Seismic Loading Research Articles

Damage assessment of self‐centering rocking piers using an input energy‐based damage prediction model coupled with self‐centering index

AbstractThe immediate functionality of bridges following severe earthquakes is vital for uninterrupted rescue operations. Regarding the significance of resiliency in bridges, post‐tensioned (PT) rocking piers with low residual displacements and minimal damages have developed over the past few decades. The rocking mechanism at two ends of the pier avoids bending moments and excessive flexural damage. The self‐centering (SC) capacity in this system is provided through post‐tensioning forces. Concerning optimum seismic design and retrofit purposes, it is essential to predict the actual degree of seismic damage and SC capacity of PT rocking systems after seismic hazards. In this case, a self‐centering index (SI) is proposed to evaluate the SC capacity when piers are subjected to cyclic and seismic loadings. This SI, when used in co‐operation with a viable damage prediction model, predicts whether or not the piers remain reparable under cyclic or seismic loading scenarios. After comparing a number of energy‐based damage indices, all of which consider the cumulative hysteresis energy, with the input energy‐based damage index (IEB‐DI), the latter was calibrated against observed damages under cyclic loading tests. This DI was chosen as the most suitable damage prediction model and was considered to be simply applicable after time history analysis. In this study, the seismic performance of a seismic‐resistant dual system, consisting of three RC bents along with an SC bent, was evaluated using the aforementioned damage limit states and the introduced SI. The damage predictions of the monolithic bridge, as the reference model, were compared with the estimated damage to the dual bridge. The results show that the joint application of the IEB‐DI and the proposed SI in predicting the performance level of SC rocking piers results in a comprehensive damage prediction model.

Analytical and numerical investigation of the seismic behavior of tubular web reduced beam section connections

AbstractThe reduced beam section (RBS) connections in steel structures are widely used to achieve sufficient ductility and avoid creating brittle failures in moment‐resisting frames. Compared to other types of connections, conventional RBS connections have the potential to reduce moment capacity and induce larger lateral deformation in the structure. In order to resolve this problem, novel forms of RBS connections have been proposed in recent years, such as tubular web RBS connections, which have shown a desirable performance under various loading conditions in previous studies. Therefore, this study conducted an analytic and numerical investigation of this connection under seismic loading. In this regard, the first step is to introduce the analytic equations related to the structural properties and stability of the reduced beam with the tubular web. Using these equations, a comprehensive procedure for the design of the tubular web RBS connections is presented. After that, a numerical model of the tubular web RBS connections is created and then analyzed under cyclic loading using the finite element method in ABAQUS software. Based on the results of this simulation, the suggested connection meets the criteria of valid international standards and can be used in the special moment‐resisting frame. In order to assess the impact of using the proposed connection in moment‐resisting frames, the performance of two 2D moment‐resisting frames with this connection is studied. This study shows that the maximum percentage increase in relative displacement caused by using tubular web RBS connections is 1.68%, whereas this figure rises to 10.6% when conventional RBS connections are used. Therefore, the designers can use tubular web RBS connections instead of conventional RBS connections to increase the lateral stability of the structure and control its lateral deflection due to the seismic loadings without having to increase the dimensions of the frame elements.

Machine learning-based prediction of statically equivalent seismic forces in pin-supported cylindrical reticulated shells

Reticulated shells exhibit complex vibrations during earthquakes, encompassing components in horizontal and vertical directions, and multiple vibration modes occur. In particular, single-layer reticulated shells with a small depth relative to their span exhibit many vibration modes, and the shapes of these modes can vary depending on the geometry. The method for rapidly setting equivalent static seismic forces remains unexplored. In response to the above background, this study proposes a novel approach for calculating the seismic forces on single-layer reticulated shells using machine learning techniques. The shells in focus are pin-supported cylindrical reticulated shells, typically for the roofs of gymnasiums used as evacuation facilities during severe earthquakes in Japan. Machine learning uses numerical analysis results for approximately 20,000 shells, with varied spans, half-open angles, and aspect ratios. A method for preprocessing the principal vibration modes as image data is proposed, after which the imaged vibration modes are predicted from the shape parameters of the shell using a neural network. The prediction accuracy is analyzed, and a method for rapidly calculating seismic loads based on combining predicted vibration modes is proposed. These seismic loads are compared with the response spectrum method results, and their effectiveness is discussed.

