Anchor Spacing Research Articles

Flexural capacity design model of reinforced concrete beams strengthened with hybrid bonded CFRP

In order to improve the calculation methodology for the flexural capacity of RC (Reinforced Concrete) beams strengthened with HB-CFRP (Hybrid Bonded-Carbon Fiber Reinforced Polymer), three-point bending tests were conducted in this study. The experimental setup involved 9 HB-CFRP strengthened T-shaped beams and 1 unstrengthened beam for comparison. The effects of anchor spacing, anchor pressure, CFRP thickness, and anchor distribution pattern on the flexural performance of strengthened beams were investigated. Additionally, the development of the full range load-deflection curves of the HB-CFRP strengthened specimens was analyzed. Two bond strength models (the Wu model and Liu model) were modified. Six parameters were considered in the modified model, namely, the CFRP elastic modulus, CFRP thickness, number of mechanical fasteners in the shear span, CFRP-concrete width ratio, concrete cylinder compressive strength and normal pressure applied to the mechanical fasteners. The accuracy of the modified models was compared on the basis of three specifications. Results indicated a notable enhancement in the flexural capacity of the strengthened beams, ranging from 61.1 % to 158.1 % compared to the unstrengthened beam. Taking the ACI specification as an example, the mean value and coefficient of variation (COV) of the flexural capacity obtained by directly using the Wu model were 1.187 and 0.169, respectively; the results obtained by using the modified Wu model based on the measured FRP strain were 1.038 and 0.125, respectively; and the results obtained by using the modified Wu model based on the ACI reversed-calculated strain were 1.012 and 0.106, respectively. After the strengthened beam reached the peak load, the load then decreased abruptly to the vicinity of the moment mid-span deflection curve of the reference beam. As the loading continued, the resistance improved by 27.4 %∼79.3 % due to the increase in interface friction in the mechanical fasteners and concrete.

Stability analysis of layered circular rock tunnels considering anchor reinforcement based on an enhanced mesh-free method

The impact of geotechnical structure and support construction on the stability of a layered circular rock tunnel was investigated based on an improved mesh-free method. The Smoothed Particle Hydrodynamics (SPH) was improved by incorporating a total bridge broken strategy into the kernel function and was validated through analysis of the mechanical behavior in circular opening problem and uniaxial compression tests. The Particle Domain Search (PDS) method is utilized to create crack pathways and implement anchor reinforcement in specific areas without the requirement for grid division. An SPH model of the Muzhailing tunnel was established to investigate the stability of the surrounding rock considering different anchor lengths and spacing. The result indicated that the enhanced SPH method provides a feasible approach for the rapid assessment of tunnel convergence displacement and damage coefficients. Furthermore, this method was validated through laboratory experiments and analytical solutions. For layered tunnels with other different dip angles, this approach offers a general optimization strategy for anchor reinforcing surrounding rock. These findings suggest that the enhanced mesh-free method, owing to its characteristics of efficient parameter calibration and computation, can be further expanded to the rapid assessment of the stability of layered slopes and foundations considering anchor reinforcement.

Investigating Load Arches and the Uplift Capacity of Rock Anchors: A Numerical Approach

Rock anchors, which can withstand substantial forces and are essential for securing the foundations of the built environment, can fail due to steel tensile failure, bond detachment, or rock mass fracturing through uplift. In this study, uplift failure of the rock mass surrounding rock anchors was simulated using both physical and numerical models. The physical models used a specially designed testing rig with predefined sizes and different joint layouts to simulate rock mass uplift failure. The numerical models were calibrated using the physical models and used to investigate scenarios involving increased complexity and greater depths. This paper presents the load distribution within rock masses with orthogonal joints when exposed to an anchor load. Extensive analysis of the numerical models revealed that symmetrical load arches were induced in rock masses that contained a joint set oriented parallel to the loading direction. However, joints that were obliquely oriented relative to the anchor axis induced asymmetrical load arching. The greatest displacement occurred in the direction parallel to the joint set with the smallest angle to the anchor loading axis. Large-scale models with zero or near-zero in situ horizontal stress revealed that the load capacity in a rock mass with continuous vertical joints was relatively low, especially when compared to rock masses with discontinuous vertical joints. It was observed that the uplift capacity of the rock mass around an anchor decreased if the load arches of adjacent anchors overlapped; consequently, a decrease in anchor spacing was found to correspond to a decrease in uplift capacity.

