Severe Seismic Excitations Research Articles

Large-scale cushion type bare and partially rubber filled mechanical couplers subjected to uniaxial cyclic loading

Large-scale bare mechanical coupler (BMC), and partially rubber-filled mechanical coupler (PFMC) were developed in this study. BMC and PFMC were created to utilize especially at high-performance hybrid post-tensioned rocking wall (HPRW) systems. BMC can couple adjoining HPRWs in the vertical direction as a yielding-type supplemental damper. PFMC can couple HPRWs to the foundation beam and/or adjacent HPRWs at the story level in the horizontal direction. It can function as a supplemental energy absorber with high bearing capacity and adequate lateral strength. Since BMC and PFMC are joined externally to HPRWs, they can be replaced easily after severe seismic excitation. The quasi-static cyclic shear and axial tests were carried out on BMCs and PFMCs to evaluate their hysteretic behaviour and determine their structural properties. The experimental parameters, besides the loading type, were the plate thickness of BMCs and the density of steel sheet layers at rubber blocks of PFMC. The experimental results demonstrated the desired performance of BMCs and PFMCs under cyclic shear and axial actions. BMCs showed high-energy dissipation capability and displacement capacity. PFMCs represented high bearing capacity with sufficient lateral strength and energy dissipation capability. Although there was no Mullin effect on the PFMCs response subjected to cyclic shear loading, it was observed on the response of PFMCS under cyclic axial effect. Monotonic and unidirectional cyclic tests of tension, planar shear, and compression were conducted on the rubber pieces to simulate the rubber blocks at PFMCs, as well. Finite element models of BMCs and PFMCs were developed to grasp comprehensively the hysteretic behaviour. The validated model was established and the modeling techniques were described in detail.

Mechanical Model and Damping Effect of a Particle-Inertial Damper

Particle dampers (PD) are safe, economical, and effective energy-dissipation devices for structures. However, the additional mass of PD must be sufficiently large to provide a better damping effect, and the initial movement condition of particles has a significant impact on the damping effect of PD. In this study, a particle-inertial damper (PID) is proposed to overcome these problems, and its mechanical model is established with and without considering particle collision. Subsequently, the influence of particle rolling friction and particle collision on the inertial amplification capacity as well as the dynamic response of a single degree of freedom (SDOF) structure with non-collision and collision PID (SDOF-PID) are systematically analysed. Finally, the control effects of a PID and a tuned mass damper (TMD) are compared based on two typical optimisation methods. The results indicate that particle rolling friction has little influence on the inertia amplification effect of a PID and the displacement response of a SDOF-PID. Under harmonic excitation, particle collision significantly affects the damping mechanism of a PID by its equivalent inertia coefficient, equivalent damping coefficient, and equivalent stiffness coefficient. The fixed-point theory and ‘performance-cost’ theory can be used to optimise the PID to a certain extent. The damping effect of a PID on the SDOF under the most severe seismic excitation is better than that of the PID under white noise excitation. With respect to the decreasing ratio of 40~50%, the additional mass of the PID is only one thousandth that of the TMD under the same damping capacity demand.

Hilbert–Huang-Transform-Based Seismic Intensity Measures for Rocking Response Assessment

Structures that can uplift and rock under severe seismic excitations present remarkable stability without exhibiting damage. As such, rocking-response-based structural systems constitute a promising design practice. Due to the high nonlinearity of the rocking response, the seismic performance of this class of structures should be evaluated probabilistically. From this point of view, in the present study, the performance of 12 novel HHT-based intensity measures (IMs) in describing the seismic behavior of typical rocking viaducts was assessed based on optimal IM selection criteria. To this end, a comparative evaluation of the performance between the proposed and 26 well-known conventional IMs was presented. Moreover, bivariate IMs were also considered, and seismic fragilities were provided. Finally, the classification of the seismic response was conducted using discriminant analysis, resulting in a reliable and rapid estimation of the maximum seismic demand. Based on the results, it is evident that HHT-based IMs result in an enhanced estimation of the seismic performance of the examined structural system.

