Search Results (321)

The steep bedding rock slope (SBRS) is easily destabilized under earthquake action, so it is crucial to research the features of this kind of slope’s seismic dynamic reactions in order to prevent and mitigate disasters. Few researchers have examined these slopes from an energy perspective, and the majority of recent research focuses on the displacement and acceleration response patterns of these kinds of slopes under seismic action. This work performed an extended study of a dynamic numerical simulation and systematically analyzed the dynamic response characteristics of this type of slope under earth quake conditions from the standpoint of energy utilizing the Hilbert–Huang transform (HHT) and marginal spectrum (MSP) theory. This was carried out in response to the slope’s shaking table test from our previous work. The findings indicate the following: (1) The ‘elevation effect’ and ‘surface effect’ are clearly seen in the acceleration amplification factor (AAF) of the slope during an earthquake. The selectivity of the slope acceleration’s Fourier spectrum amplification impact indicates that the elevation amplification effect makes the high-frequency peak’s amplitude more noticeable. (2) Although the effect of the weak layer is more pronounced in the high-frequency portion, both the elevation and the weak layer affect the seismic wave’s Hilbert energy. As a result, the weak layer at the top of the slope is usually destroyed first during an earthquake. (3) Prior to the locked segment’s penetration failure at the toe of the SBRS, the Hilbert energy of the high-frequency band of the marginal spectrum at the monitoring point on the top portion of the segment will rise sharply. This suggests that the upper portion of the locked segment has begun to sustain damage. There are antecedents even when there is no penetration failure. Full article

Settlement values calculated per the current “Code for Design of Building Foundations” demonstrate significant discrepancies when compared to the actual measured settlement values observed after disturbing a strong, cohesive soil foundation. This inconsistency introduces uncertainties in engineering design. To investigate the deformation behavior of highly structured clay, which is particularly sensitive to disturbances, this study employed a shaking table to subject undisturbed soil samples to various disturbance levels. The shaking frequencies were set at 20 Hz, 35 Hz, and 50 Hz, with durations of 30, 60, 90, and 120 min. One-dimensional compression tests were performed to examine the relationship between soil deformation parameters and overburden pressure, alongside an analysis of the deformation process and pore structure damage in the highly structured clay. A fitting process using Origin software was utilized to develop a deformation modulus calculation model that accounted for disturbance and damage effects, aiming to enhance the accuracy of foundation settlement predictions. The results indicate that the proposed empirical formula for the deformation modulus is highly reliable, which is essential for improving the precision of foundation settlement calculations and ensuring engineering safety. Full article

To address the growing need for sustainable and resilient building materials, the seismic performance of a full-scale moment-frame housing system constructed entirely from recycled Tetra Pak panels (thermo-stiffened polymeric aluminum or TSPA) was evaluated. The study presents an innovative approach to utilizing waste materials for structural applications, emphasizing the lightweight and modular nature of the system. The methodology included material characterization, finite element modeling (FEM), gravitational loading tests, and biaxial shake table tests. Seismic tests applied ground motions corresponding to 31-, 225-, 475-, and 2500-year return periods. Drift profiles and acceleration responses confirmed the elastic behavior of the system, with no residual deformation or structural damage observed, even under simultaneous peak ground accelerations of 0.37 g (x-direction) and 0.52 g (y-direction). Notably, the structure accelerations were amplified to 1.10 g in the y-direction (at the top of the structure), exceeding the design spectrum acceleration of 0.7 g without compromising stiffness or resistance. These results underscore the robust seismic performance of the system. The finite element model of the housing module was validated with the experimental results which predicted the structural response, including natural periods, accelerations, and drift profiles (up to 89% accuracy). The novelty of this research is that it is one of the first to perform shaking table seismic testing on a full-scale housing module made of recycled materials (Tetra Pak), specifically under biaxial motions, providing a unique evaluation of its performance under multidirectional seismic demands. This research also highlights the potential of recycled Tetra Pak materials for sustainable construction, providing an adaptable solution for earthquake-prone regions. The modular design allows for rapid assembly and disassembly, supporting scalability and the circular economy principle. Full article

