Monotonic Loading Behavior Research Articles

Centrifuge Modeling of the Monotonic Capacity of Offshore Ring Anchors in Sand

The development of offshore wind technology has become a feasible solution to meet the increasing demands for clean and renewable energy. The United States has a total of 4250GW offshore wind energy potential; however, 65% of it is in deep water zones (Lopez et al., 2022) where wind turbines with fixed foundations typically are economically and technically unfeasible. In those situations, floating turbines supported by subsea anchors are a more competitive solution. Based on previous studies, ring anchors can be more material-efficient than piles and caissons because they require less material. Ring anchors also perform better than drag anchors due to their greater embedment depth. To further understand the behavior of ring anchors in saturated sand, a series of centrifuge load tests were performed at the University of California Davis Center for Geotechnical Modeling (CGM) at an acceleration of 70g. This test series investigated the effect of the anchor embedment depth and loading angle on the monotonic loading behavior. The ring anchor models were embedded in dense saturated sand, and then connected to an actuator using taut steel wire ropes. Sensors were used to measure the line tension, displacement, and inclination. The results indicate that the ring anchors mobilize greater capacities as their embedment depth is increased and when they are loaded at angles close to the horizontal direction, while vertical loading leads to the smallest capacity. The anchor displacement during the tests deviated slightly from the loading direction, showing a horizontal deviation at the earlier stages of the tests and a vertical one after the peak load. Furthermore, soil disturbance induced by the anchor installation was found to have a strong effect on the vertical capacity of the ring anchors. Overall, this study provides valuable information regarding the monotonic loading behavior of ring anchors which can aid in their future field deployment.

Hysteretic energy dissipation capacity of dual-steel welded-plate preloaded bolted T-stubs

With the high- and ultrahigh-strength steels applied in the construction industry, the seismic safety of their structural components is very concerned due to the inferior material ductility of those steels. The current studies on bolted high-strength steel T-stubs mainly focus on their monotonic loading behavior. There is limited research work conducted to study their cyclic loading behavior. In this study, cyclic tests of bolted dual-steel T-stubs were conducted. Their T-elements were produced by Q690 high-strength steel flanges and Q355 normal-strength steel webs, and class 10.9 high-strength bolts with pretension were used to connect the groove-welded T-elements. Failure modes, force-deformation hysteretic and backbone curves, cumulative plastic deformation and energy dissipation capacities were tested and analyzed. The test results indicated that an optimal β ratio between the plastic resistances of Mode 1 (neglecting the influence of bolt action on a finite contact area) and Mode 3 in Eurocode 3 Part 1–8, could be 0.3 for those bolted T-stubs to maximize hysteretic energy dissipation. Accordingly, predictive formulas with good precision were proposed for the low-cycle fatigue failure criterion and hysteretic energy dissipation capacity of those bolted T-stubs, respectively.

Experimental study on the cumulative damage constitutive model of high-performance steel Q345GJ under cyclic loading

GJ series steel is a new type of high-performance structural steel, which has emerged in China steel construction, and it has been widely utilized in steel-framed building structures. To investigate the low cycle fatigue performance and cumulative damage behaviors and find a suitable constitutive relationship of GJ series steel under cyclic loading, a total of eighteen Q345GJ steel low cycle fatigue experiments have been carried out. The mechanical behavior of Q345GJ steel were discussed, including monotonic loading behavior, hysteresis loading behaviors and energy dissipation capacity. Based on the cyclic behavior of GJ series steel, a modified cumulative damage model was recommended. Then, with comparison of the Q345GJ tests data (including the data in public papers) under various loading systems, the model proposed in this paper is proved correct and can be used to simulate the cyclic behavior of Q345GJ members.

