Amplitude Cyclic Loading Research Articles

Field tests of rock-socketed monopile in coastal area subjected to lateral cyclic loading

Field tests were carried out to study the lateral cyclic loading characteristics of rock-socketed monopile in coastal area, and the variation law of pile body accumulative displacement, unloading stiffness, and pile body bending moment with the cyclic number and cyclic loading amplitude were obtained by actual measurement. Test results show that the cyclic loading history with sa small amplitude has a certain effect on the cyclic accumulative displacement and the degradation of unloading stiffness, and both the peak bending moment and locking moment of the pile body increase with the increase of cyclic numbers. By using the normalization method and formula fitting method, it is found that, the accumulative rate of cyclic displacement, the degradation rate of unloading stiffness, and the variation rate of peak bending moment of single piles in weathered rock layers are significantly smaller than those of sand foundation or clay foundation. The cyclic p-y curves at different depths are derived, and the different hysteretic characteristics between shallow cyclic p-y curve and deep cyclic p-y curve are explored. Finally, the static load test after cyclic tests was carried out, and it was found that the lateral bearing performance of the rock-socketed monopile was greatly degraded after a total of 3000 times of lateral cyclic loading.

An Experimental Study on Seismic Performance Evaluation of Multi-Ply Bellows Type Expansion Joint for Piping Systems

Piping systems are a representative social infrastructure to provide oil, gas, and water. Damage to piping systems may cause serious consequences, such as fire, water outage, and environmental pollution. Therefore, piping systems need to be protected from natural disasters, such as earthquakes. Earthquakes may cause deformation that exceeds piping design criteria. For example, large relative displacements and liquefaction of the ground resulting in loss of strength and ground subsidence, and the side-sway of primary structures subjected to a strong ground motion may cause critical damage to piping systems. Therefore, expansion joints to maintain flexibility can be applied to locations where excessive deformation is expected to improve the seismic performance of piping systems. Metal bellows, a type of expansion joints, are flexible, so they are highly durable against deformation and fatigue loads. This indicates that metal bellows can be used as seismic separation joints for piping. In this study, experimental research was conducted to analyze the seismic performance of multi-ply bellows type expansion joints, a type of metal bellows. Monotonic loading tests and cyclic loading tests were conducted on 2-ply bellows and 3-ply bellows, and the results were compared. In the cyclic loading tests, multi-step increasing amplitude cyclic loading, which used the displacement history amplified in stages, and constant amplitude cycling loading with various magnitudes were considered. The test results showed no significant difference in bending performance for monotonic loading between the two types of multi-ply bellows. The 3-ply bellows, however, showed higher performance for low-cycle fatigue than 2-ply bellows.

Fatigue Damage Mitigation for Welded Beam-to-Column Connections in Steel High-Rise Buildings Using Passive Vibration Control

To investigate the use of vibration control systems in fatigue damage mitigation for welded beam-to-column connections in steel high-rise buildings, cases of both a single connection under constant amplitude cyclic loading and multi-connections in a high-rise building under the stochastic wind, with and without the fluid viscous damper (VFD) and the tuned mass damper (TMD), are discussed respectively. The finite element analysis and the fatigue assessment are conducted so that the mitigation effect, the effect of technical parameters and the conditions of both high-cycle fatigue and low-cycle fatigue are all discussed. The results show that the VFD and the TMD systems are both effective in the mitigation of local fatigue damage along with the structural displacement for both cases. The VFD generally has a better mitigation effect than the TMD and it starts to take effect instantly with the external loading, but it causes a phase difference in structural responses, while the situation of the TMD is quite the opposite. The displacement and the local stress show similar and synchronous mitigation trends so that the damping systems can be designed based on either of them. The VFD should be designed with a smaller damping exponent and a larger damping coefficient in a braced installation form, while the TMD can be designed using the optimal parameters. The optimized VFD layout plan is that VFDs are placed between the two connections with large relative displacement and relative velocity on higher floors and these two connections with VFDs should be near to the targeted connection. The negative fatigue damage mitigation mainly stems from insufficient lateral support force so that the direct installation of VFDs may result in a negative fatigue damage mitigation effect in the connections with limited lateral support.

