The topic of this project was the definition of a new effective repair and/or reinforcement method for large steel structures with defects. Two basic steel structural types were dealt with in the CO-PATCH project, namely marine structures (mainly ships) and steel civil engineering structures (e.g. bridges). Many of the major problems that these structures face during their operational life are common, with fatigue playing a predominant role among them.
Repeated loading is a very common loading condition for these structures. In areas of stress concentrations, this leads to the initiation and growth of fatigue cracks. If not detected and properly repaired in time, cracks can grow to critical lengths and result in structural failures. An additional structural problem of steel structures is corrosion. Corroded plating or corroded beams jeopardise the strength and stiffness of the structure. Measures are required to reinstate the original structural characteristics.
Besides repairing fatigue cracks and corrosion, there is often the need for upgrading the strength and/or the stiffness of a structure to enable new (higher) loading conditions or helping in mitigating initial design deficiencies.
Welding and replacement are the traditional ways to deal with these problems and to reinforce a structural part. However, there are circumstances when these repair or reinforcement approaches are either time-consuming and costly, or simply impossible to be followed. This obviates the need for investigating and assessing the effectiveness of new solutions that will help in overcoming currently existing problems.
Composite material patching is a very promising method for repairing and/or reinforcing steel structures. It has already proven its effectiveness and cost benefits by its application in the aerospace industry. However, there are several fundamental differences between the aerospace applications and bridge/marine/offshore steel applications. These differences dictate a separate approach and investigation of the problem.
The objective of this project was the definition of an effective repair method for large steel structures with defects. The project set ou to demonstrate that composite patch repairs can be environmentally stable and therefore, that they can be used as permanent repair measures.
The objectives were mainly be achieved by:
- Studying and demonstrating through theoretical analyses, numerical simulations and experimental testing that the use of composite patch repairs leads to the reinforcement of a steel structural member;
- Determining, evaluating and quantifying the efficiency of composite patch reinforcements in the marine/bridge environment, in both the short and long term;
- Developing a generalized procedure for the design and application of composite patch reinforcements in steel marine and civil engineering infrastructure applications;
- Evaluating existing or developing new, practically applicable and sensor based monitoring techniques of the final through-life structural integrity of the patch;
- Demonstrating the effectiveness of the developed design tools and procedures through full-scale tests;
- Developing an internationally recognised training programme for personnel.
The composite patch repair technology is an innovative and highly competitive product that caters to the needs of both marine vessels and civil engineering infrastructures. It reduces quite significantly the maintenance costs of many large steel structures, and in the case of metallic bridges it prolongs their design life. This technology creates a new market. It gives the partners the capability of providing high technology and high added value services worldwide.
The overall conclusions of the CO-PATCH project are:
- There is great interest in the CO-PATCH technology among relevant stakeholders;
- Surface preparation: specimens that were grit-blasted and acetone wiped prior to repair, significantly out-performed those surface-prepared only with a needle-gun;
- Carbon fibre patches need to be designed specifically for each plate/flange, taking into account the expected loadings that the structure might experience;
- Typical failure was observed to be between the resin/adhesive and the steel surface, but not within the composite patches themselves;
- Environmental protection for the patch and, more importantly, the bond line is critical for longevity of the repair/reinforcement;
- Currently, for classification societies BV and DNV patches are being evaluated on a case by case basis. These are therefore considered to be temporary with monitoring;
- Design/analysis and training/certification requirements and guidelines are being developed. Guidelines are currently being restricted to the contributing consortium only.
Composite patching has proven its effectiveness and cost benefits in the aerospace industry for several years. With that in mind, the CO-PATCH project focuses on steel structures: i.e. ships and bridges. Composite material patching is an effective repair and/or reinforcement method for large steel structures. The use of patches will significantly reduce maintenance costs. In the case of metallic bridges, it will prolong their design life and help address the consequences of increasing live loads. This technology creates a new market and gives partners the capability of providing high technology and high added value services worldwide.
Summarised these are:
- development of guidelines for proper numerical modelling of a composite patch reinforced structure;
- development of a generalised procedure for the design of composite patch reinforcements and the development of best-practice generalised procedures for application of composite patch repairs;
- demonstration of the effectiveness of developed design tools and procedures, and the development of an internationally recognised training programme for personnel.
Innovating for the future (technology and behaviour):
- Promoting more sustainable development
- A European Transport Research and Innovation Policy