Cyclic Wave Loading Research Articles

Full-scale fatigue tests of precast reinforced concrete slabs for railway tracks

This paper describes the experimental part of a research project on the fatigue behavior of precast reinforced concrete slabs for high-speed railway slab track systems, based on the Japanese Shinkansen system. First, characterization tests on the materials and the fastening system were performed, including compressive fatigue tests over cubic specimens carried out in order to get the fatigue parameters involved in probabilistic models of fatigue. Second, three-point bend fatigue tests on the full-scale slabs were conducted. The slabs were placed on two rubber supports, the cyclic sine wave load was applied on its middle section through two rails. The loading frequency was 1.5Hz, the maximum and the minimum load were 220kN and 22kN, respectively. The number of cycles was set 106. Third, the loss of stiffness of the slabs was presented before and after the fatigue tests, and its evolution monitored throughout them. The displacement development of the middle section of the slabs under the maximum load was also stored and plotted in order to calculate the secondary displacement rates. These data enabled us to predict the number of cycles to failure of any concrete slab with only knowing its secondary displacement rate. Furthermore, the damage (cracks) was marked in the slab to show the failure pattern. The testing procedure leads to the mechanical deterioration of the slabs with only 106 fatigue cycles, while reproducing the actual loads would result in longer and more expensive tests. The results allow us to check resistance of the slab design and could be employed to validate numerical models with fatigue failure criteria.

Wave-induced seepage and its possible contribution to the formation of pockmarks in the Huanghe (Yellow) River delta

Wave-induced seepage and its possible contribution to the formation of pockmarks in the Huanghe (Yellow) River delta were investigated experimentally and numerically. Laboratory experiments were carried out to explore the response of a layered silty seabed with various saturation conditions under cyclic wave loads, in which the pore pressure and seepage-related phenomena were particularly monitored. Numerical models to simulate wave-induced seepage in the seabed were presented and evaluated, then applied to the Huanghe River delta. The experimental results show that the excess pore pressure decreases more rapidly at the surface layer, while the seepage-related phenomena are more pronounced when large cyclic loads are applied and the underlying layer is less saturated. The proposed numerical models were verified by comparing with the experiments. The calculated seepage depth agreed well with the depth of the pockmarks in the Huanghe River delta. The experimental and numerical results and the existing insitu investigations indicate that the wave-induced seepage may be a direct cause of the pockmarks in the Huanghe River delta. Extreme storm waves and the dual-layered structure of hard surface layer and weak underlying layer are essential external and internal factors, respectively. Wave- or current-induced scour and transport are possible contributors to the reformation of pockmarks at a later stage.

Nonlinear interaction between wave, breakwater and its loose seabed foundation: A small-scale case

In offshore environment, newly deposited quaternary loose sediments widely exist in the world. Sometimes, coastal engineers cannot avoid choosing these natural loose sediments as the foundation of marine structures. Under this situation, the interaction between ocean wave, marine structures and their loose sand foundation, and the wave-induced pore pressure built-up in loose seabed foundation are the key factors in which coastal engineers would most concern. In this study, the nonlinear interaction mechanism between ocean wave, a composite breakwater and its loose elasto-plastic sand bed foundation is investigated by utilizing a semi-coupled numerical model FSSI-CAS 2D. In the coupled numerical model FSSI-CAS 2D, VARANS equation for wave model, and dynamic Biot׳s equation for soil model are used for the governing equations. The advanced and excellent elasto-plastic constitutive model PZIII proposed by Pastor et al. (1990) is adopted to describe the nonlinear dynamic behavior of loose sand soil under cyclic wave loading. Taking the parameters of Neveda sand determined in the VELACS project funded by NSF as the property parameters for the loose sand bed, a small-scale computational case like the experimental set-up in Mostafa et al. (1999) is taken as a representative case to investigate the wave-structure-loose seabed foundation interaction mechanism. The numerical results indicate that the pore pressure in loose seabed foundation builts up significantly, and the marine structure subsides and tilts under wave loading. The loose sand bed becomes denser and denser due to soil compaction. Parametric studies show that both the wave characteristics and the soil properties can affect the built-up of residual pore pressure in loose seabed foundation.

