Time History Analysis Of Structure Research Articles

A practical way to apply a technique that accelerates time history analysis of structures under digitised excitations

Time history analysis using direct time integration is a versatile and widely accepted tool for analysing the dynamic behaviour of structures. In 2008, a technique was proposed to accelerate thetime history analysis of structural systems subjected to digitised excitations. Recently, this techniquehas been named as the SEB THAAT* (Step-Enlargement-Based Time-History-Analysis-Acceleration-Technique), and the determination of appropriate values for its parameter is introduced as the mainchallenge. To overcome this challenge, a procedure is proposed in this paper. The basis of the procedure is the comments on accuracy control in structural dynamics and numerical analysis ofordinary differential equations, legalised in the New Zealand Seismic Code, NZS 1170.5:2004. As themain achievement, by using the proposed procedure, we can apply the SEB THAAT and carry out thetime history analysis clearly and with less parameter setting compared to the ordinary time historyanalysis. The proposed procedure is always applicable and, except when the behaviour is very complex, oscillatory and non-linear, the reductions in analysis run-time are considerable while the changes in accuracy are negligible. The performance can be sensitive to the problem, the integration method, the target response, and the severity of the non-linear behaviour. Compared to the previous tests on the SEB THAAT, the efficiency of applying the SEB THAAT using the proposed procedure is better, the sensitivity of the performance to the problem is lower, and a measure of accuracy is available. Compared to other techniques for accelerating structural dynamic analyses, the use of the SEB THAAT according to the proposed procedure has several positive points, including the simplicity of implementation.

Time history analysis of structures under multi-support excitation by state-space method

Because of the variety of methods to simulate the dynamic behaviors of the structure under earthquake loading trying to approach the reality. This paper provides a contribution to simulate this behavior using three methods, mainly starting with state space. Secondly, we compare it with the finite element method (Duhamel integral and direct method of Newmark), taking into consideration the effect of Non-uniform excitation in the supports. The obtained results proves the three methods are efficient and very close to each other for simple structures but in term the computing time, the state space method is faster than the others. At the end, add a big structure to test the limits of each method.

Damping approaches in nonlinear seismic time history analysis for large mobile equipment with uplift

AbstractIn large mobile equipment in seismically active regions, seismic stability is often a decisive design criterion, and the behaviour of this large equipment, which is characterised by uplift, tilting and rocking, can only be calculated by means of nonlinear time history analyses. Here, the model damping approach has a significant influence on the results of these analyses but there are no scientific approaches for large mobile equipment with nonlinear behaviour such as uplift. In this paper, possible theoretical damping approaches for nonlinear time history analysis of structures with uplift such as large mobile equipment are discussed and numerical studies are conducted to investigate the influence of damping in the model on the concise results of the typical behaviour of large mobile equipment under seismic excitation. A suitable new approach is to be developed and a way of practical implementation is being prepared. Experimental studies on real typical bucket wheel machines will identify and validate important natural frequencies and associated damping for the numerical approach. These can be applied in numerical models using the damping approach engineered in the theoretical part. Thus, realistic results of the numerical models under nonlinear seismic time history analyses can be expected and more precise conclusions on the distinctive behaviour of large mobile equipment with uplift can be drawn.

Combining Discrete Wavelet Transform and Strong Ground Motion Duration to Reduce Computational Costs in Dynamic Analysis of Structures

The dynamic time history analysis is the most accurate method for calculating the structure response relative to the vibrating load. The use of this method is time-consuming due to the long-duration earthquakes and is generally less commonly used. Wavelet trans-forms are one of the new methods for filtering waves. The duration of a strong ground motion is actually a concept that can be used to turn an earthquake with a long time into an earthquake with a shorter time. In this paper, two concepts of filtration using wavelet transform and the use of a duration of strong ground motion are used for the time history analysis of structures. For this purpose, the acceleration of the earthquake in 5 states was filtered by wavelet transform. In each stage, the high and low frequencies are separated, and the number of earthquake acceleration points is half-past. Then the beginning and the end of the main earthquake and the approximate waves obtained from the wavelet transform are removed using the concept of the duration of the strong ground motion. Finally, two two-dimensional and three-dimensional structures are analyzed using the main earthquake and the waves obtained by combining the two concepts of wavelet transform and the duration of strong ground motion. The results show that by reducing the number of acceleration points of the main earthquake record to more than 95%, the dynamic response error is less than 8%.

