Analysis on Seismic Performance of ConcreteFilled Steel Tubular Columns-Composite Beam Frame Structural System Under MultiDimensional Earthquake

Based on pseudo-static tests of column end stirrup-confined on CFST columns, CFST column-composite beam joints, and CFST column-composite beam planar frame structures, a three-dimensional solid and shell element model of CFST column-composite beam spatial frame structures was established for dynamic time-history analysis. The influence of the column end stirrup-confined, the main beam heightening, the variable cross-section composite beams with the height of the mid span web reduced, and multidimensional earthquake on the seismic performance of composite structures were discussed. The displacement response, axial compression ratio time history curve, stress-strain curve of composite frame structure under various seismic wave were discussed, as well as the distribution mechanism of plastic energy dissipation, the formation and development law of plastic hinge, the evolution law of structural stiffness damage and other seismic performance indicators.
The finite element analysis results indicate that: 1)the strengthened restraint measures, such as the column end stirrup-confined and the main beam heightening, can effectively improve the seismic performance of composite frame structures and reduce the structural stiffness damage, and the greater of the seismic wave is, the better the effects of the enhanced constraint measures are. Under the same seismic wave, the strengthened restraint measure of column end stirrup-confined has more advantages than the main beam heightening, and the combined effect of two measures can further enhance the ultimate seismic capacity of the composite structure; 2)the strengthened restraint measure of column end stirrup-confined can reduce the interface slip between steel tube and infilled-concrete, enhance the energy dissipation capacity of concrete, reduce the proportion of plastic energy dissipation of CFST columns, increase the proportion of plastic energy dissipation of steel beams, and increase the total plastic energy dissipation of the structure. At the same time, the strengthened restraint measure of column end stirrup-confined can also reduce the number of plastic hinges at column ends and increase plastic hinges at beam ends, delay the emergence of “compression hinges” at the column ends, and extend the transition from “compression hinges” to “tension hinges”; 3)the variable cross-section composite beam with the height of the mid span web reduced has no effect on the seismic performance of composite frames. Using this variable cross-section composite beam not only meets the basic functional requirements of the structure, but also saves structural materials, reduces costs, and further expands the space of the building; 4)compared with the horizontal seismic wave, the ultimate seismic capacity of composite frame structure decreases significantly under the multi-dimensional seismic wave, and the failure mode of composite frame structure changes from shear failure to shear torsional failure. In addition, vertical acceleration in three-dimensional seismic wave has an amplification effect on axial compression ratio, while it has no significant impact on maximum displacement, interlayer displacement angle, plastic energy dissipation and stiffness damage. The strengthened restraint measure of column end stirrup-confined still has an improvement effect on the seismic performance of composite frame structures.