Period Elongation Research Articles

Phytotoxicity of Domestic Effluent Before and After Treatment by Stabilization Ponds

Phytotoxicity tests linked to physicochemical parameters can be used to determine the possible effects of releasing a polluting load into the environment, evaluating the efficiency of a given treatment and its toxicity effects. In this context, the present work sought to evaluate the phytotoxicity of domestic effluent before and after treatment by stabilization ponds, using kale seeds (Brassica oleracea). Toxicity tests were carried out following the methodology of the American Environmental Protection Agency (EPA, 1996) at concentrations of 100%, 80%, 40%, 20%, 10%, and 5%. The seeds were incubated in a B.O.D. incubation chamber for five days at a temperature of 25ºC ± 2ºC. After this period, germination and root elongation were analyzed. The samples were also analyzed for biochemical oxygen demand, temperature, pH, turbidity, color, total solids, ammoniacal nitrogen, and organic nitrogen. Phytotoxicity was statistically evaluated by the Relative Growth Index, T-test (p < 0.05) for samples at 100% concentration, and Kruskal-Wallis followed by Dunn’s test (p < 0.05) to compare the negative control and the different concentrations. As a result, adverse effects of reduced root elongation were observed in samples of raw effluent (100%, 80%, and 20%) and treated effluent (10% and 5%), indicating a tendency toward phytotoxicity. Regarding the physicochemical parameters studied, all were within the established parameters by legislation, and no significant correlation was observed with root elongation. This may indicate the efficiency of stabilization ponds in treating domestic effluents, particularly in reducing phytotoxicity.

Using In-Building Observations of Small-to-Large Earthquakes to Predict the Seismic Response of Structures

ABSTRACT The main goal of this study is to evaluate the potential value of data from weak-to-moderate earthquakes for structural response analysis. Data recorded over 18 yr by the seismic network installed in the 12-stories Grenoble City Hall Building (France) is considered. The building response is analyzed in terms of intensity measures and engineering demand parameters, and then compared with strong earthquake data recorded in Japanese buildings. The uncertainties of structural response prediction are estimated and defined in terms of “within-building” and “between-building” components in the same way as the components of the ground-motion model. Data complementarity in the response model is observed between the weak-to-moderate (France) and the moderate-to-strong (Japan) earthquake datasets, disclosing nonlinear processes (associated with resonance period elongation) that are activated in buildings during low-to-strong motion. For example, fundamental frequency shifts are triggered at low values of both total structural drift amplitudes and equivalent strain rates (i.e., time derivative of structural drift). In addition, strain rate thresholds from 10−11 s−1 to 10−5 s−1 representing different structural conditions from undamaged to severely damaged buildings are observed to activate nonlinearities. This confirms the link between loading rates and structural conditions. Our results highlight the interest in instrumentation in buildings located in regions of weak-to-moderate seismicity, for (1) the development and calibration of realistic models for predicting the seismic response of structures, (2) for improving our understanding of the components of uncertainties in the risk assessment of existing buildings, and (3) to investigate physical processes activated in structures during seismic loading that influence their response.

Constant damage inelastic permanent period shift ratios spectra

The phenomenon of elongation of the structural period after earthquake excitation has been widely observed, and elongated period obtained after earthquake excitations can be used for post-earthquake assessment. The inelastic permanent period shift ratio, an indicator representing the degree of stiffness degradation and closely relating to the damage state, is defined as the ratio of the elongated period Tin of single-degree-of-freedom (SDOF) systems after earthquake excitations to the initial period Tel. The objective of this paper is to investigate the inelastic permanent period shift ratios under constant damage performances through nonlinear time-history analysis of SDOF systems, and the modified Park-Ang damage index is employed to characterize the structural damage. Inelastic permanent period shift ratio spectra are statistically constructed considering both the ground motion characteristics (such as site conditions, velocity pulse, magnitude, closet distance, directivity effects, significant duration and frequency contents) and structural parameters (including damage states, hysteretic models, ultimate deformation capacity, energy dissipation factor and postyield ratio). The results showed that the permanent period shift ratio is a reliable damage indicator for assessment of global damage states. The influence caused by ground motions on the estimation of the mean of the permanent period elongation ratio under constant damage performances is limited, while the effects caused by different structural damage and deformation capacity can reach up to approximately 70% and 33%, respectively. An expression for the relationship between the damage index and the permanent period shift ratio is established. Ignoring the differences of structural performances, using the period shift ratios to directly assess the global damage states will lead to erroneous results.

