FRP bridge deck connections: a review

Proceedings of IABSE 2004 Symposium, Shanghai, China, Sept. 22-24, 2004.

Connections of Fiber Reinforced Polymer Bridge Decks Aixi ZHOU Senior Scientist & Lecturer Swiss Federal Inst. of Tech. Lausanne, Switzerland

Thomas KELLER Professor, Director of CCLab Swiss Federal Inst. of Tech. Lausanne, Switzerland

Aixi Zhou, born in 1975, received his Ph.D. degree in Engineering Mechanics from Virginia Polytechnic Institute and State University, USA.

Thomas Keller, born in 1959, received his Ph.D. degree in Civil Engineering from Swiss Federal Institute of TechnologyZurich, Switzerland.

Summary The development of connection techniques for FRP bridge decks is presented. Joining techniques for component-component connections, panel-panel connections and deck-to-support connections that have been developed and implemented in past decade are reviewed. Characteristics, performance, advantages and disadvantages of each reviewed bridge deck connection technique are discussed. Recommendations for the development of FRP deck connection design are provided. Keywords: Fiber reinforced polymer; composites; bridge deck; connections; design; construction.

1. Introduction Structural shapes made from Fiber Reinforced Polymer (FRP) composites have been increasingly used in structural systems for rehabilitation and new construction of highway bridge decks [1-12]. FRP bridge decks are usually provided in modular panel forms. In construction, deck panels are connected to their supports to transfer loads transversely to the supports that bear on abutments. Current commercially available FRP decks for rehabilitation and new construction can be classified into two categories according to the types of assembly and construction: sandwich panels and multi-cellular type panels. Sandwich panels have two basic forms: foam core sandwich panel and honeycomb sandwich panel. Multi-cellular panels have varied geometrical forms and can be used without or with foam core materials. Two basic cellular FRP deck panels have been developed according to the techniques of processing and assembly: panels from adhesively bonded pultruded shapes and panels from adhesively bonded filament-wound shapes. For each modular FRP deck panel form, connections are inevitable due to limitations on shape size imposed by the manufacturing process and the requirements of transportation. Three classes of connections involving composites are identified in the Eurocomp Design Code and Handbook [3]: (1) Primary joints, which carry major strength and stiffness to an assembly for the whole-life of the structure; (2) Secondary structural joints, whose failure would be only local failure without compromising the entire structure; (3) Non-structural connections, whose main purpose is to exclude the external environment. Connections for FRP bridge decks include all these categories. However, this research focuses on primary and secondary load-carrying connections for FRP bridge decks. These load-carrying connections include component-component connections to form modular FRP bridge deck panels (henceforth referred as Component Level Connection, or CLC), panel-panel connections to form FRP bridge deck systems (henceforth referred as Panel Level Connection, or PLC), and FRP deck-to-supports connections to form bridge superstructures (including deck-girder, deck-abutment and deck-barrier connections etc., henceforth referred as System Level Connection, or SLC).

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In general, bridge system shall be designed for specified limit states to achieve the objectives of safety, serviceability and constructability with regards to the issues of inspectability, economy and aesthetics. FRP deck connections shall be designed under the guideline of this philosophy to achieve the specified limit states for each construction. However, specific design requirements for FRP deck connections vary with the levels of connection. In component level connections, the main objective is to ensure the integrity of the deck panel and the load transfer efficiency between the jointed components. In the panel level, concerns are connected deck system’s load transferring and carrying capability (bending moment and shear force, and resistance to dynamic loads etc.), panelpanel compatibility to deformations imposed by thermal or moisture effects, and connection constructability. In the system level, shear transfer and connection constructability are major concerns. The advantages of advanced FRP composites would be lost if the characteristics of the associated joints were not properly understood and the connections were not properly designed. Key manners for joining FRP composites are mechanical fastening and adhesive bonding. The combination of bonding and fastening can be used to take the advantages of both methods when the connection is properly designed. Due to its advantages of the simplification of processing and thus a saving of production cost and possible refined joint geometry, adhesive bonding is generally used for connecting permanent FRP deck components to form bridge deck panels. In panel and system levels, adhesive bonding, mechanical fastening and the combination of bonding and fastening have been used. However, the development of connecting techniques for FRP bridge deck systems, especially in panel and system levels, has not come up with the growing demands of the FRP deck rehabilitation and new construction. In some demonstration FRP bridge deck projects, cracks and damages appeared in deck connection regions after field exposure to real traffic loadings and environmental conditions, as shown in Figure 1. The need for efficient and reliable load-carrying joints that can endure long-term fatigue and (a) At panel connection (b) At component connection environmental attacks has become Figure 1 Cracking at FRP deck connection regions apparent. Unfortunately, the technical background and the development of FRP bridge deck connections have not been documented adequately in literature. This paper attempts fill this gap by providing a brief review of developed connection techniques for FRP bridge decks. In this paper, the development of connection techniques for FRP bridge decks is presented. Joining techniques for componentcomponent connections, panel-panel connections and deck-to-support connections that have been developed in past decade will be reviewed. These techniques include mechanical fastening, adhesive bonding, and hybrid joining. Characteristics and performance of each reviewed bridge deck connection technique will be discussed. Finally, recommendations for the development of FRP deck connections will be provided.

