Seismic Response Of Building Structures Research Articles

Bandgap characteristics of a hybrid multi-resonator elastic metamaterial with negative stiffness mechanism and its application to mitigate seismic response of building structures

Seismic metamaterials have attracted extensive attention due to their unique ability to attenuate the transmission of elastic waves in their frequency bandgaps. However, generating a metamaterial with a low-frequency and wide bandgap remains challenging. Previous studies have shown that negative stiffness mechanisms can lower the frequency range of bandgaps while employing a multi-resonator technique can broaden the width of bandgaps. In this study, by combining these two techniques, a negative stiffness enhanced multi-resonator elastic metamaterial (NMEM) is first proposed. The feasibility of NMEM is validated by comparing the theoretical dispersion relation and the transmission spectra of a finite cell model. The results demonstrate that low-frequency and wide bandgaps can be realized by NMEM. To further widen the bandgap, a hybrid NMEM is proposed by connecting multiple types of cells in series. The proposed hybrid NMEM consists of two types of cells, one with a single resonator and another with two resonators, which merge individual bandgaps into a continuous and wider bandgap. The proposed hybrid NMEM is then adopted as a meta-basement for a case building to demonstrate its effectiveness in mitigating seismic responses. The results show that the seismic responses of the building with the hybrid meta-basement are considerably reduced than those of the building with the conventional basement. However, the hybrid meta-basement may lead to larger structural displacement response when the dominant frequency of ground motion is outside the designed bandgap.

Shaking table test and numerical simulation of a precast frame-shear wall structure with innovative untopped precast concrete floors

An innovative discretely connected precast concrete floor (DCPCF) was presented, in which the adjacent precast concrete hollow or sandwich flat slabs were connected by mechanical connectors embedded in the precast concrete slabs and beams. This paper summarized the seismic performance observed during the shaking table test of a precast frame-shear wall structure adopting DCPCF. A 1/4-scale model of a 4-storey 2-bay single-span frame-shear wall structure was designed and tested on the shaking table to evaluate the dynamic characteristics and seismic responses of building structures adopting DCPCF. In addition, a finite element model, including detailed modeling of beam-column joint and slab joint connections, was established using nonlinear dynamic modeling program. The predictions on the seismic performance using the finite element model agreed well with the test results for the designed frame-shear wall structure. The precast concrete frame-shear wall structure adopting DCPCF had satisfactory seismic performance during the test process. The in-plane deformation of DCPCF was observed under the horizontal earthquakes, and DCPCF could not satisfy the requirements of rigid diaphragm assumption in most cases under design basis seismic intensity. The seismic design method based on semi-rigid floor diaphragm had large error and safety risk in calculating the seismic shear force of building structure adopting DCPCF. Additionally, design suggestions for multi-storey and high-rise building structures using DCPCF were proposed based on the observed seismic responses.

Seismic assessment of the steel Moment Resisting Frame equipped with friction beam‐to‐column joints

AbstractSupplementary dissipative devices are viable solutions to enhance the seismic response of building structures. In particular, friction devices are low‐cost and easy‐to‐maintain systems that can be easily inserted into moment‐resisting beam‐to‐column joints of steel Moment Resisting Frames. The effectiveness of dissipative friction joints has been widely demonstrated in many research project. In Europe, the first building equipped with such devices will be fabricated in Italy within the framework of the ongoing RFCS DREAMERS project. The preliminary seismic assessment of this prototype building using the framework of performance‐based earthquake engineering method at different performance levels is summarized in the present paper. To this end, nonlinear dynamic analyses are carried out on three‐dimensional (3‐D) models of the prototype developed in “OpenSees”. The results show that this type of structure can be free of damage under earthquakes corresponding to significant damage and near collapse limit states.

Development of a Control Algorithm for a Semi-Active Mid-Story Isolation System Using Reinforcement Learning

The semi-active control system is widely used to reduce the seismic response of building structures. Its control performance mainly depends on the applied control algorithms. Various semi-active control algorithms have been developed to date. Recently, machine learning has been applied to various engineering fields and provided successful results. Because reinforcement learning (RL) has shown good performance for real-time decision-making problems, structural control engineers have become interested in RL. In this study, RL was applied to the development of a semi-active control algorithm. Among various RL methods, a Deep Q-network (DQN) was selected because of its successful application to many control problems. A sample building structure was constructed by using a semi-active mid-story isolation system (SMIS) with a magnetorheological damper. Artificial ground motions were generated for numerical simulation. In this study, the sample building structure and seismic excitation were used to make the RL environment. The reward of RL was designed to reduce the peak story drift and the isolation story drift. Skyhook and groundhook control algorithms were applied for comparative study. Based on numerical results, this paper shows that the proposed control algorithm can effectively reduce the seismic responses of building structures with a SMIS.

