Results Of Nonlinear Analysis Research Articles

Effects of spatially varying gravity, temperature and concentration fields on the stability of a chemically reacting fluid layer

In the present study, the effects of different types of basic temperature and concentration gradients on a layer of reactive fluid under variable gravity field are analyzed using linear and non-linear analysis. Energy method is applied to obtain the non-linear energy threshold below which the solution is globally stable. It is found that the linear and non-linear analysis are not in agreement for the considered models of temperature and concentration gradients. The obtained results of non-linear analysis for different values of reaction terms and variable gravity coefficients in each given model of temperature and concentration gradients are compared with the linear instability results. The Chebyshev pseudospectral method is used to obtain the numerical and graphical results of subsequent analysis.

Role of perpendicular to grain compression properties on the seismic behaviour of CLT walls

In-plane seismic behaviour of Cross-Laminated Timber (CLT) walls is influenced by panel-to-panel and panel-to-foundation mechanical connections, which consist of hold-downs and angle brackets. Due to the platform constructional technology, the orthogonal to grain timber-to-timber contact is also involved in the seismic response of the panels. To date, literature theoretical approaches to evaluating the flexural load-bearing capacity of CLT panels focus their attention on the schematization of hold-downs and angle brackets only, under evaluating the role of timber compressed in the perpendicular direction.In this paper the influence of orthogonal to grain timber properties on the overall seismic behaviour of CLT walls has been investigated, proposing a general theoretical model to schematize the panel-to-panel and panel-to-foundation connections. A parabola-rectangle constitutive behaviour has been defined to describe the orthogonal to grain timber behaviour in the connection zones, while hold-downs and angle brackets are modelled adopting literature models. Five different failure conditions, described by mathematical formulations, able to describe the entire axial force-bending moment interaction domain have been defined.The proposed model has also been employed to schematize the connection zones in multi-storey CLT walls with openings, allowing to investigate the effect of the orthogonal to grain properties on its seismic behaviour. Results of nonlinear analyses demonstrate a significant influence of orthogonal to grain timber properties on seismic behaviour of the walls, affecting their strength, stiffness, ductility and collapse mechanisms.

Trade-off Pareto optimum design of an innovative curved damper truss moment frame considering structural and non-structural objectives

This research aims to develop a novel and cost-effective seismic force-resisting system called “curved damper truss moment frame” (CDTMF) by coupling the recently developed curved dampers (CDs) with conventional steel trusses. In this proposed system, the CDs are adopted as primary fuses, while semi-rigid connections are used as secondary fuses to dissipate the input seismic energy through a two-phased energy dissipation mechanism called the equivalent energy design procedure (EEDP). To validate the adequacy and feasibility of incorporating the CDTMF system in multi-story framed structures, the multi-objective NSGA II optimization technique was applied to the optimum seismic design of selected CDTMF prototypes. Their seismic performance was then compared with the recently proposed buckling restrained knee braced truss moment frame (BRKBTMF) systems, which were designed based on the same procedure to make a consistent comparison. This comparison was based on the results of nonlinear static analysis (pushover), nonlinear time history analysis (NTHA) and incremental dynamic analysis (IDA) on three-, six- and nine-story steel framed structures (low- to mid-rise systems). Since damage to non-structural acceleration-sensitive elements would depend on the floor acceleration, and because the main cause of damage in non-structural displacement-sensitive elements and structural members is generally due to the story drift, the objective functions of the optimization process were the median maximum story drift and the peak floor acceleration. In order to achieve the two-phased energy dissipation mechanism, the primary constraints (PCs) and secondary constraints (SCs) corresponding to the primary and secondary fuses are applied. The outcomes of the pushover analysis showed that the optimal CDTMF structures exhibited higher ductility and energy dissipation capacity compared to the BRKBTMFs. The results of the nonlinear dynamic analysis also indicated that the newly proposed CDTMF system can control the roof displacement, story drift, and roof acceleration during an earthquake excitation more efficiently than the BRKBTMF system. Finally, the outputs of the IDA show that the CDTMFs can fulfilled the FEMA P695 code requirements. Hence, it can be considered as a reliable seismic force resisting system.

