Earthquake Engineering & Structural Dynamics最新文献

Two columns of RC double-column medium-height bents (DCMBs) are normally connected by link beams to enhance the lateral stability. Serious damage and/or large residual displacement were repeatedly observed in the DCMBs after major earthquakes, which may make the bridges lose traffic functionality or even be demolished and rebuilt. To enhance the seismic performance of bridge structures with DCMB with link beams, the self-centering energy dissipation braces (SCEBs) were applied to the DCMB in the “K”-shaped arrangement scenario to replace the traditional link beams in this study. To this end, the design philosophies of the SCEBs in the DCMB were first developed based on the configuration and force analysis of the DCMB with SCEBs. Then, 1:4 scaled RC DCMB and DCMB with link beams specimens were designed. Based on the design philosophies and the hysteretic performance of the DCMB, a novel SCEB with U-shaped steel plates (SCEB-U) was developed and tested, and the test results showed that the SCEB-U exhibited a typical flag-shaped hysteretic behavior with great deformation capacity. Subsequently, the quasi-static cyclic loading test of the DCMB with SCEBs specimen was carried out, and a DCMB with link beams and a DCMB with energy dissipation braces (EDBs) with U-shaped steel plates (DCMB with EDB-Us) were also tested for comparison. The experimental results showed that the DCMBs with braces suffered the least damage compared with the DCMB with link beams, and there was no obvious damage in the column-brace connection regions. The DCMB with SCEB-Us exhibited excellent flag-type hysteresis behavior with large carrying capacity, stable energy dissipation, and satisfactory self-centering ability.

The self-centering braced double-column rocking bent (SBR bent) consisting of a double-column rocking bent and two replaceable braces in a chevron arrangement scenario has been developed to enhance the seismic resilience of bridge structures. This paper aims to experimentally investigate the seismic performance of the SBR bent with energy dissipation braces (EDBs) and the self-centering energy dissipation braces (SCEBs). To this end, first, the design criteria of the SBR bent were developed, and a simplified analytical model was established to predict the force-displacement relationship of the SBR bent. Subsequently, in order to meet the large deformation capacity of the rocking bent, U-plate energy dissipation braces (as U-EDBs) and self-centering combined disc spring U-plate braces (as U-SCEB) acting as replaceable braces were developed and tested to investigate their hysteretic behavior. The experiments on two 1:3 scaled SBR bents with the two types of replaceable braces (i.e., U-EDBs and U-SCEBs) subjected to quasi-static loading protocols, were then carried out to investigate their seismic performance. For comparison, a cast-in-place Reinforced concrete (RC) bent and a self-centering rocking bent without brace (SR bent) were also designed and tested. The results indicated that the self-centering combined disc spring U-plate brace exhibits a typical flag-shaped curve, in particular, has a large deformation capacity. Furthermore, SBR bent featured with prominent seismic performance in terms of large load-carrying capacity, excellent self-centering capability and stable energy dissipation ability, minor or no physical damage. Moreover, the external braces can be easily replaced if they are damaged after a severe earthquake.

The displacement response of a building structure to earthquake excitations is crucial for assessing its seismic damage, which is usually accompanied by structural nonlinear behavior. This study proposes an efficient method of quickly estimating the nonlinear displacement responses of seismically damaged buildings. By designing a set of sparsely and uniformly distributed samples in the multi-dimensional parameter space, this method traverses all these samples to find the best set of parameters for a parametric numerical model of the building that minimizes the error between the simulated and the measured responses. Compared to existing model-driven methods, the proposed method can efficiently match the high-dimensional parameters of the assumed parametric model without tedious and less robust iterative optimization, even if the instrumented building sustains severe seismic damage and deviates significantly from its initial state. The shaking table test data of a full-scale four-story reinforced concrete moment-resisting frame structure is used to justify the advantage of the method over the state-of-the-art optimization-based model-driven method. The proposed method successfully estimated the structural responses of all the stories of the building with an average error of 4.6% for the maximum inter-story drift across the five earthquake loading runs. It took only approximately 19 min to complete the calculation on a personal computer, which could be greatly accelerated given more computation cores because the traversal is inherently friendly to parallel computation.

A novel probabilistic Monte Carlo-based framework to conduct regional seismic risk assessments using simplified continuous models is proposed. The hazard at rock outcrop is defined by response spectral ordinates, which are simulated to account for spatial correlation and correlation across different periods simultaneously. For sites on firm and soft soils, a simplified site response analysis using a one-dimensional continuous non-uniform shear beam model is used to transform the hazard at rock outcrops to the hazard at all sites of interest. Uncertainty in the soil properties at each site is explicitly considered. Response spectra at each site are computed at the principal orientations of each building using recently proposed directionality models that permit the estimation of the seismic hazard at specific orientations. A one-dimensional continuous coupled shear-flexural beam model is used to simulate building dynamic properties accounting for modeling uncertainty and to obtain building responses for each building. The parameters of each model only require information on the building height and the lateral resisting system. All relevant uncertainties associated with each module of the framework are explicitly incorporated and propagated. Finally, a case study of tall buildings in San Francisco subjected to a magnitude 7.0 earthquake on the Hayward Fault is presented to illustrate how the framework can be implemented.

