Maximum Seismic Response Research Articles

The Effect of Long Duration Earthquakes on the Overall Seismic Behavior of Steel Structures Designed According to Eurocode 8 Provisions

Premature and simultaneous buckling of several steel braces in steel structures due to the prolonged duration of a seismic motion is one of the issues that must be addressed in the next version of Eurocode 8. In an effort to contribute towards the improvement of the seismic design provisions of Eurocode 8, an evaluation of the overall behavior of some steel building-foundation systems under the action of long duration seismic motions is performed herein by means of nonlinear time-history seismic analyses, taking into account soil–structure interaction (SSI) effects. In particular, the maximum seismic response results—in terms of permanent interstorey drifts, overturning moments and base shears of the steel buildings as well as of the permanent settlement and tilting of their foundations—are computed. It is found that the seismic performance of steel buildings when subjected to long duration seismic motions is: (i) acceptable for the two and five-storey fixed base steel buildings and for the two-storey steel buildings with SSI effects included; (ii) unacceptable for the eight-storey fixed base steel buildings and for the five and eight-storey steel buildings with SSI effects included. In all cases of steel buildings with SSI effects included, the seismic performance of the mat foundation, as expressed by the computed values of residual settlement and tilting, is always acceptable.

Mass irregularity effect on seismic response of moment‐resisting steel frame by nonlinear time history analysis using force analogy method

SummaryNonlinear time history analysis (NTHA) is widely considered to be the most accurate and robust method of seismic analysis and, when performed with force analogy method (FAM), can result in significant reduction in computational time, as compared to the conventional displacement‐based finite element (FE) solution technique. Taking this advantage of efficient FAM, this paper investigates the effects of location (along building height) and intensity (150–225%) of single‐floor mass irregularity on seismic response of mid‐rise moment‐resisting steel frames. Three building heights (6, 8, and 10 storeys) have been considered, and the analysis results are presented in the form of floor displacements, storey drift ratio, and plastic energy dissipation. Based on the analysis, it has been observed that critical location (for the maximum seismic response) of mass‐irregular floor corresponds to the level that exhibited the maximum seismic response (i.e., storey drift ratio) in the reference mass‐regular frame. Further, criticality of the irregular frame to seismic excitation has been found to decrease when mass‐irregular floor moves towards the top of the building. The criticality of the irregular frame has been found to increase with the increase in mass‐irregular intensity. Collapse of the irregular frame has been seen to initial first near the storey level where mass‐irregular floor is located.

Damping Effect of Insulation on a Liquefied Natural Gas Tank Based on Shaking Table Tests

ABSTRACT Full-capacity large-scale liquefied natural gas (LNG) tanks comprise a steel inner tank and a concrete outer tank. The space between the walls of these two tanks is filled with expanded perlite and a resilient blanket as an insulation layer. It is well known that interactions between the outer tank, insulation, inner tank, and liquid occur under seismic loads. In this study, to investigate the effect of insulation on an LNG tank, a scale model of the tank was constructed, and shaking table tests were conducted with and without insulation at different liquid levels. A comparison of the displacement, acceleration, and axial strain of the tank walls at different test conditions indicates that the insulation exerts good damping effects on the responses of the inner tank wall. Additionally, it has a certain restraining effect on the acceleration of the outer tank wall. However, its damping effect on the displacement and axial strain of the outer tank wall is negligible; in fact, it can even amplify them. Furthermore, most of the maximum seismic responses occur at the full liquid level, for which the effects of the insulation on the tank are more evident than at other liquid levels.

Optimal design of pure-friction isolators with and without restoring device: A multi-objective cuckoo search-based approach for seismic-excited structures

