Fabio Nardone

Structural Evaluation of Full-Scale FRP-Confined Reinforced Concrete Columns

The external confinement of RC columns by means of externally bonded fiber-reinforced polymer (FRP) laminates is a well established technique for strengthening and retrofitting purposes. This paper presents a pilot research that includes laboratory testing of full-scale square and rectangular RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated American Concrete Institute (ACI) 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects peak axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity. The discussion of the results includes a comparison with the values obtained using existing constitutive models.

Analysis of RC Hollow Columns Strengthened with GFRP

Reinforced concrete (RC) hollow piers in bridges withstand high moment and shear demands ensured with reduced mass and lower stress on foundations compared with solid piers. Failure of hollow columns is typically affected by premature buckling of reinforcing bars and concrete cover spalling. At present, no guidelines are available for the design of their upgrade, and few research investigations can be found on hollow columns strengthened by using fiber-reinforced polymer (FRP) materials. This paper discusses an experimental program carried out on purely compressed RC hollow columns externally wrapped with glass-fiber-reinforced polymer (GFRP). Three specimens were tested: one specimen was unstrengthened and used as the benchmark; the other two specimens were GFRP-wrapped with different confining reinforcement ratios. Each specimen was designed according to dated codes (i.e., prior to 1970) accounting only for gravity loads. In particular, steel longitudinal bars cross section and steel tie-spacing were designed with the minimum amount of longitudinal reinforcement and minimum tie area at maximum spacing. Tests results highlight that the GFRP-jacket mainly provided ductility increases before low strength increments could be obtained. Refined and simplified numerical models for hollow square RC columns, previously proposed by the authors, herein extend to hollow rectangular members. Comparisons of experimental results and theoretical predictions on the basis of both refined and simplified confinement models were performed and showed good agreement. In the case of the simplified model, a value for the effective ultimate FRP strain was suggested.

Wall-Like Reinforced Concrete Columns Externally Confined by Means of Glass FRP Laminates

This paper discusses the laboratory testing of wall-like reinforced concrete (RC) columns externally confined with glass fiber reinforced polymer (GFRP) laminates and subjected to pure axial load. Specimens were characterized by an overall length of 3.05 m (10 ft), cross-sectional dimensions of 356 by 1,041 mm (14 by 41 in). Three specimens were tested: one was unstrengthened (benchmark) and two were confined with GFRP laminates. Two different confining reinforcement ratios were considered. The experimental investigation aimed at characterizing: the confinement contribution in terms of axial strength and prevention of instability of longitudinal bars, and the sensitivity of any enhancement in performance to the confining reinforcement ratio. The experimental axial stress – axial strain curves are also discussed.