Effect of Amplitude and Duration of Cyclic Loading on Frictional Sliding Instability in Granular Media: Implication to Earthquake Triggering of Landslides

AbstractStrong earthquakes with larger magnitude and longer durations trigger many landslides, however, how magnitude and duration affect landslides is still unclear. Many factors could contribute to this, including additional shear stress provided by strong ground motion, or “seismogenic liquefaction”; herein, we hypothesize that the dynamic weakening of sliding zone gouge is important. We explored the influence of earthquake magnitude and duration on landslide triggering by simulating the seismic response of sliding zone gouge using a dynamic ring‐shear device and glass spheres. The experiments showed that vibration with larger amplitudes and longer durations more easily trigger deformation and even instability in dry granular materials. We used a dynamic triaxial‐bender system to find that the shear modulus of these materials decreased with the increase in duration and amplitude of cyclic loading. We suggest that this universal decrease in shear modulus is an important landslide‐trigger mechanism. Our results revealed how magnitude and duration of earthquakes affect co‐seismic landslides and why earthquakes with larger magnitude and long durations can trigger more co‐seismic landslides.

Effect of particle regularity on the shear response of geogrid-granular material interface under cyclic normal loading

The investigation of shear behaviour on geogrid-granular material interface under cyclic normal loading (CNL) is significant in seismic design of reinforcement structure. The cyclic shear mechanism about the effect of particle overall regularity on reinforced soil interface was analysed using dynamic direct shear apparatus. Five mixtures of round spherical media and crushed limestone with different percentages were selected to obtain various particle overall regularity. By comparing the shear behaviour under various overall regularity, the interface shear stress and vertical displacement under the CNL condition were smaller than those under the static loading condition. The decrement in interface shear stress of lower overall regularity was smaller than that of higher overall regularity. The interface peak shear stress, final vertical displacement decreased with the increase of cyclic normal loading amplitude and overall regularity. The effect of initial normal loading on ratio of strength reduction and energy consumption was reverse to that of the overall regularity. Based on the constant relative phase shift of the peak normal stress and friction coefficient for various overall regularity, the prediction formula was proposed. The test results improve the understanding on how normal loading perturbations and particle overall regularity affect the shear behaviour of reinforced soil interface.

저주기 피로를 고려한 3ply 벨로즈형 신축관이음의 내진성능 실험

Pipes can be damaged by strong external forces such as earthquakes. In particular, gas leaks and interruptions to water supply can cause serious secondary damage. This is one of the damage factors caused by earthquakes in urban areas. Bellows-type expansion joints for pipes are flexible and have low rigidity and good adaptability to relatively large deformations. Therefore, bellows-type expansion joints can be applied as seismic separation joints to improve the seismic performance of pipes. In this study, seismic performance considering low cycle fatigue was estimated for bellows-type expansion joints. Monotonic and cyclic loading tests for bending were performed on 80A 3ply bellows- type expansion joints manufactured by laminating three layers of 0.3 mm stainless steel plates. In the cyclic loading test, the multi-step increasing amplitude cyclic loading test to which the displacement history is amplified stepwise was applied and a constant-amplitude cyclic loading test considering various amplitudes was used to estimate the low-cycle fatigue life. In the case of the constant- amplitude cyclic loading tests, low cycle fatigue behavior was observed for 1/4 amplitudes of leakage displacements of monotonic loading tests.

Fatigue resistance of metal construction materials and its relationship with changes in the state of thin surface layers

The paper considers the proven clear relationship between the fatigue resistance of a number of structural materials and the processes occurring in their thin surface layers. The fatigue studies of the samples were carried out over a wide range of temperatures and amplitudes of cyclic stresses under uniaxial tension-compression with simultaneous microhardness measurement of the thickness of the hardened surface layer. On the basis of experimental studies of the fatigue of metallic structural materials, using the microhardness method, the regularities of hardening (softening) of their surface layer are established depending on the level of the amplitude of high-cycle loading and temperature. A method for the accelerated determination of the fatigue limit of structural materials based on the determination of microhardness during cyclic loading has been developed and tested. The dependence of the formed hardened film of the surface layer on the level of plasticity of the material has been established - the greater its plasticity, the thicker the resulting hardened film. With an increase in the amplitude of cyclic loading, the thickness of the hardened surface layer decreases.

