Results Of Time History Analysis Research Articles

Effects of Base Isolation and Infill Panels on the Nonlinear Time History Analysis of Reinforced Concrete Building

This paper presents the predicted results of nonlinear time history analysis of 11 storey (G+10) Reinforced Concrete (RC) residential building under the effects of a strong earthquake. The paper includes studying the effects of using Lead Rubber Bearings (LRB) as base isolators to improve the performance of RC building to sustain the impact of an earthquake. It also includes the effects of the infill panels on the overall dynamic response of both fixed base and base-isolated buildings subjected to a strong earthquake. The main results that are presented in this study include the variation of roof acceleration, roof displacement, base shear with time. The effects of using LRB and including the infill panels on the storey drift are also presented. Maximum reduction in the story drift was obtained when infill panels are included in the analysis of the base isolated building. The inclusion of the infill panels has only marginal effects on the variation of roof displacement with time when the building is isolated by LRB. The main important improvements that emerged from using LRB as well as the infill panels in the analysis are the reduction of inelastic energy and upgrading the elastic one that is summed up along the period of the earthquake.

New performance-based plastic design and evaluation of blind bolted end-plate CFT composite frames with BRBs

The blind bolted end-plate connection to concrete-filled steel tube column (BECFT) composite frame with buckling-restrained braces (BRBs, BRB-BECFT) is a novel dual structure system that combines advantages of fast assembly ability for BECFT connections, great energy dissipation capacity for BRBs coupled with BECFT connections and superior gravity load-carrying capacity for concrete-filled steel tube (CFT) columns. Given authors’ prior experimental and theoretical studies on the BRB-BECFT structure system, and as no design method is as far introduced for this system with adequate accuracy, a new plastic design procedure based on the modified energy balance and global yield mechanism in the framework of performance-based plastic design method was proposed. The post-yielding stiffness and overall yield inter-story drift of the BRB-BECFT structure system was considered to improve the accuracy of the design base shear. Meanwhile, the BRB-BECFT structure system was decomposed into the BRB system and BECFT frame system to simplify the design process. Moreover, some formulae to avoid structural adverse yield mechanism were derived. The semi-rigid characteristic of BECFT connections was introduced into the structural global yield mechanism by work-energy principle to ensure the deformation consistency between inter-story drift and BECFT connection rotation. Finally, four prototype structures with 6, 9, 12 and, 20 stories were designed as examples to illustrate the effectiveness and robustness of the proposed design method. The results of nonlinear time-history analyses showed that the designed structures successfully achieved the pre-selected performance objectives in terms of the inter-story drift, residual drift, BECFT connection rotation, and BRB ductility demands.

Study on normalization of residual displacements for single-degree-of-freedom systems

Residual displacement spectrum is one of the most important means to predict the permanent deformation of structures after the earthquake, and various normalizations of residual displacements have generally been used for construction of the spectrum. However, the issue regarding the merits and drawbacks of each normalization has not yet been investigated thoroughly. A comparison between two normalizations that relate the residual displacements to the elastic and inelastic displacements is made in terms of the effect of ground motion and structural characteristics by means of the results of nonlinear time history analysis. The statistical results reveal that the residual-to-peak-inelastic displacement ratios have the advantages of small dispersion, samples without any outliers, and relatively symmetric distribution, which benefits from the strong correlation between residual and peak inelastic displacements. Moreover, the residual-to-peak-inelastic displacement ratios are almost independent of site conditions, significant duration, and natural periods. Consequently, the peak inelastic displacements are superior to the elastic ones as an intermediate step for residual displacements estimation, provided that the peak inelastic displacements are estimated with a low uncertainty. For providing alternatives to estimate residual displacement demands, the constant-strength residual displacement spectra are developed for both normalizations.

