Pounding And Beam Falling Research Of Skew Girder Bridge Under Strong Earthquake

Skew girder bridges have been widely adopted in highways and urban roads as this type of bridge has smooth lines which can adjust to the road alignment well. Yet, irregular layout and asymmetric bearing characteristics of skew girder bridges cause special and complex seismic response and skew bridge is destroyed more serious than straight line orthogonal bridge under earthquake. When earthquake occurs, coupling effect of bending and torsion can lead to oblique collision between girder and girder or abutment or blocks of skew girder bridge. Severe pounding may cause damages of concrete, beam falling and bridge collapse. Finite element calculation model of an assembled single span skew simply supported girder bridge and a four-span skew rigid-continuous girder bridge is established respectively. Systematic study of seismic pounding response of skew girder bridges, beam falling damage of assembled skew simply supported girder bridge and seismic collapse damage of rigid-continuous girder bridge is carried out with explicit dynamic contact search algorithm. Research contents and research achievements in this paper include the following aspects:Finite element calculation model of assembled skew simply supported girder bridge is established with pounding effect considered and two three-dimensional ground motions are input. Seismic pounding effect research of assembled skew simply supported girder bridge is carried out with explicit dynamic contact search algorithm. The following conclusions are obtained:significant difference exists between girder displacements toward the abutment (or blocks) and away from abutment (or blocks). The former displacement value is much smaller than the latter displacement values. In addition, displacement along the bridge (cross the bridge) varies is different between each beam. Ground motion spectral characteristics can also have a greater impact on girder displacement:beam displacement value along the bridge under Elcentro ground motion is greater than that under Tianjin ground motion; while the beam displacement values cross the bridge under Elcentro ground motions is smaller than that under Tianjin ground motion. Pounding effect will cause beam end and abutment back-wall to withstand great pounding force, resulting in stress increasing at beam end and at abutment back-wall. Increased stress can lead to concrete cracking at beam end and blocks and local concrete off at abutment back-wall etc. Furthermore, stress and pounding force of beam end and horizontal blocks exhibits uneven distribution. Pounding force of beam at acute angle point is smaller than that of obtuse angle point and pounding force at acute (or obtuse) angle point is greater than that at center position of the cross-section. Varying degrees of pounding occurs between adjacent main beams. Pounding between outside beams is more serious than pounding between middle beams.By considering pounding force and concrete damage, beam falling research of assembled skew simply supported girder bridge under strong earthquake is conducted. Beam falling contains three stages:pounding between beam and back wall and blocks, great deformation and failure of the blocks, loss of vertical support of beams and beam falling.Pounding effect is one important reason for beam falling. Pounding effect causes beam rotation in-plane and leads to the main beam fall off easily from the corner of the deck system. To simply supported girder bridge, main beam first loses support at obtuse angle of the beam. In addition, beam falling is often accompanied by large deformation of horizontal block. Importance should be attached to the design of the horizontal block in the seismic design process of skew bridge. Reasonable stopper setting can effectively reduce the lateral displacement and beam falling probability. Moreover, ground motion spectral characteristics have an impact on beam falling forms. Difference between spectrum characteristics determines numbers of falling beams.Through defining failure criteria, analysis of seismic pounding effect and collapsing process of a four span skew rigid-continuous girder bridge is carried out. Compared to assembled skew simply supported girder bridge, box-section beam rotates more apparently. Pounding force distribution law of integral box-section beam and assembled girder bridge is different. Pounding force of beam at acute angle point is greater than that of obtuse angle point. Pounding is not likely to occur at the center position of the beam. Seismic pounding effect will affect the collapse form of the bridge and change the damage order of the pier: rigid pier is destroyed firstly when seismic pounding effect is not considered, while the abutment pillar is not likely to be destroyed; the abutment pillar stress increases when pounding effect is considered while damage extent of rigid pier is reduced. The destruction of abutment pillar is earlier than the destruction of the bridge piers. Pounding effect reduces the damage extent of rigid pier while increasing the damage extent of the abutment pillar. In the seismic collapse resistance design of the bridge, pounding effect should be considered as much as possible and more attention should be paid to the strength of the abutment pillar.