Results Of Cyclic Tests Research Articles

A simplified and versatile element model for elastomeric seismic isolation bearings

A novel approach for two-dimensional modeling of elastomeric bearings using three springs in parallel is presented. This simplified element model considers as follows: (1) an elastoplastic spring with a smooth transition between branches; (2) a linear elastic spring; and (3) a non-linear elastic spring, and is fully defined by only six parameters. The main advantages of the simplified model are twofold: (1) versatility, as a single model is capable of accurately reproducing the main characteristics of the hysteretic behavior of different types of rubber-based seismic isolators, including low damping rubber bearings (LDRBs), high damping rubber bearings (HDRBs), and lead-core rubber bearings (LRBs) and (2) simplicity, as it requires fewer parameters and it is easier to calibrate from experimental cyclic test results than most currently available models. Model parameters’ identification is illustrated using quasi-static cyclic and earthquake simulator tests of HDRBs and LRBs, demonstrating that the model shows a good agreement between the test-measured and model-predicted hysteretic behavior. Different objective functions are evaluated in the optimization procedure, and their effect on the identified parameters is studied and discussed. This practitioner-oriented model is particularly amenable for implementation in general-purpose structural analysis software. Its usage is strongly recommended as an initial-stage design tool to select the optimal isolation system for a specific project.

Relationship between natural exposure testing and cyclic corrosion testing ISO 20340 for the assessment of the durability of powder-coated steel

ABSTRACT The corrosion propagation rate during natural exposure tests of powder-coated steel and the relationship between natural exposure and accelerated cyclic corrosion testing (ISO 20340) results were investigated. Generally, during natural exposure, an initial fast increase in the corrosion area followed by a period where the corroded area grows very slowly are observed. As a consequence, the relative ranking between coating systems varies significantly as a function of test time. Correlation between natural exposure results and cyclic test results was not found; in many cases, a better performance in one test is associated with a worst performance in the other.

Long-term dynamic bearing capacity of shallow foundations on a contractive cohesive soil

The calculation of the long-term dynamic bearing capacity arises from the need to consider the generation of maximum pore-water pressure developed from a cyclic load. Under suitable conditions, a long-term equilibrium situation would be reached, when pore-water pressures stabilized. However, excess pore-water pressure generation can lead to cyclic softening. Consequently, it is necessary to define both the cohesion and the internal friction angle to calculate the dynamic bearing capacity of a foundation in the long term, being necessary to incorporate the influence of the self-weight of soil and therefore the width of the foundation. The present work is based on an analysis of the results of cyclic simple shear tests on soil samples from the port of El Prat in Barcelona. From these experimental data, a pore-water pressure generation formulation was obtained that was implemented in FLAC2D finite difference software. A methodology was developed for the calculation of the maximum cyclic load that a footing can resist before the occurrence of the cyclic softening. The type of soil studied is a contractive cohesive soil, which generates positive pore-water pressures. As a numerical result, design charts have been developed for long-term dynamic bearing capacity calculation and the charts were validated with the application of a real case study.

A modified curve-approximated hysteretic model for partially concrete-filled steel tube bridge piers

A modified curve-approximated hysteretic model for partially concrete-filled steel tube (PCFST) bridge piers is developed based on the previous research work. The proposed model, which consists of a series of quadratic and cubic curves and takes into account the P-Δ effect, pinching behavior in unloading-reloading hysteretic loops, and deterioration of strength and stiffness, can be used to precisely describe complicated hysteretic behavior of cantilever-type PCFST bridge piers. Parameters of this model are calibrated on the basis of quasi-static cyclic test results. To verify the validity of the proposed model, a total of 12 pseudo-dynamic tests were carried out. The detailed comparisons of different seismic performance indices between experimental and numerical results, such as the maximum response displacement, the residual displacement, and the amount of energy dissipation, indicated that the proposed model can be an acceptable complementary and assisting tool for the nonlinear seismic response assessment of PCFST piers.

