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The primary purposes of this study were to experimentally investigate the influence of the degree of damage in concrete beams on bond behavior of carbon-fiber-reinforced polymer (CFRP) sheets externally bonded to concrete beams. Five concrete beams at different damage levels (evaluated based on flexural stiffness) induced by cyclic loading were externally strengthened with CFRP sheets and were tested under four-point bending load. It was observed during this test that debonding of CFRP sheets appeared for each beam specimen, and propagated from near midspan toward the free end until fracture of CFRP sheets or crush of concrete flange occurred. It was found by comparing the test results and existing bond-slip model that the existing bond-slip model can not exactly predict the bond-slip relationship for CFRP sheets bonded to damaged concrete beams. In addition, the variation of damage parameter, prestress degree and preparation method of concrete surface (notched or non-notched) have little effect on the bond strength and the fracture energy of the CFRP-to-concrete interface, but the interfacial maximum shear stress decreased with an increase in the damage parameter. [ABSTRACT FROM AUTHOR]

The detection of delaminations in composite structures due to impacts is a critical issue for any structural health monitoring (SHM) programme. In this work, an experimental campaign is carried out to investigate the presence of delamination induced in carbon-fibre-reinforced-plastic (CFRP) plates by low velocity impacts (LVI). A reduced number of piezoelectric devices for actuation and sensing purposes are employed. The proposed study starts with the choice of the proper positions of the piezoelectric sensor and actuator through the analysis of the numerical curvature mode shapes of the composite laminated plate. A wavelet packet transform (WPT)-based algorithm is applied on the vibrating response of the plates to extract wavelet-based damage sensitive features. Linear Discriminant Analysis (LDA) is then applied on the extracted damage sensitive features to enhance the performance of the proposed delamination identification procedure. Results show the effectiveness of the developed SHM routine when a reduced number of sensors is either desirable or mandatory. [ABSTRACT FROM AUTHOR]

• GFRP ribs were attached to ultra-high-modulus CFRP rods for bond improvement. • Monotonic and cyclic loading tests were conducted by using RC beams strengthened with NSM CFRP rods. • Bond-improved CFRP rods were firmly fixed in concrete, even under higher cyclic loading. The present study focuses on a near-surface-mounted (NSM) strengthening technique for cantilevered-reinforced concrete (RC) bridge-deck slabs subjected to wheel loads. A carbon-fiber-reinforced polymer (CFRP) rod of ultra-high modulus (455 GPa) is used in the NSM technique adopted in this study. In particular, the fatigue durability of the RC member strengthened with the NSM CFRP rods was examined. Notably, the ultra-high modulus CFRP rod has no shear-resistant ribs because of the pultrusion manufacturing process. Hence, the greatest concern in the strengthening of the NSM is the significant low-bonding property of the CFRP rod embedded in covering/filling materials, such as concrete, mortar, and epoxy-resin. The study uses the CFRP-rod attaching glass-fiber-reinforced polymer (GFRP) ribs to improve bond strength. The bond-improved CFRP rod, with a small diameter of 8–14 mm, can be embedded in the high-strength mortar replacing the upper-cover thickness of general RC slabs. In this study, 15 RC beam specimens of 160 mm thickness were prepared, which is the minimum thickness of a Japanese highway slab. Thirteen beams strengthened with NSM-CFRP rods were tested by monotonic and cyclic loadings, respectively. The flexural fatigue test confirmed that the strengthened beams endured 2 million cycle loadings, and the CFRP rods were firmly bonded in concrete, even under a repeated load. The study reveals the excellent load-carrying capacity and fatigue durability of the RC member, strengthened by NSM-CFRP rods of ultra-high modulus. [ABSTRACT FROM AUTHOR]