Pile Moment Research Articles

Seismic analysis of turbo machinery foundation: Shaking table test and computational modeling

Foundation plays a significant role in safe and efficient turbo machinery operation. Turbo machineries generate harmonic load on the foundation due to their high speed rotating motion which causes vibration in the machinery, foundation and soil beneath the foundation. The problems caused by vibration get multiplied if the soil is poor. An improperly designed machine foundation increases the vibration and reduces machinery health leading to frequent maintenance. Hence it is very important to study the soil structure interaction and effect of machine vibration on the foundation during turbo machinery operation in the design stage itself. The present work studies the effect of harmonic load due to machine operation along with earthquake loading on the frame foundation for poor soil conditions. Various alternative foundations like rafts, barrette, batter pile and combinations of barrettes with batter pile are analyzed to study the improvements in the vibration patterns. Detailed computational analysis was carried out in SAP 2000 software; the numerical model was analyzed and compared with the shaking table experiment results. The numerical results are found to be closely matching with the experimental data which confirms the accuracy of the numerical model predictions. Both shake table and SAP 2000 results reveal that combination of barrette and batter piles with raft are best suitable for poor soil conditions because it reduces the displacement at top deck, bending moment and horizontal displacement of pile and thereby making the foundation more stable under seismic loading.

Effectiveness of Fiber Bragg Grating monitoring in the centrifugal model test of soil slope under rainfall conditions

Centrifugal model tests are playing an increasingly important role in investigating slope characteristics under rainfall conditions. However, conventional electronic transducers usually fail during centrifugal model tests because of the impacts of limited test space, high centrifugal force, and presence of water, with the result that limited valid data is obtained. In this study, Fiber Bragg Grating (FBG) sensing technology is employed in the design and development of displacement gauge, an anchor force gauge and an anti-slide pile moment gauge for use on centrifugal model slopes with and without a retaining structure. The two model slopes were installed and monitored at a centrifugal acceleration of 100 g. The test results show that the sensors developed succeed in capturing the deformation and retaining structure mechanical response of the model slopes during and after rainfall. The deformation curve for the slope without retaining structure shows a steep response that turns gradual for the slope with retaining structure. Importantly, for the slope with the retaining structure, results suggest that more attention be paid to increase of anchor force and anti-slide pile moment during rainfall. This study verifies the effectiveness of FBG sensing technology in centrifuge research and presents a new and innovative method for slope model testing under rainfall conditions.

Experimental study of the progressive collapse mechanism of excavations retained by cantilever piles

An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the research on progressive collapse mechanisms is limited. In this paper, two categories of model tests were conducted to investigate the mechanism of partial collapse (sudden failures of certain retaining piles) and progressive collapse. The model test results show that partial collapse can cause a sudden increase in the bending moments of adjacent piles via an arching effect. The load-transfer coefficients are defined to be equal to the peak increase ratios of the maximum bending moments in adjacent piles (peak moments caused by collapse over the values before the collapse). When the maximum load-transfer coefficient is larger than the bearing capacity safety factor of the piles, the partial failure will lead to progressive collapse. The influential factors of the progressive collapse mechanism, such as the partial collapse extent, excavation depth, and capping beam, were also investigated. During progressive collapse, the previous failed pile could cause new stress arching; simultaneously, the soil behind certain nearest intact piles could become loosened and destroy the arch springing of the stress arching, causing the progressive collapse to cease gradually.

Evaluation and comparison of anti-impact performance to offshore wind turbine foundations: Monopile, tripod, and jacket

Offshore wind turbines near the ocean lane are under a potential threat caused by ship impacts during the service period. Contraposing to three common uses of foundations (monopile, tripod, and jacket) of offshore wind turbines, this study is devoted to probe and compare the anti-impact performance due to a head-on impact by ships. A series of cases are conducted to investigate the foundation damage and the OWT response of the three types of foundations using LS-DYNA, a commercial FEM tool. Through investigating and analyzing the maximum collision-force, the damage area, the maximum bending moment of piles at the seabed, the steel consumption and the maximum nacelle acceleration in different low-energy collision scenarios, it is found that the jacket generates the minimum collision-force, damage area and nacelle acceleration as well as the medium bending moment and steel consumption among the three. Therefore, the jacket has the optimum comprehensive anti-impact performance under low-energy collisions, which may be useful in developing the foundation design of offshore wind turbines.