SEISMIC ANALYSIS OF STEEL-CONCRETE COMPOSITE FRAME STRUCTURES BASED ON THE ULTIMATE BALANCE THEORY

A simplified analysis method of steel-concrete composite frame structures under rare earthquake action is established based on the ultimate balance theory. The failure mechanism of composite frames is determined by theoretical analysis and experimental phenomena. Based on the ultimate balance theory and according to the distribution law of the deformation and internal force when the structure reaches the ultimate strength under earthquake action, the seismic strength of the composite frames is calculated when the top horizontal displacement of the frame is equal to H/50, H/40 and the lateral displacement corresponding to the limit load. The calculation results agree well with the low cyclic loading test results of 19 composite frames at home and abroad. It shows that the method can effectively predict the seismic strength of composite frame structures under rare earthquakes. A simplified method is proposed to control the deformation capacity and seismic strength of the composite frame at the same time to make the structure meet the seismic requirement under rare earthquakes.

Effect evaluation of drainage condition and water content on cyclic plastic deformation of aged ballast and its estimation models

With the ballast aging, the changes in the size and shape of the ballast particle reduce the drainage capacity, as well as cause a greater permanent deformation of the railroad ballast. Therefore, it is meaningful to investigate the effect of aging on the mechanical behavior of unsaturated ballast, and to estimate the cyclic plastic deformation by considering the aging effects. Here, “aging effect” means the increase in fine fraction content and the particle shape becomes rounded and smooth as compared with fresh ballast. In this study, the influence of aging on the cyclic plastic deformation of unsaturated ballast was evaluated through a series of cyclic loading triaxial compression tests. Test results indicate that the cyclic plastic deformation of ballast is seriously affected by water content, fine fraction content and drainage condition, and the increasing trend becomes more remarkable at the water-rich aged ballast under the fully undrained condition since the effective confining pressure decreases due to the generation of excess pore water pressure. Furthermore, the applicability of two types of estimation models (i.e., a semi-empirical model named University of Illinois at Urbana-Champaign (UIUC) model, and an elasto-plastic model named subloading surface extension (SSE) model) to the prediction for cyclic plastic deformation of unsaturated ballast is also verified in this study by comparing with results of cyclic loading triaxial compression tests. As the result, it is revealed that the UIUC model is suitable for predicting the cyclic plastic deformation of fresh ballast (or slightly aged ballast) with different water contents under the fully drained condition, and the SSE model shows good potential to estimate the cyclic plastic deformation of fresh and aged ballasts by considering the effects of water content and drainage condition. The findings of this study indicate that drainage conditions have a significant effect on predicting the cyclic plastic deformation of aged ballast, and appropriate test conditions for triaxial compression tests (i.e., CD and CU tests) should be selected according to hydraulic properties (i.e., permeability and water retentivity) of the aged ballast.

Bayesian Theory-Based Seismic Failure Modes Identification of Reinforced Concrete Columns

ABSTRACT The aim of this research is to develop a probability method that can identify the flexure, shear or flexural-shear failure of RC columns. A total of 336 columns of cyclic load test results were collected, and a probabilistic model was constructed using the Bayesian procedure. Then, the model was simplified by Bayesian updating. The boundaries for each failure mode were selected through an internal search optimization. The results show that the Bayesian methodology can accurately predict the seismic failure modes of RC columns and the comparison of the identification with other methods underscore the validity of Bayesian method.

Need for Standardization: Influence of Artificial Canal Size on Cyclic Fatigue Tests of Endodontic Instruments

