Retrofitting of Existing Bridge Using Externally Bonded FRP Composite–Applications and Challenges

S. V. Chandramouli, Manager (Technical); Sindhu S Saraswathi, Manager (Technical Services), M N Ramesh, Director, BBR (India) Pvt. Ltd., and N. Munirudrappa, Professor of Civil Engineering, Dayananda Sagar College of Engineering, Bangalore.
The increase in deterioration of bridge infrastructure is a large-scale national problem. Maintaining the existing bridge infrastructure network and adapting it to new capacity requirements has become one of the most challenging tasks for today's engineers. Bridges designed and built only a few years ago are now subjected to traffic loads well above the design ones. At the same time, it has become evident that the durability of bridges is not always guaranteed, even for relatively recent constructions. For bridges in urban areas, the space concerns are predominant and building a new bridge alongside an existing one is not a viable option. It is therefore necessary to intervene on the structure with most feasible, economical and efficient methods to upgrade, repair or strengthen the existing bridges while preserving, at least partially, its traffic bearing capacity. These challenges are greater than the ones required to design and build a new bridge. Fiber Reinforced Polymer (FRP) composites represent a new and promising solution to the shortcomings of several traditional materials and upgrading techniques and has a great potential to integrate into the bridge infrastructure. In the recent years several, researchers have investigated the performance of external bonded FRP composites and found to be a successful effective technique for upgrading structural element. This paper highlights the applications of external bonded FRP composites overlay for bridge infrastructure, the challenges involved and path to implementation.

Introduction and Background

The bridge infrastructure has been deteriorating for many years, a result of sometimes like harsh environmental conditions, heavy loads, insufficient maintenance, and, frequently, unintentionally damaging maintenance practices and it has be come a large-scale national problem. It has been widely reported that approximately 40% of India's bridges are either structurally deficient or functionally obsolete. Structural "deficiency" does not imply that a bridge is unsafe or likely to collapse. With proper weight restrictions and enforcement, most deficient bridges can continue serving traffic safely when limited to posted maximum loads. The main reasons for classifying a bridge as structurally deficient are low load ratings (or weight restrictions), deteriorated decks or deteriorated substructures. Maintaining the existing infrastructure network and adapting it to new capacity requirements has become one of the most challenging tasks for today's structural engineers. Bridges designed and built only a few tens of years ago are now have to carry traffic loads well above the design ones. At the same time, it has become evident that the durability of bridges is not always guaranteed, even for relatively recent constructions. In this context, the engineer is often asked to design refurbishments, enlargements and repairs on structures that are under heavy usage. This presents challenges that are even greater than the ones required to design and build a new bridge. For bridges in urban areas the space concern are predominant and building a new bridge alongside an existing one is not a viable option. It is therefore necessary to intervene on the structure while preserving, at least partially, its traffic bearing capacity. Due to budget constraints, many authorities are forced not to proceed with strengthening but to post load restrictions on their bridges as a temporary measure. A significant number of bridges all over the world need rehabilitation and strengthening.

The economic impact of bridge replacement is represented by not only the direct costs associated with demolition and construction of a new bridge, but also by the indirect costs associated with the loss of roadway use and traffic disruption. The latter are often difficult to quantify and foresee. In addition, high traffic volumes, tight construction budgets, and challenging roadway construction areas have put a strain on the ability of conventional materials to meet the public need for rapid construction, long-lasting structural components, lightweight and easy constructed facilities. This problem has created an urgent need for effective means of structural retrofit, repair and rehabilitation of bridge infrastructure as an alternative to bridge replacement. Casting additional elements, increasing cross-section size, and bonding steel plates are techniques that have been used in the past when widening or strengthening an existing bridge. These solutions can be expensive and difficult to implement, especially for working constraints (low-vertical clearance, head room,) scheduling constraints, economical constraints (minimum labor cost, minimum shut-down costs, material costs, etc) and long-term performance with strength and durability.

In the recent past, steel plate bonding was considered as an effective method for upgrading structural members. It began in South Africa and France, where steel plates bonded with epoxy resins were used for strengthening of concrete members [5]. This method originates from the strengthening of steel beams by means of adding steel plates. But, bridges that had been strengthened using steel plates were showing signs of corrosion after few years in service that resulted in the deterioration of the original structure. In Addition to the above, steel plate bonding included high installation costs, maximum labor, low on-site flexibility of use, aesthetically poor due to large changes in member size after repair, increased dead load and traffic interruption and this called for engineers to investigate for the alternatives. Considering all the above factors Fiber Reinforced Polymer (FRP) composites represent a new and promising solution to the shortcomings of several traditional materials and this shows a great potential for integration into the bridge infrastructure. In the past years, experiments have been conducted to investigate the applicability of FRP composite in bridge structures, including the applications of FRP composite to bridge deck, column and beam strengthening, etc. [1-4]. The performance of external bonded FRP composite have found to be a successful technique and an effective method for upgrading structural element. This paper highlights the applications of external bonded FRP composites overlay in bridge infrastructure, the challenges involved and path to implementation.