The present study addresses the optimal design problem of pure-friction isolators with a restoring device for seismic-excited structures. A multi-objective cuckoo search-based design approach is proposed to create a suitable balance between the conflicting objectives i.e. the reduction of base displacement and superstructure accelerations. Numerical studies are carried out on three structures with 4, 8 and 12 stories. Sixteen performance indices related to the root mean squares (RMS) and maximum seismic responses of the isolation system and superstructure, and the maximum energy responses of the superstructure are defined for evaluation of the proposed optimal design approach. For comparison purposes, the optimal design approach is applied for the corresponding pure-friction isolated structures without the restoring device. For seven earthquakes considered in this study, the simulation results show that the pure-friction systems significantly mitigates the seismic responses and maximum input and damage energies entering to the superstructure. Furthermore, equipping the pure-friction isolation system with the optimized restoring device may result in a moderate increment in the superstructure responses. Nevertheless, the given responses are significantly less than the responses of the corresponding fixed-base structures. At the cost of increasing some seismic responses due to the use of the restoring device, important advantages are given in terms of significant reduction of the base displacement and eliminate their residual displacement. It is also found that the seismic performance of the pure-friction isolation systems, in both cases, often decreases by increasing the number of stories.

Theoretical Derivation and Method Implementation of the Pseudo-Static Method in Seismic Analysis of Underground Structures

Based on the principles of the substructure method, a quasi-static method was derived to solve the seismic response of underground structures. On the basis of this theoretical derivation, the pseudo-static calculation model was proposed, and its calculating parameters were analyzed and solution implemented. Finally, the proposed method in this paper was compared with the dynamic FEM method. The results show that the parameters of quasi-static method have clear physical meaning and convenient solution. Compared with dynamic FEM method, the calculation parameters of quasi-static method are simpler, and the maximum seismic response of the structure can be obtained by static calculation, avoiding the complicated soil-structure dynamic FEM calculation.

An approximate method for separated spectral analysis of connected buildings with added damping

SummaryThe problem of determining maximum seismic responses, or spectral analysis, of connected adjacent structures is studied in this research. The goal of the study is twofold. First, determining when the dynamic coupling is important in such a problem and, second, establishing how to analyze each of the two structures separately when coupling is important. For tall buildings in many cases, the connecting link is intentionally accommodated with an added damping to suppress the lateral displacements. Therefore, effect of the localized damping is also accounted for in the analysis. Using essentials of modal analysis, a criterion is developed for estimation of the dynamic coupling of the two adjacent structures. Also, a procedure is developed for separated analysis of each structure incorporating the stiffness and inertial effects of the adjacent structures when coupling is important. The representative examples confirm good accuracy of the presented method.

Endurance Time Analysis of skewed slab-on-girder bridges: The significance of the excitation angle

In this paper the influence of excitation angle on the Endurance Time (ET) analysis of skewed slab-on-girder bridges is studied. The excitation of the structure due to critical angle leads to the maximum seismic responses that are sometimes significantly higher than the average. The modeled bridges are slab-on-girder type which are typically used as highway bridges. The bridge models have skew angles of 0, 15, 30, 45, and 60 degrees. The ET excitations exerted on the structures cover a broad range of hazard levels. The results provide some insight for choosing multiple excitation angles in such a way that balances computational costs and retains acceptable accuracy for practical design purposes. Sensitivity of life cycle cost (LCC) to skewness is also studied.

Sensitivity analysis for the distribution of maximum responses by seismic isolation system parameters using the stochastic response database

The seismic performance of nuclear power plants can be improved by installing the proposed seismic isolation system. Due to the characteristics of this system, while acceleration seismic response and base shear can be reduced, the displacement seismic response of the isolated structure increases. Therefore, the restriction of excessive displacement responses becomes critical to the design and safety assessment of isolated structures. Such seismic design and safety assessment requires a seismic response distribution, which itself necessitates a large number of nonlinear dynamic analyses. However, the stochastic response database can directly estimate the maximum seismic response distribution of an isolated structure without nonlinear dynamic analyses. In this study, a sensitivity analysis was performed using the stochastic response database for the isolated structures that affect the maximum seismic response distribution. First, the important seismic isolation parameters were selected, followed by an investigation into the effects these parameters have on the mean and standard deviation of the maximum seismic response distribution of the isolated structure. It is believed that this information will be useful in the seismic design and safety assessment of nuclear power plants with seismic isolation systems.

