Collapse Mechanism Of Steel Arch Truss: Numerical Analysis And Experimental Study

In recent years, large-span steel arch truss is widely used in stadiums, transportation hubs, convention centers and other large public buildings. During the process of construction or normal use, part or overall collapse of large public buildings may leads to huge casualties and property losses when subjected to extreme weathers, earthquakes, loads or environmental changes. Therefore, carrying out the study of structural collapse mechanism and collapse performance and finding the technical measures to contain or prevent structural collapse have important theoretical and practical significance.At present, the research on large-span arch truss under the action of earthquakes is only limited to static analysis and dynamic response analysis, the collapse mechanism of such structures subjected to severe earthquakes is still unclear. In this article, the study of structural failure mechanism was carried out in three aspects: theoretical analysis, numerical simulation and experimental study. Two kinds of failure mode under dynamic loads(dynamic instability and strength failure) were distinguished and the impact of bracing forms on structural failure modes were analyzed. The vibration characteristics and the dynamic response of model were analyzed through the scaled model shaking table test. The weak position and the collapse ultimate displacement under severe earthquakes were identified from the test result and the numerical simulation.In chapter 1, the research status on collapse performance of spatial structure was described, the research methods for the collapse performance of spatial structures were summarized, and the main collapse reasons and the failure modes were also generalized. The collapse mechanism of grid structure, single layer latticed shell and plane truss system were separately described. Finally, the collapse criteria of spatial structure based on the structure level and the component level were proposed respectively.In chapter 2, the ABAQUS material subroutine was adopted to analyze the impact of damage cumulative effect and member buckling on structural dynamic responses such as the member forces and the nodal displacements. The results show that: the damage cumulative effect caused the member strain and the nodal displacement larger and the member stress smaller than those of the ideal elasto-plastic material. The effect of member buckling caused a downward offset of the strain curve, but had little impact on the nodal displacement.In chapter 3, the simulation of progressive collapse process of steel arch truss was conducted. The webs at columns and at the one-quarter point of the main truss failed after the earthquake, the chord members of the main truss and the longitudinal trusses were intact. The impact of damage cumulative effect and member buckling on the structural failure load were analyzed. When considering damage cumulative effect, the failure load of structure decreased by 22.3%~46.7%; when considering member buckling, the failure load of structure was maintained constant. The failure modes of structure with different bracings were comparative analyzed. Compared with other bracings, only in-plane deformation was found in the model with two cross diagonal bracings which can improve the collapse performance of steel arch truss effectively. Two kinds of failure mechanism under dynamic loads were distinguished. It can be considered as the destruction of dynamic instability when the small increment of load resulted in abnormal increase of structural responses. Conversely, when excessive development of plastic deformations was observed in the structure and the structural responses had reached the prescribed limits before instability, it can be considered as the destruction of strength failure.Chapter 4 described the shaking table test of steel arch truss, and gained the response of seismic and the failure mode of test model. The stiffness of the model decreased by 50% approximately in the X and Z directions and the stiffness of the model decreased by only 12.9% in the Y direction after the test. The dynamic responses were enlarged when the seismic wave propagated to the top of model. When the PGA(Peak Ground Acceleration) reached 0.8g, the responses of displacement increased rapidly and the structural stiffness declined significantly, large numbers of main truss diagonals buckled. When the PGA reached 1.0g, the structural stiffness decreased by 50%, the main trusses had in-plane anti-symmetric deformation.In Chapter 5, the plastic hinge distribution area gained from the nonlinear static analysis and the collapse limited state point gained from the IDA analysis were compared with the results of shaking table test and numerical simulation in this thesis. The comparison shows that, the numerical results match the experimental measurements quite well and the weak position and the collapse ultimate displacement under severe earthquakes were identified on this basis. Under the action of vertical earthquakes, the weak position is at the middle of main truss; under the action of horizontal earthquakes, the weak position is at the column of main truss; when considering member buckling, the webs at the one-quarter point of the main truss would buckled due to large slenderness ratio. The vertical ultimate displacement can be valued as 1/180 of the structural span and the horizontal ultimate displacement can be valued as 1/110 of the total height or 1/30 of the column height.Chapter 6 presented the main conclusions and expectations of the thesis.