One-way Cyclic Loading Research Articles

単純梁方式曲げ試験によるSC杭の中空部に中詰めした効果の検討

The objective of this study is to examine the concrete filled effect in the hollow part of SC pile in order to improve the deformation performance of pile. In the pile foundation structure, the improvement is prompted, assuming secondary seismic design. But, Study on the deformation capacity of precast concrete pile is not sufficiently advanced. The bending tests of plie are carried out on a daily basis for performance assessment. The purposes of the test is the confirmation of the flexural strength. Therefore, the test data accumulation is not enough to discuss the deformation performance of pile. This study focuses on the SC pile in precast concrete pile. The SC pile is a cylindrically shaped member manufactured by centrifugal casting with concrete placed in the hollow section of a steel pipe. The SC pile is a composite pile that utilizes the merits of concrete with good resistance against compressive forces and steel shell with good resistance to tensile forces. Concrete prevents local buckling of the steel pipe, while the steel pipe constrains concrete; therefore, the SC pile has excellent flexural bearing capacity and deformation capacity. This study examined effects of some parameters for deformation performance of the SC pile by the simple beam bending test. Four parameters are set for the test. The parameters are 1) Loading method, 2) Steel pipe thickness, 3) Axial force, 4) Infilled material. We observed the failure conditions, relations between the load and the displacement, and relations between the bending moment and the curvature. The knowledge obtained from this study are shown below. 1) Reinforced by infilling the hollow part of the pile with material, the following effects can be expected: prevention of depression of the steel pipe, prevention of flaking or crush of the pile body concrete, and improvement of the bending deformation performance of the pile. It is more effective to use infilled material with high Compressive strength and high Elastic modulus. 2) The results of bending tests of piles, maximum flexural strength and maximum curvature, are influenced by loading method. The results obtained by the one-way cyclic loading are greater than those obtained by the peak-to-peak alternate cyclic loading. Test value obtained by the one-way cyclic loading is on dangerous side as the evaluation of the deformation performance of the pile. Therefore, it is desirable to adopt the peak-to-peak alternate cyclic loading for appropriate evaluation of the deformation performance of the pile. 3) It is effective to increase the thickness of the steel pipe for the improvement of the flexural strength of the pile. But, it is not effective to increase the thickness of the steel pipe for the improvement of the deformation performance of the pile. 4) With respect to the maximum value of curvature, the test value of the standard specimens is not more than the analysis value. The test value of the test specimen that was reinforced with soil cement is about equivalent to the analysis value. The test value of the test specimen that was reinforced with concrete is greater than or equal to the analysis value.

Linkage between static and cyclic liquefaction of loose sand with a range of fines contents

The underlying mechanism of static and cyclic liquefaction of loose contractant sandy soil is unstable behaviour associated with deviatoric strain-softening. Such unstable (strain-softening) behaviour has been referred to as static or cyclic instability depending on whether the loading condition is monotonic or cyclic. Past research into linkage between static instability and cyclic instability of sand with fines is based largely on comparing monotonic and one-way cyclic loading behaviour of specimens of the same void ratio and fines content. In this article, the authors attempt to link the condition that defines triggering of cyclic instability to that of static instability of specimens of different void ratios and fines contents. This is achieved by the proposed concept of equivalent granular state parameter. Two specimens are considered as equivalent if they have the same equivalent granular state parameters at the start of undrained shearing. The effective stress ratio at triggering of static instability can be used to predict impending cyclic instability of an equivalent specimen of different fines content and void ratio. This linkage between static and cyclic instability was evaluated for a wide range of fines contents, initial mean effective stresses, and types of cyclic loading. The last factor includes symmetrical and nonsymmetrical two-way cyclic loading.

Time homogenization for clays subjected to large numbers of cycles

This paper discusses the reliability and the efficiency of a time homogenization method employed to reduce the computational time during cyclic loading for two common geotechnical tests and two elastoplastic models for clays. The method of homogenization is based upon splitting time into two separate scales. The first time scale relates to the period of cyclic loading and the second to the characteristic time of the fatigue phenomenon. The time homogenization method is applied to simulate an undrained triaxial test (homogeneous stress state) and a pressuremeter test (nonhomogeneous stress state) under one-way cyclic loading on normally consolidated clay. This method is coupled with two elastoplastic models dedicated to cyclic behavior of clay (a bounding surface plasticity model and a bubble model). Both linear and nonlinear elasticities are considered. The difficulty encountered when applying this method to models introducing nonlinear elasticity and kinematic hardening is pointed out. The performance of time homogenization related to the main parameters is numerically investigated by comparison with conventional finite element simulations.

Field investigation of axial monotonic and cyclic performance of reinforced helical pulldown micropiles

Helical piles are used increasingly to support new and existing foundations. This paper presents a field study on the axial monotonic and cyclic behaviour of steel fibre–reinforced helical pulldown micropiles. Test piles consisted of a round corner square helical pile with three helices attached to it, and a steel fibre–reinforced grout shaft. To assess the grout shaft contribution, one helical pile without a grout shaft was tested. Piles were instrumented with strain gauges to evaluate the load-transfer mechanism. This paper discusses the load–displacement response of this pile system, and load-sharing mechanism between the grout shaft and lead section. The study shows that the grout shaft significantly improves the helical pile axial performance. It was found that the load-transfer mechanism within the lead section is through individual bearing of each helix. Also, the findings demonstrate that the behaviour of this pile system is satisfactory under one-way cyclic loading conditions. The results suggest that the reinforced helical pulldown micropile is a viable deep foundation option for axial monotonic and one-way cyclic loading applications.

