Vertical Cyclic Loading Research Articles

Investigation of the Load-Sharing Mechanisms of Suction Buckets during Vertical Cyclic Loading in Layered Soils

Investigation of the Load-Sharing Mechanisms of Suction Buckets during Vertical Cyclic Loading in Layered Soils

Weakening characteristics of pile group foundations in clayey soil under vertical cyclic loading: Experimental and numerical investigation

Long-term cyclic loading can substantially reduce the bearing capacity of pile foundations, potentially compromising the structural integrity of offshore foundations. A small-scale model test system for vertical cyclic loading of pile foundations is independently designed. Model experiments and numerical simulations were conducted to investigate the weakening characteristics of four foundation types (i.e., slab foundation, single pile with cap, 2 × 2 pile group foundation, and 3 × 3 pile group foundation) in clayey soil under cyclic loading. The results of both methods demonstrate that 3 × 3 pile group foundations exhibit the greatest resistance to deformation, followed by 2 × 2 pile groups, single piles with a cap, and slab foundations under cyclic loading. Furthermore, a 3D numerical model was developed to simulate the real-world behavior of a pile group foundation for an offshore wind turbine. Results reveal that although the ultimate compressive bearing capacity decreases with higher cyclic loading levels, typical cyclic loads (0.1–0.2) encountered in practice do not greatly affect the long-term bearing capacity of the foundations. The proposed experimental and numerical simulation methods offer valuable insights into the weakening characteristics of pile group foundations under cyclic loading.

Dynamic behavior of kaolin clay under bidirectional cyclic loading for suction bucket foundation

The stability of offshore wind turbine (OWT) foundations is largely influenced by the dynamic characteristics of marine clay. In offshore engineering, marine clays may exposed to bidirectional cyclic stresses. To empirically examine the influence of different cyclic stress magnitudes on the dynamic characteristics of marine clay at different depth, a sequence of dynamic triaxial tests is conducted on marine kaolin clay, encompassing diverse values of the cyclic stress ratio (CSR) and effective confining pressure (p'0). Some valuable inferences have been drawn: At low cyclic stress ratios (CSR≤0.3), the axial strain (εa), stiffness (k), and excess pore water pressure (EPWP) of the specimen exhibit logarithmic increase, logarithmic decrease, and logarithmic accumulation, respectively. Under high cyclic stress ratio conditions (CSR＞0.3), the axial strain increases linearly, the stiffness deteriorates linearly, and the logarithmic excess pore water pressure accumulates. After analyzing the dynamic characteristics data of kaolin clay, the correlation between excess pore water pressure and axial strain was established. By analyzing the vertical cyclic mechanism of suction bucket foundation, a prediction model for suction bucket foundation under vertical cyclic loading was established based on the dynamic characteristics of marine clay and the model was validated. The comparison between the validation outcomes and the experimental outcomes shows good agreement. This study provides certain guidance for the design of suction bucket foundations for OWTs.

Evaluation of sensor-enabled piezoelectric geoelectric cable in cyclic shear tests of subgrade soil under vertical cyclic loads

Of late, deformation of subgrade soil has led to an increasing number of road subsidence diseases. Real-time monitoring of subgrade deformation is critical to ensure the safety of subgrade operations. In this paper, a sensor-enabled piezoelectric geoelectric cable (SPGC) with impedance strain effect and piezoelectric effect is tested. The SPGC impedance and voltage signals obtained by cyclic shear test under vertical static load and cyclic shear test under vertical cyclic load are used to evaluate the monitoring effect. The results showed that normal stress had the greatest effect on the shear strength of the soil, whereas the normal stress and horizontal shear displacement amplitude significantly influenced the strain in the soil. Varying the normal and horizontal shear frequencies had little effect on the shear strength and strain of the soil. The normalized impedance and voltage of the SPGC, respectively, decreased and increased rapidly during the initial stage of the shear cycle; these changes were relatively small during the middle and late stages of the shear cycle. The SPGC voltage waveform revealed the changes in the shear stress and vertical displacement under different normal and horizontal shear frequencies, from which the stability of the subgrade soil under the aforementioned conditions could be evaluated. The variations in the SPGC impedance and effective voltage from the cyclic shear tests under both vertical static and vertical cyclic loads remained essentially consistent with the number of cycles. However, there was a difference in that the trough of the SPGC impedance under the vertical cyclic load was larger than that under the vertical static load; likewise, the effective SPGC voltage under the cyclic load was larger than that under the static load. Through an analysis of the SPGC impedance and voltage signals in the subgrade soil, the consistency of the SPGC-normalized impedance and effective voltage with shear stress was clarified; this helped us evaluate the health of the subgrade and monitor the characteristics of the precursor signals before a slide were to occur, thereby affording us an opportunity to issue timely warnings.

