Far-fault Earthquakes Research Articles

Structural state nonlinearity-based design and modification formulae of inerter-based systems

As structural safety emerges as a paramount concern and with the advancement in vibration control technology, a notable gap persists in accurately simulating structural state nonlinearity, especially within the field of inerter-based seismic control technology. Dealing with the need to upgrade the seismic performance of practical nonlinear structures, this study proposes a structural state nonlinearity-based design method for inerter-incorporated civil structures by incorporating the target seismic performance, structural nonlinearity level, and ground motion effects. By establishing mechanical models of inerter-based systems with straightforward parameters and a prototypical bilinear model for the primary structure, governing equations for inerter-incorporated structures were derived. Later, structural state nonlinearity-based design method for inerter-based systems, including optimization criteria and parameter distribution pattern, is elaborated. Simultaneously, this study also provides structural state nonlinearity-based design curves and modification formulae related to structural state nonlinearity and peak ground acceleration of earthquake. Validated using a 10-story multiple-degree-of-freedom (MDOF) structure subjected to earthquakes, the results highlight the effectiveness of the method, emphasizing its potential in controlling seismic responses of structures within the predetermined performance target. In addition, the absolute acceleration mitigation effect of inerter-based systems is investigated. The efficiency and robustness of the proposed method are also verified under near-fault and far-fault earthquakes. In essence, this research pioneers an approach in inerter-based design, bridging structural state nonlinearity, and potentially reshaping seismic control strategies to align with diverse structural states.

Application of Supplementary Inerter-Based Damping Devices Alongside Unbonded Fiber-Reinforced Elastomeric Isolators

Earthquakes have always been a menace to the lives and properties of human beings since the beginning of modern times. Several methods have been proposed since to mitigate the various types of seismic hazards, base isolation being one of them. The base-isolated structures being very effective for general far-fault earthquakes, are, however susceptible to high responses under near-fault ground motions; thus, several inerter-based supplementary damping devices have been proposed in this study to be applied alongside a highly nonlinear and effective unbonded fiber-reinforced elastomeric isolators (UFEI) system. The dampers are optimally designed and comparatively investigated with the isolation system for mitigation of a wide range of ground motions to the benchmark structure. Furthermore, two parametric studies were also carried out, which investigated the effect of the inertance-mass ratio and floor connectivity of the grounded damper on various responses of the isolator-damper-structure system. The parametric results are further used to suggest the best configuration and inertance-mass ratios for various dampers for effective seismic mitigation of the aforementioned base-isolated structure. The results show an effective reduction in seismic responses with the use of optimal inerter-based dampers in UFEI-isolated structures.

Fragility Assessment of Single Concrete Pier and Pile-Soil Interaction Impact under Near and Far-Fault Earthquakes

Civil engineers face a significant challenge in assessing seismic vulnerability due to the complex of soil-pile-structureinteraction system. This research aims to evaluate the seismic vulnerability of individual piers under various seismicground motions. Factors like sand type, pile diameter, pier height, and mass placed were investigated for their impacton the seismic fragility of concrete piers. Using incremental dynamic analysis with a beam on a nonlinear Winklerfoundation model, the study compared the effects of near and far ground motions. Results from the dynamic analysisand fragility assessment demonstrated the effects of the parameters above-mentioned on the design of fragilitycurves, as well as its relationships to fundamental period of structural system.

Non-linear sloshing characteristics of liquid inside a chamfered bottom tank with submerged internal object under near-and far-fault earthquakes

Cylindrical and rectangular-shaped tanks have a concentration of stagnant impulsive liquid at the bottom corners that do not participate in sloshing. While used as tuned liquid dampers (TLDs), this non-participating fluid adds extra liquid mass to the tank but does not have any role in the vibration control aspect. In the present study, to decrease the stagnant impulsive liquid, a chamfered bottom-shaped tank with a submerged internal object is demonstrated. Due to the high-energy velocity pulse present in near-fault earthquakes, there is a possibility of violent liquid sloshing which may cause unwanted structural damage to the tank. Hence, the present study focuses on the influence of near- and far-fault earthquakes on the non-linear seismic behavior of the tank with submerged internal object. The non-linear sloshing is modeled using the finite element method based on a combined Eulerian-Lagrangian approach. The accuracy of the present non-linear numerical model is checked by verifying the results with the previously published results. In addition to the absolute response, the dynamic convective and impulsive response components are quantified. The proposed non-linear finite element scheme can be utilized in the context of structure-mounted chamfer bottom TLDs in the future.

