Monotonic Response Research Articles

Hybrid deep learning model for prediction of monotonic and cyclic responses of sand

Hybrid deep learning model for prediction of monotonic and cyclic responses of sand

The response of regional well-being to place-based policy interventions

Enhancing the well-being of its citizens is the central remit of the EU's regional policy, but as yet, there is no analysis of the effects of EU regional policy on local well-being. The aim of this paper is to examine this relationship. To do this, we define a novel regionalised well-being measure and we exploit a dataset on regional expenditure in a continuous treatment framework. Based on both parametric and semi-parametric approaches, our analysis demonstrates that the EU regional development policy does influence regional well-being differently from GDP. We find evidence of a linear monotonic response of well-being growth to total transfers, although this effect varies according to the time lag considered and the level of development of the region.

Viscoelastic adhesive modeling of ductile adhesive-composite joints during cyclic loading

Flexible adhesives have recently gained increased attention for their use in the joints of fiber-polymer composite structures because of their pseudo-ductile response and energy dissipation capacity. However, their structural application requires further study as their viscoelastic mechanical behavior is highly nonlinear and sensitive to the displacement rate in particular. In this study, a phenomenological model was developed, consisting of two parallel acting conventional-linear and extended-nonlinear Maxwell units, to model the monotonic and cyclic loading of an adhesive joint under various displacement rates; the viscoelastic parameters were calibrated by experimental results. Power-law relationships between 1) the monotonic viscoelastic parameters and the applied displacement rates, 2) the cyclic viscoelastic parameters and the maximum cycle displacements, and 3) the constants of the cyclic viscoelastic parameters and the applied displacement rates, well captured both the pre- and post-yield monotonic and cyclic responses, such as stretching of molecular chains (strain hardening), and formation and accumulation of damage (softening). The model was also able to predict the cyclic envelope curves and cyclic energy dissipation well.

Effect of time-varying transverse stresses on the bond-slip and global behavior of RC members under monotonic loads

The local bond behavior of reinforced concrete (RC) members is dependent on the transverse stresses of steel bars, which would further affect the global response of the members. Nowadays the influence of time-varying transverse stresses on the bond can hardly be considered in the numerical analysis of RC members, which limits the rationality and accuracy of the results. In this study, therefore, a numerical bond element is proposed to consider the time-varying transverse stresses around the steel bar during the analysis of RC members under monotonic loads. The applicability and accuracy of the element is verified by both pull-out tests under various lateral stresses and monotonic loading tests of RC columns under different axial forces. Numerical case studies are then undertaken to evaluate the effect of time-varying transverse stresses on the monotonic response of typical RC members. The results showed that it is of great significance to consider the time-varying transverse stresses for the analysis of the members which are sensitive to the local bond behavior.

The human blood transcriptome exhibits time-of-day-dependent response to hypoxia: Lessons from the highest city in the world.

SummaryHigh altitude exposes humans to hypobaric hypoxia, which induces various physiological and molecular changes. Recent studies point toward interaction between circadian rhythms and the hypoxic response, yet their human relevance is lacking. Here, we examine the effect of different high altitudes in conjunction with time of day on human whole-blood transcriptome upon an expedition to the highest city in the world, La Rinconada, Peru, which is 5,100 m above sea level. We find that high altitude vastly affects the blood transcriptome and, unexpectedly, does not necessarily follow a monotonic response to altitude elevation. Importantly, we observe daily variance in gene expression, especially immune-related genes, which is largely altitude dependent. Moreover, using a digital cytometry approach, we estimate relative changes in abundance of different cell types and find that the response of several immune cell types is time- and altitude dependent. Taken together, our data provide evidence for interaction between the transcriptional response to hypoxia and the time of day in humans.