Response of Batter Piles Subjected to Static and Seismic Loading: Review Study

Battered piles are beneficial when used as foundations where significant lateral resistance is required, which could result from extreme water waves, winds, soil pressures, massive hits of explosions, or earthquakes. Experimental and numerical research must focus on that direction to reveal how these foundations behave under different loading conditions. The present study reviews the investigations conducted on the performance of batter pile foundations and attempts to understand and cover various aspects related to this issue; after conducting the review, the results indicate that the negative battered piles provide an efficient lateral stiffness corresponding to positive battered piles and a vertical one. Also, lateral bearing capacity improved with the inclusion of battered piles. Moreover, batter piles respond better than vertical piles in liquefiable soil under seismic excitation. The current study also showed that the pullout capacity of batter piles increased with the batter angle.

Performance of an advanced sand constitutive model in modelling soil and soil-structure interaction under seismic excitation

There is a growing number of available advanced soil constitutive models aimed at capturing soil cyclic behaviour and their subsequent use in seismic applications. Nevertheless, detailed validation studies of these soil constitutive models on benchmark experimental works including seismic soil-structure interaction are still rare. This work presents a short validation study of the seismic performance of an advanced elastoplastic sand constitutive model on a boundary value problem including kinematic and inertial soil-structure interaction. The results of the finite element numerical model for the free field and structural responses are compared with the experimental work on a group of piles analysed in a flexible soil container filled with dry sand and subjected to simplified seismic loading. In general, the comparisons show a satisfactory match between the results of the simulations and the experiments, with the exception of the numerical predictions of settlements. The computed results are discussed based on: i) the dominant stress-paths in soil; ii) parametric studies on the settlement evaluation; iii) the origin of the high frequency motion oscillations to simple sinusoidal input motions; all with respect to potential improvements in the formulation of the elastic behaviour of the constitutive model in the future.

Seismic response assessment of tapered piles in sandy soils: A numerical investigation

For the same volume, tapered (non-prismatic) piles have premium advantages over conventional (prismatic) cylindrical piles with respect to the axial and lateral load resistance and, thereby, are considered an economical alternative to prismatic piles. While previous investigations have studied the behavior of tapered piles subjected to different dynamic loading conditions, their seismic response has not yet received a comprehensive examination. This study aims to investigate the seismic response of tapered piles in sandy soils using non-linear three-dimensional (3D) finite element analyses. A total of 3084 cases were studied using MIDAS software to consider a wide range of parameters, including variations in soil density (Dr), taper angle (θ°), slenderness ratio (L/DAvg), and different earthquake recorded data. A parametric analysis was also undertaken to investigate the behavior of the pile lateral displacement, pile bending moment, and frictional resistance. The findings of the study reveal that tapering enhances the lateral stiffness of the pile, resulting in reduced lateral deflections and decreased sensitivity to changes in L/DAvg and ground motion intensity. Furthermore, under higher ground motion intensity, improved pile stiffness through tapering contribute to an increase in bending moments experienced by the pile. Another significant observation is the substantial improvement in frictional resistance due to soil densification. This emphasizes the critical importance of considering the soil behavior and its density in the design of pile foundations, particularly when aiming to withstand seismic loads effectively. These insights offer valuable guidance for designing pile foundations that can reliably endure the dynamic forces present during seismic events.

