Strong Motion Research Articles

Optimization of tuned mass dampers – minimization of potential energy of elastic deformation

A tuned mass damper (TMD) optimization can be performed under various assumptions and objectives. All the variables of the optimization, such as structural model, performance index and load type affect the optimal parameters of the TMD. This paper presents a new optimization method that implements straightforward performance index and allows taking load spectral characteristics into account. Thanks to the usage of modal coordinates, the method allows fast numerical optimization of TMD attached to large or complicated structures with numerous degrees of freedom. One of the complicated tasks while optimizing TMD is the choice of a performance index. In this paper, the mean value of potential energy stored in the elastic deformation of a structure under periodic load serves as a performance index, which leads to a low numerical complexity task if the optimization is performed in the frequency domain. The new method also allows a simple inclusion of load spectral characteristics and permits TMD optimization for any loading spectral range. When applied to a structure with a single degree of freedom, this method leads to H2 optimization in the case of white noise excitation. However, it is applicable to multiple degrees of freedom structures with single or multiple TMDs and any given load. The paper also presents several examples of numerical optimization of the TMD attached to both single and multiple degrees of freedom structures under various loads, including white noise excitation, pedestrian load, and earthquake strong motion.

A non-parametric model of ground motion parameters for shallow crustal earthquakes in Europe

The current study focuses on deriving ground motion models (GMMs) for 21 ground motion parameters derived from data sourced from the Engineering Strong Motion (ESM) database. These parameters include Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), Peak Ground Displacement (PGD), PGV-to-PGA ratio, (V/H) PGA ratio Predominant Frequency (Fp), Central Frequency (Ω), Spectral Parameter (q), Significant Duration (TSig), Root Mean Square Acceleration (Arms), Arias Intensity (Ia), Cumulative Absolute Velocity (CAV), Characteristic Intensity (IC), Acceleration Spectrum Intensity (ASI), Velocity Spectrum Intensity (VSI), Total Energy (Eacc), Spectral Centroid (Ew), Spectral Standard Deviation (Sw), Temporal Centroid (Et), Temporal Standard Deviation (St), and Correlation between time and frequency [ρ(t,ω)]. Both horizontal and vertical components are considered in this study. The inherent random effects within ground motion regression, encompassing inter-event, inter-site, inter-locality, and inter-region variabilities, are addressed using cross-nested mixed effect regression utilizing a non-parametric GMM approach employing Artificial Neural Network (ANN). Quantitative assessment of the models involves correlation coefficients for regression through the origin and error measures like mean squared error and mean absolute error. These findings of the assessment confirm reliable estimates of Ground Motion Parameters (GMPs). A comparison of GMPs computed using the proposed model and those reported in the literature indicated model's superior performance. Furthermore, satisfactory performance of the proposed GMM in ground motion simulation for the ESM region is demonstrated.

Seismic Performance of Bridge Expansion Joints with and without Viscous Dampers during the 6 February 2023 Kahramanmaraş Earthquakes

Expansion joints render bridge structures highly vulnerable to damage during strong ground motions. Failures of expansion joints triggered by earthquakes not only jeopardize the post-earthquake serviceability of the bridge but also have a significant impact on the bridgeâs overall seismic performance. Despite extensive investigations and efforts to integrate these measures into design specifications aimed at mitigating the consequences of relative movements between adjacent bridge spans, major earthquakes have still revealed instances of damage related to expansion joints. On 6 February 2023, strong earthquake sequences occurred in KahramanmaraÅ, Turkey, with magnitudes of M7.7 and M7.6. The fault lines and epicenters of these shallow earthquakes were near the city and town centers and caused severe structural damage to buildings and infrastructures. There are approximately 1000 railway and highway bridges in the earthquake-affected region. Although both highway and railway bridges have generally performed well, some bridges experienced structural damage during the KahramanmaraÅ earthquakes. A large number of damage on the bridges is due to pounding and opening relative movements in expansion joints. This paper presents a comprehensive seismic evaluation of expansion joint failure mechanisms on bridges without viscous dampers during the 2023 KahramanmaraÅ earthquake sequences and an in-depth investigation into the seismic performance of bridge expansion joints equipped with viscous dampers and shock transmission unit devices are implemented utilizing the strong ground motion data collected throughout the earthquake sequences. It can be stated that the near-fault induced significant directivity and fling effects, resulting in notable velocity pulses and permanent tectonic deformations, and that these effects contributed to the failures of expansion joints, viscous damper devices, pot bearings, and shear keys.