Centrifuge modelling of monotonic and cyclic lateral responses of a hybrid monopile-bucket foundation for offshore wind turbines

Various hybrid systems combined with several foundation elements have been proposed to improve the lateral performance of monopiles. Among them, the hybrid monopile-bucket foundation which consists of a traditional monopile and a wide-shallow bucket has received more and more attention and has been used in offshore wind pilot projects for supporting OWTs. However, deep insights into its monotonic and cyclic responses are still lacking. This study aims to understand the monotonic load-bearing, the evolution of cumulative displacement, stiffness and bending moment of the hybrid foundation in soft clay. A series of centrifuge model tests were conducted to simulate a hybrid monopile-bucket foundation and a monopile subjected to lateral monotonic and multi-stage cyclic loading. The monopile with the identical pile diameter and embedded length is used as a benchmark. The experimental results show that by the addition of the bucket, the hybrid foundation shows a 30.1% increase in ultimate capacity. Compared to the monopile, the cumulative displacement, unloading stiffness and the growth of bending moment of the hybrid foundation during cyclic can be reduced by up to 25%, 30% and 35.3%, respectively, implying the effectiveness and superiority of the hybrid foundation. Apart from the centrifuge tests, supplementary three-dimensional finite element analyses have also been performed to reveal the bearing mechanism and the sharing ratios of external load and moment carried by the single pile and the bucket of the hybrid foundation. The test and numerical results presented in this study are expected to provide design references for further practical applications of the hybrid foundations.

Transient electrohydrodynamics of a liquid drop: The interplay of fluid flow evolution and dynamic response, and the density ratio effects

Computer simulations are performed to study some of the less explored aspects of the transient electrohydrodynamics of a liquid drop in uniform DC electric fields. The governing equationsof the problem are solved using a parallelized front tracking/finite difference method in the framework of Taylor-Melcher's leaky dielectric theory. For density- and viscosity-matched fluid systems, the evolution of the flow field at a high Ohnesorge-squared number Oh^{2}=μ^{2}/γρa is studied. It is shown that the instantaneous flow pattern is the result of superposition of deformation- and hydrodynamic shear-driven vortices, and that depending on the placement of the fluid systems on the deformation-circulation map, there exists two different paths for the development of the velocity field toward steady state. Examination of the steady-state flow patterns shows that the location of the maximum velocity can shift from the (classically known) drop surface to inside the drop along the poles. The effect of Oh^{2} on the dynamic response of the drop and the kinetic energy of the fluid is studied. For high Oh^{2} number flows, the dynamic response is monotonic while the kinetic energy evolves in a nonmonotonic way, achieving a distinct peak before settling to steady state. However, for low Oh^{2} number flows, both the dynamic response and kinetic energy are oscillatory. Inspection of the results show a two-way coupling between the deformation rate and the fluid flow. The effect of the density ratio ρ[over ̃]=ρ_{i}/ρ_{o} (drop to ambient) on the dynamic response and fluid flow strength shows that for high Oh^{2} number flows both parameters remain essentially intact at steady state, while their evolution modes transition from a monotonic response to an oscillatory one at high density ratio. However, for low Oh^{2} number flows, with an increase in ρ[over ̃], the oscillation frequency of both parameters remain intact, while their oscillation amplitudes increase.

Wearable Ionogel-Based Fibers for Strain Sensors with Ultrawide Linear Response and Temperature Sensors Insensitive to Strain.

Fiber-shaped stretchable strain and temperature sensors are highly desirable for wearable electronics due to their excellent flexibility, comfort, air permeability, and easiness to be weaved into fabric. Herein, we prepare a smart ionogel-based fiber composed of thermoplastic polyurethane (TPU) and ionic liquid (IL) by the facile and scalable wet-spinning technique, which can serve as a wearable strain sensor with good linearity (a correlation coefficient of 0.997) in an ultrawide sensing range (up to 700%), ultralow-detection limit (0.05%), fast response (173 ms) and recovery (120 ms), and high reproducibility. Attributed to these outstanding strain sensing performances, the designed TPU/IL ionogel fiber-shaped sensor is able to monitor both subtle physiological activities and large human motions. More interestingly, because of the fast response and high resolution to strain, the fiber-shaped sensor can be sewn into the fabric to secretly encrypt and wirelessly translate message according to the principle of Morse code. More importantly, a wearable strain-insensitive temperature sensor can be obtained from the ionogel fiber if it is designed into an "S" shape, which can effectively eliminate the interference of strain on temperature sense. It is found that the inaccuracy of temperature sense is within 0.15 °C when the sensor is subjected to 30% tensile strain simultaneously. Moreover, this strain-insensitive temperature sensor shows a monotonic temperature response over a wide temperature range (-15 to 100 °C) with an ultrahigh detecting accuracy of 0.1 °C and good reliability, owing to the fast and stable thermal response of IL. This temperature sensor can realize the detection of thermal radiation, proximity, and respiration, exhibiting enormous potential in smart skin, personal healthcare, and wearable electronics. This work proposes a simple but effective strategy to realize the essential strain and temperature sensing capabilities of wearable electronics and smart fabrics without mutual interference.