An Investigation into the Impact of Time-Varying Non-Conservative Loads on the Seismic Stability of Concrete-Filled Steel-Tube Arch Bridges

When the arch rib of the mid-bearing through and lower-bearing through arch bridges undergoes out-of-plane deformation, it is usually subject to the resilience force provided by the flexible hanger, which is known as the “non-conservative force effect” of the suspender. In contrast to the static condition, in the dynamic scenario, the time-varying non-conservative force exerted by the flexible suspender becomes more complex due to dynamic changes in external load. Moreover, the difference in fundamental frequency and vibration period between the bridge system and arch rib may influence the stress distribution within the arch rib during ground motion. This paper investigates the impact of time-varying non-conservative forces on the dynamic stability of arch ribs in concrete-filled steel tube (CFST) bridges under seismic loads. Specifically, it examines the influence of different seismic waveforms, frequency disparities between bridge slabs and arch ribs, and suspender stiffness on the non-conservative effect. The results reveal significant disparities in the impact of non-conservative forces exerted by the suspender during seismic events with identical intensity but varying frequency characteristics. The influence of non-conservative forces on the dynamic stability of bridges escalates as deck stiffness increases, while it remains relatively unaffected by changes in suspender stiffness.

Experimental study on seismic performance of damaged masonry walls reinforced with high-polymer cementitious composite material

Masonry structures are one of the most traditional and economical structural forms that are extensively used worldwide. However, severe damage to the masonry structures during past earthquakes addresses their vulnerability to seismic loadings. Therefore, it is critical to develop effective and efficient seismic reinforcement measures for masonry structures. This study proposes a structural retrofitting method for masonry walls that employs a corrosion protection liner (CPL) and high-polymer cementitious composite material (HPCCM). Cyclic in-plane pseudo-static tests were performed on six masonry wall specimens comprising three unreinforced and three seismically damaged masonry walls retrofitted with CPL-HPCCM. This experimental study explored the hysteretic behavior, deformation capacity, and failure mechanism of masonry wails after rehabilitation with the proposed retrofitting method under cyclic loading. The test results indicate that the CPL-HPCCM structural retrofitting method is an effective structural retrofitting technique that significantly enhances the lateral load-bearing capacity and energy dissipation capability of masonry walls. Even for the severely damaged masonry wall specimens, the lateral load-bearing capacity, lateral stiffness, and overall ductility of the wall specimens after retrofitting with CPL-HPCCM were restored to or improved beyond those of the intact wall specimens. Compared with the non-retrofitted specimens, the lateral load-bearing capacity of the CPL-HPCCM retrofitted specimens exhibited a substantial improvement, with a minimal increase of 14.6 %. In addition, the CPL-HPCCM method also enhanced the energy dissipation capacity of the wall specimens over 1.95 times compared to the non-retrofitted specimens. Finally, a lateral load-bearing capacity prediction equation was proposed for CPL-HPCCM-reinforced masonry walls based on experimental results.

Development of Geotechnical Seismic Isolation System in the Form of Vertical Barriers: Effectiveness and Perspective

This paper discusses the concept of geotechnical seismic isolation (GSI) systems, characterized by new principles of action, to reduce seismic loads on buildings. The advantages and disadvantages of GSIs and their environmental and economic reliability are analyzed. The aim of the study is to develop a geotechnical seismic isolation system in the form of vertical barriers, using a rubber–soil mixture (RSM). The novelty of the work lies in the definition of effective structural and technical solutions of vertical seismic barriers made of RSM, characterized by reliability in providing seismic isolation. The ground and superstructure interactions are modeled in PLAXIS 2D software from 2021, using the finite element method, using the accelerogram of the Kobe and Northridge earthquakes. The results confirm the positive impact of using an RSM as an effective GSI geometrical. The results show that the GSI system using an RSM reduces horizontal accelerations by 60%. Significant acceleration reductions of 40–60% are also observed when the thickness and depth of GSI seismic barriers are increased. The results of the study contribute to the substantiation of methodology and scientific and technical efficiency of geotechnical seismic isolation as an economically favorable design alternative to the traditional seismic isolation system.