Parametric analysis on seismic performance of reinforced concrete frame‐shear wall structures with different setback configurations

SummaryHigh‐rise buildings with vertical setbacks are more prone to damage in the event of strong earthquakes. This paper presents an extensive parametric study on the seismic performance of reinforced concrete (RC) frame‐shear wall structures with different setback configurations. Five groups of RC frame‐shear structures with 30 setback configurations were designed. Before conducting extensive non‐linear time history structural analysis, modeling of main lateral force resisting systems including RC column and shear wall was validated using previous test results. By parametric analysis on both horizontal setback ratio and vertical setback ratio, the influences of setback on structural seismic performance in terms of dynamic property, inter‐story drift ratio, acceleration, energy dissipation, and damage condition were comparatively investigated. The overall conclusion is that setbacks caused more than 50% reduction of floor area or positioned at the middle and lower height should be avoided.

Evaluation of synthetic and recorded ground motions for soil liquefaction analyses

In performance-based earthquake engineering, simulated earthquake ground motions are often generated for time history analyses of structures and geotechnical systems. Liquefaction refers to dramatic loss of stiffness and strength of soils during earthquake shaking. As a complicated nonlinear process associated with accumulation of excessive pore pressure and decrease of effective stress due to soil-fluid interaction, whether synthetic motions can be appropriately used in liquefaction assessment still remains a grand challenge. In this study, various synthetic ground motions are generated using different simulation techniques, whose performances are compared with real recorded motions through nonlinear time history analyses of liquefiable grounds with different soil densities and ground inclinations. One-to-one comparison of results in this study clearly demonstrates the importance of preserving accumulative intensity measures of synthetic motions in liquefaction assessment. Strong linear relationships are also found in a log-log space between the maximum ground displacement and evolutionary Arias intensity during post-liquefaction stage for different liquefiable grounds, and the predictive relationships seem not to be affected by the types of synthetic ground motions.

Vulnerability assessment of building structures due to underground blasts using ANN and non-linear dynamic analysis

Building structures near the mines area are prone to blast-induced ground vibration due to underground blasting. The level of ground vibration typically quantified as Peak Particle Velocity (PPV) is used to assess the vulnerability of the buildings. However, the PPV does not take into account the dynamic characteristics of the structure. To incorporate structural response in the design and assessment process, Artificial Neural Network (ANN) was used on underground blast data from the literature to obtain the Peak Ground Acceleration (PGA). Charge weight (Q), distance from the blasting point to the monitoring point (D) and soil's elastic constant (E) were taken as input to ANN and peak ground acceleration (PGA) was the output. Safe site distance for constructing structures was determined using non-linear time history analysis of structures having periods ranging from short to long duration, incorporating soil flexibility. The main findings highlight the shortcomings of considering PPV as the sole criteria for vulnerability assessment. The structural response such as interstorey drift, and damage level and locations must be taken into account.

Seismic behaviour of reinforced concrete frame structures with all steel assembled Q195 low yield buckling restrained braces

For the traditional buckling restrained braces (BRBs), the core plate is high yield strength steel, and the external restraint system is concrete filled steel tube), it has the disadvantages of high yield strength and large weight, which will produce a large additional effect on the structure. Under the same member deformation, the material with lower strength has larger plastic deformation and more seismic energy absorption, so it is easier to realize the idea that the BRBs is prior to frame structure failure So, an all steel assembled Q195 low yield point buckling restrained braces (LYBRBs), has been proposed in this paper, and the quasi-static low-cycle reciprocating load test was conducted. The results show that the failure mode of the LYBRBS is tensile failure, its hysteretic curve shows good symmetry, stability and fullness, and the LYBRBs has a good energy dissipation capacity. At the same time, based on a reinforced concrete frame (RCF) structure in the area of 8 degree seismic fortification intensity, the RCF structural model was established, and the dynamic characteristics of the RCF structure were compared by PKPM and SAP2000 software to verify the correctness of the model. On this foundation, push-over analysis of the RCF and RCF structure with the arrangement of the LYBRBs (LYBRB-RCF) is performed. The story drift ratio, the curves of the base shear force-top story drift and the plastic hinge condition obtained by push-over analysis are compared. In addition, the structural time history analysis was conducted by SAP2000 software under the action of frequent and rare earthquakes. The story drift ratio, story shear force, time history of the top displacement and acceleration, energy consumption and hysteretic curve of the LYBRBs were analysed.

