Experimental and analytical studies on performance of composite frame under column loss

In order to study the behavior of composite frame under column loss, a 4-span, single-story steel-concrete frame was fabricated. The specimen was tested under middle-column loss. The experimental results show that, the progressive collapse of composite frame under middle column loss involves six stages consisting of elastic stage, elastic-plastic stage, arch stage, plastic stage, transient stage and catenary stage, in which the structure sustains and redistributes loads through the mechanism of hinge action and catenary action; composite beam could bridge over the remaining elements and assure the formation of catenary action while arch action could enhance the resistance of structure under column loss; the composite frame designed according to current design standard possesses good progressive collapse resistance under the failure of key column. Based on the test, a finite element model was developed, whose results were validated by comparing with the experimental results. This model provides an efficient modelling method on progressive collapse analysis of high-rise buildings. Based on the experimental phenomena and results, a new type of 'truss-spring' arch model was proposed to study the arch action in composite frame. The vertical displacement-load relationship formula and the vertical displacement-horizontal displacement relationship formula were derived. The accuracy of these two formulae is validated by comparing with the tests results.