Modeling Reinforced Concrete Moment Frames Supported on Quintuple Friction Pendulum Bearings for Nonlinear Response History Analysis

Base isolation systems have attained significant advancements over the past several decades, with new technologies being developed to enhance the performance of structures when subjected to moderate and severe seismic excitations. The multi-stage friction pendulum is among the most efficient systems owing to its broad range of effective pendula with several regimes that provide excellent energy dissipation abilities. Lately, a new generation of friction pendulum bearings called “Quintuple Friction Pendulum” was introduced to the literature and has since gained the attention of researchers. This isolator’s most significant advantages are the results of its capability to achieve multi-stage adaptive behavior which shows high energy dissipation capability from structures exposed to horizontal forces. Indeed, investigations that outlined the process for nonlinear modeling of structures supported on this type of isolation system are scarce. Thus, this research is intended to illustrate and discuss the approach for developing seismic code compliance finite element models for designing and analyzing reinforced concrete moment frames supported on quintuple friction pendulum bearings for nonlinear response-history analysis in OpenSees and SAP2000. As a part of the study, the nonlinearity of the isolation system and the superstructure will be considered. Moreover, the methods for overcoming essential issues such as damping leakage and isolator’s stiffness correction will be discussed. In general, the results of the discussed numerical examples have shown that both finite element packages are capable of achieving QFP hysteresis behavior as well as computing similar superstructural responses. Furthermore, the illustrated method of overcoming damping leakage provided reliable outcomes compared to the theoretical expectations. As well as the suggested approach for correcting the isolator’s initial stiffness was helpful in terms of accurately capturing the structure’s periods.

Developing a physics-informed and physics-penalized neural network model for preliminary design of multi-stage friction pendulum bearings

Over the last few decades, the field of base isolation systems has made significant strides forward by developing new systems to improve the behavior of isolated structures under moderate and severe seismic excitations. One of the most efficient systems is the multi-stage friction pendulum that can provide a wide range of effective pendula with various regimes to reach high energy dissipation capability. The difficulty in designing such bearing at the preliminary stage comes from the relatively long process of trials to select the parameters of each sliding surface in order to ensure that the required effective period, effective damping, and displacement capacities are met. Thus, the following study proposes a direct design approach relying on a physics-informed and physics-penalized neural network model to overcome this issue. Within the context of the analysis, a large dataset composed of over 35000 isolators that covers a wide range of properties of the recently developed generation of friction pendulum “Quintuple Friction Pendulum” was generated following the mechanics-driven approach and then utilized as the case study to test the reliability of suggested design strategy and capability of the proposed multi-output neural network method. Thereafter, the performance of the physics-informed and physics-penalized model was compared to a purely data-driven approach and a physics-informed one. Generally, the results have shown that the proposed model has considerable accuracy with a maximum MAPE of 4.89% for achieving the required QFP properties. Additionally, they showed that the presented method provides an effective way for rapidly designing a quintuple friction pendulum isolator.

Intelligent modeling of nonlinear dynamical systems by machine learning

An intelligent data-driven method of modeling nonlinear dynamical systems named as LSTM network with output recurrence (OR-LSTM) is proposed, which can learn the inherent characteristics of the dynamical systems from data and predict the states of the systems given external excitation and initial conditions. For the proposed OR-LSTM architecture, the most important key point is output recurrence connections. In order to evaluate it, a teacher-forcing LSTM network without output recurrence connections (TF-LSTM) is designed for comparison. The differences between OR-LSTM and TF-LSTM from the perspective of gradient propagation and parameter updating are analyzed firstly. To verify the capability of the LSTM networks in dynamical systems modeling, the oscillation of a 42-story reinforced concrete frame-core tube building under severe and extreme seismic excitations are modeled. The results show that the OR-LSTM network performs well and maintains the long-term robustness in earthquake responses prediction, even only known displacements of 9 stories. However, the TF-LSTM network fails. In order to evaluate the extensive practicability of the OR-LSTM network, the famous Van der Pol dynamic system and Lorenz dynamic system with strong nonlinearity are also modeled by the proposed method. The results show that OR-LSTM network is competent in modeling most of nonlinear dynamic systems, while has limited in fully chaotic systems, but the predictable length of time sequence and prediction accuracy are improved.

