Plecnik, J.M., Henriquez, O. "Applications of Composites in Highway Bridges." Bridge Engineering Handbook. Ed. Wai-Fah Chen and Lian Duan Boca Raton: CRC Press, 2000 Section VI Special Topics 51 Applications of Composites in Highway Bridges 51.1 Introduction 51.2 Material Properties Reinforcing Fibers • Matrix Materials 51.3 Advantages and Disadvantages of Composites in Bridge Applications 51.4 Pultruded Composite Shapes and Composite Cables Pultruded Composite Shapes • Composite Cables 51.5 FRP Reinforcing Bars for Concrete 51.6 Composite Bridge Decks Advantages and Disadvantages • Composite Deck Systems • Truss-Type Deck System 51.7 Wearing Surface for a Composite Deck 51.8 Composite Bridge Structural Systems 51.9 Column Wrapping Using Composites 51.10 Strengthening of Bridge Girders Using CFRP Laminates 51.11 Composite Highway Light Poles 51.12 Nondestructive Evaluation of Composite Bridge Systems 51.13 Summary 51.1 Introduction Building a functional transportation infrastructure is a high priority for any nation. Equally impor- tant is maintaining and upgrading its integrity to keep pace with increasing usage, higher traffic loads, and new technologies. At present, in the United States a great number of bridges are considered structurally deficient, and many are restricted to lighter traffic loads and lower speeds. Such bridges need to be repaired or replaced. This task may be achieved by using the same or similar technologies and materials used originally for their initial construction many years ago. However, new materials and technologies may provide beneficial alternatives to traditional materials in upgrading existing bridges, and in the construction of new bridges. Composite materials offer unique properties that may justify their gradual introduction into bridge repair and construction. Joseph M. Plecnik California State University, Long Beach Oscar Henriquez California State University, Long Beach © 2000 by CRC Press LLC © 2000 by CRC Press LLC The difference between industrial or commercial composites and advanced composites is vague but based primarily on the quality of materials. Advanced composites utilize fibers, such as graphite and Kevlar ® , and matrix materials of higher strength and modulus of elasticity than industrial composites, which usually are fabricated with E-glass or S-glass fibers and with polyester or vinyl ester matrices. Advanced composites use polymer matrix materials, such as modified epoxies and polyimides, or ceramic and metal matrices. More-sophisticated manufacturing techniques are gen- erally required to produce advanced composites. Industrial composites require little or no special curing processes, such as the use of autoclaves or vacuum techniques for advanced composites. Composites are herein limited to materials fabricated with thin fibers or filaments and bonded together in layers or lamina with a polymer matrix. The polymers discussed are primarily polyesters and epoxies. The fibers considered include glass (E and S type), graphite, and Kevlar. The filaments may be of short fiber length (such as chopped fibers which may be less than 25 mm long) or continuous filaments. The ability to orient the fibers in any desired direction is one of the truly great advantages of composite materials as opposed to isotropic materials such as steel. The aniso- tropic nature of composite materials enables an engineer literally to custom design each element within a structure to achieve the optimum use of material properties. Composite materials have been successfully utilized in many other industries in the past 50 years. The leisure industry, primarily boating, was probably the first industry to successfully and over- whelmingly adopt composite materials in the construction of pleasure craft and small ships. In the industrial application fields, pipes, tanks, pressure vessels, and a variety of other components manufactured primarily with fiberglass, composite materials have been used for over 50 years. In the defense and aerospace industry, more-advanced composites have been increasingly used since the early 1960s. In all of these industries, one or several unique properties of composites were successfully exploited to replace conventional materials. The initial study [1] on the use of composites in bridges was performed for the U.S. Federal Highway Administration in the early 1980s and had as its main objective the determination of the feasibility of adapting composites to highway bridges. This study considered the adaptability of composites to major bridge components, given the unique characteristics of these types of materials. The study concluded that bridge decks and cables are the most suitable bridge components for use of composite materials. The purpose of this chapter is to introduce the current and future technologies and the most feasible applications of composites in highway bridge infrastructure. Basic composite material properties are presented and their advantages and disadvantages discussed. The applications of composites in bridges presented in this chapter include beams and girders, cables, reinforcing bars, decks and wearing surface, and techniques to repair or retrofit existing bridge structures. The methods and significance of nondestructive evaluation techniques are also discussed relative to the feasibility of incorporating composite components into bridge systems. 