Seismic behavior of reinforced concrete bridges with skew-angled seat-type abutments

This report provides analytical and design methods for the seismic design of retaining walls, buried structures, slopes, and embankments. The report details the development of the design procedures. Recommended load and resistance factor design (LRFD) specifications and design examples illustrating the application of the design methods and specifications are included in an Appendix. The material in this report will be of immediate interest to roadway and bridge designers.

Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes, and Embankments

Fragility curves of typical as-built highway bridges in eastern Canada

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...

Validated Simulation Models for Lateral Response of Bridge Abutments with Typical Backfills

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.

A Framework for Performance-Based Earthquake Engineering of Bridge-Abutment Systems

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 is compatible with current CALTRANS practice in regard to the seismic design of bridge abutments. The LSH and HFD models are powerful and effective tools for practicing engineers to produce realistic bridge response for performance-based bridge design.

Nonlinear Soil-Abutment-Bridge Structure Interaction for Seismic Performance-Based Design

Seismic design of bridges is based on a displacement-performance philosophy This type of bridge design requires that the geotechnical engineer provide abutment-embankment soil springs which are inherently nonlinear To date, a number of experiments have been performed to determine the nonlinear lateral force-displacement capacity of ordinary non-skewed bridge abutments, pile caps and walls Typical highway bridges are wide so that the abutment walls are much wider than they are tall Therefore, the nonlinear abutment backfill response behind a wide non-skewed abutment wall is essentially a two-dimensional plane-strain earth pressure problem However, the estimation of the lateral force-displacement capacity behind a skewed abutment wall is a three dimensional problem that involves bridge deck rotation during dynamic loading The capacity is developed from passive wedge failure in the soil mass which occurs when the frictional resistance along the bottom and the two sides of the wedge are mobilized The mobilized passive resistance is dependent on the bridge displacement, bridge geometry (bridge skew angle, deck width and height), the soil stress-strain properties of the abutment backfill, and ground motion characteristics In common abutment design practice, the abutment load-deformation relationship due to passive resistance is based on load test data or presumptive values where the wall is pushed normal to the soil However, the passive resistance and stiffness for the skewed wall is expected to be smaller than for the ordinary non-skewed abutment wall due to the bridge rotation A three-dimensional model is required to capture the geometry and capacity of the full passive soil wedge behind the skewed abutments walls The objective of this paper is to develop three-dimensional nonlinear finite-element models to estimate soil capacities behind a non-skewed and a skewed abutment wall as a function of wall displacement The predicted force-displacement capacities will be compared with the results obtained from a field load-deformation test of a wall pushed into typical structure backfill The nonlinear force-displacement relationship of the abutments can be used to evaluate the seismic performance of skewed highway bridges

Three-Dimensional Nonlinear Finite-Element Soil-Abutment Structure Interaction Model for Skewed Bridges

This paper investigates the impact of the bridge skew angle on the force-deformation characteristics of abutments and the seismic response of a two-span bridge subjected to seismic two-component ground motions with near-fault effects. Three-dimensional models of a two-span box girder bridge were developed incorporating 0, 25, 45 and 60-degree skew. The models included seat-type abutments with elastomeric bearing pads and shear keys, and a single-column bent on pilecaps. A hyperbolic force-displacement (HFD) relationship was used to model the interaction between abutments and the embankment soil. A nonlinear spring is used to model near-field effects in series with an elastic spring and a dashpot element to simulate far-field effects. Nonlinear time-history analyses were performed using nine two-component lateral input ground motions. The analyses show that the interaction between abutment and soil causes the overall seismic bridge behavior to become more complex with increasing bridge skew. Skewed bridges tend to rotate about the vertical axis during a seismic event. The superstructure rotation can cause excessive transverse movement at seat-type abutments that builds up mainly during the initial peak cycles of shaking and can result in unseating of the superstructure. Rotation of the deck is accompanied by pounding on the abutment backwall. The deck rotation is due to development of an non-uniform passive soil wedge behind the abutment wall that results is asymmetric soil reactions between the acute and obtuse corner of the wall. The width and capacity of the passive wedge depends on abutment (embankment) width, skew angle and ground motion characteristics. Seismic behavior of skewed bridges is also strongly influenced by the characteristics of the input ground motions. For three skew configurations, the magnitude of permanent rotation and lateral offset varied among the nine input motions with no discernible trend. This strongly suggests the bridges with significant skew should be analyzed using motions with two or three components and several earthquake records should be considered in order to capture the behavior of structure details such as bearing pads and shear keys that affect the overall bridge response.

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Nonlinear Seismic Soil-Abutment-Structure Interaction Analysis of Skewed Bridges

The current trend for bridge seismic design is to use a method that is based on a displacement performance philosophy in order to predict dynamic response of a bridge. This type of bridge design requires that the geotechnical engineer describe accurately the characteristics of resistance and stiffness of the soil backfill, which are inherently nonlinear in respect to the displacement between backfill and the bridge structure. This paper derives a Hyperbolic Force-Displacement (HFD) relationship that is coupled with average abutment backfill stiffness and ultimate resistance force provided by the bridge abutment for a specified displacement. To demonstrate a practical implementation of the HFD formulation in a bridge seismic analysis, a fully three-dimensional nonlinear dynamic finite-element model of a two-span prestressed concrete box girder bridge is developed that included elastomeric bearing pads and shear keys at the abutments. The model was subjected to ground motions with velocity pulses to simulate near-fault effects. The results indicate the importance of realistic modeling of the abutment soil backfill and the abutment structure details such as the pads and shear keys.

Practical Nonlinear Abutment Model for Seismic Soil-Structure Interaction Analysis

LRFD Seismic Analysis and Design of Transportation Geotechnical Features and Structural Foundations - NHI Course No. 130094 Reference Manual Geotechnical Engineering Circular No. 3

Anoosh Shamsabadi

Papers

Nonlinear Soil-Abutment-Bridge Structure Interaction for Seismic Performance-Based Design

Three-Dimensional Nonlinear Finite-Element Soil-Abutment Structure Interaction Model for Skewed Bridges

Nonlinear Seismic Soil-Abutment-Structure Interaction Analysis of Skewed Bridges

Practical Nonlinear Abutment Model for Seismic Soil-Structure Interaction Analysis

LRFD Seismic Analysis and Design of Transportation Geotechnical Features and Structural Foundations - NHI Course No. 130094 Reference Manual Geotechnical Engineering Circular No. 3