Theoretical Analysis And Experimental Research On Collapse Mechanism Of Large-span Arched Frame

With the development of significant social economic activities，the construction ofmajor projects supply a good chance for the development of large-span spatialstructures. There is a great challenge for the technical level of spatial structures instructure style and mechanical behavior. In the construction and working of thestructure, the change of loads, practical function, environment and suffered casualtieswill occur. All of those may affect the mechanical mode. Seriously it may causestructure damage and failure, then collapse. It is necessary for much research on thecollapse mechanism and design method of spatial structure. And the practicabledesign method and technical solution are provided so as to ensure the structural safeoperation.This paper is devoted to study collapse mechanism of large-span arched frameincluding the solid-webbed arched frame and arched truss. Static stability behaviorand instability mode are studied. The analytical solutions of in-plane instability andout-of-plane instability critical load by the linear stability theory are derived. Theinstability mode and the main factors which influence the structure stability areanalyzed. What’s more, the dynamic analysis is made, and the approximate expressionof period is acquired for in-plane deflection. Based on a shaking table experiment ofthe solid-webbed arched frame, natural vibration behaviour，dynamic response infrequent and rare earthquakes are investigated as well as plastic developmentprocesses and failure characteristics. By the energy theory with IDA method, theidentification method of collapse limited state point is put forward with numericalanalysis. The following conclusions can be drawn.1)The influence of the frame column on the instability mode and critical load isconsidered. According to the linear stability theory and introducing the arch stiffnessreduction factor, the analytical solutions of the in-plane and out-of-plane instabilitycritical load by the linear stability theory are derived when solid-webbed arched framesubjects to the radially uniform load.2)Approximate expression of the period is acquired for in-plane deflection ofsolid-webbed arched frame. Based on the energy theory, the collapse limited state point is acquired. When the earthquake ends, the hysteretic energy is equal to thelimited hysteretic energy. This state is called as the collapse limited state. And theconclusion is compared with the results of shaking table experiment.3)A shaking table experiment of the solid-webbed arched frame is carried out.The finding is that the acceleration, displacement and strain response under Tianjinearthquake wave is the more serious than that under Taft earthquake wave whileLoma earthquake wave is the least. The applied rigid braces can effectively limit theout-of-plane deformation, the collapse mode is in-plane antisymmetry deformation.The main reason is that mutual action of the plastic development and displacementchange result in the structure stiffness weakening. Until the plastic developmentreaches a certain degree, the solid-webbed arched frame tends to collapse.4)The circular arch with steel tube-truss is simplified as a model of thin-walledcircular arch with close section by the equivalent principle of the stiffness. Then bythe linear stability theory，the approximate analytical solutions of the in-planeinstability and out-of-plane instability critical load are derived when it subjects to theradially uniform load. In order to avoid losing the out-of-plane stability, the rigidbraces can be applied to the structure by the principle that the out-of-plane instabilitycritical load capacity is larger than the in-plane instability critical load capacity.Secondly the examples are given for verification. After the parametric analysis, themain factors which influence the number of braces are studied.5)The critical load expression of in-plane instability is reduced when thearched-truss frame subjects to the radially uniform load. The results are shown thatavoiding the out-of-plane instability by the rigid braces applied, the instability modesinclude antisymmetry deformation and symmetry deformation. The main factorswhich affect in-plane instability are arch radius, the arch angle(or rise to span ratio),section height of truss arch and truss column, truss column height, and the sectionarea of upper chord for truss arch and truss column.6)The critical load expression of out-of-plane instability is derived when thearched-truss frame subjects to the radially uniform load. And then the main factorswhich affect out-of-plane instability and the number of braces are analyzed. Finally,the research on stability behaviour of arched-truss frame under the vertical load. It isshown that when rise to span ratio is smaller than0.25, the critical load of instabilityfor arched-truss frame under the radially uniform load is similarly equal to that undervertical load. 7)In the incremental dynamics analysis，the inputting earthquake energy is abetter choice of earthquake intensity measure, while the structural hysteretic energyis that of structural damage measure. Combing the energy theory with IDA, theidentification method of collapse limited state point is put forward with numericalanalysis. Taking a project as a case, IDA is applied to a arched-truss frame under thehorizontal, vertical and lateral earthquake wave. The IDA curves and collapselimit-state capacities of the16%,50%and84%fractiles are obtained.