Fiber-reinforced Polymer Straps Research Articles

Retrofitting of reinforced concrete columns using near-surface-mounted steel rebars and fiber-reinforced polymer straps under eccentric loading

This experimental study focuses on the retrofitting of reinforced concrete columns subjected to axial compression loading with different eccentricities. The proposed hybrid retrofitting technique incorporates two components: near-surface-mounted longitudinal steel rebars and transverse carbon-fiber-reinforced polymer straps. The latter was implemented to preclude buckling of the near-surface-mounted steel rebars under compression, to postpone debonding of near-surface-mounted steel rebars, to increase shear capacity of columns, and to improve the confinement level of concrete. The efficiency of the adopted retrofitting technique was evaluated through experimental testing of undamaged and damaged columns. Toward this, a total of 20 small-scale reinforced concrete circular columns including 5 control, 5 repaired, and 10 strengthened specimens were tested. All specimens were built to be identical with a diameter of 150 mm and a height of 500 mm. The specimens were tested under pure compression, combined axial–flexural (with eccentricities of 30, 60, and 90 mm), and four-point flexural loadings. Comparison of the results showed the efficacy of the proposed retrofitting strategy in enhancing the structural performance of both the undamaged and damaged columns in terms of loading capacity, ultimate displacement, and ductility factor. Finally, the axial load–bending moment interaction curves were discussed for all the tested columns.

Application of FRP Strap in an Innovative Prestressed Method

Fiber-reinforced polymer (FRP) strap is one of the FRP forms. Its width is small and its thickness is large. The wave-shaped-gear-grip anchorage (WSGG) was developed specifically for the FRP strap. A brand-new method has been developed for externally anchored FRP sheet prestress strengthening, which makes full use of the features of WSGG anchors by fixing both ends and then fastening the middle to force FRP sheets to elongate geometrically and generate a pretension. Worn bridge members (solid RC plates of 8 m long) removed from the Cheng-Yu Expressway were used in this experiment of externally anchored CFRP strap prestressed strengthening. The experiment results demonstrated that the proposed method for the application of prestressing FRP straps is very simple, easy, and technically practical, and can significantly enhance the effectiveness of strengthening. It was also shown that the proposed method will have broad applications.

Seismic Retrofitting of Rectangular Bridge Columns with Composite Straps

Behavior of typical rectangular bridge columns with substandard design details for seismic forces was investigated. The poor performance of this type of column attested to the need for effective and economical seismic upgrading techniques. A method utilizing fiber reinforced polymer (FRP) composites to retrofit existing bridge columns is investigated in this paper. High-strength FRP straps are wrapped around the column in the potential plastic hinge region to increase confinement and to improve the behavior under seismic forces. Five rectangular columns with different reinforcement details were constructed and tested under reversed cyclic loading. Two columns were not retrofitted and were used as control specimens so that their hysteresis response could be compared with those for retrofitted columns. The results of this study indicated that significant improvement in ductility and energy absorption capacity can be achieved as a result of this retrofitting technique.