Dynamic response of seabed in wind power of deep-shallow sea induced by internal solitary waves

With the development of offshore wind power projects worldwide, the stability of deep and shallow sea wind power sites has become a crucial concern. Internal solitary waves (ISWs) are nonlinear and large amplitude waves in the stratified ocean. Their strong vertical and horizontal motion and vorticity and turbulence caused by fragmentation have an important impact on the marine environment, seabed sediments, and marine engineering. This study focuses on the interaction between ISWs and the seabed of wind power sites in deep and shallow seas. Specifically, we investigate the interaction between ISWs and monopile foundations or floating fan plate anchor structures in the seabed. Through the simulation of CFD software and Comsol software, a law of seabed pore pressure variation during the effect of ISWs on the structure can be well demonstrated. Our results demonstrate that ISWs induce the accumulation of excess pore water pressure around the structures. The monopile foundation experiences negative excess pore water pressure at its bottom and the plate anchor at its top. The pore water pressure at the bottom of the monopile foundation initially decreases and then increases. In contrast, the pore water pressure at the right side of the monopile foundation increases, decreases, and then increases. This phenomenon promotes the settlement of the structure. At the bottom of the plate anchor, there is a sharp increase in positive excess pore water pressure by ISW. The pore water pressure above the plate anchor structure initially decreases and then increases, while below the plate anchor, it increases and then decreases. This phenomenon leads to the movement of the anchorage structure and instability of the surrounding soil. The influence of ISWs on the seabed bottom intensifies with the obstruction of the structure, resulting in significant positive pressure at the bottom. Between the two anchoring structures, there is increased seepage of pore water, making the seabed more prone to instability. Through the study of this article, we know that ISW has different effects on the force of monopile foundation and plate anchor structure, which provides a favorable basis for its design and maintenance.

Characteristics of strong ground motions and structural damage patterns from the February 6th, 2023 Kahramanmaraş earthquakes, Türkiye

Characteristics of strong ground motions and structural damage patterns from the February 6th, 2023 Kahramanmaraş earthquakes, Türkiye

Motion Clutter Suppression for Non-Cooperative Target Identification Based on Frequency Correlation Dual-SVD Reconstruction.

Non-cooperative targets, such as birds and unmanned aerial vehicles (UAVs), are typical low-altitude, slow, and small (LSS) targets with low observability. Radar observations in such scenarios are often complicated by strong motion clutter originating from sources like airplanes and cars. Hence, distinguishing between birds and UAVs in environments with strong motion clutter is crucial for improving target monitoring performance and ensuring flight safety. To address the impact of strong motion clutter on discriminating between UAVs and birds, we propose a frequency correlation dual-SVD (singular value decomposition) reconstruction method. This method exploits the strong power and spectral correlation characteristics of motion clutter, contrasted with the weak scattering characteristics of bird and UAV targets, to effectively suppress clutter. Unlike traditional clutter suppression methods based on SVD, our method avoids residual clutter or target loss while preserving the micro-motion characteristics of the targets. Based on the distinct micro-motion characteristics of birds and UAVs, we extract two key features: the sum of normalized large eigenvalues of the target's micro-motion component and the energy entropy of the time-frequency spectrum of the radar echoes. Subsequently, the kernel fuzzy c-means algorithm is applied to classify bird and UAV targets. The effectiveness of our proposed method is validated through results using both simulation and experimental data.

Dynamic Rupture and Strong Ground-Motion Simulations of the 8 January 2022 Ms 6.9 Qinghai Menyuan Earthquake

