Abbas Abghari

Bio: Abbas Abghari is an academic researcher from California Department of Transportation. The author has contributed to research in topics: Centrifuge & Pile. The author has an hindex of 7, co-authored 7 publications receiving 703 citations. Previous affiliations of Abbas Abghari include University of California, Davis.

Seismic Soil-Pile-Structure Interaction Experiments and Analyses

Abstract: A dynamic beam on a nonlinear Winkler foundation (or “dynamic p-y”) analysis method for analyzing seismic soil-pile-structure interaction was evaluated against the results of a series of dynamic centrifuge model tests The centrifuge tests included two different single-pile-supported structures subjected to nine different earthquake events with peak accelerations ranging from 002 to 07g The soil profile consisted of soft clay overlying dense sand Site response and dynamic p-y analyses are described Input parameters were selected based on existing engineering practices Reasonably good agreement was obtained between calculated and recorded responses for both structural models in all earthquake events Sensitivity of the results to dynamic p-y model parameters and site response calculations are evaluated These results provide experimental support for the use of dynamic p-y analysis methods in seismic soil-pile-structure interaction problems

Nonlinear Seismic Soil-Pile Structure Interaction:

Abstract: Analytical design tools for evaluation of soil‐pile‐structure interaction during seismic events are evaluated and modified. Several implementations of the “Beam on Nonlinear Winkler Foundation” (BNWF) method were used to predict results of centrifuge model tests of single piles in a soft clay soil profile. This paper shows that calculations from these computer codes can be sensitive to the details of the arrangement of nonlinear springs and linear viscous dashpots. Placing the linear viscous dashpots (representing radiation damping in the far field) in series with the hysteretic component of the p‐y elements (representing the nonlinear soil‐pile response in the near field) is shown to be technically preferable to a parallel arrangement of the viscous and hysteretic damping components. Preliminary centrifuge data is reasonably modeled by the numerical calculations using this implementation of damping, but additional field or physical model data are needed to fully evaluate the reliability of BNWF ...

Strength Parameters for Bearing Capacity of Sand

Abstract: The results of centrifuge tests for bearing capacity of circular footings are used to verify the bearing capacity predictions using Hansen's equations with interpretations by Meyerhof and De Beer. The correlation with De Beer's method, which accounts for the variation of friction angle ϕ with normal pressure, is very good. An alternate proposal, using a constant ϕ and an intercept c at zero normal pressure that best fit the failure envelope in the range of interest, also gives a good correlation with the data. The proposed method does not require the iteration procedure that is required by Meyerhof and De Beer. The results are applicable to shallow circular foundations in dense sand where general shear failure is the dominant mechanism. Modeling of models tests were conducted to verify the centrifuge scaling laws over a range in scale factors. The good agreement of modeling of model tests shows that the centrifuge is a useful tool for modeling bearing capacity problems.

Soil-pile-superstructure interaction in liquefiable sand

Abstract: Soil-pile-superstructure interaction in liquefiable sand is evaluated using dynamic centrifuge model tests and pseudostatic p-y analyses. Select recordings from a recent centrifuge test are presented to illustrate typical behavior with and without liquefaction in an upper sand layer. Pseudostatic p-y analyses of single-pile systems in two recent centrifuge model tests show that the apparent reduction in p-y resistance due to liquefaction was strongly affected by changes in the relative density of the sand and drainage conditions.

Stability of Leaning Towers

Abstract: The Leaning Tower of Pisa has intrigued soil mechanicians for many years as to why it tilted in the first place. The more urgent question is, however, whether it is safe today against complete collapse? Methods available in the literature concern the stability of initially vertical towers, not tilted towers, and even for the former there exist very little physical data in verification. The centrifuge is used here to make model tests on towers having small initial tilt and to determine the critical height of tower that causes instability. Two new approaches are presented that give close correlation with experimental results. These approaches are based upon: (1) The experimental determination of rotational stiffness of the soil foundation system; and (2) a method analogous to that proposed by Southwell for predicting the stability of imperfect columns.

Seismic Soil-Pile-Structure Interaction Experiments and Analyses

Abstract: A dynamic beam on a nonlinear Winkler foundation (or “dynamic p-y”) analysis method for analyzing seismic soil-pile-structure interaction was evaluated against the results of a series of dynamic centrifuge model tests The centrifuge tests included two different single-pile-supported structures subjected to nine different earthquake events with peak accelerations ranging from 002 to 07g The soil profile consisted of soft clay overlying dense sand Site response and dynamic p-y analyses are described Input parameters were selected based on existing engineering practices Reasonably good agreement was obtained between calculated and recorded responses for both structural models in all earthquake events Sensitivity of the results to dynamic p-y model parameters and site response calculations are evaluated These results provide experimental support for the use of dynamic p-y analysis methods in seismic soil-pile-structure interaction problems

Seismic fragility assessment of highway bridges: a state-of-the-art review

Abstract: Safety and serviceability of highway bridges, during and after an earthquake, is a prerequisite to ensure continuous transport facilities, emergency and evacuation routes. Recently, fragility curves have emerged as important decision support tools to identify the potential seismic risk and consequences during and after an earthquake. There has been a substantial increase in interest among researchers in the topic of seismic fragility assessment of highway bridges as evidenced by the growing number of published literature. Advanced computational techniques and available resources have led to the development of different methodologies for fragility assessment. This study presents a review of the different methodologies developed for seismic fragility assessment of highway bridges along with their features, limitations and applications. This study presents a review of available methodologies and identifies opportunities for future development. This study mainly focuses on the key features of different method...

Pile response to lateral spreads: centrifuge modeling

Abstract: The paper presents results of eight centrifuge models of vertical single piles and pile groups subjected to earthquake-induced liquefaction and lateral spreading. The centrifuge experiments, conduc...

Scale effects of shallow foundation bearing capacity on granular material

Abstract: Scale effects of shallow foundation bearing capacity on granular materials were investigated to further evaluate the trend of decreasing bearing capacity factor, Nγ , with increasing footing width, B , observed by other researchers. Model-scale square and circular footing tests ranging in width from 0.025 to 0.914 m were performed on two compacted sands at three relative densities. Results of the model-scale footing tests show that the bearing capacity factor, Nγ , is dependent on the absolute width of the footing for both square and circular footings. Although this phenomenon is well known, the current study used a large range of footing sizes tested on well-graded sands to show that the previously reported modifications to the bearing capacity factor, Nγ , using grain-size and reference footing width do not sufficiently account for the scale effect seen in the test results from this study. It also shows that behavior of most model-scale footing tests cannot be directly correlated to the behavior of full...