Stability Analysis of the Semi-Circular Guiding Dike

A quasi static finite element method for assessing cyclic bearing capacity of semi-circular guiding dike on natural or reinforced soft clay foundation is developed by combining the concept of cyclic shear strength with D-P yield criterion. Then the proposed method is numerically implemented in the framework of the large universal finite element software. Combining with a practical engineering, the stability of semi-circular guiding dike before and after foundation reinforcement is analyzed. The results showed that the foundation bearing capacity decreases obviously when cyclic weakening effect of soft foundation was considered, so cyclic weakening effect of soft foundation under cyclic wave load should be considered in practical design. Moreover, foundation reinforcement has an obvious effect to increase foundation bearing capacity.

Failure Characteristic of Granite under Cyclic Loading with Different Frequencies

The uniaxial cyclic fatigue tests on granite coming from the ChangJiang of Hainan nuclear power first-stage construction conventional island were done on the RMT-150B multi-function automatic rigid rock servo material testing machine. Stress amplitude of 10 MPa and sine wave cyclic loads with five different frequencies of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 Hz were adopted as dynamic disturbance. The law between cyclic frequency and dynamic stress-dynamic strain hysteretic curve, dynamic elastic modulus and damping ratio are researched. The results showed that the curves of strain and stress for loading and unloading are not superposition under cyclic loading, but hysteretic loops. When cyclic frequency changes between 0.01 and 1.0 Hz, the granite hysteretic loop area, dynamic elastic modulus and damping ratio are increased with frequency increasing. The research result offered great reference value to seismic response analysis and site safety evaluation of the changjiang nuclear power.

Quantitative Characteristic of Meso-Damage Granite under Cyclic Loading with Different Frequencies

The failure damages of granite under cyclic fatigue load were caused by the propagation and coalescent of cracks at mesoscale, so it was helpful to understand the mechanical behaviours of rock by quantitatively investigating on meso-damage of granite. Stress amplitude of 10 MPa and sine wave cyclic loads with five different frequencies of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 Hz were adopted as dynamic disturbance. Then, the microtest (SEM) is carried out to study its fractography morphology and the meso-structural images of marble were processed by regional growing theory based on image processing technique. The meso-damage information of granite microcracks was obtained from SEM images. Quantitative analysis of meso-damage characteristics under cyclic fatigue load wase made from angle, length, width and area. The results showed that with the frequency of cyclic load increasing, the dispersion of microcrack growth azimuth value increased and the average of microcrack growth azimuth value fluctuated in the range. It is great helpful for seismic response analysis of the nuclear power factory in Chang Jiang.

Mesoscopic damage quantification research of the deformation and failure of granite under circulatory load with different frequencies

The failure damages of granite under cyclic fatigue load were caused by the propagation and coalescent of cracks at mesoscale, so it was helpful to understand the mechanical behaviours of rock by quantitatively investigating on meso-damage of granite. The uniaxial cyclic fatigue tests on granite coming from the ChangJiang of Hainan nuclear power first-stage construction conventional island were done on the RMT-150B multi-function automatic rigid rock servo material testing machine. Stress amplitude of 10 MPa and sine wave cyclic loads with five different frequencies of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 Hz were adopted as dynamic disturbance. The law between cyclic frequency and dynamic stress-dynamic strain hysteretic curve, dynamic elastic modulus and damping ratio are researched. Then, the microtest (SEM) is carried out to study its fractography morphology and the meso-structural images of marble were processed by regional growing theory based on image processing technique. The meso-damage information of granite microcracks was obtained from SEM images. Quantitative analysis of meso-damage characteristics under cyclic fatigue load wase made from angle, length, width and area. The results showed that the curves of strain and stress for loading and unloading are not superposition under cyclic loading, but hysteretic loops. When cyclic frequency changes between 0.01 and 1.0 Hz, the granite hysteretic loop area, dynamic elastic modulus and damping ratio are increased with frequency increasing; with the frequency of cyclic load increasing, the dispersion of microcrack growth azimuth value increased and the average of microcrack growth azimuth value fluctuated in the range. The development of microcrack length was fast, but only when the frequency was 1 Hz, the microcrack width began to develope and the method of energy dissipation changed. The research result offers great reference value to seismic response analysis and site safety evaluation of the nuclear power factory in ChangJiang.