Abstract The 2022 Ms 6.9 Qinghai Menyuan, China, earthquake is the most destructive earthquake to have occurred near the Lenglongling fault at the western segment of the Qilian–Haiyuan fault since 2016 Ms 6.4 Menyuan earthquake. The 2022 earthquake generated surface rupture measuring about 30 km with an unexpected maximum offset larger than 2.6 m in the epicentral area, and severely damaged the local infrastructure and transportation. To analyze the possible causes of the large surface slip and to reveal the rupture process, we modeled the dynamic rupture and strong ground motion of the 2022 Menyuan earthquake using the curved-grid finite-difference method. In the simulation, the geometry of the fault is constructed based on the observed trace of the surface ruptures. The background tectonic stress field is assumed to be uniform, and the slip-weakening law with the constant friction coefficients is adopted. Our modeling results showed that the rupture model with a focal depth of 6 km and a rupture width of 10 km provides a good fit to the observed surface slips and the field records. We also investigated the effects of the focal depth and the rupture size on the surface slips. It is found that under the same conditions, the dynamic rupture models with a larger rupture size generated greater coseismic slips at the surface. However, only the model with a relatively smaller rupture width produced an Mw∼6.7 event similar to the Menyuan earthquake. In contrast, the influence of the focal depth is less significant. The decrease of the focal depth only leads to a slight increase in surface slip. Our results illustrated that a surface-breaking rupture with a relatively narrow width may physically control the general characteristics of the earthquake. This study provides a new insight into the rupture dynamics of the 2022 Menyuan earthquake.

Focal mechanics and disaster characteristics of the 2024 M 7.6 Noto Peninsula Earthquake, Japan

On January 1, 2024, a devastating M 7.6 earthquake struck the Noto Peninsula, Ishikawa Prefecture, Japan, resulting in significant casualties and property damage. Utilizing information from the first six days after the earthquake, this article analyzes the seismic source characteristics, disaster situation, and emergency response of this earthquake. The results show: 1) The earthquake rupture was of the thrust type, with aftershock distribution showing a north-east-oriented belt-like feature of 150 km. 2) Global Navigation Satellite System (GNSS) and Interferometric synthetic aperture radar (InSAR), observations detected significant westward to north-westward co-seismic displacement near the epicenter, with the maximum horizontal displacement reaching 1.2 m and the vertical uplift displacement reaching 4 m. A two-segment fault inversion model fits the observational data well. 3) Near the epicenter, large Peak Ground Velocity (PGV) and Peak Ground Acceleration (PGA) were observed, with the maxima reaching 145 cm/s and 2681 gal, respectively, and the intensity reached the highest level 7 on the Japanese (Japan Meteorological Agency, JMA) intensity standard, which is higher than level 10 of the United States Geological Survey (USGS) Modified Mercalli Intensity (MMI) standard. 4) The observation of the very rare multiple strong pulse-like ground motion (PLGM) waveform poses a topic worthy of research in the field of earthquake engineering. 5) As of January 7, the earthquake had left 128 deaths and 560 injuries in Ishikawa Prefecture, with 1305 buildings completely or partially destroyed, and had triggered a chain of disasters including tsunamis, fires, slope failures, and road damage. Finally, this paper summarizes the emergency rescue, information dissemination, and other disaster response and management measures taken in response to this earthquake. This work provides a reference case for carrying out effective responses, and offers lessons for handling similar events in the future.

Smart3DMOT: Smart cascade 3D MOT tracking strategy with motion and appearance association

3D multi-object tracking (MOT) is pivotal for associating the trajectories of objects in autonomous driving. The integration of image and point cloud data in 3D MOT algorithms has emerged as a research hotspot, aiming to achieve both high precision and efficiency tracking. In this paper, we present Smart3DMOT, an novel method that leverages multi-modal detection data and incorporates a cascade matching strategy, intelligently utilizing motion and multi-modal appearance affinity for data association across frames. Our algorithm introduces two association models: the strong motion association model (SM-AM) and the multi-modal fusion feature association model (MMFF-AM), tailored to different tracking scenarios. The SM-AM robustly associates objects by enhancing motion similarity, while the MMFF-AM integrates multi-modal fusion features from images and point clouds to generate appearance similarity between objects and combine motion cues for joint reasoning. Finally, we propose a cascade tracking strategy with a “spatial tracking state confirmer” (STSC). The SM-AM and MMFF-AM models are performed staged matching facilitated by STSC. This intelligent implementation allows SM-AM or MMFF-AM to tackle instances with different tracking difficulties, maintaining the operational efficiency and tracking accuracy of trade-offs. Our approach demonstrates the effectiveness of the proposed modules through comprehensive ablation experiments and the results obtained in the KITTI and nuScenes benchmark show that our method attains state-of-the-art performance in 3D MOT.

