Hydraulic Structures are subject to varying loads of more or less cyclic character. These loads are primarily generated by differential water heads on, e.g., navigation lock gates, but also by waves, drive system forces and other actions. As a result, the designers must take account of an additional failure mode of these structures – the failure by fatigue.
Prior to the 1970’s, fatigue was of minor or no concern for designers, constructors and managers of hydraulic structures. This changed, however, with the following developments:
- Increase of navigation, and higher gate opening and closing frequency;
- Advance of welding and disappearance of riveted steel structures; welded joints are more vulnerable to fatigue;
- Higher demand for infallible, low maintenance hydraulic structures.
A number of serious fatigue damages, particularly to lock gates, emphasized the need for guidelines in this field. Such guidelines already exist for other steel structures, like bridges, cranes or pressure vessels. They do not cover, however, all specific operation conditions and demands that apply to hydraulic structures.
To fill this gap, the PIANC Inland Navigation Commission (INCOM) set up a Working Group that compiled, investigated and assessed the international expertise on the fatigue of hydraulic structures. This report is a result of the Working Group activities. It aims to offer comprehensive guidelines in the field of fatigue to all professionals involved in design, construction and management of hydraulic steel structures.
Investigation method
To meet these objectives, the Working Group comprised a number of international experts in both structural and mechanical aspects of hydraulic steel structures such as lock gates, movable weirs, gates of harbor and shipyard docks. The represented expertise of the Working Group included – among other – the following profiles:
- Structural and mechanical design engineers with long experience in hydraulic structures.
- Field managers, project and program leaders experienced in handling fatigue problems.
- Fatigue experts in similar fields, like cranes, pressure vessels, steel bridges, industrial structures and ships.
- Young professionals willing to specialize in the field of the Working Group.
In the first phase, the group collected and assessed the existing know-how on the fatigue of such structures. This covered all relevant aspects, such as the design, analysis methods, structural detailing, monitoring, material aspects, fatigue damage assessment, maintenance and repair techniques.
Fatigue of hydraulic steel structures has not yet been handled in a PIANC report. There is also little literature in this field published outside PIANC. The issue has, however, been extensively handled in relation to other structures. Interesting in this view are structures like cranes, ships, and to some extend steel bridges. The Working Group collected and studied the reports, standards and other publications on the fatigue behavior of such structures. The Group assessed the relevance of these sources for hydraulic steel structures and issued proper recommendations.
The Working Group favoured a practical approach to the fatigue issues. It followed the line that the report should in the first place address and answer the field-borne needs of the PIANC community concerning the management of fatigue, rather than deliver a scientific discussion on this issue.
Final Product
This report is the final product of the Working Group activities. It contains a detailed analysis of the current engineering practice and offers guidelines for a more uniform, systematic approach to fatigue related issues. The report provides a summary of the appropriate design tools, like analysis methods, technical codes, other guidelines and best practices. It gives examples of both correct and incorrect solutions, provides the discussion of crucial issues and presents the lessons learned from fatigue failures of hydraulic structures. Apart from the design, the report also provides proper recommendations and best practices for the repair of different fatigue damages and for the management (particularly monitoring and assessment) of structures exposed to fatigue.
The Working Group collected a number of case studies from different countries in order to compile the lessons learned on fatigue. The existing guidelines and norms that handle fatigue of structures in other fields have thoroughly be reviewed and recommended if and where appropriate. The matters that have been investigated include:
- Nature of fatigue in hydraulic structures, significance and specific character of fatigue damage.
- Identification of fatigue loads, their sources, characters and correlations. Modeling these loads for analytical purposes.
- Requirements and boundary conditions of fatigue management, e.g. gate service life, permissible damage, accessibility for repair, conditions imposed by maintenance.
- Fatigue analysis methods and their assessment in view of hydraulic structures. This includes a study of literature and a critical discussion of the existing design codes.
- Relevant material aspects of fatigue, like fatigue behavior of various steel alloys, connectors, welding details etc.
- Detailing and construction of hydraulic gate components that are crucial in view of fatigue prevention.
- Monitoring, field inspections, assessment and maintenance of fatigue sensitive details.
- Available repair techniques of fatigue damage and other methods of service life extension, like better control of fatigue loads.
- General conclusions and recommendations.