Seismic Assessment of Reinforced Concrete Skew Bridges under Near-Fault Ground Motions with Considering Soil-Structure Interaction- Case Study of Jack Tone Road On-Ramp Overcrossing Located in California

Document Type : Research Article

Authors

1 Department of Civil Engineering, Science and Research Branch, Islamic Azad University Tehran, Iran

2 Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

3 Department of Civil Engineering, Faculty of Civil Engineering, Art and Architecture, Science and Research Branch, Islamic Azad University, Tehran, iran

Abstract

Seismic behavior of skew bridges, the backbone of modern transportation networks, has not been well studied compared to their ordinary straight counterparts. Investigating past earthquakes, it can be evident that such bridges have experienced intensive damages specially due to girder unseating under the torsional effects of seismic responses coupling in longitudinal and transverse directions, which will be aggravated by local crushing of deck concrete due to pounding between the abutments and adjacent spans. Additionally, bridges are usually supported on Cast-In-Drilled-Hole extended pile-shafts. The inelastic behavior of the superstructure during an earthquake is profoundly dependant on soil strength due to the effect of surrounding soil properties on substructure stiffness. So, the main purpose of the present research is to evaluate the seismic responses of R.C skew overcrossing to variations in some structural parameters by applying analytical models capturing backfill-abutment and soil-pile nonlinearities under near-fault ground motions with high-velocity pulses, especially in their strike-normal component, comparing the results with fixed-base model and finally obtain the most efficient ground motion intensity measure. A set of nonlinear time history analyses was conducted using seven pulse-like ground motions containing horizontal and vertical components on a two-span skewed bridge. Then, the effects of abutment skew angle, base condition modeling approach and soil strength on the revision of various demands were assessed and compared for both flexible- and rigid-base conditions. Furthermore, various analyses were carried out with respect to possible changes in soil properties ranging from soft to stiff for clayey and loose to dense for sandy soils besides the skew angle variations. It was observed that most of the demands, despite the changes in soil strength, were sensitive to an increase in abutment skew angle as a factor of structural stiffness and will often increase incrementally with that, but deck rotation was significantly affected by these variations. Considering foundation flexibility by a set of nonlinear springs can refine structural responses in most cases, particularly by applying Direct Method, based on precise modeling of structural components besides a vast region of encompassed soil around, which will impose an improving effect on various demands relative to the fixed-base condition.

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