Soil-structure interaction: A state-of-the-art review of modeling techniques and studies on seismic response of building structures

The present article aims to provide an overview of the consequences of dynamic soil-structure interaction (SSI) on building structures and the available modelling techniques to resolve SSI problems. The role of SSI has been traditionally considered beneficial to the response of structures. However, contemporary studies and evidence from past earthquakes showed detrimental effects of SSI in certain conditions. An overview of the related investigations and findings is presented and discussed in this article. Additionally, the main approaches to evaluate seismic soil-structure interaction problems with the commonly used modelling techniques and computational methods are highlighted. The strength, limitations, and application cases of each model are also discussed and compared. Moreover, the role of SSI in various design codes and global guidelines is summarized. Finally, the advancements and recent findings on the SSI effects on the seismic response of buildings with different structural systems and foundation types are presented. In addition, with the aim of helping new researchers to improve previous findings, the research gaps and future research tendencies in the SSI field are pointed out.

Fragility analysis of high-span aqueduct structure under near-fault and far-field ground motions

Previous studies have shown that due to the notable characteristics of near-fault pulse-type (NFP) ground motions, such as large velocity pulse, narrow velocity-sensitive region and long period effect, there are significant differences in the seismic response of building structures caused by NFP ground motions and far-field (FF) ground motions. At present, the effect of NFP ground motions on the damage evolution characteristics of the aqueduct is still lacking. In addition, the current seismic design codes do not provide design recommendations for the dynamic response of aqueduct structures under NFP ground motions. The focus of this manuscript is to quantitatively evaluate the fragility of a high-span aqueduct system under NFP and FF ground motions. For this purpose, 10 as-recorded NFP and FF ground motions are considered, and the aqueduct bearing displacements and pier offset ratios are selected as performance evaluation indices. Then, the copula functions are introduced to establish the fragility curve of the high-span aqueduct system considering the seismic demand correlation of the aqueduct bearing and pier components. The results indicate that under same ground motion intensity conditions, the fragility probability of the aqueduct bearings is significantly larger than that of the trough pier under different performance levels, and should be considered in seismic design. In addition, the fragility probability curve of a single aqueduct component is used to describe the fragility probability of the aqueduct system, which overestimates its seismic performance. The fragility probability of a high-span aqueduct system under NFP ground motions is significantly greater than that under FF ground motions. Therefore, seismic safety assessments and seismic designs for the aqueducts should take into account the influence of NFP ground motions.

Modeling the Multi-Phased Hysteretic Friction Behavior of Aluminum Foam/Polyurethane Interpenetrating Phase Composites Damper

Aluminum foam/polyurethane (AF/PU) interpenetrating phase composites damper is a multi-phased hysteretic friction damper, which has a high potential for application to mitigating the seismic responses of building structures. In this paper, the hysteretic responses of the AF/PU composites damper subjected to different loading displacement amplitudes and loading cycles were experimentally investigated, and the main characteristics of the multi-phased hysteretic friction responses are assessed. According to the hysteretic responses of the AF/PU composites damper, a new model that is featured by a hysteresis mechanism, a nonlinear spring and a damping dashpot in parallel is constructed. Through the sensitivity analysis of relevant parameters, the optimum model is obtained and its main basic parameters ([Formula: see text]) are identified using the Universal Global Algorithm of the First Optimization software. The relationships of the main basic parameters with the loading displacement amplitude and loading cycle are then established. By the comparisons with the experimental results, it is validated that the proposed optimum model has an adequate capacity to capture and predict the important features of the multi-phased hysteretic friction characteristics under the various loading displacement amplitudes and loading cycles.

Modal-Based Ground Motion Selection Method for the Nonlinear Response Time History Analysis of Reinforced Concrete Shear Wall Structures

This paper presents a modification of the modal-based ground motion selection (MGMS) method for improving the reliability of the nonlinear response time history analysis (NLRHA) of reinforced concrete (RC) shear wall structures. The original MGMS procedure quantified the impact of frequency content combinations in the time domain (FCCTD) of input ground motions (IGMs) on the seismic response of building structures using the level of interaction of the first three modes induced by IGMs. However, previous research found that the first two modes have far larger modal mass coefficients than those of higher modes and dominate the vibration of the RC shear wall structures with a symmetric plan. Therefore, the MGMS procedure should be modified by employing the interaction of the first two modes induced by IGMs to properly account for the effect of the FCCTD of IGMs on the seismic response of structures. In the MGMS procedure for RC shear wall structures, seven IGMs that caused the most significant interactions of the first two modes were selected from a suite of twenty seed IGMs, which were chosen with a conventional spectra-matching-based IGMs selection procedure for the NLRHA of the structure. A comprehensive case study involving three RC shear walls with different heights was conducted to investigate the capability of the MGMS in selecting suitable IGMs for the NLRHA of RC shear wall structures. Sets of seed IGMs were selected, adopting conditional mean spectra and design spectra as the target spectra. It was found that the seismic demands computed using MGMS selected IGMs can ensure a more reliable and reasonable computation of seismic demands compared with conventional spectra-matching-based IGMs selection methods.

