عنوان مقاله [English]
Due to the complexity of interchange forms and the lack of space and landownership problems in urban areas, in order to utilize limited space optimally, bridge designers often tend to use skewed highway bridges to carry traffic in urban transportation systems of metropolises. Due to its special geometry, this type of highway bridge shows unique and complex behavior during strong earthquakes. The seismic behavior of skewed highway bridges in past earthquakes has revealed that they are more susceptible to seismic damage compared to straight highway bridges having regular geometry. Hence, over several past decades, different researchers have made an effort to investigate the unique seismic response of skewed highway bridges. Due to the inaccessibility and high cost of efficient software packages that are capable of nonlinear analysis, the recognition and determination of effective parameters in the seismic behavior of this type of bridge is not so easy. The aim of this research is the numerical modeling of the nonlinear behavior of skewed highway bridges and the recognition of effective and important parameters that affect their seismic behavior. As a numerical example, the southeastern bridge of Foothill Boulevard Undercrossing is modeled in OpenSees. The software is an open source and available through the official website. In this study, the seismic response of this skewed highway bridge is investigated and compared to the corresponding straight highway bridge during the 1971 San Fernando ground motion recorded in Pakoima Dam. The bridge suffered severe damage during the 1971 San Fernando Earthquake. The details of damage to the bridge, as well as the geometric and technical specifications of the structure, are available hrough observation reports and research papers. A Dual-Beam Stick Model was employed to model the behavior of the deck, including skewness effects. Elastic Beam Column elements were utilized for the cap beam and deck elements. For the column elements, however, due to their nonlinear behavior, Nonlinear Beam Columns were applied. Modal analysis, as well as nonlinear time history analysis, was performed. Longitudinal and transverse displacement and rotation of the deck, torsion as well as axial force, and the shear and flexural demands on the columns were calculated. The results indicate that the axial force and torsion of the columns at the middle pier in the model of the skewed bridge are larger than those of the straight bridge model, such that, the failure of columns based on this result is predictable.