Ground-Motion Intensity Measures for the Seismic Response of the Roof-Isolated Large-Span Structure

Ground-motion intensity measures (IMs), which quantify and describe the characteristics of earthquake ground motion, are of utmost importance in the assessment of seismic risk and the design of resilient structures with large spans. The appropriate selection of a ground-motion IM is crucial in establishing a reliable and robust correlation between seismic hazards and structural demands. The current study presents a novel ground-motion IM that incorporates the influence of multiple vibration modes and period elongation resulting from isolation based on the velocity spectrum. A comprehensive study has been conducted to examine the efficiency of 37 different ground-motion IMs on a roof-isolated large-span structure with engineering demand parameters (EDPs), using far-field ground-motion data. The initial examination of the proposed intensity measure involves a planar lumped-mass model. Subsequently, a numerical model of a large-span roof-isolated structure, specifically the Beijing Workers’ Stadium, is constructed and examined. The results suggest that the proposed intensity measure (IM) demonstrates satisfactory adequacy and achieves optimal efficiency when considering three different engineering demand parameters among 37 other ground-motion intensity measures.

A 3-DOF system for preliminary assessments of the interaction between base isolation (BI) technique and soil structure interaction (SSI) effects for low-rise buildings

Base isolation technique is based on two mechanisms: period elongation and damping increase that may considerably improve the structural performance under earthquakes. However, the effectiveness of BI may be significantly reduced by the deformability of the foundation soil and thus by soil structure interaction (SSI) effects. In this regard, considering the role of the mutual interaction between BI and SSI becomes fundamental to realistically design structural systems. In literature, the assessment of the mutual role of BI and SSI is conducted with advanced numerical simulations that require realistic definitions of the non-linear properties of the structures, the isolation system and of the soil layers. However, these methods are extremely time-consuming and more expeditious methodologies are necessary. In this paper a 3-DOF system is proposed to perform preliminary assessments for design purposes. Parametric case studies have been proposed to demonstrate the potentiality of the proposed method to represent the cases where the beneficial effects of BI are reduced and eventually when BI technique becomes detrimental.

Oscillation Dynamics of Dielectric Polymer Droplets during Electrohydrodynamic Jetting in a Wide Range of Viscosities.

The electrohydrodynamic (EHD) jetting of fluids is used for several applications such as inkjet printing, atomization of analyte in mass spectrometry, liquid metal alloy ion sources, and electrospinning of polymer fibers. Historically, the bulk of research has focused on nonviscous, highly conductive fluids which are most suitable for EHD spray and printing, while there is relatively little experimental work on EHD jetting of highly viscous liquid dielectrics. We studied the dynamics of oscillation and pulsating jetting from a suspended drop of polydimethylsiloxane (PDMS) polymers in an electric field, with particular attention to the viscosity dependence of the oscillation period and meniscus elongation and contraction time over a wide viscosity range (102-105 cSt). The reported results could help the appropriate design of EHD processes and may open new possibilities for the rheological characterization of liquid polymers using small volumes at the scale of nanoliters.

Analytical modeling and seismic performance of a novel energy dissipative kinematic isolation for building structures

The idea of separating the structure from the horizontal motion of the ground using kinematic bearings that may uplift and rock under severe ground excitations can be considered equally as a seismic isolation technique. However, the seismic demand reduction on the superstructure due to the uplift of the kinematic bearings presents an inversely proportional relation to the stability of the system. For this reason, the performance of kinematic isolation is moderate. To address this issue; the present study examines a novel high-performance kinematic isolation characterized by increased seismic demand reduction and enhanced stability. The proposed configuration comprises of slender enough concave kinematic bearings, positive post-uplift stiffness, and supplemental viscous dampers. To investigate the seismic behavior of the proposed arrangement; the nonlinear equations of motion are first derived. Due to the positive stiffness, the kinematic story serves as conventional seismic isolation, resulting in period elongation, and thereby the dynamic characteristics of the base isolation are evaluated. To this end, the system's equations of motion are linearized and analytical expressions regarding the vibration period and damping ratio are proposed. Furthermore, dynamic time history analyses are performed, and the effect of the dynamic characteristics of the kinematic story on the overall seismic response is investigated. Finally, the seismic performance of three typical isolated structures is evaluated. The study concludes that the proposed expressions of the nominal vibration period and damping ratio efficiently describe the dynamic properties of the system. Moreover, combining slender enough concave kinematic bearings with supplemental viscous dampers results in a high-performance seismic isolation system.