The aim was to evaluate the influence of artificial canal size on the results of cyclic fatigue tests for endodontic instruments. Dynamic cyclic fatigue at body temperature using continuous tapered nickel–titanium F6-SkyTaper instruments (Komet, Lemgo, Germany), size 25/.06 with an amplitude of 3 mm, was tested in four different simulated root canals: (A) size of the instrument +0.02 mm (within the tolerances of the instruments); (B) +0.05 mm; (C) +0.10 mm; (D) parallel tube with 1.25 mm in diameter. The artificial canals (angle of curvature 60°, radius 5.0 mm, center of curvature 5.0 mm) were produced by a LASER-melting technique. Time and cycles to fracture, and lengths of the fractured instruments were recorded and statistically analyzed (Student–Newman–Keuls; Kruskal–Wallis test). Time to fracture significantly increased with increasing size of the artificial canals in the following order: A < B, C < D (p < 0.05). Length of separated instruments continuously decreased with increasing canal sizes. The parallel tube produced the significantly shortest fragments (p < 0.05). Within the limitations of this study, dynamic cyclic fatigue of endodontic instruments depends on the congruency of the instruments’ dimensions with that of the artificial canals. In future cyclic fatigue testing, due to the closer match of canal and instrument parameters, it is necessary to adjust the artificial canal sizes to the size of the instruments within the manufacturing tolerances of the instruments.

Experimental behaviour of non-seismical RWS connections with perforated beams under cyclic actions

The use of perforated (in particular cellular and castellated) beams has become widespread as their manufacturing processes keep minimising wasted material and has become cost-effective by reducing self-weight of steel structures, while allowing for larger clear spans. Although their behaviour to time-invariant vertical loads has been extensively investigated and validated in laboratory setups, their response to reversible actions has not been explored to the same extent. This paper presents results of cyclic load tests of beam-column reduced web section (RWS) connections, considering setups representative of what is observed in low-rise buildings in the UK; a region with sparse seismicity. Results show that RWS connections on these frames can achieve stable hysteresis loops without significant strength degradation, due to the simultaneous occurrence of yielding of the critical cross-section and development of a Vierendeel mechanism on the edges of the perforations (web openings). Also, inelastic action is mostly observed within the beam, thus being successful in protecting the beam-column connection. Performance particularly exceeds what is observed for a benchmarking RBS connection styled according to the same underlying assumptions, hinting that RWS connections could be a more suitable solution for structural retrofitting in regions where seismicity is sparse.

Performance of Fiber Reinforced Mortar coating for irregular stone masonry: Experimental and analytical investigations

Nowadays, the application of Fiber Reinforced Mortar (FRM) is widely used for the consolidation and rehabilitation of masonry structures because represents an effective solution in terms of reversibility and applicability. The paper illustrates the results of cyclic diagonal compression tests performed in situ on stone masonry specimens isolated from the walls of a historic building of L’Aquila (Italy). The tested stone masonry is representative of existing structures of the territories of the central Apennines in Italy. Only two of four panels were strengthened by FRM to provide also the reference value of the unreinforced masonry. The FRM comprised a glass-fiber grid embedded in a natural hydraulic lime (NHL)-based mortar applied as a coating to the masonry surfaces as well as carbon shear connectors. The tests were analyzed to derive the shear strength and the shear modulus of the masonry, as well as their evolution during the tests. Moreover, these tests were compared and integrated with a consistent number of experimental data collected in the current literature aiming to validate a new analytical equation for the estimation of the shear strength of the reinforced masonry, merely based on the properties of the unreinforced masonry and the FRM mortar.

Design of prestressed, jointed columns for enhanced seismic performance

Jointed, prestressed columns have been shown to enable accelerated construction and to offer superior seismic performance, as compared with cast-in-place columns without prestressing. During an earthquake, such columns deform primarily through concentrated rotations at the joints, and special detailing at the ends of the columns prevents crushing and spalling. Unbonded prestressing steel, running vertically through the columns, provides a restoring moment that returns the columns to plumb after the ground motion stops. The use of prefabricated substructure elements speeds up the bridge assembly by eliminating building formwork, fixing steel, casting and curing concrete on-site. A variety of detailing strategies have been developed for jointed, prestressed columns, but their fundamental behavior is similar. More importantly, this behavior differs from that of conventional reinforced concrete columns for which current seismic code provisions were developed. This paper develops a displacement-based procedure for designing jointed, prestressed columns that is based on the framework provided by the AASHTO Guide Specifications for LRFD Seismic Bridge Design. To account for the unique characteristics of these systems, the design procedure introduces new performance criteria; it also provides recommendations for proportioning the prestressed and non-prestressed steel, calculating the effective column stiffness, and estimating the column displacement capacity. The focus of the paper is on columns with pretensioned strands and internal energy dissipaters, although the procedure would work for post-tensioned systems and those with external dissipaters as well. This design approach is critically evaluated through comparison to the results of both cyclic tests of cantilever columns and shaking table tests of a two-span bridge system.

