Monotonic Curve Research Articles

Cyclic Axial Compression Behavior of FRP-Confined Seawater Sea-Sand Concrete-Filled Stainless Steel Tube Stub Columns

Concrete-filled steel tube (CFST) columns have been widely used in onshore constructions. To extend its applications to coastal/offshore structures and meanwhile relieve the overexploitation on freshwater and river sand, an FRP-confined seawater sea-sand concrete-filled stainless steel tube (F-SSCFSST) column is proposed. The cyclic axial compressive behavior of this newly proposed column was investigated in this study. A total of 22 specimens (including nine pairs of specimens for cyclic compression and four individual specimens for monotonic compression) were tested. Most importantly, the influences of three loading patterns (i.e., single full unloading/reloading, repeated full unloading/reloading, and mixed of repeated full and partial unloading/reloading) were studied. The results showed that although all F-SSCFSST specimens failed from FRP rupture in the mid-height area, the FRP rupture was less fierce for specimens with repeated internal unloading/reloading cycles. Similar to the FRP-confined concrete, the envelope curve of cyclic axial load–strain response matched closely with the monotonic compression curve for a particular specimen. However, the unloading curve was less curly compared with that of a typical FRP-confined concrete. The confinement effect provided by the FRP jacket was much stronger than that by the stainless steel tube. Although Lam and Teng’s model, which is proposed for the FRP-confined concrete, could provide satisfactory estimations for strain recovery ratios and stress deterioration ratios, it underestimated the envelope plastic strains by 20%.

Experimental study on cyclic hardening characteristics of structural stainless steels

This paper studies the cyclic hardening characteristics of commonly used structural stainless steel types and grades including austenitic stainless steel grades S30408 and S31608 (equivalently to EN 1.4301 and EN 1.4401) as well as duplex stainless steel grade S22053 (equivalently to EN 1.4462) under tension-compression cyclic loading. A total of twenty-four monotonic loading tests and thirty-six cyclic loading tests were performed and two different cyclic loading protocol types were selected, namely cyclic ascend (CA) loading and cyclic constant (CC) loading with strain amplitudes ranging from ±0.5% to ±5%. Specimens with plate thicknesses of 6 mm and 8 mm were tested. The test results indicate that the cyclic hardening/softening behavior of the three grades of structural stainless steel generally shows obvious strain amplitude dependence and unsaturation before fracture under large strain amplitudes, which are significantly different from carbon steel. Meanwhile, there is a huge difference between the cyclic skeleton curves and the monotonic constitutive curves for different stainless steel grades. The effects of strain amplitude, stainless steel grade and loading history on the cyclic hardening/softening characteristics have been thoroughly studied. It should be noted that the seismic performance of stainless steel structures is greatly affected by the loading history. From the viewpoint of the seismic design of stainless steel structures, this paper proposes an equation to predict the maximum cyclic hardening degree at various strain amplitudes under constant amplitude loading.

Compressive fatigue behaviors of ultra-high performance concrete containing coarse aggregate

In this work, the uniaxial compressive fatigue behaviors of ultra-high performance concrete containing coarse aggregate (UHPC-CA) were investigated, towards a better understanding of the role of CA on its fatigue responses. Upon the constant amplitude fatigue tests performed at three stress levels (i.e. S = 0.7, 0.8, and 0.9), the emphases were focused on the effects of CA content (10%, 20%, and 30%) on the failure pattern, deformation characteristics, fatigue life, failure mechanism, and damage evolution. The results showed that compared to the UHPC specimen free of CA, the crack propagation, strain development, and fatigue life of UHPC-CA specimens are largely affected by the CA incorporation, due to the introduction of weak interfacial transition zones and the interference of fiber distribution. As a result, the risk of premature fatigue failure of UHPC-CA will be generally amplified as the CA content increases. Furthermore, inspired by the experimental observation that the fatigue failure strain of UHPC-CA stably approaches the descending branch of the monotonic stress-strain curve, a modified model based on the strain development instead of highly scattered fatigue life was proposed to estimate the nonlinear evolution of the fatigue damage. The good agreements with independent test results demonstrated the applicability of the model, representing a compromise between accuracy and practicability.