Numerical Simulation of Vertical Cyclic Responses of a Bucket in Over-Consolidated Clay

Multi-bucket foundations have become an alternative for large offshore wind turbines, with the expansion of offshore wind energy into deeper waters. The vertical cyclic loading–displacement responses of the individual bucket of the tripod foundation are relevant to the deflection of multi-bucket foundations and crucial for serviceability design. Finite element analyses are used to investigate the responses of a bucket subjected to symmetric vertical cyclic loading in over-consolidated clay. The Undrained Cyclic Accumulation Model (UDCAM) is adopted to characterize the stress–strain properties of clay, the parameters of which are calibrated through monotonic and cyclic direct simple shear tests. The performance of the finite element (FE) model combined with UDCAM in simulating vertical displacement amplitudes is evaluated by comparison with existing centrifuge tests. Moreover, the impact of the bucket’s aspect ratio on vertical displacement amplitude is investigated through a parametric study. A predictive equation is proposed to estimate the vertical displacement amplitudes of bucket foundations with various aspect ratios, based on the cyclic displacement amplitude of a bucket with an aspect ratio of unity.

Finite element method-based study for spinal vibration characteristics of the scoliosis and kyphosis lumbar spine to whole-body vibration under a compressive follower preload

Purpose To analyze the dynamic response of the lumbosacral vertebrae structure of a scoliosis spine and a kyphosis spine under whole-body vibration. Methods Typical Lenke4 (kyphosis) and Lenke3 (scoliosis) spinal columns were used as research objects. A finite element model of the lumbosacral vertebrae segment was established and validated based on CT scanning images. Modal, harmonic response, and transient dynamic analyses were performed on the lumbar-sacral scoliosis model using the finite element software abaqus. Results The first four resonance frequencies of kyphosis spine extracted from modal analysis were 0.86, 1.45, 8.51, and 55.71 Hz. The first four resonance frequencies of scoliosis spine extracted from modal analysis were 0.76, 1.45, 10.51, and 63.82 Hz. The scoliosis spine had the maximum resonance amplitude in the transverse direction, while the kyphosis spine had the maximum resonance amplitude in the anteroposterior direction. The dynamic response in transient analysis exhibited periodic response over time at all levels. Conclusion The scoliosis and kyphosis deformity of the spine significantly complicates the vibration response in the scoliosis and kyphosis areas at the top of the spine. Scoliosis and kyphosis patients are more likely to experience vibrational spinal diseases than healthy people. Besides, applying vertical cyclic loads on a malformed spine may cause further rotation of scoliosis and kyphosis deformities.

Cyclic performance of geosynthetic-encased granular pile with tire chips and aggregates mixture in soft soil – A model study