Seismic responses of multi-story building isolated by Lead-Rubber Bearings considering effects of the vertical stiffness and buckling behaviors

Elastomeric isolation bearing is one of the most commonly efficient devices and widely applied for protecting constructions in the earthquake regions. Its significant lateral deformation during operation, however, may affect its load-carrying capacity, especially the stability of the bearing. The current preliminary design method often focuses on shear behavior without effects of vertical stiffness and stability conditions that do not reflect the practical operation of devices. The paper presents the effect of vertical stiffness and buckling behavior on the seismic performance of lead-rubber bearing (LRB) used for seismic isolation in multi-story buildings. The effective parameters of LRB are estimated by the single-mode spectral analysis method, through a bilinear model, calculated by a typical target spectrum of Eurocode 8. A two-spring equivalent model is employed to study the effects of the vertical stiffness and critical buckling load that is varied as a function of lateral deformation. A set of time history nonlinear analysis is conducted to investigate the effects of vertical stiffness and critical buckling load on the seismic responses of building structures. The findings show the taking into account of the vertical stiffness and buckling behavior results in an increase of lateral displacements and a decrease of the lateral force and the floor acceleration of the isolated building.

Effect of differential settlement on seismic response of building structures

Differential settlement of footings of reinforced-concrete buildings is expected to have a considerable effect on design forces in various structural components depending on the characteristics of the soil. The differential settlement combined with the soil–structure interaction (SSI) effect during earthquakes may be a significant factor in deciding the structural response especially for structures that have already undergone differential settlement. This is generally ignored in conventional design practice. A four-storeyed building structure is considered for the study. A typical layered soil profile similar to the profile observed in the Ganges basin, India has been considered for investigation. The SSI effect under dynamic conditions has been considered by adopting Gazetas springs at the support of buildings. Twelve earthquake time histories have been considered for bedrock motion. Convoluted bedrock motions considering the soil profile have been adopted as the input motion for the structure. Effects of various earthquake parameters on the seismic response of buildings, considering the differential settlement and the SSI effect under dynamic conditions, have been investigated and presented in dimensionless terms. The results indicate that the differential settlements along with the SSI consideration may be critical in deciding the structural response. This may even render the structure unsafe during earthquakes.

Discussion of user‐defined parameters for recursive subspace identification: Application to seismic response of building structures

SummaryStructural damage assessment under external loading, such as earthquake excitation, is an important issue in structural safety evaluation. In this regard, an appropriate data analysis and system identification technique is required to interpret the measured data and to identify the state of the structure. Generally, the recursive system identification algorithm is used. In this study, the recursive subspace identification (RSI) algorithm based on the matrix inversion lemma algorithm with oblique projection technique (RSI‐Inversion‐Oblique) is applied to investigate the time‐varying dynamic characteristics. The user‐defined parameters used in the RSI‐Inversion‐Oblique technique are carefully discussed, which include the size of the data Hankel matrix (i), model order to extract the physical modes, and forgetting factor (FF) to detect the time‐varying system modal frequencies. Response data from the Northridge earthquake from the Sherman Oaks building (CSMIP) is used as an example to examine a systematic method to determine the suitable user‐defined parameters in RSI. It is concluded that the number of rows in the data Hankel matrix significantly influences the identification of the time‐varying fundamental modal frequency of the structure. An algorithmic model order selection method using the eigenvalue distribution of RSI‐Inversion can detect the system modal frequencies at each appending data window without causing any abnormality.

Hybrid seismic control of buildings using tuned mass and magnetorheological dampers

The use of magnetorheological (MR) dampers in combination with other control devices in a hybrid mode to enhance the control of the seismic responses of building structures is a subject of topical interest. This paper reports on the development of hybrid control schemes using different combinations of MR and tuned mass dampers (TMDs) to control the earthquake responses of building frames. The performance of the hybrid control schemes was evaluated by comparing the results with those of purely semi-active control schemes using three and four MR dampers consecutively placed in the bottom storeys of the frame. For the comparison, responses were obtained using four control strategies, namely a linear quadratic regulator with a clipped algorithm, passive-on, passive-off and a newly developed control strategy called velocity tracking control, which is especially suitable for partially observed states. The study showed that a maximum increase of 40–45% control of response could be achieved using a combination of a TMD and fewer MR dampers.