2. Component level connections for FRP bridge deck panels Component level connections are usually permanent. The main objective for CLC joining is to ensure the integrity and the loading-transfer efficiency of the formed deck panels. The deck panels will be evaluated, usually via laboratory testing, to make sure that the assembled deck panels satisfy the specified limit states. The connections should be designed with the consideration of ease of processing and the resistance to long-term fatigue loadings and environmental attacks. The technique of adhesive bonding fulfills the above considerations because of the advantages that adhesive bonding can offer over mechanical fastening. Therefore, adhesive bonding has been widely used in component level connections to form FRP bridge deck panels, as shown in Figure 2 (a) and (b). However, in some cases [12], mechanical fastening have been used to provide necessary binding forces when the components are in curing [see Figure 2 (c)]. Bolted joints have also been developed for joining FRP components, as shown in Figure 2(d). However, the

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comparison study [11] showed that a bonded joint is easier to design and provides a larger safety margin than the bolted connection as shown in Figure 2(d). Laboratory experiments and field application showed that there was no clear relationship between the loadcarrying capacity of the modular FRP deck panels and the ultimate strength of the adhesively bonded connections. In some laboratory tests [12], local debonding noises were (a) Bonded pultrusion shapes [5] (b) Bonded sandwich [4] observed at some loading cycles before the ultimate deck failure. The deck continued to resist loads till the deck panel failed in the FRP profiles while no visible permanent damage in the bonded connections was observed. Figure 3(a) shows the punching failure of a deck surface using a steel loading patch. Figure (d) Bolted connection [11] (c) Bonding with fastening 3(b) shows the internal FRP tube Figure 2 Deck panels through various joining techniques failure of a bonded cellular deck under a rubber-reinforced tire loading patch. In other laboratory tests [5], deck panels failed within Cracks the FRP components near the Cracks bonded line (Figure 3(c)). No failure was observed in the adhesive layer and the join interface. Delamination and buckling of FRP components were observed in laboratory tests, as (a) Surface failure [12] (b) Internal failure [12] shown in Figure 3 (d). In all these cases, the adhesive layer and the adhesive-substrate interface were stronger than the FRP components. Therefore, no pre-matured adhesion or cohesion failure occurred. These observations showed that adhesive bonding is a viable technique for joining component level connections (c) Delamination [5] (d) Delamination and buckling [5] in FRP bridge deck panels. This technique has been widely used in Figure 3 Failure modes of bonded cellular deck panels FRP deck construction projects. A criterion for designing bonded component level connections shall be that an adhesively bonded joint should be designed and fabricated to allow failure in the FRP substrate before failure in the adhesive or the interface. This criterion has been achieved for FRP bridge deck panels through results from laboratory tests. However, problems remain when bridge deck panels are exposed under long-tern traffic loadings and environmental attacks, which is shown in Figure 1(b).

3. Panel-panel connections of FRP bridge decks Panel level connections shall be designed to efficiently transfer bending moment and shear force between jointed panels, and ensure deformation compatibility due to thermal and moisture effects, as well as the ease of on-site installation. In some special cases, the panel-panel connections may be designed and constructed to provide the possibility of disassembly for repair. Several techniques have been developed for panel level connections: the splicing tongue-groove connection (Figure 3