Integration of a Novel Knowledge-Guided Loss Function With an Architecturally Explainable Network for Machine Degradation Modeling

The suitability of a health index (HI) is significant to improve machine diagnostic and prognostic performance. A life cycle HI can be applied to the detection of incipient faults and determination of the first prediction time, and then its monotonic curve after FPT can be used as an immediate variable for prognostic analysis. Although existing data-driven methodologies for HI construction have considerable nonlinear mapping, they lack transparency and interpretability for subsequent studies and analysis. Moreover, these HIs have some unknown burrs and fluctuations. To overcome these limitations, an architecturally explainable network for machine degradation modeling is proposed in this paper. The first three hidden layers are reformulated from three advanced signal processing technologies including Hilbert transform, squared envelope, and Fourier transform to map temporal signals in the time domain into demodulated signals in the squared envelope spectrum domain so as to directly link the proposed network with fault frequencies and their harmonics in the frequency domain. The fourth hidden layer consists of a full connection layer with one hidden node and a novel knowledge-guided loss function specifically designed for exploring and extracting informative degradation features. Case studies are implemented to verify the proposed methodology and show that the proposed HIs have more stable and robust performance compared to state of the art methods. Another superiority of the proposed network lies in its full transparency and interpretability by effectively integrating physics-based signal processing technologies with an interpretable artificial network structure for machine degradation modeling.

CurveP Method for Rendering High-Throughput Screening Dose-Response Data into Digital Fingerprints.

The nature of high-throughput screening (HTS) puts certain limits on optimal test conditions for each particular sample; therefore, on top of usual data normalization, additional parsing is often needed to account for incomplete read outs or various artifacts that arise from signal interferences.CurveP is a heuristic, user-tunable curve-cleaning algorithm that attempts to find a minimum set of corrections, which would give a monotonic dose-response curve. After applying the corrections, the algorithm proceeds to calculate a set of numeric features, which can be used as a fingerprint characterizing the sample, or as a vector of independent variables (e.g., molecular descriptors in case of chemical substances testing). The resulting output can be a part of HTS data analysis or can be used as input for a broad spectrum of computational applications, such as quantitative structure-activity relationship (QSAR ) modeling, computational toxicology, bioinformatics, and cheminformatics.

Experimental investigation on the stress-strain behavior of unsaturated polyester polymer concrete subjected to monotonic and cyclic loadings

The use of polymer concrete (PC) in construction requires the development of an accurate stress-strain relationship that can accurately predict the mechanical properties of PC. Given that no constitutive equation for cyclic loading of unsaturated polyester PC (UPPC) is available in the literature, the goal of the current research has been to propose a rational analytical model for estimating the mechanical characteristics of UPPC under tensile and compressive loading. Compressive and tensile cyclic and monotonic tests were performed on specimens which had been cured for 28 days and the average monotonic stress-strain curve was obtained for the monotonic tests. The average maximum stress and strain were determined for both the compressive and tensile tests and the elastic modulus and energy absorption capacity were computed and compared with the values for normal concrete (NC) and high strength concrete (HSC) materials. Analytical models for the monotonic and skeleton curves for both tensile and compressive tests have been provided, and the proposed models were compared to experimental findings and other research results for validation. Stress-strain relationships have been proposed for the unloading and reloading paths and were compared with the cyclic test results. The ultimate stress and strain for the UPPC were three and five times higher, respectively, than for the NC in tension testing. The ultimate strain for UPPC was almost 150% greater than the final strain of HSC in compression. Under compressive loading, the UPPC absorbed to 2.33 and 5.3 times more energy, respectively, than the HSC and NC. The results showed that the skeleton curves agreed well with the monotonic curves for the compressive and tensile tests. All of the proposed models agreed well with the available experimental data and previous study results.

Typical curve with G1 constraints for curve completion

This paper presents a novel algorithm for planar G1 interpolation using typical curves with monotonic curvature. The G1 interpolation problem is converted into a system of nonlinear equations and sufficient conditions are provided to check whether there is a solution. The proposed algorithm was applied to a curve completion task. The main advantages of the proposed method are its simple construction, compatibility with NURBS, and monotonic curvature.