Behavior of FRP-engineered cementitious composite layer and concrete interface with FRP anchors

The problem of low material utilization caused by premature interface debonding is prevalent in carbon fiber-reinforced polymer (CFRP)-reinforced concrete structures. In this study, the influence of anchors on the bonding and behavior of the FRP-engineered cementitious composite (ECC) layer and concrete interface was analyzed. A total of 42 single shear tests were performed to investigate the interface–bond behavior between the FRP-ECC layer and concrete under static load in case of anchor reinforcement. The variables mainly include the matrix type, anchor location, anchor spacing, and number of anchors. The results show that the anchor can increase the interfacial load-carrying capacity up to 85%; the maximum slip value of the interface can also be enhanced. Furthermore, the influence of the location, spacing, and number of anchors on the interface bonding performance is closely related to the effective bonding length and post-anchor bond length. The effective bonding length is 400 mm based on the strain distribution calculation and analysis. The test results provide valuable information for FRP anchor reinforcement in FRP-ECC composite layer-reinforced concrete structures.

Numerical Analysis of Mooring Buoy for Securing N219A Aircraft in The Anchorage Area

The development of Indonesia's N219 aircraft in recent years has been carried out on a significant scale. Likewise, developing an amphibious version known as the N219A aircraft continued. Considering that Indonesia is an archipelagic country that has potential in many sectors, such as marine tourism, the N219A aircraft is designed to be able to land on the water. Consequently, facilities are needed for the aircraft to be secured safely. The analysis of determining the configuration of the length of the anchor line on the mooring buoy to secure the N219A aircraft was carried out by varying the line length of the rope to 50 meters, 60 meters, and 70 meters by FAA recommendations. Based on the numerical calculation, the anchor line configuration with a length of 60 meters has maximum tension with allowable criteria according to API RP 2SK in intact and damaged conditions. The anchor line configuration also has a maximum offset value that is shorter than other configurations. Therefore, the result obtained from the analysis of the N219A aircraft's anchor spacing for the sea conditions of Gili Iyang, Sumenep, Madura, and East Java is 118.18 meters.

A Stochastic Model of Cortical Microtubule Anchoring and Mechanics Provides Regulatory Control of Microtubule Shape.

The organization of cortical microtubule arrays play an important role in the development of plant cells. Until recently, the direct mechanical influence of cell geometry on the constrained microtubule (MT) trajectories have been largely ignored in computational models. Modelling MTs as thin elastic rods constrained on a surface, a previous study examined the deflection of MTs using a fixed number of segments and uniform segment lengths between MT anchors. It is known that the resulting MT curves converge to geodesics as the anchor spacing approaches zero. In the case of long MTs on a cylinder, buckling has been found for transverse trajectories. There is a clear interplay between two factors in the problem of deflection: curvature of the membrane and the lengths of MT segments. Here, we examine the latter in detail, in the backdrop of a circular cylinder. In reality, the number of segments are not predetermined and their lengths are not uniform. We present a minimal, realistic model treating the anchor spacing as a stochastic process and examine the net effect on deflection. We find that, by tuning the ratio of growth speed to anchoring rate, it is possible to mitigate MT deflection and even prevent buckling for lengths significantly larger than the previously-derived critical buckling length. We suggest that this mediation of deflection by anchoring might provide cells with a means of preventing arrays from deflecting away from the transverse orientation.

