Results Of Time History Analysis Research Articles

Comparison and study of different seismic calculation methods for underground stations in Shanghai

In terms of seismic design methods for subway stations in the Shanghai area, both national and local standards have presented several pseudo-static methods, including response displacement, response acceleration, equivalent earthquake acceleration, and equivalent inertial force methods. However, certain issues are encountered when these methods are applied to the seismic design of real subway projects. The load input and results obtained from different calculation methods differ from each other. To address such discrepancies and compare the diversity of different methods, this study performs a comparative analysis based on the project case of a ground station in Shanghai. The seismic design is conducted using five different calculation methods. By referring to the results of the dynamic time history analysis, the causes of errors in the calculation results of the displacement and internal force are analyzed. The applicability of the methods is comprehensively explored in terms of a calculation model, determination of the equivalent load, error in the results, and project application. The results show that the response acceleration method exhibits the least error compared to the dynamic time history method. Therefore, the response acceleration method is recommended as the preferred method for the seismic design of underground stations in Shanghai.

Seismic Performance Evaluation of Multi-Storey Residential Building with Friction Pendulum Bearings: Indonesia case study

The methodology for seismic performance evaluation of a residential building in Indonesia with the use of seismic isolation is considered. An 8-storey reinforced concrete frame residential building with shear wall structural system was selected as a case study. Nonlinear methods of seismic response analysis were used to calculate the response of the structure: nonlinear static (Pushover) and Nonlinear-Time History Analysis, NLTHA. The analysis is performed in STERA 3D freeware. The nonlinear time history analysis was performed for seven pairs of horizontal components of earthquake ground motions, selected according to the parameters of possible earthquakes for the considered site (Bandung city). The selected earthquake records were modified using the spectral matching procedure for design spectrum. Friction-pendulum bearings developed by Nippon Steel Corporation of Japan were used as seismic isolation. The results of nonlinear time history analysis show that shallow earthquakes result in greater damage compared to megathrust earthquakes, with both scenarios providing a life safety (LS) performance level. The use of seismic isolation can reduce seismic loads, as evidenced by the reduction in top-level accelerations and shear forces at the base.

A new performance‐based seismic design method using endurance time analysis for linked column frame system and a comparison of structural systems and seismic analysis methods

SummaryThis paper presents a new performance‐based seismic design method for the design of repairable linked column frame (LCF) and linked column system (LCS). Currently, the biggest problem of these systems is the lack of a simple and practical design method that leads to the design of optimal models with sufficient seismic capacity. The interaction of the primary and secondary systems, changing the lateral load pattern during an earthquake, and the implementation of the target performance objectives have complicated the design of these systems. The evaluations carried out in this research show that the rotation of link beams must be controlled in the design. Therefore, the ultimate plastic rotation of links is determined to be 0.01 rad for the seismic intensity of design base earthquake and 0.015 rad for maximum considered earthquake. The results show that the models designed using the presented method are optimal, have sufficient seismic capacity, and achieve the target performance objectives. In addition, although previous researches have shown that these systems have a suitable seismic behavior, their seismic behavior have not been compared with other structural systems. Comparing can show the behavioral characteristics of a new structural system; hence, the elastic and plastic behavior of the LCF and LCS models have been compared with other common steel structural systems using all analysis methods. Moreover, in the presented method for the design of LCF and LCS systems, nonlinear time history analysis using the endurance time method (ETM) is used, and due to the newness of the endurance time method, its results are compared with the median results of nonlinear time history analysis at different seismic hazard levels and incremental dynamic analysis (IDA), in 45 samples. The results show that the endurance time analysis is a reasonable and efficient method, and in this comparison, the difference between the results of ETM and IDA methods is 6% on average.

Displacement Control of Existing Steel Moment-Resisting Frame Structures Using Buckling-Restrained Braces

ABSTRACT Large displacements are expected to occur in existing code-compliant steel moment-resisting frames during a severe earthquake, affecting the functionality of buildings. This study investigated the use of buckling-restrained braces for controlling the displacement response and ensuring an occupiable performance level of the structures. A design procedure for the braces based on the energy balance concept is proposed, where the hysteretic energy demand of the frame before and after attaching the braces is equated. Time-history analysis results show structures designed using the proposed procedure satisfied the targeted performance level, and no significant change in peak floor acceleration response was observed.