Seismic Response of Building Structures with Sliding Non-structural Elements

Interaction between a structure under base excitation and heavy non-structural elements that it supports is significant in the seismic analysis and design of the structure. Heavy non-structural elements may slide/rock under base excitation, and this dynamic action affects the seismic behavior of the supporting structure. Hence, in this study, a numerical model was presented to describe the seismic behavior of a primary structure (PS) supporting non-structural elements referred to as secondary bodies (SBs). The governing equations of motion for PS and SBs were developed considering Coulomb's friction model. Seismic hazard levels corresponding to Indian seismic zone III (medium hazard level) and V (highest hazard level) were considered. A parameter called displacement ratio (DR) was defined to quantify the sliding effect of SBs on the displacement response of the PS. A parametric study has been conducted to understand the variation in the DR due to varied time period of the structure, live loads to structure mass ratios and coefficients of friction between PS and SBs. From the analysis of results, it was concluded that the DR varies significantly with the time period, mass ratios, and coefficient of friction values. It can also be found from the study that the energy dissipation due to sliding of SBs was more in the highest hazard level than medium hazard level. Finally, the conditions for which the full mass of sliding secondary bodies should be considered in the seismic design of the structure are also presented.

Seismic response prediction method for building structures using convolutional neural network

In this study, a method of predicting the seismic responses of building structures based on a convolutional neural network (CNN) is proposed. In the method, the time histories of acceleration responses previously measured in a building during earthquakes are used in the CNN input layer, with the corresponding time histories of the displacement responses being used in the CNN output layer. The correlations between the features automatically extracted from the acceleration responses by the convolution and pooling operations in the various CNN layers and the displacement responses in the CNN output layer are established through CNN training. The trained CNN predicts the displacement responses for a future earthquake event using only the measured acceleration responses. To verify the validity of the proposed method, a numerical study on the ASCE benchmark model and an experimental study on a reinforced concrete frame structure are conducted. In the numerical study, the structural responses of the ASCE model subject to artificial earthquakes are utilized for CNN training, and the performance of the trained CNN is verified through seismic response prediction. In the experimental study, shaking table tests are performed for various earthquakes to measure the seismic responses of the reinforced concrete test structure. The seismic response prediction performance of the proposed method is examined using CNN trained with the measured seismic responses. Furthermore, the performances of CNNs trained with different numbers of datasets generated by the proposed data generation method based on data overlapping with the same data pool are discussed with related to the number of CNN training iteration number.

A novel robust optimum control algorithm and its application to semi-active controlled base-isolated structures

A new Robust Optimum control algorithm that combines a Linear Quadratic Regulator and a nonlinear robust compensator is presented to improve the control of the seismic response of building structures with nonlinear isolation systems. The Linear Quadratic Regulator was used to achieve the optimal performance of a nominal linear model of the controlled structure, and a robust compensator was developed to restrain the effect of nonlinearities. The Robust Optimum control method was proven theoretically, and implemented to control the response of a base-isolated structure equipped with a Tunable Friction Pendulum System isolation under different ground motions. The simulation results validated the stability, robustness, and generalization ability of the proposed control algorithm, and suggested that it is effective in controlling base isolation displacement, inter-story drift, and floor acceleration. The designed robust compensator can successfully compensate for the effect of nonlinearities.

A re-centering deformation-amplified shape memory alloy damper for mitigating seismic response of building structures

This paper presents an innovative re-centering deformation-amplified shape memory alloy damper (RDASD) to reduce the responses of civil structures under earthquake motions. The damper can amplify the displacement deformation according to actual needs and fully exploit the energy dissipation capacity of superelastic shape memory alloy materials. Cyclic tensile-compressive tests of the fabricated RDASD are conducted to study the influence of the displacement amplitude and loading rate on the damper's mechanical properties. Additionally, a theoretical model of the RDASD that can precisely simulate the hysteretic characteristics of the damper is proposed. Finally, a nonlinear time history analysis is performed on a six-story steel frame for three cases: no dampers, dampers without deformation amplification, and dampers with deformation amplified by a factor of 2.5. The results show that the proposed RDASD can not only effectively mitigate the displacement, acceleration, and interstory drift responses due to its efficient energy dissipation capacity but also provide superior re-centering by amplifying the relative deflection for building structures. In practical applications, the recommended range for the deformation amplification coefficient of the damper is 2.0–3.0.

