Anchorage Resistance Research Articles

Research on the mechanical model of anchorage resistance in deeply filled jointed rock masses

The calculation model of anchorage resistance is the core issue in the study of anchorage theory in jointed rock masses. Due to the complex geological environment of deep rock masses, the anchorage mechanism of soft rock filled in joints is even more complicated and has not yet been clearly defined. Based on the theory of structural mechanics, considering the restraining stress in the plastic extrusion deformation zone of the bolt as a rectangular distribution pattern is more in line with the interaction state between the bolt and the surrounding medium when the rod is at its limit load. Taking into account the influence of the joint filling part, the value of restraining stress is revised to include a formula expression that factors in the strength of the filling material(σcj) and the degree of filling(Δ).Develop a mechanical model of anchorage resistance for filled joint soft rock considering large deformation conditions due to turning angles. Further, conduct shear tests on anchored filled joint rock bodies under various σcj−Δ combination patterns with constant normal stiffness (CNS) boundary conditions to validate and analyze the model. The research results indicate that under the influence of deep rock mass mechanical boundaries, the ratio of the shear deformation section length to the bolt diameter differs from existing research results, with specimens l/D under different σcj−Δ combinations typically ranging between 0.7 and 1.5 times.The displacement of the bolt at turning angle θ increases with the increase of Δ and decreases with the decrease of σcj, where Δ is the main factor affecting the degree of tensile-bending deformation of the bolt. As Δ increases, the calculated contribution rates of bolt shear resistance under three different σcj conditions increase from 9.8% to 34.8%, 40.3%, and 39.4%, respectively. This indicates that an increase in Δ can reduce the increment of normal stress, further decrease the overall stress and compressive deformation zone’s normal constraint stress in the rock mass, leading to a gradual increase in the degree of tensile-bending deformation of the bolt and an increase in resistance contribution.For the specimens with three different values of σcj, the ratio of shear force to axial force providing resistance on the joint surface decreased from a maximum of 2.83 to 0.72, 1.04, and 2.01, respectively. This indicates that when σcj is relatively large, tensile-bending deformation is more likely to occur, mobilizing the axial force of the bolt to provide the main resistance. Further systematic analysis was conducted on the length of the shear deformation section of the bolt and the distribution characteristics of the anchor resistance under condition β=30°∼90°. The reasonableness of the model was verified through the comparison of model calculation results with experimental data. Finally, a series of recommendations were proposed for preventing failure of the anchored system in filled jointed rock masses in actual engineering projects.

Patterns of riparian forest disturbance caused by tree dislodging on a subtropical river during large floods

AbstractRiparian forests contribute to the resilience and biocomplexity of floodplains but may be catastrophically impacted by large floods. Forest disturbances will expose floodplains to stripping and pulses of large wood recruitment to the floodplain and channel. The widespread uprooting of trees follows hydrodynamic loading from floodwaters and the associated moments of these forces about the tree bases. A tree will uproot when the drag moment exceeds the anchorage resistance capacity. Alternatively, trunks will rupture when the tensile stresses caused by bending exceed the tensile strength of the outer trunk fibres. The likelihood and pattern of trees dislodging during floods on a subtropical river was investigated by developing a tree stability model. The modeling framework included development of a drag moment model and testing several potential formulations for anchorage resistance. Model parameters were calibrated to data collected in experiments and from observations in aerial photographs before and after a large flood in 2011. The prediction accuracy for the adopted tree stability model was 78%. Results from design flood simulations suggest that less than a third of the forest will dislodge even during the largest floods conceivable. This remarkable stability moderates the quantity of large wood recruited from riparian forests during extreme floods, which can impact infrastructure such as bridges and culverts downstream. Low rates of wood recruitment from dislodged floodplain trees in extreme floods suggests bank erosion is the dominant source of wood recruitment in these catchments.