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.

Theoretical and experimental study on an innovative seismic retrofit solution for old brick masonry buildings

An innovative retrofit scheme is proposed for the strengthening of old brick masonry buildings: the floor area is increased using newly added and isolated upper stories, and the lower brick masonry part is strengthened using precast concrete wall panels. To investigate the seismic performance of the innovative proposed strengthening scheme, a theoretical analysis and shaking-table tests were conducted, and the proposed scheme is compared with two conventional retrofitting schemes. The results of linear and nonlinear analyses of the three strengthening schemes indicated that all three schemes can mitigate seismic damage to old brick masonry buildings. The shaking-table tests confirmed that the proposed scheme is more effective than the two conventional schemes. Additionally, the seismic performance of the proposed strengthening scheme with post-test damage is investigated via a theoretical analysis and shaking-table tests. The results revealed that the stiffness degradation of the substructure can negatively affect the adding-story isolation system.

Tectonic forcing of environmental transition in Central Asia at ~11–9 Ma

A comprehensive understanding of the Neogene paleoenvironmental evolution of Central Asia is important for predicting the future climatic and environmental conditions within the region. However, our understanding of the relative roles of Tibetan Plateau (TP) uplift and global cooling in driving its paleoenvironmental evolution remain elusive. Here we present two well-dated (~16–5 Ma) independent environmental magnetic records from the northern TP, together with a comprehensive analysis of other well-dated Neogene environmental magnetic datasets for ten other sites from the northern TP. The results indicate synchronous changes in magnetic parameters which we interpret as reflecting a major environmental transition in Central Asia at ~11–9 Ma, which is supported by evidence from multiple independent paleoecological and paleoclimatic studies. A major environmental transition at 11–9 Ma is also supported by the results of linear and non-linear analyses of the magnetic records of the two studied sections. Our analyses reveal that prior to ~11 Ma, the environmental fluctuations within the QB were primarily driven by insolation variations modulated by Earth orbital parameters; however, after ~11 Ma this influence faded and there was a shift from a stable environmental system, characterized by periodic fluctuations, to an unstable system with erratic fluctuations. The timing of this phase shift in the paleoenvironment of Central Asia was not related to global cooling but it coincided with extensive tectonic activity in the TP. Together with conceptual models and previous numerical simulations results, we conclude that a major shift of the dominant driver of Central Asia paleoenvironment occurred at ~11–9 Ma and that uplift of the TP, rather than global cooling, was responsible.

A non-linear static approach for the prediction of earthquake-induced deformation of geotechnical systems

This paper illustrates an original and simple method to predict earthquake-induced deformations of geotechnical systems. The method is an extension of static non-linear analysis, and is conceived to predict the behaviour of geotechnical systems, like supported and unsupported excavations, that during the seismic motion accumulate displacements in a single direction. The seismic capacity of the system is described by its capacity curve, obtained either from a numerical push-over analysis or through a simplified procedure. The corresponding seismic demand is described by a combination of the elastic response spectrum, including basic information on the maximum amplitudes of the seismic motion, and a cyclic demand spectrum, that provides additional information about the equivalent number of cycles that contribute to the accumulation of displacements. In the paper, the method is described in detail and is validated through different procedures, namely: comparisons with experimental results obtained in the geotechnical centrifuge; comparison with results of advanced numerical analyses; extensive comparison, using a large database of seismic records, with the results of non-linear time-domain analyses. In its final part, the paper provides guidance for the practical use of the method for design.

