Strengthening reinforced concrete bridge T-beams with CFRP sheets plus bi-directional GFRP U-wraps

Abstract

The use of externally bonded Fiber Reinforced Polymer (FRP) to strengthen concrete structures has become more common. As this continues to grow, research is needed to ensure that the best design practices are being used. In this study, externally bonded Carbon FRP is used to strengthen reinforced concrete T-beams. In addition to the flexural CFRP, ±45° bi-directional Glass FRP as well as Carbon FRP splay anchors are used as anchorage systems on some of the beams. The goal of adding anchorage systems is to prevent premature failure due to debonding and allow the CFRP to reach its full capacity with a rupture failure. An experimental program is conducted in which six T-beams are designed, built, and tested in three-point bending with a clear span of 15.5 ft. The first beam was tested as a control beam failing at around 64.58 kips. The second beam was strengthened with one layer of CFRP, spanning 15 feet and starting 3 inches from each support. This beam failed 60.13 kips. The third beam was strengthened the same way as the second beam, but in addition to the CFRP sheet Carbon FRP splay anchors were added to each shear span. This beam has five splay anchors per shear span and failed at 58.88 kips by a premature rupture of CFRP sheet in between the anchors. The fourth beam was strengthened with the same layout for the CFRP sheet and had one layer of a full-length ±45° bi-directional Glass FRP U-wrap. This beam failed at a load of 80.02 kips. The fifth beam used the same layout as the fourth beam, but instead of a full-length U-wrap, this beam had one layer of one-foot wide ±45° bi-directional Glass FRP U-wraps with one foot of space between them. For this configuration the first U-wrap was centered at the mid-span of the beam. The fifth beam failed at 79.76 kips. The sixth beam was strengthened the same way as beam five but had two layers of ±45° bi-directional Glass FRP U-wraps. This beam failed at a load of 72.17 kips. These test results show that using ±45° bidirectional U-wraps is more effective for reaching higher ultimate loads. The results for beams five and six show that using one layer of bidirectional U-wraps instead of two still provides around the same amount of effective anchorage. However, the former configuration yields higher beam deflection at failure.