A diagram‐based design procedure for Intermediate Isolation System in existing buildings with inelastic behavior

AbstractVertical extensions of existing buildings can be realized through Intermediate Isolation System (IIS): the extension, equipped with a base isolation system on the rooftop of the existing building, can work as a mass damper, thus reducing the seismic demand on the old structure. The idea proposed in this paper is to predict the elastic or inelastic response of the existing structure in the IIS configuration by means of the results of simple linear analyses. Parametric response spectrum analyses are performed on simplified two degree‐of‐freedom models by varying the mass ratio and the periods of both the existing building and the new isolated vertical extension. So‐called IIS design spectra are derived, and the results are provided as design charts. Given the period of the existing building and the mass ratio, the period of the new isolated vertical extension is selected to obtain the required/desired response of the existing building. For existing buildings working in the elastic field, the designer can derive the response of the existing building by utilizing the IIS design spectra as design charts. For existing building working in the inelastic field, the design charts can still be adopted, though within a more complex procedure, which accounts for two limit behaviors that the extended building exhibits in the inelastic field. The outlined design procedure is applied to some case studies and validated through the comparison with the results of nonlinear time history analyses.

Seismic Vulnerability of Segmental Bridges with Drop-In Span by Pushover Analysis

Insight into the application of pushover analysis to prestressed concrete segmental bridges built in the 1950s–1970s by cantilevering with medium-large span length is provided. Seismic assessment must be carried out considering the whole structural response and, in particular, the task of tall piers, bearings, and drop-in spans with Gerber saddles, which are likely to be subjected to girder pounding and/or unseating. In this paper, the assessment of seismic vulnerability is initially performed by linear modal dynamic analysis; then, the efficiency in assessing the seismic response of different methods of pushover analyses is compared, assuming as a benchmark the results of non-linear time history analysis. The outcomes show that, for the bridge with the drop-in span, criteria for selecting the load pattern considered in pushover analysis, the reliable modeling of the bearings, and tall piers play a dominant role in the assessment of the seismic vulnerability, particularly in longitudinal motion.

Cyclic loading tests and numerical simulations of an assembled X-shaped flexural steel damper

This paper proposes an assembled X-shaped flexural steel damper. Welding is waived for the novel damper. As the kernel element of the damper, the X-shaped flexural steel plates have the advantages of ease of installation and replacement if necessary. In the analytical part, the effective height of the flexural steel plate was suggested, and then, the yield displacement, yield load and initial stiffness of the damper were derived. The proof-of-concept cyclic loading test was conducted using one reduced-scale specimen within a four-bar linkage experimental setup. The hysteretic performance indexes, including strength, stiffness and energy dissipation, were quantified. The high-fidelity finite element (FE) models were established by ABAQUS. The parametric study was further conducted based on the verified FE model. The considered parameters were the height and thickness of the steel plates. The testing results indicate that the proposed damper has plump hysteretic curve with good energy dissipation capacity and excellent ductility, although slight slip behavior can be found due to the gap caused by the assembling process. The results obtained from analytical method and numerical model are in good agreement with the experimental data. The results of parametric analysis show that the numerical results well agree with analytical predictions, indicating the numerical model can reflect the mechanical behavior of AXSFD. A benchmark frame building was selected to demonstrate the seismic control efficacy of the damper. The nonlinear time history analysis results indicate that the damper reduced both peak and residual interstory drift ratios for the protected structure.

Direct displacement‑based seismic design for a retrofitted RC frame by hinged wall with BRBs at base

A hinged wall (HW) with buckling-restrained braces (BRBs) at the base (HWBB) has been proposed to enhance the seismic performance of a reinforced concrete frame (RCF). In this study, a new direct displacement-based design procedure based on the bottom shear method (DDBDP-BSM) is proposed for low- and multi-rise RCFs with an HWBB (RCF-HWBB). First, the theoretical relationship between the basic period target and displacement target of the RCF-HWBB was deduced based on the DDBDP-BSM and performance targets. Then, a method to determine the HW configuration and BRB sectional area was proposed. Finally, the optimal selection of earthquake intensity at BRB yielding and the applicability of the DDBDP-BSM on a high-rise RCF-HWBB were investigated through a comparison between the design results and the time history analysis results.