The performance of encased granular piles subjected to heavy cyclic loading presents a significant concern in the current context. Meanwhile, global waste tire management poses a major challenge because it has a detrimental effect on the environment. To address both difficulties, this research utilizes recycled tire chips derived from end-of-life tires (ELTs) and substituting traditional aggregates in granular pile construction. This study summarizes laboratory model tests investigating the performance of geosynthetic encased granular piles designed for soft soil improvement under vertical cyclic loading. The composition of the granular pile comprised (25 % tire chips + 75 % aggregates). Various cyclic loading parameters were scrutinized, including the selection of encasement material and the best configuration for granular piles, cyclic loading frequency (f), cyclic loading amplitude (qca), length-to-diameter (L/D) ratios, granular pile end conditions, and strength of surrounding soft soil. The novel feature of this research is the evaluation of the cyclic induced settlement (Sc) – excess pore water pressure (Pexc) coupled performance for all considered factors and its effects on the encased granular piles improved soft ground under vertical cyclic loading. Key findings include ordinary granular piles (OGP) illustrated optimal performance when subjected to lower frequency and amplitude loading, smaller L/D ratios, and end bearing conditions. The provision of Combi-grid encasement notably improved the cyclic performance of granular piles by substantially reducing the cyclic induced settlement (Sc) on improved soft beds across all examined factors. This research also discusses the increased cyclic stress on the surrounding soft soil initiated excess pore water pressure (Pexc) development and is reduced to a greater extent with the help of Combi-grid encasement across all test cases.

Experimental and Numerical Study on the Behavior of RC Members under Combined Loads

In this paper, we present an investigation of the performance of reinforced concrete (RC) columns under combined bending loads and various axial forces using a finite element method (FEM) model developed with the ABAQUS finite element program, verified with actual experimental values. In the experimental study, we applied combined bending loads and various axial forces to four RC members. Two RC members were subjected to vertical cyclic loads using displacement control with 0% axial force, while the other two were tested with vertical cyclic loads, one with 10% axial force, and the other with 20% axial force. The axial force load was applied using a specially designed setup. The experimental results of the RC members include observations of final failure mode, ductility, and axial load–bending moment interaction curves (P–M correlation curves). The experimental study confirmed that as the axial force increased, cracks in the RC columns concentrated at the center of the column. The yield strength increased by 55% when the axial force ratio was 10%, and 106% when the axial force ratio was 20%. The maximum strength increased by 28% with a 10% axial force ratio, and 50% with a 20% axial force ratio. However, ductility tended to decrease as the axial force increased, reducing by 26% with a 10% axial force ratio and 60% with a 20% axial force ratio. The analytical study produced results consistent with the experimental research, showing similar numerical trends. Finally, when comparing theoretical values, experimental results, and analytical results using P–M correlation curves, we found that the experimental value has a safety rate of 18% compared to the theoretical value. The experimental and theoretical result values were similar. Therefore, it has been demonstrated experimentally and analytically that the current design has a safety value of about 18% for the performance of the actual structure.

Study on Seismic Performance of Concrete Columns and Beams Containing Recycled Brick Aggregate

In order to study the reinforced concrete beam and column components composed of natural concrete (NC), recycled aggregate concrete (RAC), recycled brick grain concrete (RBGC) and recycled brick aggregate concrete (RBC), the reinforced columns under the axial tension and compression cyclic load and the horizontal cyclic load and the simply supported beam under concentrated mid-span cyclic load are simulated respectively. The transient time history analysis is conducted to analyze their failure characteristics, hysteretic performance and energy dissipation performance. The results show that the damage of the column under horizontal cyclic loading is more obvious than that under vertical cyclic loading, and the energy dissipation is better, while the energy dissipation capacity of the beam is not as good as that of the column due to local concentration. The seismic performance of reinforced concrete columns and beams composed of RBGC and RBC materials is lower than that of NC and RAC materials. The materials of RBGC and RBC are more suitable for beam members.

Offshore foundations in low-plasticity cohesive soils: Cyclic degradation experimental evidence and simplified numerical analysis

The paper studies the effect of soil strength and stiffness degradation on the undrained cyclic performance of offshore foundations in low-plasticity cohesive soil using 3D finite element modelling. Cyclic triaxial tests on reconstituted kaolin are conducted at the ETH Zurich laboratory, providing insights into key parameters affecting the degradation process. A simplified soil constitutive model accounting for cyclic degradation is developed and encoded in Abaqus via a user subroutine. The model is calibrated against experimental results and validated with published centrifuge model tests of monopiles under cyclic lateral loading. It is subsequently used to evaluate the performance of suction caisson foundations with different aspect ratios (L/D = 0.5 and 2) under short-term cyclic and seismic loading. Due to its ductile resistance mechanism, the L/D = 0.5 caisson exhibits superior performance under vertical cyclic loading in fast-degrading soil. Under inclined cyclic loading, the slower degradation rate of the L/D = 2 caisson governs response, reversing the trend. Under seismic shaking, the degradation-induced resistance imbalance amplifies the irrecoverable settlements produced by kinematic shearing at the caisson sidewalls. For the fast-degrading soil examined, degradation is shown to increase settlements by up to 50%.