Numerical analysis of the seismic inertial and kinematic effects on pile bending moment in liquefiable soils

In an effort to study the seismic pile moment induced by the combined structure–pile inertial and soil–pile kinematic effects for single piles and pile groups in liquefiable ground, an extensive series of 3D finite element simulations are conducted in this paper. The roles that lateral inertial and kinematic interactions play on the pile moment are found to differ in different soil–pile–structure systems. Inertial structure force and kinematic soil displacement of the same direction could cause pile head moments of the same or opposite directions depending on the rotational constraint at the pile head. Kinematic interaction has a dominating influence on the pile moment for pile foundations with pile head rotation constrained by the existence of a pile cap, while inertial interaction is strongly influential for free-head piles. The coupling of inertial and kinematic interactions depends on the soil–pile–structure system configuration and the magnitudes of the inertial structure force and the kinematic soil displacement. Many current pseudo-static methods for calculating the seismic pile moment through summing a percentage of the kinematic induced moment with another percentage of the inertial induced moment could produce very inaccurate results under certain conditions.

Scour effects onp–ycurves for shallowly embedded piles in sand

Soil scour around a shallowly embedded pile can significantly compromise its lateral response, reducing both stiffness and capacity. Estimation of the lateral pile response must take into account both the scour-hole geometry and the overconsolidation effects on the remaining soil. A series of centrifuge model tests with various scour profiles were conducted at a scale of 1:250 to investigate the effects of both local and general scour on the response of a laterally loaded pile. Measured pile moment distributions and force–displacement data at the pile head were used to derive p–y curves quantifying the lateral pile–soil interaction. The p–y curves derived from various scour profiles were compared for equivalent depths below the new scour base, and below the original soil surface. For the general scour cases, the p–y curves for given depths below the post-scour surface are essentially identical to those at the same depths without scour. In contrast, for the local scour cases, the p–y response at a given depth below the scour-hole base is much stiffer than at the same depth below the original soil surface. As a practical approach to evaluate the effects of scour, the concept of an effective soil depth is introduced to determine the corresponding p–y curves for shallowly embedded piles in sand.

Comparative study on the seismic performance of two types of quay wall structures

ABSTRACTA new type of quay wall structure has been proposed to improve the seismic resistance capability of existing sheet pile quay wall structures. The new structure adopts a combination of stabilized soil and geogrid, and this structure is referred to simply as “SG-WALL”. This paper presents a numerical comparative study on the seismic performances of quay wall structures between the newly developed SG-WALL and the traditional anchor pile-reinforced structure. The calculated results, including displacement of sheet pile, ground settlement, bending moment and stress of sheet pile, and excess pore water pressure, were analyzed and discussed. It was shown that both types of improvement methods can effectively reduce the residual displacements of sheet piles after earthquakes. The residual displacements at the top of the sheet piles in SG-WALL structure and the anchor pile-reinforced structure decreased by 35.6 and 38.2%, respectively. In addition, the SG-WALL structure can more significantly reduce the ground settlement due to earthquakes. The maximum ground settlement in SG-WALL structure and the anchor pile-reinforced structure decreased by 67.3 and 58.9%, respectively.

Bending moment of piles on piled raft foundation subjected to ground deformation during earthquake in centrifuge model test

Bending moment of piles on piled raft foundation subjected to ground deformation during earthquake in centrifuge model test

Effects of infilled concrete and longitudinal rebar on flexural performance of composite PHC pile

Concrete infill and reinforcement are one of the most well-known strengthening methods of structural elements. This study investigated flexural performance of concrete infill composite PHC pile (ICP pile) reinforced by infill concrete and longitudinal rebars in hollow PHC pile. A total four series of pile specimens were tested by four points bending method under simply supported conditions and investigated bending moment experimentally and analytically. From the test results, it was found that although reinforcement of infilled concrete on the pure bending moment of PHC pile was negligible, reinforcement of PHC pile using infilled concrete and longitudinal rebars increase the maximum bending moment with range from 1.95 to 2.31 times than that of conventional PHC pile. The error of bending moment between experimental results and predicted results by nonlinear sectional analysis on the basis of the conventional layered sectional approach was in the range of -2.54 % to 2.80 %. The axial compression and moment interaction analysis for ICP piles shows more significant strengthening effects of infilled concrete and longitudinal rebars.