Seismic fragility assessment of load‐bearing soft‐brick unreinforced masonry piers

Unreinforced masonry (URM) made with soft bricks comprises a large percentage of the building stock in developing countries. However, the poor performance of URM piers during earthquakes has led to renewed interest in understanding their behavior under lateral loads. Little experimental data is available on the seismic response, analysis, and design of URMs made of soft bricks. In this study, the micro-modeling technique is used to simulate the in-plane behavior of load-bearing, soft-brick URM piers. The parameters required in the constitutive models are obtained from material tests and used to develop a calibrated numerical model of the URM piers. Piers with various aspect ratios subjected to various axial stresses are numerically modeled to obtain monotonic and cyclic responses, and their critical displacement limit states are identified. Changes in the failure modes of masonry piers with variations in the aspect ratio and axial stress are established. Load-bearing piers exhibit three distinct failure modes: bed sliding, diagonal shear cracking, and flexure, depending on the aspect ratio and axial stress. The seismic fragility of each pier failure type is examined using nonlinear time history analyses. The results show that bed-sliding piers collapse at extremely low PGA levels. Piers failing through diagonal shear cracking also fail at low PGA levels. Flexural piers can resist seismic forces up to a slightly higher PGA level and thus are the last to collapse. The results also indicate that the effect of uncertainty in ground motions is more significant than the effect of variability in the masonry pier capacities.

Responses of model monopile to cyclic lateral loadings in clay

Large diameter monopiles are usually used as the foundation of offshore wind turbines. Monopile foundations are subjected to laterally cyclic marine environmental loadings which tends to accumulate displacements and rotation of the monopile. To preliminarily evaluate the cyclic responses of monopile in marine clay, 1g model tests have been conducted to combine with reported centrifuge tests to efficiently illustrate the behavior. This study investigates the laterally monotonic and cyclic responses of the model pile embedded in kaolin clay. As expected, obvious differences are observed between results of the 1g model tests and the centrifuge tests owing to the effect of stress levels, but important quantitative relations between results of these two types are revealed: two equations closely related to cyclic loading magnitude ratio ζb with same cyclic loading symmetry ratio ζc, could be qualitatively obtained to predict the pile responses in centrifuge tests by using the result of 1g model tests. The normalized unloading stiffness of model pile in 1g test is less than that of obtained from centrifuge tests with the same ζb values. This result not only highlights that it is necessary to account for the stress level of soil to understand cyclic lateral responses of monopile foundations, but also reveals that it is possible to qualitatively insight responses of monopile through 1g model tests.

Effect of strain history on the monotonic and cyclic response of natural and reconstituted silts

The effect of strain history on monotonic and cyclic response of intact and reconstituted, low and high plasticity silt deposits have been investigated through a series of constant-volume, staged, stress- and strain-controlled cyclic direct simple shear tests. In many cases the specimens subjected to stress-controlled loading exhibited a progressive increase in cyclic resistance due to beneficial effects of increased density following post-cyclic reconsolidation, apparent pseudo-overconsolidation and presumably increased lateral stresses. Such effects outweighed the detrimental effects of fabric destructing as a result of the prior strain history. However, some specimens exhibited an inconsistent evolution of cyclic resistance when assessed using different shear strain cyclic failure criteria. Symmetric accumulation of shear strains in earlier shearing stages did not consistently result in an increasing trend in the post-cyclic resistance; additionally, increases or decreases in cyclic resistance can occur in subsequent shearing stages depending on the amplitude of the maximum shear strain. Staged, strain-controlled tests were used to investigate the cyclic soil response to small and large shear strains, the latter of which caused a reduction in the cyclic resistance of overconsolidated (OC) silt specimens in the following loading event, confirmed using shear wave velocity, Vs, measurements which indicated substantial fabric disturbance following the large strain event. In contrast, normally-consolidated (NC) and OC specimens subjected to multiple stages of small cyclic shear strain exhibited progressive increases in Vs, the magnitude of which varied with stress history. The increase in cyclic resistance in the NC specimens was related to increased pseudo-overconsolidation following reconsolidation. The monotonic undrained shear strength of all silt specimens subjected to staged cyclic loading increased following post-cyclic reconsolidation; the increase in strength and changes in volumetric tendencies are governed by the magnitude of post-cyclic reconsolidation and changes in soil fabric inferred from Vs, respectively.