The current study investigates the feasibility and performance of Fiber Bragg Grating (FBG) optical sensors in geotechnical engineering applications, aiming to demonstrate their broader applicability across different scales, from controlled laboratory experiments to real-world field implementations. More specifically, the research evaluates the sensors’ ability to monitor key parameters—strain, temperature, and acceleration—under diverse loading conditions, including static, dynamic, seismic, and centrifuge loads. Within this framework, laboratory experiments were conducted using the one-degree-of-freedom shaking table at the National Technical University of Athens to assess sensor performance during seismic loading. These tests provided insights into the behavior of geotechnical physical models under earthquake conditions and the reliability of FBG sensors in capturing dynamic responses. Additional testing was performed using the drum centrifuge at ETH Zurich, where physical models experienced gravitational accelerations up to 100 g, including impact loads. The sensors successfully captured the loading conditions, reflecting the anticipated model behavior. In the field, optical fibers were installed on the Perimeter Wall (Circuit Wall) of the Acropolis of Athens to monitor strain, temperature, and acceleration in real-time. Despite the challenges posed by the archaeological site’s constraints, the system gathered data over two years, offering insights into the structural behavior of this historic monument under environmental and loading variations. The Acropolis application serves as a key field example, illustrating the use of these sensors in a complex and historically significant site. Finally, the study details the test setups, sensor types, and data acquisition techniques, while addressing technical challenges and solutions. The results demonstrate the effectiveness of FBG sensors in geotechnical applications and highlight their potential for future projects, emphasizing their value as tools for monitoring structural integrity and advancing geotechnical engineering. Full article

Structural damages occurred during any earthquake arise not only from structural design flaw but also from the variability of sub-base soil behavior and the foundation system. For this reason, structure–soil–pile interaction has an important place in evaluating the behavior of a structure under dynamic effects. Bored pile application, which is one of the deep foundation systems, is a widely used method in the world to transfer the loads coming from the structure to the ground safely in problematic grounds. For this reason, in pile foundation system designs, how bored pile foundation systems will affect the structural design under earthquake loads is considered an important issue. In particular, how diagonally braced steel structures with piled raft foundation systems will behave under earthquake effects has been evaluated as a subject that needs to be examined. For this reason, this situation was evaluated as the main purpose of this study. The effect of the bored pile systems designed in different orientations on the behavior of diagonally braced steel structures during an earthquake under kinematic and inertial effects was investigated in detail within the scope of this study. Numerical analyses, based on data from shake table experiments on a scaled superstructure, examine various pile design scenarios. Experimental base shear force measurements informed the development of numerical scenarios, which varied pile lengths and inter-pile distances while maintaining constant pile diameters. This study analyzed the kinematic and inertial effects on the piles, offering insights into their structural behavior under seismic conditions. The increase in pile length and the increase in the distance between the piles caused a significant increase in the bending moment and shear force, which have an important place in pile design. Full article

Micropiles are a new type of retaining structure widely used in slope engineering due to their small footprint, low vibration and noise emissions, and simple construction process. This study aims to investigate the dynamic response and failure mechanisms of micropiles used in retaining accumulation landslides under seismic loading through shaking table tests and numerical simulation. The failure process, observed phenomena, and bending moments of micropiles in the test were discussed, and the shear force distribution of micropiles was thoroughly analyzed based on numerical simulation. The findings reveal that the natural frequency of the entire landslide system exhibits a gradual decrease and tends to stabilize under sustained earthquake excitation. The bending moment of micropiles follows an “S” shape, with a larger magnitude at the top and a smaller one at the bottom. Additionally, the shear force distribution exhibits a “W-shaped” pattern. Damage to micropiles mainly includes the flexural shear combination failure at the load-bearing section (which occurs within 1.4–3.6 times the pile diameter above the sliding surface) and the shear failure near the sliding surface. This study provides significant insights into the strengthening mechanisms of micropiles under seismic action and offers valuable guidance for the design of slope support. Full article

