How can the length of a bolt to be used in drop-in anchors be determined?

How can the length of a bolt to be used in drop-in anchors be determined?

Two factors will determine their length

• If they are too short it may mean that the bolt thread does not grip enough of the female thread of the sleeve, causing the male thread of the bolt or the female thread of the sleeve to fail.

  

• If the bolt is too long, its point may come into contact with the anchor’s expansion cone before the head of the bolt reaches the material to be fastened. In such a case, the bolt is unable to move any further, meaning that further torque may break the anchor’s sleeve due to the traction that the bolt thread exercises on the sleeve.

  

Example of the breakage of an M6 drop-in anchor (top photo) during installation due to excessive bolt length

In order to calculate the correct length of the bolt, follow the indications in the Index technical documentation, as well as European Technical Assessment ETA 14/0068 and 14/0135:

• Minimum bolt length = tfix + l_s,min
• Maximum bolt length = t_fix + l_s,max

where:

• t_fix: thickness of the fixture
• l_s,min, l_s,max: values depending on approval assessment

For example, in the case an M8 drop-in anchor (Code no. HEHOM08), where the thickness of the material to be attached: t_fix = 9 mm

Table C1: Installation parameters for HECHO / HECLO anchor

• Minimum bolt length: 9 mm + 8 mm = 17 mm
• Maximum bolt length: 9 mm + 13 mm = 22 mm

Therefore an M8 x 20 should be used

For other installation parameters, follow the values indicated in in the Index technical documentation, as well as in the European Technical Assessment.

For the installation process, consult applicable documentation and FAQ XXXXX

h_ef : Effective embedment depth

h₁ : Bore hole depth

h_nom : Embedment depth in the concrete

h_min : Min. concrete thickness

t_fix : Fixture thickness

d_o : Nominal drilling diameter

d_f : Fixture clearance hole diameter