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This paper presents basic parameters test and an efficient numerical model for the bond between reinforcing bars and concrete after elevated temperatures. The chemical adhesive and friction coefficient are measured by self-designed setups, and the variation law of the parameters is summarized. In the 3D modeling, bar-to-concrete interface has been modeled by means of an explicit discretization of the bar ribs. Surface-to-surface contact pair elements are employed for the interface, and the tangential contact behavior is elastic-plastic with a Coulomb-type friction model. Comparison between experimental and numerical results shows that the proposed model describes the behavior of steel bar relatively well in the pull-out process after elevated temperatures. The 3D modeling makes up some deficiencies of macro pull-out test, such as the detailed stress distributions and crack patterns. [ABSTRACT FROM AUTHOR]

Steel tubes internally stiffened with stringers are promising structural members of long-span transmission towers, but the study on its stability design remains insufficient. To gain insight into the inelastic buckling behavior of the tubes, compressive tests of 33 specimens are conducted. Using the test results, finite element (FE) models are first established and validated. Then, the adequacy of an equation in the literature for predicting elastic buckling stress is investigated via FE analysis (FEA), and a correction coefficient is proposed to diminish the discrepancy between the predicted and the FEA results. Afterward, the FE-based inelastic analysis is performed, wherein the initial imperfections including the local dimples, out-of-roundness, and residual stress were considered in the FE models. The effects of the imperfections on the ultimate strength are investigated. Further, the effects of the length to diameter ratio, diameter to wall thickness ratio, and stringer's number and size on the reduction factor are investigated. Comparatively, the effect of the diameter to wall thickness ratio on the reduction factor is the most significant. The test and FEA results show that the axial ultimate strength is insusceptible to the initial imperfections. In addition, to achieve an efficient design, the restriction of the height to thickness ratio of stringers is suggested to avoid the stringer instability. Finally, the corresponding formulas for design are presented. • Stability design curve for steel moderately-thick cylindrical shells in transmission towers. • Compressive tests of 33 large-scale specimens. • Correction coefficient for the estimation of elastic buckling load. • Parametric study based on inelastic finite element analysis with consideration of residual stress and geometrical imperfections. [ABSTRACT FROM AUTHOR]