Damage index assessment of seismic-excited composite frames

Abstract eng:
This paper examines the seismic performance of composite steel-concrete momentresisting frames in interrelation with the Greek aseismic code design requirements progress, from the first appearance of the code in 1959 up to its recent version. Among the several response quantities, damage indices (DI) have been selected to represent the structural response. As overall DI the maximum inter-story drift ratio (MISDR) has been used. The MISDR can be used as structural and as architectural DI. In addition, the plastic hinge rotations (as local DI at the ends of beams and columns) and the mean plastic hinge rotations have been considered. The presented damage indices have been evaluated for a ten-storey steel-concrete composite frame structure designed according to the rules of the recent Eurocode 4 (EC4) and the Greek aseismic code. The latter have been used in its first version (1959), in its intermediate version (1984) and in its recent version (2004). After the design procedure of the composite frame, a nonlinear dynamic analysis has been carried out in order to evaluate the structure’s seismic response. For this purpose the computer program DRAIN-2DX has been used to perform the nonlinear dynamic time history analyses. The present investigation utilized spectrum-compatible artificial accelerograms and recorded acceleration time-histories that generate a wide spectrum of damages, from negligible to severe, for statistical reasons. The results have shown that the increased design requirements of the Greek aseismic code can be exposed by the corresponding decrease of the evaluated DI. Thus, for accelerograms those represent the seismic excitations in the area of Greece, the MISDR decreased up to 53% using the design rules of the recent aseismic code in comparison with them provided by the rules of the 1959 code. In addition, the mean plastic hinge rotations decreased up to 49% comparing the same versions of the aseismic code. In contrast, the comparison of the DI results provided by the structures designed in accordance to the aseismic code versions of 1959 and 1984, have not shown similar significant DI reduction. This is explained by the low upgrading between the two code versions. Finally, the design procedure in accordance with the recent version of the Greek aseismic code ensures that a far lesser number of plastic hinges in columns will appear.

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