9);
  • Striking structures for wind, crowd or rotating machinery;
  • Structures and components designed for earthquake action in medium or high earthquake and DCM or DCH ductility classes;
DCL,DCM, DCH: Ductility classes according to EN 1998-1 (eurocode-8)
SC1= static load    SC2=fatigue stress

The maps with seismic indices can be downloaded from the site of the Civil Protection at: http://www.protezionecivile.gov.it/jcms/it/classificazione.wp,
Alternatively, you can download the updated map from the following link: mappa.pdf, It is important to note that regions such as the Marche, Abruzzo, Umbria and the provinces such as Rimini, Arezzo, Forlì-Cesena, are almost entirely classified as seismic zone 2 (MEDIUM HIGH RISK).
On the site at Arcelor Mittal http://www.constructalia.com/ a useful dispensation is available on the design methodologies in the seismic zone and on the choice of ductility classes DCL, DCM, DCH anti-microbial structures in accio.pdf, briefly, the Technical Building Regulations, for dissipative structures only allowed two classes of ductility:

  • CDA equivalent to the DCH class of Eurocodes
  • CDB equivalent to the DCM class of Eurocodes
  • the DCL class of Eurocodes simply was not contemplated

Now the Eurocodes, in particular the Eurocode 8 UNI EN 1998-1, provide that any of the ductility classes, but with particular geographical constraints that must be defined by the states concerned, should be used, in the national appendix recently published in the Official Gazette and freely prepaid from the official site http://www.gazzettaufficiale.it/, it is possible to use the DCL duct class in any seismic zone including high seismicity at the condition of designing the structure as non-dissipative with the limitations of the case!
Also on this topic was expressed also the CTS (Technical Committee of Scentifico) of the Emilia Romagna region http://www.ambiente.regione.emilia-romagna.it the opinion is freely available at the address parere in merito alla progettazione di strutture poco dissipative.pdf
Although the choice of the ductility class to be adopted and the designer's exclusive prerogative, as can be understood from various publications, the DCL class should be used predominantly, if not exclusively in low seismic areas (due to forces in play) while in other areas could be more correct or at least sensible even in the light of recent seismic events in Emilia Romagna (see Finale Emilia, zone considered as medium-low zone 3) to build into DCM and DCH ductile classes

Definition of Production Categories: (PC Production Categories).

Category Parameters
  • Non-welded components manufactured with any steel class
  • Welded components manufactured with lower steel class S355 (= S275max)
  • Welded components manufactured with steel grade equal to or higher than the S355
  • Essential components for structural integrity that are assembled on site by welding
  • Components that are hot products or that receive heat treatments during production
PC1<S355(=S275)         PC2=S355

Determining the EXecution Class: (EXC Execution Classes).

Conseguence Classes
Service Categories  SC1  SC2 SC1 SC2 SC1 SC2 
Production Categories PC1 EXC1 EXC2 EXC2 EXC3 EXC3* EXC3*
* EXC4 should be applied to special structures or structures with extreme consequences of a structureal failure as required by national provision

Now, as an example of the destination, the province of Rimini, Perugia or Pesaro is quite obvious that, unless there are plans or realization of greenhouses for the cultivation of vegetables or simple warehouses for non-hazardous materials and where the presence of human staff is to be regarded as completely occasional and absolutely limited over time, the correct execution class to use is only EXC3 even with S275 or S235 quality materials regardless of thickness. So if you exclude regions such as Sardinia and part of Northern Italy it is absolutely essential to design and trust EXC3 certified class companies!