Effect of Cr on Aqueous and Atmospheric Corrosion of Automotive Carbon Steel.

This study investigated the effect of Cr alloying element on the corrosion properties of automotive carbon steel (0.1C, 0.5Si, 2.5Mn, Fe Bal., composition given in wt.%) in aqueous and atmospheric conditions using electrochemical measurement and cyclic corrosion tests. Three steels with 0, 0.3, and 0.5 wt.% Cr were studied by electrochemical impedance spectroscopy. Polarization resistance (Rp) of 0.3 Cr and 0.5 Cr steels was higher than that of 0 Cr steel, and the Rp also increased as the Cr content increased. Therefore, Cr increases the corrosion resistance of automotive carbon steel immersed in a chloride ion (Cl−)-containing aqueous solution. In the cyclic corrosion test results, Cl− was concentrated at the metal/rust interface in all of the steels regardless of Cr content. The Cl− was uniformly concentrated and distributed on the 0 Cr steel, but locally and non-uniformly concentrated on the Cr-added steels. The inner rust layer consisted of β-FeOOH containing Cl− and Cr-goethite, while the outer rust layer was composed of amorphous iron oxyhydroxide mixed with various types of rust. FeCl2 and CrCl3 are formed from the Cl− nest developed in the early stage, and the pitting at CrCl3-formed regions are locally accelerated because Cr is strongly hydrolyzed to a very low pH.

The influence of cyclic loading on the response of soft subgrade soil in relation to heavy haul railways

The design of rail tracks is often challenged by the highly compressible behaviour of soft estuarine clays over which they must pass. It is prudent that the realistic long-term behaviour of subgrade materials under repeated loading applied by fast moving heavy haul trains is properly understood. One feature that should not be ignored when estimating the long-term performance of track foundations is the continuous principal stress rotation (PSR) induced by moving wheel loads. The main purpose of this research is to combine the traditional cyclic triaxial test results (fixed axes, no PSR) with those obtained from the dynamic hollow cylinder apparatus (allowing PSR) to examine the relative influence of cyclic stress ratio (CSR) and frequency on the behaviour of soft subgrade subjected to simulated heavy haul train loading. Employing these two types of equipment applying contrasting stress path regimes, a series of cyclic undrained laboratory tests was conducted on reconstituted sandy clay specimens at varying frequencies (f = 0.1–1 Hz) and cyclic stress ratios (CSR = 0.2–0.3). The hollow cylinder test results have shown that higher CSR values and lower frequencies induce greater permanent deformations and excess pore water pressures at a given number of loading cycles (N). For CSR = 0.2, pore pressures and axial strains were found to increase even after a large number of cycles (N = 50,000). However, when the higher CSR value of 0.3 was imposed, the soil failed in less than 300 cycles by reaching 5% of axial strain. Undoubtedly, PSR adversely affected the accumulation of axial strains and soil degradation, whereas in contrast, the development of pore water pressure was less influenced by PSR.

Influence of the specimen production and preparation on the compressive strength and the fatigue resistance of HPC and UHPC

The results of tests under monotonically increasing load and cyclic compression load are often analysed by means of probabilistic methods. Although there is a considerable scattering in the results, especially in the number of cycles to failure, the cause of these cannot be completely explained. The imperfections of the specimens tested are among the causes of this scattering mentioned in the literature. Based on a round robin test the influence of HPC and UHPC production and specimen preparation techniques on the mean values of the compressive strengths, number of cycles to failure and data scattering have been evaluated. The main findings of the study are that the production techniques have an influence on the compressive strength, however, do not affect the mean number of cycles to failure. Moreover, the accurate preparation of the specimens has a positive influence on the compressive strength and the scattering of the results of both compression and cyclic load tests. The mean number of cycles to failure of HPC specimens is not influenced by the preparation techniques, whereas the polishing technique may have a positive influence on the mean number of cycles to failure of UHPC specimens.

