Uplift Resistance Research Articles

Behavior of V-shaped angle shear connectors: experimental and parametric study

In this paper a new shear connector called V-shaped angle shear connector for steel–concrete composite system is proposed. This shear connector was proven to improve some mechanical properties of shear connectors, including high shear transfer, uplift resistance, sufficient ductility, and strength degradation resistance under cyclic loading, as well as to being cost effective compared with similar shear connectors, such as C-shaped channel and angle shear connectors. A total of 14 push-out tests were performed on composite beams with these connectors under monotonic and low cyclic loading. The failure mode, shear resistance, and ductility of the push-out specimens were investigated. The study also comprises of finite element and parametric analysis using an effective numerical model of the experimental push-out tests using the program ABAQUS. The finite element models were validated against the test results presented in experimental tests. Results showed that V-shaped angle shear connector has excellent behavior in terms of both shear strength and ductility. In addition, high resistance under cyclic loading was exhibited since the shear resistance of this connector was almost similar in both monotonic and cyclic loadings. Finite element results show good agreement with experimental results. The results discussed on the ductility and strength of this connector with different size and slope of inclination. In addition, the channel and angle shear connectors were compared with V-shaped angle shear connectors. V-shaped angle shear connectors behave much better than other similar connectors, such as normal angle shear connectors, and are superior to channel shear connectors in most specimens.

Effects of preloading and consolidation on the uplift capacity of skirted foundations

Centrifuge tests investigating the effect of compressive preloading and consolidation on the subsequent uplift capacity of shallow skirted foundations that rest on lightly over-consolidated kaolin clay are reported. The uplift resistance, total and pore pressures at the foundation invert were monitored during the installation, consolidation and uplift. The results show that uplift performed immediately after the preloading generates a lower capacity due to the remoulding of the clay and reduction in soil strengths that result from the application of preloading. The soil strength can be recovered and eventually enhanced by the subsequent consolidation process. A theoretical framework, where the variation of the soil operative strength with preloading and consolidation is interpreted using the critical state concept, is proposed to explain and justify the experimental observations. The framework is validated through retrospective prediction of the uplift resistance of the centrifuge model tests with good agreement for a wide range of levels of preloading and degrees of consolidation demonstrated.

Reliability of Roof Panels in Coastal Areas Considering Effects of Climate Change and Embedded Corrosion of Metal Fasteners

AbstractRoof panels have been recognized as the most vulnerable components in wood construction under hurricane events, which can result in enormous economic losses and human casualties. This paper presents a reliability analysis of roof panels considering effects of climate change on altering patterns of hurricane hazard and embedded corrosion of metal fasteners in hurricane risk assessment. On the one hand, it has been found that the hurricane wind intensity may increase due to the effects of climate change, and the intensified hurricanes will result in more severe damage to coastal constructions. On the other hand, there is corrosion on the shanks of the fasteners that are tightly embedded in the wood roof panels, and the reduced diameter of shanks will reduce the uplift capacity of roof panels. Uncertainties in hurricane wind load and roof panel uplift resistance (the effects of embedded corrosion on the diameter of metal fasteners) are considered. The effectiveness of several retrofitting strategies ...

Uplift Resistance of Interfering Pipelines Buried in Sand

The vertical uplift resistance of interfering pipelines buried in sands has been computed using the lower-bound limit analysis in conjunction with finite elements and nonlinear optimization. The soil mass is assumed to follow the Mohr-Coulomb failure criterion and an associated flow rule. It is specified that all the pipes fail simultaneously at the same magnitude of the failure load. For different clear spacing (S) between the pipes, the magnitude of the efficiency factor (xi(gamma)) is determined. Because of pipes' interference, with a reduction in the spacing between the pipelines, the magnitude of xi(gamma) is found to decrease continuously. The results were found to compare quite well with the available data from literature for horizontal strip anchors. (C) 2015 American Society of Civil Engineers.