EFFECTS OF SHEAR WALLS ON A TYPICAL FOUR-STORY REINFORCED CONCRETE STRUCTURE SUBJECTED TO SEVERE EARTHQUAKE EVENTS

Various seismic-resistant design methods are used to ensure the stability of multi-story buildings against lateral forces caused by earthquakes. Utilization of reinforced concrete shear walls is one of the most reliable methods of design and construction of earthquake-resistant buildings because it increases structural resistance to lateral loads and stiffens and strengthens the structure, thereby minimizing earthquake-induced damages. This paper investigates the beneficial effects of using shear walls in the structural design of a typical low-rise building to improve its resistance to earthquake events. To this end, a four-story reinforced concrete structure is modeled first without shear walls, then with the addition to shear walls. The 2002 Denali Alaska earthquake is used as an example of a severe seismic excitation because it is considered the most massive strike-slip earthquake in North America in almost 150 year. SAP2000 is used to perform the dynamic analysis. In order to obtain an accurate representation of the structure’s behavior, response modal nonlinear time-history dynamic analysis is utilized to analyze and compare the response of the building with and without shear walls. Study results showed that shear walls are very effective in achieving compliance with seismic design codes. In addition, the use of shear walls significantly reduces the shear stresses, bending moments, and displacements of the various members of the structure.

A Parametric Study on the Effects of Shear Wall Locations in a Typical Five-Story Reinforced Concrete Structure Subjected to a Severe Earthquake

To minimize earthquake-induced damages in structures, one of the most reliable ways to design and construct earthquake-resistant buildings is to utilize reinforced concrete shear walls because they increase the structural resistance to lateral loads and effectively stiffens and strengthens the structure. This is known as the best seismic-resistant design method that ensures the stability of multi-story buildings against lateral forces when subjected to strong earthquakes. This paper investigates the effects of the shear wall location in a typical low-rise building to improve earthquake resistance. The study initially models a five-story reinforced concrete structure without shear walls and then adds shear walls at different locations in the structure. SAP2000 is used to perform dynamic analysis under the 1994 Northridge earthquake, an example of severe seismic excitation. Response modal nonlinear time-history dynamic analysis is utilized to obtain an accurate representation of the structure’s behavior. The response of the building with and without shear walls is analyzed and compared for various locations of the shear walls in the structure. Study results show that shear walls effectively reduce horizontal displacements and story drifts to achieve compliance with seismic design codes. The use of shear walls also significantly reduces shear stresses, bending moments, and displacements of various members of the structure. Numerical values and maximum percent of possible changes in the design parameter are reported in the paper. Various seismic demands of the elastic models (with and without shear walls) have been evaluated and compared. The presented work claims that shear walls effectively reduce shear stresses. It is a fact that increasing the stiffness of the structure in severe seismic zones could simultaneously attract more seismic forces, and if the reinforcement is not detailed appropriately, it could reduce the ductility of the structure. The structural elements, including frame elements and the shear walls are inelastic.

3D FEM Soil-Structure Interaction Analysis for Kashiwazaki–Kariwa Nuclear Power Plant Considering Soil Separation and Sliding

In the 2007 Niigataken Chuetsu-oki earthquake, soil settlement, considered to be a result of the relative displacement between the soil and the structure, occurred alongside buildings at Kashiwazaki–Kariwa nuclear power plant. The objective of this study is to evaluate accurately the influence of the nonlinear behavior of the soil-structure interface on the response of the reactor building using a three-dimensional finite element model. To achieve this, we modeled the separation and sliding from sidewalls during a severe earthquake using joint elements, and evaluated the effect on the horizontal response of the structure. Through the soil-structure interaction analyses based on the recorded seismic data on the foundation for unit 7 reactor building using the three-dimensional finite element model, it was confirmed that the simulated horizontal responses of the building corresponded to the recorded seismic data. In addition, the comparison of the cases with and without separation and sliding revealed that the separation and sliding of soil from sidewalls reduces the embedment effects of the structure and that the reduction causes an occurrence of the foundation uplift. Moreover, in this study, it was clarified that the increase of the foundation uplift affected both the soil pressure characteristics beneath the foundation and along the sidewalls, and the maximum acceleration response of structures. In this study, the separation and sliding of soil from sidewalls had only a limited influence on the structural responses; however, under severe seismic excitation, it is expected that the embedment effects will be significantly reduced due to the separation and sliding of soil. Therefore, a precise response evaluation of the building including the nonlinear behavior due to separation and sliding should be considered in the seismic response analyses under severe seismic excitation.

