Seismic Loading Research Articles

A novel semi-analytical approach based on scaled boundary finite element method for fluid-structure coupling analysis of liquid sloshing in 3D containers

In this paper, a novel semi-analytical approach is proposed for the three-dimensional fluid-structure coupling analysis of liquid sloshing in elastic containers subjected to harmonic and seismic loading in the horizontal direction, based on the scaled boundary finite element method (SBFEM). A modified SBFEM model, referred to as the scaling surface-based SBFEM, is developed to simulate the container wall, which is treated as a thin shell structure. Within the framework of the scaling surface-based SBFEM, the geometry of the shell structure is entirely determined by scaling one surface of the structure. This approach differs significantly from the standard SBFEM, where approximation is achieved through coordinate mapping based on a scaling center, thereby enhancing the modeling accuracy and efficiency. Hydrodynamic pressure is treated as an independent nodal variables in the governing equations of the fluid domain, which is modeled using the standard scaling centre-based SBFEM. The coupled fluid-structure system is assembled by applying equilibrium and compatibility boundary conditions to ensure the balance of interaction forces. A synchronous solution algorithm, combined with the implicit-implicit scheme of the Newmark method, is used to determine the dynamic responses of the coupled system. The main advantage of this novel approach is that it meshes and discretizes the boundaries instead of the entire structural and fluid domains, thereby reducing computational costs. Additionally, analytical solutions can be obtained along the radial direction of the interior domain, enhancing the accuracy and convergence of the results. Another advantage is the approach's ability to provide a unified modeling framework for structures of any shape. Furthermore, the asymmetry issue of the coefficient matrix can be effectively avoided by using a synchronous solution algorithm. Benchmark examinations confirm the superior computational accuracy and robustness of the proposed approach. A comprehensive parametric study is conducted, focusing on the effects of liquid filling levels, as well as geometric and material parameters, on the transient vibration and distribution behaviors of the fluid-structure coupling system.

Seismic performance of compressed earth block walls reinforced with common reeds

Compressed earth block (CEB) is a sustainable and cost-effective option for eco-friendly constructions. The blocks are produced without burning fossil fuels and have low embodied energy. The abundance of its constituents, including clay and sand, is another merit. However, the susceptibility of CEB constructions against seismic forces is still considered a prominent hindrance to their widespread acceptance. The study aims to improve the in-plane seismic performance of CEB walls by using common reeds as a natural reinforcing material. For this purpose, seven wall panels with dimensions of 1000×900×120 mm3 were constructed. Seismic loading was simulated using an incrementally increasing lateral cyclic displacement combined with a constant vertical stress of 0.3MPa. The results are discussed in terms of the hysteresis load-displacement responses, displacement ductility, energy dissipation, and stiffness degradation. Based on laboratory experiments, the strength and lateral displacement of the reinforced specimen with four vertical reeds were increased by 44% and 76%, respectively, compared to the non-reinforced ones. Ultimately, Seismic assessments and damage indexes of the tested walls indicated that the in-plane seismic performance of CEB walls could be significantly improved by using vertical sand-coated reeds.

Fragility analysis of tubular structures based on local-buckling driving variables

Performance-Based Earthquake Engineering (PBEE) is computationally demanding, due to the multiple high-fidelity nonlinear dynamic structural response analyses required to compute fragility curves. Local buckling of tubular steel structures is not properly characterized by typical Engineering Demand Parameters (EDPs) such as story drifts or plastic rotation angles. Targeting the two issues above, in this manuscript we propose using state variables based on Lumped Damage Mechanics (LDM) to characterize Local Buckling (LB) in PBEE. Hence, we propose an efficient and innovative procedure for the fragility analysis of complex tubular structures prone to fail due to local buckling. Moreover, local buckling produces a loss of stiffness, with loads transferred to intact or to less-damaged elements. Eventually, the structure forms a global collapse mechanism. Herein, we show how to identify the most likely global collapse mechanism in non-symmetrical tubular structures subjected to random seismic loading. This involves evaluating damage indices in different elements and their correlation, as well as identifying the combination of LB failures that are more likely to form a global collapse mechanism. Fragility curves characterizing the onset of LB at individual elements, and the most likely global collapse mechanism, are constructed. A simple frame structure is addressed, where the accuracy of the LB-LDM model is checked against experimental results. Another case study involving a non-symmetric tubular wharf illustrates the search for the most likely global collapse mechanism, and the derivation of its fragility function.