Effect of internal defect on the low-cycle bending fatigue behavior of a single-strand wire rope

• The low-cycle bending fatigue behavior of a defective wire rope is analyzed. • The minimum fatigue life of the wire rope occurs near the defective area. • The internal defect increases the risk of stress yielding of the wire rope. • The internal defect reduces the minimum fatigue life of the wire rope. • An increment in radial position of defect causes a worse performance of the rope. In order to explore the evolution rules and failure mechanism of bending fatigue behavior of a defective single-strand wire rope under cyclic bending load, the influence of average stress and elasto-plasticity on the bending fatigue behavior is considered in this paper. Based on the characteristics of constant amplitude cyclic load, a finite element analysis model of the low-cycle bending fatigue behavior of the single-strand wire rope with an internal defect is established. Then the fatigue lives of the defective rope and non-defective rope are compared, and the influence of the defect’s radial position on the bending fatigue behavior of the rope is discussed. The results show that under the cyclic bending load, the minimum fatigue life of the defective rope in the cross section occurs in the defective area, while that of the non-defective rope lies in the interwire contact area. The defect changes the fatigue life distribution of the single-strand wire rope, and improves the fatigue life locally but reduces the rope’s bearing capacity. Additionally, a larger distance between the defect and neutral layer causes an earlier stress yielding in defective area and makes a greater risk of fatigue failure.

Pullout behavior of a bearing polymeric strap under monotonic and cyclic tensile loads

Soil-reinforcement interaction consists of three factors including frictional resistance, shear strength of the soil and passive resistance. In the ordinary polymeric strap (PS) reinforcement, only frictional resistance contributes to pullout resistance. In this study, in order to develop passive resistance in the soil, a number of angles as transversal elements were attached to PS reinforcement, which is called bearing polymeric strap (BPS). The post-cyclic pullout behaviour of the BPS is evaluated using a large-scale pullout apparatus adopting multistage pullout (MSP) test and one-stage pullout (OSP) test procedures. The results show that a spacing-to-high ratio of angles equal to 3.33 gives the maximum pullout resistance. MSP tests were performed on the BPS with an optimum arrangement to evaluate the influence of various factors including cyclic tensile load amplitude, load frequency and number of load cycles, and also the influence of vertical effective stress on the pullout resistance and the peak apparent coefficient of friction mobilized at the soil-BPS interface. Moreover, for BPS system with a single isolated transverse member, the bearing capacity factor Nq was calculated using equations based on three failure modes and it was found that the Nq calculated in the punching shear failure mode makes the best prediction.

Experimental investigation into the cyclic behaviour of geogrid enhanced base layer aggregate through large-diameter triaxial tests

The base layer is constructed of coarse-grain soils, usually reinforced by geogrid. In the study, a large-diameter cyclic triaxial testing system was employed to study the cyclic behaviour of geogrid enhanced soil, especially the long-term deformation behaviour. The multi-stage cyclic loading test was performed to determine the shakedown behaviour of soil enhanced by different geogrid layers under different cyclic loading amplitudes. Then, single-stage tests with one cyclic loading amplitude in plastic creep range and the other in the incremental range were performed on soils enhanced by different geogrid layers. Test results indicated that the effect of geogrid on the long-term deformation of soil is dependent on the shakedown response of soil: the enhancement effect was observed to be much more significant for specimens that exhibit the incremental collapse response than those that exhibit the plastic creep response. Besides, the resilient modulus was found limited affected by the geogrid layer, irrespectively the specimen that exhibits plastic creep or incremental collapse. Furthermore, the reinforcement mechanism was discussed in detail from the consistent/inconsistent deformation of soil and geogrid, which benefits geogrid design and construction.

