- Determine the effect of surface coating, environment and cathodic protection on fatigue strength of large bolts through a programme of fatigue tests.
- Investigate options for measuring remaining pre-tension in bolted connections and carry out fatigue tests to determine the effect of pretension on fatigue strength of bolted connections.
- Carry out a literature review and survey of members to collate current guidance and industry practice for installation of bolts so that recommendations can be made.
A recent literature review carried out by TWI reviewed the structural integrity requirements for bolted connections and identified the following areas, which have been validated through discussion with industry, that require more research:
- Better understanding of the effect of surface coating, environment and cathodic protection on fatigue performance, particularly for high strength bolts (hydrogen embrittlement issues).
- A better understanding of the effect of pretension relaxation on fatigue strength of bolted connections.
- Guidance on the use of large bolts in fatigue applications (ie those greater than the range given in BS7608, 19 to 52mm diameter), which are commonly used in offshore wind applications.
- Since the installation method may have an influence on the fatigue strength of bolted connections, a review of current industry practice and existing guidance of installation methods is required, followed by recommendations.
This project will gather and generate fundamental knowledge on the fatigue behaviour of large bolts used in offshore structures. The information will be disseminated for use by industry via conference papers, a TWI Industrial Member Report and updates to BS7608.
Benefits to Industry
The project outcomes will be disseminated for use by industry via conference papers, a TWI Industrial Member Report and updates to BS7608. Industry will have access to experimental data on the fatigue strength of bolts to assist design decisions. Guidance and recommendations on bolt pre-tension and installation will also be provided.