Experimental Testing of Post‐installed Anchors for Use in Retrofitting of RC Frame with Steel Braces

AbstractThe retrofitting of deficient Reinforced Concrete (RC) frames, particularly those with strength and stiffness irregularities such as Open Ground Story, has been widely researched. Steel braces are a great option for retrofitting these buildings, but the narrow section sizes of existing beams and columns pose a challenge. However, post‐installed chemical anchors can provide an efficient, cost‐effective solution for connecting such structures with steel braces, provided that they are designed properly to account for all possible failure modes. This study investigates the use of post‐installed chemical anchors to connect steel braces with narrow‐beam column subassemblies in existing low‐ to mid‐rise Open Ground Story buildings. The three experiment are considered to test the bracing conditions with elastic and yielding brace. The gusset plate is designed as per Balanced Design Procedure to obtain an economical section with controlled yielding and failure sequence. The forces on gusset plate are computed using the Uniform Force Method, which helps in designing the post‐installed anchor dimension and spacing. A comparison is drawn between the three test from which it is seen that the chemical anchors perform well in all cases and conventional brace shows expected performance.

Characterization of interface properties for modeling the shear behavior of T-beams strengthened with ultra high-performance concrete

The application of Ultra high-performance concrete (UHPC) lateral layers on normal-strength concrete (NSC) beams substantially improves their shear performance. However, the impact of the NSC-UHPC interface properties on the shear performance has been scarcely studied and may hinder the strengthening efficiency and modify the failure mode. This study has characterized the complete shear and tensile behavior of interface specimens and evaluated the effect of anchors at the interface. Then, the complete curves of the interface allowed calibration of an interface concrete fracture (CF) model that was introduced in finite element (FE) simulations replicating the shear behavior of UHPC-strengthened T-beams tested in the same project. Parametric studies were then made with FE simulations. Results showed the FE simulations with the CF model better capture the stiffness evolution and failure mode of strengthened beams than that with the perfect bond model. The increase of UHPC layer thickness up to 80 mm and anchor spacing at the interface smaller than 300 mm considerably increased the stiffness and shear capacity of the strengthened beams. Existing dead load on beams did not impair UHPC strengthening and a substantial increase in shear capacity can still be achieved in real-size strengthened T-beams.

Axial compression testing of concrete prisms confined by FRP spike anchors and estimation of failure modes

Reinforced concrete (RC) walls can exhibit poor drift capacity and premature concrete crushing if the compression region lacks sufficient confinement. Although fiber-reinforced polymer (FRP) jacketing has been used for confinement, wrapping FRP around the edges becomes challenging when adjacent components obstruct the process. To overcome this issue, a novel solution using FRP spike anchors is proposed in this study. These anchors provide confinement without requiring access to the wall edges, and they are installed by drilling holes through the structures, effectively addressing the obstructions. The study investigates the axially compressive behavior of concrete under this confinement approach. Axial compression tests were conducted on 18 concrete prisms confined with FRP spike anchors in addition to five unconfined concrete prisms. Their height by width by length dimensions were all 360 mm × 150 mm × 150 mm or 360 mm × 150 mm × 200 mm. The variables included anchor spacing and cross-sectional aspect ratio, namely length-to-width ratio. Test results indicate that the strain at peak and the failure strain of the confined concrete was respectively up to 1.85 and 5.28 times the ones of unconfined concrete when anchor spacing was 90 mm. An analytical method was developed to estimate the failure modes of the confined concrete prisms.

Shaking table tests of veneer masonry wall retrofitted with long-rawlplug screw anchors

Veneer masonry walls are vulnerable to lateral forces such as seismic loads, and their failure has caused human casualties and property damage. This study developed a new anchor for existing veneer walls and evaluated its seismic performance using shaking table tests. The presence or absence of retrofit anchors, combination of anchors and steel strips, and anchor spacing were considered as the experimental variables. Out-of-plane excitation was applied to the specimens, and the magnitude of the seismic acceleration was calculated according to the required response spectrum defined in ICC-ES AC156. The experimental results showed that overturning occurred on the non-retrofitted veneer wall; however, the veneer wall reinforced using the proposed anchor exhibited no overturning. The peak ground acceleration, relative displacement, amplification coefficient, and shear force of the reinforced specimens decreased relative to those of the unreinforced specimens. Notably, the proposed method achieved a high seismic reinforcement performance even when the anchor spacing was set to 800 mm.