Probabilistic investigation of transmission length formulations considering model uncertainties

Transmission length is a key parameter for detailing and assessing shear and anchorage resistance of pre-tensioned concrete members, and according to the main design codes, semi-empirical models are adopted to estimate its value. In these approaches, model uncertainty may affect the results and often plays an important role in achieving the desired reliability. The purpose of this study is to investigate the current code design formulations for the transmission length described in the upcoming Eurocode2:2020 and fib Model Code 2020, and to propose new coefficients to consider the model uncertainties. To this end, a database with 951 experimental measures of transmission length was collected from the existing literature and properly filtered to obtain a homogeneous sample of 561 experimental observations on which model formulations were applied. The uncertainties of the two models were estimated and suitable probability models were derived. Results show that the prestress force release methodology strongly affects the uncertainties, both in terms of mean value and dispersion of the prediction. Finally, new probabilistic coefficients were proposed to adjust the formulations and ensure the achievement of the target reliability length to be adopted in each design situation, both at the serviceability and ultimate limit states.

Evaluation of cuspid cortical anchorage with different sagittal patterns using cone-beam computed tomography: a retrospective study

BackgroundNo studies have focused on cortical anchorage resistance in cuspids, this study aimed to characterize the cortical anchorage according to sagittal skeletal classes using cone-beam computed tomography (CBCT).MethodsCBCT images of 104 men and 104 women were divided into skeletal class I, II, and III malocclusion groups. Skeletal and dental evaluations were performed on the sagittal and axial cross-sections. One-way analysis of variance followed by least significant difference post-hoc tests was used for group differences. Multiple linear regression was performed to evaluate the relationship between influential factors and cuspid cortical anchorage.ResultsAll cuspids were close to the labial bone cortex in different sagittal skeletal patterns and had different inclinations. There was a significant difference in the apical root position of cuspids in the alveolar bone; however, no significant difference in the middle or cervical portions of the root was found between different sagittal facial patterns. The middle of the cuspid root was embedded to the greatest extent in the labial bone cortex, with no significant difference between the sagittal patterns. For all sagittal patterns, 6.03 ± 4.41° (men) and 6.08 ± 4.45° (women) may be appropriate root control angles to keep maxillary cuspids’ roots detached from the labial bone cortex.ConclusionsComparison of skeletal class I, II, and III malocclusion patients showed that dental compensation alleviated sagittal skeletal discrepancies in the cuspid positions of all patients, regardless of the malocclusion class. Detailed treatment procedures and clear treatment boundaries of cuspids with different skeletal patterns can improve the treatment time, periodontal bone remodeling, and post-treatment long-term stability. Future studies on cuspids with different dentofacial patterns and considering cuspid morphology and periodontal condition may provide more evidence for clinical treatment.

Numerical investigation on the debonding of cement anchorage in clay rocks based on a hybrid FEM/DEM model

In this study, the failure process of the cement mortar-clay rock (C–C) binary was analyzed using a composite hybrid FEM/DEM model. First, an improved pressure-related cohesive element was used to simulate the mechanical properties of the binary interface. Then, a numerical model of the cement anchorage body in clay rocks was constructed based on the new interfacial cohesive element and FDEM model of clay rock. Finally, the debonding and slip failure process of the anchorage was analyzed by the numerical model and a corresponding physical model test. The results show that: except for the debonding of the interface, the fracture of weaker side material (clay rock) is also a potential failure mode of the C–C binary. The clay rocks have a larger internal friction angle but smaller cohesion, so the failure mode changes from the shear failure of clay rock to the debonding of the interface when the normal pressure is up to 200 kPa. The failure of the anchor may also cause by the generation of the shear failure zone in soft rock instead of the interface debonding. Therefore, the shear strength of the rock should also be considered in the calculation of anchorage resistance.

Nonlinear spring modelling approach for concrete edge breakout failure of shear loaded anchorages of arbitrary configurations

The failure of anchorages placed close to the concrete edge and loaded in shear perpendicular towards the edge is often governed by the concrete edge breakout failure. Several assumptions are made in the current design methods to calculate the anchorage resistance, which simplify the calculations but may also lead to over-conservative or even unconservative design solutions. This paper presents a novel nonlinear spring modelling approach for the realistic evaluation of shear loaded anchor groups in case of concrete edge failure. The model follows a displacement-based approach and is developed on the basis of evaluation of a comprehensive experimental study carried out on shear loaded anchor groups. The basic philosophy follows the principles of the nonlinear spring model for the concrete cone failure mode of tension loaded anchorages, published earlier by the authors. In the nonlinear spring modelling approach for shear, it is assumed that the shear forces acting on a group are transferred from the base plate directly to the anchors. Nonlinear springs are used for modelling the anchor behavior to account for the distribution of forces among the anchors of the group. The nonlinear springs are provided to resist the forces acting in the loading direction and opposite to the loading direction, which might occur case of eccentric loading. While defining the properties of the nonlinear anchor springs, due consideration is given to the neighboring anchors through a tributary volume approach, to the vicinity of further edges and to the hole clearance. The friction between base plate and concrete is conservatively neglected. The postulates of the method are justified through a detailed evaluation of test results. The accuracy of the model is validated against a vast number of experimental results on anchor groups of arbitrary configurations.