Empirical approaches for non-linear site response: results for the ESG6-blind test

As a contribution to step 3 of the ESG6 blind prediction exercise, we present an application of two different, purely empirical approaches to estimate the strong ground motion at a soft site ("KUMA") from the observed ground motion at a reference rock site ("SEVO") for the two largest shocks of the Kumamoto 2016 sequence. The two methods estimate the non-linear transfer function between a reference rock and a sedimentary site by modifying the linear transfer function derived from weak motion recordings. The modification is based either on a machine learning tool based on a wide collection of Japanese weak and strong motion recordings and the associated site metadata (method 1), or on an estimate of a site-specific parameter related to an average non-linear site response (method 2). The acceleration time series are then derived at the sedimentary site of interest using an estimation of the time delay between wave arrivals at the rock and site stations, and a minimum phase assumption for the site transfer function. These predictions were made blindly, but after the ESG6 conference they could be compared both with the actual ground motion recorded at KUMA during the two shocks, and the average and range of all other predictions preformed for this benchmark. Both of these purely empirical methods provide an honorable prediction of usual engineering ground motion parameters of the two target events. The performance of these two purely empirical approaches is at least comparable to those of the numerical simulation methods for the foreshock—if not better—and slightly worse for the (largest) mainshock. As the methods required only recordings of weak motions at the target and a referent sites and very simple description of the soil profile. The use of moderate motions to constrain the frequency shift prediction for the second method and the consideration of an alternative phase modification are possible ways to improvement.Graphical

Source characteristics of the 2006 Pingtung earthquake doublet off southern Taiwan and the possible contribution of submarine landslides to the Tsunami

On 26th December 2006, two successive large earthquakes of Mw ∼7.0, occurred offshore southwest Taiwan, being 8 min apart, known as the 2006 Pingtung earthquake doublet. The earthquakes triggered a hazard chain consisting of regional-scale tsunamis, submarine landslides, and turbidity currents. The tsunami waves with moderate height (10–60 cm) were recorded by 12 tide gauges along southern Taiwan, Guangdong, and Fujian provinces. Submarine landslide-induced turbidity currents inflicted widespread damage to telecommunication cables across the Kaoping Canyon and Manila Trench. Although the mechanisms of the individual hazard in the chain have been investigated previously, the interaction mechanisms and the causal relationship among them remain unclear due to the complexity of the dynamic process. Here, with the best available instrumental records of these events, we first reexamined the earthquake doublet's source characteristics and obtained the earthquake source models using regional seismic waves, high-rate GPS displacements, and strong motion waveforms. We then conducted forward tsunami modeling, along with spectral analysis of the tide gauge records and backward tsunami ray tracing technique, to gain insight of the hydrodynamic features of tsunamis and the contribution of landslides to tsunami generation. The main findings can be summarized as follows. The centroid depth of the first earthquake was found to be ∼28 km, which is shallower than the local CWB catalog suggested. The slip distribution was characterized by two close slip patches, ranging over depths of 15–35 km and occupying 40 km along the strike. The shallower focal depth and normal-faulting mechanism can well explain the recorded tsunami waves. Notably, wave analysis suggests that tsunami waves induced by landslides may have occurred in two episodes. The first round was likely produced by the landslides triggered simultaneously by the initial earthquake doublet. The largest aftershock, which occurred 14 h after the doublet with a strike-slip mechanism, may have caused the landslides near the head of Kaoping Canyon and possibly the second-round tsunami.

High-Performance Suspension Bead Sensor Based on Optical Tweezers and Immuno-Rolling Circle Amplification.

In recent years, optical tweezers have become an effective bioassay tool due to their unique advantages, especially in combination with suspension beads, which can be applied to develop a high-performance analysis platform capable of high-quality imaging and stable signal output. However, the optical tweezer-assisted bead analysis is still at the early stage, and further development of different favorable methods is in need. Herein, we have first developed the optical tweezer-assisted immuno-rolling circle amplification (immuno-RCA) on beads for protein detection. Prostate-specific antigen was selected as the model analyte, and the immunosandwich structure on beads was built by the high affinity of "antibody-antigen". The "protein-nucleic acid" signals were effectively converted through the covalent coupling procedure of antibodies and oligonucleotides, further initiating the RCA reaction to achieve signal amplification. The individual beads with the strong irregular Brownian motion in a fluid environment were eventually trapped by the optical tweezers to acquire the accurate and high-quality signal. Compared with the conventional immunoassay on beads, the sensitivity of the developed strategy was increased by 587 times with a limit of detection of 4.29 pg/mL (0.13 pM), as well as excellent specificity, stability, and reproducibility. This study developed the new optical tweezer-assisted beads imaging strategy for protein targets, which has great potential for being applied to clinical serology research and expands the application of optical tweezers in the bioassays.

