<p>In view of the large calculation research situation of the seismic fragility of bridges, the paper takes a continuous girder bridge as case-study, accounts for the uncertainties derived from the structural and earthquake ground motion. Combined with the uniform design (UD) and response surface methodology (RSM),an alternative seismic fragility analysis method is proposed. In order to verify the validity and applicability of the proposed method, what through comparisons in sampling frequency and computing time, response surface model accuracy and seismic fragility curves between the proposed method, Monte Carlo (MC), orthogonal design (OD) and central composite design (CCD) of response surface methodology. The case-study shows that the proposed method can be well applied to seismic fragility analysis efficiently and effectively. The results of fragility analysis of the proposed method are very close to Monte Carlo of response surface methodology. In terms of the sampling frequency and computing time, compared with Monte Carlo (MC), orthogonal design (OD) and central composite design (CCD) of response surface methodology, the proposed method is reduced by 99.70%, 58.49% and 8.70% respectively. And as for the structures response surface fit coefficients, compared with orthogonal design (OD) and central composite design (CCD) of response surface methodology, the proposed method are increased by 8% to 12% and 3% to 5% separately. Therefore, the proposed method has good application value in seismic fragility analysis.</p>
Bridges in a marine environment have been suffering from the chloride attack for a long period of time. Due to the fact that different sections of piers may be exposed to different conditionals, the chloride-induced corrosion not only affects the scale of the deterioration process but also significantly modifies over time the damage propagation mechanisms and the seismic damage distribution. In order to investigate the seismic damage of existing RC bridges subject to spatial chloride-induced corrosion in a marine environment, Duracrete model is applied to determine the corrosion initiation time of reinforcing steels under different exposure conditionals and the degradation models of reinforcing steels, confined concrete, and unconfined concrete are obtained based on the previous investigation. According to the seismic fragility assessment method, the damage assessment approach for the existing RC bridges subject to spatial chloride-induced corrosion in a marine environment is present. Moreover, a case study of a bridge under two kinds of water regions investigated the influence of spatial chloride-induced corrosion on the seismic damage of piers and other components. The results show that the spatial chloride-induced corrosion may result in the section at the low water level becoming more vulnerable than the adjacent sections and the alteration of seismic damage distribution of piers. The corrosion of pier will increase the seismic damage probability of itself, whereas it will result in a reduction of seismic damage probability of other components. Moreover, the alteration of seismic damage distribution of piers will amplify the effect. Due to the fact that the spatial chloride-induced corrosion of piers may alter the yield sequence of cross section, it then affects the seismic performance assessment of piers. A method to determine the evolution probability of yield sequence of corroded piers is proposed at last. From the result, the evolution probability of yield sequence of piers in longitudinal direction depends on the relationship between the height of piers and submerged zone. Moreover, the height of piers, submerged zone, and tidal zone have a common influence on the evolution of yield sequence of piers in transversal direction.
<p>Super High-pier Multi-span Cable-Stayed (SHMCS) bridges has been used to span the wide canyon terrain around the world, such as the Millau Viaduct in France, the Mezcala Bridge in Mexico and the Chishi Bridge in China. To study the seismic behaviour of SHMCS bridges that rare literature mentioned previously for practical application, the Chishi Bridge is taken as an example in this work. We first introduced the unique characters of this bridge. To study the seismic behaviour of SHMCS bridges, we built the finite element dynamic model of the case-study bridge by considering complex nonlinearities of structure. Then, according to the specification standard spectrum, three motions are selected to perform the nonlinear time history analysis. The structure dynamic responses for different connection conditions between the girder and the tower are compared to determine appropriate connection conditions for SHMCS bridges. It is concluded that the influence of connection conditions on the deformation of bridge is more remarkable than internal force due to the flexible super high piers and the isolation measure of suspend the girder isn't suitable for SHMCS bridges. Non-uniform connection conditions should not be used because it will lead to irregular distribution of internal force. Damper can expedite the ability of dissipating energy and but can't decrease the maximum displacement or deformation significantly, so the seismic performance of structure can't improve remarkable by simply adding damper. Generally, the connection conditions that the girder consolidate to all the four towers and set damper at the end of girder can be used as the optimal SHMCS bridge connection conditions.</p>
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