عنوان مقاله [English]
In many projects, there are bridges with skewed construction due to river or junction condition. In this paper, the effect of the skew angle on continuous composite girder bridges is discussed using three-dimensional finite-element analysis. Seventy-two models of two-span bridges with various span/width ratios (N = 1, 1.55, and 1.82), skew angles (0-$60^circ$), and various rrangements of intermediate transverse diaphragms are analyzed. Iran's Standard Truck and AASHTO HS20 44 loading are applied to all models, then the reactions for skewed bridges are compared with the reference non skewed bridge, according to the AASHTO standard specifications. The results show that as the skew angle increases, the support moment in interior and exterior girders decreases. It decreases about 8% when the skew angle is less than $20^circ$ and dramatically rises to 30% for a $45^circ$ skew angle, when these numbers are 10% and 37% for AASHTO loading in similar situation. The shear force of girder increases in pier support for the exterior girders and decreases at the interior ones with increasing skew angle. The overestimation of shear force for internal bridges is about 18% for a skew angle of $45^circ$ which increases up to about 23% for exterior girders according to Iran loading standard, when these changes are about 22% and 31% for AASHTO standard for that specific angle. Furthermore, diaphragms' arrangement has direct influence on result and decreases the overestimation of moment from 30% to about 7% for Iran and from 37% to 7% for AASHTO code, when internal diaphragms are perpendicular to girders and are parallel to skew angle. Previous studies support this conclusion in similar situation for both AASHTO LRFD and AASHTO formulas. Moreover, simple equation which was suggested in previous studies is conservative in calculation of bending moments to some extents, compared to results of finite-model. Generally, it can be concluded that both AASHTO and Iran's standards overestimate the maximum bending moment skewed bridge, where AASHTO is a little more conservative in estimation.