The Effect of Pier and Deck Connection on the Seismic Response of U-Turn Curved Bridge

The maximum seismic response of irregular U-turn curved bridge is significantly related to the pier and deck connection. An irregular U-turn curved bridge with radius of 45m, 8.5m total width and 154m total length was analyzed in this paper. This highly horizontally curved bridge was evaluated by performing nonlinear time history analysis on the representative bridge model with 3 types of connection between pier and deck: (i) rigid connection, (ii) hinge connection, and (iii) lead rubber bearing connection. Nonlinear hinge was modelled at the base and the top of the pier by using fiber hinge. Moreover, the effect of the number of connection between pier and deck was evaluated. The results indicate that bridges with one connection give better performance level than those with two connections; however, bridges with only one connection is more critical to the torsion issue.

Numerical Study on Inelastic Seismic Design of Piping Systems Using Damping Effect Based on Elastic–Plastic Property of Pipe Supports

This study describes inelastic seismic design of piping systems considering the damping effect caused by elastic–plastic property of a pipe support which is called an elastic–plastic support. Though the elastic–plastic support is proposed as inelastic seismic design framework in the Japan Electric Association code for the seismic design of nuclear power plants (JEAC4601), the seismic responses of the various piping systems with the support are unclear. In this study, the damping coefficient of a piping system is focused on, and the relation between seismic response of the piping system and elastic–plastic behavior of the elastic–plastic support was investigated using nonlinear time history analysis and complex eigenvalue analysis. The analysis results showed that the maximum seismic response acceleration of the piping system decreased largely in the area surrounded by pipe elbows including the elastic–plastic support which allowed plastic deformation. The modal damping coefficient increased a maximum of about sevenfold. Furthermore, the amount of the initial stiffness of the elastic–plastic support made a difference in the increasing tendency of the modal damping coefficient. From the viewpoint of the support model in the inelastic seismic design, the reduction behavior for the seismic response of the piping system was little affected by the 10% variation of the secondary stiffness. These results demonstrated the elastic–plastic support is a useful inelastic seismic design of piping systems on the conditions where the design seismic load is exceeded extremely.

Dynamic Behaviour and Seismic Response of Ground Supported Cylindrical Water Tanks

Liquid storage tank such as in water distribution systems, petroleum plants etc., constitute a vital component of life line systems. Reducing earthquake effects on liquid storage tanks, to minimize the environmental and economic impact of these effects, have always been an important engineering concern. In this paper, the dynamic behavior of cylindrical ground supported concrete water tanks with different aspect ratios is investigated using finite element software ANSYS. The natural frequencies and modal responses are obtained for impulsive and convective modes of vibration. The natural frequency of vibration of the tank is observed to be the lowest at maximum water depth. The fundamental impulsive frequency increases as water level reduces and for water level less than 1/3 of tank height, there is significantly no change in impulsive frequency. The effect of wall flexibility on dynamic behavior of the tank is investigated by performing the modal analysis of flexible and rigid tanks. For a partially filled tank, the results of the present study are of significant relevance. The response of the tank to the transient loading as horizontal ground motion of El Centro earthquake is studied for various water heights. As the height of water on the tank increases, the ultimate maximum seismic response parameters are also observed to be increased. The location of maximum hoop stress varies in accordance with the variations in input ground motion and water fill condition whereas shear and bending moment are maximum at the base.

Generalized corrective eccentricities for nonlinear static analysis of buildings with framed or braced structure

The nonlinear static method of analysis has become the most popular tool for the seismic assessment of existing buildings. However, seismic codes do not allow its use for in-plan irregular buildings because it does not provide accurate predictions of the deck rotation. To overcome this limitation, the “corrective eccentricity method” evaluates the maximum seismic response as the envelope of the results of two nonlinear static analyses. In these analyses, the lateral force is applied with two different (corrective) eccentricities with respect to the centre of mass of the deck. The corrective eccentricities were calibrated on single-storey systems with unidirectional resisting elements, i.e. with elements that are representative of walls or braced frames. This paper proposes new corrective eccentricities aiming at generalizing and simplifying the previous corrective eccentricity method. In particular, new equations are defined for the corrective eccentricities devoted to predict the displacement demand on the stiff side of the building. These equations are defined based on the response of a set of single-storey systems representative of buildings with uni-directional or bi-directional resisting elements (e.g. moment resisting frames). Further, the displacement demand on the flexible side of the building is determined assuming a null eccentricity of the lateral force. The response of a set of multi-storey buildings is predicted by means of the new and original corrective eccentricities and compared to the maximum response obtained by nonlinear dynamic analysis. This comparison is made in terms of floor displacements, storey drifts and storey shears. The set of the examined structural systems comprises buildings with steel braced structure as well as buildings with r.c. framed structure.