Multiple Sloped Wall Tuned Liquid Dampers for Vibration Control of Structure Excited by Near and Far-Fault Earthquakes

Multiple Sloped Wall Tuned Liquid Dampers for Vibration Control of Structure Excited by Near and Far-Fault Earthquakes

Behavior of Base-Isolated Liquid Storage Tanks with Viscous Dampers under Historical Earthquakes Considering Superstructure Flexibility

Liquid storage tanks (LSTs) can be efficiently protected from far-fault earthquakes by base-isolation. However, large isolation system and sloshing displacements may threaten the tank’s safety under near-fault earthquakes. Although the application of supplemental viscous dampers (VDs) at the base-isolation systems of LSTs located in near-fault areas may help, it may also increase superstructure demands under far-fault earthquakes. In addition to the characteristics of the earthquake, the isolation system and the superstructure properties may affect the success of base-isolated LSTs with supplemental VDs. Therefore, a numerical investigation is conducted in this study in order to determine the influence of the supplemental viscous damping ratio, the isolation system period, the tank wall flexibility, and the tank slenderness ratio on the seismic responses of base-isolated cylindrical steel LSTs with supplemental VDs including the base displacement, the sloshing displacement, and the normalized isolation system shear force under both near-fault and far-fault historical earthquake records. The tank is modeled by single-degree-of-freedom systems representing different modes on a common isolation basemat and the nonlinear dynamic analyses are carried out in 3D-BASIS-ME software. Findings show that while supplemental damping is required especially when LSTs with long-period isolation systems are subjected to large magnitude near-fault earthquakes, it may also cause amplifications in the sloshing displacement and isolation system shear force demands in case of far-fault earthquakes. Furthermore, it is determined that the influence of tank flexibility on both the superstructure and the isolation system responses is negligibly small while the tank slenderness ratio may have considerable effects.

The effect of near-fault earthquakes and wavelet-generated artificial near-fault earthquakes on the seismic behavior of rockfill dams

Strong earth vibrations may destroy high asphalt concrete core rockfill dams (ACCRDs) and cause unanticipated economic and social losses. Due to favorable geographical, geological, and environmental characteristics, ACCRDs are always near ruptured fault zones. Compared to far-field and non-pulse earthquakes, near-fault (NF) earthquakes with pulse effect may put high dams under stress. However, seismic design and dynamic assessments of high ACCRDs under pulse-type earthquake stimulation are less popular than NF earthquake recordings. The fundamental explanation is that most earthquake data pertain to non-pulse-type seismic occurrences, whereas pulse-type earthquakes have more sophisticated seismology. This work uses the finite element approach to illustrate the seismic behavior of the ACCRD under pulse-type NF, non-pulse-type NF, and far-fault (FF) earthquake excitations. The pulse-type artificial NF earthquakes are generated using wavelet multi-scale decomposition incorporation (WMSDI), a simplified wavelet theory-based approach. Next, the WMSDI approach of artificial NF earthquake synthesis is tested and compared to earthquake data and structure responses. Forward-directivity pulse-type and fling-step pulse-type earthquakes may induce higher horizontal accelerations and stresses of the high ACCRD than FF earthquakes. FS and FD earthquake excitations with high PGV/PGA ratios cause severe residual deformation and relative settlement ratio to the high ACCRD. The dynamic response of the high ACCRD under pulse-type artificial NF earthquakes also depends on the pulse parameters of the artificial equivalent pulse mathematical models. Thus, pulse-type NF earthquake seismology should be included in rockfill dam seismic design assessments.

