Research On Weak Beam-strong Column Failure Mechanism Of Steel-concrete Mixed Frame Structures

Steel-concrete mixed structure could take full advantage of the excellent characterof steel and concrete. Now, this new structure type has been developed rapidly andwidely used in China. Howe ever, it is a short time that this structure type developed inour country, so they lack the opportunity to undergo earthquake. How to ensure itsapplication safety in high-intensity area has become an urgent problem waiting to besolved. In order to achieve the performance target of “No Collapsing in the StrongEarthquake”, guiding the failure mechanism of structure reasonably which contributesto improving its seismic performances during severe or mega earthquake. As a basicstructure type, steel-concrete mixed frame that consists of composite column and steelbeam or composite beam is widely applied in other structure systems. The existingdesign codes have yet to provide specific stipulations concerning the Weak Beam-strongColumn mechanism of mixed frame. Further more, the current study aimed at thisproblem is quite rare. Based on theoretical analysis and numerical simulation, the WeakBeam-strong Column mechanism of steel-concrete mixed frame structure is studied.The main achievements of this dissertation are as follows:①The fiber model and solid element model are established to simulate theelastic-plastic model of composite members and both of them are proved to beapplicable. Also neglecting the bond-slip at the interface between steel pipe and coreconcrete has little impact on calculations. This conclusion also provides evidence forassumption of strain compatibility in the fiber model.②Pushover analysis with three common lateral load patterns and nonlineartime-history analysis of mixed frame structure with steel beam and concrete filledcircular steel tubular column are performed. Their results are compared from globalresponses (such as the maximum roof displacement and inter-story drift ratio) and localresponses (such as the plastic hinge distribution and the curvature ductility). It isindicated that the pushover analysis method with first mode lateral load pattern isapplicable.③The main parameters that influence failure mechanism of mixed frame structureare studied. The effects of ultimate moment ratio (column to beam) and line stiffnessratio on the failure mode of mixed frame structure are investigated, also axialcompression ratio is discussed. The result shows that ultimate moment ratio controls the failure mechanism. Under certain axial compression ratio and line stiffness ratio, thefailure mode of structure ranges from column-hinge mechanism, hybrid yieldmechanism to beam-hinge mechanism with the increase of ultimate moment ratio. Toguarantee Weak Beam-strong Column mechanism, an appropriate value of ultimatemoment ratio is preliminary advised. Line stiffness ratio almost has no effect on failuremode of structure. Under certain ultimate moment ratio, the decrease of line stiffnessratio would put off the appearance of the first column-hinge and lower the bearingcapacity of structure. While the failure mode and the order of appearance and positionsof plastic hinges haven’t changed in general.