4(a)) and the splice-plates connection via bonding, the shear key connection (Figure 4(b)) and the clip-joint connection (Figure 4(c)) via mechanical fixing. Joining details of bonded panel level connection are shown in Figure 4(d). Splicing connections require quality control on the dimensions of deck panels. It was shown that panels from pultruded shapes have better dimension uniformity than decks from sandwiched panels through VARTM and sandwiched panels from hand layup [10]. For easy on-site (b) Mechanical shear key [2] (a) Adhesive-bonding [10] installation, adequate tolerance in panel dimensions must be ensured for splicing-bonding connections. However, a disadvantage of bonded connections is the difficulty of disassembly for repair. Mechanical fixing has the advantage of easy disassembly. However, load transfer and failure resistant capability of mechanical fixing (such as the shear key and (c) Clip-joints [3] (d) Bonded joints in details [7] the clip-joint) is not as efficient as Figure 4 Typical panel connections for FRP deck systems bonded joining. Results from constructed projects show that splicing-bonding connections have potential for application. For the shear key connection, cracks appeared after a period of exposure to highway vehicle loadings, which is shown in Figure 1 (a). The cracking at the shear key connection region shows that mechanically fixed connections are not reliable to resist dynamic vehicle loadings. In panel level connections, the joints shall be designed to provide enough connecting force to resist repeated loadings to maintain the integrity of the panel-connection-panel system.

4. Deck-support connections of composite bridge superstructures The design of efficient deck-to-support connections is the most challenging topic in the development of FRP bridge deck connections. System level joints deal with connecting large-scale structures, and usually between different materials. Since some CLC and PLC techniques have been well developed to ensure the functions of the deck panels, the efficiency of deck-to-support joint governs the overall behavior of the formed superstructure. Among all deck-to-support connections, the deck-girder (or stringer) connection is the most prominent. Depending on the requirements of a specific project, the deck-girder connection could be a permanent joint with composite action or a joint with ease of disassembly without the necessity of composite action between the deck and its supports. In all cases, the efficiency of shear transfer and constructability are major factors directing the connection design. Mechanical fixing, adhesive bonding and hybrid joints have been explored in connecting FRP bridge deck panels to their underneath supports, as shown in Figure 5. The connection designs in Figure 5 (a) are approximated as simply supported conditions and not intended to develop composite action between the deck and the supporting girders. A large portion of impact loads is taken by the FRP deck; therefore, this design is suitable for rehabilitation or repair to reduce the loading impacts on the existing supports. While in most cases, a composite action between the deck and its support is desirable. Composite action via bonding and hybrid joining offers several advantages for FRP decks: (1) Reliable shear force transmission can be achieved because of the composite action. (2) The overall stiffness and load resistance capability of the connected system can be significantly increased compared to their individual components [5,6]. (3) The overall superstructure can have ductile characteristic when the girder is made from ductile material (steel 4


or concrete) due to the loads transfer efficiency between the brittle FRP deck and its ductile support [6]. (4) The redundancy of the connected system can be achieved when the joint is appropriately designed [8]. (5) When the girder is made from brittle materials (FRP composites), a ductile bonding layer in the connection can provide potential ductile behavior of the formed superstructure even the deck and its support are brittle. Research is under way to confirm this concept [8]. Composite action, structural redundancy and system ductile characteristic are main objectives when designing hybrid or adhesive-bonded FRP deck-support connections for bridge superstructures. So far, the majority of FRP deck-girder connections have utilized hybrid joining in which conventional shear studs or stirrups (see Figures 5(c) and 5(d)) are used to provide composite action for shear resistance, structural redundancy and ductility. These types of connections have a proven history in the civil engineering domain, therefore are generally accepted by bridge engineers. However, these connections are developed for steel or concrete deck-girder connections. In these connections, holes are required at some desired spacing in the deck. The cutouts bring concerns about the stress concentrations and possible vulnerability to fatigue loads and environmental attacks in the deck panel’s cutout regions. Efforts must be taken to protecting the cutout regions from environmental attacks. For example, Figure 5(d) shows a deck-girder connection with a closed cavity in the connection region, which has been used in construction [9]. Some FRP deck-railing and deckbarrier connections used in current construction also utilize well-developed connection techniques for steel and concrete bridge systems (Figures 5(e) and 5(f)). However, since FRP decks are different from steel decks and concrete decks in constitutive materials and structural forms, efforts shall be taken to develop adapted connection techniques for FRP deck-girder and FRP deck-railing connections. FRP Deck

Steel Girder Joining Bolt (a) Fastened connection [12]

(b) Bonded connection [6]

(d) Detailed deck-girder connection [9]

(e) Deck–railing Connection [9]

(c) Hybrid connection [2]

(f) Deck–barrier Connection [9]

Figure 5 Various deck-to-support connections for FRP bridge superstructures When the deck supports are wide and flat, it is possible to use all-adhesive connection (Figure 5(b)). In this case, adhesive bonding is preferable than hybrid connecting because of the simplicity and ease of installation of the bonding process. However, the difficulty of quality control of adhesive bonding during on-site installation and a lack of confidence in the fatigue and durability of the adhesive layer have hindered its application. Research is currently underway to tackle these problems [6, 8]