Seismic evaluation of reinforced concrete bridges using capacity‐based inelastic displacement spectra

AbstractA simplified seismic evaluation method using capacity‐based inelastic displacement spectra is proposed for reinforced concrete (RC) bridges. The proposed method can not only estimate the maximum displacements of bridges, but can also discriminate the damage indices between the bridge columns, where the Park and Ang's damage index () is considered a promising performance indicator due to its good relationship with the strength capacity state and actual visual damage condition of the bridge column regardless of the imposed loading history. To realize the accuracy and reliability of the proposed method, a hypothetical case study bridge was constructed and analyzed using various structural analysis programs and seismic evaluation methods. It was found that the proposed method can receive satisfactory estimates of the maximum displacement and for both far‐field and near‐fault ground motions when compared to the nonlinear time history analysis results of the bridge. In contrast, the AASHTO's and Caltrans’ methods cannot reflect the response amplification effects caused by the frequency‐content characteristics of near‐fault ground motions and would therefore significantly underestimate the inelastic responses of bridges. When applying the proposed method to bridges having unequal‐height columns and subjected to longitudinal seismic actions, it was found that for the short column of the bridge, the AASHTO's regularity criteria (maximum bent/pier stiffness ratio of 4 for the three‐span case study bridge) would lead to a of approximately 3.5 times that of the tall column, resulting in significant damage localization and, hence, decreasing the overall lateral deformation capacity of the bridge.

Seismic response reduction of elastoplastic structures with inerter systems

Several studies have focused on the mechanism of an inerter, which is an acceleration-dependent two-terminal element, while other studies have concentrated on developing a design method for a structure with an inerter system. However, to the best of the authors’ knowledge, the nonlinearity of the primary structure has never been considered, leading to uncertainty in design results. Particularly when a structure experiences a rare earthquake, its safety becomes uncertain because of the deterioration of structural stiffness. Therefore, this study focused on seismic control of an elastoplastic structure and explored a demand-oriented design method for it. In this paper, the basic concept of an inerter system is firstly introduced. Then, various aspects of the design method are elaborated, including the performance index, design parameters, and optimal equation for elastoplastic single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) structures. Specifics of the design procedure are also described. A parameter distribution pattern is employed to reduce the computation cost for the MDOF structure. Subsequently, an elastoplastic SDOF structure and a two-dimensional steel benchmark model are employed to carry out seismic design, and the parameters of the inerter systems are obtained. Nonlinear time history analysis results indicate that the performance of structures with inerter systems satisfies the target requirements, thereby illustrating the effectiveness of the proposed design procedure. The results demonstrate that the proposed method considers the nonlinearity of a structure with an inerter system subjected to an earthquake, which improves the reliability of the seismic design and the safety of the structure. The proposed design method can be used to design structures with inerter systems that achieve their expected performance and minimize the control cost.

Evaluation of efficiency index of friction energy dissipation devices using endurance time method

Various methods have been presented to improve the performance of buildings against earthquakes. Friction damper device is one of the energy dissipation devices that appropriately absorbs and dissipates the input energy and decreases displacements. In this paper, the possibility of using endurance time method to determine the efficiency index and optimum slip load for these dampers was investigated by comparing the results of endurance time and nonlinear time history analyses. The efficiency indexes acquired from the average of results for nonlinear time history and endurance time analyses were close to each other. In this research, by assuming identical optimum slip load for the dampers in all stories, the normalized damper strength was increased in a number of equal steps ranging from zero to one to determine the efficiency index of dampers in each step. Then, the optimum slip load of dampers in the steel frames was calculated according to the minimum efficiency index of dampers. As a result, employing the endurance time method instead of a high number of nonlinear time history analyses is also possible, and using the endurance time method diminishes 57% of computational endeavors. Lastly, a relation for acquiring the optimum slip load of the friction damper devices in steel structures was proposed in terms of the weight of the structures. After adding optimal FDDs to the structures and investigating the effectiveness of the dampers, it was concluded that by using endurance time excitation function with better energy consistency, the endurance time results could be improved.