On the deflection of composite reinforced steel truss-concrete beam under static and dynamic load

In this study, a test beam model of negative moment region was designed to study its deflection characteristics under over-limit static load and variable amplitude cyclic load scenarios. (1) According to the deflection test results of the test beam under over-limit static load, the load-deflection curve under static load before and after 10000 times of over-limit fatigue load tended to sharply increase in the first place and then slow down afterwards. At the ultimate load, the maximum deflection value of the two was 8.625 mm and 8.76 mm, respectively. The maximum deflection value after 10000 times of over-limit fatigue load increased by 1.57% compared with that before. (2) The deflection test results of the test beam under variable amplitude cyclic load showed that both the total deflection and the residual deflection percentage increased firstly and decreased with the increasing fatigue load times. The total deflection ranged from 4.07–4.3 mm, and the residual deflection percentage was 0.1–1.65%; The residual deflection percentage reached a maximum of 1.65% when the fatigue load times reached 2 million. (3) The deflection test results of the test beam under over-limit variable amplitude fatigue load showed that the maximum residual deflection reached 0.08 mm (maximum residual deflection percentage 1.75%), 0.11 mm (maximum residual deflection percentage 2.30%), 0.16 mm (maximum residual deflection percentage 2.65%) after 1.5, 2 and 3 times over-limit variable amplitude fatigue load was imposed respectively. The maximum deflection did not fluctuate obviously, indicating that the test beam was had sound working performance. (4) In this study, the shear stiffness and fatigue load times were fully considered, the mean value of the ratio of the deformation value to the measured value of the test beam was 0.89, and the standard deviation was 4.86%. When the fatigue load times exceeded 2.8 million, the ratio of the calculated value to the measured value was less than 0.85. In conclusion, the model had its own limitations.

The influence of geotextile on the characteristics of railway subgrade mud pumping under cyclic loading

The mud pumping beneath railways is both widespread and harmful and seriously affects the stability of railroad tracks and their operational safety. This paper presents a series of mud pumping tests, and analyses the influence of geotextile on the characteristics of saturated subgrade mud pumping. Our results show that the addition of geotextile between subgrade and gravel layers can significantly reduce accumulated axial strain by 40% to 76%, reduce residual excess pore water pressure by 33% to 92%, and reduce soil moisture content at the interface between the subgrade and gravel layers. However, we find that geotextile has no significant effect on soil dynamic stress. This suggests that the geotextile can act as a separator between the subgrade and gravel layers thus significantly reducing the thickness of an interlayer. Additionally, geotextile can also act as a filter and reduce the displacement caused by the migration of fine particles. In general, placing geotextile between the subgrade and gravel layers can mitigate railway subgrade mud pumping under cyclic loading, but with an increase in cyclic loading amplitude, the mitigating effectiveness of geotextile on mud pumping gradually weakens.

Ultimate strength and fracture failure of hull stiffened plates based on plastic accumulation under cyclic loading

Relying on nonlinear finite element analysis of ANSYS software, the ultimate strength and fracture failure of hull stiffened plates based on plastic accumulation have been studied under cyclic compression and compression-tension load. In addition, the shakedown is also preliminarily discussed. According to different cyclic load patterns, the influence of material models such as elastic-perfectly plastic, isotropic hardening, and Chaboche model on plastic accumulation, ultimate strength, and fracture characteristics of stiffened plates is mainly researched. Studies have shown that material models have a significant impact on the plastic accumulation region, plastic accumulation speed, and the ultimate strength of hull stiffened plates under cyclic loading. As the number of cycles increases, plastic accumulation will cause hull stiffened plates to fracture or reach a shakedown state. When the Chaboche model is adopted, the plastic accumulation speed of hull stiffened plates under cyclic loading is the slowest, and the decrease in ultimate strength is the most moderate. For the cyclic load amplitude and pattern selected in this study, when plastic accumulation causes stiffened plates to fracture, its ultimate strength drops to 24–55% of the first compressive ultimate strength.

