Effektiv konstruktion och uppgradering av stål och stål-FRP komposit broar - med fokus på långtidsbeteendet

Forskningsprojekt, 2012 – 2015

At the present time, sustainable development is a key issue in a wide range of fields, including production technology, life-cycle management and the use of natural resources. It is also one of the most challenging goals in the construction industry. This applies not only to the design of new structures but also to the management of the huge stock of existing structures. Sustainability, in this context, covers three important areas, including society, environment and the economy. Bridge owners and authorities are currently dealing with a large number of structurally deficient and obsolete bridges because of ageing and the more rigorous safety demands imposed in current regulations. Two strategies can be considered when dealing with deficient bridges in networks: upgrading and replacement (reconstruction). Traditional upgrading and construction methods involve several drawbacks, of which traffic disturbance/disruption is the most important. The trend in the past few years has therefore been to develop upgrading and construction techniques which minimise the operation time and have a minimal effect on traffic flow. In this context, the use of fibre reinforced polymer (FRP) materials, together with an adhesive bonding technique, in the upgrading and construction of bridges has attracted a great deal of attention in recent years. The outstanding properties of FRP materials, such as high strength, high modulus of elasticity, light weight, corrosion resistance, enhanced fatigue life and tailorability of properties, have made them a suitable material for upgrading existing bridges and constructing new ones. The advantages offered by using FRP materials, in terms of the construction of new bridges and the upgrading of existing ones, have been demonstrated in a number of scientific publications. Despite extensive research work on the short-term load effects, the method still faces some questions about the long-term performance of adhesive joints. Unfortunately, the extent of our knowledge of the negative effects of environmental parameters, such as temperature, humidity, corrosion and de-icing salts, on the durability of adhesive joints is still very limited. This lack of knowledge is compensated for by the application of large safety factors to the strength of composite materials, which in turn increases the cost dramatically (in some cases less than 30% of the capacity of the composite material is effectively used). This simply means that about 70% of the resources, including the raw material and energy consumed to produce the FRP material, are wasted. For this reason, considerable benefits in terms of material utilisation and economic savings can be made if realistic and accurate design methods, taking account of the long-term performance of FRP systems, could be developed. In the construction of new steel-FRP composite bridges (steel girders with an FRP deck), the composite action (integrity of the girders and the FRP deck) is an important aspect. The principal aim of this research project is to develop a design model for adhesive joints between steel and FRP composites to take account of the long-term effects. Within this overall aim, there are two sub-aims that relate to the main aim of this project: (1) to improve our knowledge of the long-term performance of adhesive joints beyond the state of the art, with special emphasis on the effects of corrosion, temperature, humidity and de-icing salts on the load-carrying capacity, stiffness and fatigue strength of adhesive joints, and (2) to develop an overall design model based on the knowledge obtained in the previous sub-aim which takes account ? in an appropriate manner of important factors that affect the load-carrying capacity, stiffness and fatigue strength of joints. The research work will be carried out over a period of four years and will be divided into three tasks: (1) improve our knowledge of the long-term performance of FRP systems beyond the state of the art, (2) establish a degradation model and (3) develop an overall design model and verification.

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