Numerical Analysis of a Pile-Anchor Retaining Structure of Deep Foundation Pit Engineering

Based on a deep foundation pit engineering of Tangshan, considering the interaction of pile-anchor-soil, the finite difference software FLAC3D is adopted in this paper to simulate and analyze the effect of dip angle of anchor and the embedded depth of pile on the horizontal displacement and the variation laws of earth pressure, horizontal displacement of pile with the process of excavation. The results show that the maximum value of horizontal displacement and positive moment of pile appear in 0.85H (H stands for the depth of excavation) and the negative moment appears in 1.3H after the excavation; the maximum value of active and passive earth pressure appear in 1.3H rather than the bottom in the range of pile length; the requirements of deformation control and overall stability of foundation pit can be satisfied with 0.5H which as the embedded depth of the pile, and the dip angle of anchor is appropriate when it ranges from 5°to 25°but less than 30°.

Earthquake-induced bending moment in fixed-head piles in soft clay

This paper examines seismic effects on fixed-head, end-bearing piles installed through soft clay, using centrifuge and numerical modelling. The numerical analyses were conducted using a non-linear hysteretic, stiffness-degrading model for the clay and were validated using centrifuge data. Numerical analyses were used to extend the range of soil, pile and ground motion parameters which could not be studied in the centrifuge. Based on the centrifuge and numerical results, a framework for estimating earthquake-induced bending moments in fixed-head piles was established, which takes into account superstructural mass, ground motion and, in an approximate way, non-linear stress–strain behaviour. In this framework, pile response is sub-divided into two kinds, namely, ‘stiff' and ‘flexible', based on the notion of an active length over which significant bending moment is developed. A relationship for the active length is developed based on regression of the centrifuge and numerical data. If the pile length is shorter than its active length, it is considered to be stiff and significant bending is expected to develop over its entire length. The regressed bending moment relationship for stiff piles shows that the stiffness of the pile–soil system is dominated by that of the pile, and non-linearity in the stress–strain behaviour of soil does not feature strongly. Piles whose lengths are longer than their active lengths are termed ‘flexible' piles. The regressed bending moment relationship for flexible piles shows that the supporting effect of the soil is more significant, and the non-linearity in the stress–strain behaviour of the soil correspondingly becomes more important. For all piles, the study shows that the pile head and soil masses have significant influence on the bending moment.

Finite element analysis of effect of soil displacement on bearing capacity of single friction pile

Effect of soil displacement on friction single pile in the cases of tunneling, surcharge load and uniform soil movement was discussed in details with finite element method. Lateral displacement of the pile caused by soil displacement reached about 90% of the total displacement, which means that P-Δ effect of axial load can be neglected. The maximum moment of pile decreased from 159 kN·m to 133 kN·m in the case of surcharge load when the axial load increased from 0 to the ultimate load. When deformation of pile caused by soil displacement is large, axial load applied on pile-head plays the role of reducing the maximum bending moment in concrete pile to some extent. When pile is on one side of the tunnel, soil displacements around the pile are all alike, which means that the soil pressures around the pile do not decrease during tunneling. Therefore, Q-s curve of the pile affected by tunneling is very close to that of pile in static loading test. Bearing capacities of piles influenced by surcharge load and uniform soil movement are 2480 kN and 2630 kN, respectively, which are a little greater than that of the pile in static loading test (2400 kN). Soil pressures along pile increase due to surcharge load and uniform soil movement, and so do the shaft resistances along pile, as a result, when rebars in concrete piles are enough, bearing capacity of pile affected by soil displacement increases compared with that of pile in static loading test.

Simplified Analysis of the Effect of Soil Liquefaction on the Earthquake Pile Response

The time-history response of a structure-pile system during soil liquefaction is highly complicated and several analytical methods have been proposed through the accuracy verification based on the comparison with the experimental works. However, the analytical methods with higher accuracy often require large computational loads and are not necessarily preferred in the actual design practice. On the other hand, while the response spectrum method is not accurate compared to the aforementioned methods, it can provide useful design guidelines in the preliminary stage for structure-pile systems under soil liquefaction with acceptable accuracy. In this paper, the previously proposed response spectrum method for a structure-pile-soil system is used where the effect of soil liquefaction is taken into account by introducing the so-called p-multiplier method. It is shown that, while in the case of inner partial liquefaction with a non-liquefied layer at the top, the demand on the pile moment is large due to the inertial effect of that non-liquefied layer at the top, in the case of overall liquefaction near the ground surface, the demand is smaller than the case of inner partial liquefaction.

Kinematic Bending Moment of Piles under Seismic Motions

Soil pile structure interaction under seismically loadings is a very complex phenomenon involving of kinematic and inertial interaction among soil, pile and superstructure. Piles experience kinematic bending moments caused by the soil deformations due to the passage of the seismic waves through the surrounding layered soil. These moments are increased at each the levels of the soil deposit with the different modulus. A model of the soil pile interaction 2D is developed in this paper. The main results of parametrical study on single piles obtained by this model are compared with the exiting design methods for evaluating the kinematic interaction between soil-pile subjected to the seismic excitations. The shear strain and the shear stress are evaluated by the linear equivalent method of the free field site response analyses. The results show that the kinematic bending moment at the interface is changed by the soil nonlinearity behavior and the frequency content of the seismic motion even in absence superstructure.