51.2 Material Properties 51.2.1 Reinforcing Fibers Fibers provide the reinforcement for the matrix of composite materials. Fiber reinforcement can be found in many forms, from short fibers to very long strands, and from individual fibers to cloth and braided material. The fibers provide most of the strength of the composites since most matrix materials have relatively low strength properties. Thus, fibers in composites function as steel in reinforced concrete. The most typical fiber materials used in civil engineering composite structures are glass, aramid (Kevlar), and graphite (carbon). A variation in mechanical properties can be achieved with different types of fiber configurations. A comparison of typical values of mechanical properties for common reinforcing fibers is provided in Table 51.1. © 2000 by CRC Press LLC Glass fiber has been the most common type of reinforcement for polymer matrix. Glass fibers, which are silica based, were the first synthetic fibers commercially available with relatively high modulus. Two common types of glass fibers are designated as E-glass and S-glass. E-glass fibers are good electrical insulators. S-glass fibers, which have a higher silica content, possess slightly better mechanical properties than E-glass. Some applications require fibers with better strength or elastic modulus than glass. Graphite (carbon) and aramid fibers can provide these desired properties. The use of these fibers is generally selective in civil engineering applications, given their higher cost compared with glass fibers. 51.2.2 Matrix Materials Thermosetting polymer resins are the type of matrix material commonly used for civil engi- neering applications. Polymers are chainlike molecules built up from a series of monomers. The molecular size of the polymer helps to determine its mechanical properties. Thermosetting polymers, unlike thermoplastic polymers, do not soften or melt on heating, but they decom- pose. Other matrix materials, such as ceramics and metals, are used for more-specialized applications. The most common thermosetting resins used in civil engineering applications are polyesters, epoxies, and to a lesser degree, phenolics. A summary of typical properties for resins is provided in Table 51.2. Polyester resins are relatively inexpensive, and provide adequate resistance to a variety of environmental factors and chemicals. Epoxies are more expensive but also have better properties than polyesters. Some of the advantages of epoxies over polyesters are higher strength, slightly higher modulus, low shrinkage, good resistance to chemicals, and good adhesion to most fibers. Phenolic resin is generally used for high-temperature (150 to 200°C) applications and relatively mild corrosive environments. TABLE 51.1 Typical Fiber Design Properties Property E-Glass (Strand) S-Glass (Strand) Kevlar-49 (Yarn) High-Modulus Graphite (Tow) High-Strength Graphite (Tow) Tensile strength (MPa) 3100 3800 3400 2200 3600 Tensile modulus (GPa) 72 86 124 345 235 Specific gravity 2.60 2.50 1.44 1.90 1.80 Tensile elongation (%) 4.9 5.7 2.8 0.6 1.4 TABLE 51.2 Typical Properties of Polymer Resins Property Polyester Epoxy Phenolic Tensile strength (MPa) 55 27–90 35–50 Tensile modulus (GPa) 2.0 0.70–3.4 7.0–9.7 Specific gravity 1.25–1.45 1.1–1.4 1.4–1.9 Elongation (%) 5–300 3–50 — Coefficient of thermal 70–145 18–35 27–40 expansion (10 –6 m/m/K) Water absorption (% in 24 h) 0.08–0.09 0.08–0.15 0.30–0.50 © 2000 by CRC Press LLC 51.3 Advantages and Disadvantages of Composites in Bridge Applications The rapid rise in the use of composites in many industries, such as aerospace, leisure, construction, and transportation, is due primarily to significant advantages of composites over conventional materials, such as metals, concrete, or unreinforced plastics. The following presents a brief discussion on the probable advantages and disadvantages of composites in highway bridge type applications. The first and primary advantage of composites in bridge structures will probably be a significant reduction