Predicting Dynamic Response of Structures under Earthquake Loads Using Logical Analysis of Data

In this paper, logical analysis of data (LAD) is used to predict the seismic response of building structures employing the captured dynamic responses. In order to prepare the data, computational simulations using a single degree of freedom (SDOF) building model under different ground motion records are carried out. The selected excitation records are real and of different peak ground accelerations (PGA). The sensitivity of the seismic response in terms of displacements of floors to the variation in earthquake characteristics, such as soil class, characteristic period, and time step of records, peak ground displacement, and peak ground velocity, have also been considered. The dynamic equation of motion describing the building model and the applied earthquake load are presented and solved incrementally using the Runge-Kutta method. LAD then finds the characteristic patterns which lead to forecast the seismic response of building structures. The accuracy of LAD is compared to that of an artificial neural network (ANN), since the latter is the most known machine learning technique. Based on the conducted study, the proposed LAD model has been proven to be an efficient technique to learn, simulate, and blindly predict the dynamic response behaviour of building structures subjected to earthquake loads.

Direct adaptive algorithm for seismic control of damaged structures with faulty sensors

In recent decades, the application of semi-active control strategies has gained much attention as a way to reduce the seismic response of civil infrastructures. However, uncertainty in the modeling process of systems with possible partial or total failure during an earthquake is the main concern of engineers about the reliability of this strategy. In this regard, adaptive control algorithms are known as an effective solution to adjust control parameters with different uncertainties. In the current study, the efficiency of the simple adaptive control method (SACM) is investigated to control the seismic response of building structures in the presence of unknown structural damage and fault in the sensors. The method is evaluated in 20-story steel moment resisting frames with different arrangement of smart dampers and sensors with various damage and fault scenarios. The results show that the SACM control system can effectively reduce the maximum inter-story drift of the structure in all different assumed magnetorheological damper arrangements. Furthermore, combination of a Kalman–Bucy filter with the SACM improves robustness of the controller to the uncertainties of sensors faults and damages of structural elements.

Effects of nonlinear soil–structure interaction on the seismic response of structure-TMD systems subjected to near-field earthquakes

The present investigation illustrates the performance of structure-Tuned Mass Damper (TMD) system to suppress the excessive vibration of structure buildings subjected to near-field ground motions involving the nonlinear effects of three dimensional soil–structure interaction (SSI). Accordingly, three medium-to-high-rise controlled structures based on a shallow mat foundation located on soft to very dense soil are examined. The ground motion database compiled for nonlinear time history (NTH) analyses of the soil–structure-TMD systems consists of an ensemble of 52 near-field ground motions. Comparisons are made in terms of maximum inter-story drift ratio as well as maximum inter-story acceleration ratio for the three possible conditions of the foundation: fixed-base structure, linear SSI (LSSI) and nonlinear SSI (NLSSI). The seismic responses of building structures are studied under the variation of key parameters such as peak ground velocity, factor of safety against vertical load bearing of the foundation (FS), non-dimensional frequency (a 0), ground motion characteristic and number of stories. On the one hand, the results indicate that the nonlinear effects of SSI significantly modify the structural responses in comparison with the LSSI counterpart. On the other hand, soil failure decreases the effectiveness of TMD. In a more precise view, it can be demonstrated that installing TMD can suppress the response of structures with linear SSI and without SSI (fixed-base structure) more significantly than that of structures considering NLSSI. Consequently, the responses would generally be underestimated if a linear behavior of the soil is assumed.

Influence of earthquake direction on the seismic response of irregular plan RC frame buildings

The nonlinear response of structures is usually evaluated by considering two accelerograms acting simultaneously along the orthogonal directions. In this study, the influence of the earthquake direction on the seismic response of building structures is examined. Three multi-story RC buildings, representing a very common structural typology in Italy, are used as case studies for the evaluation. They are, respectively, a rectangular plan shape, an L plan shape and a rectangular plan shape with courtyard buildings. Nonlinear static and dynamic analyses are performed by considering different seismic levels, characterized by peak ground acceleration on stiff soil equal to 0.35 g, 0.25 g and 0.15 g. Nonlinear dynamic analyses are carried out by considering twelve different earthquake directions, and rotating the direction of both the orthogonal components by 30° for each analysis (from 0° to 330°). The survey is carried out on the L plan shape structure. The results show that the angle of the seismic input motion significantly influences the response of RC structures; the critical seismic angle, i.e., the incidence angle that produces the maximum demand, provides an increase of up to 37% in terms of both roof displacements and plastic hinge rotations.