Experimental and numerical analysis of the lateral response of full-scale bridge piers

This paper presents the results of in-situ testing of two integrated pile-columns of a partially demolished bridge located in Auckland, New Zealand. A series of tests involving lateral monotonic pushover and subsequent dynamic free vibration snapback tests were used to quantify the variation in the stiffness and damping behaviour of the pile-column specimens over a range of lateral load levels. Each testing sequence consisted of incrementally increasing peak monotonic loads followed by the dynamic snapback, with a series of varying peak loads at the end of the testing sequence to evaluate the influence of loading history on the monotonic and dynamic response. The secant stiffness between the monotonic pushover tests performed to the same loading levels before and after the maximum load was applied, reduced by up to 40% in both the pile-columns, primarily due to soil gapping effects, highlighting the significant potential softening of the system prior to pile or column yielding. Progressive reduction in the damping of the system during each snapback test was evident, due to the varying contributions of different energy dissipation mechanisms, and the level of damping varied depending on the peak load applied. These results highlighted the significant influence of soil gapping and nonlinearity on the dynamic response of the system. Numerical models were developed in the open source structural analysis software OpenSeesPy using a Nonlinear Beam on Winkler Foundation approach to further investigate the response of the pile-columns. Models of both the pile-columns using existing p-y curves for clay soils showed good agreement with the experimental data in load-displacement, period and snapback acceleration time histories. Sensitivity analysis showed that the surface soft clay layer had a significant effect on the lateral response and dynamic characteristics of the model, reinforcing the need for good characterisation of the near surface soil profile to capture the behaviour of the system.

The contribution of the spatial hydrological niche to species diversity in rare plant communities of English floodplain meadows

The hydrological niche is one of the few below ground spatial environmental niches, which has been shown to structure English floodplain meadows and other European and African herbaceous ecosystems. However, both the relative contribution of hydrological heterogeneity to the structure of English floodplain meadows across spatial scales and the forms of the individual species’ responses to hydrological heterogeneity remain largely unknown. Here, we use a survey database of 2440 evaluation units sampled in 15 English floodplain meadows to dissect the spatial architecture of this metacommunity and describe the relationship between the abundance of individual species and hydrological heterogeneity. Of the tested species, 65% responded to spatial hydrological heterogeneity, with both monotonic and hump-shaped responses. We found that between-site beta-diversity is much stronger than within-site beta-diversity, with between-site scale hydrological variation explaining twice as much variation in community structure as within-site scale. This leads to the conclusion that a conservation strategy of rare plant communities should include not only the preservation of the diversity of local hydrological regimes, but also, specially, the inclusion in the conservation system of as many and environmentally varied local plant communities as possible.

Lumped spring model parameters of RC frame elements for seismic performance assessment

AbstractThis study presents lumped spring model parameters for nonlinear seismic analysis of reinforced concrete (RC) frame structures. The modified Ibarra‐Medina‐Krawinkler (M‐IMK) hysteresis model is used as a lumped spring to simulate the inelastic behaviour of a RC frame element. The influence of loading protocols on the calibration of model parameters is investigated and compared with other hysteresis models, such as the original IMK and Bouc‐Wen‐Baber‐Noori (BWBN) models. Less dependent on the loading protocol used for model identification, the parameters of the modified IMK hysteresis model are calibrated to model a database of 383 rectangular RC columns. To simplify the calibration process, the model parameters that define the monotonic response are determined based on code and empirical equations, while the parameters that control the hysteretic degradations are calibrated against the experimental results. The calibrated model parameters are used to develop regression equations for the model parameters based on physical variables, such as loading, dimensions, and material properties. It is found that the model parameters obtained from the experimental calibration and regression equations generate similar hysteresis curves. The performance of the lumped spring model to nonlinear time history analysis of RC structures subjected to earthquakes is also evaluated through a series of pseudo‐dynamic hybrid simulations.