A novel single-step explicit time integration method based on momentum corrector technique for structural dynamic analysis

In this study, a novel single-step explicit time integration method based on momentum corrector technique is proposed. The algorithmic procedure is formulated using cubic B-spline interpolation and Taylor series expansion. The momentum corrector is introduced to enhance solution accuracy of problems, especially for discontinuous load problems. Through the theoretical analysis of local truncation errors, spectral radius, algorithmic damping and period elongation, several parameter cases are obtained to achieve enhanced accuracy and stability. Numerical examples, including a standard single-degree-of-freedom problem, two discontinuous load problems, a seismic response analysis problem, a wave propagation problem and a nonlinear problem, are tested. The results illustrate the new method achieves high level of accuracy for discontinuous load problems, while simultaneously exhibiting significant accuracy improvement when dealing with other problems.

Family of Structure-Dependent Methods for Structural Dynamics

A family of structure-dependent methods is proposed based on discrete control theory. Although the displacement and velocity expression of this family method are similar to those of the previously published method developed by Mohammad Rezaiee-Pajand, the structure-dependent parameters of this family are different from the previously published method. The family of structure-dependent methods is named the MUSE algorithm method. Based on discrete control theory, a new family of integration algorithms is proposed by using the poles of the Newmark-[Formula: see text] method. Theoretical analysis indicated that the MUSE algorithm method possesses properties of zero amplitude decay and is self-starting. Also, its Period Elongation can be reduced by parameter ‘[Formula: see text]’. Numerical examples show that parameter ‘[Formula: see text]’ introduced in this paper can improve control Period Elongation and improve the accuracy of this method.

Numerical evaluation of period elongation for the assessment of seismic damage and usability of RC residential buildings

During an earthquake, the progressive damage of structural and nonstructural components of a structure yields to the degradation of their stiffness, thus resulting in a progressive increase of the vibration period of the structure as a whole.Also, the damage amount on structural and nonstructural elements, also known as Damage State (DS), can be determined by visual inspection or predicted, for a given earthquake scenario, by means of numerical analyses by relating the exceedance of a certain Engineering Demand Parameter (EDP) threshold to the attainment of a certain DS. Also, upon an earthquake, the observation of a certain DS in a building is the basis for the decision regarding its usability.In this work, numerical incremental time-history analyses are performed on case-study reinforced concrete residential buildings. The analyses results are used to establish the expected DS attained by structural and nonstructural components and, so, by the considered building: this is also related to a certain usability judgment, as already mentioned. In tune, the analyses results are also used to evaluate the period elongation of the building at increasing intensity of the seismic demand.The objective of the study is establishing a preliminary relationship between a) the DS attained by a certain building due to the occurrence of an earthquake with a certain intensity, and, so, the consequent usability judgment, with b) its period elongation. This is done in order to establish whether the vibration period elongation – which can be practically evaluated by means of ambient vibration tests – can be used for the assessment of structural usability after an earthquake as a tool for decision supporting in the aftermaths of a destructive event

Field testing of gravel-rubber mixtures as geotechnical seismic isolation

We present the results of the forced-vibration experiments performed at the large-scale prototype structure of EuroProteas founded on gravel-rubber mixture (GRM) layers acting as a means of Geotechnical Seismic Isolation (GSI). Three GRM with different rubber content per mixture weight (0%, 10%, and 30%) but the same mean grain size ratio were used as foundation soil. Each GRM-structure system was subjected to harmonic forces in a wide range of excitation frequencies and force amplitude. It was found that a 0.5 m thick GRM foundation soil layer with 30% rubber content can effectively isolate the structure. The strong effect of the rubber fraction was expressed in the detected period elongation and the dominating rocking component which leads to a more “rigid-body” response of the structure. Moreover, the developed base shear and base moment are significantly reduced regardless of the excitation frequency, while the increased damping of the system and the important energy dissipation demonstrate the effectiveness of the GRM foundation soil layer. Overall, the experimental results demonstrated that the use of GRM as a GSI system can be considered as a low-cost alternative seismic isolation technique.

