Summary This paper proposes a novel passive mass damper, namely, asymmetric nonlinear energy sink (Asym NES), which is characterized by integrating linear and nonlinear restoring forces to mitigate the unwanted responses of building structures. The Asym NES, configured based on a cubic NES, consists of an auxiliary mass connected to the primary structure through a linear and nonlinear springs. These two springs are statically balanced at a deformed position, producing an asymmetric restoring force in the Asym NES. The study commences with a detailed working principle of the Asym NES, and the equations of motion of an Asym NES‐attached system are derived. Subsequently, experimental studies on the Asym NES designed for a small‐scale three‐story steel frame are conducted; the natural frequencies of which can be altered by changing the number of columns per story. Moreover, the performance of the Asym NES is compared with a tuned mass damper (TMD) and a cubic NES under impulsive excitations. Test results demonstrate the effectiveness of the Asym NES as well as its robustness against changes in the structural frequency. Following the experimental studies, the validated Asym NES model is further applied in the numerical investigation on a six‐story benchmark building to highlight its effectiveness and robustness in potential practical applications. Besides the impulsive excitations, an ensemble of 106 seismic ground motions with wide‐ranged energies is applied to the structures with original and decreased frequencies. Numerical results show that the proposed Asym NES is as effective as the in‐tune TMD in response mitigation under seismic excitations and exhibits strong robustness against changes in both the energy level and the structural frequency. The ingenious design and excellent efficiency of the Asym NES can offer a promising type of high‐performance device for structural control under extreme events.

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The cross-sea bridges play an important role to promote the development of regional economy. These bridges located in earthquake-prone areas may be subjected to severe earthquakes during their lifetime. Group pile foundations have been widely used in cross-sea bridges due to their structural efficiency, ease of construction, and low cost. This paper investigates the seismic performance of bridge pile foundation based on the seismic fragility analysis. Based on the analysis platform OpenSees, the three-dimensional finite model of the bridge pile foundation is developed, where the pile-water interaction is replaced by the added mass method, nonlinear p-y, t-z, and q-z elements are used to simulate pile-soil interaction, and the displacement of the surface ground motion due to seismic excitations is applied on all spring supports. The seismic fragility curves of the bridge pile foundation are generated by using the earthquake records recommended by FEMA P695 as input motions. The curvature ductility based fragility curves are obtained using seismic responses for different peak ground accelerations. The effects of pile-water interaction, soil conditions, and different types of ground motions on the bridge pier fragilities are studied and discussed. Seismic fragility of the pier-group pile system shows that Sec C (the bottom section of the pier) is the most vulnerable section in the example fluid-structure-soil interaction (FSSI) system for all four damage LSs. The seismic responses of Sec E (a pile section located at the interface of the soil layer and water layer) are much lower than other sections. The parameter analysis shows that pile-water interaction has slight influence (less than 5%) on the fragility curves of the bridge pier. For the bridge group pile foundations considering the fluid-pile-soil interaction, PNF may induce larger seismic response than far-field (FF) and no-pulse near field (NNF). The bridge pile foundation in stiff soil is most vulnerable to seismic damage than soft condition.

This article studies the seismic response of a symmetric long-span cable-stayed bridge under longitudinal uniform excitations by finite element analysis and shaking table tests. The feasibility and method of performing shaking table tests are examined using a simplified half-bridge scale model. By taking advantage of the symmetry, it is possible to construct a scale model with a larger scale ratio than a full-bridge scale model. The main components of the scale model (i.e. tower, piers, girder, and cables) were fabricated using the same or similar materials as in the prototype. The design and construction of the scale model is presented. Longitudinal structural responses obtained from the finite element analysis and shaking table tests are compared. The seismic mitigation effects of viscous dampers are examined through shaking table tests.

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