Collapse of the Dharahara Tower During the April 25, 2015 Nepal Earthquake: A New Interpretation Based on Video-Camera Footage

ABSTRACT Among the various important monuments impacted by the April 25, 2015 Mw7.8 Nepal earthquake, the Dharahara Tower located in Kathmandu suffered complete collapse. The collapse of the tower, a slender 60-meter-high old brick masonry structure with an almost cylindrical hollow shape, was captured by a low-quality video camera, which nonetheless helped to identify the critical moments. Initially, the tower descended more than 10 m vertically after a rupture at the base. After a few seconds, it overturned, disintegrating upon impact on the ground. At a distance of 1.3 km, an accelerometric station recorded the strong motion which was used as input of a discrete element model of the structure. Mechanical properties were taken from lab tests made on similar building materials. The Dharahara Tower had previously been analysed by other researchers using various methods. However, since they were apparently not aware of the mechanism observed in the video footage, their collapse models do not agree with this new evidence. For the initial phase of the collapse, the present model explains with great accuracy the observations of the video footage, but the final phase is dependent on various details, and modelling is not so robust.

A rapid and automated analysis procedure for seismic response of arch dams

The seismic safety of arch dams has long been a focal point of research. Due to the complexity of modeling and computation, analyzing the seismic response of arch dams using traditional finite element methods requires a considerable amount of time. In the event of a sudden earthquake, it is challenging to quickly obtain stress analysis results or conduct a safety assessment. To address these issues, a rapid and automated analysis procedure is proposed in this paper, providing seismic response of arch dams within hours after an earthquake. The procedure includes a pre-processing program, a computing program EACD-3D-2008, and a post-processing program, achieving a fully automated process from generating non-uniform earthquakes to analyzing dam dynamic responses and visualizing computation results. As a case study, the 294.5 m high Xiaowan arch dam in southwest China is analyzed, which is equipped with strong motion instruments that have recorded several small earthquakes. The case study revealed that accounting for the non-uniformity of the earthquake significantly improves simulation results, with maximum principal stresses typically occurring near the dam-foundation rock interface. Additionally, the procedure effectively compensates for missing data, allowing for the successful supplementation of the missing acceleration records. For stronger earthquakes, high-stress regions are clearly displayed in the result visualization, providing an effective reference for safety assessment. The case study validated the accuracy and wide applicability of the procedure, demonstrating its potential to offer valuable insights for similar analyses in various engineering projects.

Unveiling the Mechanisms of the 1819 M 7.7 Kachchh Earthquake, India: Integrating Physics‐Based Simulation and Strong Ground Motion Estimates

AbstractThis study provided a comprehensive understanding of the source process of the 1819 M 7.7 Kachchh Indian earthquake using physics‐based dynamic rupture modeling and strong ground motion simulations. We successfully simulated the spontaneous dynamic rupture along a curved non‐planar fault using the 3‐D curved‐grid finite‐difference method (CGFDM). The estimated earthquake magnitude is around 7.6, consistent with previous estimations. Our simulations accurately replicated macroscopic rupture patterns and surface deformation, showing agreement with observed data along the Allah Bund fault (ABF) with a maximum displacement ∼5.5 m at the Earth's surface. The maximum modeled coseismic slip on the fault was approximately 7.5 m. Notably, the ABF exhibited characteristics of a weak barrier (leaky barrier) at the bending part, allowing the rupture to propagate further. Despite limitations in surface deformation calculations, the modeled values aligned with the trend of surface fault slip, with a slight deviation in the epicenter toward the east compared to earlier studies. We observed a homogeneous principal stress oriented N25°E, consistent with the present day Indian plate motion. The estimated horizontal peak ground velocities (PGVh) and the maximum value of Intensity X+ aligns well with observations. Furthermore, conducting thorough case studies on significant earthquakes and potential seismic scenarios in stable continental regions is crucial. Such studies play a vital role in validating and improving dynamic rupture models. When combined with statistical methods, this research holds great promise for advancing seismic hazard assessments, earthquake engineering, and strategies for disaster management.