Research on Bearing and Seismic Isolation Design of Extrodosed Cable-stayed Bridge With Ultra-wide A-type Tower in High-intensity Areas

In order to improve the support and isolation performance of the escape cable-stayed bridge with super wide A-type tower in high-intensity areas, the paper takes Jingyuan Jinshatan Yellow River Bridge as the background, based on the finite element method, and takes the design of 20000 ton isolation bearing as the case, optimizes the design parameters, structural composition and friction pair settings of the bearing, and develops the actual bearing to meet the needs of the project by combining simulation analysis and experimental testing. The results of time history analysis show that the displacement of the strength support seat at the bottom of the pier and the expansion joint at the beam end can meet the design requirements.

Performance-Based seismic design and evaluation of out-of-code structure on Nanjing Financial City

The main scope of performance-based seismic design and evaluation study focuses more on the seismic performance of the simple structure or the regular structure, instead of out-of-code structure. The C1 tower in Nanjing Financial City is taken as an engineering case study. Many design indexes of the original design scheme of the structure exceed the requirements of the existing Chinese specifications, such as the height exceed the limits, the torsional irregularity, the partial floor slab discontinuity etc., which are summarized in detail in this paper. Then, several special structural design strategies are adopted to improve the overall seismic performance of this out-of-code structure. For example, multiple lines of seismic defences are set and the outrigger trusses are strengthened to solve the height overrun. For torsion irregularity, the influence of the bidirectional seismic torsion effect is considered in the calculation. Finally, according to the results of dynamic elastoplastic time history analysis under rare earthquakes, the seismic performances of the out-of-code structure are evaluated in detail. The analysis results show that the overall seismic performances of the structure are all within a reasonable range, and the seismic performance of the main components in the structure all meet the specification requirements.

Simulation analysis of structural nonlinear seismic response

Faced with the difficulty of analyzing structural nonlinear seismic response, this study focuses on the reinforced concrete frame structure and designs a frame that meets the specifications. Artificial synthetic seismic records and natural seismic records were selected, and the acceleration response of the first story of the structure was used as the output sample for the study. On the basis of a nonlinear autoregressive moving average model with external inputs, a neural network model was constructed and nonlinear seismic response simulation analysis was conducted. These results confirm that the research method has good predictive performance and can effectively predict structural nonlinear seismic response. Under the action of artificial earthquake records, there is a small difference between them and the acceleration time history curve and acceleration response peak obtained from time history analysis. Under the action of artificial seismic record ACC12, when the time is 25 s, the calculation results of time history analysis and research methods are 1.715 m/s2 and 1.403 m/s2, respectively, with the former being 0.312 m/s2 smaller than the latter. In natural earthquake records, with a characteristic period of 0.30 s, under the action of natural earthquake record USA00668, the relative energy of time history analysis is 4.997 m2/s when the time is 30 s, which is 0.938 m2/s higher than the research method. The research method can accurately analyze the nonlinear seismic response of the results.

Residual displacement ratios of highly damped SDOF systems by considering soft soil conditions

In this paper, residual displacement ratios, Cr, of highly damped single degree of freedom (SDOF) systems are studied by considering soft soil effects. For this purpose, a large number of ground motions recorded on soft soil deposits are used in the analysis. In order to calculate the residual displacement ratios, linear and nonlinear time history analysis are conducted for 79 SDOF systems with lateral strengths of R = 2, 3, 4, 5, 6, damping ratios of ξ = 0.05, 0.1, 0.2, 0.3, and post-yield stiffness ratios of α = 0, 0.03, 0.1 subjected to 426 pairs of earthquake ground motions recorded on soft soil. Therefore, a large number of data is obtained for Cr by using the results of time history analysis. After investigating the impact of lateral strengths, damping ratios, and post yield stiffness ratios on residual displacement ratios, a simplified new equation is proposed with nonlinear regression analysis. The results show that higher damping ratios cause the residual displacement ratios to reduce. Furthermore, comparison of Cr for soft soil and stiff soil conditions indicates the soil condition influence on Cr.

