Analysis On Earthquake Dynamic Response Of Compound Tunnel Anchorage Of Suspension Bridge

With the construction of the long span bridges, the suspension bridge was applied dominantly in the practice for so many preferences. The tunnel compound anchoring system is a new type of anchoring structure. The conditions and domain of the construction application was extended for the large axial stiffness of the pretension cables. The stress distribution was optimized and the costs and the harm to the environment were reduced. As a consequent, much more attention was pay on the anchoring system stability in the working period of the suspension bridge especially on the dynamic response and stability of the anchor in the seismic motivation. The related research was in blank until now. The dynamic response of the tunnel compound anchoring in the seismic motivation was analyzed with numerical simulation. The scientific and reliable guidance can be provided for the anti-seismic design and treatment of the structures.The tension force of the main push-towing rope was balanced with the pretension cables and the interaction of the male cone and the surrounding rock in the tunnel compounding anchoring system. The dynamic response of the compound system and the rock of the shallow slope overburden was complicated because the mechanical characteristics of the surround rock was influenced significantly by the weaken surfaces or zones of the structures as well as the different bearing mechanism of the sub-structures in the compound system. The related seismic response was analyzed with dynamic method based on the propagation rules of the seismic waves in the rock body, the damage characteristics and the failure mechanism of the underground structures and the seismic analysis methods of the underground structures.(1) The wave propagation rules in the rock body were analyzed with the help of the wave theory. The explicit formulation of some factors were provided such as the coefficient of transmission and reflection on the structure surfaces of the seismic wave, the wave impedance of the bilateral rock body, the incident frequency. The relationship of the coefficient of transmission and reflection when the seismic wave passing through the soft and weaken layer with the wave impedance and the thickness of the layer was offered. The seismic wave propagation in the simple joint and parallel joints was analyzed with the numerical simulation as well as in the weaken surfaces or zones of the structures. The influencing factors were discussed and the reliability of the dynamic results was verified with the theoretical methods.(2) Many problems were discussed such as the artificial conditions, the correction of the seismic waves, the zone discretion of the compute range, the dynamic analysis methods. The slope height influencing on seismic response was analyzed as well as the slop toe, the mechanical parameters of the rock body and the characteristics of the input seismic waves. It was shown that the seismic response was incremented non-linearly with the slop height and slop toe degree. The shallow rock body was loosed or damaged because of the free surface effects induce by the seismic motivation of the rock body below the given depth. The maximum value was generally generated on the waist of the slope. The weak parts were located on the minor the fracture zones weak structure zones.(3)The pretension cables were prior than the male cone in the bearing procedure of the compound system. The axial force distribution and value was kept stable in the working period of the suspension bridge. A zone was produce at the adjacent field of the free part of the cables and the front end of the male cone where the compress stress was incremented. While, a compress stress depression zone was produced at the anchoring zone of the cables and the inferior parts, the outward oblique part behind end of the male cone. The inverse male cone displacement and tendency along the direction of the tensile force of the main J push-towing rope were produced induced by the tensile force of the main push-towing rope. The bearing requirements of the main push-towing rope can be satisfied.(4)The seismic response of the compound system was controlled by the imposed deformation of the surrounding rock. Each sub-structures seismic dynamic response of the compound system on the fortification seismic motivations was analyzed individually such as pretension cables, the male cone, the anchoring hall and the surrounding rock. The incidence angle of the different seismic waves and the buried depths of the anchoring system and the intensity of the seismic waves were analyzed.(5)The safety and stability of the tunnel compound system were valuated. It was shown that tunnel compound anchor system was main stable in the 7 grad fortification requirements. The velocity of the surrounding rock was the key factor influencing on the failure of the rock body in the period of the earthquake. More strong confines of the adjacent radium, more the seismic response reduced. The failure possibility was reduced. The outward permanent displacement of the shallow slop rock was generated in the process of the earthquake. The damage extent and the magnitude of the permanent displacement were reduced significantly from the surface to the interior of the slope. The anti-seismic engineering efforts were insignificant with the consolidation of the surrounding rock according the underground structures buried in the hard rock stratum While, the changes of the structure style and the structure materials were advantageous to the earthquake-proof such as constructing the invert, installing the locking angle cables, increasing the lining toughness and ductility.