Experimental Investigation to local settlement of steel cylindrical tanks with constant and variable thickness

Nowadays the use of thin-walled structures is widely accepted. The main reason for this is low weight and high resistance of these structures. In order to reduce the weight and cost of the structure, cylindrical steel tanks can be made in variable thickness. In general, foundation's settlement occur beneath the reservoir walls due to specific soil properties, which are divided into three general components: 1- Uniform Settlement 2- Tilt Settlement 3- Local Settlement. Among these components, Local settlement has the greatest impact on the reservoir shell. This component can cause large radial displacements, shell buckling and even tank failure. In this research, three steel cylindrical tanks, two specimens of constant thickness and one specimen of variable thickness, are first modeled in Finite Element and then made in the laboratory and subjected to local settlement at the edge of their floor. And the values of settlement, buckling load, final load, stress and radial deformation is compared. The data obtained from the eigenvalue analysis show that the effect of increasing the thickness on the critical buckling load is extremely high and the higher thickness at the lower part of the shell is highly influential. The results of Nonlinear analysis indicate that the behavior of tank with variable thickness is acceptable compared to other samples. Also in all samples, the radial deformation is initially negligible and then increases sharply due to the structural buckling, which is the same for all samples. According to experimental result the out of plane deformation recorded by the transducer mounted at a 45-degree angle indicates that in the samples of constant thickness the values are close together, whereas in the sample of variable thickness the amount of this deformation decreases, which is a positive result. Comparison of the results between numerical and experimental modeling also indicate good agreement between these two methods.

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.

Evaluation of Seismic Fragility Analysis of the Mega Sub-Controlled Structural System (MSCSS)

The improved mega sub-controlled structure system (MSCSS) significantly reduced the building responses and improved the control effectiveness as compared to conventional mega substructure (MSS). However, since the MSCSS is designed to resist future earthquakes, the seismic risk assessment of the structure remains a significant concern. In this study, the seismic risk analysis of MSCSS is performed to probabilistically compare the building performance and its resistance to future earthquake damage at certain categories of limit states (LSs), which include category one (slight damage, moderate damage, and collapse damage LS) and category two (damage control and collapse prevention). The comparison is realized with the result of the traditional MSS. The probability of exceedance of the above damage LS for a particular ground motion (GM) intensity (i.e. Sa (T1,5%)) is evaluated to assess and compare the vulnerability of these buildings. The evaluation is done through developing fragility curves and relationships for MSCSS and MSS. The result showed that the improved MSCSS has strong seismic resistance ability and provides a better response from a nonlinear analysis result. Furthermore, the fragility curve of moderate and collapse damage LSs indicated that MSCSS requires higher GM intensity to reach a moderate and collapse damage LS than MSS. That means MSCSS is the most stable with a significant difference as compared to its counterpart. This is also true for the second category of LS, that is, damage control and collapse prevention. While at the slight damage LS, both the MSCSS and MSS require approximately the same GM intensity to reach a slight damage LS, as the difference is not significant.

Nonlinear analysis of functionally graded beams using the dual mesh finite domain method and the finite element method

In this paper, geometrically nonlinear analysis of functionally graded beams using the dual mesh finite domain method (DMFDM) and the finite element method is presented. The DMFDM makes use of a primal mesh of finite elements and associated approximation for the variables of the formulation and a dual mesh of control domains, which does not overlap the primal mesh, for the satisfaction of the governing equations. The dual variables can be postcomputed uniquely and accurately at the control domain interfaces. The method is used to obtain nonlinear (due to the von Kármán nonlinear strains) bending solutions of straight, through-thickness functionally graded beams using the Euler–Bernoulli and the Timoshenko beam theories. Mixed models, which contain displacements and the bending moment as degrees of freedom, and displacement models are developed. Numerical results of linear and nonlinear analyses are presented to illustrate the methodology and a comparison of the generalized displacements and bending moments obtained with the DMFDM and FEM models while bringing out certain interesting features of functionally graded beams.

Heart Rate Variability Analysis on Electrocardiograms, Seismocardiograms and Gyrocardiograms on Healthy Volunteers.