ECM Architecture-Mediated Regulation of β-Cell Differentiation from hESCs via Hippo-Independent YAP Activation.

Changes in the extracellular matrix (ECM) influence stem cell fate. When hESCs were differentiated on a thin layer of Matrigel coated onto PDMS (Matrigel_PDMS), they exhibited a substantial increase in focal adhesion and focal adhesion-associated proteins compared with those cultured on Matrigel coated onto TCPS (Matrigel_TCPS), resulting in YAP/TEF1 activation and ultimately promoting the transcriptional activities of pancreatic endoderm (PE)-associated genes. Interestingly, YAP activation in PE cells was mediated through integrin α3-FAK-CDC42-PP1A signaling rather than the typical Hippo signaling pathway. Furthermore, pancreatic islet-like organoids (PIOs) generated on Matrigel_PDMS secreted more insulin than those generated from Matrigel_TCPS. Electron micrographs revealed differential Matrigel architectures depending on the underlying substrate, resulting in varying cell-matrix anchorage resistance levels. Accordingly, the high apparent stiffness of the unique mucus-like network structure of Matrigel_PDMS was the critical factor that directly upregulated focal adhesion, thereby leading to better maturation of the pancreatic development of hESCs in vitro.

Cyclic Performance of GFRP-RC T-Connections with Different Anchorage and Connection Details

This study investigated the effects of different configurations of connection reinforcement and anchorages on the cyclic behavior of glass fiber–reinforced polymer (GFRP) reinforced-concrete (RC) exterior beam–column connections (T-connections). Three full-scale GFRP-RC T-connections were tested under reversed cyclic loading. One connection was detailed with 90-degree hooked anchorage and horizontal stirrups, while the other two connections were detailed with L-shaped anchorage by placing additional Z- or U-shaped bars at the connection region. The objective of this study was to investigate the influence of the anchorage type (90-degree hook or L-shaped) at the end of the longitudinal bars of the beam on the cyclic performance (strength, ductility, and energy dissipation) of GFRP-RC T-connections. Moreover, the anchorage performances in terms of anchorage resistance, bond stress–slip of bars within the joint were evaluated and compared with each other. Test results indicated that all the connections passed a 5.09% drift ratio without any loss of strength. The addition of U-bars into the L-shaped anchorage connection significantly improved the strength, ductility, and energy dissipation compared with the other two connections.

Impact of soil water content on the overturning resistance of young Pinus Pinaster in sandy soil

Background and aimsThe tree resistance to uprooting is crucial to face wind damage in temperate forest. Tree anchorage varies considerably with site conditions, species, and tree age. Only few studies have focused on the influence of the site soil properties on the tree anchorage. With ongoing climate change, the soil hydrologic conditions are changing in Europe due to higher precipitations during winter, with possible higher risk of wind damage in forests. MethodsThis study investigates the role of soil hydrology on tree anchorage of Pinus pinaster in sandy soil with a combination of field experiments and simulations. Tree pulling experiments until root-soil system failure were performed for 12 Pinus pinaster of 14 years-old growing in podzol to measure the tree resistance to uprooting Mc for two contrasted soil water conditions. In addition, simulations were conducted to analyze how Mc changes during the progressive wetting of the layered soil. For that purpose, a new model was developed for Mc. This model also includes a sub-model for the shear mechanical strengths of the sandy soil layers and their variation with soil water content. The model was calibrated with different data sets: (1) the Mc-data obtained from the tree pulling experiments performed on 14 years-old Pinus pinaster; (2) the 3D root system architectures of the pulled trees; and (3) the soil shear mechanical strength as function of the soil water content measured in laboratory by direct shear tests and soil water retention curve measurements. After calibration, Mc-calculations were performed when simulating a progressive soil wetting by water table increase or by water saturation front progression. ResultsField-data and simulations show that Mc depends little on soil water content outside the domain of complete soil saturation. Close to saturation, simulations show that Mc decreases drastically up to 40 % of its value. This is specific to sandy soil whose mechanical strength is mainly due to the capillarity forces between grains. As illustrated by simulations, the anchorage resistance results from two components. The first friction component slightly increases with soil water content. The second suction component decreases little with soil water content and drops down at saturation when all the interstitial water in the soil porous network merges. ConclusionsThis loss of anchorage resistance at full saturation may increase considerably the risk of wind damage of forest growing in sandy soil as floods increase with climate change in Europe.