DEVELOPMENT OF PEAK GROUND ACCELERATION USING A NON-LINEAR APPROACH TO EVALUATE LIQUEFACTION POTENTIAL IN SEI WAMPU BRIDGE, LANGKAT, NORTH SUMATRA, INDONESIA

The design of building structures requires compliance with seismic codes and all their consequences. Based on geotechnical investigation reports, the construction of Sei Wampu Bridge in Langkat, North Sumatra, Indonesia, is located in an area where the soil layers are predominantly sand with shallow water levels because of its proximity to a river and is a high earthquake zone due to the Semangko fault. That condition will affect the potential of liquefaction occurring. This study aims to identify the liquefaction potential in the Sei Wampu Bridge. Based on Indonesian National Standard (SNI) 1726-2019, sites prone to liquefaction are categorized as site class-specific soil (F) and requires site-specific response analysis (SSRA) methods. Non-linear analysis 1-D is chosen to propagate earthquake waves with the software DEEPSOIL V7. The input parameter for soil movement utilizes an average spectral matching method with a minimum of 7 pairs of soil movement selected from the earthquake recording website, PEER Ground Motion Database. The selection of earthquake considers a 1000-year earthquake load return period, or a 7% probability exceeded within 75 years. Site-specific response analysis (SSRA) resulted in a peak ground acceleration (PGA) value for each borehole depth used in liquefaction potential analysis. Using a historical earthquake scenario with a 6.3 Mw shows that the research location has liquefaction potential at 0 m-15 m deep with high vulnerability levels, where the LPI value reaches 36.21.

Seismic Safety Evaluation of Mechanically Stabilized Earth (MSE) Wall for Highway Construction

The usage of Mechanically Stabilized Earth (MSE) Walls has grown in popularity over the last few decades and has been widely used in many countries for highway construction, including Indonesia. As a country with a high risk against seismic hazards, a considerable stability analysis against earthquakes for construction must be conducted. This paper is directed to evaluate the static and seismic stability of MSE wall by adopting design criteria from SNI 8460:2017 using the pseudo-static approach with Limit Equilibrium Method (LEM) which modelling earthquake as a seismic coefficient, a one-way constant load and dynamic response approach with Finite Element Method (FEM) which modelling earthquake as ground motion, a fluctuating load which varies in time. The stability analysis is performed by considering three failure mechanisms that mostly occurred in MSE Walls; base sliding, tensile overstress, and slope failure. The earthquake load is modelled based 1000-year return period earthquake. Based on the analysis result, the most potential failure mechanism that may occur in the MSE wall is tensile overstress, while the least potential failure is base sliding. The analysis result also shows that the finite element method obtained higher safety factors compared to limit equilibrium, while on the other hand, the remaining two failure mechanisms shows the different result, with the finite element method obtaining lower safety factors than limit equilibrium. Modelling seismic load as an accelerogram indicates that earthquakes have higher impacts on structure stability compared to seismic coefficient, based on seismic safety factor reduction of each method. Although show differences in the value of the safety factor, the minimum safety factor required still complies with both methods.

Effectiveness of Friction Damper and Outrigger System on 3d RC Frame for Seismic Loading

Effectiveness of Friction Damper and Outrigger System on 3d RC Frame for Seismic Loading

Evaluation of seismic bearing capacity on layered geological strata by the upper-bound numerical method

This study introduces the Energy Method Upper-bound (abbreviated as EMU), originally proposed by Donald and Chen (1997), for calculating bearing capacities with a focus on earthquake loadings affecting layered geological strata. The theoretical components of this study consist of (1) an extension of Prandtl's solution for bearing capacity analysis to inclined surface loads, (2) a mathematical demonstration of the theoretical congruence between EMU and the Prandtl-Reissner solution, and (3) a validation of the numerical outcomes through four illustrative bearing capacity examples with known closed-form solutions. This innovative approach eliminates the semi-empirical coefficients typically required in conventional bearing capacity evaluations, thus enhancing its relevance to seismic analysis for stratified geological formation that can hardly be evaluated with empirical coefficients accurately. The study also discusses various technical aspects such as seismic load determination, the use of undrained shear strength, and specifications for allowable safety factors under seismic conditions. With these methodologies, the paper assesses the seismic bearing capacities of two different buildings, with different scales and footing types. Additionally, a computer program, BEARING-IWHR, featuring an Excel interface and open-source coding, is available online. This method provides a theoretically sound and practically feasible framework for addressing seismic bearing capacity on stratified foundations.