Complete implicit stress integration algorithm with extended subloading surface model for elastoplastic deformation analysis

SummaryThe subloading surface model released from a purely elastic domain is capable of describing not only monotonic but also cyclic loading behaviors accurately. It is expected that elastoplastic deformation analyses can be performed with high accuracy and efficiency by the complete implicit stress integration algorithm with a return‐mapping projection. Various implicit stress integration algorithms for the subloading surface model have been proposed. However, they are applicable only to the monotonic loading behavior since they adopt the incorrect loading criterion presuming that the subloading surface expands in the plastic loading process. In fact, however, the plastic strain rate is induced even when the subloading surface contracts in the elastic trial step. Therefore, erroneous results in the descriptions of unloading‐reloading and cyclic loading behaviors are caused in the calculations with the existing algorithms. The complete implicit stress integration method is formulated adopting the rigorous loading criterion and implemented in Abaqus in this study. Numerical analyses for the elastoplastic deformation behaviors in the single‐element are performed by the present and the existing algorithms. In addition, the deformation analysis of the R‐notched cylinder is performed by the present algorithm. High performability of the present algorithm is confirmed by these numerical calculation results.

Evaluation of cyclic and monotonic loading behavior of bucket foundations used for offshore wind turbines

Suction caissons are considered as an alternative foundation solution for offshore wind turbines. In the present study, three-dimensional finite element (FE) analyses are performed to assess the behavior of a bucket foundation and soil supporting the bucket under cyclic and monotonic loading conditions. A parametric study is also performed for a wide range of bucket geometries and two different soil densities. The results indicate that bucket geometry and soil properties significantly affect the foundation response due to cyclic loading conditions. The bucket with the smallest geometry installed in medium dense soil exhibits the lowest stiffness in initial loading and then with the progress of cyclic loads experiences lower stiffness compared to the caissons with larger geometries. The sensitivity of the foundation response to the soil density is higher than its geometry. The bucket under the lowest vertical load experiences the lowest stiffness in both virgin loading and during the progress of cyclic loads. The highest soil displacement is observed near the lid at the interior of the bucket. Stresses caused by cyclic loading belong to certain ranges. Additionally, increases in the skirt length result in increases in the stress ranges and shift the range to the right side. With respect to the monotonic loading conditions, normalized diagrams are proposed that can be used for the preliminary design of suction bucket foundations.

Numerical approach of the steel-concrete bond behavior using pull-out models

This paper deals with the analysis of monotonic loading behavior in pull-out tests. The main objective is to obtain a reliable numerical model to represent the steel-concrete bond behavior using previously obtained experimental results. The tests were performed in RILEM pull-out specimen using 10 mm steel bar and concrete with compressive strength of 30 MPa. The numerical study used Ansys® software, based on FEM (Finite Elements Method). The numerical simulation adopted non-linear constitutive relationships to represent the behavior of both concrete and steel. A contact surface composed of special finite elements modeled the interface between the concrete and the steel bar, allowing a steel–concrete slip. The numerical analysis performed with variation of the main parameters of the software permitted determining the best ones, and choosing them to obtain a good representation of the bond phenomena. The numerical results had a good agreement with the experimental results. Both linear and non-linear approaches represented the pre-peak behavior, however only the non-linear model gave the best approach for the pull-out force. In addition, the numerical results had shown the simplified model can be used to represent the steel-concrete bond behavior reducing the processing time for current structures analysis. Keywords: bond strength, pull-out tests, numerical approach, contact surface, finite element method.

Experimental and constitutive model study of structural steel under cyclic loading

In order to study extremely low cycle fatigue performance of structural steel and find a suitable constitutive relationship under cyclic loading, a total of fifty Q235B and Q345B steel extremely low cycle fatigue experiments have been carried out. The mechanical behavior of Q235B and Q345B structural steel including monotonic loading behavior, hysteresis loading behavior and hysteresis criterion are discussed. With fully recognized cyclic behavior of structural steel, a uniaxial and simplified constitutive relationship of structural steel under cyclic loading is proposed. Then the uniaxial steel constitutive relationship is developed as user-defined material based on the user subroutine interfaces UMAT provided by Finite Element Software ABAQUS. By introducing the fiber beam element method, the steel uniaxial constitutive model can be used for steel structural analysis. With comparison of Q235B and Q345B tests data under various loading systems, the model proposed in this paper is proved correct and can be applied in nonlinear time history analysis of steel frame. Both tests and analysis results show that the response of Q235B and Q345B steel under cyclic loading and monotonic loading are quite different, and the skeleton curve under cycle loading is much higher than monotonic loading after steel yielding. Both cyclic loops and amplitudes seriously affect the fracture ductility of steel material. While the structural steel bearing cyclic loading, the necking and the fracture behavior will occur ahead of time, it means that the cumulative damage makes the ductility of steel reduced.