Monotonic and cyclic stress-strain models for confined concrete-masonry shear wall boundary elements

Simulation of the seismic response of fully grouted reinforced masonry shear walls (RMSWs) built with reinforced masonry boundary elements (RMBEs) necessitates reliable nonlinear models of their RMBEs. The axial monotonic and cyclic full stress-strain curves of RMBEs are essential for predicting the lateral cyclic response of RMSWs with boundary elements. Therefore, a reliable stress-strain constitutive model for the axial monotonic and cyclic behavior of RMBEs is required. The authors recently investigated the axial monotonic compressive behavior of unconfined and confined RMBEs built with different section configurations, vertical reinforcement arrangements, transverse confinement ratios, and different construction procedures. In the current study, the authors investigated the cyclic behavior of some RMBEs whose counterparts were previously tested under axial monotonic compression. In addition, more specimens with different confinement configurations and different grout strengths were tested. Comparisons of the test results showed that increasing the vertical reinforcement ratio increased the axial load carrying capacity of the tested RMBEs but decreased their strain ductility. In addition, using a low compressive strength grout significantly reduced the strain ductility of the RMBEs. Moreover, monotonic and cyclic stress-strain models for confined and unconfined concrete-masonry boundary elements subjected to axial compression loading were developed. The proposed models showed good-to-excellent agreement with the experimental results, predicting the stress-strain rising curve, stress drop, and postpeak behavior. Furthermore, unloading and reloading curves, strength degradations, and softening of reversal and reloading branches due to cyclic degradations were well captured by the proposed model.

Effect of loading protocol on the mechanical properties of 316L stainless steel

Two types of loading protocol, i.e., monotonic loading and cyclic loading, were compared to investigate the effect on the mechanical properties of 316L stainless steel. The specimen used is a dog-bone specimen in accordance with ASTM E8 and ASTM E606 standard. For cyclic loading, the multiple-step method is used to obtain the hysteresis loop of the material. A total of 13 strain amplitude conditions had been carried out, ranging from 0.05%-0.65%. The stress-strain curve shows that the cyclic stress-strain curve is higher than the monotonic stress-strain curve due to the cyclic hardening behaviour in the 316L stainless steel. The cyclic hardening behaviour increases the ultimate tensile stress of the material. However, when the material gains its strength through cyclic hardening, the ductility in the material will decrease.

The effect of perforation on aerodynamic characteristics and the vortex flow field around a flat plate

The aim of the present investigation is to obtain and analyse vortex flow field and aerodynamic characteristics of perforated plates at different angles by numerical simulation using OpenFOAM software package. For fully perforated plate’s passive gas injection through the holes close to the leading edge induce separation zone deformation and affect the whole flow structure downstream. Perforation along the leading edge tends to result in more monotonous curves of normal force and pitching moment coefficients.

CONSTITUTIVE RELATION OF DUPLEX STAINLESS STEEL S22053 UNDER CYCLIC LOADING

To study the mechanical properties and constitutive relation of DSS (duplex stainless steel) S22053 under cyclic loading, specimens machined from S22053 hot-rolled steel plate were tested under monotonic and cyclic loading patterns. Based on the monotonic curves, the material mechanical properties under monotonic load were analyzed. The material parameters of the Chaboche model were obtained using the results of the specimens with constant strain amplitude, and the test curves were simulated by the finite element software ABAQUS. The results reveal that DSS S22053 has good ductility and low proportional limit. No obvious yield platform or yield point was observed. The cyclic backbone curve can be well fitted with the Ramberg-Osgood model. The three types of combined parameters calibrated by different component models can simulate the hysteresis curve of materials well, and the three-back stress component model (N2L1) has the best fitting effect. The results can be used to analyze and calculate the mechanical performance of DSS structures under seismic load.

Planar Typical Bézier Curves with a Single Curvature Extremum

This paper focuses on planar typical Bézier curves with a single curvature extremum, which is a supplement of typical curves with monotonic curvature by Y. Mineur et al. We have proven that the typical curve has at most one curvature extremum and given a fast calculation formula of the parameter at the curvature extremum. This will allow designers to execute a subdivision at the curvature extremum to obtain two pieces of typical curves with monotonic curvature. In addition, we put forward a sufficient condition for typical curve solutions under arbitrary degrees for the G1 interpolation problem. Some numerical experiments are provided to demonstrate the effectiveness and efficiency of our approach.