Characteristics of Excess Pore Water Pressure of Nanjing Saturated Fine Sand Under the Interaction of Wave and Earthquake Loading

A stress path with continuous rotation of the principal stress direction and continuous alteration of amplitude of deviatoric stress difference under the interaction of wave and earthquake loading was proposed based on the characteristics of the stress path under wave and earthquake loading, respectively. Using a GDS dynamic hollow cylinder apparatus, a series of cyclic triaxial-torsional coupling shear tests were performed on Nanjing saturated fine sand via the stress path mentioned previously under different relative densities, effective initial confining pressures, plastic fines contents, and loading frequencies to study the development of excess pore water pressure (EPWP) of saturated sand under the interaction of wave and earthquake loading. It was found that the development of EPWP follows the trend of fast-steady-mutative-drastic, which is different from that under the cyclic triaxial test or wave loading. The number of cycles causing initial liquefaction (NL) of saturated sand increases remarkably with relative densities. However, the relationships between NL and effective initial confining pressures, plastic fines content, or loading frequencies are more complex.

Field Tests and Observation of Wave-Loading Influence on Erodibility of Silty Sediments in the Huanghe (Yellow River) Estuary, China

(1) Simulations of wave action and erosion, using a wave-producing device and a recirculating flume, were established on the Haigang mudflat, in the Yellow River estuary, China, along with the geotechnical-parameter tests of the water content, bulk density, undrained shear strength, penetration strength, and grain-size distribution. Moreover, the variety of seabed morphological characteristics under different wave actions was also observed in field. The experimental results showed that the erodibility of the silty sediment was significantly affected by the cyclic wave loading in Yellow River estuary. The erodibility varied with the changing wave loading and was closely related to the liquefaction and topography characteristics of the surficial sediment, which restricted the physical and mechanical properties of the sediment. Additionally, the wave loading transformed the sediment components and the size grading, which also had a remarkable effect on the erodibility. Increasing the length of the time vibration during wave loading clearly reduced erosion resistivity, although fluctuations appeared in the overall downward trend, consistent with the strength indexes of the silty sediment. The other geotechnical parameters, size grading, and sediment components show the wave's dynamic variation with the changing conditions, but no clear internal relationship could be found between the varying physical parameters and the variation in erosion during the changing conditions of the wave during the experiments.

A wave flume experiment for studying erosion mechanism of revetments using geotextiles

