Horsetail Creek Bridge: Design Method Calibration and Experimental Results of Structural Strengthening with CFRP and GFRP Laminates

Abstract

The Horsetail Creek Bridge, constructed in 1912, is located along the Historic Columbia River Highway in Oregon. In a recent rating of bridges, the cross beams of the structure were found to be 50 percent deficient in flexure and 94 percent deficient in shear, mainly due to the traffic loads increase. In order to identify suitable Fiber Reinforced Polymer strengthening system, few commercially available systems were reviewed and alternative designs were carried on. Concurrently, four full size beams were constructed to simulate the retrofit of the bridge. One served as a control, while the other three were reinforced with various configurations of FRP composites. Third point bending tests were conducted. Load, deflection and strain data were collected. Results revealed that addition of either GFRP or CFRP composites provided static capacity increase of 45 percent compared to the control beam. The beam strengthened with CFRP for flexure and GFRP for shear, which simulated the HCB cross beams after the retrofit, exhibited near 100 percent of moment capacity increase. The addition of GFRP for shear alone was sufficient to offset the lack of steel stirrups in the actual bridge, allowing for a conventionally reinforced concrete beam with significant shear deficiency to fail by yielding of the flexural failure. The resulting ultimate deflections of the shear GFRP reinforced beam were nearly twice those of the control shear deficient beam. A design method for flexure and shear was proposed before the onset of this experimental study and used on the HCB. The design procedure for flexure was refined to include provisions for non-crushing failure modes. It allowed for predicting the response of the beam at any applied moment.