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Earthquake-induced pounding in bridges is a complex contact phenomenon in which the dynamic responses of structures, including collisions between deck and abutments, are strongly related to structural properties and earthquake excitation. The goal of this study is to develop and compare the seismic fragility curves of overall system and individual components of regular and irregular box-girder highway bridges in two cases: with pounding and without pounding. For this purpose, four levels of altitudinal irregularity, ranging from regular to highly irregular, are considered. To extend the results for all bridges in the same class, different sources of uncertainties related to earthquakes, structural geometries, and material properties are taken into account. The analytical fragility curves have been developed based on nonlinear time history analyses in OpenSees finite element software for the cases with and without pounding effects. The process has been repeated for each two-, three-, and four-span classes at four irregularity levels. The fragility function parameters for the two cases with and without pounding have been compared for all classes considered in this study. Using fragility functions, this paper clarifies the interactive roles of irregularity and pounding between deck and abutments for seismic vulnerability of multi-span box-birder highway bridges. The results indicate that collisions often show an adverse effect on all structural components. It has also been observed that the detrimental effect of pounding on seismic fragility is more apparent in irregular bridges when compared with regular ones. In addition, the study introduces a conversion coefficient to clarify the effects of pounding on the fragility of bridge components and the overall system. This coefficient can be applied in both conventional analytical methods like static or simplified analysis and technical earthquake models like HAZUS, adjusting fragility values for pounding and irregularity effects. [ABSTRACT FROM AUTHOR]

The accuracy of local contractors in constructing Low-rise RC structures located in small towns is subjected to substantial fluctuations that increase the vulnerability of these structures, especially when sequential excitations are under consideration. Four major construction deficiencies are identified in this study by an initial field survey and are then considered in numerical modeling of a 3-story RC moment frame. The median collapse capacity (MCC) of Low-rise RC moment frames under sequential excitations is evaluated in presence of construction faults identified in a field study. Various mainshock levels represented by their maximum inter-story drifts are then imposed on the as-designed and the deficient structures. Following each mainshock, the median collapse capacities (MCCs) of the structures under the aftershock are computed using the IDA method. Investigating the obtained MCCs showed that unintended increase of the beams' width can help in reducing structure's vulnerability against sequential excitations. Despite this, the comparison of the residual drifts imposed by the mainshocks showed the decreased ductility caused by this construction deficiency. Ranking the MCC reductions caused by the other deficient models, the highest vulnerabilities were posed by the models that caused larger column plasticities at the collapse state and prevented effective yielding of the beams. [ABSTRACT FROM AUTHOR]

It has been observed from failures of highway bridges during major earthquakes that skew bridges are among the most vulnerable to seismic loading. It has been shown that the coupling between the translational motions of the deck and the collision of the deck with the abutments are two major factors influencing the vulnerability of skew bridges. This paper studies the influence of deck–abutment collision (seismic pounding) on the coupled motions of decks of skew bridges during strong earthquakes using an analytical approach. A three-degree-of-freedom model is presented to study key dynamic features of skew bridges. It is assumed that the deck of the model is rigid and the columns remain elastic during the ground motion. Contact planes between the deck and the abutments are idealized by several contact points pairwise arrayed at the end-span expansion joints. The mechanism of energy absorption and dissipation during the contact duration is simulated through the implementation of a nonlinear contact element between the contact points. A parametric study has been carried out by varying different parameters, including the skew angle (β), the size of the gap between the deck and the abutments at the end-span expansion joints (gap), and the normalized stiffness eccentricity along the x-axis (ex/r). The results of this study show that the transverse displacements of acute corners of the deck and the rotation of the deck about the mass center noticeably increase with the increases of β and ex/r, and with the decrease of the gap. [ABSTRACT FROM AUTHOR]

Due to the correlation of natural vibration modes of skewed bridges, and the multi-directional nature of the earthquake ground motions; piers of skewed bridges would be subjected to combined axial, flexural and torsional loadings. The characteristic of combined loading of the piers depends upon several parameters including the strong ground motion characteristics and the structural system type. In this research, seismic performance of a group of torsion sensitive skewed bridges with three different pier-deck connections is studied. Skew angles vary from 0° to 60°. Seismic performance of the bridges is investigated conducting bidirectional nonlinear time history analysis in OpenSees. Considering the effect of different pier-deck connection types, combined loading demand on the skewed piers is compared with those on the straight piers. On the basis of results, for both pinned and fixed piers, ductility demand increases with the skew angle. Opposed to pinned piers, fixed piers are subjected to combined torsional-flexural loadings, and the torsional demand increases with an increase in the skew angle. The value of torsional demand on fixed piers is limited to one half of cracking torque of the section (Tcr/2). Concerning the collapse prevention criteria, 30 degree skew angle is found to be a threshold skew angle. For bridges with skew angles greater than 30 degree, applying monolithic pier-deck connections is more sensible. [ABSTRACT FROM AUTHOR]