Structural Investigation of a Historical Masonry Arch Bridge under Far-Fault Earthquakes

Structural Investigation of a Historical Masonry Arch Bridge under Far-Fault Earthquakes

Dynamic performance of the Mosque-Cathedral of Córdoba under different earthquake scenarios: The Abd al-Rahman I sector

The Mosque-Cathedral of Córdoba is one of the most important monuments in Spain. Owing to its authenticity, its integrity and its influence on later architecture, it was declared as a World Heritage Site by the UNESCO in 1984. The monument is located in Andalusia, in southern Spain. This region presents a moderate seismic hazard, and it is affected by two kinds of seismic sources: a) far away earthquakes of large/very large magnitude; b) close earthquakes of moderate magnitude. Particularly, the Mosque-Cathedral had to endure the well-known 1755 Lisbon's earthquake (Mw = 8.5, at 488 km) and the 1504 Carmona earthquake (Mw = 6.8, at 82 km). This research has analysed its dynamic behaviour under several earthquake scenarios: code-base response spectrum, previous historic earthquakes and fault maximum magnitude earthquakes. However, after the seismic hazard analysis and due to the lack of faults registered surrounding the building, no worst-case scenario considering the maximum expected magnitude has been found. Owing to the complexity of the building, this work has focused on the Abd al-Rahman I sector, which is the most aged part, dating from the VIII century. A refined 3D numerical model has been developed and calibrated through free ambient vibration tests. The distribution of the maximum amplitudes (internal displacements and absolute accelerations) under the different scenarios has been comparatively presented. Also, the seismic performance has been assessed considering the drifts and the damage expected. The results showed that the damage would be concentrated in the contact between the arcades and the courtyard wall. Also, the lower part of the North-South closing wall would be damaged. According to the seismic performance, the building is expected to present moderate damage. In contrast, the analysis of the drifts, according to the codes, suggest that the building would resist each damage limit. Also, it was shown that the far fault earthquake scenario is more demanding than the close fault earthquake scenario. Next, it should be noted that the behaviour of the building for a seismic action of 475-year return period is expected to be similar to the far-fault earthquake scenario. The most demanding earthquake scenario has been the 975-year return period one.

Damage-Controlling Seismic Design of Low- and Mid-Rise RC Buildings Considering Mainshock-Aftershock Sequences

Recently, the modified equivalent linearization method (MELM) is used to estimate the maximum deformation response for a structure under a near-fault or far-fault earthquake. However, most works in which the equivalent linearization method is used consider only one earthquake event. When a reinforced concrete (RC) building structure is damaged by a mainshock, which is the main seismic event of an earthquake, its stiffness and strength are reduced by concrete cracking and rebar yielding and then its period is longer in the sequent seismic events or so-called aftershock. Therefore, for seismic design of low- and mid-rise RC building structures, this work is aim to propose a simplified method that can be used to quantify the damage that is subjected to an MSAS sequence in a near-fault or far-fault earthquake using MELM. Additionally, a formula that can be used to do the damage-controlling seismic design considering an MSAS sequence is also suggested.

Numerical study on the influence of near-fault and far-fault earthquakes on a subway station with emphasis to scattering on the wave propagation

Numerical study on the influence of near-fault and far-fault earthquakes on a subway station with emphasis to scattering on the wave propagation

Seismic responses of liquid storage tanks subjected to vertical excitation of near-fault earthquakes

This study aims to evaluate the effect of vertical seismic component on dynamic responses of liquid storage tanks, with a special focus on near-fault earthquakes. A shaking table test was performed on a 1:25 scaled steel tank, which was loaded by both far- and near-fault ground motions with horizontal unidirectional, vertical unidirectional, and combined horizontal and vertical bi-directional excitations. Seismic responses, including sloshing height and hydrodynamic pressure were recorded and compared. Subsequently, a refined finite element (FE) model of the scaled tank model was established by utilizing the structured Arbitrary-Lagrange-Eulerian (S-ALE) solver and Fluid-Structure Interaction (FSI) algorithm, which was verified by comparison with the test results. Afterward, the modeling methodology was further applied to a prototype large-scale liquefied natural gas (LNG) inner tank for seismic analysis. In addition, seismic responses of the LNG inner tank were compared with the recommendations given in seismic design codes for cylindrical tanks. The experimental and numerical findings showed that both the convective and impulsive motions of liquid was amplified by vertical excitations, especially under near-fault earthquakes. The peak sloshing heights under near- and far-fault earthquakes were increased by 14–142% and 8–56% due to the existence of vertical action, respectively. The LNG inner tank was more vulnerable to inelastic buckling due to the presence of vertical seismic component. Moreover, the effect of vertical excitations of near-fault earthquakes on hydrodynamic pressure and tank stresses was underestimated by the current seismic design codes.

