SEISMIC ENERGY BASED FATIGUE DAMAGE ANALYSIS OF BRIDGE COLUMNS: PART I - EVALUATION OF SEISMIC CAPACITY. TECHNICAL REPORT

This is the second part of a two-part series on the seismic energy based fatigue damage analysis of bridge piers. This second part deals with the determination of energy and fatigue demands on bridge columns. A smooth asymmetric degrading hysteretic model is presented, capable of accurately simulating the behavior of bridge piers. The model parameters are determined automatically by using a system identification routine integrated into a computer program OPTIMA. The program can use either real experimental data or simulated experiment results from a reversed cyclic loading fiber element analysis. A SDOF inelastic dynamic analysis program was implemented capable of using different hysteretic models. Spectral results were produced by using the smooth model presented which had been calibrated with full-size bridge column experimental data to determine global parameters to simulate column behavior. Design recommendations regarding the assessment of fatigue energy are made based on the results obtained through the nonlinear dynamic analysis. A complete methodology of seismic evaluation of existing bridge structures is proposed, which incorporated the traditional strength and ductility aspects plus the fatigue energy demand. The relevance of fatigue aspects for the seismic design of new bridge structures is also demonstrated. It is shown that the present code use of force reduction factors, that are independent of natural period, are unconservative for short period stiff structures. Recommendations are made for force reduction factors to be used in fatigue resistant design.