Resistance of corroded RC beams: Extending fib Model Code 2010 models

AbstractThe residual resistance of corroded reinforced concrete members depends on steel and concrete cross section loss and deterioration of material properties for steel, concrete, and bond. The paper considers these phenomena in models for resistance calculations, starting from the cross section and stress field models in Model Code 2010. The aim of this study is to develop models proposed by Coronelli et al., using a recently proposed approach by Blomfors et al. to model bond of corroded reinforcement based on the Model Code 2010 bond stress–slip relation. Flexure, shear, and anchorage resistance of corroded reinforced concrete beams are studied. The verification is carried out by comparison with tests on corroded beams with different shear span‐to‐depth ratios. The bond deterioration leads to changes in the inclination of the stress fields in B regions and anchorage failures. The reduced resistance and the changes of the failure modes caused by the deterioration phenomena are captured by the modeling approach.

GFRP Bars Anchorage Resistance in a GFRP-Reinforced Concrete Bridge Barrier.

In the present paper, experimental and numerical investigations were conducted on concrete bridge barriers utilizing glass fiber reinforced polymer (GFRP) bars with a hook at their ends. Implementation of these hooked bars instead of the bent bars or headed-end bars in the bridge barriers presented in the Canadian Highway Bridge Design Code (CHBDC) was investigated on American Association for State Highway and Transportation Officials (AASHTO) test level 5 (TL-5) concrete bridge barriers. This research aimed to reach a cost effective and safe anchorage method for GFRP bars at the barrier–deck junction, compared to the conventional bend bars or headed-end bars. Therefore, an experimental program was developed and performed to qualify the use of the recently-developed, small radius hooked bars at the barrier–deck junction. The experimental findings were compared with the design factored applied transverse load specified in CHBDC for the design of the barrier–deck junction as well as factored applied bending moment obtained at the barrier–deck junction using a recently-conducted finite-element modeling. Satisfactory behavior for the developed hooked GFRP bars as well as their anchorage resistance was established and a reasonable factor of safety in design of barrier–deck joint was achieved.

The effect of miniscrew length and bone density on anchorage resistance: An in vitro study

With conventional anchorage, it is usually hard to accomplish a satisfactory result with an absolute anchorage, and this limitation could be resolved by the usage of mini-screw. The successful rate of miniscrew usage depends on its stability, which was determined by its length, bone density, cortical bone thickness, the insertion technique, the insertion angle, and the applied loads. To observe the effect of miniscrew length and bone density on anchorage resistance. Thirty pieces of miniscrew with 1.6mm in diameter were divided into three groups based on its length (n=10): 10mm (L), 8mm (M), and 6mm (S). Each group was further divided into 2 sub-groups: to be planted in optimal density bovine ribs (L1, M1, S1) and to be planted in low-density bovine ribs (L2, M2, S2). The density of bovine ribs was measured by CBCT. After the insertion of miniscrews based on respective groups, tensile test was done by means of Autograf Univerval Testing Machine to measure its stability. The data recorded was analysed using the Least Significant Difference (LSD) Fisher's test. The results of this study showed that L1 provided the greatest stability than other groups. On the other hand, the least stability was found in S2. The length of miniscrew and the density of bone affect the stability of miniscrew. In bone with optimum density, 10mm and 8mm miniscrew equipped good anchorage resistance while in bone with low-density only 10mm miniscrew provided favourable anchorage resistance.

