Study On Direct Displacement-based Design Approach Of Prestressed Concrete Frame Structures For Seismic Resistance

The new features of huge economic losses caused by earthquake, and simultaneously to meet the different behavior levels for the owners, under the circumstances the direct displacement-based design emerged. In this approach, the displacement is used to control the behavior of the structures under the earthquake action and the actual performance of the structures under the earthquake action can be known, not just for the structural capacity to some degree.Based on researches at home and abroad, in this paper the DDBD theory and approach have been illuminated, the achievements of this research group have been summarized, the approach proposed in reference [46] has been improved, and the rationality of the improved DDBD approach has been proved by nonlinear analysis of numerical examples. The main research work is illustrated as follows:①Yielding stiffness. As an important parameter in the bilinear hysterical model, an approach for yielding stiffness using elastic displacement response spectrum has been proposed in this paper. In this approach the yielding displacement of the structure is defined to equal to (2.5~2.7) times of elastic displacement firstly; secondly, based on the experiment, the equivalent damping ratio for the prestressed concrete frame at the yielding moment is defined to equal to 0.065; thirdly the seismic force coefficientαmax is defined to equal to 0.42 at the yielding moment through theoretical derivation; then the equivalent period can be determined by the above parameters and the displacement response spectrum; at last the equivalent stiffness can be obtained through the formula k eq = (2π/ Te q )2meq in which the Te q is equivalent period and the me q is equivalent mass.②Displacement pattern. In the regular multi-storey prestressed concrete frame, from the results calculated by the cantilever column displacement pattern and the displacement pattern loaded by inverted triangle force, it can be seen that there is a little difference from the two displacement patterns, moreover the cantilever column displacement pattern more accurately. From the practical engineering application the cantilever column displacement pattern can be operated more conveniently.③Equivalent damping ratio. The hysteresis loop of prestressed concrete structure shows comparatively severe pinching effect from the relative research, so the formula has been adopted to calculate the equivalent damping ratio by this research group, in whichξis inherent damping ratio,ξ∧eq is hysterical damping ratio,αis stiffness enhancement coefficient andμis ductility coefficient. Compared with equivalent damping ratios by other formulas, the equivalent damping ratio by the formula above is closer to the actual equivalent ratio through the Pushover analysis of numerical examples.④Nonlinear analysis. There is certain difference of the lateral sway between static Pushover analysis and elastic-plastic time history analysis, moreover differing greatly in individual cases. However, from the average difference of the three natural seismic waves and one artificial seismic wave, the difference of the lateral sway is not evident between results by the cantilever column displacement pattern and the average of the four seismic waves after regularization; simultaneously there is comparatively difference of the storey displacement between static Pushover analysis and elastic-plastic time history analysis and the maximum difference can achieve 25.1%.