Application of particle image velocimetry (PIV) in the study of uplift mechanisms of pipe buried in medium dense sand

Geotechnical centrifuge modeling, which can effectively simulate the stress field of soil in the prototype, was adopted to help investigate the effects of the uplifting of pipes buried at different depths within a medium dense sand under (1) a static state and (2) a dynamic state. To acquire the displacement vector fields and strain contours in the soil around pipes, particle image velocimetry technology was applied. The study focused on the deformation mechanisms of soil surrounding the pipes and ground surface. Two different deformation triggers, external forces and soil liquefaction, were considered. When uplifting was caused by an external force, the relationship between the soil deformation and uplift resistance was similar to the typical ground load–deformation characteristic relationships. There was little displacement of soil during the elastic stage. Along with the uplifting of the pipe, a plastic zone within the range of one pipe diameter (1D) above the pipe appeared in the soil at peak resistance. During the post-peak period, a shear failure plane extended upwards to the ground surface, at an inclined angle forming a trumpet-like shape. The ground surface deformation range expanded according to the buried depth of the pipe. Meanwhile, in a liquefied field, the soil flowed within a heart-shaped region around the pipe. The soil deformation region surrounding a shallow buried pipe, with a width of 5D–6D, was far larger than that found for a pipe buried at the same depth in a static field. Both heave and settlement could be observed on the ground surface.

Uplift Capacity of Strip and Circular Anchors in Soft Clay with an Overlay of Sand Layer

Vertical uplift resistance of strip and circular horizontal plate anchors embedded in soft clay with an overlay of a sand layer has been computed by using plane strain and axisymmetric lower bound limit analysis in conjunction with finite elements and linear optimization. The improvement in the magnitude of the uplift resistance, with an overlay of the sand layer, has been expressed in terms of non-dimensional efficiency factors. It is found that the magnitude of the uplift resistance increases continuously with an increase in the thickness (H sand ) of sand layer up to a certain critical value of H sand /B; where B refers to either the width of strip anchor or the diameter of circular anchor. For c/(γB) = 1 and with ϕ = 40° for the overlying sand layer, the values of [H sand /B] cr become approximately equal to 3.1 and 1.6 corresponding to strip and circular anchor, respectively. For H sand /B > [H sand /B] cr , the analysis reveals that the anchor plate needs to be placed on the top of the clay stratum rather than embedding within the clay medium at a given depth (H). As compared to the circular anchor, the improvement in the uplift resistance with an overlay of sand layer becomes always more extensive for a strip anchor. The computational results have been obtained for different combinations of H/B, H sand/B and c/(γB). These results have been found to compare well with the different available theoretical and experimental data reported from literature.

Numerical Modeling of Suction and Trench Formation at the Touchdown Zone of Steel Catenary Riser

Steel catenary risers (SCR) are widely used in deepwater oil and gas production. The riser-seabed-water interaction near the touchdown zone is one of the main concerns in the design of fatigue life of SCR. During upward displacement, suction develops under the riser and a trench might be formed when it separates from the seabed near the touchdown point. In the subsequent downward movement, the riser penetrates through this trench to the seabed. Therefore, modeling of suction and trench formation is very important. In the existing models available in the literature for uplift resistance, these factors are incorporated using empirical relationships. It is also recognized that the available finite-element (FE) modeling techniques for this large-deformation problem are computationally very expensive, although penetration behavior can be simulated. In the present research program, both penetration and uplift behavior are simulated using FE and computational fluid dynamics (CFD) approaches. The simulation results for penetration are presented in Hawlader et al. (2014). In this paper, CFD simulations of uplift resistance, suction and trench formation using ANSYS CFX are discussed. A new model for undrained shear strength of soft clay is proposed that is applicable to a wide range of shear strain rates. The effects of strain rate and strength degradation are incorporated properly in ANSYS CFX and simulations are performed for one penetration-uplift cycle. Comparing with empirical models developed from experimental results and also with FE results for idealized conditions, it is shown that the present CFX model can simulate the suction and uplift resistance. Moreover, the CFX model developed in this study using the subdomain approach is computationally very efficient. The suction under the riser is the main source of uplift resistance for shallow embedments. The parametric study shows that the maximum uplift resistance and depth of trench depend on uplift velocity and the undrained shear strength of clay.

