Adhesive Anchors Research Articles

Coacervate Dense Phase Displaces Surface-Established Pseudomonas aeruginosa Biofilms.

For millions of years, barnacles and mussels have successfully adhered to wet rocks near tide-swept seashores. While the chemistry and mechanics of their underwater adhesives are being thoroughly investigated, an overlooked aspect of marine organismal adhesion is their ability to remove underlying biofilms from rocks and prepare clean surfaces before the deposition of adhesive anchors. Herein, we demonstrate that nonionic, coacervating synthetic polymers that mimic the physicochemical features of marine underwater adhesives remove ∼99% of Pseudomonas aeruginosa (P. aeruginosa) biofilm biomass from underwater surfaces. The efficiency of biofilm removal appears to align with the compositional differences between various bacterial biofilms. In addition, the surface energy influences the ability of the polymer to displace the biofilm, with biofilm removal efficiency decreasing for surfaces with lower surface energies. These synthetic polymers weaken the biofilm-surface interactions and exert shear stress to fracture the biofilms grown on surfaces with diverse surface energies. Since bacterial biofilms are 1000-fold more tolerant to common antimicrobial agents and pose immense health and economic risks, we anticipate that our unconventional approach inspired by marine underwater adhesion will open a new paradigm in creating antibiofilm agents that target the interfacial and viscoelastic properties of established bacterial biofilms.

Numerical study on enhancing shear performance of RC beams with external aluminum alloy plates bonded using steel anchors

This article compromises a three-dimensional numerical study employing the Abaqus program to investigate the behavior of reinforced concrete (RC) beams externally strengthened in shear using aluminum alloy (AA) plates bonded utilizing steel anchors. Based on previous experimental tests, a numerical validation study was conducted in two parts. The first part modeled the interaction behavior using different bonding methods between steel plates and the surface of the RC beams, whether utilizing epoxy adhesive only, steel anchors only, or a dual system between them. The second part modeled the performance of shear-defected RC beams that externally strengthened by the AA plates using epoxy adhesive. To take into account debonding collapse due to epoxy adhesive bonding, the interaction between the AA plates and beam surface was simulated with a cohesive-damage interaction. Comparing the numerical results with previous experimental studies shows the success of the numerical model in simulating the performance of different bonding methods, as well as the behavior of the RC beams defected in shear and strengthened by the AA plates, which qualified it to study some additional variables. From the study it was found that by utilizing only epoxy adhesive, the strengthening technique using the AA plate over the entire shear span zone (AASP method) was capable of increasing the ultimate capacity of the defected beam by 104%, which represents 77% of the load of the non-defected beam. It was also demonstrated that the AA plates were susceptible to collapse by the out-of-plane buckling when bonded using the steel anchors only. By utilizing a dual system for bonding the AA plates consisting of epoxy adhesive and steel anchors, the AASP method was capable of enhancing the ultimate capacity of the defected beam by 164% and changing its failure pattern to the preferred ductile bending pattern.

Aggregate Type and Concrete Age Effects on Anchor Breakout Performance: Large Database and Insights

This contribution summarizes the largest available literature data collection on tensile and shear loaded anchor tests, obtained in two independent studies and performed by two different research groups. It was the objective of the two studies to investigate a possible effect that petrographically different coarse aggregate types may have on the tensile and shear load capacity for concrete breakout failure modes. In total, seven normal-strength and four high-strength concretes were tested at two different ages. Structural tests were performed on cast-in (tensile and shear tests) and post-installed adhesive anchors (shear tests). Parallel to the structural tests, each concrete was characterized in terms of compressive and tensile strength. Finally, the combined experimental data offer novel insights into the predictive quality of available design models for concrete cone capacity in tension and edge breakout in shear with respect to a potential aggregate effect. Systematic analyses indicate only minor aggregate effects after normalization by compressive strength (less than 7% difference between normalized values). However, the study reveals potential curing and concrete age effects where a 9% increase in predicted values is shown when concrete cures longer. The predictive equations remain conservative in comparison to all the investigated properties and their validity is shown in this study.

Tensile and shear capacity of post-installed chemical adhesive anchors in lightweight concrete

Due to construction efficiency and performance, chemical anchors have been widely applied to long-span or high-rise structures or infrastructures. This study investigates the capacity of post-installed anchors in concrete with lightweight aggregates. Extensive static experiments are conducted to investigate tensile and shear capacities of chemical adhesive anchors in lightweight concrete. Both confined and unconfined tensile conditions are considered. In total, 102 tests are performed with various anchor diameters (12–30 mm), embedment depths (80–300 mm), and types of concrete. The test results show that cone breakout and combined failures dominate the unconfined tensile tests, which have about 40% capacity for the anchors in normal-weight concrete. Chemical adhesive anchor failure models in lightweight concrete are also summarized with respect to the input parameters. Finally, multiple nonlinear regression analyses are further performed, and revised empirical and analytical equations are proposed for lightweight concrete to accommodate different failure modes.