Study on Characteristic of Saturated Soft Clay under one-Way Cyclic Loading

Simulating traffic loading, the high liquid limit clay specimens and the low liquid limit clay specimens of the Pearl River delta are engaged in cyclic triaxial tests under one-way cyclic loading respectively. The influence of axial stress, confining stress and plasticity index are taken into account. A critical dynamic stress ratio of saturated soft clay under one-way cyclic loading and the variations of axis strain and pore pressure with number of cycles were obtained. The conclusions are helpful to compute the settlement of saturated soft foundation under traffic loading after work.

Experimental Investigation of Recron3s Fiber-reinforced Hybrid Ferrocement Hollow Slabs

The limit state of serviceability of deflection and cracking is verified for recron3s fiber-reinforced ferrocement hollow slabs with mesh and skeletal reinforcements. About nine slabs are considered for the investigation. The slabs were subjected to one-way cyclic loading by applying two line loads at one-third span. A theoretical model is developed for the deflection of recron3s fiber-reinforced ferrocement hollow slabs and it is validated by the experimental data. The experimental results are very close to the analytical values, especially at the service load, and it is established that such slabs satisfy the serviceability requirements of deflection and crack width as specified by the Ferrocement Model Code.

Accumulated Deformation of Sand with Initial Shear Stress and Effective Stress State Lying Near Failure Conditions

This study concerns the development of residual deformations in soil subjected to static shear and cyclic stress components. This problem plays an important role in such situation as natural slopes, slopes of embankments and dams, quay walls. Among them, the present study focuses in particular on cyclic undrained behavior with static shear stress. Furthermore, in the case of structures with static shear stress and subjected to the earthquake shaking, the forces acting in the shear plane are generally one-way cyclic loading without reversing its direction. Experimental research was focused on the accumulation of shear strain in the soil element during one-way cyclic loading (torsional stress loading only on positive or negative side). Series of torsional shear tests on hollow cylindrical specimens of Toyoura sand with relative density of 40% and 60%, with isotropic stress condition under effective pressure of 98 kPa, 196 kPa and 294 kPa as well as anisotropic conditions were made in order to investigate the incremental shear strain per cycle during cyclic loading. The level of static shear stress was set equal to half of the ultimate stress under drained conditions (factor of safety equal to two). The experimental results showed that the presence of static shear stress increases the resistance of sandy soil. The experimental results of the shear strain increment per cycle and the number of cycles were plotted in a logarithmic scale to show a linear relationship with each other. Based on these findings a simple model for prediction of shear strain was developed.

Degradation model for one-way cyclic lateral load on piles in soft clay

Abstract The analysis of laterally loaded piles in soft clay is carried out idealising the pile as beam elements and the soil by nonlinear inelastic spring elements modeled with elasto-plastic sub-elements. The nonlinear hyperbolic model for static load condition is developed based on the undrained shear strength and modulus of subgrade reaction. An iterative procedure is adopted to perform a nonlinear finite element analysis and the effect of static lateral load on deflection is studied. Based on the lateral deflection at the end of first cycle (static load), the degradation factor is assumed and the p-y curve is modified. The cyclic load analysis is carried out using the static analysis program idealising the soil by modified p-y curve, which considers the effect of number of cycles and magnitude of cyclic lateral load. The results of the proposed analytical model compare well with the published experimental results, on piles subjected to one-way cyclic loading for different magnitude of cyclic lateral load and number of cycles.

Cyclic direct simple shear testing of a Beaufort Sea clay

Results are presented for undrained direct simple shear tests on a Beaufort Sea cohesive soil. Monotonic and one-way cyclic loading response characteristics are identified for a number of loading scenarios. The critical level of repeated loadings (CLRL) is determined for two overconsolidation ratios from tests having 30 000 cycles of loading. Postcyclic strength tests indicate that one-way cyclic loadings not causing failure have a strain-hardening effect on the material. High strain-rate testing is found to increase soil strength by as much as 40% compared with typical testing strain rates. Key words : strength, cyclic testing, clay, simple shear, strain rate.

Stability criteria for marine clay under one-way cyclic loading : A. F. L. Hyde, K. Yasuhara & K. Hirao, Journal of Geotechnical Engineering - ASCE, 119(11), 1993, pp 1771–1789

Stability criteria for marine clay under one-way cyclic loading : A. F. L. Hyde, K. Yasuhara & K. Hirao, Journal of Geotechnical Engineering - ASCE, 119(11), 1993, pp 1771–1789

Pile Load Tests: Cyclic Loads and Varying Load Rates

Two series of axial load tests were performed on four 14-in. (356-mm) diam, open-end, steel pipe piles at an interval of about 320 days. Pile lengths of 40 ft or 50 ft (12.2 or 15.2 m) were installed below conductors driven to depths ranging from 115 ft to 320 ft (35 m to 98 m) into a strong underconsolidated clay. Each pile was subjected to as many as 26 tests. Data presented includes: (1) Compression and tension tests; (2) tests performed at different times after driving and after previous tests; and (3) incremental loading and constant rate of loading. Pile capacity increased 40% to 75% when the loading rate increased by three orders of magnitude. The one-way cyclic loading applied in this study did not effect the ultimate capacity, but large displacement began to accumulate when the maximum cyclic load reached 80% of the static capacity.