in weight, due to the higher specific strength (strength/density) of composites over conventional materials, such as steel and concrete. The lightweight advantage of composites in bridge decks is clearly illustrated in Table 51.3. In most short bridge applications, the lighter struc- tural system, if adequate from the structural point of view, will probably not affect the dynamic performance of the bridge. In longer bridges, it is conceivable that a lighter-weight system may require additional design considerations to avoid dynamic behavioral problems. The second and equally important advantage of composites is their superior corrosion resistance in all environments typically experienced by bridges throughout the world. Corrosion resistance of composites can be further enhanced by the use of premium resin systems, such as vinyl esters or epoxies in comparison with conventional resins, such as polyesters. The excellent corrosion resis- tance characteristics of composites, and the lower maintenance costs, may result in lower life-cycle costs than those of bridge components manufactured with steel or concrete materials. The lower life-cycle costs may be the third significant advantage of composite bridge components. However, it is anticipated that the initial cost of such composite bridge components will be considerably greater than that of conventional materials. The fourth significant advantage of composites in bridge applications is their modular construc- tion. It is envisioned that composite bridge deck components will be fabricated in large modules, either in the shop or at the bridge site, then assembled at the bridge site to form a desired structural system. Such modular construction will not only reduce construction costs, but also reduce the time of construction. Fifth, it is envisioned that the initial usage of composites in bridges will involve rehabilitation or retrofitting of existing bridges in large urban areas. The modular construction described above will greatly reduce the time required for retrofitting, thus reducing traffic conges- tion, accidents, and time delays for commuters in heavily traveled urban areas. The layered structure of composites is also an advantage that may be highly beneficial for fatigue-type loads in bridges. By placing fibers in appropriate directions, both the strength and fatigue resistance of the composite laminate is greatly enhanced. The fatigue behavior of composites when properly designed is superior to that of ductile materials, such as the conventional A36 steel. The disadvantages of utilizing composites in infrastructure applications such as bridges are considerable, but not overwhelming. The first, but not necessarily the most significant, disadvantage of composites is their relatively high initial costs. This topic was discussed in the previous section relative to initial vs. life-cycle costs. Although graphite and other advanced fibers will probably reduce in cost with increased volume of consumption, it is very doubtful that the cost of glass fibers can be significantly reduced with increasing volume of consumption. The cost of matrices, such as polymer-based resins, will also not be reduced significantly with increased consumption. The second disadvantage of composite structural systems is the lack of highly efficient mechanical connections. The mechanical bolted connections in composite applications are not as efficient or as easily designed as in the case of steel-type welded and bolted connections used in steel structures. To reduce mechanical-type connections, adhesive-type joints are required. However, adhesion of one part to another requires detailed knowledge of the adhesive and the bond surfaces, as well as quality control. All of these factors generally result in relatively low allowable adhesive stresses. Furthermore, many engineers tend to dislike adhesive-type connections in the presence of fatigue and vibration-type loads. TABLE 51.3 Comparison of Dead Load (D.L.) of Deck Systems and Superstructure Bridge Type Bascule with 1.22 m Stringer Spacing (span = 76.2 m, width = 18.9 m) Deck on Steel I-Girder 2.13 m Girder Spacing (span = 16.3 m, width = 8.5 m) Deck on AASHTO Type III Prestressed Girders Spaced at 2.13 m (span = 16.3 m, width = 8.5 m) Deck Type 127 mm Open Steel Grid 152 mm Deep X-Shaped FRP with Sand Layer Wearing Surface 127 mm Concrete-Filled Steel Grid 152 mm Deep X-Shaped FRP with Sand Layer Wearing Surface 165 mm Thick Concrete with 5 mm Wearing Surface 229 mm Deep X-Shaped FRP with Sand Layer Wearing Surface 178 mm Thick Concrete with 5 mm Wearing Surface 229 mm Deep X-Shaped FRP with Sand Layer Wearing Surface Deck weight only (KN) 1379 1155 5654 1155 541.4 157 583.2 