Mechanical behavior of longitudinally continuous slab tracks reinforced by adhesive anchors under nonlinear temperature load

Adhesive anchors have been widely used as a post-reinforcement measure to strengthen longitudinally continuous slab tracks. However, the mechanical behavior of the longitudinally continuous slab tracks reinforced by adhesive anchors under nonlinear temperature load has not been thoroughly investigated. Therefore, this paper was motivated to conduct experimental and numerical investigation on the temperature-induced deformation and damage of the reinforced track. Firstly, experimental tests were carried out to investigate the influence of the borehole conditions on the bond properties of post-installed adhesive anchors. Next, the bond-slip relationships between anchors and concrete were established for anchors in various borehole conditions. Then, a novel finite element model of the reinforced track incorporating a nonlinear cohesive zone model of structural interfaces was developed and validated by filed monitoring data. Finally, the effects of borehole conditions and number of invalid anchors on the deformation and damage behavior of the reinforced track under nonlinear temperature load were systematically studied. Results show: (1) The cubic compressive strength grade of concrete has a significant effect on the bond-slip curves between concrete and anchors of the longitudinally continuous slab track. (2) Wet boreholes and uncleaned boreholes would reduce elastic stiffness and ultimate bond strength between anchors and concrete by 11–37% respectively, compared with dry and cleaned boreholes. (3) The maximum vertical displacement of slabs could increase by 7% and 4% if the boreholes are wet and uncleaned respectively. (4) The interface at the center of slab end near damaged joint will not fail for the track with 1 or 2 invalid anchors when the temperature reaches its highest. However, interface debonding will occur with a temperature rise of 34.6 ℃ if there are 3 invalid anchors.

Design approach and its optimization for bolted steel plate strengthened RC beams considering the effect of connection bolt slip

The use of bolted steel plates (BSP) has been found to be an effective method for increasing the flexural capacity of reinforced concrete (RC) beams. However, slip in bolt connections is an inevitable occurrence that affects the mechanical behavior of the BSP beam. While prior studies have thoroughly examined the effects of bolt connection slip on the flexural capacity of BSP beams, assuming unlimited slip, experimental results revealed that bolt connection failure takes place when slip surpasses a specific threshold. The current design methodology does not accommodate this finding. To address this issue, a simplified design method for practical applications is proposed. Comprehensive parameter studies were conducted on the enhanced moment capacity ratio and maximum bolt slip, involving a total of 13,824 and 276,480 calculations, respectively. It is found that several parameters (e.g., the aspect ratio of RC beam, the tensile longitudinal reinforcement ratio, the height of steel plate) affect the two above-mentioned indexes. Equations were then developed to determine the enhanced moment capacity ratio and maximum slip. It is noteworthy that the recommended effective yield slip (0.55 mm) is obtained based on adhesive anchor, which should be checked when other types of anchors would be used. Relying on these equations, an optimized design approach for BSP beams is introduced that avoids complex iterative processes. The effectiveness of the optimized design methodology is substantiated through a practical example.

Shear strength of the anchor embedded into masonry

This paper focuses on any straight bar, herein called “anchor”, inserted within a hole drilled into a masonry structure, installed orthogonally to the masonry surface, and bonded to the masonry either with an anchoring material or without (adhesive or mechanical anchors). The anchor is subjected to a transverse force applied at the end that protrudes from the masonry (i.e., a shear force having direction parallel to the masonry surface), while no appreciable axial force is applied to the anchor (shear anchor). In brief, the paper is devoted to the post-installed horizontal anchor that transfers vertical loads from a horizontal structure to a vertical masonry structure.On site experiments on real anchors allowed the author to establish the mechanical assumptions that govern the behavior of the shear anchor. Based on those assumptions, an analytical (closed form) model was created. The model is comprised of a function that gives the ultimate contact pressures, and a two-equation system whose solution is the maximum shear force that the anchor can bear, therefore called “shear strength”. The model also provides the elastic limit shear strength. The data to be entered into the model is composed of the geometry of the anchor and the strength of the masonry.The paper presents the experimental campaigns, the model, the application of the model to case studies, and a comprehensive discussion. The results put forward the optimal technical solutions for the masonry shear anchor, which are described.