Assess seismic resilience of unreinforced stone loess cave retrofitted with composite materials by shaking table tests

Unreinforced masonry (URM) structures have consistently suffered significant seismic damage in past earthquake events, leading to considerable losses in both life and property. Unreinforced stone loess cave (URSLC), a type of URM structure, are commonly used in the loess regions of northwestern China due to their affordability for low-income populations. Developing cost-effective and easily implementable reinforcement technologies to enhance the seismic performance of URSLC is therefore critical. In this study, a series of shake table tests were conducted to improve the strength and ductility of URSLC. Initially, the unreinforced structure was subjected to six progressively intense bidirectional seismic excitations, driving the structure to near-collapse. Subsequently, the damaged structure was retrofitted using composite materials, including steel bar/wire mesh mortar, steel belts, and epoxy resin. To compare the performance, a shaking table test was repeated on the retrofitted structure using the same seismic input as the initial test. Throughout the experiments, the damage progression, crack development, and failure characteristics of both the unreinforced and reinforced specimens were meticulously recorded. Additionally, dynamic properties before and after reinforcement were analyzed to assess the effectiveness of the retrofitting. The results demonstrated that the composite materials provided a strong bond between the stone layers and reinforcement, significantly improving the seismic resistance of the damaged loess caves. Moreover, the use of these materials was found to be both efficient and economical in enhancing the structural performance—particularly in terms of strength, stiffness, and damage tolerance. This study confirms that composite reinforcement can significantly improve the safety of masonry buildings, even under severe seismic loading conditions.

Dynamic Analysis of Soil-Structure Interaction in Earthquake-Prone Areas

This study used a thorough experimental method to examine the dynamic interaction between soil and structures in earthquake-prone locations. The study challenge concentrated on how different soil types and configurations influence the diversity of structural reactions under seismic loading conditions. The research utilized a mixed methods approach, which involved quantitatively analyzing soil parameters and assessing structure dynamics. The methods employed included the creation of scaled replicas depicting common architectural structures situated on various soil types, including sandy, clayey, and mixed compositions. We used high-precision sensors to record ground motion characteristics such as Acceleration, velocity, and Displacement. The data was then evaluated using statistical methods such as ANOVA and regression analysis. The results revealed substantial differences in the structural reaction based on the type of soil and the parameters of the structure. Structures built on sandy soils saw greater peak accelerations (up to 0.170 g) but smaller displacements. On the other hand, structures on clayey soils had moderate accelerations (up to 0.140 g) but had bigger inter-story drifts. The varied soil layers, ranging from 1.500 Hz to 1.780 Hz, influenced the natural frequencies of the buildings. The damping ratios ranged from 5.000% to 7.800%, indicating that structural damping effectively reduces seismic forces. The results emphasized the critical importance of the interaction between soil and structures in seismic design and the necessity for customized engineering solutions based on the individual soil conditions at the site. Suggested measures include improving methods for soil characterization, optimizing structural dynamics using cutting-edge dampening technologies, and upgrading seismic design codes to enhance the ability of structures to withstand earthquakes in places prone to seismic activity.

A two-step dynamic FEM-FELA approach for seismic slope stability assessment

AbstractThe determination of the factor of safety (FoS) of slopes during seismic excitation can be complex if the relevant effects of pore water pressure accumulation, nonlinear material response and variable shear strength are duly accounted for. A rational two-step approach to tackle this task based on a hydro-mechanically coupled dynamic simulation and finite element limit analyses is henceforth introduced. To ensure accurate transfer of the hydro-mechanical soil state, a mapping concept is presented, accounting for spatial distributions of stresses, excess pore water pressures, inertial forces and shear strength. The proposed approach is compared to limit equilibrium method (LEM) for the case of a large-scale water-saturated open cast mine slope subjected to seismic loading. In comparison with LEM, the new approach to assess seismic slope stability proves to be simpler in its implementation and straightforward, which could be an important asset for practitioners.

