Performance assessment of post-tensioned concrete-filled steel tube beams using unbonded tendons with uncertainty quantification

The centerpiece of many research projects is evaluating the structural performance of the concrete-filled steel tubes (CFSTs). When these structural elements are employed as flexural members, some parts of the concrete infill are subjected to tension, and consequently the concrete is cracked so that the confinement effect is reduced. Therefore, the application of tendons and modification of the CFST configuration are deployed to improve the serviceability of the CFST beams. A non-linear finite element (FE) model considering the effects of the material and geometrical non-linearity and initial imperfection is developed. Concurrently, an analytical model based on the plastic stress distribution method (PSDM) is proposed to compare the results. In addition, a probabilistic assessment along with the uncertainty quantification is conducted to calculate the reliability indices and the sensitivity of the beams to the variation of the input variables. The results of the study demonstrate that the implemented measures considerably enhance the moment capacity and serviceability performance of the CFST beams. Moreover, the sensitivity analyses show the significance of the variables on the model output with different steel yield stress values and the importance is ordered as the steel tube width followed by the steel tube thickness and the concrete strength.