Weighted and Unweighted Scaling Methods for Ground Motion Selection in Time-history Analysis of Structures

ABSTRACT A weighted scaling method (WSM) is developed for the selection and modification of structure-specific earthquake records in time-history analysis. The matching errors and scaling factors are calculated by weighted least-squares method to match with target spectrum. The weight factors are determined by the modal-mass participation factors. The 3-, 9-, and 20-story steel moment-resisting frame structures are used as examples. Their mean structural responses were calculated by the WSM and the unweighted scaling method (USM). WSM is as accurate as USM for estimating mean structural responses, but WSM has a better capacity for reducing the variability of structural responses.

The correlation between the ground motion intensity measure parameters of earthquakes

In performance-based seismic engineering, the choice of ground motion goes hand in hand with dynamic analysis. This paper presents the relationship between the various intensity measures (IMs) parameter of ground motions that can be used in evaluating the behavior of structures. This is through the relationship between them and the ratio of the peak ground acceleration to the peak ground velocity (PGA/PGV). The PGA/PGV ratio has been used an empirical parameter to estimate ground motion frequency content and categorizes ground motion suites for performing nonlinear time history analyses of structures. Regression analyses are performed on data obtained from ground motion records with different PGA/PGV ratios. The regression analyses indicate that the best correlation IMs parameter with the PGA/PGV ratio in both near- and far-source earthquakes is the mean period (Tm). Also, the relationships between PGA/PGV ratio and some IMs parameters in near-source earthquakes are stronger than it in far-source earthquakes.

Evaluation of seismic performance measures for MDOF RC structures subjected to simulated and real ground motions

Nonlinear time history analyses of structures require full time series of ground motion records. For regions with sparse seismic networks or potential large earthquakes, ground motion simulation has gained more attention in recent years. Simulated records are required to be generated using regional input dataset and then verified against existing recorded ground motions of past events. To use simulated ground motions in engineering applications, estimation of reliable seismic demand parameters is essential. In this study, the real and simulated records of the 2009 L’Aquila, Italy earthquake with (Mw=6.3) are investigated for their use in engineering practice. In the first step, misfits are evaluated for alternative seismological measures (peak values, duration and frequency as well as energy content of the time histories). Next, varying multi-degree-of-freedom reinforced concrete structures with different number of stories are selected. Numerical models of the structures are performed in the OpenSees platform. Seismic performance measures in terms of inter-story drift ratio for the selected structures are assessed through nonlinear time history analyses for both the real and simulated ground motions. Then, the misfits are estimated in terms of structural demand parameters. Results reveal a good fit between the seismological and engineering demand misfits for the selected ground motion simulation approaches.

The effect of duration of strong ground motion on the ductility demand of SDOF structure

As one of the basic parameters of strong ground motion, the duration of strong ground motion has not been considered in the seismic design codes over the world. To study the ground motion duration on the effects of the SDOF structure ductility demand, the Ds5-75 is chosen as the duration index, and the ductility demand ratio spectrum under long and short ground motion is calculated, then the effect of duration on structural ductility demand under different strength reduction factor is analyzed. The results show that the ductility demand of the structure under long duration ground motion is significantly greater than that under the short duration ground motion. For most periods, the ductility demand of long-duration ground motion is 1.3 times that of short-duration ground motion, and the maximum is 2.5 times. It is suggested that the effect of duration should be considered when the time history analysis of structure is carried out.

Sensitivity analysis of the influence of ground motion intensity levels on the seismic behavior of steel frames in assessment of the target displacement considering near-fault effects

Nonlinear time-history analysis conducted as part of a performance-based seismic design approach often require that the ground motion records are selected and then scaled to a specified level of seismic intensity. In such analyses, besides an adequate structural model, a set of acceleration time-series is needed as the most realistic representation of the seismic action. In this paper, the effects of scaling procedure on seismic demands of steel frames are investigated. To this, two special steel moment-resisting frames with considerable higher mode effects, and two sets of ground motions, including near-fault and far-fault motions are considered. Moreover, three scaling procedures are introduced for performing nonlinear dynamic time-history analysis of structures. Among different demands, lateral roof displacement and interstory drift are selected as seismic demands. The height-wise distribution of demands shows that the inelastic seismic demands of the near-fault pulse-like ground motions differ considerably from those of far-fault ones. These results show that the story drifts are mostly larger for far-fault motions in the upper story levels in comparison to near-fault records and in the lower floors, the reverse is true. Thus, the scaling procedures directly affect the results of seismic demands and choosing different methods would result in varying responses. Moreover, a low-cost and fairly effective procedure is proposed to estimate the target displacement demands of buildings from response-spectrum analyses, considering near-fault effects. The precision of this method is verified by nonlinear time-history analysis results, as the benchmark solution, and acceptable improvements have been achieved.