This study presents the results of an experimental investigation conducted on a 2:3 scale model of a two-story stone masonry building. We tested the model on the UniKORE L.E.D.A. lab shake table, simulating the Mw 6.3 earthquake ground motion that struck L’Aquila, Italy, on 6 April 2009, with progressively increasing peak acceleration levels. We installed a network of accelerometric sensors on the model to capture its structural behaviour under seismic excitation. Medium-to lower-cost MEMS accelerometers (classes A and B) were compared with traditional piezoelectric sensors commonly used in Structural Health Monitoring (SHM). The experiment assessed the structural performance and damage progression of masonry buildings subjected to realistic earthquake inputs. Additionally, the collected data provided valuable insights into the effectiveness of different sensor types and configurations in detecting key vibrational and failure patterns. All the sensors were able to accurately measure the dynamic response during seismic excitation. However, not all of them were suitable for Operational Modal Analysis (OMA) in noisy environments, where their self-noise represents a crucial factor. This suggests that the self-noise of MEMS accelerometers must be less than 1 µg/√Hz, or preferably below 0.5 µg/√Hz, to obtain good results from the OMA. Therefore, we recommend ultra-low-noise sensors for detecting differences in the structural behaviour before and after seismic events. Our findings provide valuable insights into the seismic vulnerability of masonry structures and the effectiveness of sensors in detecting damage. The management of buildings in earthquake-prone areas can benefit from these specifications. Full article

Seismic isolation and damping technologies, though extensively used in buildings, are less common in large hydraulic structures, underscoring the importance of researching seismic mitigation methods for these constructions. This research first establishes that saturated sandy soil can act as a damping material through experimental and theoretical analysis. Subsequently, a novel hollow concrete gravity dam containing saturated sandy soil is proposed, utilizing the EOS (equation of state) subroutine for viscous fluids to model the liquefied sand. The findings indicate that the new-type dam exhibits a reduction in displacement of approximately 20% along the flow direction under an 8-degree seismic event compared to conventional gravity dams. This decrease correlates inversely with the characteristic wave speed of the saturated sandy soil, while the energy dissipation capacity of the saturated sandy soil is directly proportional to the soil layer’s thickness. Finally, a small-scale shaking table test revealed that saturated sandy soil effectively reduces displacement and acceleration at the dam crest. These findings were corroborated by numerical simulations, which further substantiated the reliability of both the experimental and simulated data. Utilizing saturated sandy soil for energy dissipation and seismic damping in dams offers cost benefits, high durability, and significant effectiveness, representing a promising direction for the advancement of seismic mitigation in concrete gravity dams. Full article

Unmanned aerial vehicle (UAV) vision-based sensing has become an emerging technology for structural health monitoring (SHM) and post-disaster damage assessment of civil infrastructure. This article proposes a framework for monitoring structural displacement under earthquakes by reprojecting image points obtained courtesy of UAV-captured videos to the 3-D world space based on the world-to-image point correspondences. To identify optimal features in the UAV imagery, geo-reference targets with various patterns were installed on a test building specimen, which was then subjected to earthquake shaking. A feature point tracking-based algorithm for square checkerboard patterns and a Hough Transform-based algorithm for concentric circular patterns are developed to ensure reliable detection and tracking of image features. Photogrammetry techniques are applied to reconstruct the 3-D world points and extract structural displacements. The proposed methodology is validated by monitoring the displacements of a full-scale 6-story mass timber building during a series of shake table tests. Reasonable accuracy is achieved in that the overall root-mean-square errors of the tracking results are at the millimeter level compared to ground truth measurements from analog sensors. Insights on optimal features for monitoring structural dynamic response are discussed based on statistical analysis of the error characteristics for the various reference target patterns used to track the structural displacements. Full article