Energy-based assessment of reinforced concrete walls with two outriggers

In this paper, different kinds of energy dissipation in reinforced concrete (RC) core–wall systems with two buckling-restrained braced outriggers, subjected to forward-directivity near-fault and ordinary far-fault earthquakes, have been compared. The level of the first outrigger was fixed at the top and the second outrigger was placed at different levels. In the non-linear model, two approaches for the RC core–wall were considered: the extended plastic hinge (EPH) approach and the four plastic hinges approach (4PH). In the 4PH approach, only four plastic hinges are allowed in the RC core–wall, one at the base, another adjacent to and beneath the top outrigger, and two others at the level's adjacent second outrigger. For the EPH approach, the plasticity can extend anywhere in the core–wall. Principally for the EPH approach, at the base of core–wall and adjacent to the top outrigger, as well as above and below the second outrigger level, more inelastic energy demands occur due to the large moment demand resulting from seismic load. On average for both EPH and 4PH approaches, the inelastic energy at the base from far-fault records is almost 1.5 times the corresponding value from near-fault records.

Story shear distribution of high strength steel frame with D-eccentric braces based on multi-seismic-hazard levels

High-strength steel frame with D-eccentric braces (D-HSS-EBF) refer to the link that uses Q355 steel (The yield strength fy ≤ 355 MPa), while the non-energy element, such as column and beam, uses the high-strength steel Q460 or Q690 (fy = 460 MPa or 690 MPa), which is a new seismic resistant structure. The links developed full plastic deformation when the structure suffered rare earthquakes, to protect the high-strength steel frame. The story shear distribution is not suitable for the capacity-based design method, due to the stiffness of D-HSS-EBF being changed under plastic state. Therefore, this paper presents the elastic–plastic story shear distribution of D-HSS-EBF under various seismic hazard levels, including frequent earthquakes, moderate earthquakes, rare earthquakes and super-rare earthquakes. Based on this, the prototype structures of D-HSS-EBF are designed considering different stories (4-, 8-, 12-, and 16-stories) and different link lengths (900 mm, 1000 mm and 1100 mm), and the story shear distribution modes under various seismic hazard levels are raised under near-fault ground motions and far-fault ground motions. Furthermore, the parameters of story shear distribution under rare earthquakes are determined by the elastic–plastic lateral force. The time history analysis results indicated that the link length has little impact on the story shear distribution, and the near-fault and far-fault earthquakes show different story shear distribution due to the velocity pulse effect. The story shear distribution coefficient βi declines with seismic acceleration increasing. Besides, the proposed inelastic story shear models of D-HSS-EBFs have a better reflect the actual seismic response.

The effects of the duration, intensity and magnitude of far-fault earthquakes on the seismic response of RC bridges retrofitted with seismic bearings

This paper investigates the effects of earthquakes’ duration, intensity, and magnitude on the seismic response of reinforced concrete (RC) bridges retrofitted with seismic bearings, such as elastomeric bearings (EB), lead rubber bearings (LRB), and friction pendulum bearings (FPB). In order to investigate the effects of the seismic isolation, the condition of the deck with a rigid connection on the cap beams and abutments (i.e., without isolation) was investigated as the first model. The EB, LRB and FPB bearings are used between the superstructure and substructure of the studied bridge in the second, third and fourth models, respectively. First, the effects of using seismic bearings on the seismic retrofit of an RC bridge under the Tabas earthquake were investigated. The results of the nonlinear dynamic analysis showed that the use of seismic bearings leads to seismic retrofit of the studied bridge, and FPB and LRB had the best results among the studied isolation equipment, respectively. The same models were also studied subjected to the Landers and Loma Prieta earthquakes. The magnitude of the Landers and Tabas earthquakes is equal to 7.3 Richter, and the magnitude of the Loma Prieta earthquake is equal to 6.7 Richter. However, the duration and intensity of the Landers and Loma Prieta earthquakes are much larger than the Tabas earthquake. The Landers and Loma Prieta earthquakes caused instability in the isolated models due to their significant duration and intensity. This issue shows that using seismic bearings is very useful and practical for seismic retrofitting bridges subjected to far-fault earthquakes. According to most seismic codes, selecting earthquakes in far-region of faults is based on just magnitude criterion. However, this study indicates that there are two main factors in the features of far-fault earthquakes, including duration and intensity. Ignoring these factors in selecting earthquakes may lead to the instability of structures. Considering earthquakes’ duration, intensity, and magnitude are vital for selecting earthquakes in the far region of the fault.