Two-dimensional nonlinear energy sink for effective passive seismic mitigation

Structures and machines are often exposed to sudden high-amplitude vibrations that may cause local or extended structural failure. This calls for effective and reliable methodologies for vibration mitigation, one of which is the use of linear or nonlinear dynamic vibration absorbers. Current studies in this area have focused mainly on uni-directional vibration absorbers, thus limiting their applicability in practical applications where the excitation is applied in the plane. For example, real-life structures are subjected to a multitude of multi-directional seismic excitations, so uni-directional devices for mitigating such effects would have limited effectiveness. Accordingly, in this work we propose a two-dimensional nonlinear passive absorber, which we term two-dimensional nonlinear energy sink (2D-NES), and investigate its efficacy to robustly suppress seismic excitations in arbitrary directions on the plane. First, a numerical optimization process is formulated to optimize the 2D-NES for the especially severe Kobe seismic excitation through a set of quantitative measures related to the seismic response of the primary structure. Then, its robustness is confirmed by applying two additional historic earthquakes with different frequency and energy contents. The results demonstrate that the optimized 2D-NES is capable of effectively and rapidly suppressing seismic, multi directional excitations. This work is one of the first studies of 2D nonlinear vibration absorbers capable of robust passive mitigation of seismic loads applied in arbitrary planar directions. This design can be suitable for broad applications ranging from the nano/micro- to the macro-scale.

Extremely Low Cycle Fatigue Failure Behavior of Box-column to I-beam Welded Joints

In this paper, cyclic loading tests are carried out to study the extremely-low-cycle fatigue (ELCF) failure behavior of the beam-to-column welded joints of steel structures subjected to severe seismic excitation. Firstly, the fatigue crack evolution and local strain of the weld zone obtained from experiments are adopted to investigate ELCF failure behavior for steel structures. In these experiments, three large scale specimens of box-column to I-beam connection are controlled by different cycle displacement ranges greater than the yield displacement. Secondly, the crack initiation and propagation law as well as the damage and deterioration mechanism are examined; then, the preliminary criterion for crack initiation for the box-column joint is proposed. Finally, failure characteristics and strain distribution of the box-column joint are analyzed. This study shows that the ELCF failure of the box-column to the I-beam joint is multiaxial and nonproportional. Based on the crack initiation and propagation along the thickness direction of the beam flange, the crack macro-penetration mode can be divided into two categories, i.e., standard failure mode and mixed failure mode. Moreover, load drop, change rate of load drop, and loading amplitude are key factors of the damage mechanism.

Effect of ground motion directionality on the seismic response of base isolated buildings pounding against adjacent structures

Seismic isolation is considered an effective design approach in averting structural and non-structural damage under severe seismic excitations. However, considerable relative displacements at the isolation level during a strong ground motion may lead to structural collisions with the surrounding moat wall and neighboring structures. Such pounding incidences, which may have detrimental consequences on the anticipated seismic behavior and performance of base isolated structures, are investigated in the presented research work. A computational methodology with the ability to capture impact forces is employed, in order to spatially examine potential structural impact with adjacent structures. Specifically, nonlinear time-history analyses of base isolated buildings, pounding with nearby conventionally fixed-supported buildings and/or the surrounding moat walls are carried out in order to examine the conditions that lead to pounding and quantify the effect of certain critical parameters on the corresponding peak seismic response. Specifically, the directionality of the imposed seismic excitations with respect to the primary construction axes of the simulated base isolated buildings is considered as an influencing parameter. The effect of other parameters, such as the clearance between the base isolated building and adjacent structures, the structural characteristics of the neighboring structures and the inclusion of accidental torsion for the seismically isolated structures in terms of mass eccentricities, is also investigated.