Development of the compound intensity measure and seismic performance assessment for aqueduct structures considering fluid-structure interaction

The primary motivation of this investigation is to develop the compound ground motion intensity measure (IM) for the seismic performance assessment of aqueduct structures. To achieve this goal, taking the typical aqueduct structure in Southwestern China as a case study, a three-dimensional finite element model of aqueduct-water-foundation fully coupling system is established. Moreover, for the seismic hazard, a total of 300 as-recorded ground motions based on the design response spectrum are selected from PEER-NGA strong ground motion database, including near-field non-pulse (NFNP), near-field pulse-type (NFP) and far-field (FF). Then, the nonlinear correlation between single IMs is considered by Copula function, the compound IM is proposed that can comprehensively characterize the seismic performance of the aqueduct structure. Based on evaluation criteria, the applicability of the proposed compound IM is compared and verified. Finally, the conditional probability function and the unconditional probabilistic seismic risk analysis is employed to evaluate the seismic performance of aqueduct structures. It can be concluded that the compound IM considers the acceleration, velocity and displacement factors, which improves the correlation, efficiency and proficiency of probabilistic seismic demand analysis. Furthermore, the compound IM can help to improve the accuracy of the structural seismic performance assessment and reduce the uncertainty of structural response estimation. In summary, the findings of this study highlight the significance of proposing the compound IM and developing fragility curves when evaluating the seismic performance of aqueduct structures.

ESenTRy: an on-site earthquake early warning system based on the instrumental modified Mercalli intensity

Earthquake early warning systems (EEWSs) are real-time seismology-based applications that purpose to reduce earthquake damage by taking some precautions for environments that are likely to be damaged. These systems are divided into two categories as on-site and regional. In this study, an on-site EEWS called ESenTRy, consisting of an accelerometer, GPS and communication components, has been designed. In this scope, a Windows operating system-based software has been developed using the .NET Framework and C# language. The developed software has the ability to read the Güralp Compressed Format strong motion data in real-time, compute the strong motion indices such as destructive intensity, real-time intensity and instrumental modified Mercalli intensity, issue an alarm in the target area and alert the defined Modbus clients. To test the reliability of ESenTRy, two simulations have been performed using the strong motion data belonging to the magnitude 7.7 Kahramanmaraş-Pazarcık earthquake that occurred in Türkiye on February 6, 2023, at 01:17:32 UTC and magnitude 5.9 Düzce-Gölyaka earthquake that occurred in Türkiye on December 23, 2022, at 01:08:15 UTC. In the test applications, depending on the distance between the stations and earthquake epicenters, the time difference between the Level-2 alarm trigger times and S-wave arrival times varied between 1.5 and 16 s, while the time difference between the Level-2 alarm trigger times and P wave arrival times varied between 0.5 and 29.5 s. The flowchart diagrams of the developed algorithm and results obtained from the simulations are presented in detail.

Development and experimental evaluation of cam-grip type compression-free energy dissipative braces

Recent efforts have focused on developing novel energy dissipation braces that allow only tensile yielding to overcome certain limitations of conventional braces and buckling-restrained braces (BRBs). Such limitations include insufficient information regarding the damaged state of braces in a post-earthquake scenario and the challenges associated with replacing heavy restraints to prevent steel cores from buckling. Generally, the available techniques adopt a saw-tooth mechanism that grips the core and only mobilizes the tensile forces in the brace. However, the discrete nature of saw-tooth systems may result in a slippage at the onset of the tensile loading cycle, thereby reducing the efficiency of the energy dissipation mechanism. This study introduces a novel Direction-based Force Control Mechanism (DFCM) utilizing a cam-type grip that ensures continuous gripping under reversed-cyclic loading. Using this mechanism, a new type of so-called compression-free energy dissipative braces (CEDBs) are developed and tested under reversed-cyclic loading. For this purpose, six CEDB specimens were fabricated and installed in a steel frame sub-assemblage. The frame-brace system was then subjected to quasi-static lateral drifts with increasing amplitudes to test the efficiency of the proposed device. The experimental results demonstrate that the proposed bracing system only mobilizes the tension forces with significantly low slippage with about 1 % drift (Δ ≈ 2 mm). The system also exhibits a stable energy dissipation mechanism and reliable hysteretic properties under multiple cycles of large inelastic deformations. Furthermore, the damaged steel cores can be conveniently observed and replaced after a severe shaking event, while the same DFCM can be repeatedly used. Therefore, the proposed bracing system emerges as a cost-effective option for enhancing the lateral performance of structures subjected to dynamic loadings and strong ground motions. Besides, an idealized hysteretic model for this system was developed and validated; two examples of specimens were conducted as uniaxial elements with the proposed bilinear hysteretic; based on experimental results, it is shown that the proposed bilinear hysteretic model can capture important mechanical properties and energy dissipation of the specimens with reasonable accuracy of both CEDB specimens which the average difference between experiment results and Idealized CEDBs in yield force is about 10.87 %, the ultimate force is about 1.90 %, and the corresponding cumulative energy dissipation is about 6.98 %.

