Composite Reinforcement for Bridges

Principal Investigators:
Antonio Nanni (Currently at Univ. Missouri-Rolla)
Charles E. Bakis (Engineering Science & Mechanics)
Thomas E. Boothby (Architectural Engineering)
Andrew Scanlon (Civil and Environmental Engineering)

Penn State is one of the nation's leading institutions investigating the use of fiber reinforced composite materials for concrete reinforcement. Fiber reinforced plastic (FRP) composites offer particular advantages over conventional steel reinforcement in situations such as bridges, piers, parking decks, and various structures where magnetic properties are important (magnetic resonance imaging rooms in hospitals and magnetically levitated train guideways). However, before FRP reinforcement becomes widely accepted in a traditionally conservative construction industry governed by codes, there is a need to understand the long-term performance of FRP's in aggressive environments. This particular research program deals with the development of test methods for the accelerated characterization of FRP reinforcement in concrete. Penn State is involved in this research project with two other universities: Georgia Tech and The Catholic Univeristy of America. The focus of the program at GA Tech is on stand-alone FRP shapes, while that of CUA is on environmental degradation of FRP. Penn State is focusing on the bond between FRP and concrete.

One aspect of the research at Penn State deals with the development of a simple test method for the accelerated characterization of FRP/concrete bond behavior. To this end, the direct pullout test shown to the left is used. In this figure, an FRP rod is embedded in a 150 mm cube of concrete so that one end can be loaded (bottom) and the other end remains free (top). A 60 kip load frame in the Composites Manufacturing Technology Center is used to apply loads while loaded and free end slips are measured with an array of LVDT's connected to a digital data acquisition system. In addition, some rods are instrumented with an in-house designed strain probe which measures the distribution of strain within the embeddment length of the rod. This test method enables the measurement of load-slip relationships as well as the transfer of stress between the rod and concrete. By measuring internal bond stress development after various accelerated environmental conditionings, the performance of the rod after many years of natural exposure to the highly alkaline environment of concrete can be predicted. The effectiveness of the test method with rods of various shapes has been proven, as has the accuracy of the internal strain probe.

A close-up view of the strain probes, which consist of thin aluminum tubes instrumented with strain gages and bonded inside the rod, is shown to the left. Tests to verify the acceleration of long term performance are underway. Verification of the test method by comparison with data obtained with the RILEM-type split beam shown to the left has been carried out. It was found that the more realistic bending condition obtained in the beam specimen provided similar results to the more simple direct pullout method described above. This means that the results obtained with the bond test method developed at Penn State can be used for design and prediction in real-life beam structures.

A second aspect of the research concerns the development of a model to be used for the prediction of bond behavior in the event it is not possible to run many direct pullout tests described above. The model used to date consists of a finite element discretization of the rod and surrounding concrete. A simple axisymmetric model has been used with great success to date to determine the important FRP material parameters which govern pull-out behavior. Depending on the geometry of the undulations on the surface of the rod and the observed failure mode, different parameters were found to be most important. For example, in some cases, the transverse stiffness and swelling of the rod were dominant, while in others the shear strength of lugs on the rod were dominant. The finite element model is useful both as a guide for improved rod design and also as a predictor of bond behavior in different rod materials and configuration with and without environmental degradation. The model has been demonstrated to predict very well the measured stress transfer in the direct pullout tests for carbon and glass FRP rods with and without surface lugs.

Nanni, A., Bakis, C. E., and Boothby, T. E., "Test Methods for FRP-Concrete Systems Subjected to Mechanical Loads: State of the Art Review," J. Reinforced Plastics and Composites, 14:524-588 (June 1995).

Bakis, C. E., Nanni, A., Boothby, T. E. Huang, H., Al-Zaharani, M. M., and Al-Dulaijan, S. U., "Measurement of Bond of FRP Composite Reinforcement in Concrete Structures," Proc. 10th Intl. Conf. on Composite Materials, Vol. 6, A. Poursatip and K. Street, Eds., Woodhead Publishing, Ltd., 1995, pp. 635-642.

Boothby, T.E., Nanni, A., Bakis, C.E., and Huang, H., "Bond of FRP Rods Embedded in Concrete," Engineering Mechanics, Proc. 10th Conf., Vol. 1, S. Sture, ed., American Soc. Civil Engineers, New York, 1995, pp. 114-117.

Nanni, A., Al-Zaharani, M. M., Al-Dulaijan, S.U., Bakis, C.E., and Boothby, T.E., "Bond of FRP Reinforcement to Concrete - Experimental Results," Proc. 2nd Intl. Symp. on Non-Metallic (FRP) Reinforcement for Concrete Structures, L. Taerwe, Ed., E & FN Spon, London, 1995, pp. 135-145.