Seismic Design of Underground Structures’ Vulnerability – Review.

This article examines the vulnerability of underground structures to seismic activity, with a particular focus on design and mitigation strategies. Underground buildings are essential to the development of modern infrastructure and must include tunnels, subway stations, and storage facilities. Because of its deep location, seismic design and earthquake performance are both more challenging. In this study of seismic susceptibility, topics such as ground motion characterization, soil-structure interaction, structural reaction, and failure mechanisms specific to underground structures are discussed. According to the paper, their susceptibility can be affected by geotechnical conditions, the kind of structures they have, and the construction methods that are used. The seismic stability design and analysis process involves measuring the dynamic response of subsurface structures to seismic loads. The goal is to keep earthquake and seismic forces from toppling structures in any way that is possible. Advanced analytical and numerical approaches are used in seismic stability design. Some examples of these methods are finite element analysis (FEA), discrete element modeling (DEM), and the boundary element method (BEM). In addition to that, it investigates contemporary methodologies for assessing seismic vulnerability as well as international design standards. In addition, seismic retrofitting and design advances for underground structures are analyzed and discussed in this paper. This document compiles and evaluates previous research to gain an understanding of the seismic susceptibility of subsurface structures and to promote more seismic engineering research on this extremely important topic.

A dynamic strain prediction method for malfunction of sensors in buildings subjected to seismic loads using CWT and CNN.

Structural health monitoring (SHM) is a technique used to evaluate the safety of a structure based on the structural response. In the SHM, sensors may fail to measure the structural response, or data loss can occur during the data transmission and reception. In this regard, this paper proposes a method of predicting the strain response when a sensor installed in a structural member suffers a malfunction. To this end, a convolutional neural network (CNN) is introduced to predict the strain response. Time-history strain data for seismic loads measured in adjacent structural members are set as the input layer of the CNN, and continuous wavelet transform (CWT) results are additionally set in the input layer of the CNN to reflect the dynamic structural behavior during earthquakes in the CNN predictions. Time-history strain data for a member, the target of prediction, are set as the output layer of the CNN. Then, the trained CNN uses the time-history strain data of adjacent members with no sensor failure and the CWT result of the data to predict the strain response of a structural member with sensor failure. A numerical study on the seismic load of a single-span three-story steel moment frame and an experimental study on a single-span three-story reinforced concrete frame were carried out to verify the validity of the proposed method. This study presents a method of applying CWT data to the input layer of the CNN and discusses the effectiveness of CWT data for predicting the nonlinear response of a structural member with damaged sensors.

Seismic Damage Identification Using a Combination of Mixture of Gaussian and Harris Hawks Optimization

ABSTRACTThe present study aims to identify damage in structures using seismic responses and a two‐stage method based on mixture of Gaussian (MOG) and Harris hawks optimization (HHO). Two‐dimensional (2‐D) frame structures under seismic loads are simulated using the finite element method (FEM). The placement of sensors is optimized using a combination of an iterated improved reduced system (IIRS) and the binary differential evolution (BDE) algorithm. The MOG classifier is trained to find the damaged story and damaged element type (i.e., whether it is a beam or a column) using the nodal acceleration responses at the optimal sensor placement of the seismically loaded structure. Thus, as the first step, the possibly damaged elements are located through the classifier. Then, in the second step, the damage is accurately located and quantified by HHO algorithm. The performance of the proposed method is assessed using the numerical results of 2‐D frames of 7 and 14 stories in different damage scenarios with and without considering noise. As a result, the efficiency of the proposed method for the seismic damage identification of 2‐D frames is revealed. Sensor positions are well optimized, and it causes the method to be highly effective. Moreover, MOG correctly finds a damaged story and identifies whether a damaged element is a beam or a column. Damage in the presence of noise is also localized and quantified precisely by HHO.