Unfavorable erosion to a revetment can affect the stability of the bank and may jeopardize the safety of adjacent structures, thus improvement work is needed to increase the stability of the revetment as well as reducing the possibility of failure. The use of geotextiles as a protection material for banks is not only environmentally friendly, but also stable in the long run. However, improper design of geotextiles may cause considerable loss of soil, which might result in failure. The actual flow behavior in revetments using geotextiles is rather complicated and can be categorized into three zones, namely, the uni-directional flow zone, the cyclic flow zone, and the tangential flow zone. In this study, a wave flume experiment was performed on model revetments using two kinds of geotextiles as the filter material to prevent erosion induced by cyclic flows. Soil migration behaviors were monitored. Furthermore, two kinds of cover blocks, riprap and concrete blocks, were carefully placed on the revetments in order to avoid puncture and abrasion of geotextiles during construction of revetments. The main purpose of this study is to elucidate the erosion control and filtration performance of soil-geotextile filtration systems under wave action. Two nonwoven needle punched geotextiles were tested. The geotextiles both have the same characteristic opening size, but have a different number of constrictions and different structures. One is a thin double-layer nonwoven material consisting of continuous filaments and the other is a thick one-layer nonwoven material consisting of short fibers. The test result reveals that two different erosion mechanisms occur during wave action. The cyclic wave loadings triggered higher excess pore-water pressure in the upper part of the model and resulted in soil collapse. The geotextile with a higher number of constrictions produced more serious collapse than that with a lower one. At the middle part of the revetments, soil was eroded by the up-and-down drag force of the flow along the bank. In this zone, the thick geotextile displayed better performance in retarding the drag force on the soil surface. In addition, the opening size and thickness of the geotextile as well as the coverage condition provided by the geotextile were the key factors controlling soil erosion.

Shakedown limit of elastic–plastic offshore structures under cyclic wave loading

This paper uses theorem of shakedown to assess the shakedown limit of elastic–plastic offshore structures. For this aim, an envelope of elastic response of the structure to cyclic loading cases is required. The shakedown limit is basically a valid collapse mechanism and can be quantified using yield line analysis. In this work, Melan theorem of shakedown (lower bound) is employed. Requiring simple elastic envelope and the domain defining yield lines only are the advantages of the Melan theorem. The shakedown analysis can be conducted by the finite element method (FEM), which is the main body of this paper. In order to evaluate the method of this paper, which is in fact combining the Melan theorem and the FEM, two steel offshore frames are analyzed using the proposed method and the results obtained are compared with the results of classical non-linear analysis method.

Shear effects in shakedown analysis of offshore structures

In this paper, a formulation for shakedown analysis of elastic-plastic offshore structures under cyclic wave loading is presented. In this formulation, a fast numerical solution method is used, suitable for the Finite Element Method (FEM) analysis of large offshore structures on which shear effects in addition to bending and axial effects are taken into account. The Morison equation is adopted for converting the velocity and acceleration terms into resultant forces and it is extended to consider arbitrary orientations of the structural members. The theoretical methods of the shakedown analysis are discussed in detail and the formulation is applied to an offshore structure to verify the concept employed and its analytical capabilities.

Strength and elastic properties of sandstone under different testing conditions

A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties (elastic modulus and Poisson ratio) under different conditions and influence of pore fluid on them. When the loading strain rates are 10−5, 10−4 and 10−3/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress (strain) to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and Poisson ratio display asymmetric ‘X’ shape with various strain, and the average unloading modulus is larger than the average loading modulus.

State-space solution of seabed–geotextile systems subjected to cyclic wave loadings

Analytical solutions for dynamic responses of seabed–geotextile systems subjected to cyclic wave loadings are presented in this paper, which contains the solutions of the transient and harmonic responses. The theory is based on the Biot consolidation equations in which the pore fluid as well as the soil skeleton is considered compressible and the flow in the porous seabed is assumed governed by Darcy's law. The present analysis is completely based on the state-space formulations, which is very effective for laminated systems analysis. Together with Laplace–Fourier transform techniques, state-space methods are used to solve the governing equations. Responses of seabed–geotextile systems can be calculated by using the matrix theory, boundary conditions and inverting integral transform. As illustrative examples, laboratory experiments, which conducted at the Oregon State University Wave Research Facility in USA by McDougal [1981. Ocean wave–soil–geotextile interaction. Ph.D. Dissertation, Oregon State University], are analysed. It is shown that the numerical results are in good agreement with those obtained from laboratory experiments, and the distinction between the transient and harmonic response should be taken into account for design of marine geosynthetic systems. Under the transient condition, the seabed is apt to liquefy. Seabed stability may be increased by placing geotextile beneath an armour layer. The numerical evaluations of the solution in the seabed–geotextile systems can be easily achieved with high efficiency and accuracy.