The assessment of the interaction between base isolation (BI) technique and soil structure interaction (SSI) effects with 3D numerical simulations

Base Isolation (BI) is a well-known technique that aims to reduce the seismic vulnerability of structures by increasing the structural deformability and the damping. However, these beneficial effects are significantly reduced when the system is founded on deformable soils and then Soil Structure Interaction (SSI) effects are considered. Even if both BI and SSI have been extensively studied in literature, the mutual effects of the two mechanisms are still object of discussion and this paper aims to fill this gap by performing 3D numerical simulations. Several structural systems of different soil conditions are herein modeled in order to account the period elongation and damping increase of the isolated systems. In particular, the paper proposes relationships to calculate these two effects to be used for preliminary estimations avoiding complex and time-consuming analyses. The models have been performed with Opensees to reproduce non-linear hysteretic materials and advanced soil models and consider the non-linear structural performance.

Seismic fragility of tall buildings considering soil structure interaction (SSI) effects

Soil Structure Interaction (SSI) effects have been extensively studied for low-rise buildings, while less contributions considered tall buildings. In this regard, 3D numerical simulations were herein performed to evaluate the seismic performance of a 20-floor building founded on pile foundation. SSI effects have been studied with a probabilistic-based approach in order to develop analytical fragility curves. Opensees was applied to perform non-linear dynamic analyses in order to consider soil hysteresis and plasticity that cause non-linear mechanisms in the ground and are responsible for structural damage. The principal findings consist of considering both the cases where SSI helps reducing the vulnerability of the system and the mechanisms of site amplification that are driven by SSI effects (kinematic and inertial interaction). In particular, the developed fragility curves show the role of the mutual interaction of the soil and of the structure (in terms of period elongation, lateral deflections, roof accelerations and floor drifts). Therefore, neglecting the role of SSI was shown to be responsible of the increase of the vulnerability of the entire system (soil-foundation-superstructure).

Development of a Stable Implicit Method Without Numerical Dissipation for Nonlinear Structural Dynamic Analysis

This paper develops a self-starting implicit time integration method for nonlinear dynamic analysis. The method is single-step and is based on a non-dissipative second-order accurate approximation scheme. The method employs simple expressions for velocity and acceleration while internal forces are calculated at a specified point. This point results from a weighted combination of the relevant displacements and velocities at the bounds of the time step. In the linear case, the scheme is unconditionally stable, there is no amplitude decay for any time step value and the period elongation is the same as in the Newmark scheme. In nonlinear case, the scheme maintains the same numerical characteristics of dissipation and dispersion of the Newmark scheme while demonstrating a substantial improvement in stability. Summarizing, the presented scheme (i) is a single-step scheme with self-starting attribute; (ii) does not involve additional variables or artificial parameters chosen by the user; (iii) has at least second-order accuracy; (iv) shows to have very wide stability ranges in nonlinear analyses. It also proves that the computational effort per step required by the presented scheme is the same as the effort required in the widely used implicit single-step methods and a substantial reduction in the number of Newton–Raphson iterations in the steps is obtained. For comparison, methods with similar characteristics such as Newmark, generalized-[Formula: see text] and Bathe schemes are tested. Stiff nonlinear problems regarding elastic behavior and finite element structural models are analyzed to compare the considered solution methods.

Photometric Observations of the Binary Near-Earth Asteroid (65803) Didymos in 2015–2021 Prior to DART Impact

We performed photometric observations of the binary near-Earth asteroid (65803) Didymos in support of the Double Asteroid Redirection Test (DART) mission that will test the Kinetic Impactor technology for diverting dangerous asteroids. It will hit the Didymos secondary, called Dimorphos, on 2022 September 26. We observed Didymos with 11 telescopes with diameters from 3.5 to 10.4 m during four apparitions in 2015–2021, obtaining data with rms residuals from 0.006 to 0.030 mag. We analyzed the light-curve data and decomposed them into the primary rotational and secondary orbital light curves. We detected 37 mutual eclipse/occultation events between the binary system components. The data presented here, in combination with 18 mutual events detected in 2003, provide the basis for modeling the Dimorphos orbit around the Didymos primary. The orbit modeling is discussed in detail by Scheirich & Pravec and Naidu et al. The primary light curves were complex, showing multiple extrema on some epochs. They suggest a presence of complex topography on the primary’s surface that is apparent in specific viewing/illumination geometries; the primary shape model by Naidu et al. (Icarus 348, 113777, 2020) needs to be refined. The secondary rotational light-curve data were limited and did not provide a clear solution for the rotation period and equatorial elongation of Dimorphos. We define the requirements for observations of the secondary light curve to provide the needed information on Dimorphos’s rotation and elongation when Didymos is bright in 2022 July–September before the DART impact.

