Study On Rotational Mechanism Of Multi-span Simply Supported Skewed Girder Bridges Under Strong Earthquake

Compared with right bridge, skewed bridge is irregular structure, its seismic damage is characterized by rotation of the deck around the vertical axis due to the complexity and particularity of its seismic response. In this paper, software Midas/Civil and Open Sees were used to establish dynamic calculation models of multi-span simply supported skewed girder bridges. Through the modal analysis and the time-history analysis of seismic response, the rotational mechanism of multi-span simply supported skewed girder bridges under strong earthquake was revealed. The main contents of this paper are described as follows:(1) By consulting abundant documents in home and abroad, the seismic researches statuses on skewed bridge were reviewed. The superstructure and pounding models were summarized in detail, and the simulation methods of bridge bent, transverse retainer and bearing were introduced.(2) According to the modal analysis of skewed bridge models with different skew angle, width-span ratio, number and arrangement of diaphragms, and eccentric effect, muli-modal coupling mechanism was revealed. The reserch results prove that the main vibration modes of skewed bridge have shown translation in longitudinal,transversal directions and rotation around the vertical axis. The rotation vibration mode of skewed bridge appears earlier than right bridge.(3) Based on the modal analysis, the functional mechanism of all influence factors on the rotation of two-span simply supported skewed girder bridges from the aspect of seismic response was studied in the following cases: ignoring the pounding effect, considering the effect of unilateral longitudinal pounding between adjacent decks, and considering the effects of unilateral longitudinal pounding between adjacent decks and transverse pounding between decks and retainers. The results indicate that the main reason for comparatively large rotation angle occurring in two-span simply supported skewed girder bridges under strong earthquake is not the effect of unilateral longitudinal pounding between adjacent decks, rather than, theasymmetry of supporting stiffness at the end of each bridge span; Taking the effect of unilateral longitudinal pounding between adjacent decks into consideration, it is concluded that: when η(27)1(η(28)sin 2?/ 2(W/ L), where ? and W/ L : skew angle and width-span ratio), the moments produced by the pounding always restrain the rotation of each deck; when η(29)1, the moments always intensify the rotation of one of the two decks, and restrain the other one; eccentric effect caused by larger span ratio or the asymmetry of supporting stiffness of substructure will intensify the rotation of each deck; Transverse retainers can effectively restrain the rotation of each deck.(4) For three-span simply supported skewed girder bridges, the effects of skew angle, width-span ratio, and number and arrangement of diaphragms on the rotation of midspan were studied in the following cases: ignoring the pounding effect,considering the effect of unilateral longitudinal pounding between adjacent decks,and considering the effect of bilateral longitudinal pounding between adjacent decks.The results show that the main reason why rotation of deck at midspan occurs in three-span simply supported skewed girder bridges under strong earthquake is the effect of longitudinal pounding between adjacent decks; When consider the second case, the peak rotation angle of deck at midspan will increase with the increase of η;When consider the third case, the peak rotation angle of deck at midspan presents the changing law of increasing first and decreasing then with the increase of η.