Pullout Response of Inextensible Sheet Reinforcement Subject to Oblique End Force

The kinematics of failure of reinforced structures such as reinforced retaining walls, embankments, slopes, and grounds suggest that the failure surface intersects the reinforcement obliquely, thus causing an oblique pull to the reinforcement. In this paper, pullout resistance of sheet reinforcement is evaluated for the condition when the reinforcement is subjected to an oblique end force assuming a linear subgrade response and an inextensible reinforcement. At high obliquities of the end force, increase in friction resistance due to the downward component of the end force becomes high; however, the high obliquity also causes bending of the reinforcement which reduces the friction resistance and thus pullout occurs. Equilibrium equations are applied to the final deformed shape of the reinforcement after considering proper variation in normal stresses and friction resistance with the deformed shape. The horizontal component of the oblique pullout force is found to increase by over 50% of the pure axial pullout capacity of the reinforcement for a typical case of an obliquity of 60° and an angle of interface shearing resistance of 30°. The most important factors affecting the horizontal component of the pullout capacity are the obliquity of the end force and the interface angle of shearing resistance. A comparison of results with finite-element analysis of pullout tests and back-analysis of model test results on the reinforced wall suggests that the present model leads to a more rational and better prediction of pullout failures.     

Continuous Interface Elements Subject to Large Shear Deformations

Abstract: In this paper, an interface or joint subject to large shear deformation is modeled. In the proposed algorithm, continuous interface elements with a finite thickness are reconstructed at every load step based on current interface configuration, by employing the concept of contact band element. Special strain expressions for the continuous interface elements are derived with regard to the characteristics of shear strain concentration along the interface. The elastic cross-anisotropic model with the special Mohr–Coulomb criterion is applied for the continuous interface elements in view of the anisotropy of interface materials. Simulation of a pullout test has shown that large pullout displacement and realistic structure configuration might be effectively modeled and smooth distributions of mobilized shear stresses along the interface and axial forces in the reinforcement can be obtained without any fluctuation for different interface element thicknesses. However, the stress and axial force distributions along the interfaces and the reinforcement, especially near left end of the reinforcement, vary with the interface thickness. It strongly implies that the continuous interface element with an appropriate thickness should be a good choice for a rock interface or joint with fillings in.     

Pullout Behavior of Geogrid by Test and Numerical Analysis

This paper presents a study of geogrid pullout behavior in laboratory pullout tests and finite element modeling of the laboratory pullout tests. The pullout tests and the finite element method (FEM) analyses were carried out on two geogrid types with different stiffness values in dense sand under different overburden pressures. The pullout test results show that the geogrid behavior can be categorized into three types based on the bond stress distributions. The FEM results show reasonable agreement not only with the pullout force against the geogrid displacement, but also with the distributions of geogrid displacements, strains, tensile forces, and bond stresses along the geogrid length during deformation. This research demonstrates that the deformation characteristics of geogrids play an important role in the pullout tests while the interface properties play a significant role in the FEM simulations of geogrid pullout behavior. A method to obtain suitable interface parameters for designing of actual reinforced structures from the laboratory pullout tests is provided.     

Long-Term Reinforcement Load of Geosynthetic-Reinforced Soil Retaining Walls

As increasing number of geosynthetic-reinforced soil (GRS) retaining walls are built for permanent purpose, and their long-term behaviors have become one of the most critical issues in design. However, there has been very limited study on long-term reinforcement load and its relation to various parameters of GRS walls. A finite-element procedure for the long-term response of geosynthetic-reinforced soil structures with granular backfills was first validated against the long-term model test. Extensive finite-element analyses considering the viscous properties of geosynthetic reinforcements were then carried out to investigate the load distributions in geosynthetic reinforcements of GRS walls under operational condition. Construction sequence was simulated and a creep analysis of 10?years was subsequently conducted on each model wall. The effects of wall parameters, including backfill soil, reinforcement length, reinforcement spacing, reinforcement stiffness, and creep rate of reinforcement were investigated. It is found from the analyses that: (1) the maximum reinforcement load of GRS walls under working stress condition was generally smaller than that estimated using the FHwA design but it is dependent on the global reinforcement stiffness Sglobal; (2) the surface of maximum reinforcement load did not coincide with the Rankine’s surface suggested by FHwA design guidelines for vertical GRS walls and it was affected by the strength of backfill soil, reinforcement length, reinforcement spacing, and reinforcement stiffness; (3) for GRS walls under operational condition, reinforcement loads were closely related to the mobilized stiffness of backfill soil; (4) isochrone curves can be used to interpret the effects of reinforcement stiffness and creep rate on both short-term and long-term performances of GRS walls under operational condition, and with an increase in the reinforcement stiffness, the maximum reinforcement load increased; and (5) the global reinforcement stiffness Sglobal, which is related to the isochrones stiffness of reinforcement as well as reinforcement spacing was related to the total reinforcement load Ttotalmax and with an increase in the global stiffness, the total reinforcement load increased.     

