Using fiber-reinforced polymer (FRP) composites in bridge construction and monitoring their performance: an overview

B. Wan,    Marquette University, USA

Abstract:

The superstructure and substructure of bridges can be made from all fiber-reinforced polymer (FRP), or from FRP composited with concrete or steel. The different applications of FRP composite materials in bridges are discussed. Common nondestructive evaluation/testing (NDE/NDT) methods are reviewed for their potential application in monitoring FRP bridges. Smart FRP bars and cables can be used to monitor the bridge, as well as help the bridge resist loads. A case study of monitoring a bridge with an FRP stay-in-place formwork deck is presented. A short commentary on likely future trends in FRP bridges and monitoring techniques is provided. Sources of further information related to FRP bridges and monitoring are listed at the end of this chapter.

Key words

fiber-reinforced polymer (FRP) bridge; FRP repaired and strengthened bridge; nondestructive evaluation/testing (NDE/NDT); smart FRP bridge; monitoring FRP bridge

1.1 Introduction

Because of their high strength and low density, fiber-reinforced polymer (FRP) composite materials have been widely used in the aerospace and automotive industries since the middle of the last century. FRP composites do not corrode in concrete in the way steel does. Goldsworthy (1954) predicted that FRP composites could be used as reinforcements in concrete and as structural members subject to corrosive environments. Glass fiber reinforced polymer (GFRP) rods were used first as reinforcements for concrete buildings. Since the late 1980s, FRP rebars have been used more extensively in concrete structures, especially in highway bridge decks, because of their resistance to corrosion (Bank, 2006). For the same reason, FRP composites have been used more and more widely when repairing and retrofitting deteriorated bridge superstructures, to reinforce bridge decks, girders and piles, and when replacing structural members (e.g. decks). FRP materials are also increasingly being used in bridges because new manufacturing techniques have reduced their cost (Telang et al., 2006). Although FRP materials have been used in the manufacture of missiles, planes, cars, boats, tanks, sporting goods, etc. for over half a century, their use in building bridges is still relatively recent. How well FRP composites in bridges will perform in the long term is one of our major concerns. Therefore, a monitoring program is normally set up to examine the behavior of FRP composites in demonstration bridges constructed around the world.

In this chapter, we consider how the superstructure and substructure of bridges can be made up of all FRP, or of FRP composited with concrete or steel. We discuss the different applications of FRP composites in bridge construction. Then we look at how bridges constructed using FRP composites are monitored by visual inspection and experimental nondestructive evaluation (NDE) techniques. Such evaluation can reveal damage such as blistering, voids, discoloration, fiber exposure, cracks, and scratches. We review common NDE techniques to see if they are suitable for monitoring FRP bridges, and we present a case study of a bridge with an FRP stay-in-place (SIP) formwork deck. This chapter also comments briefly on likely future trends, and includes sources of further information and advice.

1.2 Fiber-reinforced polymer (FRP) composites for bridge construction

FRP composite materials have been widely used to repair deteriorated bridges and to retrofit bridges that do not meet updated code requirements, and especially to retrofit columns to improve their seismic load capacity. They are also used in new construction as reinforcement in concrete decks, SIP formworks, pure FRP bridge decks, composite columns/piers, cables for suspension bridges, pedestrian bridges, and more. In fact, FRP composite materials can be used to replace steel in almost any component in bridge construction.

1.2.1 FRP pedestrian bridges

Because of their light weight and corrosion resistance properties, FRP profiles have been increasingly used in the decks and superstructure members of bridges since the mid 1970s (Bank, 2006). FRP was first used in short-span pedestrian bridges, the first FRP pedestrian bridge being built by the Israelis in 1975 (Tang and Podolny, 1998). Since then, hundreds of FRP footbridges have been built worldwide. The main structural type of these bridges is the truss. Cable-stayed and other traditional styles are also used (Feng, 2012).

