72-1 THE WEST GATE BRIDGE: STRENGTHENING OF A 20TH CENTURY BRIDGE FOR 21ST CENTURY LOADING G. Williams, R. Al-Mahaidi and R. Kalfat Synopsis: Retrofitting of existing concrete structures and civil infrastructure has become necessary due to environmental degradation, changes in usage and heavier loading conditions. The use of advanced carbon fiber composite materials (CFRP) as externally bonded reinforcement has found wide application in recent years and has proven to be an effective method of improving the structural performance of existing structures. A good example of this is the West Gate Bridge in Melbourne, Australia for which the following case study is presented. Key innovations in CFRP technology developed specifically for this project have been described in the areas of design and testing of CFRP anchorage technology, involving the utilization of unidirectional and bidirectional fabrics together with mechanical substrate strengthening. These have all resulted in increases in material utilizations and enabled successful transfer of combined shear and torsional forces. Key aspects of the detailing, application, quality control and monitoring program adopted in the project are also presented along with the key aspects which resulted in the successful execution of this world class project. Key words: West Gate Bridge, CFRP, anchorage, concrete box girder, quality control, application, strengthening. 72-2 Williams et al. Grahme Williams is a practicing bridge engineer working for Sinclair Knight Merz (SKM) in Melbourne, Australia. His particular area of interest is in the use of CFRP strengthening systems having been involved with a range of activities including laboratory investigations, field monitoring of repaired structures, design and optimization of systems and application to in-service bridges. Riadh Al-Mahaidi is a Professor of Structural Engineering at Swinburne University of Technology and Adjunct Professor at Monash University in Melbourne, Australia. He received his MSc and PhD degrees from Cornell University. His research interests include rehabilitation of concrete and steel structures using FRP composites, finite element modeling of concrete structures, and strength assessment and rehabilitation of bridges. He is a member of ACI-ASCE Committee 447 and ACI-440. Robin Kalfat is a practicing Structural Engineer for Structural Systems Limited and postgraduate PhD student at the Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, in Melbourne, Australia. His interests include: design of CFRP strengthening systems, post-tensioning, CFRP Anchorage research, experimental investigations and numerical modeling using finite element method. INTRODUCTION The increasing transportation demands of the 21st century have resulted in additional pressures placed on our existing infrastructure to accommodate higher traffic loading and volume requirements. In addition, many concrete bridges currently in use have exceeded their original design life. Together with the introduction of more stringent bridge design and evaluation specifications (AS 5100 2004; BS 5400 1988; AASHTO 1994) has resulted in an increasing number of bridge upgrade and restoration projects. A good example of this is the West Gate Bridge in Melbourne (pictured below), Australia, which is currently one of the largest CFRP strengthening projects in the world (Hii & Al- Mahaidi 2006). Figure 1 – View of the West Gate Bridge The West Gate Bridge: Strengthening of a 20th Century Bridge for 21st Century Loading 72-3 The West Gate Bridge is one of Australia’s most iconic and important links in the national transportation network. The 2.6 km (1.6 mile) structure is comprised of a central steel box girder portion with cable stays, 850m (2,790 ft) in length. Eastern and western approach viaducts, 870m (2,850 ft) and 670m (2,200 ft) long respectively, are composed of segmental pre-stressed concrete box girder sections. In addition, there are minor approach spans which pass over local roads and railway lines, constructed with steel girders and a composite concrete deck which link the viaducts to the West Gate Freeway. The approach viaducts consist of 3 cell pre-cast concrete box segments which were originally assembled span-by-span to form a central spine. Pre-cast transverse cantilevers protrude at right angles from the spine to support the remaining width of the deck. These were erected and post-tensioned to the central spine in order to carry a concrete slab constructed from pre-cast panels and in-situ concrete as shown in Figure 2 below. Although the bridge has been in operation for over 40 years, during this period various rehabilitation measures and structural upgrades have been implemented. Currently a major project is under way to