Interface Load Transfer Degradation During Cyclic Loading: A Microscale Investigation

The shaft capacity of piles in sand subjected to cyclic (wave) loading has been observed to decrease significantly with loading cycles (Poulos, 1989). A number of researchers (Boulon and Foray, 1986; Tabucanon et al., 1995; Shahrour et al., 1999) have replicated the characteristics of the load transfer degradation behavior in the laboratory through cyclic interface shear testing with a constant normal stiffness confinement condition (Vesic, 1972). However, no consensus currently exists as to the primary microscale mechanisms that govern cyclic interface shear behavior and load transfer degradation. A research program was undertaken to quantify the contribution of soil properties, cementation, confinement condition, and displacement mode, in load transfer degradation. Monotonic and cyclic interface shear tests were performed using a modified interface direct shear device with a Perspex side window. The specimen particle displacement fields were quantified during selected cycles by capturing high resolution digital images (1600 x 1200 pixels) and using Particle Image Velocimetry (White et al., 2001a). Results indicate that the confinement condition, which is intended to replicate the elastic response of the far-field soil, is of primary importance as it allows for normal stress relaxation with soil contraction adjacent to the interface. The displacement magnitude, particle characteristics, and particle-particle cementation were also observed to affect the magnitude and rate of degradation. It is anticipated that these findings will provide a fundamental rationale to identify field conditions where shear stress degradation is likely to occur and a basis from which more rigorous models may be developed.

Erosion stability of punctured geotextile filters subjected to cyclic wave loadings—a laboratory study

The alternating flow through the geotextile filter creates a cyclic flow regime quite unlike the uni-directional flow that has been extensively studied. Most of the filter design criteria and codes are based on tests from uni-directional flow conditions, which may not truly reflect the cyclic flow of in situ tidal conditions. A new laboratory apparatus has been used to investigate the influence of the hydraulic conditions on the behavior of soil-geotextile interaction and the stability of the coastal revetment system. This apparatus is capable of simulating cyclic flow conditions normal to the soil-geotextile interface. In this study, a series of tests were conducted with geotextile specimens with pre-cut L-shaped holes of different size, to simulate the punctured holes on the geotextile filter caused by installation damage. Various overburden pressures (0, 25, 110 kPa) and different periods of wave (2, 5, 7, 10 s) and different geotextiles, nonwoven (NW1, NW2) and woven (W1), were employed in this tests series. Results show that a given geotextile, with holes up to a certain critical size, can still perform satisfactorily if soil arching can be fully developed. It will be stable under certain cyclic wave load of a specific wave period. The geotextile filter with punctured holes can form a stable filter, and the presence of punctured holes in the geotextile filter does not imply failure of the revetment system if they are smaller than the critical size. The critical size of the pre-cut hole, before the filtration function was impaired, was found to be a function of the geotextile properties, wave period, cycles of wave load applied on to the soil for a given soil type under retention.

Experimental Investigations of Response of Suction Caissons to Transient Vertical Loading

Suction caissons are a relatively new design being considered for use as foundations in a wide variety of offshore applications. They are unusual in that, in contrast with the development of offshore piling, there is no onshore experience that can be used as the basis for the development of designs. It is therefore essential to identify key behavioral patterns and mechanisms that govern capacity under a wide variety of loading regimes, particularly those derived from the cyclic wave loading. The object here is to establish a broad framework of response. More detailed work specific to a site or project would be required for detailed design. This paper describes experimental investigations into the vertical loading response of a suction caisson foundation. The experiments are carried out on the laboratory floor using a sophisticated three-degree-of-freedom loading rig. The caissons are embedded in sand saturated with viscous silicon oil so that modeled drainage times are representative of typical offshore conditions. The experiments involve cyclic loading about different mean loads, including cycling into tension and monotonic loading at different rates. The relationship between the cyclic loading and monotonic loading is explored. One of the key conclusions from the results is that serviceability requirements will dictate design rather than capacity. Perhaps surprisingly, for the experiments undertaken, the rate of loading had little effect on the response.