Blast-Resistant Window Anchors. I: Experimental Investigation

A comprehensive experimental investigation was conducted on blast-resistant window anchors involving 46 tests of double-pane insulated glass units (IGUs) anchored to structural steel, reinforced concrete, concrete block masonry, and stone masonry substrates. The tests were conducted using a shock tube. The windows were glazed with security films of different thickness. Different number and spacing of steel anchors were used to secure the window frames to substrates. Each window was subjected to two levels of blast loads, consisting of 28 kPa, 207 kPa-ms, and 69 kPa, 621 kPa-ms reflected pressure–impulse combinations. The windows were instrumented to measure anchor forces. The anchors developed out-of-plane shear forces and in-plane axial tension associated with postbreak membrane action. The results indicate that anchor shear forces show variations with window stiffness, substrate type, and anchor arrangements, often developing lower forces than those computed based on the static application of blast loads, indicating significant inertia resistance. Rigid substrates produce higher anchor forces. In addition to the experimental results, the paper presents single-degree-of-freedom analysis results for anchor force computation, indicating good correlations with experimental data.

Influence of anchor design parameters on flexural performance of hybrid bonded-fiber reinforced polymer strengthened reinforced concrete beams

Strengthening concrete structures using adhesively bonded fiber-reinforced polymer (FRP) has been demonstrated as an effective method to improve the structural capacity. However, premature debonding of FRP material has limited the application of this technique. A number of anchorage methods have been proposed to enhance the bond performance, among which the hybrid bonded FRP (HB-FRP) has appeared to be more attractive as it can provide adhesive bond, frictional bond and dowel action. Previous studies have reported that the HB-FRP technique can considerably improve the bond strength and the flexural capacity of the strengthened beam. Yet, the influence of some key parameters on the flexural performance of the strengthened member is still not completely clear, and an accurate design method that can account for these parameters is not available for estimating the ultimate load capacity. In this paper, an experimental study was conducted on the HB-FRP strengthened beams to investigate the effects of anchoring pressure, anchor spacing, anchor distribution pattern, and FRP bonding mode. The test results indicate that the ultimate load-carrying capacity of the HB-FRP retrofitted member can be enhanced by increasing the anchorage pressure or decreasing the anchor spacing provided that the retrofitted beam fails by FRP debonding. The anchor distribution pattern has negligible influence on the flexural strength of the strengthened member, but uniform distribution of anchors along the bond length can yield higher flexural stiffness than the end anchoring approach. In addition, different FRP bonding mode can cause various strengthening mechanism in the HB-FRP system, leading to distinct flexural behavior of the retrofitted member. The dowel action of the anchor is suggested to be released by means of unbonding the FRP with the steel cap plate of the anchor since it may induce premature brittle anchorage failure. Based on the test results, a modified model is proposed for predicting the adhesive bond strength in HB-FRP system, in which a new parameter, referred to as spacing coefficient, is introduced to quantify the influence of the anchor spacing. Lastly, a theoretical model is developed in this study to design the ultimate moment capacity of the HB-FRP strengthened beam. A good correlation is achieved between the model predictions and the experimental results.

CentroidNet：a light-weight，fast nuclei centroid detection model for breast Ki67 scoring