The Influence of Fracture Strain Energy on the Burst Tendency of Coal Seams and Field Application

Coal is typically considered a special engineering rock mass because of its low strength, high internal fracture development, good permeability, and random distribution of microparticles and fractures. The results of cyclic loading and unloading tests indicate that the strain energy during the coal deformation process can be divided into three parts: plastic strain energy; fracture strain energy; and base-material strain energy. The energy composition ratio differs depending on coal strength. Lower proportions of fracture strain energy are associated with higher elastic energy indexes, and there is a negative correlation between fracture strain energy and other coal burst tendency indexes. The results were applied on the 4206 isolated island working face of coal mine A in Yan’an, Shanxi, China, yielding good benefits. The findings presented here provide a theoretical basis for understanding the principle of coal seam bursting and guidance for reducing burst risks.

Nonlinear static characterisation of masonry-infilled RC building portfolios accounting for variability of infill properties

The seismic assessment of existing masonry infilled reinforced concrete (RC) building portfolios is a highly relevant issue in Italy and other Mediterranean countries, particularly in regions where a large part of the built environment was not designed according to modern seismic codes. In the past, masonry infills were generally considered as non-structural elements and were not accounted for in the design process. However, the results of experimental tests and past earthquake evidence demonstrated the influence of masonry infills on the global and local behaviour of RC buildings. Furthermore, the acknowledgment of different construction practices points out the significant variability affecting the masonry infills in terms of material properties, thickness, presence of openings and manufacturing techniques. This paper deals with the large-scale performance analysis of existing masonry infilled RC building portfolios accounting for the uncertainty related to the variability in the mechanical properties and the modelling of masonry infills. To accomplish this goal, a fully integrated building stock, representative of masonry infilled RC buildings designed according to the Italian codes in force between 1960 and 1980, was developed, using a simulated design approach. Statistical data and results of experimental tests were used to identify the main masonry infill typologies adopted in the Italian context. Detailed numerical models, whose prediction capability was appraised through the results of cyclic quasi-static tests, were developed to estimate the lateral response of the analysed RC buildings. Different response parameters, which can be easily implemented in seismic risk assessment frameworks, were considered and quantified, at the portfolio level, to understand the uncertainty propagation and impact of the masonry infills’ variability on the expected performance of existing RC buildings. The results demonstrated that the variability related to the definition and modelling of the masonry infills induces significant dispersion, with respect to the mean, on the lateral response of different classes of buildings within a given portfolio. Moreover, the provided parameters for multi-linear idealised capacity curves can be used in simplified seismic fragility and risk models for existing buildings, including a proper estimate of the associated uncertainty, leading to a more accurate quantification of economic losses.

Fractional-Order Elastoplastic Modeling of Sands Considering Cyclic Mobility

Seabed soil may experience a reduction in strength or even liquefaction when subjected to cyclic loadings exerted by offshore structures and environmental loadings such as ocean waves and earthquakes. A reasonable and robust constitutive soil model is indispensable for accurate assessment of such structure–seabed interactions in marine environments. In this paper, a new constitutive model is proposed by enriching subloading surface theory with a fractional-order plastic flow rule and multiple hardening rules. A detailed validation of both stress- and strain-controlled undrained cyclic test results of medium-dense Karlsruhe fine sand is provided to demonstrate the robustness of the present constitutive model to capture the non-associativity and cyclic mobility of sandy soils. The new fractional cyclic model is then implemented into a finite element code based on a two-phase field theory via a user subroutine, and a numerical case study on the response of seabed soils around a submarine pipeline under cyclic wave loadings is presented to highlight the practical applications of this model in structure–seabed interactions.

