Anoosh Shamsabadi

In this study, a lightweight prestressed steel jacket (PSJ) was proposed and developed for rapid and cost-effective repair of a severely damaged circular reinforced concrete column. The PSJ is composed of several prestressed strands, and a thin steel sheet is restrained by these strands, which can be manually wrapped around and jointed to form a jacket on the column as part of a 12-h repair job by two workers. The prestressed strands restrain the thin sheet from buckling, while the steel sheet in turn prevents the strands from cutting into cracked concrete and thus preserves the prestressing forces. The PSJ was validated with cyclic (reversed) testing of two large-scale columns with lap-splice deficiency under incrementally increased displacements every three cycles. The ultimate strength and displacement ductility of the damaged column were restored to 115% and 140%, respectively, of those of the as-built column. The initial stiffness of the damaged column, however, was restored to only 84% of t...

A graphical user interface is developed to combine nonlinear dynamic time history analysis of bridge-abutment-ground systems with an implementation of a performance-based earthquake engineering (PBEE) framework. The user interface builds upon earlier code that allows for analysis of three-dimensional pile foundations in a soil domain under nonlinear monotonic and dynamic loads (OpenSeesPL). Functionality was extended for analysis of multiple suites of ground motions and combination of results probabilistically using the performance-based earthquake engineering framework developed by the Pacific Earthquake Engineering Research (PEER) Center. Definition of a two-span bridge, abutments, and underlying ground configuration is greatly facilitated using this new interface. In addition, all stages of the involved analyses are executed in a systematic fashion, allowing the end user to conveniently conduct extensive parametric investigations. In this paper, the analysis framework and the main components of the graphical user interface are presented. Abutment passive earth-pressure resistance to excessive bridge longitudinal displacement is modeled by a newly proposed hyperbolic force-displacement relationship. Using the interface, a representative bridge model is studied under a large ensemble of input ground motion excitations. Overall system response is investigated and the PBEE results are discussed.

Abutment-backfill soil interaction can significantly influence the seismic response of bridges. In the present study, we provide numerical simulation models that are validated using data from recent experiments on the lateral response of typical abutment systems. Those tests involve well-compacted clayey silt and silty sand backfill materials. The simulation methods considered include a method of slices approach for the backfill materials with an assumed log-spiral failure surface coupled with hyperbolic soil stress-strain relationships [referred to as “log-spiral hyperbolic (LSH) model”] as well as detailed finite-element models, both of which were found to compare well with test data. Through parametric studies on the validated LSH model, we develop equations for the lateral load-displacement backbone curves for abutments of varying height for the two aforementioned backfill types. The equations describe a hyperbolic relationship between lateral load per unit width of the abutment wall and the wall defl...

This paper presents a brief summary of seismic analyses for Caldecott Tunnel Improvement Project. It includes seismic hazard analysis, wave scattering analyses to evaluate soil structure interaction (SSI) for the proposed 4^th bore, and development of seismic coefficient for slope stability design. Probabilistic Seismic Hazard Analysis (PSHA) was used to establish the rock motion criteria; 1,500-year and 300-year return periods were adopted for the Safety Evaluation Earthquake (SEE) and Functional Evaluation Earthquake (FEE), respectively. The wave scattering analyses were performed using the spectrum-compatible time histories to account for localized geologic features including site specific topography and soil properties specific to the current project. The analyses enable evaluation of the degree of ground distortion that contributes to racking and ovaling of the tunnel liner. Seismic coefficients for several critical slopes near portals were also derived considering the concept of wave propagation within the slope mass.

The abutment-soil-structure-interaction plays a significant role in the global response of bridge structures. This paper presents nonlinear closed-form formulas to describe force-displacement backbone curves of bridge abutments with typical backfill soils. The original closed-form formulas are modified Hyperbolic Force-Displacement ("HFD") equations developed to simulate the results of two field abutment tests for an abutment wall height of 5.5 feet. To extend the formulas to be applicable to abutment walls with other heights, a series of analyses are performed using the limit-equilibrium method that implements mobilized Logarithmic-Spiral failure surfaces coupled with a modified Hyperbolic soil stress-strain behavior ("LSH" model). The limit-equilibrium method with LSH model, which is a relatively simple approach, has been verified through analyses using a complex finite element model and also has been validated by abutment and pile cap field tests conducted on various typical structure backfills. Based on the results of the analyses, two height adjustment factors are derived for typical sandy and clayey backfill soils. The recommended closed-form formulas are the products of the original closed-form formulas and the height adjustment factors. The formulas are simple enough to be used by the practicing engineers and are capable of capturing the major characteristics of the force-displacement backbone curves.

Current seismic design of bridges is based on a displacement performance philosophy using nonlinear static pushover analysis. This type of bridge design necessitates that the geotechnical engineer predict the resistance of the abutment backfill soils, which is inherently nonlinear with respect to the displacement between soil backfill and the bridge structure. This paper employs limit-equilibrium methods using mobilized logarithmic-spiral failure surfaces coupled with a modified hyperbolic soil stress–strain behavior (LSH model) to estimate abutment nonlinear force-displacement capacity as a function of wall displacement and soil backfill properties. The calculated force-displacement capacity is validated against the results from eight field experiments conducted on various typical structure backfills. Using LSH and experimental data, a simple hyperbolic force-displacement (HFD) equation is developed that can provide the same results using only the backfill soil stiffness and ultimate soil capacity. HFD i...