Major earthquakes and rainfall may occur at the same time, necessitating further investigation into the dynamic characteristics and responses of reinforced soil retaining walls subjected to the combined forces of rainfall and seismic activity. Three sets of shaking table tests on model retaining walls were designed, a modular reinforced earth retaining wall was utilized as the subject of this study, and a custom-made device was made to simulate rainfall conditions of varying intensities. These tests monitored the rainwater infiltration pattern, macroscopic phenomena, panel displacement, tension behavior, dynamic characteristics, and acceleration response of the modular reinforced earth retaining wall during vibration under different rainfall intensities. The results indicated the following. (1) Rainwater infiltration can be categorized into three stages: rapid rise, rapid decline, and slow decline to stability. The duration for infiltration to reach stability increases with greater rainfall. (2) An increase in rainfall intensity enhances the seismic stability of the retaining wall panel, as higher rainfall intensity results in reduced sand leakage from the panel, thereby diminishing panel deformation during vibration. (3) Increased rainfall intensity decreases the shear strength of the soil, leading to a greater load on the reinforcement. (4) The natural vibration frequencies of the three groups of retaining walls decreased by 0.21%, 0.54%, and 2.326%, respectively, indicating some internal damage within the retaining walls, although the degree of damage was not severe. Additionally, the peak displacement of the panel increased by 0.91 mm, 0.63 mm, and 0.61 mm, respectively. (5) The amplification effect of rainfall on internal soil acceleration is diminished, with this weakening effect becoming more pronounced as rainfall intensity increases. These research findings can provide a valuable reference for multi-disaster risk assessments of modular reinforced soil retaining walls. Full article

Today, various systems are used to reduce vibrations in civil engineering structures. Among these systems, tuned liquid dampers are the preferred passive systems due to their ability to be designed in different geometries, their low cost, their ease of installation, and their low maintenance costs. This study examines the effectiveness of tuned liquid dampers (TLD) and tuned liquid column dampers (TLCD) under identical geometric conditions and harmonic ground motion to assess which is more efficient in controlling the behavior of a three-storey steel shear frame model equipped with these systems. A small-scale, three-storey shear frame model placed on a uniaxial shaking table was subjected to harmonic motion with a 5 mm amplitude, 1.4 Hz frequency, and 10 cycles. The chosen frequency aligns with the resonance frequency of the undamped building model’s first mode. Both TLD and TLCD tanks, positioned atop the structure, share a geometry of 30 cm in length and 10 cm in width, with variable liquid heights of 5, 10, 15, and 20 cm. Mounting TLD and TLCD models with four different liquid heights on the undamped model resulted in nine distinct setups. In this designed scenario, the TLDs and TLCDs on the undamped shear frame were compared according to liquid heights at rest. To identify the best-performing system based on liquid height, response displacement–frequency graphs were generated for all models within a frequency range of 0.5–2.5 Hz, and damping ratios were calculated using the half-power bandwidth method. Additionally, harmonic ground motion experiments at the resonance frequency compared both acceleration and displacement values over time for damped and undamped models. Peak acceleration and displacement values on each floor were also analyzed. The results highlight which system proves more effective based on damping ratio, acceleration, and displacement values under equivalent conditions. Full article

The seismic vulnerability of reinforced concrete (RC) buildings has been an important issue, especially in earthquake-prone regions with limited seismic design codes such as South Sudan. Improving the seismic performance of reinforced concrete buildings is critical for maintaining structural functionality under normal service loads and for rapid recovery after natural disasters such as earthquakes. This research aims to thoroughly assess the methods used to evaluate the seismic vulnerability of RC frame structures in pre- and post-earthquake scenarios. The primary objective is to provide a comprehensive framework that integrates empirical, analytical, and experimental methods, categorizing existing assessment methods and proposing improvements for resource-constrained environments. However, empirical methods have always used historical earthquake data to estimate potential damage. In contrast, analytical methods have used computational tools such as fragility curves to assess the probability of damage at different seismic intensities. Additionally, experimental methods, such as shaking table tests and pseudo-dynamic analyses, have validated theoretical predictions and provided insights into structural behavior under simulated conditions. Furthermore, key findings highlight critical vulnerabilities in RC buildings, quantify damage probabilities, and compare the strengths and limitations of different assessment methods. However, challenges such as limited data availability, computational limitations, and difficulties replicating actual conditions in test setups highlight areas for improvement. By addressing these challenges, the review provides recommendations for future studies, including integrating advanced computational and regional hazard characterization methods, improving experimental methods to enhance the accuracy of vulnerability assessments, and ultimately supporting the design of more resilient RC structures and increasing disaster preparedness. Full article

