Research On Method For Improving Anti-collapse Performance Of Composite Beam-column Substructure Withthe Top-set Angle With Double Web Angle Connection Based On Unequal Span

Under the accidental load,the local destruction of the building structure may cause continuous collapse.Because the possibility of extreme events is difficult to predict,under the traditional design for conventional loads,if there is no effective backup path,the collapse is inevitable,so after evaluating the structural collapse resistance,it is necessary to explore design methods to improve its collapse resistance.The current redundant design countermeasures for structural anti-continuity mainly focus on equal-span structures.The asymmetry of beam members has an important impact on the continuous collapse resistance of the structure.Therefore,it is necessary to raise the efficient design method for performance improvement based on the anti-collapse response of the composite beam frame structure.Based on the alternate load path method,the monotonic static loading test was carried out on a composite beam-column substructure with the top-set angle with double web angle connection based on unequal span,focusing on the analysis of the substructure failure mode,strain,resistance mechanism development and overall effectiveness.The test results show that the large rotational deformation capacity of the top-set angle with double web angle connection,the composite beam section loses the composite characteristics due to the first failure of the concrete;the development process of the resistance mechanism of the specimen is the beam mechanism stage(including compression arch mechanism),flexural mechanism and catenary mechanism mixing stage and suspension mechanism stage;the asymmetry of the span leads to the uncoordinated deformation development of the double-span beam,and the overall effectiveness of the substructure is only 83% of its effectiveness reserve.The ABAQUS finite element analysis software was used to establish a refined model of composite beam-column substructure of the top-set angle with double web angle connection based on unequal span and verify with the test results.The simulation results are in good agreement with the test results,using the same modeling method,a full-scale model corresponding to the substructure is established.By analyzing the parameters of the height-span ratios of the double-span beam,the impact of the asymmetry of the double-span beam on the overall effectiveness of the substructure is clarified.The double-span beam has good synergy deformability,the flexural mechanism and catenary mechanism play efficient roles,the double-span beam can work together to make the substructure have good collapse resistance,and the unequal-span substructure can provide similar collapse resistance to the equal-span substructure,the difference is within 6%;the overall performance of the substructure under asymmetric conditions(1)and(2)is not fully exerted.The efficiency change law obtained from the parameter analysis shows that the asymmetric substructure can be improved by two deformation coordination ideas Anti-collapse efficiency,One is to increase the deformation capacity of the beam with larger height-span ratio.It increases the overall deformation capacity of the substructure to further exert the catenary mechanism,thereby improving the collapse resistance,and the other is to weaken the resistance of beam with larger height-span ratio.The deformation capacity of beam with smaller height-span ratio is coordinated with larger span,it strengthen the flexural mechanism to improve the collapse resistance of the substructure.Based on the principle of component method,the simplified analysis of the deformation behavior of the angle steel in the composite beam-column substructure of the top-set angle with double web angle connection based on unequal span,combined with bearing capacity-deformation calculation method of the angle steel T-piece,the two deformation coordination forms can be achieved by changing the angle steel related parameters and giving Detailed parameter calculation process.According to the finite element analysis,designed by the method(1),the flexural mechanism and catenary mechanism have been improved in different amplitudes.The method(2)mainly strengthened the flexural mechanism.Both design methods can improve the collapse resistance of the asymmetric sub-structure,and the ideal state of the double-span beams working together is basically achieved.As the symmetrical ratio of the double-span beams decreases,the two design methods increase the effectiveness of the substructure accordingly.After the design,the substructure effectively overcomes the adverse effects on the effectiveness of the substructure.