Physiological variation of the interval between consecutive heartbeats is known as the heart rate variability (HRV). HRV analysis is traditionally performed on electrocardiograms (ECG signals) and has become a useful tool in the diagnosis of different clinical and functional conditions. The progress in the sensor technique encouraged the development of alternative methods of analyzing cardiac activity: Seismocardiography and gyrocardiography. In our study we performed HRV analysis on ECG, seismocardiograms (SCG signals) and gyrocardiograms (GCG signals) using the PhysioNet Cardiovascular Toolbox. The heartbeats in ECG were detected using the Pan–Tompkins algorithm and the heartbeats in SCG and GCG signals were detected as peaks within 100 ms from the occurrence of the ECG R waves. The results of time domain, frequency domain and nonlinear HRV analysis on ECG, SCG and GCG signals are similar and this phenomenon is confirmed by very strong linear correlation of HRV indices. The differences between HRV indices obtained on ECG and SCG and on ECG and GCG were statistically insignificant and encourage using SCG or GCG for HRV estimation. Our results of HRV analysis confirm stronger correlation of HRV indices computed on ECG and GCG signals than on ECG and SCG signals because of greater tolerance to inter-subject variability and disturbances.

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.

Stick-IT: A simplified model for rapid estimation of IDR and PFA for existing low-rise symmetric infilled RC building typologies

The prediction of seismic performances of buildings in terms of engineering demand parameters EDP, such as interstorey drift ratios IDR and peak floor accelerations PFA, represents a fundamental step towards the assessment of potential direct economic losses.This paper proposes a simplified model for the rapid assessment of EDPs in infilled moment resisting frames subjected to seismic loadings suitable for large scale assessment studies. The proposed model, named Stick-I (Stick model for Infilled frames), is a multi-degree of freedom MDOF system consisting of a series of lumped masses connected by means of nonlinear shear link elements. The shear link behavior is suitably calibrated adopting a multi-objective Genetic Algorithm procedure that employs the results of nonlinear cyclic pushover analyses performed on refined nonlinear FEM. Based on the regression study performed on a suitably generated Stick-I model database, a more general Stick-IT model, representative of RC Infilled frame Typologies of assigned storey number and dimensions in plan, is introduced. Simplified formulas for the definition of Stick-IT model are proposed depending on low-level information data that can be easily retrieved from rapid on-site surveys or remote sensing techniques.Both Stick-I and Stick-IT models are validated comparing the results of NRHA performed on refined FEMs with the results obtained adopting the simplified models and good agreement in terms of maximum EDP values and distribution along the building height is obtained.The typological Stick-IT model, which is defined as a function of few geometric and mechanical parameters, can be easily applied for simplified evaluation of expected response for building typologies. Hence, it can also be usefully employed for assessment of direct losses at the large scale, with a significant reduction in computational burden with respect to more refined methods.

Efficient intensity measures and machine learning algorithms for collapse prediction of tall buildings informed by SCEC CyberShake ground motion simulations

In contrast to approaches based on scaling of recorded seismograms, using extensive inventories of numerically simulated earthquakes avoids the need for any selection and scaling of motions which implicitly requires assumptions on intensity measures (IMs) that correlate with structural response. This study has the objectives to examine seismogram features that control the collapse response of tall buildings and to develop efficient and reliable collapse classification algorithms. To that end, machine learning techniques are applied to the results of nonlinear response history analyses of a 20-story tall building performed using about two million simulated ground motions. Feature selection of ground motion IMs generally confirms current understanding of collapse predictors based on previous studies using scaled recorded motions. In addition, interrogations of the large collection of hazard-consistent simulations demonstrate the utility of different IMs for collapse risk assessment in a way that is not possible with recorded motions. Finally, a small subset of IMs is identified and used in development of an efficient collapse classification algorithm which is tested on benchmark simulated data at several sites in the Los Angeles basin.

