Uplift behaviour of tapered piles established from model tests

2000 ◽  
Vol 37 (1) ◽  
pp. 56-74 ◽  
Author(s):  
M Hesham El Naggar ◽  
Jin Qi Wei
Keyword(s):  
Load Transfer ◽  
Compressive Loading ◽  
Compressive Load ◽  
Tensile Load ◽  
Confining Pressure ◽  
Cohesionless Soil ◽  
Uplift Capacity ◽  
Experimental Modelling ◽  
Confining Pressures ◽  
Load Tests

Tapered piles have a substantial advantage with regard to their load-carrying capacity in the downward frictional mode. The uplift performance of tapered piles, however, has not been fully understood. This paper describes the results of an experimental investigation into the characteristics of the uplift performance of tapered piles. Three instrumented steel piles with different degrees of taper were installed in cohesionless soil and subjected to compressive and tensile load tests. The soil was contained in a steel soil chamber and pressurized using an air bladder to facilitate modelling the confining pressures pertinent to larger embedment depths. The results of this study indicated that the pile axial uplift capacity increased with an increase in the confining pressure for all piles examined in this study. The ratios of uplift to compressive load for tapered piles were less than those for straight piles of the same length and average embedded diameter. The uplift capacity of tapered piles was found to be comparable to that of straight-sided wall piles at higher confining pressure values, suggesting that the performance of actual tapered piles (with greater length) would be comparable to that of straight-sided wall piles. Also, the results indicated that residual stresses developed during the compressive loading phase and their effect were more significant on the initial uplift capacity of piles, and this effect was more pronounced for tapered piles in medium-dense sand.Key words: tapered piles, uplift, axial response, load transfer, experimental modelling.

Load transfer of fibre-reinforced polymer (FRP) composite tapered piles in dense sand

2004 ◽  
Vol 41 (1) ◽  
pp. 70-88 ◽  
Author(s):  
Mohammed Sakr ◽  
M Hesham El Naggar ◽  
Moncef Nehdi
Keyword(s):  
Analytical Solution ◽  
Load Transfer ◽  
Compressive Loading ◽  
Centrifuge Modeling ◽  
Rational Approach ◽  
Dense Sand ◽  
Reinforced Polymer ◽  
Cylindrical Piles ◽  
Confining Pressures ◽  
Fibre Reinforced Polymer

This paper describes an experimental study conducted using a large, laboratory-scale testing facility to test pile segments at different stress levels. The objectives of the study were twofold: to examine the load-transfer mechanism of tapered piles in compression, and to evaluate the effect of pile material on pile performance characteristics. The results of axial compressive loading tests on 26 pile load tests were presented using fibre-reinforced polymer (FRP) concrete composite tapered piles and steel piles. Two installation techniques were used, including conventional head driving and toe driving using a new technique. Piles were tested at different confining pressures to represent a pile segment at depths of 4.0 and 8.0 m. The load distribution along the pile shafts was measured and the results were compared with those from an analytical solution in terms of the taper coefficient Kt. The comparison showed reasonable agreement between Kt values established from the experiments and those obtained from the analytical solution. The measured toe resistance of tapered and cylindrical piles was compared with those from the analytical solution. A simple rational approach was proposed for the design of tapered piles.Key words: tapered piles, FRP, pile capacity, axial performance, centrifuge modeling, shaft resistance, toe resistance.

Effect of loading history on the compression and uplift capacity of driven model piles in sand

1992 ◽  
Vol 29 (2) ◽  
pp. 334-341 ◽  
Author(s):  
R. C. Joshi ◽  
Gopal Achari ◽  
Shenbaga R. Kaniraj
Keyword(s):  
Key Words ◽  
Load Transfer ◽  
Uplift Capacity ◽  
Loading History ◽  
Pile Capacity ◽  
Rate Of Penetration ◽  
Constant Rate ◽  
Tip Resistance ◽  
Tension And Compression ◽  
Load Tests

Model piles were tested in dry uniform sand to study the effect of loading history on the behaviour of piles in compression and tension. A sand bed was prepared by the raining technique, and a smooth cylindrical instrumented pile was driven into the sand. Load tests on piles were conducted at a constant rate of penetration of 0.5 mm/min. The effects of length to diameter (L/D) ratio and sand density were also investigated. The load transfer along the pile surface was studied for an L/D ratio of 33. The pile tip resistance was measured for model piles with L/D ratios of 20–33 and was generally found to be constant. A significant decrease in the pile capacity both in tension and compression was noted for piles having a loading history. When a pile was loaded in compression after being loaded in tension, the tip load could be mobilized only after a certain movement of the pile. The mobilization of the shaft load, however, started immediately. Key words : load tests, model piles, dry sand, loading history, tip capacity, shaft capacity, compression, tension, load transfer.