Inquiry into bond behavior of CFRP sheets to concrete exposed to elevated temperatures – Experimental & analytical evaluation

Efficiency of strengthening with Fiber Reinforced Polymer (FRP) relies on bond properties of FRP to concrete. Exposing concrete to elevated temperatures would reduce its strength. This research is, therefore, aimed at investigating the bond behavior of carbon FRP sheets to heated concrete. To do so, concrete blocks were initially heated up to 300, 400 and 500 °C and then strengthened with FRP sheets. A total of 16 single lap shear tests were carried out. Two-dimensional Digital Image Correlation (2D-DIC) was utilized to measure full-field displacements. Analytical studies were performed as well to evaluate the effective bond length, strain and bond shear stresses. Experimental results showed that exposing concrete to elevated temperatures prior to FRP installation, significantly increased the anchorage resistance. Surprisingly, between 30 and 100% increase in maximum load was experienced for different temperatures. Moreover, slip and effective bond length increased as the preparation temperature increased, contributing to an increased anchorage resistance. Although heating concrete to elevated temperatures would reduce the concrete strength, experimental and analytical results demonstrated that bond properties of FRP-to-concrete improved considerably.

Behaviour of Prestressed CFRP Anchorages during and after Freeze-Thaw Cycle Exposure.

The long-term performance of externally-bonded reinforcements (EBR) on reinforced concrete (RC) structures highly depends on the behavior of constituent materials and their interfaces to various environmental loads, such as temperature and humidity exposure. Although significant efforts have been devoted to understanding the effect of such conditions on the anchorage resistance of unstressed EBR, with or without sustained loading, the effect of a released prestressing has not been thoroughly investigated. For this purpose, a series of experiments has been carried out herein, with concrete blocks strengthened with carbon fiber-reinforced polymer (CFRP) strips, both unstressed, as well as prestressed using the gradient anchorage. The gradient anchorage is a non-mechanical technique to anchor prestressed CFRP by exploiting the accelerated curing property of epoxy under higher temperatures and segment-wise prestress-force releasing. Subsequently, strengthened blocks are transferred into a chamber for exposure in dry freeze-thaw cycles (FTC). Following FTC exposure, the blocks are tested in a conventional lap-shear test setup to determine their residual anchorage resistance and then compared with reference specimens. Blocks were monitored during FTC by conventional and Fabry–Pérot-based fiber optic strain (FOS) sensors and a 3D-digital image correlation (3D-DIC) system during gradient application and lap-shear testing. Results indicate a reduction of residual anchorage resistance, stiffness and deformation capacity of the system after FTC and a change in the failure mode from concrete substrate to epoxy-concrete interface failure. It was further observed that all of these properties experienced a more significant reduction for prestressed specimens. These findings are presented with a complementary finite element model to shed more light onto the durability of such systems.

Long-term residual anchorage resistance of gradient anchorages for prestressed CFRP strips

Abstract This paper presents findings from a series of experimental investigations on the long-term resistance of the gradient anchorage, a purely epoxy-based non-mechanical anchoring technique for prestressed carbon fiber reinforced polymer (CFRP) strips, after exposure to accelerated ageing conditions. A segment of the complete anchorage solution is simulated by anchoring a prestressed CFRP strip to a concrete block. A custom-designed clamping system on one end allows for maintaining the prestress force constant during exposure to accelerated ageing. Upon such an exposure, the specimens are tested in a conventional lap-shear test setup. Several exposure scenarios and their effect on the residual load carrying capacity are considered, namely the effect of carbonated concrete (CC), freeze-thaw cycles (FTC), as well as their combination. Forces and full-field displacements, the latter by means of a 3D-DIC system, were measured during the prestress-force-release and lap-shear tests. Results indicate a higher anchorage resistance for CC compared to the reference specimens. For both groups a debonding in the concrete substrate was observed. Specimens subjected to FTC exposure suffer from a significant reduction in residual anchorage resistance, as well as a shift in failure mode from a concrete substrate dominated to an epoxy/concrete interface failure. The current knowledge on the residual resistance of gradient anchorage has to be adapted accordingly.