Analysis of axial force variations and seismic performance of subway station columns under earthquake loading

Central column failure is a predominant seismic damage mode in subway station structures. During seismic events, the central columns’ vertical compressive force, as indicated by the axial compression ratio (ACR), undergoes continuous variations, significantly impacting both their failure modes and the seismic performance. This study involved establishing a finite element model of a subway station and conducting time history analyses to identify the distinct variation patterns of ACR in central columns for various seismic design scenarios. Based on these summarized patterns, appropriate ACR variations were designed for the columns, and the validity of the column model was confirmed using experimental data, enabling analyses of their failure modes and hysteresis characteristics under cyclic loads. Lastly, a sensitivity analysis of the parameters associated with the central columns was performed. The results demonstrated that the horizontal displacement and the ACR of the top of the central column were asynchronous, the frequency of the latter was 1.4–3.8 times that of the former, and the amplitude of the ACR was 0.08–0.68. When the frequency of the variable ACR was odd times, the damage and hysteresis curve of the column showed obvious asymmetry and harmfulness, and it exacerbated the damage to the core concrete of the column. Compared to applying a constant ACR, the bearing capacity and energy dissipation of the column were even reduced by about 50 % and 74 %, respectively. The specimens with the upper limit value of 0.95 of variable ACR had even more adverse effects on the damage and hysteresis behavior of the column than the scheme with a constant ACR of 0.95. In addition, the even multiple frequency of variable ACR had a limited effect on the seismic performance of the column, but the harm caused by the large amplitude variation of variable ACR could not be ignored. As to the impacts of structural parameters under cyclic loadings, elevating the longitudinal reinforcement ratio and decreasing the stirrup spacing within the central columns would substantially enhance energy dissipation capacity, with a maximum increase of about 69 %. Meanwhile, for columns with the same cross-sectional area, square columns exhibited superior hysteresis behavior compared to their circular counterparts. The findings of this study could provide guidance for the engineering design of the central columns.

Effect of valley topography on dynamic response of arch dams

Arch dams are typically built in the mountain and gorge regions with complex terrain. In the current engineering practice, foundation models are commonly simplified as the half-space with the canyon of regular geometry. The complex topography conditions above the dam crest are neglected. This study investigates the effect of realistic valley topography on the dynamic response of arch dams. The direct finite element method is generalized and applied to the dam-reservoir-foundation system with realistic valley topography. The input ground motions are transformed into the effective earthquake loads at the truncated boundaries by performing several dynamic reaction calculations using one-dimensional (1D) and two-dimensional (2D) auxiliary finite element models. The effect of valley topography on the seismic response of the Baihetan arch dam is evaluated as a case study. Results indicate that the valley topographic irregularities significantly influence the dynamic responses of the arch dam, including relative displacement and stress distribution. Notably, the valley topography effect on the seismic response of arch dams depends on the incident ground motions and is hardly predicted in advance, demonstrating the necessity to account for the realistic topography conditions.

Slope Stability Analysis of Earthen Dam under Seismic Loading

Slope Stability Analysis of Earthen Dam under Seismic Loading

Performance of corroded RC beam–column joints repaired using a hybrid scheme with HSFRC and stirrups replacement

AbstractThe present study proposes a new technique for retrofitting corroded beam–column joints (BCJs) using high‐strength fiber reinforced concrete (HSFRC) and stirrups replacement. The entire corrosion‐affected concrete was removed and replaced with HSFRC. The corroded reinforcing bars were cleaned and treated to resist the progression of the corrosion mechanism. The severely pitted stirrups were replaced with new stirrups. Four exterior BCJ specimens were tested under seismic loading to determine the effectiveness of the proposed retrofitting scheme. The efficacy of the proposed retrofitting scheme is determined in terms of the hysteresis response, stiffness degradation, cumulative energy dissipation, ductility, and damage index. A significant delay in the fracture of severely pitted reinforcing bars was experienced for the corrosion‐damaged retrofitted specimens compared to the corroded unretrofitted specimen. The cumulative energy dissipation of the corroded unretrofitted and corroded retrofitted specimens was 0.4 and 1.3 times that of the reference specimen, respectively, indicating the effectiveness of the retrofitting strategy, as both specimens had similar corrosion rates. The test results indicated that the proposed retrofitting technique effectively improved the seismic performance of the corrosion‐damaged BCJs.