Anchor chains—A simple low‐cost device to assist passage of small‐bodied mass fish

AbstractAttention has been placed on a variety of barriers that hinder fish passage in modern times. The most prevalent fish barriers were culverts which have negatively impacted waterway connectivity and fish habitats. For small‐bodied mass fish, high barrel velocities and turbulence have reduced fish swimming performance because of their weak swimming capabilities. In the present study, physical testing was conducted under controlled flow conditions to assess the extent and magnitude of turbulence characteristics, secondary flow and low‐velocity zones in a 0.5‐m‐wide box culvert barrel. Two cases were investigated; a reference case consisting of a smooth rectangular channel and a low‐cost design solution to improve upstream fish migration consisting of a single galvanized anchor chain fitted within a smooth rectangular channel. The single anchor chain was positioned towards one corner of the channel to induce asymmetric flow, reducing overall energy losses and enhancing the existing low‐velocity zone in the adjacent channel corner. The anchor chain induced a strong turbulent flow motion away from the anchor chain, characterized by higher Reynolds stress and turbulent kinetic energy, along with a distinct channel flow asymmetry. Conversely, the low‐velocity zone, between the anchor chain and the bottom channel corner, was significantly expanded with reduced longitudinal mean velocities and turbulent scales. Whilst the anchor chain link contributed to some complex localized wake flow, the anchor chain also influenced the distributions of normal turbulent stresses (v'z2 – v'y2), which in turn influenced the location of secondary flow cells. This secondary flow redirected low momentum fluid into the low‐velocity zones, setting the conditions for the favorable upstream passage of small‐bodied mass fish species.

Empirical relationships between Arias Intensity and peak ground acceleration for western China

There is little available attenuation relationship for Arias Intensity (AI) in China. Empirical relationships between AI and peak ground acceleration (PGA) provide another option for predicting AI. We establish empirical relationships for AI and PGA for western China, utilizing 3,169 horizontal and 979 vertical strong motion records with PGA ≥0.01 g from 274 earthquakes (MS 4.0–8.0), originating in eight provinces in southwest (Yunnan, Sichuan) and northwest China (Gansu, Shaanxi, Ningxia, Qinghai, Inner Mongolia, and Xinjiang). The influences of MS epicenter distance, and site conditions indicators VS30, generic site classes (i.e., rock and soil) are explored. The results show that the logarithm of AI increases linearly with the increase of the logarithm of PGA and MS, and decreases with the logarithm of VS30. However, the influence of site conditions on AI-PAG relationships can't be recognized by the simple generic rock and soil site classes. The epicenter distance has little effect on the AI-PAG relationships. Empirical relationships are developed to estimate horizontal or vertical AI as a function of PGA (basic model), PGA and MS (model 2) for southwest, northwest, and western China, using all the records. Empirical relationships for AI as a function of PGA, MS, and VS30 (model 1) are established using the 2,248 horizontal (70.9% of the total) and 670 vertical (68.4% of the total) records with VS30 between 148 and 841m/s. The notable disparity between model 1 of the southwest and northwest regions is chiefly attributed to local site conditions, indicating that the AI-PGA correlation is region-dependent. These findings enable one way of estimating AI for western China and will contribute to a better understanding of AI attenuation.