Seismic Analysis Of Long Span Continuous Rigid Frame Bridge With High Piers Under Irregular Topographic Condition

Over the past decades, As the china`s economy continued to develop rapidly, a number of infrastructure constructions were built in some western provinces which is located in mountain and plateau area. In those constructions, bridge, as it could link two areas directly, is wildly applied. Due to the topographic inequality and irregularity in western wild landform, the high-pier long-span bridge becomes the majority in those areas. Western China is an earthquake-prone area, The history records of earthquakes indicates that topographic irregularity will have effect on the seismic motion, and the scale of this effect varies with different terrains. Based on the irregular terrain, A high-pier long-span bridge is, especially, easily, influenced by the topographic effect of seismic motion which could finally lead to a major failure on the structure. Research focusing on the behavior of high-pier long-span rigid frame bridge under topographic effect of seismic motion is necessary, As it will be conducive to provide a reference and improve seismic performance of relevant bridge design. For above perspectives, this paper studies on following aspects:(1) Summarize and discuss the effect between topographic irregularity and seismic motion, also the research status and method of the simulation of the seismic motion,specifically, high-pier long-span bridge with multi-support seismic excitation.Meanwhile, explore the theory of viscoelastic artificial boundary and artificial transmitting boundary, as well the method of earthquake loading. Then select viscoelastic artificial boundary as the site boundary. Adopt the applicable parameters of the models and elements. Choose the soil material property. Five site models, 3two-dimensional models and 2 three-dimensional models, including valley site and hill site were created by program ANSYS.(2) Comparing with an input by using a horizontal seismic wave loading in S-wave form with vertical incidence, The law of peak acceleration and displacement of the canyon and hilly area(PGA, PGD) is summarized in this article: topographic irregularity has a significantly effect on seismic motion. The higher elevation is, the greater seismic response appears. And the seismic response varies with different terrain models. The seismic response of valley site is all greater than the hill site. The smaller slope is, the smaller seismic response escalates. Moreover, the responses between two seismic waves are different. The PGA&PGD in all observation points of wave Taft aresmaller than wave El centro. This result was considered it is related with the site own predominant period and the spectrum characteristic of seismic wave. In a same site model, the seismic response also differs from the dimension of model. On average, the response of three-dimensional models is smaller than two-dimensional models.(3) Based on a practical high-pier long-span bridge project, adopting three-dimensional beam-finite-element, a ANSYS analysis model was established.Choose seismic wave El centro as the acceleration time history of a three-dimensional site. Load the seismic wave with multi-support seismic excitation. The structure response was complicated and differs from different members to different stress situation. Generally speaking, under multi-support seismic excitation, pier has a better seismic performance. And primary beam and bridge pedestal have a worse one. The higher pier have a better seismic performance than the shorter due to the small stiffness.Therefore, the influence of multi-support seismic excitation on bridge stress condition needs to be considered, and the relevant member needs to be reinforced.(4) Establish diverse curvature radius curved continuous rigid frame bridge model.Comparing with straight bridge, under either multi-support seismic excitation or single-support seismic excitation, the bigger curvature radius of curved bridge is, the greater seismic response shows. It illustrated that curved bridge has a better seismic performance than straight bridge. Beside, asymmetric bridge was analysed in the same approach. Asymmetric high pier long-span continuous rigid frame bridge and symmetrical bridge under the influence of the topographic effect, its sensitivity is slightly larger than the symmetrical Bridge.while with multi-support seismic excitation the seismic response of shorter pier of asymmetric bridge will enhance significantly.Thus, it is better to apply symmetric shape during the bridge design.