Seismic Analysis and Design of SDOF Elastoplastic Structures with Self-centering Viscous-hysteretic Devices

ABSTRACT A self-centering viscous-hysteretic device (SC-VHD), composed of a viscous damper and ring springs in parallel, which combines velocity-proportional viscous energy dissipation and displacement-proportional hysteretic energy dissipation is studied. To evaluate the seismic behavior of structures with self-centering viscous-hysteretic devices and obtain appropriate parametric combinations between the main structure and the added self-centering viscous-hysteretic devices, a parametric study was conducted on SDOF elastoplastic structures with SC-VHDs. The results show that the SC-VHD can reduce about 30–50% of peak displacement and more than 80% of residual deformation, whilst a small increase in peak acceleration was observed. The reduction of the residual deformation is mainly influenced by the ring springs damping ratio and the ratio of preload to structural yielding strength, while the reduction of the peak displacement is significantly influenced by the viscous damping ratio and the ratio of loading stiffness to structural elastic stiffness. When the SC-VHD was designed with a viscous damping ratio of no less than 5%, a ring springs damping ratio of 15% at most, a ratio of preload to yielding strength of no less than 0.1 and a ratio of loading stiffness to elastic stiffness of no less than 0.1, the 2% peak drift and 0.2% residual drift criteria can be satisfied. Based on the parametric analysis results and an improved equivalent damping model parallel to ASCE 7, a displacement-based design method of SDOF elastoplastic structure was then proposed and evaluated by comparison with nonlinear time-history history analysis results.

Dynamic responses on traditional Chinese timber multi-story building with high platform base under earthquake excitations

The multi-story timber structure with high platform base is one of the important architectural types in the traditional Chinese buildings. To study the dynamic characteristics and seismic responses on this kind of traditional structure, the 3-D finite element models of Xi'an drum tower which included the high platform base, upper timber structure and whole structure was established considering the structural form and material performance parameters of the structure in this study. By the modal analysis, the main frequencies and mode shapes of this kind of traditional building were obtained and investigated. The three kinds of earthquake excitations included El-Centro wave, Taft wave and Lanzhou wave were separately imposed on the upper timber structure model and the overall structure model, and the seismic responses on the tops of columns were analyzed. The results of time history analysis show that the seismic response of the upper timber structure is obviously amplified by high platform base. After considering the effect of high platform base, the mean value on the lateral displacement increments of the top column in the overall structure is more than 20.478% and the increase of dynamic coefficients was all above 0.818 under the above three different earthquake excitations. Obviously, it shows that the existence of high platform base has a negative influence on the seismic responses of upper timber structure. And the high platform base will directly affect the safety of the upper timber structure. Therefore, the influence of high platform base on the dynamic response of its upper timber structure cannot be neglected.

Investigation of Uncertainties in Nonlinear Seismic Analysis of the Reinforced Concrete Shear Walls

In this study, the use of the displacement-based fibre element (DBFE) method for modelling the nonlinear seismic response of reinforced concrete shear wall structures with a variation of damping ratios and types of structural damping is evaluated. The experimental seismic responses of the CAMUS I and NEES-UCSD shear wall structures are compared with nonlinear time-history analysis results obtained using the DBFE method. Comparisons are made in terms of the absolute maximum values of the top displacement, the base shear force, the base bending moment values and minimum differences between overlaps of top displacement time-history graphs. The Hilber-Hughes-Taylor-α integration method is selected for the dynamic solution algorithm. Recommendations are made for appropriate damping ratios for stiffness-proportional, mass-proportional, and Rayleigh damping to be used for the structural damping of nonlinear seismic analyses of the shear walls. The minimum difference between experimental and numerical analysis results is obtained less than 11% using Rayleigh damping. Additionally, the optimal number of fibre elements is researched with regard to the ratio of the mean length of the fibre elements to the longitudinal length of the shear wall. When the ratio is smaller than 3%, the differences between experimental and numerical analysis results for both shear walls are less than 2% at the optimal damping ratios.

Assessment of Earthquake Destructive Power to Structures Based on Machine Learning Methods

This study presents a machine learning-based method for the destructive power assessment of earthquake to structures. First, the analysis procedure of the method is presented, and the backpropagation neural network (BPNN) and convolutional neural network (CNN) are used as the machine learning algorithms. Second, the optimized BPNN architecture is obtained by discussing the influence of a different number of hidden layers and nodes. Third, the CNN architecture is proposed based on several classical deep learning networks. To build the machine learning models, 50,570 time-history analysis results of a structural system subjected to different ground motions are used as training, validation, and test samples. The results of the BPNN indicate that the features extraction method based on the short-time Fourier transform (STFT) can well reflect the frequency-/time-domain characteristics of ground motions. The results of the CNN indicate that the CNN exhibits better accuracy (R2 = 0.8737) compared with that of the BPNN (R2 = 0.6784). Furthermore, the CNN model exhibits remarkable computational efficiency, the prediction of 1000 structures based on the CNN model takes 0.762 s, while 507.81 s are required for the conventional time-history analysis (THA)-based simulation. Feature visualization of different layers of the CNN reveals that the shallow to deep layers of the CNN can extract the high to low-frequency features of ground motions. The proposed method can assist in the fast prediction of engineering demand parameters of large-number structures, which facilitates the damage or loss assessments of regional structures for timely emergency response and disaster relief after earthquake.