Centrifuge Modeling on Seismic Behavior of Pile in Liquefiable Soil Ground

Dramatic failure of pile foundations caused by the soil liquefaction was founded leading to many studies for investigating the seismic behavior of pile. The failures were often accompanied with settlement, lateral displacement and tilting of superstructures. Therefore soil-structure interaction effects must be properly considered in the pile design. Two tests by using the centrifuge shaking table were conducted at an acceleration field of 80 g to investigate the seismic response of piles attached with different tip mass and embedded in liquefied or non-liquefied deposits during shaking. It was found that the maximum bending moment of pile occurs at the depth of 4 m and 5 m for dry sand and saturated sand models, respectively. The more tip mass leads to the more lateral displacement of pile head and the more residual bending moment.

Observed integral abutment bridge substructure response

Two integral abutment bridges in Vermont, USA were instrumented and monitored to report behavior under seasonal thermal load. This paper describes substructure response from 30months of field data. The bridges are single span steel girder bridges of approximately 40m on pile foundations. One bridge is straight while the other has a 15° skew. Variations in substructure displacements, backfill pressures and pile moments are reported under hot, cold and moderate ambient temperatures. Abutment and pile deformation plots highlight maximum displacements at the top of piles that are often only 1/3 to 1/2 of the values at the top of the abutment. Maximum pile moments correspond to concentrated curvature at the pile–abutment interface which did not correspond to peak temperatures. Substructure deformation response was predominantly elastic under bridge contraction, but highly non-linear under bridge expansion and varied from year to year. No indication of soil ratcheting was observed in the backfill materials and design for full passive pressure appears to be overly conservative for these single span structures. No indications of pile yielding were observed in the Grade 345 steel piles. Backfill pressures were consistent across the abutment in the straight bridge, but highly variable in the 15° skew bridge.

Integral Abutment Bridge behavior under uncertain thermal and time-dependent load

Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

Sensitivity Analysis on Influencing Factors of Double-Row Piles for Excavation

Sensitivity analysis of double-row piles is often obtained by changing the value of single influencing factor and doesn’t considering the interaction of influencing factors. So, a new sensitivity analysis method is proposed which can consider the interaction of influencing factors. In this method, uniform design (UD) and alternating conditional expectations regression (ACE) are used. The embedded depth of the forward pile, row space, length of the back pile, equivalent thickness of forward pile, equivalent thickness of coupling beam, and equivalent thickness of back pile are six input parameters called influencing factors. The maximum horizontal displacement of the pile head (MDP), maximum bending moment of forward pile (MMF), maximum ground settlement (GS), and coefficient of global stabilization (CGS) are four outputs as target parameters. The sensitivity can be obtained in this geological condition, excavation depth and surrounding environment. It is showed that the stiffness of back pile is the critical influence factor to MDP, the stiffness of forward pile is the critical influence factor to MMF and GS, and the length of back pile is the critical influence factor to CGS.

2011年東北地方太平洋沖地震による浦安市運動公園での杭基礎被害とその要因分析

Performance of three pile foundations then under construction thus without superstructures during the 2011 Tohoku Pacific earthquake was examined on the basis of field investigation including inclinometer and camera survey as well as of numerical analysis. It is shown that: (1) a single and a 2x2 group pile foundations were vitally damaged at a depth of about 10 m, the bottom of the liquefied layer, and displaced horizontally by about 10-60cm, whereas the other large group pile foundation did not suffer any damage; (2) the largest bending curvature in the two damaged pile foundations occurred at a depth of about 10 m, suggesting that the pile damage was probably caused by cyclic ground displacement of the liquefied sand; and (3) the difference in pile moment capacity as well as pile head connection might have differentiated the performance of the three pile foundations during the earthquake.

Research of the Pile Bent Property under the Horizontal Load

The ship impact is one of the main reasons, causing damage to pile wharf. In order to explore the pile bent property under the horizontal load, the finite element numerical analysis software was used to construct the model of the bent, and the data of each pile of the bent has been obtained. According to this data, the basic changing rule of the bending moment and displacement of piles along the pile length was found. Comparing a single vertical pile and fork piles, the difference between them was got. And on that basis, this article preliminarily researched the elastic-plastic characteristics of pile bent.