Compressive behavior of FRP-confined concrete-encased steel columns

FRP-confined concrete-encased steel I-section columns (FCSCs) are an emerging form of hybrid columns. An FCSC consists of an outer FRP tube, an encased steel section and a concrete infill. The FCSCs possess many advantages over conventional reinforced concrete columns, including the excellent corrosion resistance, excellent ductility and ease for construction. Existing studies on FCSCs, however, have been rather limited. This paper presents a combined experimental and theoretical study on the behavior of FCSCs under concentric and eccentric compression. The experimental program included the testing of a total of 14 specimens, with the main variables being the section configuration, the thickness of the FRP tube and the loading scheme. The theoretical part included the development of a model for section analysis based on the so-called fiber element approach. The test results showed that the buckling of steel section was well constrained and the concrete was effectively confined in FCSCs, leading to a very ductile response under both concentric and eccentric compression. The theoretical model was shown to provide reasonably accurate predictions of the test results

Reinforced concrete beams strengthened in flexure with near-surface mounted (NSM) CFRP strips: Current status and research needs

The near-surface mounted (NSM) FRP strengthening technique has attracted worldwide attention as an effective alternative to the externally bonded (EB) FRP strengthening technique. In the NSM FRP strengthening method, grooves are first cut in the concrete cover of a concrete member for the FRP reinforcement to be inserted and embedded using an adhesive. The NSM FRP method has many advantages over the EB FRP method, including a higher bonding efficiency and a better protection of the FRP reinforcement. Existing experimental studies have shown that FRP strips owned a better bond efficiency compared with other section shapes (e.g. round bars and square bars), due to the fact that they had a larger perimeter-to-cross-sectional area ratio. This paper presents a state-of-the-art review, particularly on the flexural strengthening of RC beams with NSM CFRP strips. The observed failure modes in laboratory experiments of such FRP-strengthened RC beams are classified and the existing strength models are examined along with the failure mechanisms behind. The main knowledge gaps to be bridged in future studies are also identified. This review partially formed the basis of the development of design provisions on the NSM strengthening technique in the relevant Hong Kong design guideline

Relation Between Gravitational Mass and Baryonic Mass for Non-Rotating and Rapidly Rotating Neutron Stars

With a selected sample of neutron star (NS) equations of state (EOSs) that are consistent with the current observations and have a range of maximum masses, we investigate the relations between NS gravitational mass Mg and baryonic mass Mb, and the relations between the maximum NS mass supported through uniform rotation (Mmax) and that of nonrotating NSs (MTOV). We find that for an EOS-independent quadratic, universal transformation formula (Mb=Mg+A×M2g)(Mb=Mg+A×Mg2), the best-fit A value is 0.080 for non-rotating NSs, 0.064 for maximally rotating NSs, and 0.073 when NSs with arbitrary rotation are considered. The residual error of the transformation is ∼ 0.1M⊙ for non-spin or maximum-spin, but is as large as ∼ 0.2M⊙ for all spins. For different EOSs, we find that the parameter A for non-rotating NSs is proportional to R−11.4R1.4−1 (where R1.4 is NS radius for 1.4M⊙ in units of km). For a particular EOS, if one adopts the best-fit parameters for different spin periods, the residual error of the transformation is smaller, which is of the order of 0.01M⊙ for the quadratic form and less than 0.01M⊙ for the cubic form ((Mb=Mg+A1×M2g+A2×M3g)(Mb=Mg+A1×Mg2+A2×Mg3)). We also find a very tight and general correlation between the normalized mass gain due to spin Δm = (Mmax − MTOV)/MTOV and the spin period normalized to the Keplerian period PP, i.e., log10Δm=(−2.74±0.05)log10P+log10(0.20±0.01)log10Δm=(−2.74±0.05)log10P+log10(0.20±0.01), which is independent of EOS models. These empirical relations are helpful to study NS-NS mergers with a long-lived NS merger product using multi-messenger data. The application of our results to GW170817 is discussed

Concrete-encased steel columns confined with large rupture strain FRP composites: axial compression tests

Fibre Reinforced (FRP)-confined concrete-encased steel composite columns (FCSCs) are an emerging form of hybrid columns. The idea of a combined use of FRP-confined concrete and an encased steel section not only offers a durable and ductile structural form for new construction, but also can be practiced as an efficient method to retrofit/strengthen deteriorated steel columns. This paper presents a series of axial compression tests on concrete-encased steel columns confined with Large Rupture Strain (LRS) FRP composites, namely, Polyethylene Terephthalate (PET) FRP composites. A total of 12 circular specimans, including 6 FCSCs and 6 FRP-confined concrete circular columns (FCCCs) were tested, with the main test variables being the thickness of the FRP tube. The test results shoed that FCSCs with PET FRP possessed excellent performance in terms of both axial strength and ductility