Closure to “Design and Construction Guidelines for Deep Soil Mixing to Stabilize Expansive Soils” by Raja S. Madhyannapu and Anand J. Puppala

The writers would like to express their appreciation to the discusser for the comments provided on the original paper. Following are the responses to the comments by the discusser. As noted by the discusser in Item 1a of the discussion, predrilling of deep soil mixing (DSM) locations prior to soil mixing was necessary and achieved using a flight auger of diameter similar to the one used for the construction of DSM columns [0.6-m (2-ft) diameter]. Due to the stiff to very stiff nature of unsaturated in situ soils, spoil produced was minimal during the predrilling process. During retrieval of flight auger, few of the loosened soil lumps were reintroduced into the predrilled DSM hole prior to soil mixing step. The extra material shown in Fig. 12 in the original paper was produced during actual soil mixing process and it shows the low amounts of spoil produced during the field mixing operations. The primary objective of this research was to understand the behavior of a treated composite expansive soil test section as a whole system subjected to seasonal climatic changes. Though the writers did not specifically study the zone of influence of soil mixing beyond the DSM columns, the following explanation on the potential zone of influence of DSM columns in the expansive soils is offered. Previous studies based on the laboratory tests on soft soils noted that the zone of influence was close to four times the diameter of the DSM columns. The present expansive soils, on the other hand, are stiff to very stiff in nature and also highly impervious. Hence, the writers opine that the zone of influence due to soil mixing in expansive soils will be less than the ones observed in soft soils. The discusser mentioned the potential heave-related protrusion from isolated rigid inclusions into the soil mass. The writers do not agree with this assessment and offer the following reasons explaining that the heave movements less than the allowable magnitude are anticipated within the treated composite section. Differential soil movements are more prevalent in soft soils than in expansive soils. In present design methodology, the treated composite section is designed based on the treatment area ratio determined using an allowable heave of less than 25 mm for the composite section. Thus, the differential swelling anticipated within the treated area is expected to be less than 25 mm and potentially insignificant. The uplift resistance of DSM columns primarily depends on the depth of treatment, strength and stiffness characteristics of subsoils, and zone of influence beyond the diameter of the DSM column. Chemical modification is the primary method of treatment for expansive soils because alteration of physicochemical properties from chemical reactions result in reduced or insignificant swelling. Also, the placement of a geosynthetic layer over the treated area was to provide additional mechanical reinforcement to transfer any induced swell pressures from untreated soils to treated columns through the inverse of arching behavior. All these factors contribute to minimizing the potential heave across the treated composite area. The writers agree with the discusser in extending the anchoring system into the pavement shoulder area. Further research studies are also recommended on deep soil mixing treatments of expansive soils, which would help in addressing issues such as zone of influence, load transfer mechanism within the composite section, and others.

Determination of pile failure mechanism under pullout test in loose sand

Estimating the deformation of soil around the pile contributes to reliable design of structures under pullout force. This work presents the results of a series of small-scale physical modelling tests designed to investigate the uplift resistance of piles with diameter of 5 cm and slenderness ratios of 1, 2, 3 and 4 in loose sand. Close photogrammetric technique and particle image velocimetry (PIV) were employed to observe the failure patterns due to uplift force on piles. The results show that the shear zones curve slightly outward near the ground surface. After peak resistance, the shear strain concentrates into a pair of narrow shear bands, then a flow around mechanism is formed accompanied by a reduction in the uplift resistance. The results from the laboratory tests were verified by analytical method proposed by Chattopadhyay and PLAXIS 2D and 3D finite element method software. It is found that the depth and width of the failure surface increase with the increment of the slenderness ratio. A good agreement is observed among the measured bearing capacity and obtained failure surface of the models and the results of numerical modelling. Finally, the maximum deformation of loose and dense sand respectively with densities of 25% and 75% were compared in the stage of fully removing pile. The results shows that the deformation of the soil is related to its density, therefore it depends on its dilatancy.