Concrete Cracking in Tension Members and Application to Deck Slabs of Bridges

Currently, estimations of the crack width in the deck slab of bridges given by codes of practice are based on either theoretical or empirical approaches considering mainly the monotonic loading behavior. However, cracking in reinforced tensile members is highly influenced by the loading history (including both the loading and unloading processes) because of the irreversible nonlinear behavior of bond and of tensile response of concrete, resulting into residual cracks of non-negligible width. This paper investigates the influence of this phenomenon and presents a physical model describing it. An analytical model is developed and its results are compared to various tests with good agreement. Finally, a simple design formula is derived and recommendations for its application to practical cases are proposed.

Localized necking analysis by the subloading surface model with tangential-strain rate and anisotropy

A rational approach to the localized necking problem was given by Storen and Rice [J. Mech. Phys. Solids 23 (1975) 421] but this approach is limited to the description of monotonic loading behavior near a proportional loading of the isotropic, rigid-plastic materials with von Mises yield surface. In this article it is extended so as to be applicable to the arbitrary loading behavior of elastoplastic materials with an arbitrary yield surface by introducing the subloading surface model with the tangential-stress rate effect [Met. Mater. 4 (1998) 652; Int. J. Plasticity 17 (2001) 117]. The localized necking condition under biaxial stretching of a uniform and homogeneous thin sheet subjected to biaxial stretching in the plane stress state is formulated in such a way that elastic deformation and compressibility are allowed. Based on this condition, the localized necking for metals is analyzed showing the forming limit diagrams (FLDs). It becomes clear that not only the tangential-strain rate but also the inherent/induced anisotropy due to the kinematic hardening intensely influence the onset of localized necking.

Modeling the Stress-Strain Relations of Sand in Cyclic Plane Strain Loading

A modeling procedure to simulate stress-strain relations of sand subjected to cyclic loading is proposed. Results from drained plane strain compression, extension, and cyclic loading tests on Toyoura sand are analyzed. The monotonic loading behavior is simulated by the generalized hyperbolic equation to use as the skeleton curves in the simulation of cyclic behavior. To construct hysteretic stress-strain curves based on the skeleton curves, the Masing’s rule is generalized to the proportional rule consisting of the internal and external rules. The drag rule is then introduced to simulate cyclic stress-strain behavior in which the stress amplitude increases at a decreasing rate during cyclic loading with a constant strain amplitude. It is assumed that any plastic shear strain increment taking place in a certain direction drags the whole skeleton curve for loading in the opposite direction towards the direction of the concerned shear strain increment. The measured cyclic stress-strain behavior is well simulated by the proposed method.

The yielding, plastic flow, and fracture behavior of ultra-high molecular weight polyethylene used in total joint replacements

The yielding, plastic flow, and fracture behavior of UHMWPE plays an important role in wear and failure mechanisms of total joint replacement components. The primary objective of this study was to compare the yielding, plastic flow, and fracture behavior of two implantable grades of UHMWPE (GUR 1120 vs 4150 HP). The first part of this work explored the hypothesis that up to the polymer yield point, the monotonic loading behavior of UHMWPE displays similar true stress–strain behavior in tension and compression. Uniaxial tension and compression tests were conducted to compare the equivalent true stress vs strain response of UHMWPE up to 0.12 true strain. During monotonic loading, the equivalent true stress–strain behavior was similar in tension and compression up to the yield point. However, investigation of the unloading behavior and permanent plastic deformations showed that classical deviatoric rate independent plasticity theory may dramatically overpredict the permanent strains in UHMWPE. A secondary goal of this study was to determine the ultimate true stress and strain for UHMWPE and to characterize the fracture surfaces after failure. Using a fracture mechanics approach, the critical flaw sizes were used in combination with the true ultimate stresses to predict the fracture toughness of the two resins. A custom video-based strain measurement system was developed and validated to characterize the true stress–strain behavior up to failure and to verify the accuracy of the incompressibility assumption in calculating the true stress–strains up to failure. In a detailed uncertainty analysis, theoretical expressions were derived for the relative uncertainty in digital video-based estimates of nominal strain, true strain, homogeneous stress, and true stress. Although the yielding behavior of the two UHMWPE resins was similar, the hardening and plastic flow behavior clearly discriminated between the GUR 1120 and 4150 HP. A statistically significant difference between the fracture toughness of the two resins was also evident. The long-term goal of this research is to provide detailed true stress–strain data for UHMWPE under uniaxial tension and compression for future numerical simulations and comparison with more complex multiaxial loading conditions.