157 Deck D.L. % reduction 16 80 71 73 Girder weight (KN) 3610 3610 111.8 693.5 Curbs and railing (KN) 300.3 300.3 166.6 166.6 Future wearing surface (KN) 0 17.8 0 17.8 166.6 2.2 166.6 2.2 Details, stiffeners, etc. (KN) 290.9 290.9 35.7 23.8 Inspection walkway (KN) 66.7 66.7 None None Total D.L. (KN) 5647 5441 9922 5441 1022 473.3 1634 1043 Total D.L. % reduction 3.6 45 54 36 © 2000 by CRC Press LLC © 2000 by CRC Press LLC The third disadvantage is the relatively low modulus of glass fiber composites. Unless all fibers are oriented in a single direction, the modulus of elasticity of glass-type composites (E- or S-glass) will be somewhat similar to that of concrete. Since design of bridges is often governed by deflection or stiffness criteria, as opposed to strength, the cross-sectional properties of the fiberglass component would have to be nearly identical to that of concrete. The use of high-modulus fibers, such as graphite, enhances the modulus or stiffness characteristics of composites. However, even if all the graphite fibers are placed in the same direction (unidirectional laminate), the modulus of elasticity of the composite may not approach that of steel. Only with the use of very high modulus fibers (above 350 GPa), will the tensile modulus of the composite approach that of steel. To alleviate this very significant stiffness disadvantage, composite structural systems must generally be designed differently when stiffness criteria govern the design. The fourth significant disadvantage is the relatively low fire resistance of structural composites where polymer-based matrices are used, which represent the bulk of the composites utilized outside of the aerospace industry. This disadvantage has effectively disallowed the use of polymer-based composites in fire-critical applications such as buildings. In bridge applications, fire is a relatively infrequent phenomenon. Elevated temperatures, such as in the southwestern part of the United States, may, however, affect the structural properties of composites on bridge applications. Several additional disadvantages of composites include relatively complex material properties and current lack of codes and specifications, which tend to dissuade engineers from understanding and utilizing such materials. The presence of local defects, which are difficult and perhaps impossible to detect on a large structural system, are also viewed as a significant quality control problem. 51.4 Pultruded Composite Shapes and Composite Cables 51.4.1 Pultruded Composite Shapes Composites are commercially available in a variety of pultruded shapes [2–4]. Some of the most common shapes available for construction purposes are I-beams, W-sections, angles, channels, square and rectangular tubes, round tubes, and solid bars. However, almost any shape of constant cross section can be pultruded. Composite pultruded beam shapes have a potential use in bridges. However, the relatively low modulus of glass and graphite composite shapes limits their use. The effect of modulus of elasticity can be seen with the following comparison between A36 steel beams with modulus of elasticity E = 200 GPa, fiber-reinforced polymer (FRP) beams with E = 17.2 GPa, graphite beams with E = 103.5 GPa, and glass fiber–reinforced polymer (GFRP)/graphite hybrid beams for a two-lane, 16.76-m- span bridge. Assuming full lateral support, a total of five beams spaced at 2.29 m, and a 178-mm- thick concrete slab, the following results are obtained. For the case of noncomposite action between beams and concrete slab, a steel beam, W36 × 194, with cross-sectional area, A = 36,770 mm 2 , satisfies all AASHTO requirements for HS20-44 loading [5,6]. Using GFRP beams, the deflection requirement of L /800, which controls the design, cannot possibly be satisfied using a depth of 914 mm and a flange width of 457 mm. A GFRP I48 × 24 × 3.25 with A = 187,700 mm 2 or I60 × 30 × 1.5 with A = 113,200 mm 2 beam is necessary. If an all- graphite beam is used, an I36 × 18 × 1.25 with A = 56,060 mm 2 will satisfy all requirements. A hybrid beam with a 1320-mm total depth, 660-mm flange width, and 45.7-mm web and flange thickness also satisfies stiffness requirements. For this example, the hybrid beam should have a 7.6-mm-thick layer of graphite in the center of both flanges, and for the total width of the flange. If composite action is achieved between the concrete slab and the beams, a W30 × 99 with A = 18,770 mm 2 steel beam is adequate for this bridge. An all-FRP I48 × 24 × 1.0 beam with A = 60,650 mm 2 or I42 × 21 × 1.5 with A = 78,390 mm 2 will also meet stiffness and stress requirements when composite action is included. A comparison of sizes for all the beam cross sections