5. Discussion and conclusion The techniques for connecting FRP deck panels vary according to the levels of joining. In the component level, adhesive bonding is the most efficient way. The majority of current FRP bridge 5


decks use adhesive bonding to assemble individual components to form deck panels. In some cases, the assembly process is assisted with mechanical means. In panel-panel connections, bonded splicing connections and mechanically fixed connections have been developed for installation. Improvement should be made to ensure mechanical fixing’s ability to resist dynamic loadings. The system level deck-support connection is the most challenging issue in developing FRP deck connections. Because of their advantages, adhesive bonding and hybrid joining are promising connecting techniques for system level connections. In some situations, adhesive bonding possesses advantageous characteristics over hybrid joining because of its simple installation process. In each design and construction, efforts shall be taken to provide structural redundancy for the connected superstructure, i.e., the underneath girders can still take the loads in case of failure in the bonded or hybrid joints. In terms of adhesive-bonded bridge superstructures, research should be conducted to provide structural redundancy, and to investigate the long-term fatigue loading and environmental effects on the adhesive-bonded system level connections.

6. References [1]

BAKIS, C.E., BANK, L.C., BROWN, V.L., COSENZA, E., DAVALOS, J.F., LESKO, J.J., MACHIDA, A., RIZKALLA, S.H., AND TRIANTAFILLOU, T.C., “Fiber-reinforced Polymer Composites for Construction – State-of-the-art Review”, ASCE Journal of Composites for Construction, Vol. 6, No. 2, 2001, pp. 73-87. [2] BURGUENO, R., SEIBLE, F., KARBHARI, V.M., DAVOL, A., AND ZHAO, L., “Manufacturing and Construction Support Document for the Kings Stormwarter Channel Bridge”, Technical Report No. SSRP-99/05, Division of Structural Engineering, University of California, San Diego, La Jolla, California, USA, 1999. [3] CRIPPS, A., Fiber-reinforced Polymer Composites in Construction, Construction Industry Research and Information Association, London, U.K., 2002. [4] DAVALOS, J.F., QIAO, P., XU, X.F., ROBINSON, J., BARTH, K.E., “Modeling and Characterization of Fiber-reinforced Plastic Honeycomb Sandwich Panels for Highway Bridge Applications”, Composite Structures, Vol. 52, 2001, pp. 441-452. [5] KELLER, T., SCHOLLMAYER, M., “Plate Bending Behavior of A Pultruded GFRP Bridge Deck System”, Composite Structures, article in press. [6] KELLER T., GÜRTLER H., “Composite Action and Adhesively Bonded Connections between FRP Bridge Decks and Main Girders”, Submitted to ASCE Journal of Composites for Construction (CC/2003/022440). [7] KELLER, T., Use of Fiber Reinforced Polymers in Bridge Construction, IABSE-AIPCIVBH Publishers, Zurich, 2003. [8] KELLER, T., DE CASTRO, J. AND ZHOU, A., “System Ductility and Redundancy of FRP Structures with Flexible Adhesive Joints”, Proceedings of the 4th International Conference on Advanced Composite Materials in Bridges and Structures (ACMBS-IV), July 20-23, 2004, Calgary, Alberta, Canada. [9] MMC, DuraSpan Fiber-reinforced Polymer Bridge Deck Systems, Martin Marietta Composites (MMC), Raleigh, USA, 2002. [10] REISING, R.M.W., SHAHROOZ, B.M., HUNT, V.J., NEUMANN, A.R., HELMICKI, A.J., AND HASTAK, M., “Close Look at Construction Issues and Performance of Four Fiberreinforced Polymer Composite Bridge Decks”, ASCE Journal of Composites for Construction, Vol. 8, No. 1, 2004, pp. 33-42. [11] ZETTERBERG, T., ASTROM, B.T., BACKLUND, J., BURMAN, M., “On Design of Joints between Composite Profiles for Bridge Deck Applications”, Composite Structures, Vol. 51, 2001, pp. 83-91. [12] ZHOU, A., COLEMEN, J.T., TEMELES, A.B., LESKO, J.J., AND COUSINS, T.E., “Laboratory and Field Performance of Cellular Fiber Reinforced Polymer Composite Bridge Deck Systems”, ASCE Journal of Composites for Construction (Accepted for publication, CC/2003/022446)

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