On the nature of Hawking’s incompleteness for the Einstein-vacuum equations: The regime of moderately spatially anisotropic initial data

In the mathematical physics literature, there are heuristic arguments, going back three decades, suggesting that for an open set of initially smooth solutions to the Einstein-vacuum equations in high dimensions, stable, approximately monotonic curvature singularities can dynamically form along a spacelike hypersurface. In this article, we study the Cauchy problem and give a rigorous proof of this phenomenon in sufficiently high dimensions, thereby providing the first constructive proof of stable curvature-blowup (without symmetry assumptions) along a spacelike hypersurface as an effect of pure gravity. Our proof applies to an open subset of regular initial data satisfying the assumptions of Hawking’s celebrated “singularity” theorem, which shows that the solution is geodesically incomplete but does not reveal the nature of the incompleteness. Specifically, our main result is a proof of the dynamic stability of the Kasner curvature singularity for a subset of Kasner solutions whose metrics exhibit only moderately (as opposed to severely) spatially anisotropic behavior. Of independent interest is our method of proof, which is more robust than earlier approaches in that (i) it does not rely on approximate monotonicity identities and (ii) it accommodates the possibility that the solution develops very singular high-order spatial derivatives, whose blowup-rates are allowed to be, within the scope of our bootstrap argument, much worse than those of the base-level quantities driving the fundamental blowup. For these reasons, our approach could be used to obtain similar blowup-results for various Einstein-matter systems in any number of spatial dimensions for solutions corresponding to an open set of moderately spatially anisotropic initial data, thus going beyond the nearly spatially isotropic regime treated in earlier works.

A predictive model for salt nanoparticle formation using heterodimer stability calculations

Abstract. Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore salt heterodimer (a cluster of one acid and one base) stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment and polarizability for salts comprised of sulfuric acid, methanesulfonic acid and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. We then analyzed the relationship between heterodimer stability and J4×4, the theoretically predicted formation rate of a four-acid, four-base cluster, for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K and found that heterodimer stability forms a lognormal relationship with J4×4. However, temperature and concentration effects made it difficult to form a predictive expression of J4×4. In order to reduce those effects, heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J4×4 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J4×4 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J4×4 vs. Φ collapses to a single monotonic curve for weak sulfate salts (difference in gas-phase acidity >95 kcal mol−1) and can be used to accurately estimate J4×4 within 2 orders of magnitude in atmospheric models.

A Nonlinear Macro-Model for the Analysis of Monotonic and Cyclic Behaviour of Exterior RC Beam-Column Joints

The study presents a numerical investigation on exterior reinforced concrete (RC) beam-column joints under seismic actions based on a macro-modelling approach proposed by the authors in a recent paper. The followed approach makes use of the well-known “scissors model” where two nonlinear rotational springs arranged in series were introduced to schematize the shear behavior of the joint panel and, moreover, the possible occurrence of the debonding of longitudinal steel rebars at the beam-joint interface. In this paper, the scissor model is employed in the context of a novel predictive approach with the twofold objective to: 1) develop a new model for the estimate of the maximum shear strength of RC joints by performing a multivariate linear regression analysis on a set of experimental tests and, 2) define a new multilinear backbone joint shear stress-strain law to be assigned to one of the mentioned springs. In particular, the identification of the shear strain parameters is obtained by performing a sensitivity analysis in which a number of monotonic load-drift numerical curves are derived by varying the strain values in ranges opportunely a-priori defined and compared with the experimental ones to investigate their accuracy. Finally, cyclic analyses on RC joints collected in the experimental database are carried out by considering the backbone joint shear stress-strain law identified in the calibration process. The analyses are performed by using the nonlinear open-source finite element platform, OpenSees, in which the “pinching4” uniaxial material model, available in the software library, is implemented to set the parameters governing the hysteresis rules and pinching effect. To this purpose, five literature proposals suggesting the values to use for such parameters are taken into account and their assessment is presented in the paper. The obtained outcomes have allowed, on the one hand, to identify the proposal providing the best numerical simulations of the experimental results and, on the other end, to draw useful indications on how to further improve the cyclic modelling by opportunely modifying the setting of the “pinching4” material model parameters.

Planar class A Bézier curves: The case of real eigenvalues

We consider planar, special Bézier curves, i.e., polynomial Bézier curves in the plane whose control polygon is fully identified by the first edge and a 2×2 matrix M. We focus on the case where M has two real eigenvalues and we formulate, in terms of the Schur form of M, necessary and sufficient conditions for a regular, planar special Bézier curve to be a class A curve, i.e., a curve with monotone curvature, for any degree and any choice of the first edge. The result is simple in its formulation and can thus be easily used for both designing class A curves and analyzing given special Bézier curves.