used in this example is presented in Figure 51.1. © 2000 by CRC Press LLC 51.4.2 Composite Cables Composites in the form of cables, strands, and rods have potential applications in bridges. Among these applications are suspension and stay cables and prestressing tendons. High tensile strength, corrosion resistance, and light weight are the most important characteristics that make composites strong candidates to replace steel for these types of applications. Corrosion of traditional steel cables and tendons may impose a significant maintenance cost for bridges. Composite cables, with proper selection of materials and design, may exceed the useful life of traditional bridge cables. Carbon fiber–reinforced polymer (CFRP) composite cables have been used for cable-stay bridges [7]. Compared with steel, carbon composites can provide the equivalent tensile strength with only a fraction of the weight. GFRP tendons have been used to prestress concrete bridge girders. The compu- tation of section strength using GFRP tendons is very similar to the methods used for steel tendons. In the case of post-tensioned structures, an adequate anchorage system must be used to minimize pre- stressing losses. One of the advantages of GFRP compared with steel tendons is that a lower modulus of elasticity is translated into lower prestressing losses, due to creep and shrinkage of the concrete. FIGURE 51.1 Comparison of different beams for a two-lane 16.80-m-span bridge, with a total of five beams spaced at 2.30 m, and a 180-mm-thick concrete slab. (a) Noncomposite action between beams and slab; (b) composite action between beams and slabs. © 2000 by CRC Press LLC A key issue in the design of composite cables is the anchoring system. Development of the full tensile strength of the composite cable is not yet possible; however, a good design of the anchors can allow the development of a large percentage of the total available cable strength. A potted-type anchor is shown in Figure 51.2 [1]. This assembly utilizes a metal end socket into which the composite cable is fitted and subsequently potted with various polymers such as epoxies. The load is transferred from the cable to the metal anchor through the potting material by shear and radial compressive stresses. The aluminum wedge is used to split the cable into four equal sectors to create greater wedging action, but this also creates large radial compressive stresses. Since the largest stresses at the stress transfer region occur at the cable perimeter, several related parameters affect the strength property of such potted anchors and, therefore, the ultimate strength of the cable system. Another type of anchoring system [7], specifically designed for CFRP cables, utilizes a conical cavity filled with a variable ceramic/epoxy mix (Figure 51.3). The variable formulation is designed to control creep and rupture of the cable. 51.5 FRP Reinforcing Bars for Concrete Fibers such as glass, aramid, and carbon can be used as reinforcing bars (rebars) for concrete beams. The use of these fibers can increase the longevity of this type of structural element, given the corrosive deterioration of steel reinforcement in reinforced concrete members. Tests have shown that a higher ultimate strength can be achieved with FRP rebars than with mild steel rebars. This strength can be achieved due to the high tensile strength of most fibers. The lower stiffness of FRP fibers, such as glass, will result in larger deflections compared with steel-reinforced concrete. An important factor in the use of FRP bars is the bond between the bar and the concrete [8]. The use of smooth FRP bars results in a significant reduction of flexural capacity. Thus, smooth FRP bars must be surface-treated to improve bonding by methods such as sand coating. Test results have also shown that smaller-diameter FRP rebars are more effective for flexural capacity than larger-diameter bars. However, in general, bond characteristics are variable due to the variations in FRP reinforcing bar products. Other factors that affect the bond characteristics are concrete strength, concrete confinement, type of loading, time-dependent effects, amount of concrete cover, and type and volume of fiber and matrix. In the State-of-the-Art Report 440R-96 on FRP Reinforcement for Concrete Structures [9], the American Concrete Institute (ACI) recognizes the need for additional testing data to develop expressions that will be valid for different conditions, and can be included in a design code. Some expressions for FRP bar development lengths have been proposed recently. FIGURE 51.2 Potted end anchorage assembly for composite cables; cross sectional view (left) and longitudinal view (right) [...]