Low-cycle fatigue behaviour and fracture feature of stainless-clad bimetallic steel

The stainless-clad (SC) bimetallic steel that is manufactured by metallurgically bonding stainless steels as cladding metal and conventional mild (CM) steel as substrate metal, is a kind of advanced steel with low cost, high strength and outstanding corrosion-resistant performance. Such advanced steels are especially competitive in the application of engineering structures with demands of high corrosion resistance. Unfortunately, the cyclic behaviour of the SC bimetallic steel is different from that of CM steel or stainless steel, and the research work on the SC bimetallic steels from material level to structural design level for the applications in structural engineering field is very limited. Therefore, this paper aims to investigate the low-cycle fatigue behaviour of the SC bimetallic steel made by hot roll bonding of austenitic stainless steel (S31603) and CM steel (Q355B). The test adopted a constant strain amplitude cyclic loading system with strain ratios of −1 and 0, a strain rate of 0.5%·s−1 and strain amplitudes varying from 1.00% to 2.50%. The fracture feature, cyclic characteristic, stress-strain response and the influence of surface defect and strain rate are analysed herein, and the strain-fatigue life curves are fitted and predicted by adapting the Basquin-Coffin-Manson model and Kuroda model. Research outcomes show that the introduction of cladding steel could significantly improve its ductility and low-cycle fatigue life; the fatigue life of the SC bimetallic steel is generally 30% ~ 60% higher compared with the corresponding CM steel, indicating its excellent low-cycle fatigue behaviour. The low-cycle fatigue life of the two steels could be well predicted by the strain-life relationship with adapted Basquin-Coffin-Manson model and Kuroda model, and the former is indicated superior to the latter in terms of the essential meaning and applicability.

Scouring effects on lateral cyclic responses of piles in sand

The wind turbine has become an efficient way for clean energy. For offshore wind turbine in a sandy area, the monopile is a widely used foundation type under proper water depths. During the life time, monopiles are subjected to millions of cyclic loads from winds and waves and scouring around the pile is a common phenomenon, both of which can influence the operation safety of the offshore turbine. To study the coupled effects of cyclic loading and scouring on the horizontally loaded pile, a series of horizontal monotonic and cyclic loading tests on model piles were carried out in sandy soil. The influence of pile diameter, cyclic loading amplitude, and scour depth on the long-term residual accumulated displacements of a monopile is investigated. The test results show that the deformation mode of pile and the dilatancy of sand result in different static responses of the pile. A quantised work is presented to estimate the accumulated residual displacements of the pile, in which the effects of the three factors can be expressed in a united expression. Since the lateral capacity is a crucial parameter for the normalisation in regression analysis, the confirmation of a lateral capacity should be related to the corresponding concern in practical projects.

Macro‐meso damage cracking and volumetric dilatancy of fault block‐in‐matrix rocks induced by freeze–thaw‐multistage constant amplitude cyclic (F‐T‐MSCAC) loads

AbstractIn this study, we experimentally investigated the mechanical behaviors of a fault unwelded bimrock exposed to first freeze–thaw weathering and then disturbed stress conditions. The impact of freeze–thaw damage on volumetric deformation, damage propagation, and mesoscopic instability mode was studied. Test results show that the block‐matrix interface cracking easily occurs after freeze–thaw treatment. The strain rate increases with the increase of the freeze–thaw cycle, and an early instability precursor is issued from the evolution of volumetric strain rare. In addition, a coupled evolution model considering the mechanical damage and the freeze–thaw weathering damage was defined, and it was suggested that the model pattern has obviously correlation with the occurrence of freeze–thaw damage. Moreover, posttest CT scanning revealed the influence of freeze–thaw on meso‐cracking and volumetric dilatancy pattern. It is found that the block contact, interlocking, occlusion, and separation contribute a lot to bimrock volumetric expansion.