Seismic response of a tall tower on deep soil – A case study

The DYNAMIC response of a 100 m tall tower on a deep soil deposit is studied. The considered tower model is investigated for different loading/boundary conditions present at the base. The analyses are carried out using a finite element program SAP 2000. To demonstrate the effect of soil depth on the estimated seismic response of the tower, three different soil depths are considered. In order to study the effect of structural inelasticity and period elongation on the estimated seismic response of the structure, a yield strength ratio, Ry equal to 4 is also considered. The study primarily shows that soil-pile-structure interaction (SPSI) may increase or decrease the base shear and lateral deflection of the structure, in different directions and for different depths of soil strata. The sensitivity of the SPSI effects to the dynamic characteristics of the ground motion and structure has been brought out in the present case study. It is concluded that the effect of soil depth on seismic response of the structure is not monotonic and the role of ductility demand on superstructure in SPSI effects is important.

Comparison between recent implicit time integration methods with frequency dissipation for nonlinear structural applications

The present paper aims to test recent (Truly self-starting two sub-step method and three-parameter single-step implicit method) and classical (Generalized-α, HHT-α, and WBZ-α methods) time integration methods using the geometrically nonlinear Positional Finite Element Method (PFEM). The numerical formulation is based on the total Lagrangian approach and uses the Hessian matrix to obtain the response. The mixed hardening inelastic model applied to PFEM is also presented. Two examples validate the time integration algorithms and the inelastic model. In the first example, the mixed hardening inelastic model is compared with the the bilinear stress-strain model and the elastic-perfectly plastic hinge model, and aspects such as amplitude decay and period elongation are discussed. In the second example, the implemented algorithms are verified in a severe geometrically nonlinear example, considering the influence of numerical dissipation, time interval, and the number of elements in the response. Results show the relevance of numerical damping for numerical stabilization and the good performance of the Generalized-α algorithm.

Performance of a Three-Substep Time Integration Method on Structural Nonlinear Seismic Analysis

In this work, a study of a three substeps’ implicit time integration method called the Wen method for nonlinear finite element analysis is conducted. The calculation procedure of the Wen method for nonlinear analysis is proposed. The basic algorithmic property analysis shows that the Wen method has good performance on numerical dissipation, amplitude decay, and period elongation. Three nonlinear dynamic problems are analyzed by the Wen method and other competitive methods. The result comparison indicates that the Wen method is feasible and efficient in the calculation of nonlinear dynamic problems. Theoretical analysis and numerical simulation illustrate that the Wen method has desirable solution accuracy and can be a good candidate for nonlinear dynamic problems.

A Novel Framework to Assess Soil Structure Interaction (SSI) Effects with Equivalent Fixed-Based Models

Soil structure interaction (SSI) effects have been extensively studied with advanced numerical simulations even if these approaches are time consuming and require much effort to perform. In particular, when SSI models are compared with fixed based ones, two main effects need to be considered: period elongation and damping increase. The paper proposes numerical models to build fixed based models calibrated on these two parameters and perform complex SSI analyses. A new framework that may be used to assess SSI with equivalent fixed-based models is herein presented and validated with non-linear dynamic numerical simulations. Opensees was performed to reproduce non-linear numerical simulations by considering hysteretic materials and advanced soil models.

An improved quartic B-spline based explicit time integration algorithm for structural dynamics

In this study, an improved explicit time integration method based on quartic B-spline interpolation is generalized for linear and nonlinear dynamics. The accuracy order of the proposed method is analytically obtained as well as its spectral radius, period elongation, and algorithmic damping. The analysis shows the proposed method achieves third-order and at least second-order accuracy for displacement and velocity, respectively. With one algorithmic parameter, the proposed method can adjust numerical dissipation and accuracy. Linear dynamic examples demonstrate that the effectiveness of the proposed method as well as its high-order accuracy. Nonlinear dynamic problems show the proposed method can provide desirable solutions. Numerical results demonstrate the proposed method can provide more stable and accurate solutions than other classical explicit methods.