Implementation of a Critical State Two-Surface Model to Evaluate the Response of Geosynthetic Reinforced Pavements

A finite-element model was developed using ABAQUS software package to investigate the effect of placing geosynthetic reinforcement within the base course layer on the response of a flexible pavement structure. A critical state two-surface constitutive model was first modified to represent the behavior of base course materials under the unsaturated field conditions. The modified model was then implemented into ABAQUS through a user defined subroutine, UMAT. The implemented model was validated using the results of laboratory triaxial tests. Finite-element analyses were then conducted on different unreinforced and geosynthetic reinforced flexible pavement sections. The results of this study demonstrated the ability of the modified critical state two-surface constitutive model to predict, with good accuracy, the response of the considered base course material at its optimum field conditions when subjected to cyclic as well as static loads. The results of the finite-element analyses showed that the geosynthetic reinforcement reduced the lateral strains within the base course and subgrade layers. Furthermore, the inclusion of the geosynthetic layer resulted in a significant reduction in the vertical and shear strains at the top of the subgrade layer. The improvement of the geosynthetic layer was found to be more pronounced in the development of the plastic strains rather than the resilient strains. The reinforcement benefits were enhanced as its elastic modulus increased.     

Bond Tests of Short NSM-FRP and Steel Bar Anchorages

Performance of near-surface mounted (NSM) bars as additional reinforcement in strengthening of existing reinforced-concrete construction largely depends on the development capacity of the bar inside the groove. This is controlled primarily by the surface characteristics of the bar and its interaction with the surrounding groove filler and the cover concrete. In this paper, the bond strength of short NSM-bar anchorages is explored experimentally, using a modified eccentric pullout test specimen designed to alleviate some of the deficiencies associated with bond testing. A total of 45 tests were conducted to study the influence of the most important technological parameters of this upgrading method, namely the groove dimensions, the embedment length, and the surface pattern of the bars. NSM bars were 12?mm diameter rods: CFRP bars used had a sandblasted surface and winding helical lengthwise indentations. Steel bars were either standard deformed bars or smooth reinforcement. The variety of bar type considered was intended to highlight and to quantify through the tests the bond strength that may be mobilized by postinstalled reinforcement according to surface profile and stiffness. Test results are used to establish a limit-state bond-slip model for near-surface mounted bars, so as to enable implementation of this emerging technology in practical design.     

Analysis of Dynamic Response of Architectural Glazing Subject to Blast Loading

The effect of blast loading on civilian structures has received much attention over the past several years. The behavior of architectural glazing is of particular interest owing to the disproportionate amount of damage often associated with the failure of this component in a blast situation. This paper presents the development of a simple yet accurate finite element-based tool for the analysis of architectural glazing subjected to blast loading. This has been achieved through the creation of a user-friendly computer program employing the explicit finite-element method to solve for the displacements and stresses in a pane of glass. Both monolithic and laminated panes have been considered, in single and insulated unit configurations, and employing several types of glass. In all cases, the pane of glass has been modeled as a plate supported by an array of boundary conditions that include spring supports, and two failure criteria are employed. Furthermore, the program is designed to predict the hazard level, given a particular glazing configuration and blast load.     

Estimating Subgrade Reaction Modulus for Transversely Isotropic Rock Medium

Most of the rock medium possesses intrinsic grain orientation or preferred bedding and joint directions, thus requiring the use of at least transverse isotropy to describe its elastic behavior. This paper presents a series of charts, based on extensive finite element parametric studies along with nonlinear regression analysis of FE simulation results, for estimating the subgrade reaction modulus (or initial tangent to the p-y curve) using five elastic constants of a transversely isotropic rock mass. The proper characterization of subgrade reaction modulus is critical for accurate prediction of the elastic lateral deflection of a rock socketed drilled shaft under the applied lateral loads. The sensitivity of the response of a laterally loaded drilled shaft to the degree of anisotropy and orientation of the plane of anisotropy (bedding plane direction of the rock medium) was demonstrated in this paper for an actual lateral load testing case in Ohio. It is highly recommended to use five elastic constants to estimate subgrade reaction modulus of rock medium exhibiting high degree of cross anisotropy.     