Optimisation of cold-formed steel beams for best seismic performance in bolted moment connections

Typical thin-walled cold-formed steel (CFS) elements and connections used in portal frames are not generally suitable for moment-resisting frames in high seismic regions due to their low ductility and energy dissipation capacity and inherited susceptibility to local/global instabilities. This study aims to improve the seismic performance of CFS moment-resisting frames by developing a methodology to obtain more efficient bolted moment connections using optimised CFS beams with enhanced non-linear post-buckling behaviour. By taking into account material non-linearity and geometrical imperfection effects, the detailed Finite Element (FE) models of a typical CFS bolted moment connection is developed using ABAQUS software, and then validated based on experimental cyclic test results. Particle Swarm Optimisation (PSO) algorithm is linked to GMNIA ABAQUS FE analysis to optimise CFS bolted moment connections based on either energy dissipation capacity or ductility. To demonstrate the efficiency of the method, connections with five different beam cross-sectional shapes are optimised, and the results are compared with a standard CFS channel section used as a benchmark. The relative dimensions of the cross-sections, the inclination of the lip stiffeners, and the location of triangular intermediate stiffeners are selected as main design variables. To provide practical beam cross-sections, the plate slenderness limit values defined by Eurocode 3 (EC3) along with a range of manufacturing limitations are imposed as design constraints in the optimisation process. It is shown that, for a given plate width and thickness, the proposed optimisation framework results in a considerable (up to 195%) improvement in the energy dissipation capacity and ductility of the CFS bolted moment connections.

Methodology for calculate bearing capacity of soft soils under cyclic loading

The bearing capacity in soft soils under cyclic loading has not been widely studied as the static bearing capacity. In soft saturated soils under cyclic load, the phenomenon of cyclic softening occurs, this consists of an increase in the generation of pore-water pressure due to the cyclic load and a decrease in effective soil stresses. The purpose of this work was to propose a methodology for calculating the bearing capacity in soft soils under cyclic loading. The research is based on the results of monotonic and cyclic simple shear tests carried out with samples from the PRAT port of Barcelona. From an analysis carried out on all the experimental data, an equation for the generation of pore-water pressure is proposed. This formulation was implemented in the FLAC2D finite difference software and is part of the methodology. The methodology of the proposed calculation process consists of 6 stages and verification under two criteria. This process is iterative in case of not meeting any of the two verification criteria. Under this methodology of the calculation process, charts are proposed to calculate the bearing capacity of soft soils under cyclic loading. This application takes into account the properties of the soil, the static bearing capacity (P he), and the effective load outside the foundation (q). Also, an analysis of the parameters that most influence the bearing capacity of soft soils under cyclic loading was carried out.

Failure behavior of SA508 Gr.1a LAS and SA312 TP316 SS pipes with a circumferential through-wall crack under large amplitude cyclic loads

This paper presents cyclic fracture test results using small-scale through-wall cracked pipe specimens to investigate the effects of large-amplitude cyclic loads on failure behaviour for different pipe materials. SA508 Gr.1a low-alloy steel (LAS) and SA312 TP316 stainless steel (SS) pipes were used in the experiment. The tests were conducted under quasi-static monotonic, displacement-controlled, and load-controlled cyclic loadings at room temperature (RT). Regardless of the pipe material, displacement-controlled reversed cyclic loading significantly reduced deformation-ability and fracture resistance, promoting crack growth. These effects were more pronounced in the SA312 TP316 SS than in the SA508 Gr.1a LAS specimen. The material-dependence on fracture behaviour was considerable under monotonic load, but was near-negligible under displacement-controlled reversed cyclic loading. Under load-controlled cyclic loading, the number of cycles to failure, the maximum allowable crack extension, and deformation-ability of pipe specimens decreased as the amplitude and compressive level increased. For all load-controlled cyclic loads, the SA312 TP316 SS specimen was less resistant to failure than the SA508 Gr.1a LAS specimen. Regardless of the loading type, a circumferential through-wall crack grew out of the initial crack plane for the SA508 Gr.1a LAS specimen, but propagated in a straight line from the initial crack plane for the SA312 TP316 SS specimen.