Numerical Study and Design Recommendations of Eccentrically Loaded Partially Encased Composite Columns

A numerical investigation is presented in this paper on partially encased composite (PEC) columns subjected to eccentric loading. 3D finite element (FE) models were established based on the dynamic explicit method, which were validated by comparing the FE outcomes with some available test results in previous literature. Using the verified model, a parametric study was conducted to investigate the effects of several factors on the strength and behaviors of PEC columns, including the concrete strength, the steel yield strength, and the load eccentricity. The outcomes of the FE analyses, together with the test results reported in previous studies, were compared with the capacities predicted by the current design codes for eccentrically loaded PEC columns. It was found that the existing design methods with the assumption of rectangular stress blocks (fully plastic assumption) could be unconservative in some circumstances. Therefore, a modified partially plastic design approach was proposed based on the Eurocode 4 design method, which was confirmed to be conservative yet economic in predicting the interactive force–moment (N–M) capacity of PEC columns under eccentric compression.