Influence of Vertical Load on the Lateral Response of Piles in Normally Consolidated and Over-Consolidated Clay: Centrifuge and Numerical Modelling

Although pile foundations are usually subjected to both lateral and vertical loads, there have been few studies on the pile response under the combined loadings. Moreover, those few studies led to inconsistent conclusions concerning the influence of vertical load on the lateral pile response. This study aims to investigate the effect of vertical load on the monotonic and cyclic lateral response of piles in normally consolidated (NC) and over-consolidated (OC) clay through a series of centrifuge tests. Three-dimensional finite element analyses using an advanced hypoplastic clay model were also performed to gain deep insight into the mechanism. It is revealed that after applying the vertical load and allowing the dissipation of the induced excess pore pressure, the lateral initial stiffness and ultimate capacity of the pile in the NC clay increased by 10.0 and 49.4%, respectively. However, in the OC clay, the application of the vertical load resulted in a 12.6 and 32.4% reduction in the lateral pile initial stiffness and ultimate capacity, respectively, showing a distinct response from that in the NC clay. The above-mentioned distinct influence of vertical load for piles can be attributed to the different evolutions of stress ratio (q/p’) of the soil around the pile in the NC and OC clay, which determines the soil mobilisable shear strength and consequently the lateral pile responses.

Effect of stress-relief heat treatments on the microstructure and mechanical response of additively manufactured IN625 thin-walled elements

Metallic structures fabricated with laser powder-bed fusion (LPBF) often have elemental segregations that are far from equilibrium and high levels of residual stresses due to the localized melting and rapid solidification that occur during printing. These unique characteristics result in mechanical property debits that make it difficult to employ such printed parts in critical applications. However, post-processing heat treatments can minimize the negative effects of residual stresses and reduce segregation. In this study, we measure the effect of two stress-relief heat treatments, 870°C for 1 h (industry-recommended) and 800°C for 1 h (potential alternative), on the microstructure and room temperature, monotonic quasi-static mechanical response of LPBF-processed thin-walled Inconel 625 T-elements. Electron backscatter diffraction analysis revealed an overall columnar microstructure with a strong <001> texture that is closely aligned with the build direction. The well-developed dislocation cell walls in both stress-relieved cases were found to be decorated with two types of blocky precipitates, namely, (Nb, N)-rich MX and (Nb, Mo, Si, N)-rich -M6X with scant evidence of the deleterious δ phase. The slightly larger size and higher volume fraction of precipitates in the 870°C case was found to have a small effect on the mechanical response of the T-elements under the current loading conditions and the difference in mechanical response of the two heat treatments was only significant at the very later stages of deformation. These findings make 800°C for 1 h a viable stress-relief alternative for our IN625 samples under the loading conditions studied here.

Prediction of flexural drift capacity in masonry walls through a nonlinear truss-based model

In this paper, the in-plane flexural drift capacity of masonry walls is numerically investigated. In particular, a nonlinear truss-based model is specifically developed to predict the monotonic response of in-plane horizontally-loaded masonry walls undergoing flexural failure, so that to investigate their deformation capacity. This novel modelling strategy assumes a band of nonlinear truss elements at the wall toe to account for flexural failure. The truss elements are supposed no-tension with plastic-softening behaviour in compression. This simple and original model is easily and fully characterizable by experimentally-based compressive stress–strain relationships available in the literature for different masonry types. The modelling strategy is validated against two different pier-scale experimental tests which experienced flexural failure. The model is then used to predict the flexural drift capacity of walls with different masonry types and geometrical features, subjected to a full-range of axial load ratios. As a result, drift capacity is found to nonlinearly decrease while increasing the axial load ratio, and to be sensibly dependent on the wall width (i.e. drift capacity diminishes while increasing wall width), for any masonry type. Finally, a simple analytic expression based on numerical results is deduced for the flexural drift capacity of masonry walls, function of axial load ratio, masonry type, and wall size. Accordingly, this analytic expression could be implemented in any structural analysis masonry-oriented commercial code to account for a consistent description of the flexural drift capacity of masonry walls.