Finite-Element Analysis of Chemical Transport and Reinforcement Corrosion-Induced Cracking in Variably Saturated Heterogeneous Concrete

Reinforcement corrosion owing to chemical attack could lead to premature steel-mortar debonding, concrete cracking, and catastrophic failure of structures if not well attended. In conventional design and maintenance practices, heterogeneous concrete matrix is commonly treated as a homogeneous medium when the evolution of chemical ingress and concrete cracking need to be determined. Such oversimplification has caused significantly inaccurate prediction and evaluation of structural service life. This paper presents a finite-element (FE) model developed to evaluate the service life of reinforced concrete (RC) structures in three key steps: chemical ingress, steel corrosion, and concrete cracking. The mass conservation principle is employed in the first step to model the ingress of multiple chemical species into variably saturated heterogeneous concrete matrix. By using Faraday’s law, steel corrosion and the incurred diametric expansion are then formulated as a transient displacement boundary condition for subsequent analysis of concrete cracking. The cracking pattern of concrete under the expansion force of corrosion products is finally characterized by using a cohesive-fracture approach. The FE model is validated with laboratory experiments.     

￠550紧凑式轧机拉杆强度分析及结构改造

拉杆是紧凑式轧机的主要受力件 ,经常发生断裂事故。采用三维有限元对 5 5 0紧凑式轧机的拉杆进行应力分析 ,发现其底部钩头圆角处的应力已超过材料疲劳极限。针对存在的问题 ,对拉杆进行了相应的结构改造。改造后应力集中部位的最大应力显著降低 ,保证了轧机安全可靠的运行。     

Analyzing the Reinforcement Loads of Geosynthetic-Reinforced Soil Walls Subject to Seismic Loading during the Service Life

It is more rational to analyze permanent geosynthetic reinforced soil (GRS) walls against seismic loading based on their behavior during service life, but it has seldom been attempted. Calibrated finite-element procedure was used to investigate the reinforcement loads of GRS walls subject to seismic loading during service life, the results of which were compared to those predicted by Federal Highway Administration (FHwA) guideline. Parametric studies were carried out to investigate the effects of various wall parameters and characteristics of earthquake excitations. It is found that due to the isotach behavior of geosynthetics, the reinforcement loads during earthquake that occurs 10 years after construction were similar to those if the earthquake occurs at the end of construction. The FHwA method predicted roughly the maximum reinforcement load but it could not consider strain softening of soil and characteristics of earthquakes. The horizontal locations of maximum reinforcement load in lower reinforcement layers were farther away from the facing units than Rankine’s surface, which is believed to come from the potential compound failure.     

Complete Elastic Contact Subject to Cyclic Shear in Partial Slip

A fretting fatigue test for a complete contact problem is modeled using the finite element method. The objective is to obtain the response of the specimen-indenter contact under loading–unloading cycles. These are generated by applying a cyclic shear load to the indenter, whose maximum value does not cause global sliding of the indenter, but only partial slip. The evolution of the contact conditions over several cycles is studied, as well as the intensity of the singularities present at the left and right corners, measured through the generalized stress intensity factors. In addition, some conclusions regarding the conditions that lead to partial slip are inferred. This represents a stage in the development of an asymptote-based fretting fatigue model.     

Buried Pipelines Subject to Subgouge Deformations

Engineers often model pipe/soil interaction events based on the concept of subgrade reactions originally proposed by Winkler. Engineering models often utilize beam and nonlinear/plastic spring elements to represent pipelines and the surrounding soil medium, respectively. The spring formulations, defining soil resistance to deformations in three-dimensional space, are usually assumed to be independent and the responses are discrete between adjacent soil zones. However, this idealization does not truly replicate a soil medium behavior. This study presents coupled numerical analyses of pipeline for the specific problem of subgouge deformations due to ice gouge events. Three dimensional continuum analyses of coupled pipe/soil/ice keel interaction using an explicit arbitrary Lagrangian finite- element approach were performed. The study compares the continuum finite-element results with Winkler-type analysis for the specific analyzed problem. A Lagrangian adaptive meshing technique was employed to model very large movement and achieves a steady-state condition; and reasonable ice/soil and soil/pipe interaction interfaces are employed. The numerical analysis shows the potential for continuum modeling of pipe/soil interaction events and develops a better understanding of ice gouging and pipe/soil/ice keel interaction.     

