According to alternative load path method,three double-span assemblies with double web angles connection based on different span ratios (1.0:0.6,1.0:1.0,1.0:1.4) of steel frame were chosen as the research objects.The failure mode,mechanical behavior,the resistance mechanism of specimens and the failure mechanism of joint were studied by monotonic static loading tests and numerical analysis under the condition of progressive collapse.The results showed that the failure of all specimens are the fracture of double angles connecting the failure column and beam due to severe tension,in which the axial force in the beams,the beam end rotation angle and the dimension of angles are main factors influencing the fracture of the angle leg.The deformation patterns and failure modes,as well as the peak loads,of three specimens are very close.Whereas the horizontal displacement of the failure column corresponding to the peak load reduces with the increase of span ratio successively.Differently,the short beam bears most horizontal load and is failure before long beam for the internal force redistribution of assemblies,which lead to the rotation at beam end of the short beam being greater than the long one under large deformation.And the plastic rotations at beam end of the specimens with unequal spans are larger than the specimen with equal spans.The process of anti-collapse mechanism appears the flexure-catenary mixed phase and catenary phase,in which the reliably tension force between beam and column could make the catenary mechanism of the structure into full play.Moreover,assisted by the validated numerical models considering the material and geometrical nonlinearities,contact nonlinearity and the fracture of the steel,the effect of the restraints provided by peripheral components on anti-collapse performance of assembly with such connection is analyzed in-depth.Then,if the side columns has enough rigidity,the restraints provided by peripheral components has little effect on enhancing the bearing capacity of assembly.
