Double Skin Steel Tubular Stub Research Articles

Ultimate compressive capacity of tapered concrete-filled double skin steel tubular stub columns with large hollow ratio

Recent developments in towers of wind turbine have heightened the need for tapered Concrete-Filled Double Skin Steel Tubular columns with Large Hollow Ratio (LHR-CFDST). It is necessary to further investigate the mechanical behaviour, key parameters' effects and design methods of tapered LHR-CFDST columns. This paper thus presents an analytical study on the tapered LHR-CFDST stub column under axial compression. A comprehensive finite element (FE) modelling is developed and then verified with the experimental data. A parametric study is conducted to reveal the effects of tapered angles, hollow ratios and diameter to thickness ratios of steel tubes. Further analysis is carried out to understand the compressive behaviour in terms of the full-range load-deformation relation, the axial compressive force distribution and the limitation of steel tube's diameter to thickness ratio. A simplified method for predicting the ultimate compressive capacity of tapered LHR-CFDST stub columns is proposed and the prediction agrees well with the test data.

Behaviors of RPC-filled double skin steel tubular stub columns under axial compression loading

This paper presents the compressive behaviors of RPC-filled double skin steel tubular (RFDST) stub columns. Six RFDST stub column specimens, with different hollow ratios and constraint coefficients, were tested under axial compression loading. The compressive behaviors, such as failure mode, strength and ductility, were analyzed. It is found that the failure mode of RPC filled steel tube (RFST) stub column is shear failure, while RFDST stub columns are waist drum failure. The load deformation curves of RFDST specimens with different hollow ratio and constraint coefficient show different characteristics. RFDST specimens exhibit high bearing capacity and good ductility. Based on the test results of existing RFDST stub columns, a design formula for predicting the ultimate bearing capacity is given. A finite element model is also presented to analyze the compressive behaviors, and good agreement is obtained. The influences of hollow ratio and constraint coefficient on the ultimate bearing capacity are discussed.

Mechanical Performance of Stiffened Concrete Filled Double Skin Steel Tubular Stub Columns under Axial Compression

This paper presents the mechanical performance of Concrete Filled Double Skin Steel Tube (CFDST) columns stiffened by Welded Reinforcing Bars (WRBs) under axial compression. A series of experiments were carried out on sixteen CFDST columns using two different D/t ratios and different patterns of WRBs as parameters. The steel reinforcing bars were welded either on the external surface of the inner tubes or on the internal surface of the outer tubes. Various patterns were used to enable a better understanding of the stiffened CFDST columns performance. Moreover, the compressive loading vs. end shortening curves, failure modes, strength index and concrete-steel contribution ratio were analysed. The results showed that a certain pattern of the WRBs affords additional ductility and strength capacity of the stiffened CFDST columns. Furthermore, WRBs play an important role in the mitigating failure modes and work consistently with the shell concrete of these columns. Design methods were developed for the calculation of the strength capacity of stiffened CFDST columns and assessed against the experimental results to trace the suitable formulation for design purposes. The outcomes of modified analytical procedures mostly match well with the experimental results of the stiffened CFDST columns.

Mechanical behaviour of concrete filled double skin steel tubular stub columns confined by FRP under axial compression

The present study focuses on the mechanical behaviour of concrete filled double skin steel tubular (CFDST) stub columns confined by fiber reinforced polymer (FRP). A series of axial compression tests have been conducted on two CFDST stub columns, eight CFDST stub columns confined by FRP and a concrete-filled steel tubular (CFST) stub column confined by FRP, respectively. The influences of hollow section ratio, FRP wall thickness and fibre longitudinal-circumferential proportion on the load-strain curve and the concrete stress-strain curve for stub columns with annular section were discussed. The test results displayed that the FRP jacket can obviously enhance the carrying capacity of stub columns. Based on the test results, a new model which includes the effects of confinement factor, hollow section ratio and lateral confining pressure of the outer steel tube was proposed to calculate the compressive strength of confined concrete. Using the present concrete strength model, the formula to predict the carrying capacity of CFDST stub columns confined by FRP was derived. The theoretically predicted results agree well with those obtained from the experiments and FE analysis. The present method is also adapted to calculate the carrying capacity of CFST stub columns confined by FRP.

Axial Behavior of Concrete-Filled Double Skin Steel Tubular Stub Columns Filled with Demolished Concrete Lump

To analyze the axial compression bearing capacity of concrete filled double skin steel tubular (CFDST) stub columns which are filled with demolished concrete lump, twelve stub columns are tested. The main experimental parameters were the diameter-to-thickness ratio, mixing ratio and hollow section ration.Load-displacement curves and failure mode were analyzed, the compressive capacity determined from related design rules were compared with the peak load obtained in the tests. All specimens have a good performance of ductility and late bearing capacity. When the width-thickness is 72 and have a same mixing ratio, CFDST have the same bearing capacity with CFT. When the mixing ratio is 0 and width-thickness is 120, the bearing capacity of CFDST increase 16% than CFT. When the new concrete have similar compressive strength with old and mixing ratio is 25%, the bearing capacity of CFDST increase 18.8% than CFT.

Axial Behavior of Concrete-Filled Double Skin Steel Tubular Stub Columns Filled with Demolished Concrete Lump

To analyze the axial compression bearing capacity of concrete filled double skin steel tubular (CFDST) stub columns which are filled with demolished concrete lump, twelve stub columns are tested. The main experimental parameters were the diameter-to-thickness ratio, mixing ratio and hollow section ration.Load-displacement curves and failure mode were analyzed, the compressive capacity determined from related design rules were compared with the peak load obtained in the tests. All specimens have a good performance of ductility and late bearing capacity. When the width-thickness is 72 and have a same mixing ratio, CFDST have the same bearing capacity with CFT. When the mixing ratio is 0 and width-thickness is 120, the bearing capacity of CFDST increase 16% than CFT. When the new concrete have similar compressive strength with old and mixing ratio is 25%, the bearing capacity of CFDST increase 18.8% than CFT.