Evaluation of railhead material damage of insulated rail joints due to cyclic wheel loadings

Although insulated rail joints (IRJs) are important railway track components and, because of their low bending rigidity, a dynamic wheel impact results as wheels pass over them. Proper attention is needed to address this problem. Focussing on this point, a 3D finite element analysis (FEA) is carried out on IRJs to evaluate on damage analysis of sub-surface railhead material for endpost materials: fiberglass (fb), nylon 66 (ny), and polytetrafluoroethylene (ptfe). A cyclic vertical wheel load up to a total of 2000 cycles in non-Hertzian pressure form is applied at the wheel/rail contact patch on an IRJ. The residual longitudinal stress damage parameter is considered to rank the endpost material based on sub-surface railhead damage. It exhibits a new pattern described as ‘vertical flat type’ for a depth up to 8 mm initially and, as the cyclic loading increases, the vertical flat pattern damage changes to an ‘inclined flat type’ pattern.

Mind the gap – an experimental study on the need for grouting suction buckets in sand under vertical cyclic loading

Suction bucket jackets are increasingly being used to support bottom-fixed offshore wind turbines. It is generally assumed that contact between the underside of the bucket lid and the seabed is mandatory to safeguard against additional settlement. Lid contact is usually ensured by underwater grout injection, albeit this has a significant impact on the duration and costs of installation. Although grouting is routine, there are limited available data regarding the benefits of ensuring contact between the lid and the soil. This paper presents data from centrifuge tests of completely and partially installed buckets in dense sand subjected to vertical cyclic loading to investigate the role of lid contact. Lid contact was shown to have a discernible effect on displacement accumulation when buckets were loaded beyond the drained skirt capacity in compression. Under these conditions, settlement of a completely installed bucket was limited by lid contact with the soil plug, while partially installed buckets experienced continuous settlement, as expected. The physical evidence indicates complex load transfer mechanisms that are influenced significantly by the drainage conditions. Hence, an understanding of the soil drainage characteristics at a particular site would provide value when evaluating the requirement for under-lid grouting.

Experimental study on the behavior of single pile foundation under vertical cyclic load in coral sand

The bearing behaviors of piles in coral sand are critical for project safety due to the unique physical and mechanical properties of coral sand, such as high void ratio, high compressibility, high friction angle and easy to break. A series of model experiments were carried out in this study to evaluate the vertical behavior of single pile in coral sand foundation under cyclic dynamic load with the consideration of the influence of the amplitude of cyclic load, the static biased load and the number of cyclic. Load-settlement relationships, settlement-cyclic number relationships, pile tip and pile side resistances have been thoroughly investigated. Results showed that the load in coral sand foundation will transfer to the pile tip more obviously compared with the pile foundation in quartz sand. Therefore, the pile side resistance will be reduced while the corresponding pile tip resistance will be increased. Particularly, the weakening of side resistance mainly occurs in the first 500 cycles. The development of cyclic cumulative settlement is affected by the combination of the magnitude of static biased load and cyclic amplitude. The existence of static biased load is conducive to restrain the cyclic cumulative settlement when the amplitude of cyclic load is less than static load.