目的 Ki67分数是乳腺癌预后评估的重要指标，计算该分数的关键步骤是检测阴性与阳性癌细胞核。人工检测面临疲劳与主观差异的问题。卷积神经网络有望实现高质量、自动化的细胞核检测，然而需要病理专家为其标注细胞核。为了减轻标注的工作量，不少研究者提出以中心点标注训练卷积神经网络。然而这些方法采用过于复杂的卷积神经网络和后处理流程，未能充分提高易用性和效率、发挥卷积神经网络的质量。对此，提出CentroidNet模型，旨在提高中心点检测的质量、效率和易用性。方法 CentroidNet模型在图像上放置均匀排布的锚点，为每个锚点预测一个候选点，一部分候选点通过基于阈值的筛选策略成为预测点。本文提出最近锚点匹配策略用于生成训练标签，既保证了端到端推理，又规避了其他一对一标签匹配算法所具有的标签抖动问题。本文建议锚点间距应尽可能接近训练集答案点间最短距离的第一百分位数，并指出这样的锚点间距能够在前景标签数、坐标回归难度与效率之间取得良好的平衡。本文在设计卷积神经网络的结构时，没有采纳广为使用的U-Net或特征金字塔（feature pyramid network，FPN）中的多级上采样与旁路连接，反而提高了质量和效率。结果 本文在BCData数据集上评估CentroidNet模型的质量与效率。BCData是目前规模最大的、公开的乳腺癌Ki67癌细胞核中心点检测数据集。在质量方面，CentroidNet取得的综合F1分数为0.879 1，媲美当前的最高质量。在效率方面，CentroidNet的推理速度为12.96 ms/幅、显存占用为138.8 MB/幅，达到了当前最高的效率，远低于若干主流或最新的模型。结论 CentroidNet具有高质量、高效率和高易用性；与现有同类模型相比，进一步提高了乳腺癌Ki67细胞核中心点检测的可行性。;Objective Breast cancer-prognostic Ki67 score can be as a key indicator for the proliferation rate of malignant （invasive）cells. Negative and positive nuclei detection is an essential part of Ki67 scoring. An automated algorithm for nuclei detection can alleviate the negative impact of intra/inter-observer variation and labor-intensive nuclei counting. In recent years，deep learning methods have been developing intensively in relevant to recognition tasks on pathology images in terms of their learning potentials. Deep learning-based model can learn features derived from the raw data and relieve labor-intensive annotation of training images for pathologists. To alleviate the labor cost of annotation，our research is focused on modeling Ki67 nuclei detection as the centroid detection problem. The existing centroid detection models are commonly used to convert the centroid annotation into a probability map with the same size as the input image，the centroid detection problem is thus converted to a semantic segmentation-like problem. However，a semantic segmentation model has restricted by huge computation cost due to its huge amount of convolutional layers-related decoder. Nevertheless，due to the non-deep-learning post processing on the output heatmap，the whole detection process is complicated and inefficient， and the quality of a deep learning model is required to be developed further. Our CentroidNet model is facilitated to optimize nucleus centroid detection. Method The CentroidNet consists of a fully convolutional centroid detector initiated by ResNeXt，along with the detector’s training and inference methods. The CentroidNet can place evenly spaced anchor points on the input image. Actually，the anchor points are the places where the center of the detector’s receptive field is sited on. Each anchor point-interconnected detector can predict the classification probabilities and the offset to the anchor point，which is called a candidate point as a whole. In this way，the anchor points are the niches of the candidate points. A candidate point has the highest probability and is higher than 0. 9. It is treated as predicted point. To assign labels for anchor/candidate points，we implement the“nearest anchor”strategy. This strategy can assign any annotated point to its nearest anchor point literally. Those anchor points are not assigned via any background label-assigned annotated point， whereas those classified label is“background”and label-coordinated is the anchor’s coordinate. This strategy is mutualbenefited between annotated points and anchor/candidate points. The label jittering problem can be avoided，which is often seen in current one-to-one assignment strategies. The anchors-between spacing is concerned about more. We recommend that the anchor spacing approximate the First Percentile of the minimal distance between each annotated point in the training set to its neighboring annotated points. Such spacing can balance the ratio of foreground labels，regressioncoordinated，and optimal efficiency. The CentroidNet’s detector can avoid the commonly adopted paradigm of U-Net or feature pyramid network（FPN），which involves shortcut connections and multiple upsampling layers. This lightweight detector can improve quality and efficiency. Result We evaluate the quality and efficiency of CentroidNet model on BCData，the largest publicly available dataset for centroid detection of Ki67 carcinoma nuclei in breast cancer. For quality analysis，the CentroidNet can achieve an averaged F1 score of 0. 879 1 compared to the SOTA（state of the art）score. For efficiency evaluation，the CentroidNet can achieve SOTA with an inference speed of 12. 96 ms/image and a GPU memory footprint of 138. 8 MB/image. Conclusion The CentroidNet is featured of light-weight，efficient and ease of use. It has the potentials for centroid detection of Ki67 carcinoma nuclei in breast cancer.