Experimental investigation on the seismic performance of reinforced concrete frames with decoupled masonry infills: considering in-plane and out-of-plane load interaction effects

AbstractMasonry infills are frequently employed as both outer and inner partitions in reinforced concrete (RC) frame structures due to their outstanding characteristics in terms of energy efficiency, fire resistance and sound isolation. However, common construction practice typically involves the mortar connection between masonry infills and RC frames. For this reason, the unforeseen frame-infill interaction takes part under seismic loading, which leads to severe and uncontrollable damage to masonry infills. This interaction also causes damage or even the collapse of the RC frames and thus of the whole structures. The poor performance of infilled RC frame structures in recent earthquake events is a strong motivation for the development of innovative engineering solutions, which aim to mitigate the detrimental effects of frame-infill interaction. This article introduces an innovative decoupling system founded on the concept of decoupling the RC frame from the masonry infill. The decoupling is achieved by inserting elastomeric material between the masonry infill and RC frame. The properly designed decoupling system allows infill activation only at high in-plane drifts. Simultaneously, it provides boundary conditions for seismic loads acting perpendicular to the infill plane. Firstly, the article explains the design of the masonry infill with the decoupling system and its installation. Afterwards, the results of small specimen tests carried out to determine the load-bearing capacity of the decoupling system are presented. Furthermore, the article discusses the findings of an extensive experimental campaign conducted on nine real-size RC frames with decoupled infills subjected to separate and combined in-plane and out-of-plane loadings. In addition to different loading types, various infill configurations are considered – solid infill, infill with centric window, and infill with centric door opening. Finally, the experimental results of RC frames with decoupled infills are compared with the experimental results of traditionally infilled RC frames, which were tested within the framework of the same project. The thorough evaluation and comparison of the experimental findings demonstrate the significant improvement of seismic performance of infilled RC frames if the decoupling system is applied.

Sustainable mitigation method for earthquake-induced liquefaction using gravel-tire chips mixture: an integrated approach

This study investigates the potential of using Gravel-Tire Chips Mixture (GTCM) drains to mitigate soil liquefaction during earthquakes through an integrated experimental and numerical approach. The experiments involved a controlled setup with three distinct scenarios, evaluating the effectiveness of GTCM drain configurations in controlling excess pore water pressure in foundation soils, thereby reducing liquefaction and building settlement under seismic loading. Numerical simulations were performed to complement the physical tests and provide deeper insights into soil-drain interactions during dynamic events. The experimental results showed that GTCM drains significantly reduced settlement, with a reduction of up to 40 times in cases where GTCM drains were used compared to unmitigated conditions. Additionally, the presence of GTCM drains was effective in dissipating excess pore water pressure, which is a primary cause of liquefaction. Numerical simulations confirmed the experimental findings, indicating minimal pore water pressure buildup and reduced deformation in soils reinforced with GTCM drains. This research demonstrates that GTCM drains provide a sustainable and effective method to mitigate liquefaction and reduce earthquake-induced structural damage. The findings emphasize the importance of strategic drain placement and highlight the environmental benefits of repurposing waste materials such as tires for geotechnical applications, offering a cost-effective solution for enhancing infrastructure resilience in earthquake-prone regions.

