Bolts in Structure

There are two main types of junction between steel carpentry:

Welded Joint
Given the special process character is regulated there are numerous and articulated rules in this regard;
Bulloned joints
We will mainly focus on understanding what is required by D.M.14 / 01/2008 and what will be required under UNI EN ISO 1090-2 (end of transition period July-2014)

Below we refer to what D.M. 14/01/2008 Bolts and nails Bolts

The bolts - coforms for the dimensional characteristics to UNI EN ISO 4016: 2002 and UNI 5592: 1968 standards must belong to the following classes of UNI EN ISO 898-1: 2001 standard, as indicated in Tab 11.3.XII.


NormalHigh Resistence
bolt 4.6 5.6 6.8 8.8 10.9
nut 4 5 6 8 10

Stressing tensions fyb and rupture ftb of the screws belonging to the classes indicated above taella 11.3.XII.a are shown in the following table 11.3.XII.b

Table  11.3.XII.a
 fyb /(N/mm2 240 300 480 649 900
 ft/(N/mm2) 400 500 600 800 1000 Friction joint bolts

The friction joint bolts must comply with the requirements of the Rab 11.3.XIII screws and nuts, must be associated as shown in Tab 11.3.XII.

Tabella 11.3.XII

 Bolt 8.8 -10.9 according to UNI 898-1:2001 UNI EN 14399:2005 parti 3-4
 Nut 8 -10 according to UNI 20898-2:1994
Washers Steel C50 UNI EN 10083-2:2006 quenched and tempered HRC 32÷40 UNI EN 14399:2005 parti 4-6
Platelets Steel C50 UNI EN 10083-2: 2006 quenched and tempered HRC 32 ÷ 40

The high strength structural linking elements adapted to the drawing must meet the requirements of European harmonized standard EN 14399-1 and bear the relevant CE marking, with the specifications specified in point A of § 11.1 (end of extract DM 14 / 01/2008)

Below is the UNI EN ISO 1090-2: 2011 standard

5.6 Mechanical connectors

5.6.1 Generality

  • The corrosion resistance of the joints of the connectors and the sealing washer must be comparable to that of the elements to be connected.
  • Hot-dip zinc coatings must comply with EN ISO 10684. The electrolyte coatings of connecting elements must comply with ISO 4042.
  • The protective coatings of the mechanical coupling components must comply with the requirements of the relevant product standards or, failing this, comply with the manufacturer's recommendation.
  • Note Attention is drawn to the risk of hydrogen fragilization during the electrolytic coating process or hot dip galvanizing of bolts 10.9. "

5.6.2 Terminology

The following terms are used in the text:

  • "washer" means: "flat or bevel washer";
  • "assembly" means: "a bolt with a nut and a washer if necessary".

5.6.3 Non-tight structural steel structure

The non-tightened steel-carbon steel or austenitic stainless steel structural bolts must comply with EN 15048-1.
The tightening carried out in accordance with EN 14399-1 can also be used for non-tightened structural bolts.
The characteristics of the bolts and nuts classes and, if appropriate, the finishing conditions must be specified in conjunction with any other optional requirement that the product standard permits.
Mechanical characteristics must be specified for:

  1. the steel connection elements with diameters larger than those specified in EN ISO 898-1 and EN 20898-2;
  2. the austenitic stainless steel connecting elements with diameters larger than those specified in EN ISO 3506-1 and EN ISO 3506-2;
  3. ferritic austenitic assemblies.

Unless otherwise specified, the connectors according to EN ISO 898-1 and EN 20898-2 must not be used to connect stainless steels according to EN 10088. If an insulation kit is to be used, all details of its use.

5.6.4 Checked structural structural steel

The high-strength controlled structural bolting bolts include HR, HV and HRC bolt systems. These must comply with the requirements of EN 14399-1 and the appropriate European standards as listed in Schedule 7.
The characteristics of the bolts and nuts classes and, where appropriate, the finishing conditions must be specified in conjunction with any other optional requirement granted by the reference product standard.

end extract UNI EN ISO 1090-2

(source article written by Fontana s.p.a.)

  1. Until now high-strength metal hardware in Italy with standard UNI 5712 (for screws), UNI 5713 (for nuts) and UNI 5714 (for washers) has undergone the same criteria for acceptance or rejection of other types of bolts: the conformity of these elements was verified individually for screws, nuts and washers (UNI 3740 p. 8 °). No further evidence was required when these elements were paired with each other. This bolt was arbitrarily closed in pairs according to the tables dictated by CNR 10011 or DM 96. In both cases, the pairs were only indicative since it started from the assumption that the coefficient K (coefficient that measures the assembly fringes) was a constant.
  2. The new European standards on controlled tightening bolts prescribe the provision of homogeneous batch assemblies (this applies to screws, nuts and washers) which must also exceed 2 additional attitudinal tests when the individual elements are assembled. This is required to ensure that, with a certain tightening torque, the required preload is obtained with considerable reliability and that there are sufficient safety margins to avoid excessive tightening resulting in plastic screw deformation.

You can easily recognize the structural hardware with Marking

On screw product:

  • resistance class (according to EN ISO 898-1 or EN 3506-1)
  • assembly manufacturer logo
  • special brand "SB"
  • es. FONTANA HV 10.9 CE F
  • es. GFD 189 SB H8.8 NF

On nut product:

  • resistance class (according to ISO 898-2 or EN 3506-2)
  • assembly manufacturer logo
  • special brand "SB"
  • es. HV 10 CE F
  • es. GFD SC SB 8 NF

On washer product:

  • no particular marking required

The European Construction Products Directive (CPD 89/106 / EEC) PROVIDES THE OBLIGATION BY THE SUPPLIER OF THE NUT-BOLT-WASHING ASSISTANT to expose the CE mark to the supplied products. In order to comply with this requirement, the supplier has the obligation of EC certification issued by an accredited body, recognized at European level.  

The CE mark affirms that:

  • The product complies with national standards, in accordance with the corresponding harmonized European standards.
  • The company is equipped with an active and well-applied quality system (factory production and control system) that guarantees the above-mentioned compliance.
  • The total traceability of the product is constantly active for a period of at least 10 years

It is evident that, in the light of the Ministerial Decree of 14 January 2008 known as NTC as against the UNI EN ISO 1090-2 standard (whose transition phase will end in July 2014 becoming all-important), it is impossible to use in the boloneria structures other than the structural structure that either SB HV HR or HRC!

Normal bolts (not suitable for preloading) are used for cutting joints, where the joint resistance is entrusted to the cutting strength of bolt sections engaged in the joint, while high strength ones are used for friction joints , in which the joint efficiency is entrusted to the friction produced by the tensile stress due to the tightening moment to which the bolt is subjected.

High-strength bolts can also be used for cutting joints, but in this case their use is unjustified and uneconomic.