Uplift resistance of buried pipes anchored with geosynthetics

ABSTRACT: Buried pipes are important components of the oil industry for the transportation of different types of fluids. Accidents with such pipes can cause severe damage to the environment and to neighbouring structures and, unfortunately not rarely, with the loss of human lives. Among others, the action of waves, buoyance and pipe bucking can cause undesirable vertical or lateral displacements of buried pipes. This paper examines the use of geosynthetics as anchorage of buried pipes. Model tests were carried out with different types of geogrids and anchorage arrangements. The results showed that the presence of the anchorage can increase maximum pipe uplift forces as much as 180% in comparison with the result obtained for the unanchored pipe. Equations for estimates of maximum uplift force for anchored pipes were developed and comparisons between predictions and measurements are presented and discussed. The results obtained show the potential use of geosynthetics to anchor buried pipes.

사질토지반에서 그룹 마이크로파일의 설치조건에 따른 인발거동특성

마이크로파일은 직경 300mm 이하의 소규모 말뚝기초형식으로, 기초구조물의 보강을 위해 널리 적용되고 있다. 본 연구에서는 일련의 인발재하시험을 통하여 그룹 마이크로파일의 설치조건에 대한 영향을 조사하였다. 본 연구를 위하여, 다양한 설치간격과 설치각도로 설치된 그룹 마이크로파일을 이용한 인발재하시험을 수행하였으며, 실험결과를 통해 인발지지력 증가특성과 인발변위 감소특성을 조사하였다. 인발저항력은 주로 마이크로파일의 설치각도에 영향을 받는 것으로 나타났으며, 인발저항력의 증가는 설치각도 15도, 30도, 45도에서 각각 33%, 59%, 5%가 증가되는 것으로 나타났다. 설치간격에 따른 인발변위의 감소량은 더 좁은 설치간격조건에서 크게 나타났으며, 동일한 설치간격조건에서의 설치각도에 따른 인발변위 저감율은 설치각도 15도, 30도, 45도에서 각각 50%, 53%, -45%가 되는 것으로 나타났다. The micropile is small diameter pile foundation of which diameter is below 300 mm. This system has been applied to reinforce the foundation structure. In the present study, the effects of embedded conditions of group micropiles were investigated from a series of uplift load tests. For the study, uplift load tests were performed using group micropiles in various pile spacing and installation angle. The increase of uplift resistance and the reduction of uplift displacement were investigated in the tests. As the result, the resistances were principally changed by embedded pile angle, the resistance increase were 33%, 59% and 5% for <TEX>$15^{\circ}$</TEX>, <TEX>$30^{\circ}$</TEX> and <TEX>$45^{\circ}$</TEX> of embedded pile angle. The uplift displacement reduction increases with lower pile spacing condition and the reduction ratios of uplift displacements in the same spacing condition were 50%, 53%, -45% for <TEX>$15^{\circ}$</TEX>, <TEX>$30^{\circ}$</TEX> and <TEX>$45^{\circ}$</TEX> of embedded pile angle.

Mechanical analysis of anti-buoyancy safety for a shield tunnel under water in sands

Tunnels located under rivers and seas are subject to buoyancy from water or grouting pressure during tunneling. Because of road alignment, and topographic and geologic conditions, shield tunnels in soft soil locations are buried as shallowly as possible. However, shallow earth cover, especially for large cross-section tunnels, may not sufficiently ensure the anti-buoyancy safety of tunnels. This paper investigates tunnel uplift resistance using the limit equilibrium method. Models and formulas for uplift resistance are proposed that include a consideration of the dilation effect of sands. The test results from relevant literature show that an analysis based on the dilatant failure mechanism can provide an improved method for tunnel uplift resistance prediction. After the uplift resistance model is established, the formulas for calculating the minimum buried depth for achieving anti-buoyancy safety for shield tunnels are supplied. Grout weight and buoyancy are discussed. The projects indicate that the failure mechanism calculation that takes into account the dilatancy of the soil is reliable for setting the minimum buried depth of the tunnel along with consideration of other factors, such as riverbed erosion. The minimum ratios of buried depths to tunnel diameter are supplied along with safety factors for various sand properties, which may serve as a useful reference for tunnel designers.