Micromotion and dynamic fatigue properties of the dental implant–abutment interface

Statement of problem. Clinical loading may result in micromotion and metal fatigue in apparently stable implant screw joints. This micromotion may contribute to tissue inflammation and prosthesis failure.Purpose. This study investigated dental implant screw joint micromotion and dynamic fatigue as a function of varied preload torque applied to abutment screws when tested under simulated clinical loading.Material and methods. Fifteen noble alloy single-tooth implant restorations, each containing a hexed UCLA-style gold cylinder, were randomly assigned to 3 preload groups (16, 32, and 48 N·cm). Each group consisted of 5 implants (each 3.75 × 15 mm) and 5 square gold alloy abutment screws. A mechanical testing machine applied a compressive cyclic sine wave load between 20 and 130 N at 6 Hz to a contact point on each implant crown. A liquid metal strain gauge recorded the micromotion of the screw joint interface after 100, 500, 1,000, 5,000, 10,000, 50,000, and 100,000 cycles. Baseline data at 0 N·cm were collected before the application of the specified preload torque.Results. The 16 N·cm group exhibited greater micromotion (P<.001) than both the 32 and 48 N·cm groups at all cycle intervals (2-way ANOVA, Tukey HSD). Micromotion of the implant-abutment interface remained constant (P=.99) for each of the preload groups through 105 cycles.Conclusion. Under the loading parameters of this study, no measurable fatigue of the implant–abutment interface occurred. However, dental implant screw joints tightened to lower preload values exhibited significantly greater micromotion at the implant–abutment interface. (J Prosthet Dent 2001;85:47-52.)

Fatigue crack growth in stiffened steel tubular joints in seawater environment

Welded steel tubular structures commonly used for offshore platforms are susceptible to fatigue failure due to stress concentration at welded joints and environmental loading which is cyclic in nature. Offshore structures contain flaws ranging from microscopic material defects to macroscopic geometric imperfections, due to fabrication and construction process. Such flaws can develop into cracks due to influence of cyclic wave loading in an aggressive marine environment. Due to this and many other causes, maintaining structural integrity of these structures has been a major concern for the oil industry. Hence a model for crack initiation life and crack growth life estimation has been developed by conducting constant amplitude corrosion fatigue tests on internally ring-stiffened steel tubular T and Y joints under freely corroding conditions. Biologically inert synthetic seawater was used as the corrosive environment. Tests in seawater were carried out with a loading frequency of 0.2 Hz. The studies were made with respect to tropical environment similar to Indian offshore. The corrosion fatigue crack growth data obtained during the tests and the Fracture Mechanics (FM) model developed are discussed in this paper.

Effects of Impurities on Environmentally Assisted Crack Growth of Solution-Annealed Austenitic Steels in Primary Water at 325°C

Abstract Effects of impurities (Si, P, and S) in steel on environmentally assisted cracking (EAC) behavior of solution-annealed austenitic steels in pressurized water reactor (PWR) primary water at 325°C were investigated. The basic chemical composition of the steels was 12% Cr-28% Ni, simulating the grain boundary (GB) composition of irradiated Type 304 (UNS S30400) stainless steel. The EAC crack growth behavior of the steels was examined by performing trapezoidal wave cyclic loading testing on precracked specimens. Results showed that Si significantly affected the EAC by promoting intergranular cracking, with only 0.48% Si promoting almost fully intergranular cracking under trapezoidal wave loading; increasing the crack growth rate; and tending to make cracking easier in the near-surface region rather than in the center of specimens. Only transgranular cracking with relatively low crack growth rates took place in the steels without Si but doped with S and P, respectively. The stress corrosion cracking (...