Developing energy-based loading protocols for seismic evaluation of steel moment frames' components

One of the main obstacles at the very first step of every experimental or numerical investigation is to select proper loading scenarios for evaluating the seismic performance of structural elements. For both qualifying the structural members and developing behavioral models as the primary input for nonlinear analysis of structures, there is a need for loading regimes that are able to simulate loading conditions similar to real earthquakes. This paper discusses the methodology used to develop a series of energy-based loading protocols for testing beam to column connections and columns of steel special moment frames. Several relationships controlling the configuration of loading protocols are proposed based on results obtained from multiple nonlinear time history analyses that have been conducted on a variety of structures. The histories of cycles obtained from these loading regimes are case-specific in order to dissipate a certain amount of energy from each structural component within a definite time based on its properties. In the case of column axial loading protocol, in addition to a force-control regime, a displacement-control one is also introduced to eliminate the instability issues arising when force-control loading scenarios are employed. After presenting the required steps to implement the proposed loading protocols, their accuracy is investigated by comparing them to the results of nonlinear time history analyses as well as some conventional and well-known loading protocols.

Seismic assessment of earthquake‐resilient tall pier bridges using rocking foundation retrofitted with various energy dissipation devices

While conventional seismic isolation bearings are usually inefficient for bridges with tall piers, rocking foundation is a promising approach mitigating their seismic demands and improving post-earthquake resilience. However, excessive tilt angle might occur at rocking interface and lead to overturning during strong earthquake excitations. This paper investigates the efficiency of various energy dissipation devices in improving the seismic performance of rocking foundations employed in tall pier bridge systems. The devices considered in this study include yielding steel cable (YSCs), viscous dampers (VDs), and super-elastic shape memory alloy cables (SMAs), and they are implemented out of the pier columns for convenience of replacing if damaged during earthquakes. The results of nonlinear time history analysis show that all these devices are capable of suppressing the seismic responses of tilt angle at rocking interface; however, the seismic vulnerability of piers is increased as well, since these devices impose extra demands on columns. Consequently, the parameters of energy dissipation devices should be carefully determined in engineering practice, achieving balance between the seismic performance of tilt angle at rocking interface and nonlinear demand of pier columns. Note that the maximum demands of columns are determined by the design parameters of devices, which could improve the seismic resilience of tall pier bridges and facilitate the post-earthquake rescue operations.

A New Method for Drawing the Capacity Spectrum for Seismic Analysis and Structural Rehabilitation

A review of previous studies shows that there are two general views on how to determine demand in structures through incremental nonlinear static analysis. In the first view, multi-modal methods are used to determine demand in structures. In this view, the applied load pattern is applied to the structure according to the shape of each vibration mode, assuming that the structure deformation follows the shape of the vibration mode, the capacity spectrum is drawn and after determining the target displacement and the corresponding demand for each vibration mode, the final demand is determined by combination of response modes. In the second view, structural analysis is performed as a single run nonlinear static analysis and the effect of different vibration modes is shown in one load pattern. In this method, the load pattern that has somehow the effect of different modes is applied to the structure and the structure is analyzed under this load pattern. In the second view, due to the non-conformity of the structure deformation and the lateral load of a particular vibration mode of the structure, the conventional capacity spectrum method cannot be used. Therefore, the purpose of this paper is to propose a method for drawing the capacity spectrum and determining the target displacement in single run nonlinear static analysis for non-adaptive load patterns. After presenting the equations, three frames including 3-storey, 9-storey and 20-storey frames have been selected and the results of the proposed method have been evaluated along with modal pushover method and time history analysis for the frames. Comparison of the results of the proposed method and the modal pushover with the results of the nonlinear time history analysis shows that the proposed method is more efficient in determining the lateral displacement of the stories and roof than the conventional modal pushover method.

