Experimental study on eccentric compressive behavior of special-shaped multi-cavity mega-bifurcated concrete filled steel tubular columns

To investigate the influences of different detailings on the behavior of multi-cavity mega-bifurcated concrete filled steel tubular (CFST) beam-columns designed based on the China Zun project in Beijing, two specimens with a 1/10 reduced scale of multi-cell mega-bifurcated CFST beam-columns were designed. Specimen BEC was a standard reduced-scale prototype of the beam-columns, and specimen SEC-2 was that with enhanced flexural rigidity of the lower part compared with specimen BEC. Several factors including failure modes, distribution of deflection along height, vertical load-displacement and skeleton curves, and plane cross-section assumption were examined, and the influence of detailings on the performance of the two specimens were investigated via tests. A nonlinear computer algorithm was developed based on fiber models. The stress-strain relationship of steel was elastic-perfectly plastic model. The models considered for the concrete core included that stipulated in the GB 50010-2010 'Code for design of concrete structures' (GB model) as well as the Hu's model and Han's model. Using the elastic-perfectly plastic model for steel, the results show that the GB model and the Hu's model have poor consistency with the moment-curvature curves considering flexure second-order effect (P-δ effect), but the Han's model has a good agreement with them. To study the composite confinement effect of the diaphragms and multi-cavity steel tube at the compressive zone, the modified Han's models were used for computing the moment-curvature curves, where a good agreement with the peak value of the moment-curvature curves considering P-δ effect was achieved, although the predicted moment at the descending stage was slightly lower. © 2018, Editorial Office of Journal of Building Structures. All right reserved.