Cyclic lateral response of FRP-confined circular concrete-filled steel tubular columns

Concrete-filled steel tubular (CFT) columns are widely used as columns in many structural systems and a common failure mode of such tubular columns is inelastic outward local buckling near a column end. The use of fibre-reinforced polymer (FRP) jackets/wraps for the suppression of such local buckling has recently been proposed and has been proven to possess excellent potential in both retrofit/strengthening and new construction. This paper presents the results of an experimental study into the behaviour of large-scale FRP-confined CFT (CCFT) columns under combined axial compression and lateral loading. The test parameters included the stiffness of the FRP jacket and the loading scenario. The test results showed that the FRP jacket can effectively delay or even prevent outward local buckling at the end of a cantilevered CFT column, leading to significantly improved structural performance under combined constant axial compression and cyclic lateral loading. Compared to monotonic lateral loading, cyclic lateral loading was found to introduce more severe localized deformation near the column end and may lead to earlier FRP rupture within that region

Joint analysis of three genome-wide association studies of esophageal squamous cell carcinoma in Chinese populations

We conducted a joint (pooled) analysis of three genome-wide association studies (GWAS) 1-3 of esophageal squamous cell carcinoma (ESCC) in ethnic Chinese (5,337 ESCC cases and 5,787 controls) with 9,654 ESCC cases and 10,058 controls for follow-up. In a logistic regression model adjusted for age, sex, study, and two eigenvectors, two new loci achieved genome-wide significance, marked by rs7447927 at 5q31.2 (per-allele odds ratio (OR) = 0.85, 95% CI 0.82-0.88; P=7.72x10−20) and rs1642764 at 17p13.1 (per-allele OR= 0.88, 95% CI 0.85-0.91; P=3.10x10−13). rs7447927 is a synonymous single nucleotide polymorphism (SNP) in TMEM173 and rs1642764 is an intronic SNP in ATP1B2, near TP53. Furthermore, a locus in the HLA class II region at 6p21.32 (rs35597309) achieved genome-wide significance in the two populations at highest risk for ESSC (OR=1.33, 95% CI 1.22-1.46; P=1.99x10−10). Our joint analysis identified new ESCC susceptibility loci overall as well as a new locus unique to the ESCC high risk Taihang Mountain region

Design-oriented stress–strain model for concrete under combined FRP-steel confinement

Extensive research has been conducted on fiber-reinforced polymer (FRP)-confined plain and RC columns, leading to a large number of stress–strain models. Most of these models have been developed for FRP-confined plain concrete and are thus applicable only to concrete in FRP-confined RC columns with a negligible amount of transverse steel reinforcement. The few models that have been developed for concrete under the combined confinement of FRP and transverse steel reinforcement are either inaccurate or too complex for direct use in design. This paper presents an accurate design-oriented stress–strain model for concrete under combined FRP-steel confinement in FRP-confined circular RC columns. The proposed model is formulated on the basis of extensive numerical results generated using an analysis-oriented stress–strain model recently proposed by the authors and properly captures the key characteristics of FRP-steel-confined concrete as revealed by existing test results. The model strikes a good balance between accuracy of prediction and simplicity of form and is shown to provide close predictions of test results and perform significantly better than existing stress–strain models of the same type

Interaction forces in RC beams strengthened with near-surface mounted rectangular bars and strips

The flexural performance of a reinforced concrete (RC) beam can be improved using the near-surface mounted (NSM) FRP strengthening technique. In the NSM technique, grooves are first cut in the concrete cover, and FRP bars are then placed in the grooves using a suitable bonding adhesive. In such an FRP-strengthened RC beam, debonding failure at the two bar ends may occur due to local high interaction forces in the bar-end regions between the RC beam and the FRP bars. This paper presents a theoretical investigation into these interaction forces in RC beams strengthened with NSM FRP rectangular bars (including FRP strips with a narrow rectangular section as a special case). By introducing and defining two interfacial stiffness parameters, an analytical solution for the tangential and the normal interaction forces between the beam and the NSM bars is first obtained based on the analytical solution developed by Smith and Teng for beams strengthened with an externally bonded FRP plate. The accuracy of the analytical solution is demonstrated by comparing its predictions with those from a 3-D linear elastic finite element (FE) model. The numerical results from both the analytical solution and the 3-D FE model confirms the existence of high interaction forces in the bar-end regions as the cause for bar-end debonding failure which has been commonly observed in tests. While the present paper is focused on RC beams strengthened with NSM rectangular bars, the proposed approach is general and is applicable to a range of similar problems such as RC beams strengthened with NSM bars of other cross-sectional shapes (e.g. circular and elliptical shapes) as well as timber beams strengthened with NSM bars

Finite element analysis of end cover separation in RC beams strengthened in flexure with FRP

The use of externally-bonded (EB) or near-surface mounted (NSM) FRP reinforcement in the strengthening of reinforced concrete (RC) beams in flexure has become increasingly popular in recent years. Such beams are likely to fail by end cover separation in which a major crack in the concrete initiates at a cut-off point of the FRP reinforcement and propagates along the level of steel tension bars, leading to the detachment of the FRP reinforcement together with the cover concrete. Due to the complexity of this failure mode, no reliable finite element (FE) approach for its accurate prediction has been published despite many previous experimental and theoretical studies on the problem. This paper presents a novel FE approach for predicting end cover separation failures in RC beams strengthened in flexure with either externally bonded or near-surface mounted FRP reinforcement. In the proposed FE approach, careful consideration is given to the constitutive modelling of concrete and interfaces. Furthermore, the critical debonding plane at the level of steel tension bars is given special attention: the radial stresses exerted by the steel tension bars onto the surrounding concrete are identified to be an important factor for the first time ever and are properly included in the FE approach. The proposed FE approach is shown to provide accurate predictions of test results, including load-deflection curves, failure loads and crack patterns