Use of recycled coal bottom ash in reinforced concrete beams as replacement for aggregate

In this research, it is studied the crack and flexural behavior of reinforced concrete beams with various bottom ash ratios (BARs) considered as fine aggregate in an experimental and numerical investigation. For experimental purposes, different concrete series are considered varying aggregate sizes ranging from 0 to 25 mm. To supplement concrete, bottom ash is put to use in conjunction with material from 0–5 mm in size aggregate particles as replacement for fine aggregates with ratios of 25%, 50%, 75%, and 100%. Experiments were done to investigate the behavior of the beams and how flexural and fracture behaviors are represented. 75% BARs gave optimum results in terms of displacement capacity. Increasing BAR to 100% decrease deflection capacity of the beam. Also, ANSYS software is used to build 3D finite element models (FEMs) of beams to compare with experiment data. Experimental and 3D numerical tests show exceptionally tight flexural and fracture behaviors. Following this, a computer-generated structure is made by running SAP 2000, and the strength of the beams is then utilised in an RC structural model. Every stage of the building’s construction is thoroughly assessed utilizing multiple types of seismic testing, employing the SAP2000 program, with the resulting analysis providing significant findings on how the seismic force of 75% BAR affects horizontal displacement of each floor. The results showed that the weight of the structure dramatically decreases as the number of columns and RCBs are raised while also increasing the number of BARs. Moreover, the magnitude of earthquake and BAR have a significant effect on the horizontal displacement behavior of reinforced concrete structures. The strength of the concrete structure varies between close- and far-fault earthquakes, and for close-fault earthquakes, concrete strength is stronger than for far-fault earthquakes. This brings us to the second disadvantage of BAR which is the 75% strain produces a severe displacement of reinforced concrete structures. Besides, it was seen that the simulations and experiments yield tiny cracks with very identical configurations.

Optimization of Seismic Base Isolation System Using a Fuzzy Reinforced Swarm Intelligence

The current study deals with the optimization of seismic isolation system parameters applied in base-isolated buildings. In this regard, to consider the more realistic condition, both near-fault and far-fault earthquake ground motions are taken into account by simultaneously imposing six different acceleration records during the direct time integration analysis of the structure. The minimization of the system's peak acceleration ratio is defined as the objective function of the optimization model. To get feasible results, the determining parameters of the isolator are restricted. Such that, while the isolation system period and damping ratio are kept within a predefined range, the maximum displacement of the system is monitored and limited during the optimization process. To solve the proposed optimization model, an enhanced version of the Deferential Evolution method so-called Fuzzy Differential Evolution incorporated Virtual Mutant (FDEVM) is employed. The FDEVM method applies a fuzzy decision-making mechanism to adopt its search behavior based on the governing conditions of the current problem. It also uses a new mutant vector called virtual mutant to contribute information of all population based on each agent's quality. So, the FDEVM works as a self-adaptive and parameter-free search algorithm. The acquired results show that the FDEVM works properly to find the optimal values for the dynamic parameters of the seismic base isolation system.

