A Study on Development of Ultimate Earth quake-Resistance Design and Retrofit Methods for Steel Bridge Piers

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The present study is aiming at developing ultimate earthquake-resistance design and retrofit methods for steel bridge piers. For this purpose, elasto-plastic behavior of steel bridge piers is investigated analytically and experimentally. Based on the results obtained from both the analysis and test, the findings can be summarized in the following aspects.1) Strength and ductilityTo improve the seismic performance (i.e., strength and ductility) of steel bridge piers, two ways are considered : (1) to specify certain limits tothe structural parameters such as plate slenderness ratio, column slenderness ratio, and stiffener's rigidity, (2) to fill concrete into the section near the base so as to prevent or delay buckling of plate panels. As for the concrete-filled steel bridge piers, we proposed an ultimate earthquake-resistance design method based on a large numbers of tests and numerical analyzes. In the proposal, a push-over analysis is employed to compute the load-displacement relation … More of the pier. The strength and ductility computed with the proposed method are compared with experimental results. Moreover, a similar analytical investigation on the strength and ductility of steel octagonal section columns is also carried out. Furthermore, the application of the present proposal is extended to generalized commercial software such as MARC and ABAQUS for practical design.2) Pseudo-dynamic TestsSteel box column specimens modeling steel bridge piers are tested pseudo-dynamically using the accelerograms obtained during the Hygoken-nanbu earthquake that struck Kobe area on Jan.17,1995. The results indicate that the natural period and presence of the filled-in concrete have a significant effect on the seismic response (maximum displacement response and residual displacement response) of steel piers. A relation between the maximum displacement response and residual displacement response is proposed on the basis of the test results, and verified by an extensive elasto-plastic seismic response analysis. On the other hand, the validity of the proposal for designing high ductility steel bridge piers is verified by the pseudo-dynamic test.3) Elasto-plastic Seismic Response AnalysisFrom the results of static and quasi-static tests, a hysteresis model of the steel bridge pier is constructed. The developed model named 2-Parameter Model is verified using the pseudo-dynamic test results, and applied to clarify the seismic behavior of steel bridge piers under the Hyogoken-nanbu carthquake. The results show that the JMA accelerogram is a tremendously severe wave for short piers or those with low natural periods. Also, a hysteresis model is constructed for the concrete-filled steel bridge piers.4) Elasto-plastic Cyclic AnalysisElasto-plastic Behavior of steel bridge piers with box or pipe sections under cyclic loading is studied using the ABAQUS program with the inclusion of the modified two-surface model developed at Nagoya University. Comparison between the analytical and experimental results indicates that the modified two-surface model can be used to predict the inelastic cyclic behavior of steel structures with good accuracy. From the parametric study some empirical formulas are proposed to predict the strength and ductility of such piers. Less