Because of the low modulus of FRP composite materials, the stiffness of a pure FRP deck is relatively low, and thus deflection control is an issue. Relatively small amounts of concrete can be used to increase the stiffness of an FRP footbridge deck, keeping the total weight low. Bank et al. (2010) used pultruded GFRP planks with a cement board or concrete topping slabs to form a 75 mm deep hollow section to be used in place of traditional timber decking in pedestrian bridges. Neto and La Rovere (2010) developed a footbridge deck system consisting of a fiber reinforced concrete (FRC) top layer supported by GFRP wide-flange pultruded profiles, with foam blocks filling the voids to keep the bottom flat.

Researchers also tried combining FRP materials with other newly developed construction materials to improve the performance of pedestrian bridges. Mendes et al. (2011) designed and analyzed a 12 m long single span pedestrian bridge with two GFRP I-shape profiles and a thin steel fiber reinforced self-compacting concrete (SFRSCC) deck. Both steel anchors and epoxy resin were used to ensure the composite action between the two materials. The SFRSCC deck increases the flexural stiffness of the whole structure, resists compression stress, and provides better crack control. The GFRP I-shape resists tensile stress in this bridge.

The structural style can also be modified to counteract the disadvantage of the low modulus of FRP composite materials. Caron et al. (2009) proposed a self-stressed footbridge in which energy stored elastically in the bent bow generates the required stress to maintain the stability of the whole structure. This self-stressed FRP footbridge takes advantage of the low stiffness of the pultruded FRP profile.

1.2.2 FRP vehicular bridges

Using knowledge and experience gained from building FRP pedestrian bridges, engineers went on to build all FRP vehicular bridges. The first FRP vehicular bridge was built in Beijing, China in 1982. It has six hand-laminated GFRP sandwich girders, spans 20.7 m, and is 9.2 m wide (Ye et al., 2003). In the early 1990s, many FRP deck systems were developed and evaluated in laboratories and in demonstration projects supported by federal or local departments of transportation and FRP manufacturers. Many of these FRP bridges were built with short spans over secondary or rural roads where traffic is light. The first US all-composite vehicular bridge went into public service on 4 December 1996 in Russell, Kansas (Tang and Podolny, 1998). In 1998, the US Federal Highway Administration (FHWA) set up the Innovative Bridge Research and Construction (IBRC) Program to develop cost-effective innovative material applications in highway bridges (FHWA, 2003). This program boosted the use of FRP materials in highway bridges in the US. Many FRP vehicular bridges have also been constructed in Europe, China, and Japan over the past two decades.

Replacing deteriorated reinforced concrete decks with FRP decks is an attractive option for increasing the live load capacity of old bridges because FRP decks are much lighter than concrete decks. For example, the non-composite concrete deck of the Bentley Creek Bridge in New York was replaced with an FRP deck in 1999. Changing the weight and stiffness changes the natural frequencies of such a bridge (Hag-Elsafi et al., 2012). FRP decks are also composited with steel or concrete girders and trusses in new bridges (Turner et al., 2003; Liu et al., 2008).

FRP deck configurations can be cellular, honeycomb, or hybrid/sandwich. Cellular decks are manufactured by combining several pultruded FRP profiles to create different geometries. Although the weight of cellular decks is very low compared to other deck formats, their stiffness is relatively low and may cause buckling. An FRP honeycomb panel consists of top and bottom face sheets and a sinusoidal core (Davalos et al., 2012), whereas the compression zone of an FRP-concrete hybrid deck often uses concrete (Aref et al., 2005; Schaumann et al., 2009). A sandwich panel consists of upper and lower layers and a core, with the bottom layer usually made of FRP, and the top layer and the core made of FRP and/or traditional materials. Many creative FRP sandwich decks have been invented. For instance, Schaumann et al. (2008) produced a sandwich deck panel consisting of three layers: an FRP sheet with T-upstands for the bottom skin, lightweight concrete for the core, and a thin layer of ultra-high-performance reinforced concrete for the top layer. Ji et al. (2009) proposed a composite sandwich panel consisting of a wrapped hybrid core of GFRP grid and multiple steel box cells with upper and lower GFRP layers.

1.2.3 FRP reinforced concrete bridge decks

FRP composite materials were first used to reinforce concrete structures in the...