Characterization of radial and circumferential mechanical energy components in bi-directional nonlinear seismic response of steel bridge piers

In this study, the bi-directional nonlinear elaso-plastic seismic response of steel bridge piers subjected to bi-directional ground motions is analyzed with a particular interest in the role of the radial and circumferential components of mechanical energy. In order to explore the influencing factors to the maximum bi-directional seismic response, dynamic characteristics of a circular steel bridge pier are expressed by two modeling techniques: the multiple shear spring (MSS) model, and the fiber model. The calculated bi-directional dynamic responses of the steel bridge pier models under artificially generated bi-directional ground motions are characterized by introducing a technique to divide the strain and kinetic energies to the radial and circumferential components. The analysis result indicates that the level of circumferential strain energy that effectively contributes to dissipation of the total kinetic energy is of great importance in assessing the maximum bi-directional response. When the two models are subjected to the identical bi-directional ground motion, the circumferential strain energy induced in the fiber model is higher than that obtained by the multiple shear spring model, resulting in smaller radial displacement. Also, the analyses of the fiber model for various cases of directivity property of the input bi-directional seismic ground motion show that the bi-directional response is smaller than the unidirectional response in some cases. The reason can be explained by higher circumferential strain energy which can be related to the reduction of radial displacement in those cases.

Mohr Circle-based Graphical Vibration Analysis and Earthquake Response of Asymmetric Systems

The maximum seismic response of torsionally coupled plan asymmetric structures can be rationally visualized and computed through a Mohr Circle Response Spectrum Analysis (MCRSA). This is done combining the graphic modal properties of the torsional dynamic equations of motion with the structural earthquake demand in terms of a displacement spectrum as a function of the modal eigenvalues SD(ω2). A compact representation of the modal properties and of the response envelope is built and visualized in the Mohr plane. The maximum modal responses are then combined using a graphic adaptation of the SRSS and CCQ combination rules based on the elastic response spectrum. This Graphic Dynamic rule proves to be an effective response prediction tool, and is particularly suited to estimate the response of seismic base isolation systems.

Evaluation of combination rules for multi-story buildings with asymmetric set-backs

The effectiveness of 100/30, 100/40 and SRSS directional combination rules on the response of asymmetric setback buildings is examined. Because of the irregularity in setback buildings, the maximum seismic response would be correlative with the direction of earthquake. To verify the directional combination rules of mode superposition methods, the time history analyses of setback buildings to real earthquake records are carried out. Example analyses have been used to compare the validty and accuracy of SRSS and percentage methods for frame and dual frame-wall systems.

ANALYSIS OF NORMALIZED TIME‐FREQUENCY RESPONSE SPECTRA FOR THREE SEISMIC RECORDS

AbstractTime‐Frequency Response Spectrum (TFRS) is a three‐dimensional spectrum, which includes three main characteristics of ground motion: amplitude, frequency characteristic and duration. Based on it, Normalized Time‐Frequency Response Spectrum (NTFRS) was proposed and the NTFRS of three typical seismic waves were calculated. The comparison of three NTFRS shows that spectra amplitudes distributed along period axis and duration axis are different from each other; the large difference may cause different effect on the structures. One 12‐storey reinforced concrete frame structure was analyzed by using elastic‐plastic time‐history analysis method. The comparison of the seismic response, structural damage curve and NTFRS of input ground motion shows that the maximum seismic response of structure might not be the cause of its collapse. It implies that the traditional response spectrum theory has limitation because in the theory the maximum elastic response of structures is used to make seismic design. It could be concluded that the Normalized Time‐Frequency Response Spectrum is better for analyzing the characteristics of ground motions and the structural failure mechanism in the earthquakes.