Seismic Loading and Reinforcement Effects on the Dynamic Behavior of Soil Slopes

Seismic Loading and Reinforcement Effects on the Dynamic Behavior of Soil Slopes

Evaluation of Permeable Piles Foundation Performance in Liquefiable Soils under Seismic Loading

Evaluation of Permeable Piles Foundation Performance in Liquefiable Soils under Seismic Loading

Test-Based Assessment of the Seismic Response of Bracing Systems for Concealed Grid Suspended Ceilings

ABSTRACT Despite not directly contributing to a structure’s load-bearing capacity, non-structural elements like partitions, cladding, ceilings, floor finishes, and facades play a pivotal role in the overall building design and occupant safety. Their susceptibility to damage during seismic events, however, can lead to substantial economic losses, business interruptions, and potential risks to occupants. Focusing on concealed grid suspended ceiling systems, this study focuses on enhancing their seismic resilience introducing and experimentally evaluating two innovative bracing systems (Typology N and Typology W) that utilize steel members, already used in non-seismic application, as braces. Unlike prior research using shake tables, this study employs a specially designed set-up on a universal testing machine, offering a cost-effective and efficient approach for cyclic testing and considering the spatial variability of seismic loads. As a complementary task, component-level tests were conducted on the compressed strut to extend the results for suspended ceiling systems having suspension height up to 2 meters. The results show that Typology N performs better than Typology W, with 1.7 times greater resistance and 2.5 times greater stiffness on average, demonstrating the importance of considering different directions of horizontal seismic loading in the performance assessment. The study provides valuable insights, including design resistance values and a step-by-step procedure for determining the maximum ceiling area that a single bracing system can cover, aiding in optimizing bracing system selection and mitigating seismic vulnerability in concealed grid suspended ceilings for seismic-prone regions.

Experimental Investigations of Seismic Performance of Girder–Integral Abutment–Reinforced-Concrete Pile–Soil Systems

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment–reinforced-concrete (RC) pile (IAP)–soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder–integral abutment–RC pile (GIAP)–soil system was conducted for an IAB in China. The experiment’s results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of −8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP–soil system was better than that of the IAP–soil system. Therefore, to accurately reflect the seismic performance of GIAP–soil systems in IABs, it is suggested to consider the influence of the girder.

Dynamic response analysis of a floating bridge structure under combined actions from seismic loading and waves at different incident angles

Abstract This paper investigates the complex coupled response of a cross-sea floating bridge under the combined actions of seismic loading and wave at different incident angles. The bridge structure is modeled using the finite element method, considering the interaction between the girder, pier, pontoon, and mooring chains. Wave forces are calculated based on potential theory, and an added mass approach is applied to simulate the hydrodynamic forces induced by the earthquake. Simulations were conducted using a one-year random wave at three different incident angles of 0o, 45o, and 90o, combined with three-dimensional seismic loading of varying magnitudes: 0.3 g, 0.5 g, and 1 g. The simulation results indicate that the direction of the incident wave significantly influences the bridge's response. The coupling effect between wave and seismic forces on the floating bridge's response is not simply additive. Generally, when the earthquake magnitude is low, the wave loading significantly impacts the bridge's dynamics. However, as the earthquake magnitude increases, the bridge's response becomes dominated by the seismic forces, rendering the influence of wave forces negligible.

Non‐linear time history analyses of a rigid block isolated with unbonded fiber‐reinforced elastomeric isolators (UFREIs): A comparison between 3D finite element and phenomenological models

AbstractNumerical modeling represents a pivotal tool in the seismic analysis and design of structural systems, enabling the detailed prediction and examination of structural responses under seismic loading. This research conducts a comparative analysis of two numerical modeling approaches aimed at simulating the seismic response of unbonded fiber‐reinforced elastomeric isolators (UFREIs). The research focuses on a finite element (FE) model developed using Abaqus and a developed phenomenological model implemented in OpenSees, outlining the development and calibration processes for each. The FE model is developed based on simple rubber material testing data, while the phenomenological model is calibrated using experimental results from cyclic shear tests conducted on the UFREI device and the FE model. The primary objective of this study is to assess the effectiveness of these modeling approaches in predicting UFREI behavior under seismic conditions. This evaluation entails comparing model predictions with experimental data obtained from unidirectional shake table tests performed on a rigid block isolated by two UFREIs. This paper highlights the distinct advantages and limitations of each model in simulating UFREI dynamic responses during seismic events. Furthermore, it provides insights into the modeling techniques and discusses the computational demands and data requirements of each model, thereby aiding in their application to various aspects of seismic analysis and design.