Analysis of the Effect of Pore Water Pressure on a Small Radius Curve Section of a Fine Sand Layer under Cyclic Metro

Small curved metro shield tunnels located in fine sand layers are sensitive to the response of horizontal and vertical cyclic loads from train operations, especially for centrifugal horizontal loads. The majority of Zhengzhou’s strata are dominated by this geological composition. Therefore, the dynamic response of the fine sand layer under the train vibration load will lead to the settlement of the sand layer, which brings great hidden danger to the train operation. Long-term pore water monitoring was carried out in this paper, and the use of MIDAS-GTS (Multi-candidate Iterative Design with Adaptive Selection) finite element calculation platform to establish the metro ballast-lining-soil coupling dynamic model for mutual verification. The variation patterns of pore water pressure and super pore water pressure during train operation and the vibration response pattern of the soil layer around the tunnel were investigated. The results suggest that: (1) The pore and excess pore water pressures generated at the start of vibration are not easily dissipated and transferred, making them larger in the early stages of train operation. In contrast, the fine-grained powdered sandy soil has a small amount of clay particles, giving strength and cohesion to the soil layer. Vibrating hole pressure and excess pore water pressure stabilize with the train at a later stage; (2) The low probability of liquefaction in the silt layer surrounding the tunnel; (3) Under vibrating loads, areas of significant soil settlement are concentrated on the soil surface, on the upper side of the tunnel in the silty sand layer and at the bottom 3 m of the tunnel, however, its low variation in settlement has a low impact on the tunnel.

Optimal insertion positions of anterior-posterior orientation sacroiliac screw.

To explore the optimal insertion positions of anterior-posterior orientation sacroiliac screw (AP-SIS). Pelvic CT data of 80 healthy adults were employed to measure the anatomical parameters including the insertable ranges of S1 and S2, the length, width and height of the channel with three different horizontal and vertical anterior insertion points starting from the ilium-acetabular recess. To compare pelvic stability by replicating a type C Tile lesions, fifteen synthetic pelvises were fixed with an anterior plate and a posterior AP-SIS employing different anterior insertion points, the whole specimen displacements and shifts in the sacroiliac gap under a cyclic vertical load of 300 N in a biomechanical machine recorded. The posterior and anterior insertable ranges averaged 17.9 × 8.5mm2 and 47.1 × 21.2 mm2, respectively. The channel lengths for three horizontal anterior insertion points gradually decreased from front to back with significant difference (p < 0.05), whereas the width and height for three horizontal anterior insertion points and the parameters for the three vertical anterior insertion points were similar (p > 0.05). The displacements and shifts for three horizontal insertion points gradually increased from front to back (p < 0.05) whereas the measurements involving the three vertical insertion points were similar (p > 0.05). The posterior insertable range is small, where the center between adjacent nerve roots (foramens) is the optimal posterior insertion point. The anterior insertable range is large, where the iliac-acetabular recess is the optimal anterior insertion point for S1 and S2, providing the longest channel and best stability.

Theoretical and experimental investigation on disc spring isolation system with loading rings

A novel disc spring isolation system (DSIS) design for buildings is proposed to isolate vibrations in the vertical direction. The system with nonlinear stiffness consists of disc springs and loading rings that reduce the influence of Coulomb friction between multiple disc springs. Theoretical analysis was first applied to establish a four-curve (FC) model to describe the force-displacement relation of DSIS by considering the influence of slip behavior and Coulomb friction between the loading rings and disc springs. Then, a series of vertical cyclic loading tests were carried out to study the different mechanical properties of DSIS with or without loading rings, and the effectiveness of the loading rings was verified. By comparing with the test results, the accuracy of the proposed FC model was verified. Then, the numerical solution method using the proposed FC model to solve the dynamic response of the single degree of freedom (SDOF) system was investigated. The nonlinear transfer function curves of DSIS with loading rings were compared with those of DSIS without loading rings by numerical analysis. Finally, the comparison study of SDOF for DSIS under the specific harmonic and train-induced vibration was carried out as a case study. The comparison shows that DSIS with loading rings more effectively reduces the start frequency of the isolated system, revealing the significant advantages of adopting DSIS with loading rings in vertical isolation.