Experimental and Theoretical Research on the Bearing Mechanism of Group Anchors in Sand

To investigate the bearing mechanism and efficiency of group anchors in sand, upward pulling tests of model group anchors were carried out for different conditions of the sand density, anchor burial depth ratio, and anchor spacing. The results show that the load-displacement relationships for group anchors is similar to that for single anchors, both being nonlinear for the same relative density and embedment ratio. The load-carrying capacity of group anchors is not a simple superposition of the capacities of two single anchors, but has a clear superposition effect, depending on the relative density, embedment ratio, and anchor spacing. The load carrying capacity increases with the anchor spacing up to a limiting critical value. The bearing mechanism of group anchors was qualitatively analyzed and quantitatively characterized using the strain field and shear stress field obtained through the digital image correlation. Adopting the test data and theoretical derivation, a critical anchor spacing equation is proposed and the relationship between critical anchor spacing, embedment ratio, and relative density is quantitatively characterized. Theory is proposed for predicting the group efficiency of group anchors with different configurations. Comparisons between the results of the developed model and experimental results reported in the literature show good agreement.

Modulating pipe-soil interface friction to influence HPHT offshore pipeline buckling

High-Pressure High-Temperature offshore pipelines laid on the seafloor are subject to large temperature and pressure variations which manifest as axial pipeline loading. Pipes become unstable in this condition and buckles form to relieve the axial stress. Considerable theoretical and experimental energy has been directed at establishing controlling mechanisms and parameters to predict buckling and design pipeline systems to be resilient and serviceable. The pipe-soil interface friction plays a pivotal role in the rate of build-up of axial loads and in controlling the critical buckling threshold. Pipes adopting smooth polymer coatings have very low friction coefficients but experimental work has shown that simple roughening techniques make greater friction coefficients available to a designer. Presented are a series of numerical analyses carried out using Abaqus to model a pipeline resting on the seabed subject to typical HPHT pipeline conditions. Global stability response is assessed with pipe-soil friction coefficients varying from 0.25 to 0.75 and differential friction regimes are adopted. It is shown that targeted application of pipe sections with greater interface friction may be a useful design tool for manipulating global buckling phenomena and could be a useful additional tool for influencing the spacing in Virtual Anchor Spacing analysis.

Calculation model of shotcrete support thickness based on elastic thin plate theory

In order to accurately calculate the thickness of shotcrete in tunnel, the support load, inter-anchor row distance and concrete mechanical properties are selected as influencing factors, and a mechanical model of shotcrete support thickness is established based on the elastic thin plate theory to derive the relationship between support load, inter-anchor row distance, concrete mechanical properties and concrete thickness. The controlled variable method (CVM) was used to study the variation law of support load and inter-anchor row distance with concrete thickness. The results show that: the mechanical properties of the concrete slurry remain unchanged, the required thickness of the concrete support increases with the increase of the support load, in a power of 1/2 relationship, with the increasing thickness of the shotcrete, the concrete is prone to shear damage to tensile damage until the thickness meets the engineering requirements; the support load remains unchanged, the thickness of the concrete support is linearly related to the anchor rod spacing, with the increase of the anchor rod spacing As the anchor spacing increases, the required thickness of concrete support also increases linearly. This paper successfully defines the relationship between the required concrete support thickness, support load and anchor rod parameters for shear and tensile damage, and through the analysis of the anchor spraying case, it is believed that the calculation model is reasonable and the results can provide a theoretical basis for the quantitative design of the support system.