An intelligent method for generating artificial earthquake records based on hybrid PSO–parallel brain emotional learning inspired model

Simplicity and high speed of brain emotional model made it an effective computational method, which is used in various applications. In this study, a modified model of brain emotional learning is used for generating artificial earthquake records. In fact, in earthquake engineering, strong ground motions are valuable information, which are recorded in each earthquake. These records could be used for linear and nonlinear time-history analysis of structures. Unfortunately, the numbers of recorded strong ground motions are not enough for most areas of the world. Therefore, many seismic codes permit to use artificial records, which contain specific characteristics. Because of the advantages of emotional models, a hybrid PSO–parallel brain emotional learning model is used for generating artificial records based on a dataset of real records in this research. PSO algorithm is combined with the model for finding the best values of learning parameters. In addition, wavelet packet transform is used for decomposing the earthquake signal to use as the suitable output of network. Despite of original brain emotional model, the proposed modified parallel model is applicable on multiinput–output data. Numerical examples show that the proposed model in this research could be successfully used for generating artificial records with acceptable error for statistical properties of the required pseudo spectral acceleration.

Time History Analysis of Structure having Water Tank at the Top of Building Acting as a Tuned Liquid Damper

Time History Analysis of Structure having Water Tank at the Top of Building Acting as a Tuned Liquid Damper

Time History Analysis of Structures on Vlasov Type Elastic Subgrade

Yapilarin statik yukler ve deprem etkileri altindaki analizlerinde zemin modeli olarak genellikle Winkler modeli olarak bilinen model esas alinmaktadir. Bu modelde, bir noktadaki zemin gerilmesinin ayni noktadaki yer degistirme ile dogru orantili oldugu kabul edilmekte, noktalar arasindaki etkilesim terkedilmektedir. Bu zemin modelinden daha gercekci olan Vlasov zemin modeli, Winkler modeline ek olarak zemini ikinci bir parametre ile modellemekte, boylece noktalar aralarindaki etkilesim de bir olcude dikkate alinabilmektedir. Bu modelde ayrica temel altindaki zemin tabakasi kalinliginin ve temel disinda kalan zemin bolgesinin hesaba etkisi de goz onune alinabilmektedir. Vlasov zemin modelinde Ikinci parametre olarak da adlandirilan parametre zemindeki kayma etkilerini ifade etmektedir. Tasarim sirasinda kullanilan genel amacli yazilimlar zemin davranisina ait ikinci parametreyi hesaba dogrudan katamamakta, ancak program kutuphanelerinde bulunan bazi sonlu eleman modelleri probleme adapte edilmek ve zemin eleman olarak kullanilmak suretiyle dolayli olarak gozunun alinabilmektedir. Ancak, bu durumda Zaman Tanim Alaninda yapilan analizler sirasinda her adimda zemin parametrelerinin guncellenmesi gerektiginden ikinci parametrenin hesaba tam olarak alinmasi mumkun degildir. Bu calisma kapsaminda gelistirilen bilgisayar yaziliminda ise, her bir zaman artimi sirasinda zemin parametreleri guncellenmekte ve gercege daha yakin sonuclar elde edilmektedir. Bu amacla secilen yapi modelleri, gelistirilen program yardimi ile cozulmus ve daha once genel amacli bir bilgisayar programi ile cozulen ornekte soz konusu parametrenin hesaplar uzerindeki etkisi tartisilmistir.