Accumulative deformation-based design method for special concentrically braced frames with H-section braces

Accumulative deformation-based fracture models of braces have been developed by researchers for nearly 30 years. These models are used to predict the fracture of braces in a specific time-history analysis of SCBF. However, no attempt has been made to explore statistical accumulative deformation demands of braces under severe earthquakes. Eight SCBF models are designed in this paper for nonlinear time-history analysis to summarize the accumulative deformation demands of SCBF braces. Meanwhile, accumulative deformation-based fracture models of SCBF braces with H-section are proposed by experimental data. Accumulative deformation demands of braces are in good correlation with hysteretic energy demands according to the results of time-history analysis. Hysteretic energy spectrum, energy demands, and accumulative deformation demands of braces are set up in this paper. The method is proposed by balancing the accumulative deformation demands and accumulative deformation limit index of braces. Finally, an example designed by the proposed method is given. Configuration detailing parameters of braces is not only determined by expected ductility but also the strength of SCBF according to the result of the example. The proposed design method can help designers to determine the configuration detailing parameters of braces complied with the strength of SCBF.

Influence of soil–structure interaction on seismic demands of historic masonry structure of Kashan Grand Bazaar

Heritage structures are an important part of the history of each community as well as an economic resource. This study aims to investigate the earthquake damage and failure mechanism of a historic Bazaar located in Kashan (center of Iran), which dates back to the eighteenth century. Numerical models were built by a macro method, considering two cases of fixed support and soil–structure interaction (SSI). To assess the structural behavior, modal, nonlinear static, and dynamic time history analyses were performed using a three dimensional finite element method. The results of SSI analysis show an intense weakness of the structure against the required demand based on the design spectrum. Also, foundation flexibility has a great impact on the vibration characteristics, displacement demand, and damage distribution. By comparing the results of time history analysis to the pushover procedure, a lower shear value and higher displacement are obtained. Furthermore, the damage process is as dome collapse alongside short arch, consequently long arch collapse followed by pier wall overturning.

Influence of considering substructures on seismic performances of suspen-dome structure

In order to investigate the influence of substructures on the seismic performance of the suspen-dome structure, taking the suspen-dome roof structure of the Lanzhou Olympic sports centre complex as the prototype, a method that replaces complex concrete substructures of the prototype structure with steel substructures in shaking table tests was proposed and a scale model considering substructures was established. First, the natural frequencies of the test model were compared with the modal analysis results of the prototype structure considering the scale ratio. Then, an integral numerical model considering substructures was established using Abaqus – the results of modal analysis and dynamic time history analysis were compared with the test results. Finally, two simplified numerical models with boundary conditions of fixed bearings and three-directional hinged bearings were established. The seismic performances of simplified models and the integral model were compared. It is observed that the method of considering complex concrete substructures of the prototype structure in the shaking table test is accurate and effective. In addition, the numerical model and the modelling method are correct. Moreover, the substructure has a significant impact on the seismic performance of the suspen-dome. The substructure should be considered in the analysis and design stages.

Performance-based seismic design of full and partial self-centering steel braced frames using modified lateral force distribution

Design base shear and lateral force distribution are two important aspects of the seismic design process. Different design methods have been proposed to obtain the design base shear of different types of structures. However, the study related to the lateral force distribution is limited, especially for self-centering (SC) structures. The primary objective of this research is to develop a performance-based seismic design (PBSD) procedure for steel braced frames considering the modified lateral force distribution. Six-story steel braced steel frames are designed to explore the influence of the energy dissipation factor on the lateral force distribution of the frames. Results of nonlinear time-history analyses indicated that the lateral force acting on the roof increases with the decrease in energy dissipation factor. Following the parametric analyses of single-degree-of-freedom (SDOF) systems, the energy factor design spectra are established and the corresponding PBSD procedure for the steel braced frames is proposed. Finally, the four six-story braced steel frames are redesigned using the PBSD procedure with the modified lateral force distribution to illustrate the efficiency of the proposed design method. Analyses results indicate that the steel braced frames designed by the proposed design can satisfy the expected inter-story drift limit with a reasonably uniform distribution of peak inter-story drifts. Furthermore, the ‘partial’ SC system appears to be a desirable option that effectively controls the residual displacement and peak acceleration responses at the same time, and could achieve a manageable cost control compared to the full SC systems.