Chromite is considered a strategic mineral in the global economy. It is mainly used as an essential raw material in the production of stainless steel and other metal alloys due to its corrosion and heat resistance properties. High-grade chromite resources are gradually depleting; with the increasing chromite demand in metallurgical applications, studies have focused on exploring low-grade and alternative chromite sources. This study proposes a cost-effective processing flowsheet for the low-grade middle group 2 (MG2) chromite layer, a poorly explored chromatite seam within the South African bushveld igneous complex (BIC). The study involved mineralogical characterization followed by gravity and magnetic separation of the low-grade MG2 ore at 18.18% Cr₂O₃. Characterization by XRD and Auto-SEM revealed that the ore mainly consists of pyroxene, chromite, and feldspar, with other minerals in trace quantities. The gravity separation test by shaking table upgraded the chromite (Cr₂O₃) to 42.0% at high chromite recoveries, whereas the laboratory Slon wet high-intensity magnetic separation method (SLon WHIMS) upgraded the chromite in the feed to 42.95% grade at lower chromite recoveries. Desliming the sample before the gravity and magnetic separation tests significantly improved the separation. The magnetic separation tests further demonstrated that chromite within the MG2 layer is sensitive to magnetic separation due to its high iron content. The adapted flowsheet is proposed as a cost-effective flowsheet for processing the low-grade MG2 layer. The flow sheet can be optimized by conducting the SLon WHIMS tests at high intensities followed by fine gravity tests by spiral circuits to maximize the chromite recovery while achieving commercial chromite grades and a Cr:Fe ratio greater than 1.5. Full article

The accurate and timely acquisition of high-frequency three-dimensional (3D) displacement responses of large structures is crucial for evaluating their condition during seismic excitation on shaking tables. This paper presents a distributed high-speed videogrammetric method designed to rapidly measure the 3D displacement of large shaking table structures at high sampling frequencies. The method uses non-coded circular targets affixed to key points on the structure and an automatic correspondence approach to efficiently estimate the extrinsic parameters of multiple cameras with large fields of view. This process eliminates the need for large calibration boards or manual visual adjustments. A distributed computation and reconstruction strategy, employing the alternating direction method of multipliers, enables the global reconstruction of time-sequenced 3D coordinates for all points of interest across multiple devices simultaneously. The accuracy and efficiency of this method were validated through comparisons with total stations, contact sensors, and conventional approaches in shaking table tests involving large structures with RCBs. Additionally, the proposed method demonstrated a speed increase of at least six times compared to the advanced commercial photogrammetric software. It could acquire 3D displacement responses of large structures at high sampling frequencies in real time without requiring a high-performance computing cluster. Full article

The results of shaking table tests from previous studies on a one-story, two-bay reinforced concrete frame—exhibiting both shear and axial failures—were compared with nonlinear dynamic analyses using simplified models intended to evaluate the collapse potential of older reinforced concrete structures. To replicate the nonlinear behavior of columns, whether shear-critical or primarily flexure-dominant, a one-component beam model was applied. This model features a linear elastic element connected in series to a rigid plastic, linearly hardening spring at each end, representing a concentrated plasticity component. To account for strength degradation through path-dependent plasticity, a negative slope model as degradation was implemented, linking points at both shear and axial failure. The shear failure points were determined through pushover analysis of shear-critical columns using Phaethon software. Although the simplified model provided a reasonable approximation of the overall frame response and lateral strength degradation, especially in terms of drift, its reduced computational demands led to some discrepancies between the calculated and measured shear forces and drifts during certain segments of the time-history response. Full article