2019i Table of Contents

Bolt length calculation

Last updated September 10, 2019 by Tekla User Assistance tekla.documentation@trimble.com

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Bolt length calculation

Bolt length calculation

Tekla Structures uses values from the bolt catalogcatalog that displays objects that can be used in a bolt assembly catalog

Objects in the bolt catalog are bolt elements, for example, bolts of different sizes and lengths, washers, and nuts.

and the bolt assembly catalogcatalog that displays bolt assemblies and their properties

The user can add, modify, and delete bolt assemblies.

when calculating the bolt length. If the bolt cataloguser interface for displaying or modifying information in categorized lists

For example, profile catalog and shape catalog are catalogs.

does not contain long enough bolts for your purposes, you need to add them to the bolt catalog.

The following Assembly settings in the Bolt properties affect the bolt length calculation process. If the check box is selected, the bolt element is used in the bolt assemblyset of bolt elements that consists of a bolt, a stud, or a screw, and possibly the related washers and nuts


Table 1.
Bolt assembly Bolt elements

1: If the check box is clear, only a hole is created

2: Washer (1)

3: Washer (2)

4: Washers (3)

5: Nut (1)

6: Nut (2)

The chart and the detailed steps below explain the process of bolt length calculation.

  1. Tekla Structures calculates the minimum possible length of the bolt as follows:

    washer (1) thickness (if the check box is selected) +

    material thickness +

    washer (2) thickness (if the check box is selected) +

    washer (3) thickness (if the check box is selected) +

    nut (1) thickness +

    nut (2) thickness +

    extra length

  2. Tekla Structures searches for the closest match in the bolt catalog.

  3. Tekla Structures calculates the number of washers required (must not exceed 10) so that the length of the shaft is less than :

    nut (1) thickness +

    material thickness +

    nut (2) thickness +

    washer (1) thickness +

    washer (2) thickness +

    (number of washers*washer (3) thickness)

  4. Tekla Structures checks that the bolt found in step 2 is longer than :

    extra length +

    nut (1) thickness +

    material thickness +

    nut (2) thickness +

    add. dist (from the bolt catalog) +

    washer (1) thickness +

    washer (2) thickness +

    (number of fittingadjustment of a part end

    washers * washer (3) thickness)

  5. If the selected bolt does not fulfill the criteria in step 4, Tekla Structures returns to step 2, otherwise it continues on to step 6.

  6. Tekla Structures checks that the selected bolt fulfills all the following conditions :

    • Can the thread be inside the material to be connected? Even if this is not allowed, the calculation always allows 3 or 4 mm of thread to be inside the material, depending on the bolt diameter. If the bolt diameter is ≥ 24 mm, it allows 4 mm, otherwise it allows 3 mm.

    • Shaft length must be more than:

      material thickness +

      extra length +

      washer (1) thickness (if checked) -

      maximum thread in material allowed (if thread in material = no) = 3 mm or 4 mm

    • Shaft length is calculated as:

      Screw length - screw thread length - thread end.

    • Thread end is the part of the bolt between the shaft and the thread. It is calculated as follows:

      Diameter of bolt (mm)

      Thread end (mm)

















  7. If the selected bolt does not fulfill all the above conditions, Tekla Structures returns to step 2 and tries the next longest bolt.

  8. If the advanced option XS_BOLT_LENGTH_EPSILON is set, the epsilon thickness is added to, or subtracted from, the material thickness to avoid inaccurate bolt length calculation.

    For example, if this value is not taken into account, and the calculated length is 38.001 mm, a 39 mm bolt might be selected.

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