Efficiency of ground motion intensity measures with earthquake-induced earth dam deformations

In a seismic hazard analysis (SHA), the earthquake loading level should be predicted for one or more ground motion intensity measures (IMs) that are expected to relate well with the engineering demand parameters (EDPs) of the site. In this study, the goal was to determine the IMs that best relate to embankment dam deformations based on nonlinear deformation analysis (NDA) results of two embankment dams with a large suite of recorded ground motions. The measure utilized to determine the “best” IM was standard deviation in the engineering demand parameter (e.g., deformation) for a given IM, also termed “efficiency.” Results of the study demonstrated that for the NDA model used, Arias intensity (AI) was found to be the most efficient predictor of embankment dam deformations. In terms of pseudo-spectral acceleration (PSA)-based IMs, the PSA at short periods and then in the general range of the natural period of the dams was seen to be the most efficient IM, but was in almost all cases not as efficient as AI.

Investigation of the Effects of Link Beam Length on the RC Frame Retrofitted with the Linked Column Frame System

This study investigates the effect of different link beam lengths in the Reinforced Concrete (RC) frame retrofitted with the Linked Column Frame (LCF) system. It also investigates the ratio of the link beam length (e) to the span length of the RC frame (L) from 0 to 1.5 for the 9 models of the RC frame retrofitted by the LCF system has been investigated. In addition, it studies the formation of plastic hinges in the RC and Linked Column (LC) frame, distribution of stiffness between the RC and LC frame and the ratio of the structural displacement with the formation of the first plastic hinge in the member of the RC frame at the collapse prevention level (Dp LCF) to the structural displacement with the formation of the first plastic hinge in the link beam (Dy LCF) has been studied. Based on the nonlinear static analysis results, the model with the ratio of e/L= 0.45 has a better performance than other different lengths of the link beam. In this model, the stiffness of the LC frame has increased about 78% in comparison with the model with the ratio of e/L that is more than 0.6. Also, the ratio of Dp LCF to Dy LCF for the model of e/L = 0.45 in comparison with two models of e/L = 0.3 and 0.6 is more about 14% and 22%, respectively. It means that, the model of e/L = 0.45 has more potential to reach the performance level of Rapid Repair (RR) to occupancy.

Approximate Analysis for Shear Force Amplification Effect in Ordinary RC Shear Walls

An approximate analysis method is proposed to predict the dynamic amplification of shear forces in ordinary reinforced concrete shear walls as a preliminary study. First, a seismic design for three groups of ordinary reinforced concrete shear walls higher than 60 m was created on the basis of nonlinear dynamic analysis. Causes for the dynamic amplification effect of shear forces were investigated through a detailed evaluation of the nonlinear dynamic analysis result. A new modal combination rule was proposed on the basis of that observation, in which fundamental mode response and combined higher mode response were summed directly. The fundamental mode response was approximated by nonlinear static analysis result, while higher mode response was computed using response spectrum analysis for equivalent linear structural models with the effective stiffness based on the nonlinear dynamic analysis result. The proposed approximate analysis generally predicted vertical distribution of story shear and shear forces of individual walls from the nonlinear dynamic analysis with comparable accuracy.

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.

Seismic Assessment of Asymmetric Single-storey R/C Buildings by Two New Methodologies: Enforced Displacement-Based and Forced-Based Pushover Procedures

?wo new documented non-linear static (pushover) procedures on asymmetric single-storey R/C buildings are presented in detail herein, aiming directly at the Near Collapse state. Both procedures apply relative to the “Capable Near Collapse Principal reference system” of the single-storey building. The main objective of the two proposed procedures is to fully consider the coupling between torsional and translational vibrations of the floor-diaphragm under translational seismic excitation of the building’s base. The first pushover procedure, which is a Direct Displacement-Based one, uses floor enforced-displacements as action. In the second pushover procedure, which is a Force-Based one, the floor lateral static forces are applied eccentrically to centre of mass using suitable inelastic design eccentricities (dynamic plus accidental ones). The floor enforced-translations/rotation and the appropriate inelastic dynamic eccentricities used in the two proposed procedures derive from extensive parametric non-linear response history analysis and are given by figures or equations. In order to clarify in detail and evaluate the new pushover procedures, a torsionally-flexible, double-asymmetric, single-storey R/C building is seismically assessed. The validation of both procedures relative to the results of non-linear response history analysis shows that both predict with safety the in-plan displacements of the building.