strengthen the bridge in flexure, shear and torsion in order to provide two additional lanes for peak hour traffic. This upgrade was undertaken as part of a consortium known as the West Gate Bridge Strengthening Alliance, including VicRoads, Flint & Neill, SKM and John Holland. Figure 2 – Exploded View of Concrete Viaduct Components 72-4 Williams et al. In 2002 the western concrete viaduct was strengthened for an additional lane of traffic on the city-bound carriageway. The strengthening consisted of internal post tensioning and external application of carbon fiber reinforced plastics (CFRP). Carbon fiber laminates were applied to the cantilevers to increase flexural strength and a combination of laminates and fabric were installed to the central spine girder to increase the shear and torsion capacity. CFRP was chosen as the preferred strengthening method based on the systems inherent advantages when applied to existing structures. The materials are excellent because of their high tensile strength, light weight, resistance to corrosion, superior durability, reduced labor costs and minimal traffic disturbances. These combined factors resulted in CFRP being a viable and cost effective solution (Khalifa 2000). The current strengthening works, which are the focus of this paper, have been carried out on both the eastern and western viaducts. On the eastern viaduct, supplemental post tensioning has been added to increase the flexural and shear resistance of the concrete box girder section. Additionally, CFRP has been applied to the cantilevers to increase their flexural capacity while carbon fiber fabric was applied to the base of the cantilever struts to provide the necessary confinement, thereby increasing their compressive strength. A combination of carbon fiber laminates and fabric have been applied to the spine girder to increase the shear and torsion capacity. Similar supplementary strengthening works were carried out on the western viaduct to enhance what was done previously in 2002. Existing carbon fiber design codes are presently limited in civil structure applications. Due to the unique challenges specific to this bridge a typical carbon fiber strengthening approach was not necessarily appropriate or achievable. The complex geometry of the structure and the requirement for combined shear and torsional strengthening resulted in a need for appropriate anchorage of the externally bonded fibers into the deck to provide the necessary continuation to engage the torsional hoop stresses. Two areas of focus included the development of CFRP forces around the corners of the box section, involving lap-splice CFRP anchorage; and sufficient anchorage of the external CFRP outer web reinforcement into the bridge deck. It was found that the deck had sufficient in plane capacity to adequately carry the additional shear forces resulting from the increased torsional demand. A specially tailored laboratory research program was therefore undertaken to evaluate the suitability of various CFRP prototype anchorage solutions (Al-Mahaidi et. al. 2009). Although, there remains a lack of sufficient experimental data to substantiate the widespread use of such anchors, design guidelines such as ACI 440.2R-08 recognize the benefits of anchorage systems and permit designers to utilize these provided that the anchorage device is verified by sufficient experimental testing (Refer section 11.4.1.2). The benefits of CFRP anchorage were also seen to optimize cost and constructability by allowing higher CFRP strain utilization levels, enabling a significant reduction in material quantities. The combined effort of laboratory investigation and theoretical development, made it possible to optimize cost and constructability while gaining an assurance of the functionality of the chosen systems. The West Gate Bridge: Strengthening of a 20th Century Bridge for 21st Century Loading 72-5 Once completed, and to the author’s knowledge, the West Gate Bridge will be the largest bridge in the world ever repaired with carbon fiber. In total, nearly 40km (25 miles) of carbon fiber laminates of various grades and dimensions will be applied to the structure along with 11,000 sq. m (118,000 sq. ft) of carbon fiber fabric. At the time of submission of this paper strengthening works were still underway, due to be completed by the end of 2010. The entirety of works will be delivered in approximately 16 months through a combination of innovative solutions that were developed in both design and construction. RESEARCH SIGNIFICANCE This paper has two main areas of interest to present to the reader; a case study reviewing application of carbon fiber strengthening of an in-service concrete structure and the introduction of carbon fiber detailing based on laboratory