Research on the Dynamic Response of a Bedding Rock Slope Reinforced by Pile–Anchor Structures Under Earthquakes: A Case Study of a Section of the Duyun-Shangri-La Expressway Project in Ludian County, Yunnan Province, China

Pile and anchor structures are extensively employed for slope stabilization. However, their dynamic response under seismic loading remains unclear and current seismic designs primarily use the pseudo-static method. Here, a three-dimensional numerical simulation of the dynamic behavior of a bedding rock slope supported by pile–anchor systems under earthquakes is conducted. The dynamic calculation for the slope subjected to seismic forces with varying excitation directions and acceleration amplitudes is performed. The dynamic behavior of both the slope and the pile–anchor system is investigated with respect to the slope’s failure mode, the dynamic soil pressure behind the pile, the anchor axial force, the bending moment, and the lateral displacement of the pile. The results indicate that the anti-slide piles cause a reflective and superposition effect on seismic waves within weak rock layers. As the input seismic intensity increases, the axial force in the anchor cables also increases, with the peak axial force occurring during the main energy phase of the seismic waves. The dynamic soil pressure acting behind the piles varies with the stratification of the slope rock layers, with lower peak dynamic earth pressure observed in weak layers. The weak layers on the slope surface experience through-shear failure. Under strong seismic loading, the structural element state undergoes significant changes.

Evaluation of overstrength-based interaction checks for columns in steel moment frames

Current design guidelines in the United States require a check for only column axial force under overstrength seismic loads for capacity-designed steel moment frames. A study is presented to examine the implications of this guidance, which disregards the column interaction check (including both axial force and moment) under overstrength seismic loads. A set of thirteen steel moment frames are designed using multiple rules that apply and disregard overstrength, drift, and cross-sectional compactness checks in various combinations. The frames are subjected to a suite of simulations including linear elastic, nonlinear static pushover, nonlinear response history, and continuum finite element simulations that are able to represent a range of physical behavior modes in the columns including interactive nonlinear geometric instabilities that could trigger loss of the load carrying capacity of the member. The simulations indicate no significant distinction between the seismic performance of steel moment resisting frames designed as per current code-based provisions (i.e., disregarding the column interaction check for overstrength seismic loads), and those designed with the use of the interaction check, with each providing acceptable response without failure. The simulations also indicate that design checks for drift and cross-sectional compactness play a significant role ensuring acceptable response, providing additional margin of safety beyond the member strength checks.

Pseudo-dynamic stability analysis of 3D rock slopes considering tensile strength-modified Hoek–Brown failure criterion: Seismic UBLA implementations

The Hoek-Brown (HB) criterion has found extensive application in the stability analysis of intact or jointed rock slopes, in both two-dimensional (2D) and three-dimensional (3D) contexts. In the early days, the assessment of Hoek-Brown slopes rarely incorporated tensile strength until, recently, limited studies examined the tension-controlled toppling failure at the sliding head. Nevertheless, the adapted tensile strength, which is extrapolated from the HB envelope the tensile regime, has been found overestimate experimental results. Thus, for more realistically representing the influence of rock tensile strength, the present study introduces a novel procedure for assessing the seismic stability of 3D HB slopes. In this study, the tensile strength-modified HB envelopes considering cut-off effects are derived in the principal stress space and Mohr space. To assess the slope stability, the obtained HB envelope is employed in a multi-cone mechanism based on upper bound limit analysis (UBLA). Specifically, the counter of this mechanism is determined by 10 optimized dependent rupture angles, highly considering the nonlinearity of the Hoek-Brown envelope compared to the traditional linearization strategies. As an improved seismic stability analysis, the seismic load is characterized by a modified pseudo-dynamic method. Analytical expressions for two stability indicators, i.e., the stability number and safety factor, are derived. Comparisons with numerical simulations demonstrate the rationality of the proposed procedure. Parametric analysis indicates the significant effect of the tension cut-off on the HB rock slope stability and the contour of the sliding surface.