Emrah Erduran

Enhanced Displacement Coefficient Method for Degrading Multi-Degree-of-Freedom Systems

The displacement coefficient method proposed in FEMA 440 was evaluated using response statistics from a comprehensive set of nonlinear simulations of multi degree of freedom systems under both far-fault and near-fault ground motions. The study finds that it is practically difficult to achieve high relative strength factors (R values equal to or greater than 6.0) for very stiff systems thereby dictating the need to define R-dependent demand coefficients. The approximate expressions proposed in FEMA 440 for the C2 coefficient is shown to underestimate the displacement demand of stiffness-degrading short period systems. Additional nonlinear simulations were performed to investigate the combined effect of strength degradation and P-Delta effects on the displacement demands of MDOF systems. A new expression for the modification factor that reflect combined P-Delta and degrading effects for the estimation of displacement demands is proposed.

A Critical Look at the Use of Design Spectrum Shape for Seismic Risk Assessment

The effects of using design spectrum shape over actual response spectra on earthquake damage estimates has been investigated. A series of numerical simulations were conducted to estimate the expected damage. The simulations were conducted with four different spectral shapes, two different ground-motion prediction equations (GMPEs) and three different soil classes. As a result of the numerical simulations, it was observed that the use of design spectrum shape leads to over- or underestimation of damage estimates relative to those obtained from the actual spectrum computed using GMPE. The damage estimates were observed to be sensitive to the selected design spectrum shape, the GMPE used to compute the spectral values, the soil type, and the fundamental period of the building typology. It was also observed that Eurocode- and IBC-type design spectrum shapes led to significantly different damage estimates compared to one another.

Development of Innovative Foundation Systems to Optimize Seismic Behavior of Bridge Structures

Preliminary results from a study to develop innovative bridge foundations to optimize bridge performance under earthquake events are presented. Numerical models of bridges with both flexible and stiff footings are compared to demonstrate the potential importance of soil-footing stiffness on the performance of a soil-footing-column-deck-abutment system. Detailed numerical models were developed to capture the inelastic behavior of soil-footing systems. This article summarizes two types of foundation models developed using the OpenSees computational platform. One model uses a contact interface model, soilFootingSection2D, to simulate the foundation and has been proven to be effective in analyzing the cyclic response and displacement of soil-foundation-bridge system. The other uses 2-D nonlinear Winkler foundation consisting of various constitutive springs. Although the former model is more detailed and fundamentally sound in modeling the footings, in its current state it is limited to 2-D use only. The latter model, once verified via comparison to experimental data, can be extended to 3-D. Future work will use the 3-D nonlinear footing models to more accurately simulate the 3-D response of a bridge system to 3-D ground motions.