A Comparative Study on Optimal Structural Dynamics Using Wavelet Functions

Wavelet solution techniques have become the focus of interest among researchers in different disciplines of science and technology. In this paper, implementation of two different wavelet basis functions has been comparatively considered for dynamic analysis of structures. For this aim, computational technique is developed by using free scale of simple Haar wavelet, initially. Later, complex and continuous Chebyshev wavelet basis functions are presented to improve the time history analysis of structures. Free-scaled Chebyshev coefficient matrix and operation of integration are derived to directly approximate displacements of the corresponding system. In addition, stability of responses has been investigated for the proposed algorithm of discrete Haar wavelet compared against continuous Chebyshev wavelet. To demonstrate the validity of the wavelet-based algorithms, aforesaid schemes have been extended to the linear and nonlinear structural dynamics. The effectiveness of free-scaled Chebyshev wavelet has been compared with simple Haar wavelet and two common integration methods. It is deduced that either indirect method proposed for discrete Haar wavelet or direct approach for continuous Chebyshev wavelet is unconditionally stable. Finally, it is concluded that numerical solution is highly benefited by the least computation time involved and high accuracy of response, particularly using low scale of complex Chebyshev wavelet.

Comparing of the effects of scaled and real earthquake records on structural response

Time history analyses have been preferred commonly in earthquake engineering area to determine earthquake performances of structures in recent years. Advances in computer technology and structural analysis have led to common usage of time history analyses. Eurocode 8 allows the use of real earthquake records as an input for linear and nonlinear time history analyses of structures. However, real earthquake records with the desired characteristics sometimes may not be found, for example depending on soil classes, in this case artificial and synthetic earthquake records can be used for seismic analyses rather than real records. Selected earthquake records should be scaled to a code design spectrum to reduce record to record variability in structural responses of considered structures. So, scaling of earthquake records is one of the most important procedures of time history analyses. In this paper, four real earthquake records are scaled to Eurocode 8 design spectrums by using SESCAP (Selection and Scaling Program) based on time domain scaling method and developed by using MATLAB, GUI software, and then scaled and real earthquake records are used for linear time history analyses of a six-storied building. This building is modeled as spatial by SAP2000 software. The objectives of this study are to put basic procedures and criteria of selecting and scaling earthquake records in a nutshell, and to compare the effects of scaled earthquake records on structural response with the effects of real earthquake records on structural response in terms of record to record variability of structural response. Seismic analysis results of building show that record to record variability of structural response caused by scaled earthquake records are fewer than ones caused by real earthquake records.

비구조요소의 내진 설계를 위한 기존 층응답스펙트럼의 평가

The seismic damage of non-structural components, such as communication facilities, causes direct economic losses as well as indirect losses which result from social chaos occurring with downtime of communication and financial management network systems. The current Korean seismic code, KBC2009, prescribes the design criteria and requirements of non-structural components based on their elastic response. However, it is difficult for KBC to reflect the dynamic characteristics of structures where non-structural components exist. In this study, both linear and nonlinear time history analyses of structures with various analysis parameters were carried out and floor acceleration spectra obtained from analyses were compared with both ground acceleration spectra used for input records of the analyses and the design floor acceleration spectrum proposed by National Radio Research Agency. Also, this study investigates to find out the influence of structural dynamic characteristics on the floor acceleration spectra. The analysis results show that the acceleration amplification is observed due to the resonance phenomenon and such amplification increases with the increase of building heights and with the decrease of structure`s energy dissipation capacities.

Initial versus tangent stiffness‐based Rayleigh damping in inelastic time history seismic analyses

SUMMARYIn the inelastic time history analyses of structures in seismic motion, part of the seismic energy that is imparted to the structure is absorbed by the inelastic structural model, and Rayleigh damping is commonly used in practice as an additional energy dissipation source. It has been acknowledged that Rayleigh damping models lack physical consistency and that, in turn, it must be carefully used to avoid encountering unintended consequences as the appearance of artificial damping. There are concerns raised by the mass proportional part of Rayleigh damping, but they are not considered in this paper. As far as the stiffness proportional part of Rayleigh damping is concerned, either the initial structural stiffness or the updated tangent stiffness can be used. The objective of this paper is to provide a comprehensive comparison of these two types of Rayleigh damping models so that a practitioner (i) can objectively choose the type of Rayleigh damping model that best fits her/his needs and (ii) is provided with useful analytical tools to design Rayleigh damping model with good control on the damping ratios throughout inelastic analysis. To that end, a review of the literature dedicated to Rayleigh damping within these last two decades is first presented; then, practical tools to control the modal damping ratios throughout the time history analysis are developed; a simple example is finally used to illustrate the differences resulting from the use of either initial or tangent stiffness‐based Rayleigh damping model. Copyright © 2013 John Wiley & Sons, Ltd.