Gaussian process regression for seismic fragility assessment of building portfolios

Seismic fragility assessment of building portfolios is often based on the analysis of “average” building models representative of structural types (or building classes), thus neglecting building-to-building variability within a structural type. This paper proposes the use of Gaussian process (GP) regressions to develop flexible and accurate metamodels explicitly mapping building-class attributes to the seismic fragility parameters. The proposed metamodels can enable analysts to account for building-to-building variability in simulation-based seismic risk assessment of building portfolios. Unlike other commonly-used metamodels, GP regressions do not require the a-priori definition of a prediction function and they quantify the uncertainty on the predictions in a refined and explicit fashion. The proposed method is demonstrated for a portfolio of seismically-deficient reinforced concrete school buildings with construction details typical of some developing countries. Based on the available information about the building attributes (e.g. geometry, materials, detailing), building realisations are generated based on two alternative approaches, which are critically compared: design of experiment and Monte Carlo sampling. Cloud-based time-history analysis for each building realisation is performed using unscaled real ground-motion records; fragility relationships are derived for four structure-specific damage states. A GP regression is then developed for each considered fragility parameter (i.e. median and dispersion). To further increase the tractability and scalability of the methodology, alternative metamodels are defined based on numerical non-linear static pushover analyses or analytical “by-hand” pushover analyses, through the Simple Lateral Mechanism Analysis (SLaMA) method. The results show that, for the considered portfolio, the fitted GP regressions have a high predictive power in surrogating the modelled fragility, demonstrating the feasibility of the approach in practice. It is also shown that the choice of the sampling technique could be based on the input data availability, rather than on the expected computational burden. Finally, the use of simplified methods for response analysis shows acceptable error levels with respect to the full time-history analysis results. Such simplified methods can be promising alternatives to generate large training datasets for the proposed GP regressions. This increases the potential of training metamodels in practical portfolio risk assessment applications, in which a high number of building types, each characterised by a large number of attributes, is generally involved.

Seismic Retrofit of an Existing RC Building With Isolation Devices Applied at Base

Nowadays, seismic retrofit through isolation strategy represents a consolidated technique of protection against design earthquakes. This technique is also widespread applied on existing structures, due to the fact that usually it does not require any interruption of the building use and occupants evacuation. If applicable, it rapidly allows of seismically retrofitting a building installing seismic devices with low horizontal stiffness between the structure and the foundation decoupling, in fact, the motion of the superstructure from the ground one. In this paper an application on an existing RC building of the seismic isolation is presented. The chosen building was built in the ‘90s only for vertical loads and realized without any detailing rule for structural ductility. The seismic retrofitting requirement stems from the fact that only recently, after the National seismic hazard maps update in 2003, the considered area has been upgraded to a medium-low seismic intensity zone, while at construction time no seismic classification was in existence by law. The case study peculiarity is that the seismic retrofitting has required in addition to seismic devices at the base with related interventions, also the application of a bracing system consisting of two elastic steel frames. This intervention is required for stiffening the superstructure and, therefore, for minimizing the higher vibration modes effects. The paper presents the main results obtained with a FEM model, implemented for simulating the initial and the design state when the interventions are considered. Finally, some results of non-linear dynamic time-history analyses are illustrated and commented for verifying superstructure elements and seismic devices.

Evaluation of uniaxial contact models for moat wall pounding simulations

SummaryMoat wall pounding occurs when a base‐isolated building displaces beyond the provided clearance and collides with the surrounding retaining wall, inducing very high floor accelerations and interstory drifts. Previous studies on moat wall pounding typically employ simplified models of the superstructure, with a uniaxial contact spring used to model the entire moat wall. Consequently, researchers have developed sophisticated contact models to estimate the normal‐direction contact force that is generated during seismic pounding. This study examines how the choice in contact model affects the seismic response of a base‐isolated building subjected to impact‐inducing ground excitation. Five widely used state‐of‐the‐art contact models are summarized and implemented into an experimentally‐calibrated numerical model of a base‐isolated moment frame. Results of nonlinear dynamic time history analyses are shown in detail for one ground motion, followed by a larger parametric study across 28 near‐fault ground motions. This work shows that peak impact force and base acceleration are moderately sensitive to the choice in contact model, while upper floor accelerations and interstory drifts are practically not affected.