A Granular Material Model Based on Associated Flow Rule Applied to Monotonic Loading Behavior

ABSTRACT The stress-strain behavior of a granular material is highly complicated relative to that of a cohesive soil. Due to the frictional nature of the material, a plasticity framework based on non-associated flow rule is generally considered to be most suitable for modeling its constitutive behavior. By employing two surfaces, it is shown in this paper that a plasticity model based on an associated flow rule provides a satisfactory means of simulating, under a monotonic loading, the stress-strain behavior of dense and loose sands under triaxial undrained and drained loading conditions.

Cylindrical members in offshore structures

This paper presents several simplified methods of determining the strength and behavior of offshore cylindrical members and simple frames subjected to monotonic and reversed loading conditions. The important factors such as the effects of the external hydrostatic pressure, the local buckling, the residual stresses, and the initial geometrical imperfections on the member behavior and strength are all considered in the analysis. Typical results for the ultimate strength and behavior of these members and simple frames are given. Ultimate strength-design interaction equations recommended and proposed in the United States for different categories of beam-columns are also presented. The first part of the paper deals with the monotonic loading behavior and strength, and the latter part deals with the reversed and one-cycle loading behavior. Directions of further research are also indicated. In addition to an extensive citation of references in the paper, a Bibliography containing general references relevant to the subject area and reported recently in the North American literature is also included.

Effect of pH on corrosion and monotonic loading behaviour of 90Cu–10Ni in 3·5% sodium chloride solution

Polarisation studies were performed on 90Cu–10Ni (alloy UNS C70600, hot rolled and annealed) in 3·5% NaCl solutions over a range of initial pH levels. It was found that film formation was dependent on the applied current and the relative concentrations of the ionic species H+, (OH)−, and Cl− in solution which ultimately influenced the formation of the corrosion products. Constant extension rate tests at different applied currents and pH levels suggested that a higher pH level increased the time to failure although no evidence of stress corrosion cracking was found. These observations are rationalised through surface film formation mechanisms.

The uniaxial and biaxial, monotonic and cyclic plasticity behaviour of a lead alloy model material

A chill-cast, antimony-arsenic-lead alloy model material has been used to investigate the monotonic and cyclic loading, uniaxial and biaxial plasticity behaviour of a metal at elevated temperature, i.e., T/ Tm ≈ 0.5. For the lead alloy used, a post-machining heat treatment of 96h at 100 C considerably reduced the scatter in the material behaviour. Uniaxial monotonic loading tests showed that the behaviour is relatively independent of temperature and strain-rate for strains less than about 1 per cent. Under cyclic loading conditions, between fixed strain limits, a stable hysteresis loop is obtained after the first cycle for both uniaxial and biaxial stress systems. By taking into account the biaxiality ratio and the increase in yield-range caused by cyclic hardening, the uniaxial and biaxial, cyclic plasticity behaviour was reasonably accurately predicted from the uniaxial, monotonic loading behaviour.

On a Class of Models for the Yielding Behavior of Continuous and Composite Systems

A class of one-dimensional models for the yielding behavior of materials and structures is presented. This class of models leads to stress-strain relations which exhibit a Bauschinger effect of the Massing type, and both the steady-state and nonsteady-state cyclic behavior are completely specified if the initial monotonic loading behavior is known. The concepts of the one-dimensional class of models are extended to three-dimensions and lead to a subsequent generalization of the customary concepts of the incremental theory of plasticity.