Foreword

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This document was prepared by Technical Committee ISO/TC 167, Steel and aluminium structures.

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Introduction

This document has been prepared to provide provisions and guidance in the determination of the loss of pretension of bolts in the presence of coatings on the faying surface of a joint. For pretensioned bolted joints, the potential loss of pretension can be checked when the coatings applied to any of the individual coated faying surfaces are thick or consist of a creep-prone material. In this context, coatings exclude adherent mill scale, and include liquid applied coatings as well as coatings that are the result of a galvanizing or metallizing process. Examples of coatings include duplex coating and thermal spray coating. Loss of pretension due to other material, such as insulation, in the grip of a bolt is not considered in this document.

This document provides provisions and guidance on the measurement of pretension loss, considering that the suitability of the protective coatings or coating systems for use in pretensioned bolted joints depends on the extent of the possible system reserves due to the tightening procedure, the target of pretensioning, and the losses over the service life of a structure. The test methods in this document can be also applied to uncoated faying surfaces.

1 Scope

This document specifies test methods to determine loss of pretension in high-strength bolts due to the presence of coatings on the faying surface(s) of a bolted joint to be used in structural steelwork, when any of the coatings are thick enough to affect the pretension in a bolt in the short term, or can show significant deformation over time under sustained loads (creep-prone materials).

The presence within the grip of the bolt of other materials having considerably smaller stiffness than steel, such as insulation, is not included in this test method.

2 Normative references

3 Terms and definitions

4 General

4.1 Principles

4.2 Significant variables

4.3 Pretension loss over time

5 Test equipment and preparation

5.1 Test instrumentation

5.2 Test plate preparation

5.3 Test execution

5.4 Data acquisition

6 Test assemblies

6.1 General

6.2 Test A (Single-bolt test assembly)

6.3 Test B (Multiple bolt test assembly)

6.4 Test results

6.5 Test report

Bibliography