scholarly journals Theory of the deformation of aligned polyethylene

2015 ◽  
Vol 471 (2180) ◽  
pp. 20150171 ◽  
Author(s):  
A. Hammad ◽  
T. D. Swinburne ◽  
H. Hasan ◽  
S. Del Rosso ◽  
L. Iannucci ◽  
...  
Keyword(s):  
Load Transfer ◽  
Tensile Load ◽  
Equation Of Motion ◽  
Dislocation Dynamics ◽  
Viscoelastic Deformation ◽  
Transfer Length ◽  
Soliton Dynamics ◽  
Fluctuation Dissipation ◽  
Pull Out ◽  
Definition Of

Solitons are proposed as the agents of plastic and viscoelastic deformation in aligned polyethylene. Interactions between straight, parallel molecules are mapped rigorously onto the Frenkel–Kontorova model. It is shown that these molecular interactions distribute an applied load between molecules, with a characteristic transfer length equal to the soliton width. Load transfer leads to the introduction of tensile and compressive solitons at the chain ends to mark the onset of plasticity at a well-defined yield stress, which is much less than the theoretical pull-out stress. Interaction energies between solitons and an equation of motion for solitons are derived. The equation of motion is based on Langevin dynamics and the fluctuation–dissipation theorem and it leads to the rigorous definition of an effective mass for solitons. It forms the basis of a soliton dynamics in direct analogy to dislocation dynamics. Close parallels are drawn between solitons in aligned polymers and dislocations in crystals, including the configurational force on a soliton. The origins of the strain rate and temperature dependencies of the viscoelastic behaviour are discussed in terms of the formation energy of solitons. A failure mechanism is proposed involving soliton condensation under a tensile load.

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

scholarly journals Modified mortar pad behavior in the transfer of compressive stresses

2016 ◽  
Vol 9 (3) ◽  
pp. 414-434
Author(s):  
J. D. Ditz ◽  
M. K. EL Debs ◽  
G. H. Siqueira
Keyword(s):  
Precast Concrete ◽  
Concrete Strength ◽  
Compressive Load ◽  
Stress Transfer ◽  
Compressive Stresses ◽  
Bonded Phase ◽  
Concrete Blocks ◽  
Load Tests ◽  
Styrene Butadiene ◽  
Concrete Elements

ABSTRACT This research aims to analyze the compressive stress transfer between precast concrete elements using cement mortar pads modified with polypropylene fibers, styrene-butadiene latex and heat-expanded vermiculite. The stress transfer analyses are performed interleaving a cementbearing pad between two concrete blocks, subjecting the entire specimen to different compressive load tests. The parameters analyzed in the tests are: surface roughness (using bosses on the bonded phase of different thicknesses), compressive strength with monotonic and cyclic loadings. The main results obtained in this study are: a) the presence of pad increased the strength in 24% for thicknesses of imperfections of 0.5 mm and approximately 12% for smooth faces blocks; b) gain of effectiveness of the bearing pad when the concrete strength was reduced; c) for cyclic loading, the bearing pad increased in 48% the connections strength.

scholarly journals Tissue Modification of the Lateral Compartment of the Tibio-Femoral Joint Following In Vivo Varus Loading in the Rat

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
M. L. Roemhildt ◽  
B. D. Beynnon ◽  
M. Gardner-Morse ◽  
K. Anderson ◽  
G. J. Badger
Keyword(s):  
Articular Cartilage ◽  
Subchondral Bone ◽  
Compressive Loading ◽  
Compressive Load ◽  
Lateral Compartment ◽  
Peripheral Region ◽  
Degenerative Changes ◽  
Medial Compartment ◽  
Compressive Loads

This study describes the first application of a varus loading device (VLD) to the rat hind limb to study the role of sustained altered compressive loading and its relationship to the initiation of degenerative changes to the tibio-femoral joint. The VLD applies decreased compressive load to the lateral compartment and increased compressive load to the medial compartment of the tibio-femoral joint in a controlled manner. Mature rats were randomized into one of three groups: unoperated control, 0% (sham), or 80% body weight (BW). Devices were attached to an animal’s leg to deliver altered loads of 0% and 80% BW to the experimental knee for 12 weeks. Compartment-specific material properties of the tibial cartilage and subchondral bone were determined using indentation tests. Articular cartilage, calcified cartilage, and subchondral bone thicknesses, articular cartilage cellularity, and degeneration score were determined histologically. Joint tissues were sensitive to 12 weeks of decreased compressive loading in the lateral compartment with articular cartilage thickness decreased in the peripheral region, subchondral bone thickness increased, and cellularity of the midline region decreased in the 80% BW group as compared to the 0% BW group. The medial compartment revealed trends for diminished cellularity and aggregate modulus with increased loading. The rat-VLD model provides a new system to evaluate altered quantified levels of chronic in vivo loading without disruption of the joint capsule while maintaining full use of the knee. These results reveal a greater sensitivity of tissue parameters to decreased loading versus increased loading of 80% BW for 12 weeks in the rat. This model will allow future mechanistic studies that focus on the initiation and progression of degenerative changes with increased exposure in both magnitude and time to altered compressive loads.