Effects of soil reinforcement on uplift resistance of buried pipeline

Pipeline failure caused by low uplift resistance in soil is a serious environmental and economic issue. Hence, having access to higher uplift resistance of pipeline through soil reinforcement has received considerable attention. The objective of this study is to examine the effect of performing geogrid to increase the uplift resistance of buried pipelines. To examine the effect of burial depth, pipe diameter, length of geogrid layers and the number of geogrid layers on the peak uplift resistance (PUR) of loose sand, 33 small-scale tests were performed in the laboratory. Results of laboratory tests reveal that depth of burial and pipe diameter have a direct effect on the PUR results. The findings show that the number of geogrid layers does not have a remarkable influence on PUR values. While the residual PUR values are of interest, for the same length of geogrid, the use of two layers of geogrid instead of one is advantageous. To verify the experimental results, 33 experiments were back analyzed using “PLAXIS 3D TUNNEL” program. It was found that experimental and numerical results are in good agreement.

Deformation model of sand around short piles under pullout test

Piles as a member of structures can be failed due to structural collapses or soil’s body failure. Extensive experimental studies have been conducted in literatures to identify the behavior of piles failure mechanism in sand. Nevertheless, the number of researches with respect to uplift failure of short piles are limited and this issue needs to be studied. In this study, three small-scale physical tests were performed to investigate the uplift resistance of short piles in loose sand with pile diameter of 5cm and slenderness ratio of 2, 3 and 4. Close photogrammetric technique and Particle Image Velocimetry (PIV) were also employed to observe the deformation patterns due to uplift force. For verification purposes, the results obtained from the laboratory tests were compared to the results of ABAQUS finite element method (FEM) software. It was found that the slenderness ratio is the most influential factor on the pile uplift capacity values obtained by experiments. In addition, a reasonable error was observed between the measured bearing capacities obtained by experiments and the results of the numerical modeling. The minimum and maximum errors of 0.6% and 11% between experimental and numerical results reveal that the ABAQUS software can simulate the experimental tests behavior with high degree of accuracy. Besides, similar failure zone was achieved by both PIV and numerical techniques.

Effect of Groundwater Seepage on Uplift Resistance of Buried Pipelines

The uplift resistance of pipelines buried in sands, in the presence of inclined groundwater flow, considering both upward and downward flow directions, has been determined by using the lower bound finite elements limit analysis in conjunction with nonlinear optimization. A correction factor (f (gamma) ), which needs to be multiplied with the uplift factor (F (gamma) ), has been computed to account for groundwater seepage. The variation of f (gamma) has been obtained as a function of i(gamma (w) /gamma (sub) ) for different horizontal inclinations (theta) of groundwater flow; where i = absolute magnitude of hydraulic gradient along the direction of flow, gamma (w) is the unit weight of water and gamma (sub) is the submerged unit weight of soil mass. For a given magnitude of i, there exists a certain critical value of theta for which the magnitude of f (gamma) becomes the minimum. An example has also been presented to illustrate the application of the results obtained for designing pipelines in presence of groundwater seepage.

Comparative Analysis of Bearing Capacity of Inclined and Vertical Excavated Foundation

Excavated foundation has widely used in the field of transmission line engineering because of its large capacity to resist uplift and moment force. Elastic-plastic numerical model were established by using the finite element software ABAQUS focusing on the difference of bearing characteristics of inclined and vertical excavated foundation. There is very slight difference of axial uplift resistances between the both foundations because almost the same soil mass are mobilized at the same displacement loading. However, failure modes and horizontal resistances of negative, positive and vertical foundations are very different. The larger soil mass along the shaft of negative foundation is mobilized than positive and vertical foundations. The uplift resistances of vertical and negative foundations are about 5% and 25% higher than positive foundation at horizontal displacement of 50mm respectively.