Numerical investigation on horizontal deformation of large diameter monopile under cyclic wave loading with local scour holes

Seabed liquefaction and local scour around the offshore wind turbine (OWT) monopile have significant effects on the horizontal bearing capacity of the foundation. The horizontal displacement of the monopile at the seabed mudline is one of important factors considered in the foundation design. In this study, the effects of local scour and soil liquefaction on the monopile horizontal displacement were investigated. The dynamic response of sandy seabed with various densities under wave loading was simulated by adopting the Cyclic Mobility (CM) model. The numerical model was compared with previous experimental results. Then, the effects of local scour and soil liquefaction on the monopile horizontal bearing capacity were discussed. The differences in the effects of local scour and liquefaction on the horizontal displacement of monopile in the case of sandy seabed with different densities were compared. Numerical results shown that the effect of soil liquefaction caused by the vertical cyclic wave loading on the monopile horizontal bearing capacity is more significant than that of local scouring and horizontal cyclic loading, especially in loose sandy seabed. For dense sandy seabed, the local scour of the seabed has a more significant impact on the horizontal bearing capacity of the foundation.

Experimental behavior of steel-beam to flat rectangular CFST column connections with small-sized external diaphragms

This paper experimentally investigates the hysteretic behavior of beam-to-column connections between steel beams and flat rectangular concrete filled steel tubular (CFST) columns with small-sized external diaphragms to enable the implementation of the connections in steel structure residential buildings. The flat rectangular CFST columns are characterized by the width-to-depth ratio of the cross-section greater than 2.0. Five test specimens, including three corner connections and two interior connections in a frame structure, with 400×200 mm rectangular CFST column cross-section and various sizes of external diaphragms are designed for the investigation. During the tests, the specimens are subjected to constant axial loads on the columns and cyclic vertical loads at the beam ends that impose bending moments about the strong and weak axis of the columns. Failure modes including buckling in beam flanges, cracking at the welded connections between beam flanges and external diaphragms, and shear failure in panel zones are observed. The load-displacement hysteresis and strain distribution are obtained to evaluate the elastoplastic behavior of the connections. The moment resistance capacity, ductility, energy dissipation capacity, as well as stiffness and strength degeneration of the connections are respectively evaluated. The test results demonstrate that the connections have adequate hysteretic performance for earthquake resilient design of steel structure residential buildings. It is applicable to use small-sized external diaphragms beyond the limitation of existing design specifications for beam-to-column connections with flat rectangular CFST columns.

Uses of Usumacinta River sediments as a sustainable resource for unpaved roads: An experimental study on a full-scale pilot unit

PurposeTransportation is a key factor for economic growth and poverty reduction because it improves access to services and opportunities for rural communities. Unpaved roads, however, still represent 80% of the global road network. The state of Tabasco, Mexico, is not an exception. Materials and methodsGeotechnical identifications of raw and lime-treated sediments are performed. A methodology is developed to reproduce a soil-model close to the raw sediment's properties. The reconstituted soil-model is used for full-scale testing including CBR indexes determination, cyclic vertical plate testing and horizontal traffic loads tests. ResultsThe rutting generated from the cyclic plate and traffic load tests, on both the untreated and the lime-treated soil-model, are compared. The lime treatment appears to improve the properties of both the soil-model and the sediments. ConclusionsThe findings give promising perspectives regarding the use of Usumacinta River sediments for the construction of unpaved roads.

Ratcheting evaluation of pressurized straight pipe using Ahmadzadeh–Varvani hardening rule

This study evaluates the Ahmadzadeh–Varvani (A-V) hardening rule for the ratcheting behavior of pressurized straight pipe made of austenitic stainless steel Z2CND18.12N under bending loading and vertical displacement control, respectively. Based on the quasi-three point bending apparatus, the straight pipe specimen is placed in a nearly horizontal position, and the applied displacement to the specimen achieves cyclic bending. The displacement is called as vertical displacement in this study. Firstly, the A-V model is implemented into ABAQUS with the radial return scheme with sub-increments; and the consistent tangent modulus is derived for A-V model, and gives quadratic convergence for the solution. And then the numerical calculation is developed to simulate ratcheting behavior of pressurized straight pipe. The influences of internal pressure, cyclic bending loading or cyclic vertical displacement, loading history and control modes on ratcheting strain of straight pipe are studied, respectively. By comparison with the experimental data, it is found that the predicted results of A-V model are in good agreement with the experimental data of pressurized straight pipe.