Residents' journal review

Residents' journal review

Transplant depth of cabbage plug seedlings affects root distribution and anchorage resistance

Lodging of cabbage plants (Brassica oleracea var. capitata) can reduce crop efficiency and yield during machine harvesting, and this is a problem in Japan in the context of growing demand for cabbage crops from the food processing and retail industries. We have previously described a method, involving transplantation of plug-grown seedlings at increased depth, which addresses these problems, but the reasons for this result were unclear. We therefore sought to determine the underlying mechanism by a further study assessing the distribution and anchorage of roots in cabbages transplanted at different depths. Cabbage plug seedlings were transplanted with the top of the plug-soil positioned either 5mm above (shallow planting) or 20mm below (deep planting) the surface of the planting soil. The number and diameter of the roots were determined during the head-filling stage. After removal of the cabbage head and leaves, the stem was artificially pushed downwards, in order to assess the type and resistance of root anchorage. The shallow-planted cabbages showed a few thick roots near the soil surface, in contrast with the deep-planted cabbages, which had grown many fine roots at a depth of 3–5cm. Artificial lodging caused the roots and surrounding soil to rotate to an extent that was dependent on the angle of the stem from the vertical. An angle of 30° from the vertical would appear to be critical for cabbage lodging. The deep-planted cabbages showed high resistance to lodging and improved anchorage resistance. The higher anchorage resistance, probably resulting from deeper root development, could be a contributory factor in the lower susceptibility to lodging of cabbages grown from deep planting of plug seedlings.

Calculation Technique for Externally Unbonded CFRP Strips in Structural Concrete Retrofitting

AbstractThis paper presents a calculation procedure for externally unbonded carbon fiber–reinforced polymer (CFRP) strips anchored at their ends in flexural strengthening of existing reinforced concrete structures. Due to strain incompatibility between the composite strip and the neighboring concrete surface, the well-known conventional cross-section analysis (CSA) employed for bonded reinforcements cannot be implemented. An iterative force equilibrium and strip strain adaptation with previously defined constitutive materials laws together with an optimization procedure in a numerical computing environment are used to overcome the computational complexities. For validation purposes, two static loading tests on reinforced concrete beams with an externally prestressed CFRP strip without bond except in the anchorage zones are compared to the numerical predictions. Prior to the final evaluation, a model for the anchorage resistance is implemented in the algorithm in order to capture the ultimate load due to a...

Anchorage resistance of CFRP strips externally bonded to various cementitious substrates

This paper presents a study on the anchorage capacity of Carbon Fiber Reinforced Polymer (CFRP) strips bonded to a cementitious substrate used for concrete surface reprofiling. The structural strengthening of a large-scale prestressed concrete girder in the framework of a bridge retrofitting project by means of prestressed CFRP strips required the levelling of an initial negative camber of about 2–4cm. Both midspan and girder end situations were investigated with lap-shear and prestress force-releasing tests. Four different solutions regarding the levelling material, i.e. three mortars applied by hand as well as dry shotcrete, were tested. The results in terms of strain, slip and total anchorage resistance are presented and compared. In the end, dry shotcrete is recommended for the girder application. In addition to a very convincing bond behavior, the application is, despite the necessity of involving a specialized company from the field, clearly less time-consuming and easier. The retained solution represents an interesting approach for future applications in bridge retrofitting when an even surface is necessary for bonding CFRP strips.

Effects of a newly designed apparatus on orthodontic skeletal anchorage.

Objective:An appliance was designed to increase the cortical bone surface contact area of miniscrew implants (MSIs). The purpose of this in vitro study was to evaluate the effects of this appliance on the anchorage force resistance and the stability of orthodontic MSIs.Materials and Methods:A total of 48 MSIs were placed into bone specimens prepared from the ilium of bovines. Half were placed with the newly designed apparatus and half were placed conventionally. All the specimens were subjected to tangential force loading perpendicular to the MSI with lateral displacement of 0.6 mm, using an Instron Universal Testing machine. The maximum removal torque of each tested specimen was also recorded. Both study and control groups were divided into two subgroups based on whether they had thin and thick cortical bone.Results:The test group had statistically higher force anchorage resistance and maximum insertion torque values than the control group (P < 0.001). The results were found to be more significant in cases in which the cortical bone was thin (P < 0.001).Conclusions:Within the limits of this in vitro study, the present findings suggest that the newly designed apparatus might have a favorable effect on MSI stability in patients presenting with thin cortical bone. Clinical studies are necessary to confirm the results that were observed in vitro.