A New Hybrid SPH–FEM Model to Evaluate Seismic Response of TSD Equipped-Structures

Tuned Sloshing Dampers (TSD) are passive devices, working based on shallow liquid sloshing in a rigid tank to suppress the horizontal structural vibrations induced by wind loading or earthquake excitations. The key parameters in design of a TSD could be referred to the natural frequency of the liquid sloshing motion and the inherent damping of the TSD during the excitation. Due to the highly nonlinear behavior of the liquid free-surface occurring in TSDs, accurate prediction of the TSD-structure’s behavior during strong excitations is highly desirable. In the current paper, Weakly Compressible form of Smoothed Particle Hydrodynamic (SPH) method is used to simulate the flow within rectangular TSDs during large movements. Characteristics of the flow such as wave height and sloshing forces acting on the container’s walls are calculated and compared with the existing experimental and numerical data. A hybrid SPH-Finite Element Method (FEM) was developed to investigate the seismic response of MDOF structures equipped with multiple TSDs. The proposed model was employed to evaluate the dynamic response of MDOF structures under severe seismic excitations with different frequency contents. The results showed that depending on the frequency content of the ground motion, having the TSDs tuned to a frequency close to the natural frequency of the structure could significantly alter the seismic response of the structures. The effectiveness of TSD is also related to the higher modes effect for MDOF structures and location of TSDs placed on the structural floors.

Three-dimensional seismic response of two-story wooden buildings with seismic devices using mechanical linkage

In the previous study by the authors, the seismic device which consists of mechanical linkage and steel dampers (MLD) has been proposed to prevent wooden houses from soft-story mechanisms under severe seismic excitation. In this study, the static cyclic loading test on the connection between the MLD and the wooden member is conducted to examine the mechanical performance of the connection. It is shown through experimental and numerical studies that the proposed detail of the connection has enough stiffness and strength and the MLD successfully works to prevent the wooden houses from the soft story collapse.

Shake Table Test on Seismic Response of a Precast Frame with Recycled Aggregate Concrete

A precast frame model made of Recycled Aggregate Concrete (RAC) was constructed with precast beams, columns and Cast-In-Place (CIP) joints. Then a shaking table test was carried out with three types of earthquake ground motions, namely Wenchuan, El Centro and artificial Shanghai waves. Based on the shaking test, structural responses such as dynamic characteristics, cracking and failure pattern, seismic responses as well as the overall seismic performance of the model were analyzed and evaluated. The results indicate that the precast RAC frame structure has an adequate load bearing potential as well as ductility against moderate and severe seismic excitations. Therefore, the perfect combination of RAC and precast structures is feasible to apply and popularize precast RAC frame structures with mid-rise buildings in the seismic regions.

Strongback System: A Way to Reduce Damage Concentration in Steel-Braced Frames

This paper examines a newly developed seismic force-resisting system: the strongback system (SBS). To achieve improved seismic performance, this system combines aspects of a traditional concentric braced frame with a mast to form a hybrid system. The mast acts like a strong back to help resist the tendency of concentric braced frames to concentrate damage in one or a few stories during severe seismic excitations. The purpose of the strongback system is to promote uniform story drifts over the height of a structure. Three SBS prototypes were designed and analyzed considering a variety of earthquake excitations. Computed responses are compared with responses for three other braced frame systems. Results of quasi-static inelastic analyses, both monotonic and cyclic, are presented to demonstrate differences in the fundamental hysteretic behavior of the braced frame systems considered. A series of nonlinear dynamic response history analyses were then performed to compare the global and local dynamic response of each system. Results show that the SBS can effectively reduce the concentration of deformations using the proposed design strategy. Simplified cost analyses demonstrated the economic feasibility of incorporating the SBS for newly constructed buildings located in seismically active regions.

Near-fault isolation of cable-stayed bridges using RNC isolator

This paper investigates the near-fault (NF) seismic performance of a recent isolation system, referred to as Roll-N-Cage (RNC) isolator, considering the cable-stayed Bill Emerson Memorial Bridge in Missouri, USA. Under NF ground motion, the seismic isolation devices might perform poorly because of large isolator displacements caused by long-period large velocity and displacement pulses associated with such strong motion. The RNC isolator is designed to achieve a balance in controlling isolator displacement demands and structural accelerations. It provides in a single unit all the necessary functions of rigid support, horizontal flexibility with enhanced stability and energy dissipation characteristics. Moreover, it is distinguished from other isolation devices by two unique features: (1) it has a built-in energy absorbing buffer to limit the isolated deck displacement under severe seismic excitations to a preset value and (2) it has a built-in linear recentering mechanism that prevents residual displacement after earthquakes. The seismic response of the RNC-isolated cable-stayed bridge is investigated using nonlinear time history analysis under three recorded NF earthquakes and three synthetic ground accelerations that capture many of the kinematic characteristics of recorded NF ground motions. The results show that the RNC isolator is a convenient isolation system in protecting cable-stayed bridges against NF earthquakes.