Elastic Displacement Spectrum-Based Design Approach for Precast Concrete Frame with Replaceable Energy-Dissipating Connectors

ABSTRACT A precast concrete frame with replaceable energy-dissipating connectors (REDC) is designed as an innovative system. The REDCs are placed at the top and the bottom of the beam-ends to dissipate energy during major earthquakes. A displacement spectrum-based design method is presented, which can directly determine the target period under strong earthquakes. The results of nonlinear time-history analysis of an example structure indicate that the displacement response of the innovative structure under strong earthquakes can be estimated accurately only using elastic response spectrum, without considering additional plastic parameters such as equivalent damping or ductile factor during the design process.

The development of a multi-level unseating prevention device (MLUPD) for bridges

During the previous major seismic events, the unseating of the bridge superstructure was caused by large relative displacements which exceeded the bridge seat length. Therefore, this paper aims to introduce a multi-level unseating prevention device (MLUPD) to control deck movement. This device is capable of providing lateral resistance force with different performance levels of bridge girder movement in order to limit relative displacement between the superstructure and substructure. The device consists of a combination of a number of springs with different or equal length depending on the bearing type assembled inside each other in parallel to demonstrate multi-levels of stiffness. The design procedure and working mechanism of the device are based on the code of practice. In this study, the MLUPD prototype was fabricated and installed in two different configurations of the steel frame for testing under pushover and cyclic loading to evaluate the MLUPD performance. Additionally, the device performance was also assessed using numerical study.Hence, a constitutive model for the developed MLUPD was derived. Then, the analytical model of the bridge with and without MLUPD device was codified by the finite element program in order to evaluate the seismic performance of the bridge equipped with the developed device. The experimental and finite element results of the MLUPD prototype revealed that the device is capable of unseating prevention through the multi-level performance.In addition, the results indicate that the developed system demonstrated a significant force resistance in two frame configurations. Moreover, the numerical results of bridge time history analysis in terms of girder displacement, pier base shear and drift ratio demonstrated that the bridge seismic behavior is enhanced by utilizing the developed device along with different bearing cases.

Inelastic displacement ratio for high damping SDOF systems built on soft soil sites

The main purpose of this study is to estimate the inelastic displacement ratio, C1, of highly damped systems built on soft soil sites. For this purpose, results of linear and nonlinear time history analysis of 79 single-degree-of-freedom (SDOF) systems with damping ratios of 0.05, 0.1, 0.2, 0.3 and post-yield stiffness ratios of -0.01, 0, 0.05 and 0.1 under a large number of ground motion records obtained at soft soil deposits, were used. Oscillators exhibited ductility levels as high as 6. Based on the results, a new simplified equation as a function of the period of vibration normalized by the predominant period of ground motion records, the level of inelastic deformation, post-yield stiffness ratio and damping ratio for structures built on soft soil, has been proposed using nonlinear regression analysis.

Seismic Damage Assessment of RC Buildings Subjected to the Rotational Ground Motion Records Considering Soil-Structure Interaction

The significance of the seismic rotational components have been overlooked in the seismic evaluation of structural behavior. As researchers have measured seismic components more accurately using sensitive rotational velocity sensor, it was observed that the magnitude of rotational components is considerable and could not be neglected. Hence, some parts of seismic damage or failure of structures cannot be exclusively attributed to the translational components. In this regard, this paper used seven accelerograms in which rotational components were measured by advanced sensors. The considered RC buildings which designed as per intermediate moment-resisting frame system were analyzed using OpenSees in nonlinear dynamic domain. In the numerical modeling, lumped plasticity model was used to simulate the behavior of RC component members considering the rotational motions and soil-structure interaction as main parameters. The results of numerous nonlinear time history analyses showed that the contribution of rotational components to the seismic behavior of RC frames is considerable and should be included in the seismic design codes.