Uppuluri, V. S., Bakis, C. E., Nanni, A., and Boothby, T. E., "Bond of Smooth and Machined RP Reinforcement to Concrete - Finite Element Analysis," Proc. 51st Ann. Conf. of the Composites Institute, Soc. Plastics Engineers, New York, 1996, pp. 24E.1-24E.7.

Al-Zahrani, M. M., Nanni, A., Al-Dulaijan, S. U., and Bakis, C. E., "Bond of Fiber Reinforced Plastic (FRP) Rods to Concrete," Proc. 51st Ann. Conf. of the Composites Institute, Soc. Plastics Engineers, New York, 1996, pp. 3A.1-3A8.

Boothby, T. E., Nanni, A., and Bakis, C. E., "Accelerated Test Methods for FRP/Concrete Systems in Highway Structures," 4th Natl. Workshop on Bridge Research in Progress, I. G. Buckle and I. M. Friedland, eds., 17-19 June 1996, Buffalo, NY, pp. 349-354.

Uppuluri, V. S., Bakis, C. E., Al-Dulaijan, S. U., Nanni, A., and Boothby, T. E., "Analysis of the Bond Mechanism in FRP Reinforcement Rods: The Effect of Rod Design and Properties." Proc. ACMBS-II, 2nd International Conf. on Advanced Composite Materials in Bridges and Structures, M. M. El-Badry, ed., Canadian Soc. for Civil Engineering, Montreal, Quebec, Canada, 1996, pp. 893-900.

Al-Zahrani, M. M., Nanni, A., Al-Dulaijan, S. U., and Bakis, C. E., "Bond of FRP to Concrete for Rods with Axisymmetric Deformations," Proc. ACMBS-II, 2nd International Conf. on Advanced Composite Materials in Bridges and Structures, M. M. El-Badry, ed., Canadian Soc. for Civil Engineering, Montreal, Quebec, Canada, 1996, pp. 853-860.

Al-Dulaijan, S. U., Nanni, A., Al-Zahrani, M. M., Bakis, C.E., and Boothby, T.E., "Bond Evaluation of Environmentally Conditioned GFRP/Concrete Systems," Proc. ACMBS-II, 2nd International Conf. on Advanced Composite Materials in Bridges and Structures, M. M. El-Badry, ed., Canadian Soc. for Civil Engineering, Montreal, Quebec, Canada, 1996, pp. 845-852.

Freimanis, A. J., Bakis, C. E., Nanni, A., and Gremel, D., "A Comparison of Pull-Out and Tensile Behaviors of FRP Reinforcement for Concrete," Proc. 2nd International Conference on Composites in Infrastructure, Vol. II, H. Saadatmanesh and M. R. Ehsani, Eds., 5-7 Jan. 1998, University of Arizona, Tucson, AZ, pp. 52-65.

Nanni, A., Rizkalla, S., Bakis, C. E., Conrad, J. O., and Abdelrahman, A. A., "Characterization of GRRP Ribbed Rod Used for Reinforced Concrete Construction," Proc. Intl. Composites Expo '98, Soc. Plastics Industry, New York, 1998, pp. 16A.1-16A.6.

Bakis, C. E., Al-Dulaijan, S. U., Nanni, A., Boothby, T. E., and Al-Zahrani, M. M., "Effect of Cyclic Loading on Bond Behavior of GFRP Rods Embedded in Concrete Beams," J. Composites Technology and Research, 20:29-37 (1998).

Al-Zahrani, M. M., Al-Dulaijan, S. U., Nanni, A., Bakis, C. E., and Boothby, T. E., "Evaluation of Bond Using FRP Rods With Axisymmetric Deformations," Construction and Building Materials, 13:299-309 (1999).

Focacci, F., Nanni, A., and Bakis, C. E., "Local Bond-Slip Relationship for FRP Reinforcement in Concrete," J. Composites for Construction, 4:24-31 (2000).

Lu, Z., Boothby, T. E., Bakis, C. E., and Nanni, A., "Transfer and Development Length of FRP Prestressing Tendons," Precast Concrete Institute J., 45:84-95 (Mar./Apr. 2000).

Bakis, C. E., Nanni, A., Terosky, J. A., and Koehler, S. W., "Self-Monitoring, Pseudo-Ductile, Hybrid FRP Reinforcement Rods for Concrete Applications," Composites Science and Technology, 61:815-823 (2001).

Bakis, C. E., Bhat, B. B., Schokker, A. J., and Boothby, T E., "Flexure of Concrete Beams Prestressed with FRP Tendons," Proc. 5th Intl. Symp. on Fiber Reinforced Polymer Reinforcement for Concrete Structures, (FRPRCS-5), C. Burgoyne, Ed., Thomas Telford, London, 2001, pp. 689-697.

To obtain more information on this research, please contact Prof. Charles E. Bakis (email: cbakis@psu.edu).

Last updated, 16 Aug 01. Copyright 1998, 1999, 2000, 2001, C. E. Bakis.