Performance of Geosynthetic-Encased Stone Columns in Embankment Construction: Numerical Investigation

This paper presents the results of a numerical investigation into the performance of geosynthetic-encased stone columns (GESCs) installed in soft ground for embankment construction. A three-dimensional finite-element model was employed to carry out a parametric study on a number of governing factors such as the consistency of soft ground, the geosynthetic encasement length and stiffness, the embankment fill height, and the area replacement ratio. The results indicate among other things that additional confinement provided by the geosynthetic encasement increases the stiffness of the stone column and reduces the degree of embankment load transferred to the soft ground, thereby decreasing the overall settlement. It is also shown that the geosynthetic encasement has a greater impact for cases with larger stone column spacing and/or weaker soil. Also revealed is that unlike isolated column loading conditions, full encasement may be necessary to ensure maximum settlement reduction when implementing GESCs under an embankment loading condition. Practical implications of the findings are discussed in detail.     

Failure Analysis of Modular-Block Reinforced-Soil Walls during Earthquakes

Several modular-block reinforced-soil retaining walls failed during the 1999 Ji-Ji (Chi-chi) earthquake of Taiwan. Similar walls showed distress during the 1994 Northridge, Calif., earthquake. The instability or failure of these walls offered an opportunity to validate the simplistic pseudostatic limit-equilibrium procedures. In this study, the Ta Kung Wall of the Ji-Ji earthquake is analyzed, and the Gould and Valencia Walls of the Northridge earthquake are revisited with an improved estimation of local site acceleration. The local acceleration was estimated by using simple attenuation relationships obtained through the earthquake records. The results of analysis indicate that these three walls had adequate internal stability under estimated site acceleration. The geosynthetic length was inadequate to resist compound modes of failure where the potential failure surface extends beyond the reinforced zone. The external stability was most critical in the presence of horizontal and vertical accelerations.     

Field Evaluation of a Glass-Fiber Soil Reinforcement System

A soil reinforcement system using the combination of glass-fiber-reinforced polymer (GFRP) pipe and pressure grouting has been developed by a Korean company. The system is being adopted as slope stabilization measures in Hong Kong. Individual GFRP pipes were designed and installed as soil nails with the exception that two-stage pressure grouting was applied instead of gravity grouting. A full-scale field evaluation on constructability and in situ performance of the system was performed in Hong Kong. The performance of the constructed nails was evaluated by pullout tests. The construction procedure, site adaptations of the Korean product made in Hong Kong, field test procedure, and performance of the constructed soil nails are reported in this paper.     

无横梁高刚度轧机机架有限元分析

利用有限元法对２５０ 无横梁高刚度轧机机架强度、刚度进行分析，从中找出机架的薄弱环节，为机架的设计制造提供理论依据。     

Response Analysis of Field-Scale Fully Grouted Standard Cable Bolts Using a Coupled ANN–FDM Approach

This paper presents a coupled approach using an artificial neural network (ANN) and the finite difference method (FDM) that has been developed to predict the distribution of axial load along fully grouted standard cable bolts in the field using laboratory pullout test data. A back-propagation training algorithm was used in ANN to determine axial loads in the cables tested in the laboratory. The ANN component of the computational model was trained using two different types of data sets. At first, the ANN was trained to predict the axial loads in a series of short cables grouted with Portland cement at a specific water-to-cement ratio and subjected to different radial confining stiffness values. Next, the ANN model was trained for an expanded case to include the influence of lateral confining stress on the distribution of axial load in the cable reinforcement. Finally, the ANN model was implemented into a widely used, FDM-based geotechnical software (FLAC). The accuracy of the ANN–FDM model is demonstrated in this paper against measured data from laboratory and field tests. The analysis approach introduced in this study is a valuable computational tool that can be used to determine the axial load distribution in long standard cable bolts, which are commonly installed to stabilize rock masses in various geotechnical, transportation, and mining applications.     

管材矫直机预紧机架力学模型及有限元分析

根据矫直机工作原理以及无缝钢管的特殊工艺,通过弯矩理论和材料力学理论从理论上计算出了六个辊的矫直力解析解。分析了预紧力规律和预紧理论,从而确定了矫直机机架需要施加的预紧力。创新性的完成了矫直机机架的力学模型的实体有限元化。有限元计算结果显示机构符合设计要求。计算结果有助于同类机构的设计。