Viscoelastoplastic and incremental analysis of bridge with functional bearing

The functional bearing is one kind of the seismic isolation merging the advantages of the sliding system and the bearing system and it is widely used in Taiwan. To evaluate the performance of the functional bearing in a bridge effectively, a simple but accurate model is appreciated. The present paper attempts to model a bridge with functional bearing taking into account that the rate-dependent pier with hardening behavior. The proposed model is viscoelastoplastic and contains four phases including a viscoelastic-sticking, a viscoelastic-sliding, a viscoplastic-sticking, and a viscoplastic-sliding phase. The theoretical analysis in the state-space space enables us to obtain an exact solution for each phase. In order to simulate the exact behavior of the bridge system, the phase switching criteria with four conditions are derived and four computing modules for computations in four phases as well as four pull-back modules to direct toward to an exact module are developed. The four-phase model and the exact arrangement of computation qualitatively and quantitatively provide the exact duration of each phase and the proper indices for the plastic degradation of the pier as well as the consumption of the friction interface. One comparison between the simulation and the experimental result of a bridge’s shaking table test demonstrates the accuracy of the proposed model and its algorithm for the response of the bridge with functional bearing. Three numerical demonstrations show the performance of the proposed incremental analysis and the capability of the proposed model to distinguish the behavior of the bridge system under the near-fault and the far-fault earthquake. The duration of each of the four phases is accurately determined and the plastic degradation of the pier as well as the consumption of the friction interface are exactly evaluated. The difference of the behavior of the bridge system under the near-fault and the far-fault earthquake is qualitatively and quantitatively recognized.

Residual displacement demand for non-degrading bilinear SDOF oscillators with self-centering viscous-hysteretic devices

The self-centering viscous-hysteretic device (SC-VHD) is a high-performance self-centering system that was recently developed to reduce structural residual displacement and damage during severe earthquakes. This study focuses on developing a residual displacement ratio C r spectrum and a residual displacement estimation method for non‐degrading bilinear SDOF oscillators with SC-VHDs. Statistical analysis is conducted to investigate the effect of design parameters on the constant-ductility residual displacement ratio C r spectrum under near-fault pulse-like earthquake ground motions (NFPE) and far-fault earthquake ground motions (FFE). Based on statistical data, a formula for the mean C r spectrum is proposed. Subsequently, an iterative calculation method for residual displacement is presented according to the equivalent linearization method and the proposed mean C r spectrum formula. Finally, using the iterative calculation method, the residual displacement of a two-story steel moment-resisting frame (MRF) with SC-VHDs is predicted, demonstrating its application. The results indicate that the mean C r spectrum under the NFPE is significantly larger than that under the FFE. Besides, the mean constant-ductility C r spectrum decreases with increasing post-yield strength ratio, ratio of preload to yield strength, ratio of loading stiffness to elastic stiffness increases, or ratio of unloading stiffness to loading stiffness, but increases with increasing viscous damping ratio. When estimating the C r spectrum, increasing the ductility ratio and decreasing the ratio of preload to yield strength can both reduce record-to-record variability. Both the formula for the mean C r spectrum and the iterative calculation method for residual displacement are validated by comparing with statistical data. • The influence of design parameters on the residual displacement C r spectrum is investigated. • A formula for the normalized mean C r spectrum is developed. • An iterative calculation method for residual displacement is proposed. • An example application is used to validate the calculation method.

Analysis of general functional bearing model in a single-span bridge to identify structure response and suitable friction coefficient under near- and far-fault earthquakes

ABSTRACT Analysis of a single-span bridge with rubber bearing as the isolation system is performed under earthquakes. The conventional bridge seismic design requires the whole structure to be perfectly connected to avoid interrupting the transfer of earthquake energy from the ground through the bridge. A bridge with this typical design requires a high-cost construction due to the need for a huge section of the bridge to resist the earthquake force demand. Thus, many bridges in Taiwan are designed with a rubber bearing only put in between the column and girder without an anchor system. Thus, the bridge movement by rubber displacement is permissible, but the sliding displacement must be accommodated to limit the movement. The sliding displacement is the method to exploit the friction force provided by the sliding on the top and bottom interface of the rubber with the girder and column to dissipate the earthquake input energy transmitted to the structure. By involving the role of surface friction, the shear force transmitted to the structure can be reduced and the bridge performance optimized. General Functional Bearing Model (GFBM) analysis is a rubber bearing analysis which unmerges the function of friction and restoring force. In contrast with the conventional method, the rubber bearing designed with GFBM analysis may reduce the bridge stiffness and deck acceleration, and it is more convenient because only sliding displacement needs to be controlled. This research proposed GFBM analysis to simulate the rubber bearing that is reflected in the real conditions of bridges in Taiwan.