... The strain gauge method of determining localized stresses and strains is well understood in civil engineering, and is widely used in the analysis of structures such as bridges, both in the laboratory and the field The strain gauge technique is a localized type of an NDE technique and, therefore, may yield only the stress and strain levels in the lamina to which the strain gauge is attached Strain gauge... visual bridge inspections of steel and concrete bridges Visual inspections are global in nature but cannot detect any possible degradation of the interior lamina within a laminate This is a distinctive drawback to any method that involves visual inspection of external surfaces only Ultrasonic NDE has been widely used as an NDE technique in advanced and aerospace composites In industrial composites, such... about the possible delamination of inner lamina or the presence of defects within the laminate The strain gauge method is currently used for evaluation of stresses and strains in composite tanks, pressure vessels, buildings, and various composite bridge applications which have been described here As in other materials, the strain gauge technique is extremely beneficial in determining stress concentrations... longitudinal bars from buckling, even after a plastic hinge has formed in the confined region, and to improve the performance of lapped longitudinal reinforcement in regions of plastic hinge formation The shear capacity of the column can also be increased by wrapping a column using composites Several materials have been used to retrofit bridges with the wrapping method The most common types of fibers... composite facing plates and a core of pultruded rectangular tubes oriented in the transverse direction of the bridge The total weight of the composite bridge was approximately 100 kN, including the guardrails, but excluding the asphalt wearing surface © 2000 by CRC Press LLC 51.9 Column Wrapping Using Composites A unique application of composite materials in bridge infrastructure is bridge column wrapping or... wrapping with composites may have some advantages over steel jacketing, such as reduced maintenance, improved durability, speed of installation, and reduced interference with ongoing operations, including traffic A reinforced concrete column can be retrofitted using the wrapping technique to increase its flexural ductility and shear strength A proper confinement of the concrete core and longitudinal reinforcement... jacketing This procedure involves the application of multiple layers of a composite around the perimeter of columns Since the late 1980s, column wrapping with composites was seen as an alternative to the conventional steel jackets used to retrofit reinforced concrete columns of bridges in California Column wrapping may also be used to repair columns that suffered a limited amount of damage Column wrapping... test [12] Variation of the average British Pendulum Number (BPN) with number of tire passes is shown in Figure 51.5 A stabilized BPN above the minimum acceptable BPN of 60, after 1 million cycles, may indicate that the wearing surface will maintain its serviceability for an extended amount of time The sand patch readings, shown in Figure 51.6, also indicate a reduction in the rate of mean average texture... structural elements of highway bridges may not be feasible in the near future Therefore, the initial use of composites in bridges will probably be limited to those bridge elements where the unique properties of composites will result in more favorable design than with the use of conventional materials © 2000 by CRC Press LLC References 1 Plecnik, J M and Ahmad, S H., Transfer of Composites Technology... Seismic retrofit of RC columns with continuous carbon fiber jackets, J Composites Constr., 1(2), 52, 1997 16 Meier, U., Deuring, M., Meier, H., and Schwegler, G., Strengthening of structures with CFRP laminates: research and applications in Switzerland, in Advanced Composite Materials in Bridges and Structures, Canadian Society for Civil Engineers, 1992, 243 17 Arduini, M and Nanni, A., Behavior of precracked . Applications of Composites in Highway Bridges 51.1 Introduction 51.2 Material Properties Reinforcing Fibers • Matrix Materials 51.3 Advantages and Disadvantages of Composites in Bridge Applications 51.4. also reduce the time of construction. Fifth, it is envisioned that the initial usage of composites in bridges will involve rehabilitation or retrofitting of existing bridges in large urban areas techno- logically. The strain gauge method of determining localized stresses and strains is well understood in civil engineering, and is widely used in the analysis of structures such as bridges, both in the laboratory and