A New Strengthening Possibility
The aim of the SUREbridge project is to realize and provide a solution to utilize the remaining capacity of the concrete deck in an existing bridge by preserving it while refurbishing/ strengthening the bridge superstructure to the desired service level.
Investigations show that approximately 70% of the problems in existing concrete and concrete-steel bridges are related to concrete decks and in many cases, the refurbishment procedure involves demolition of the existing concrete deck and replacing it with a new one.
One consistent trend in current construction is the increasing demand for higher quality, shorter construction times and reduced environmental impact. This applies both to the construction of new structures and to refurbishment and renewal work on existing structures, the latter accounting for an increasing percentage of the construction work in general. Construction activities on site, such as demolition of existing concrete decks and abutments, soil compaction, or excavation, generate a great deal of noise and vibration which could have a negative impact on the environment, disturb inhabitants and, in unfavorable conditions, cause damage to buildings and installations close to the construction site especially in populated areas.
This situation is aggravated by growing public awareness of environmental issues and the increasing use of vibration-sensitive electronic equipment and machinery in industry. In many countries, environmental regulations are enforced more stringently and limit or even prohibit the use of impact or vibratory hammers.
There is currently a need for new upgrading techniques that can meet the requirements imposed by stakeholders and end users. A study conducted within the European “Sustainable Bridges” project (FP6) reveals that – from the point of view of bridge management authorities – the second most important field towards which research efforts should be directed is non-disruptive strengthening and repair techniques for bridges (www.sustainablebridges.net).
Fiber reinforced polymer (FRP), materials have attracted a great deal of attention in recent decades in infrastructural applications. This is mainly due to their superior mechanical properties such as high specific strength and stiffness and very good durability characteristics. The first application of carbon fiber polymers for strengthening of concrete bridges took place in the seventies and ever since the FRP technology has evolved so that full FRP bridge superstructures could be constructed today. Advantages such as ease of application, fast assembly and thus less traffic disruption, more effective and durable construction are among the advantages of using FRPs compared to conventional construction materials and methods.
The advantages offered by bonded composite materials such as carbon fiber-reinforced polymer (CFRP) laminates to upgrade the load-carrying capacity of existing structures and building new bridge structures have been demonstrated in the European project PANTURA (FP7).
An accepted solution in the past 20 years, which has been widely practiced in many countries, is to replace the existing concrete decks with lightweight FRP decks. This solution has several advantages including: less self-weight of the deck (an FRP deck weighs about 20% of an equivalent concrete deck) which provides extra capacity for traffic load, fast assembly compared to in-situ casted concrete decks, and ease of installation which does not need heavy machinery and site complications.
Challenges faced by infrastructure-owners
As the backbone of European transportation systems, the road and railway transport network account for more than 80% of passenger transport and 50% of goods transport in Europe. The performance of the road and railway network is largely dependent on the state of the critical transport infrastructure such as bridges. According to the ECTP Strategic Research Agenda (December 2005), road transport is expected to double within the next 15-35 years. In its statement on 31 May 2007, the European Conference of Ministers of Transport (ECMT) pointed out that road congestion in Europe annually costs one per cent of the Gross Domestic Product and bridges are among the main bottlenecks in the road networks.
Today, bridge owners and managers are dealing with a large number of structurally deficient and obsolete bridges. A review of the population of railway bridges in Europe shows that 30% of all steel and steel-concrete composite railway bridges are more than 100 years old and more than 70% are older than 50 years, and it is expected that these figures increase continuously. Similar statistics could be expected to be applicable to road bridges.
With the expected increase in the traffic volume, existing bridges will be subjected to more severe actions. Consequently, the need to refurbish this part of the infrastructure will increase dramatically in the future. The refurbishment, in this context, includes not only strengthening, repair and upgrading of bridge structures, but also geometric changes such as widening the bridge deck to provide more traffic capacity.
Construction processes for bridges, especially in densely populated areas, with a minimum negative impact and with the most efficient use of resources clearly call for holistic innovative solutions. The SUREBridge research project will focus on developing and promoting a new mind set when it comes to the design and, engineering of refurbishment in existing bridges which leads to achieving the main goal of this project.
Enhanced durability and life-time extension will be in hte focus of this project, in connection with:
– Strengthening for increased load bearing capacity
– Extending the capacity of road infrastructure by geometric modification, i.e. bridge deck widening
– Application of nocel materials for increased durability
– Rapid, non-intrusive construction and maintenance systems and techniques
Fiber reinforced polymers are cost-effective materials compared to conventional construction materials such as steel and concrete. FRPs are often referred to as super materials as they offer many advantages. Generally, what makes FRPs cost-effective is their long-service life and reduced maintenance costs. Structures made of composites have a long service life and need very little maintenance. FRPs do not rust and can be manufactured to resist chemical corrosion.
Tailor- made laminate stack up and many available protection and coatings will help add life and protection to the structural FRP elements. Durability alone, in some cases, will provide enough benefit to make composites a better choice compared to steel and concrete. From sustainability point of view, FRP materials are considered to be very sustainable.
The energy consumption to produce FRP composites is lower than that for traditional construction materials such as steel and concrete.
It is possible to recycle the FRP materials. FRPs could be crushed and granulated. The granulated material can be used as filler, reinforcement and lately they have been used to manufacture railway sleepers.
This project proposes the following advantages: elimination of the need for removing the existing
concrete deck which results in maximum possible utilization of the existing materials, greatly reduced waste production, limited environmental impact, minimized traffic disturbance and overall considerable reduction in the project cost and therefore LCC of the bridge.