Seismic Upgrading Strategies for Non-Ductile Plan-Wise Irregular R/C Structures

Abstract This study investigates the effectiveness of different strategies for the seismic retrofitting of a gravity-load-designed plan-wise irregular R/C building tested at the JRC Elsa Laboratory. An alternative retrofitting intervention based on both FRP wrapping and R/C jacketing applied to selected critical columns was proposed. The retrofitting strategy was focused on two main objectives: 1) relocating the centre of stiffness and strength in order to reduce the torsional component of the response of the structure; 2) increasing the local deformation capacity of columns and thus the global deformation capacity of the structure. Nonlinear dynamic time- history analyses and simplified procedures based on nonlinear static pushover analyses were carried out and comparison with the retrofitting interventions carried out at the JRC ELSA Laboratory were performed. Bidirectional damage indexes were used to identify the most critical columns affecting the seismic performance of the structure. The simplified procedure provided results consistent with the experimental evidence and allowed to easily select a suitable retrofitting strategy. Numerical results showed the effectiveness of the strength-and- stiffness relocation strategy based on R/C jacketing of selected columns, but the local ductility increase based on FRP wrapping of the other columns was necessary for significantly improving the global seismic performance of the structure in case of severe seismic excitation.

Seismic Protection of Steel Frames Using Friction Damper Devices

This study investigates a friction damping bracing system in order to improve the response of steel frames when subjected to severe seismic excitations, beyond the design earthquake. A simplified model describing the behavior of the friction damper device was developed for global analyses of steel frames. Parametric analyses based on numerical simulations were carried out to evaluate the slip force with the aim of minimizing the values of top displacement and hysteretic energy dissipated by the steel frame. The main results of nonlinear dynamic analyses performed on a six-story steel frame incorporating friction damping bracing systems are presented and compared with the response of the unprotected counterpart. The effectiveness of the protection system was also assessed by examining the seismic response of the frame equipped with traditional braces, without friction devices. The results of the numerical investigations showed that the use of the friction damping bracing system caused an increase of the dissipative capacity of the frame, above all for high seismic actions. The plastic deformation concentrated inside the device, protecting the main structural elements from severe damage. The formation of the plastic hinges at the column base was delayed with respect to the unprotected frame. Numerical analyses indicated that the introduction of supplemental damping by using friction devices in steel bracings is very effective for seismic protection of steel frames subjected to severe seismic excitations.

Seismic Response of Steel Buildings with Different Structural Typology

This study investigates the influence of the in-plan structural layout on the seismic response of symmetric and asymmetric steel structures. A five-storey steel frame building was used as reference structure and two different structural systems were employed to represent torsional stiff and torsional flexible structures. Accurate numerical models of the different typologies of structures were developed and both nonlinear static and dynamic analyses under bi-directional ground motion were carried out. The influence of axial force-bending moment interaction in columns in the two main directions and second order effects were taken into account in the numerical analyses. The results of the numerical investigations on symmetric structures showed that the reduction of the number of moment resisting connections may lead to an increase of the structural damage. Asymmetric variants of the investigated structures were created by assuming different mass eccentricities in each of the two main directions and extensive parametric studies were performed. For the torsionally flexible building, the influence of ground motion intensity was very strong. A transition from torsionally flexible to torsionally stiff behaviour in the weaker direction of the initially torsionally flexible structure was observed for severe seismic actions. The change of the stiffness of the structure in one direction due to high levels of plastic deformations affected the structural response in the orthogonal direction. Torsional effects decreased in case of severe seismic excitations and high levels of plastic deformations. The reduction of torsional effects observed for low seismic actions on the stiff side of torsionally stiff buildings disappeared under strong seismic excitations.