Effects of tendon viscoelasticity on the distribution of forces across sutures in a model of tendon-to-bone repair

Tears to the rotator cuff typically require surgical repair. These repairs often culminate in re-tearing when sutures break through the tendon in the weeks following repair. Although numerous studies have been performed to identify suturing strategies that reduce this risk by balancing forces across sutures, none have accounted for how the viscoelastic nature of tendon influences load sharing. With the aim of providing insight into this problem, we studied how tendon viscoelasticity, tendon stiffness, and suture anchor spacing affect this balancing of forces across sutures. Results from a model of a three-row sutured re-attachment demonstrated that optimized distributions of suture stiffnesses and of the spacing of suture anchors can balance the forces across sutures to within a few percent, even when accounting for tendon viscoelasticity. Non-optimized distributions resulted in concentrated force, typically in the outermost sutures. Results underscore the importance of accounting for viscoelastic effects in the design of tendon-to-bone repairs.

Numerical and Experimental Investigation on Concrete Splitting Failure of Anchor Channels

Concrete splitting failure due to tension load can occur when fastening systems are located close to an edge or corner of a concrete member, especially in thin members. This failure mode has not been extensively investigated for anchor channels. Given the current trend in the construction industry towards more slender concrete members, this failure mode will become more and more relevant. In addition, significantly different design rules in the United States and Europe indicate the need for harmonization between codes. Therefore, an extensive numerical parametric study was carried out to evaluate the influence of member thickness, edge distance, and anchor spacing on the capacity of anchor channels in uncracked and unreinforced concrete members. One of the main findings was that the characteristic edge distance depends on the member thickness and can be larger than 3hef (hef = embedment depth) for thin members. Based on the numerical and experimental test results, modifications of the design recommendations for the splitting failure mode are proposed. Overall, the authors recommend performing the splitting verification separately from the concrete breakout to design anchor channels in thin members more accurately.

Analytical Investigation of Tension Loaded Deformed Rebar Anchors in Concrete

Experimental testing of deformed rebar anchors (DRAs) has not been performed extensively, so there is limited test data to understand their failure behavior. This study aims to expand upon these limited tests and understand the behavior of these anchors, when loaded in tension. Analytical benchmark models were created using available test data and a parametric study of deformed rebar anchors was performed. Anchor diameter, spacing, embedment, and number of anchors were varied for a total of 49 concrete breakout simulations. The different failure modes of anchors were predicted analytically, which showed that concrete breakout failure is prominent in the DRA groups. The predicted concrete breakout values were consistent with mean and 5% fractile concrete capacities determined from the ACI concrete capacity design (CCD) method. The 5% fractile factor determined empirically from the simulation results was kc = 26. This value corresponds closely with kc = 24 specified in ACI 318-19 and ACI 349-13 for cast-in place anchors. The analysis results show that the ACI CCD formula can be conservatively used to design DRAs loaded in tension by applying a kc factor no greater than 26.

Anchoring Parameters Optimization of Tunnel Surrounding Rock Based on Particle Swarm Optimization

In the highway tunnel project, due to the uncertainty and complexity of geotechnical parameters, it is difficult to design and optimize the anchorage parameters. In order to solve this problem, based on the Zhenfengling tunnel project as the research object, 3D tunnel model was established by ANSYS software, the model was imported into FLAC3D software for numerical analysis and calculation for the displacement and stress of surrounding rock during construction, using orthogonal experiment methods to analyze factors affecting the stability of surrounding rock. The influence of anchor length, anchor spacing, anchor diameter, the thickness and elastic modulus of spray layer on the displacement of arch waist, arch crown and arch bottom of the tunnel was obtained by using range and variance analysis. The regression model of the relationship between arch surrounding rock displacements and anchorage parameters was determined by fitting regression. The particle swarm optimization algorithm was used to optimize the anchorage parameters in combination with the tunnel section cost formula, and the parameters were compared with those not optimized. Finally, the anchor length is designed as 3 m, the anchor spacing is designed as 1.4 m, the anchor diameter is designed as 21 mm, the thickness of spray layer is designed as 24 cm, and the elastic modulus of spray layer is designed as 24 GPa. The stability requirements can be met, and the economic efficiency is also greatly improved. The cost of support with optimized parameters is 19.4% lower than that of the original design parameters.