For shaking table tests, it is essential to increase the density of the structure by adding artificial masses, which serves as an equivalent density. This modification ensures adherence to the dynamic similarity criterion. However, for underwater shaking table and wave tests, the density of water cannot change, and an increase in the equivalent density of the structure results in a distortion of the test simulation of the fluid–structure interaction. To solve this problem, an innovative similarity law is proposed for the design of fluid–structure models by changing the cross-sectional dimensions of the structure. A series of bidirectional underwater shaking table tests and unidirectional wave tests were conducted to validate the proposed similarity law, and the traditional similarity law was analyzed for comparison. The test results indicated that the traditional scale model predicted the hydrodynamic pressure acting on the prototype with an error of approximately 50%. In contrast, the proposed scale model reduced this error to about 10%. Furthermore, the relative errors in predicting the displacement, acceleration, and strain of the prototype using the proposed scale model were all below 15%. This demonstrated the reliability of the proposed similarity law applied in the test design for fluid–structure models in underwater shaking table and wave tests.

While performing the capacity spectrum method in seismic design, it is essential to select a reasonable objective. In practice, the design objective is typically determined by estimated structural response. However, factors like ground-motion randomness, the deviation between the structural analysis model and the actual behavior, and other factors would introduce errors in estimation. Therefore, a redundancy design with consideration of safe storage from these errors is necessary. This study focused on errors in the structural analysis model specifically, particularly reinforced concrete members’ estimated yield deformation—an essential parameter in estimating structural response. Initially, the influence on yield deformation of the structure due to each member's estimated yield deformation was clarified theoretically in the capacity spectrum method. To supplement theoretical analysis, a pushover analysis was conducted based on an E-defense shaking table test specimen. Then, the effect of structural yield deformation on estimated response deformation was deduced according to Japanese seismic design guidelines and was verified based on a single-degree-of-freedom (SDOF) numerical analysis. By integrating these discussions, errors in estimated structural response caused by members’ estimated yield deformation can be evaluated. Consequently, a redundancy factor was proposed to include the safe storage from errors in RC member estimated yield deformation.

The urgent global drive to mitigate greenhouse gas emissions has significantly boosted renewable energy production, notably expanding offshore wind energy across the globe. With the technological evolution enabling higher-capacity turbines on larger foundations, these installations are increasingly situated in earthquake-prone areas, underscoring the critical need to ensure their seismic resilience as they become a pivotal component of the global energy infrastructure. This study scrutinises the dynamic behaviour of a 15 MW offshore wind turbine (OWT) under concurrent earthquake, wind and wave loads, focusing on the performance of the ultra-high-strength cementitious grout that bonds the monopile to the transition piece. Employing LS DYNA for numerical simulations, we explored the seismic responses of four OWT designs with diverse transition piece cone angles, incorporating nonlinear soil springs to model soil-structure interactions (SSIs) and conducting a site response analysis (SRA) to account for local site effects on ground motion amplification. Our findings reveal that transition pieces with larger cone angles exhibit substantially enhanced stress distribution and resistance to grout damage, evidenced by decreased ovalisation in the coned sections of the transition piece and monopile, and improved bending flexibility. The observed disparities in damage across different cone angles highlight shortcomings in current design guidelines pertaining to the prediction of grout stresses in conical transition piece designs, with the current code-specified calculations predicting higher stresses for transition piece designs with larger cone angles. This study also highlights the code's limitations when accounting for grout damage induced by stress concentrations in the grouted connections under seismic dynamic loading conditions. The results of the study demonstrate the need for refinement of these guidelines to improve the seismic robustness of OWTs, thereby contributing to the resilience of renewable energy infrastructure against earthquake-induced disruptions.

Post-tensioned self-centering (PTSC) structures that use PT tendons to assemble precast members and provide structural resistance have demonstrated superior seismic performance and self-centering capacity. Current PTSC frames generally serially connect all beams in a floor. This assembly method would induce interferences among different spans and increase the risk of progressive failure once local damage occurs in a bay. This paper proposes a new type of PTSC joint to avoid such serial connection of beams. By employing steel beams to serve as the anchorages of PT tendons, each bay of the frame is separately prestressed. The composite prestressed beams can be readily fixed to columns by high-strength bolts, hence facilitating the construction of such separately-anchored self-centering (SASC) frame building. External friction dampers are installed to enhance the energy dissipation capacity of SASC connections. Eight full-scale cyclic loading tests are performed to compare the performance of the new SASC connections with conventional PTSC joints and also comprehensively evaluate the seismic behavior of SASC connections with different parameters. The test results validate the excellent damage mitigation abilities of both types of connections while the superior mechanical performance of the new SASC connections. In addition, the effects of key design parameters such as initial prestress level, damper force, and tendon number on the seismic behavior of the SASC connection are evaluated, and design recommendations for the application of the proposed precast beam-column connection are also provided.