Uplift Resistance of Buried Pipelines Enhanced by Geogrid

Failure of an oil or gas pipeline due to low uplift resistance of soil has serious economic and environmental consequences; hence, increasing the uplift resistance through soil reinforcement is of interest. The main purpose of this paper is to investigate the possible use of geogrid to enhance the uplift resistance of buried pipelines. For this reason, 11 small-scale laboratory tests were performed. The tests were conducted to investigate the effect of pipe diameter, burial depth, as well as length and number of geogrid layers on the uplift resistance of sandy soils. The experimental results suggest that although pipe diameter and burial depth are directly related to uplift resistance, the direct effect of geogrid incorporation is more pronounced. While Peak Uplift Resistance (PUR) is of interest, findings indicate that the number of geogrid layers does not have a pivotal influence on PUR. In addition, for verification purpose, the PUR of 11 laboratory tests were back analyzed numerically using finite element software PLAXIS 3D TUNNEL. The findings show that numerical and experimental results are in good agreement.

Experimental and numerical investigation of uplift behavior of umbrella-shaped ground anchor

In the past decade, different types of underreamed ground anchors have been developed for substructures requiring uplift resistance. This article introduces a new type of umbrella-shaped anchor. The uplift behavior of this ground anchor in clay is studied through a series of laboratory and field uplift tests. The test results show that the umbrella-shaped anchor has higher uplift capacity than conventional anchors. The failure mode of the umbrella-shaped anchor in a large embedment depth can be characterized by an arc failure surface and the dimension of the plastic zone depends on the anchor diameter. The anchor diameter and embedment depth have significant influence on the uplift behavior. A finite element model is established to simulate the pullout of the ground anchor. A parametric study using this model is conducted to study the effects of the elastic modulus, cohesion, and friction angle of soils on the load-displacement relationship of the ground anchor. It is found that the larger the elastic modulus and the shear strength parameters, the higher the uplift capacity of the ground anchor. It is suggested that in engineering design, the soil with stiffer modulus and higher shear strength should be selected as the bearing stratum of this type of anchor.

Wind Uplift Resistance of Artificially and Naturally Aged Asphalt Shingles

AbstractDamage assessment surveys performed following the 2004 and 2008 hurricane seasons indicate that the vulnerability of shingle roofs to wind-induced damage increases with age. This paper presents two interrelated experiments on the wind uplift resistance of asphalt shingle seals. The objective is to identify whether and to what extent aging reduces the wind uplift capacity. In the first experiment, asphalt shingles were artificially aged, and the mechanical uplift resistance was measured at discrete intervals. In the second experiment, mechanical uplift tests were performed in situ on ≥9-year-old shingle roofs installed on four central Florida homes. Results from the first experiment demonstrate that heat exposure can reduce uplift resistance along its sealant strip in some products; however, the excess capacity in the bond may be sufficiently large to prevent the mechanical resistance from dropping below the design requirement. Inclusion of ultraviolet and water in the heat-exposure tests did not a...

Numerical and Experimental Study of Uplift Mobilization of Buried Pipelines in Sands

Offshore oil and gas pipelines are commonly buried in seabed to provide environmental stability, thermal insulation and mechanical protection. These pipelines are frequently subjected to high thermal and pressure loadings that induce pipeline upheaval buckling (UHB). The uplift resistance provided by the cover soil increases with pipeline upward mobilization and reaches its peak at peak mobilization. This peak mobilization is fundamental for safe UHB designs. This paper highlights that the design guidelines underestimate the peak mobilization. The paper presents full-scale uplift results and finite-element parametric studies in which loose and dense cover soils of up to 3 m (soil cover height to diameter ratio up to 15) and pipeline diameters of 114 and 200 mm were investigated. Results from full-scale and finite-element modeling show that the peak pipe mobilization can be much greater than that suggested by current guidelines, and it is a function of the soil cover height to diameter ratio and soil relative density. A new relationship is proposed to predict peak mobilization from the soil cover height to diameter ratio for a given soil state.