Seismic response estimation method for earthquake‐damaged RC buildings

SummaryThis study proposes a procedure for identifying spectral response curves for earthquake‐damaged areas in developing countries without seismic records. An earthquake‐damaged reinforced concrete building located in Padang, Indonesia was selected to illustrate the identification of the maximum seismic response during the 2009 West Sumatra earthquake. This paper summarizes the damage incurred by the building; the majority of the damage was observed in the third story in the span direction. The damage was quantitatively evaluated using the damage index R according to the Japanese guidelines for post‐earthquake damage evaluation. The damage index was also applied to the proposed spectral response identification method. The seismic performance of the building was evaluated by a nonlinear static analysis. The analytical results reproduced a drift concentration in the third story. The R‐index decreased with an increase in the story drift, which provided an estimation of the maximum response of the building during the earthquake. The estimation was verified via an earthquake response analysis of the building using ground acceleration data, which were simulated based on acceleration records of engineering bedrock that considered site amplification. The maximum response estimated by the R‐index was consistent with the maximum response obtained from the earthquake response analysis. Therefore, the proposed method enables the construction of spectral response curves by integrating the identification results for the maximum responses in a number of earthquake‐damaged buildings despite a lack of seismic records. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd.

Combination rules and critical seismic response of steel buildings modeled as complex MDOF systems

The Maximum seismic responses of steel buildings with perimeter moment resisting frames (MRF), modeled as complex MDOF systems, are estimated for several incidence angles of the horizontal components and the critical one is identified. The accuracy of the existing rules to combine the effects of the individual components is also studied. Two and three components are considered. The critical response does not occur for principal components and the corresponding incidence angle varies from one earthquake to another. The critical response can be estimated as 1.40 and 1.10 times that of the principal components, for axial load and interstory shears, respectively. The rules underestimate the axial load but reasonably overestimate the shears. The rules are not always inaccurate in the estimation of the combined response for correlated components. On the other hand, totally uncorrelated (principal) components are not always related to an accurate estimation. The correlation of the individual effects (<TEX>${\rho}$</TEX>) may be significant, even for principal components. The rules are not always associated to an inaccurate estimation for large values of <TEX>${\rho}$</TEX>, and small values of <TEX>${\rho}$</TEX> are not always related to an accurate estimation. Only for perfectly uncorrelated harmonic excitations and elastic analysis of SDOF systems, the individual effects of the components are uncorrelated and the rules accurately estimate the combined response. The degree of correlation of the components, the type of structural system, the response parameter under consideration, the location of the structural member and the level of structural deformation must be considered while estimating the level of underestimation or overestimation.

Prediction Method of Maximum Seismic Response for Vibration Control Steel Frames With Scaling-Frame Device Installed

The innovated vibration control device called as scaling frame a²¯SFa²° structure has been proposed by the authors, and the SF structures are applied to low-rise wooden structures already. This paper aims to investigate the applicability of SF structure on steel frames. Herein, SF structure consists of beam-column frame, diagonal bracing, and SF device a²¯SFDa²° installed, and SFD is made of Steel or aluminum. And vibration energy is absorbed by the plastic behavior of the diagonal deformation of SF device. In previous study, the experimental study on SFD and steel frame specimen with SFD installed were conducted to clarify the seismic response and seismic mitigation effect. And also, from observation of test results, analytical method has been suggested. From the comparison of test results, the proposed method shows good agreements with test results. Furthermore, the enormous past studies have suggested prediction method of maximum seismic response of vibration control frames. So this study aim to develop the prediction method of seismic response on vibration controlled steel frames with SFD installed, and the simple design procedure can be provided. The first, the simplified restoring force characteristics which can chase the test results is applied on prediction method procedure. So the prediction method is reformulated to adapt the bilinear model and strain hardening rule. The time history response analysis is performed to investigate the applicability and effectiveness. From the comparison of analysis results and predictions, it is confirmed that the proposed prediction method shows enough accuracy.

A method for rapid estimation of dynamic coupling and spectral responses of connected adjacent structures

SummaryA simple method is presented for estimation of dynamic coupling and maximum seismic responses of structures connected through links. The purpose is preparing a simple measure for distinguishing the cases where two connected structures interfere in the response of each individual structure and incorporating such cases in spectral analysis. First, each structure is analysed independently, and the natural modes with considerable interference with the other structure are identified. Then the spectral responses corresponding to such modes are modified in modal space. It is shown that the proposed method can estimate the spectral responses of adjacent systems with good accuracy. Copyright © 2015 John Wiley &amp; Sons, Ltd.