Study on Multisize Effect of Mining Influence of Advance Speed in Steeply Inclined Extrathick Coal Seam

Abstract Aiming at the multisize effect of mining in steeply inclined extrathick coal seam, taking the fully mechanized top-coal caving mining in B3+6 coal seam +425 level in the south of Wudong coal mine as the background, this paper studies the mining stress evolution law under the influence of advancing speed, analyzes the mechanical characteristics of coal samples under the mining action of steeply inclined extrathick coal seam, and completes the multisize effect study of mining in steeply inclined extrathick coal seam. The results show that the stress change theory of fully mechanized top-coal caving mining in steeply inclined seam is deduced, and the loading and unloading stress of fully mechanized top-coal caving mining is positively correlated with the advancing speed of the working face. The numerical simulation experiment shows that the ideal advancing condition increases with the advancing speed of the working face, and the cyclic loading and unloading amplitude under the mining stress path increases, the cyclic times decrease, the main influence area increases, and the acting time decreases. The peak value of mining stress, the width of the plastic zone, and its elastic energy under high-speed propulsion are obviously larger. A method of mechanical behavior analysis of coal samples is proposed, which takes the mining stress path of the numerical simulation experiment as the indoor scale loading and unloading stress path of coal samples. The average compressive strength of coal samples under the mining stress path increases with the advancing speed of the working face, and the damage degree of coal samples increases with the advancing speed of different stress paths. The input strain energy of coal cyclic loading and unloading increases with the increase in the advancing speed of the stress path. The input strain energy of the coal sample has obvious linear relationship with the advancing speed of different paths. The research results can be used for reference in the study of multisize effect of mining impact of advancing speed.

Failure Rate Model of Materials under Uncertain Constant Amplitude Cyclic Load

Failure rate is an important reliability index of mechanical components. Failure rate is usually used to characterize the degradation rule of material performance under the cyclic load, which is critical to fatigue life prediction as well as reliability assessment of Ti–6Al–2Sn–4Zr–6Mo (Ti-6246) alloy. In order to reveal the probability characteristics of failure rate of Ti-6246 alloy under uncertain cyclic load, the equation of P-S-N curve is studied in this paper. Firstly. The probability density function for fatigue life under uncertain cyclic loading is derived from the probability density function for external stresses. A probabilistic model for the failure rate is then presented based on the basic assumptions. It is assumed that the failure rate and fatigue life of the material depend on the same damage state. Finally, the validity of the proposed model is verified by the Ti-6246 alloy fatigue test. The results show that the fatigue life of Ti-6246 alloy is more affected by material parameters (internal factors) than stress (external factors) under uncertain constant amplitude cyclic loading.

Study seismic performance of duplex stainless steel under large strain amplitude by cyclic loading test

The existing experimental data on stainless steel are limited to a small strain range (<1.50%), which is not enough to analyze the response of stainless steel structures in large plastic strain under a strong earthquake. This paper presents cyclic loading tests containing constant and variable strain amplitude up to 5.0% to study the low-cycle fatigue properties of duplex stainless steel S2205. The cyclic skeleton curve and the fatigue life equation are established and the hysteretic behavior and cyclic hardening-softening characteristics are discussed. The analyzed results show that steel S2205 exhibits a nonlinear stress-strain relationship with high yield strength and good ductility. The hysteresis loops of the material are plump and the equivalent viscous damping ratio is about 0.5 at strain of 5.0%, indicating a good energy dissipation capacity. Under constant amplitude cyclic loading, steel S2205 exhibits cyclic hardening in the first few fatigue cycles and then undergoes prolonged cyclic softening until fracture. The plastic strain energy-life model is found to be appropriate for fitting the low-cycle fatigue life equation. Furthermore, the parameters of the cyclic constitutive model are derived, providing basic data for seismic analysis of duplex stainless steel structures under large plastic strain values.

Effects of anisotropy and pre-strain on the shear fatigue behaviour of DP600 steel

The effects of anisotropy and pre-strain on the low-cycle-fatigue properties of DP600 steel sheet under shear path were investigated. Fully reversed strain-controlled fatigue tests were performed along the 0° and 90° directions with the initial strain direction. The cyclic-loading amplitude determined whether the pre-strained material had a hardening process. The high dislocation density in the crystals of pre-strained material can promote the formation of low-energy substructures, obviously accelerating the cyclic-softening rate and reducing the fatigue life. Average plastic strain energy density was affected by the pre-straining state and loading direction and had a linear relationship with the strain amplitude. Overall, these results can be used to verify the calculation model of structural parts.