A low computational cost seismic analyses framework for 3D tunnel-form building structures

Numerical modeling of tunnel-form buildings entails the utilization of 3D finite element models consisting of large numbers of shell and fiber elements. Accordingly, the non-linear analysis of such models under seismic excitations is both time-consuming and computationally expensive, especially in the case of large scale structures. To address this challenge, this study investigates the efficiency of the Endurance Time Method (ETM) to evaluate the structural responses, location of damage initiation, and the overall performance of tunnel-form structures under the Design Basis Earthquake (DBE) hazard level. Comparison with results derived from pushover and time-history analyses indicated the acceptable accuracy of ETM with significantly less computational efforts. The computation time required for the ETM was less than 25% of pushover (until total failure of the system) and time history analyses on the five- and ten-story tunnel-form buildings. The maximum differences between the results of ETM and time history analysis used to estimate the story drifts and shear forces were 4–6% and 1–4.5%, respectively. Considering the reliability of ETM and its appropriate accuracy, this method can be considered as a suitable alternative to the conventional methods to provide a low computational cost seismic analyses framework for non-linear tunnel-form buildings and similar structural systems.

A simple method for approximate estimation of the displacement response of base-isolated structures

The present study is a new attempt to provide a simple method for approximate estimation of the displacement response of base-isolated structures. For this purpose, first the accuracy of the existing methods which have been presented for base-isolated buildings is examined by comparison their estimations with the results of time history analyses of the 2, 4, 6, 8, 10 and 12 stories base-isolated models under 40 near-field and 40 far-field ground motion records. Then, a new method is proposed which is based on equivalent linear SDOF system with considering modified values of optimum damping ratio and effective period factor for base-isolated structures. The optimum damping ratio for base-isolated structures is obtained 31% and 23% for far- and near-field ground motion records, respectively. An effective period factor of 2.02 and 1.99 is extracted as a suitable value for obtaining the period of equivalent linear structure subjected to far- and near-field ground motion records, respectively. Results show that the proposed method not only has practically more simple procedure than the others, but also can provide reasonable estimates of the maximum nonlinear roof displacement of base-isolated structures subjected to an individual ground motion record. It’s worth mentioning that most of the equivalent linearization methods presented in the past use displacement ductility ratio as a key parameter for estimating the nonlinear displacement of base-isolated structures while the proposed method doesn’t need to such a parameter which cannot be easily predicted without performing nonlinear time history analysis. Therefore, as another attempt in this study, suitable approximate values of ductility ratio and other important coefficients are recommended for a number of existing approximate methods to improve their estimations for base-isolated structures.

A method for seismic design of RC frame buildings using fundamental mode and plastic rotation capacity

A seismic design method is proposed for RC frame buildings, with focus on two of the seven virtues of earthquake resistant buildings, namely deformation capacity and desirable collapse mechanism. Fundamental lateral translation mode of the building and plastic rotation capacity of beams are included as input to estimate lateral force demand. Guidelines are provided to proportion beam and column cross-sections through: (a) closed-form expressions of flexural rigidities to maximize participation of the fundamental mode, and (b) relative achievable plastic rotation capacity using current design and detailing practice. This method is seen to surpass two prominent displacement-based design methods reported in literature. Results of nonlinear static pushover and nonlinear time history analyses of buildings of three different heights designed by this and the said two methods are used to make a case for the proposed method; the proposed method is able to control plastic rotation demand in beams and provide at least 20% more lateral deformation capacity than the said methods.

Seismic analysis of extended piles in sand considering effect of scouring and effect of water as added mass

Scouring is one of the major causes of the failure of bridges and offshore wind turbines. Piles under extreme scouring and earthquake loads are vulnerable to failure and need to be investigated thoroughly. In this study, the seismic responses of an extended concrete pile with no scour and four scouring depths conditions are investigated under an input motion based on a Kobe earthquake record. The effect of water during an earthquake has a significant impact on the structure as hydrodynamic pressure; however, it is generally ignored in the seismic analysis of piles. The present study uses the concept of added mass to consider the effects of water. The combined soilstructure-interaction and shear beam model is used to simulate pile and soil using the beam-on-nonlinear-Winkler foundation (BNWF) method. Soil is divided into multiple layers with increasing shear modulus and the mass of each soil layer is lumped into two nodes of the layer. Modal analysis and nonlinear time history analysis are performed on different models. Results of the modal analysis show the decrease in fundamental frequencies of the pile with increasing scouring depths. The time history analysis results are reported in the form of Arias and Housner intensities, envelopes of acceleration, velocity, displacement of pile top, and envelopes of shear force and bending moment of the pile. Results show significant changes with scouring depth and the effect of water.