Development of novel low-cost isolator UMELI (unbonded mesh elastomeric layered isolator): experimental investigations

Seismic isolation is a highly efficacious method for reducing the seismic load on structures. This technique is widely adopted to safeguard structures from earthquakes. Despite the promising results demonstrated by numerous isolation techniques, their implementation remains a significant challenge, particularly in developing countries, due to the high costs associated with manufacturing. Therefore, a novel and affordable base isolation technique has been proposed, namely unbonded mesh elastomeric layered isolator (UMELI). UMELI consists of steel mesh sandwiched between the unbonded layers of elastomers, resulting in an affordable isolator to be used for lightweight, low-rise structures. One of the crucial characteristics of this novel isolator is that it does not require a specialised manufacturing process unlike other elastomeric isolators. In the present study, experimental investigations are conducted to evaluate the dynamic characteristics such as dynamic vertical stiffness, equivalent lateral stiffness, and equivalent viscous damping ratio of UMELI. Its characteristics were studied for different layered isolators and are compared with the unreinforced elastomeric isolator. The investigations have demonstrated the effectiveness of the UMELI by increasing its vertical stiffness and reducing lateral stiffness, thereby enhancing the isolation period with the addition of a steel mesh layer.

Tunable High-Static-Low-Dynamic Stiffness Isolator under Harmonic and Seismic Loads

High-Static-Low-Dynamic Stiffness (HSLDS) mechanisms exploit nonlinear kinematics to improve the effectiveness of isolators, preserving controlled static deflections while maintaining low natural frequencies. Although extensively studied under harmonic base excitation, there are still few applications considering real seismic signals and little experimental evidence of real-world performance. This study experimentally demonstrates the beneficial effects of HSLDS isolators over linear ones in reducing the vibrations transmitted to the suspended mass under near-fault earthquakes. A tripod mechanism isolator is presented, and a lumped parameter model is formulated considering a piecewise nonlinear–linear stiffness, with dissipation taken into account through viscous and dry friction forces. Experimental shake table tests are conducted considering harmonic base motion to evaluate the isolator transmissibility in the vertical direction. Excellent agreement is observed when comparing the model to the experimental measurements. Finally, the behavior of the isolator is investigated under earthquake inputs, and results are presented using vertical acceleration time histories and spectra, demonstrating the vibration reduction provided by the nonlinear isolator.

Analyzing MSW Landfill Failures: Stability and Reliability Evaluations from Five International Case Studies

This study investigates five cases of municipal solid waste (MSW) landfill slope failures in the USA, China, Sri Lanka, and Greece, with the aim of assessing the safety margins and reliability of these slopes. The stability and reliability of the landfill slopes were evaluated under both static and seismic loading conditions, using pre-failure geometries and geotechnical data, with analyses conducted in accordance with Eurocode 7, employing all three design approaches. Under static loading, the factors of safety were close to unity, and reliability indexes ranged from 1.0 to 2.8, both falling below the recommended values set by Eurocode. The landfill slopes failed to meet the stability criteria in Design Approaches 2 and 3, while in Design Approach 1, four out of five landfills met the criteria. Under seismic conditions, safety factors and reliability indexes were significantly lower than the prescribed criteria in all analyses. Sensitivity analyses revealed that in two cases, unit weight and friction angle were the dominant parameters, while cohesion was the dominant parameter in one case. The findings of this study underscore the importance of establishing minimum design requirements for MSW landfill slope stability to mitigate potential risks to public health and the environment.