Numerosity tuning in human association cortices and local image contrast representations in early visual cortex

Human early visual cortex response amplitudes monotonically increase with numerosity (object number), regardless of object size and spacing. However, numerosity is typically considered a high-level visual or cognitive feature, while early visual responses follow image contrast in the spatial frequency domain. We find that, at fixed contrast, aggregate Fourier power (at all orientations and spatial frequencies) follows numerosity closely but nonlinearly with little effect of object size, spacing or shape. This would allow straightforward numerosity estimation from spatial frequency domain image representations. Using 7T fMRI, we show monotonic responses originate in primary visual cortex (V1) at the stimulus’s retinotopic location. Responses here and in neural network models follow aggregate Fourier power more closely than numerosity. Truly numerosity tuned responses emerge after lateral occipital cortex and are independent of retinotopic location. We propose numerosity’s straightforward perception and neural responses may result from the pervasive spatial frequency analyses of early visual processing.

Micromechanical constitutive modeling of tensile and cyclic behaviors of nano-clay reinforced metal matrix nanocomposites

Metal matrix nanocomposites are emerging rapidly among both research and industry communities. Nonetheless, the studies for their use in Low-Cycle Fatigue (LCF) applications are rarely documented. Prior to tailoring the microstructure for the desired LCF performance, it is a fundamental task to understand the structure-property correlations of the nanocomposites. In the present paper, a continuum-based micromechanical model starting from the nanostructure is proposed to fulfill such a task. The proposed model is applied to a piston aluminum alloy reinforced with 1 wt% nano-clay subjected to fully-reversed strain-controlled LCF loading at room temperature. The model, formulated within Eshelby's inclusion framework, considers the active clay/matrix interactions, the intercalation/exfoliation effect via the equivalent stiffness method, and the size effect through the introduction of the interphase thickness as a characteristic length scale. To render the model able to reproduce the cyclic hysteretic behavior of the nanocomposites, the isotropic/kinematic hardening rule is considered to describe the aluminum alloy plasticity. The model results are favorably compared to the experimental observations in terms of monotonic and cyclic elastoplastic stress-strain responses of the aluminum/clay nanocomposite. A parametric study is then carried out in order to understand the separate and synergic effects of clay weight fraction, clay geometrical parameters (e.g., shape and size), and clay structural parameters (e.g., number of silicate layers and interlayer spacing) on the overall monotonic and cyclic responses of the present nanocomposite. The reinforcing effect of each parameter is discussed concerning the micromechanical model.

Monotonic and cyclic bond responses of steel bar with steel-polypropylene hybrid fiber reinforced recycled aggregate concrete

The bond failure between steel bars and concrete is the main reason for the strength degradation and deformation increase of structures in service. In this study, the bond behavior of steel bars with steel-polypropylene hybrid fiber reinforced recycled aggregate concrete (HFRAC) under monotonic and cyclic loadings was investigated. The acoustic emission (AE) technique was applied to monitor the bond response and the inner damage evolution of specimens during the loading process, and the microstructure of HFRAC was analyzed through the scanning electron microscope (SEM). The hysteresis curves, failure modes, bond strength degradation rate, and energy dissipation capacity, were systematically investigated by considering the effects of water-cement ratio, recycled aggregate replacement ratio, steel fiber volume fraction, and polypropylene fiber volume fraction. Experimental results demonstrated that there was more obvious degradation in the bond strength for the HFRAC specimens under cyclic loading, compared with that under monotonic loading. In the case of cyclic loading, the bond strength was degraded with the increase of the number of cycles, and the degradation rate increased quickly with the increase of the displacement amplitude. Moreover, the analysis of AE parameters measured on steel bar bonded recycled aggregate concrete (RAC) and HFRAC specimens, including the AE hits, AE energy, localization of AE events, and average frequency, was performed. Results showed that the AE technique could effectively monitor the bond damage of HFRAC specimens at different stages. A good correlation between the results of AE parameters analysis and the cracking process of specimens was confirmed. Based on the Weibull cumulative distribution function, the bond-slip models of steel bars with HFRAC under monotonic and cyclic loadings were proposed by considering the coupling effect of hybrid fibers and recycled coarse aggregates.