Steel connection - screw forces and welds

Product Support
, , ,
1

Hello,
I have modeled a moment-rigid flange plate connection in RFEM 6.

My question concerns the tensile forces in the bolts (marked in green in the attached image). In a rough hand calculation, I obtain higher tensile forces than RFEM 6.

For the upper bolts, RFEM 6 indicates a tensile force of Ft,Ed = 134.85 kN. For the hand calculation, I used the design moment My,Ed = 145 kNm and the lever arm between the compression flange and the upper bolt pair of h = 0.3035 m. This results in: Ft,Ed = 145 kNm / 0.3035 m = 477.8 kN. This corresponds to the resultant tensile force in the upper bolt pair. If this force is evenly distributed between the two bolts, the tensile force per bolt is about 238.9 kN. Could you please explain to me what causes this deviation?

image
image1563×875 123 KB

Additionally, I have a question regarding the welds of the connection.

For the welds, the opposite picture emerges: while the tensile forces in the bolts from the RFEM 6 Steel Connections add-on are lower than in my hand calculation, higher stresses are indicated for the welds than the values I calculated (equivalent stress in the compression flange = 161.4 N/mm² and in the web = 114.9 N/mm²).

Could you explain how RFEM 6 Steel Connections add-on determines the weld stresses and which effects are taken into account?

image
image748×821 147 KB

Attached I am also sending the RFEM file.
Stirnplattenanschlussttest1.rf6 (1.4 MB)

Best regards
Eric Thiry

3

Hello @Eric1998 :waving_hand:

For a connection where only a single row of bolts takes tensile forces, this calculation would be applicable. Here, however, there are three rows of bolts taking tensile forces.

In such cases, the lever arm can be roughly estimated as the distance between the point of pressure and the geometric centroid of the two bolts under the highest tensile stress.

In this case, it results in:

(303.5 mm + 208.5 mm) / 2 = 256 mm

From the bending moment, this yields a force of:

145 kNm / 0.256 m = 566.4 kN

Divided among 4 bolts, this results in:

566.4 kN / 4 = 141.6 kN per bolt

For the weld seam stresses, an orthotropic material model was developed. Therefore, in the seam only:

  • Normal stresses perpendicular to the seam axis
  • Shear stresses parallel to the seam axis
  • Shear stresses perpendicular to the seam axis

are considered.

The yield strength is adapted to the failure modes of the weld seam according to EN 1993-1-8, i.e., to:

  • Equivalent stress
  • Normal stress

Further information can be found in this thread:
Ergebnisschnittauswertung Ergebnisstab

Best regards
Fabian

4

Hello Fabian,

Thank you very much for your feedback. Your response was very helpful.

Best regards,
Eric Thiry