A Step-by-Step Probabilistic Seismic Soil-Structure Interaction Analysis with Ground Motion Incoherency for a Bridge Pier on Bored Pile Foundations  
[PERSON]  
1 Civil Engineering Department, Faculty of Civil Engineering, Transilvania University of Brasov, 500152 Brasov, Romania; [EMAIL_ADDRESS]  
[PERSON]  
2 Ghiocel Predictive Technologies, Inc., Pittsford, NY 14534, USA; [EMAIL_ADDRESS]  
[PERSON]  
4 Department of Strength of Materials, Bridges and Turnels, Faculty of Railways, Roads and Bridges, Technical University of Civil Engineering, 020396 Bucharest, Romania; [EMAIL_ADDRESS]  
[PERSON]  
1 Civil Engineering Department, Faculty of Civil Engineering, Transilvania University of Brasov, 500152 Brasov, Romania; [EMAIL_ADDRESS]  
dynamic amplification. The SSI effects on weaker soil become important with heavier and larger structures, such as nuclear facilities, high-rise buildings and large bridges, where the ground motion incoherency and local variations of the soil profile may influence the behavior of the structure to a large degree [1]. A concept that is widely spread in the structural engineering design based on broadened design spectra is that the soil-structure interaction will always have a beneficial effect on the seismic behavior of the structure, due to the increase in the vibration period, which should reduce the seismic accelerations acting on the structure. This has not always been the case for real earthquakes with narrow-band excitation spectra, such as the Vrancea 1977 earthquake for the Bucharest city site. Another example when design recommendations failed is the widely known collapse of the bridge on the Hanshin Expressway, due to the Kobe earthquake, which was the result of neglect at the design stage of the soil-structure interaction and the very important differential seismic wave effects due to the proximity to the fault [3]. On the other hand, if the SSI effects are beneficial on a particular case, overlooking them would lead to an excessively conservative and expensive design [4; 5]. The SSI effects may reduce the acceleration, but also introduce the relative displacements that can be detrimental to infrastructures. In order to obtain the most reliable design, SSI effects have to be included in the analysis through the coupled approach and not through any overly simplified, decoupled approach. Even Eurocode 8 presents a simplified approach for the current design of normal bridges, but it recommends the more complex SSI methodology for detailed analyses on structures of larger importance [6]. One of the cornerstones of the dynamic soil-structure interaction field was the work of the team from the Earthquake Engineering Research Center, Berkeley, California led by [PERSON], which developed a novel approach to model the soil-structure interaction phenomena. [PERSON]'s teamwork [7; 8; 9; 10; 11; 12] matured in the release of the SASSI program (System for Analysis of Soil-structure Interaction) in 1981 [13]. Continuing to work on the same problems, the Geotechnical Engineering Division from the University of Berkeley released, in 1999, the updated version of the original software, which was now called SASSI 2000 [14]. Other important contributions to the field of seismic soil-structure interaction have been made by [PERSON] and [PERSON] [15], [PERSON] [16; 17], [PERSON] [18], [PERSON] and [PERSON] [19], [PERSON] [20; 21] and [PERSON] et al. [22]. Most studies regarding soil-structure interaction have been focused on nuclear structures, which usually have large surface foundations. As the sites for future nuclear powerplants were carefully chosen, deep foundations were never necessary. Thus, the vast majority of SSI studies on pile foundations were looking into different types of structures, most of them being bridges. [PERSON] was one of the first to research the soil-pile interaction problem.