Loop Algorithms for Ductility Analysis of Column Reinforced Steel with Yield Strength Above 500 MPA

There are many benefits to the use of high-strength reinforcement (above 500 MPa) in reinforced concrete buildings. The advantages of using high-strength reinforcement are reduction steel volume and dimension, reduced construction time, reduction in reinforcement congestion, as well as savings in materials and worker cost. Meanwhile, the investigation of ductility of reinforced concrete element with high-strength reinforcement to resist earthquake effects under current design procedure is needed. In the current standard, ACI 318-71, The maximum specified yield strength was restricted to 60 Ksi (413 MPa) for reinforcement in special seismic system. There were also no ASTM standard specifications for reinforcement with yield strength above 500 MPa. In the design of seismic resisting structures, the analysis of curavture ductility and flexural overstrength factor is of important consideration in order to avoid brittle failure. This paper attempts to anaylze the ductility and re-evaluate the flexural overstrength factor of reinforced concrete column. The tensile tests of steel reinforcement with yield strength above 500 MPa generates stress-strain curve. An idealisations for the monotonic stress-strain curve proposed by mander was adopted in this study. Whereas in this numerical study of confined concrete columns, the behavior of concrete cored is modeled by the stress-strain relationship of confined concrete proposed by Kappos-Konstantinidis. This stress strain model was used for the momen, curvature, ductility, and flexural overstrength factor analysis.

Hysteretic moment-curvature relations for the analysis of RC flexural members subjected to blast loading

A hysteretic moment-curvature relation for analyzing reinforced concrete (RC) members subjected to blast loading is introduced in this paper. After constructing a monotonic envelope curve for the moment-curvature relation, the hysteretic behaviors of unloading and reloading are defined based on the hysteretic curve of steel. The use of the moment-curvature relation in the blast analysis becomes possible by introducing a dynamic increase factor (DIF), which is defined in terms of the curvature rate. This makes it possible to analyze RC structures composed of many bending structural members. In addition to defining a basic hysteretic moment-curvature relation, additional influencing factors such as the bond-slip effect and direct shear behavior, which are expected to affect the structural responses, are taken into consideration for an exact simulation of the nonlinear dynamic response of RC flexural members. The validity of the introduced hysteretic moment-curvature relation is established by correlation studies between the analytical results and experimental data experiencing repeated unloading and reloading phases. The obtained numerical results also show the importance of the bond-slip effect and the hysteretic behavior on the structural response of RC flexural members subjected to blast loading.

Behavior of FRP spiral strip-confined concrete under cyclic axial compression

FRP spiral strip wrapping strengthening technique is effective in enhancing both strength and deformation capacity of reinforced concrete (RC) columns. Although some investigations have been conducted on axial monotonic compressive behaviour of FRP spiral strip-confined concrete, cyclic compressive behaviour of FRP spiral strip-confined concrete has never been studied. To this end, 18 FRP spiral strip wrapped concrete cylinders of three different levels of confinement under cyclic axial compression and 12 reference specimens under monotonic axial compression have been conducted. The test results show that the actual confinement effectiveness factor significantly influences the monotonic axial stress-strain curves of FRP spiral strip-confined concrete, which lie closely to the envelop curves of the corresponding cyclic stress-strain curves. However, the level of confinement has limited influence on reducing the plastic strain. The existing axial stress-strain model developed for FRP fully confined concrete cylinders under cyclic compression underestimates the plastic strain and overestimates the envelop stress for FRP spiral strip-confined concrete. A revised model is developed based on the test results, and the predicted cyclic axial stress-strain curves match reasonably well with the test results.

The significance of a piecemeal geometric model of mudstone compaction: Pinghu Slope, Xihu Depression, Eastern China

The geometric model of the loading curve used to express mudstone compaction behaviour profoundly influences the quantitative estimation of pore-pressure and identification of the origin of overpressure. The verification of field data from the Pinghu Slope Belt indicates that as burial depth increased, the compaction process was divided into three sections of mechanical compaction fitted by a convexity function, chemically enhanced mechanical compaction fitted by a concavity function, and stable compaction fitted by a convexity function. The piecemeal geometric model of mudstone compaction expressed by the loading curve is more appropriate than previous monotonous loading curves for characterising compaction behaviour, amplifying the effect of chemical compaction, and expressing chemical compaction behaviour. The piecemeal geometric model of mudstone compaction behaviour yields more precise results of formation pressure prediction and overpressure origin identification.