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The spherical surface of the friction pendulum system (FPS) inevitably introduce a constant dominant period, which may lead to resonance problem when subjected to the ground motions with long-period components. In this study, a multiple-variable frequency pendulum isolator (MVFPI) was developed to overcome this limitation. The sliding surface of the MVFPI was predefined as a continuous piecewise function to combine the seismic performance of MVFPI with different seismic intensities. The high-performance materials, polytetrafluoroethylene (PTFE) fabric and shape memory alloy (SMA) were utilized to improve its durability and control the deformation. Based on the underlying principles of operation, the force-displacement relationships of the MVFPI were derived. A series of tests of high-performance materials and MVFPI were conducted to verify the accuracy of the derived hysteresis model. Parametric studies and optimal analysis were carried out on the critical parameters of the MVFPI. The results indicate that the MVFPI has the desired hysteretic behavior as prescribed by the derived formulas. Moreover, the seismic responses of the structure isolated by MVFPI with optimal parameters could be controlled within the desired range.

Orthotropic steel decks are vulnerable to fatigue cracking in welded connections and complex geometrical details. A total of three fatigue tests were conducted on segments of orthotropic steel deck to evaluate the fatigue performance of trough‐to‐crossbeam connections with various cut‐out configurations. In the tests, the specimens were subjected to cyclic three‐point bending load and the fatigue cracks were more likely to initiate from the cope holes in the crossbeam web rather than the trough‐to‐crossbeam fillet welds. Three‐dimensional finite element models (FEM) of the specimens were built and validated by the measured deflections and stresses. Using the validated FEM, the characteristic stresses based on the theory of critical distances (TCD) were calculated for the stress concentrations along the cope holes. The fatigue crack initiation life, predicted by the TCD‐based stress combined with the plain material S–N curve, agreed reasonably with the fatigue test results. The TCD method could further form a basis of fatigue crack propagation analysis using the fracture mechanics approaches.

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Summary Identification of nonlinear hysteretic systems has practical significance for the prediction of structural response. This paper develops a novel parameter identification method for nonlinear hysteretic systems. The Bouc–Wen model and its improved models are used to parametrically characterize the structural systems. Model parameters are identified using a given load‐displacement trajectory. The proposed method is developed under the framework of the sequence model optimization, which provides a broader search domain and needs fewer iterations. Firstly, a series of sensitivity analyses were conducted to investigate the effects of the Bouc–Wen parameters on the hysteresis behavior and to guide the identification process. Subsequently, based on the framework of the sequence model optimization, a novel strategy for identifying the model parameters of the nonlinear hysteresis system was proposed. Finally, the effectiveness and accuracy of the proposed algorithm were verified by the experimental data and numerical simulation results. The results indicate that the identified numerical model can accurately capture the strength and stiffness degradation and the pinching effect of the structural system. As a result, the predicted hysteretic trajectories are well agreed with the actual structural responses. The case studies demonstrate that the proposed method is sufficiently accurate and computationally efficient for the nonlinear hysteretic systems.

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