Experimental Research On Seismic Behavior Of Continuous Rigid Frame Concrete Bridge With High Pier And Long Span

Because the continuous rigid frame concrete bridge with high pier and long span has large spanning ability and graceful shapes and big rigidity, low cost, easy to be constructed in mountain and forest areas, especially in the seismic area in western China, in addition it has lower cost. There are few systematic research results and earthquake damage data,so it is rather ambiguous to design the seismic continuous rigid frame concrete bridge, as well as practical engineering design is relatively conservative,which can be wrong to spend unwisely and lack of an accurate understanding of real seismic performance for this style bridge. It is of great theoretical significance and application value to summarize the experience of seismic damage deeply and conduct research on seismic performance of the continuous rigid frame concrete bridge with high pier and long span systematically.In this paper, Niulan River Bridge with 126m height pier,for example, the study of seismic performance for the continuous rigid frame concrete bridge with high pier and long span was carried on systematically by measurement on the bridge, model test and numerical analysis, to explore limits seismic capacity and seismic weaknesses of the bridge and to confirm seismic damage mechanism of "wagging tail" of long span bridges. The research results of this paper can provide reference for the engineering design of this bridge type. Specific study results of this paper are as followed:1. The dynamic characteristics test of Niulan River Bridge was completed.The modal parameters in the vertical, longitudinal and transversal directions of this bridge were obtained by environment incentives and incentives caused by obstacles of passing traffic. Accroding these datas transversal bridge is equivalent to the cantilever with a minimum of constrains,and the transvers is a weak seismic direction. Furthermore modes of the bridge of each drder were calaulated with numerical simulation by the finite element program MIDAS. The results obtained by MIDAS was almost agreed with the test measured modal data.2. The long span concrete continuous rigid frame bridge model (I) was established according to the ratio of 1:12. The model had 4-piers and 3-span, and its length was 24m and height was12m. The seismic performance experiment of bridge model(I) was conducted applied with Pseudo-dynamic experimental technique.Test results showed that the bridge model had a strong seismic capacity,and the bottom of the pier only appeared moderate bending failure when the PGA reached strong earthquake of 1.5g. To increase the test sample, the model(I) was reinforced and the cross-section of pier body was nearly doubled, then another bridge model (â…¡) was got.The natural period of model (â…¡) was significantly lower than model(â… ). According to a similar pseudo dynamic test procedure, the model (â…¡) appeared a similar bending failure mode, but the ultimate seismic capacity of model (â…¡) is reduced by 20% compared with the model (â… ).3. In this paper the pseudo-dynamic test method was improved. The control system of pseudo-dynamic test supporting loading system of the existing structure was designed and set up, which can transmit instruction and collect feedback signal and solve dynamic equilibrium equation. In order to simulate gravity load effect, an axial force was applied to central vertical axis of piers with prestressed method.4. The damaged continuous rigid frame concrete bridge with high pier and long span in Wenchuan earthquake was detailed investigated, i.e. Miaoziping bridge,which is only 16km away from the epicenter. The relationship between bridge structure and seismic damage was analyzed and "wagging tail" of side-span was explained.The main reason caused serious seismic damage of continuous rigid frame concrete bridge with high pier and long span,such as damage of bearings and the end of the beam and and the stopper, was "wagging tail" of side-span. The process of "wagging tail" of side-span was reappeared by elastoplastic numerical simulation.The methods to control the damage caused by the wagging tail were to provide a metal-containing rubber stopper and collapse-proof oil damper.According to these stydy results, it is indicated that the continuous rigid frame concrete bridge with high pier and long span designed as current codes has a strong integral seismic capacity. Even under the accident strong earthquake, bending failure only appeared on the bottom of pier of the bridge. In this failure model tensile strength of steel was fully applied, and bridge pier appeared good ductility to avoid collapse. However, study results also revealed that "wagging tail" of side-span and its corresponding impact and rubbing grind failure were the seismic weaknesses of bridge structure. The specific recommendations were provided according to the experimental results and analysis in this paper.In summary, it is verified that this style bridge has strong seismic capacity by the structural numerical analysis and pseudo-dynamic test of the models of continuous rigid frame concrete bridge with high pier and long span. The weaknesses and seismic failure mechanism of continuous rigid frame concrete bridge with high pier and long span under strong earthquakes has also been solved. The research results of this paper can provide a scientific basis for the research and design of this style bridges.