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This paper proposes an alternative time-dependent seismic fragility assessment framework for aging highway bridges considering the non-uniform chloride-induced corrosion and various modeling uncertainty parameters. Firstly, sensitivity analysis with the tornado diagram technique is performed to determine the sensitivity of some typical bridge engineering demand parameters (EDPs) to 22 modeling related uncertain parameters, and then 10 critical parameters are identified. Subsequently, based on a series of nonlinear time history analyses (NLTHAs) on the sample models generated by using the Latin hypercube sampling (LHS) method, comparative studies for the time-invariant and time-evolving seismic response, as well as the time-dependent seismic fragility estimates incorporating different levels of uncertainty are performed, respectively. It is concluded that (1) the uncertainty of the modeling related uncertain parameters may lead to the difference in the trajectory of seismic hysteretic response for a given bridge member, whereas the variation of the peak value of seismic response may result from the couple contributions of the uncertainty of ground motions and modeling related parameters; (2) the inclusion of only ground motion uncertainty is inadequate and inappropriate, and the proper way is to incorporate the uncertainty of the identified critical modeling parameters and ground motions into the time-evolving seismic response and the time-dependent seismic fragility assessment of the deteriorating highway bridges. [ABSTRACT FROM AUTHOR]

This paper proposes an improved uniform design (UD)-response surface model (RSM) method to reduce the impacts of sample correlation among small sample data caused by UD method and variable substitution process in the traditional UD-RSM method. The proposed B-spline-PLS-UD-RSM method, which is a systematic approach that combines nonlinear B-spline functions, the conventional UD-RSM method and the partial least-squares (PLS) regression technique, assesses the reliability of structures with high nonlinearity and multi-dimensionality. First, two reliability examples from the literature are investigated to demonstrate the efficiency and accuracy of the proposed RSM method. Subsequently, to investigate the applicability of the proposed method in seismic fragility analyses considering various parameter uncertainties and variable correlation, an alternative seismic fragility assessment framework is developed for highway bridges. Furthermore, this paper uses a typical multi-span reinforced concrete continuous girder (MSRCCG) bridge as a case study and performs a comparative analysis of the corresponding seismic fragility evaluations at both bridge component and system levels by using traditional and improved RSM methods. The results indicate the following conclusions: (1) The proposed B-spline-PLS-UD-RSM method can properly reduce the effect of sample correlation and achieve satisfactory reliability results for structures with highly nonlinear and multi-dimensional features through a much smaller sample size; (2) The proposed seismic fragility assessment framework is a good candidate for evaluating the seismic vulnerability of highway bridges incorporating variable correlation of structural parameters; (3) Seismic fragilities of bridge structures tend to be overestimated by using traditional UD-RSM methods and by ignoring the variable correlation of structural random parameters. [ABSTRACT FROM AUTHOR]

Traditional sacrificial concrete shear keys are generally employed in highway bridges to restrain the excessive transverse displacements of the bridge superstructures and protect the substructures from being seriously damaged under the earthquakes. However, the post-earthquake rehabilitation or reconstruction of the conventional concrete shear keys are difficult and inconvenient. To this end, this paper proposed and designed a novel modified post-tensioned unbonded prestressing ultra-high-performance-concrete (UHPC) prefabricated retaining block (UHPC-PRB) structure with the straight joint connection. The novel UHPC-PRB structure consisted of a prefabricated UHPC retaining block, a prestressing anchorage system, and a cast-in-situ cap beam. The prefabricated UHPC retaining block was installed to the cast-in-situ cap beam using the unbonded prestressing tendons. The proposed UHPC-PRB structure is supposed to be effective in not only providing the same functionality as that of the traditional concrete shear keys, but also is expected of simplifying the retrofit procedure and reducing the rehabilitation expense simultaneously. To investigate the seismic behavior of the proposed UHPC-PRB structure, four test specimens were designed and the pseudo-static tests were carried out. The damage process, displacements, strains, and stress states of the specimens were studied. In addition, the influences of the loading height, thickness of the UHPC retaining block, and the initial tension of prestressing tendons on the seismic performance of the proposed UHPC-PRB structures were also examined. Finally, the experimental results indicated that, (i) the proposed UHPC-PRB structures had excellent lateral deformation capacity and self-resetting ability; (ii) the initial tension of prestressing tendons had significant effects on the lateral displacement, critical rotational load, and horizontal load-carrying capacity of the UHPC retaining blocks; (iii) the prestress loss of prestressing tendons had certain effect on the development of the bilinear analytical model of the UHPC retaining blocks, but this effect could be ignored in practical highway bridges; and (iv) increase of the horizontal loading height could reduce the critical rotational load and load-carrying capacity of the UHPC retaining blocks. [ABSTRACT FROM AUTHOR]

In this study, the longitudinal seismic fragility of a five-span cable-stayed bridge with tall piers is investigated using the fragility method. The OpenSees is applied to develop a finite element model of the cable-stayed bridge, and both the geometric and material nonlinearities are considered. A suite of 80 ground motions is selected to perform the nonlinear time history analysis, and the seismic responses of the expansion joint, deck, cables, and piers are discussed to determine the damage indexes of these components. Next, fragility curves are developed to assess the seismic performance of the cable-stayed bridge. The results show that the expansion joint, deck and cables are the vulnerable components, while the failure probability of the pier is relatively low. Moreover, the effects of the deck-pier connections and viscous fluid dampers on the vulnerability of the components and the bridge system are also studied. It is shown that the vulnerability of the cable and deck is sensitive to the deck-pier connections. Moreover, the deck-pier connection enhances the stiffness of the cable-stayed bridge. Therefore, it affects the seismic response of the cable-stayed bridge. However, the deck-pier connection has relatively slight effect on the system fragility. Furthermore, the location of the viscous fluid dampers significantly affects their effectiveness. [ABSTRACT FROM AUTHOR]