scholarly journals Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhiwei Cai ◽  
Tongqing Wu ◽  
Jian Lu ◽  
Yue Wu ◽  
Nianchun Xu
Keyword(s):  
Shear Crack ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Deformation And Failure ◽  
Fracture Development ◽  
Confining Pressures ◽  
The Law ◽  
Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

scholarly journals Multi-configuration Stiffened Panels under Compressive Load: Part 1 – Theoretical Analysis

2018 ◽  
Vol 7 (3.11) ◽  
pp. 38
Author(s):  
Ramzyzan Ramly ◽  
Wahyu Kuntjoro ◽  
Amir Radzi Abdul Ghani ◽  
Rizal Effendy Mohd Nasir ◽  
Zulkifli Muhammad
Keyword(s):  
Theoretical Analysis ◽  
Experimental Analysis ◽  
Critical Loads ◽  
Input Parameter ◽  
Compressive Loading ◽  
Compressive Load ◽  
Cross Sectional ◽  
Stiffened Panels ◽  
Compression Load ◽  
Main Input

Stiffened panels are the structure used in the aircraft wing skin panels. Stiffened panels are often critical in compression load due to its thin structural configuration. This paper analyzes the critical loads of a multi configuration stiffened panels under axial compressive loading. The study comprised three main sections; theoretical analysis, numerical analysis and experimental analysis. The present paper deals only with the theoretical analysis. This first part of analysis is very important since the results will be the main input parameter for the subsequent numerical and experimental analysis. The analysis was done on the buckling properties of the panels. Four panel configurations were investigated. Results showed that even though the stiffened panels have the same cross-sectional area, their critical loads were not identical.   

scholarly journals The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

scholarly journals Intragranular deformation mechanisms in calcite deformed by high-pressure torsion at room temperature

2020 ◽  
Vol 114 (2) ◽  
pp. 105-118
Author(s):  
Roman Schuster ◽  
Gerlinde Habler ◽  
Erhard Schafler ◽  
Rainer Abart
Keyword(s):  
High Pressure ◽  
Twin Boundary ◽  
Brittle Failure ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Confining Pressure ◽  
Temperature Deformation ◽  
Orientation Relationships ◽  
High Confining Pressure ◽  
Confining Pressures

AbstractPolycrystalline calcite was deformed to high strain at room-temperature and confining pressures of 1–4 GPa using high-pressure torsion. The high confining pressure suppresses brittle failure and allows for shear strains >100. The post-deformation microstructures show inter- and intragranular cataclastic deformation and a high density of mechanical e$$ \left\{01\overline{1}8\right\} $$011¯8 twins and deformation lamellae in highly strained porphyroclasts. The morphologies of the twins resemble twin morphologies that are typically associated with substantially higher deformation temperatures. Porphyroclasts oriented unfavorably for twinning frequently exhibit two types of deformation lamellae with characteristic crystallographic orientation relationships associated with calcite twins. The misorientation of the first deformation lamella type with respect to the host corresponds to the combination of one r$$ \left\{10\overline{1}4\right\} $$101¯4 twin operation and one specific f$$ \left\{01\overline{1}2\right\} $$011¯2 or e$$ \left\{01\overline{1}8\right\} $$011¯8 twin operation. Boundary sections of this lamella type often split into two separated segments, where one segment corresponds to an incoherent r$$ \left\{10\overline{1}4\right\} $$101¯4 twin boundary and the other to an f$$ \left\{01\overline{1}2\right\} $$011¯2 or e$$ \left\{01\overline{1}8\right\} $$011¯8 twin boundary. The misorientation of the second type of deformation lamellae corresponds to the combination of specific r$$ \left\{10\overline{1}4\right\} $$101¯4 and f$$ \left\{01\overline{1}2\right\} $$011¯2 twin operations. The boundary segments of this lamella type may also split into the constituent twin boundaries. Our results show that brittle failure can effectively be suppressed during room-temperature deformation of calcite to high strains if confining pressures in the GPa range are applied. At these conditions, the combination of successive twin operations produces hitherto unknown deformation lamellae.

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