Extracellular vimentin is sufficient to promote cell attachment, spreading, and motility by a mechanism involving N-acetyl glucosamine-containing structures

Vimentin intermediate filaments form part of the cytoskeleton of mesenchymal cells, but under pathological conditions often associated with inflammation, vimentin filaments depolymerize as the result of phosphorylation or citrullination, and vimentin oligomers are secreted or released into the extracellular environment. In the extracellular space, vimentin can bind surfaces of cells and the extracellular matrix, and the interaction between extracellular vimentin and cells can trigger changes in cellular functions, such as activation of fibroblasts to a fibrotic phenotype. The mechanism by which extracellular vimentin binds external cell membranes and whether vimentin alone can act as an adhesive anchor for cells is largely uncharacterized. Here, we show that various cell types (normal and vimentin null fibroblasts, mesenchymal stem cells, A549 lung carcinoma cells) attach to and spread on polyacrylamide hydrogel substrates covalently linked to vimentin. Using traction force microscopy and spheroid expansion assays, we characterize how different cell types respond to extracellular vimentin. Cell attachment to and spreading on vimentin-coated surfaces is inhibited by hyaluronic acid (HA) degrading enzymes, HA synthase inhibitors, soluble heparin, or N-acetyl glucosamine (GlcNAc), treatments that have little or no effect on the same cell types binding to collagen-coated hydrogels. These studies highlight the effectiveness of substrate-bound vimentin as a ligand for cells and suggest that carbohydrate structures, including the glycocalyx and glycosylated cell surface proteins that contain N-acetyl glucosamine, form a novel class of adhesion receptors for extracellular vimentin that can either directly support cell adhesion to a substrate or fine-tune the glycocalyx adhesive properties.

Pullout characteristics of functionally graded and degraded adhesive anchors

Three-dimensional axisymmetric elasticity solutions for pull-out stresses in bonded anchors with spatially stiffness-varying adhesive are presented. A stiff rod embedded in a semi-infinite rigid half-space through an adhesive bondlayer, representing a general anchor problem is analyzed. The adhesive layer is considered to have a smoothly varying stiffness over embedded length. Two cases of particular engineering relevance are considered: (i) stiffness grading of the bondlayer to enhance performance while retaining the critical length characteristics of bonded anchors, and (ii) modulus reduction of the bondlayer representing adhesive degradation proximal to the loaded-end. Theoretical solutions are developed adopting a stress function approach in conjunction with a variational method that compare well with 3D axisymmetric finite element (FE) results. Both theoretical and FE results indicate that the maximum shear stress in the adhesive decreases over 60% for a graded bondlayer for the parameters considered here without warranting a longer embedment length. In contrast, the degraded bondlayer reduces shear stress peaks significantly but warrants a larger embedment length to enable shear-dominated stress-transfer, disadvantageously loading the embedded-end in tension. A design map showing the critical embedment length required for degraded bondlines as a function of fractional embedment length over which bondline is regarded to have degraded is presented. In addition, interfacial fracture behaviors of the tailored and degraded adhesive anchors were examined through FE analyses finding that the tailoring reduces the energy release rate and has the potential for enhancing damage tolerance. The findings of the study indicate that the stiffness-tailored and -degraded bondlayers significantly redistribute the stress field with concomitant influence on stress-transfer and interfacial debonding characteristics of bonded anchors.

INFLUENCE ON THE LOAD‐DISPLACEMENT BEHAVIOUR OF STEEL‐TO‐CONCRETE CONNECTIONS WITH POST‐INSTALLED ADHESIVE ANCHORS

AbstractDesigning frame structures requires knowing the behaviour of each member of the frame (beam, column, joint, etc.) regarding the axial forces, shear forces, and bending moments. Furthermore, the ductility of the structure under seismic loading is essential in earthquake regions. Nowadays, structural frames are built from different materials such as concrete and steel, to achieve better performance. Therefore, the behaviour of the connections between steel and concrete is essential. The steel‐to‐concrete joints were the focus of the INFASO project, where joint solutions with easy fabrication, quick assembly, applicability in old structures, sufficient ductility, and high loading capacity were developed. They proposed the use of anchor plates with welded studs or post‐installed fasteners such as adhesive anchors to connect the steel and concrete members. This paper focuses on the performance of post‐installed adhesive anchors. During their service life, post‐installed anchors are subjected to monotonic, constant, and seismic loading. Each of these loading approaches is described in the current standards. Seismic and constant loading tests are of importance to the long‐term behaviour of the anchors. Seismic loading tests are carried out using a predefined cycle pattern. According to TR049, seismic tests of category C1 (tension and shear) are performed with 140 load cycles, where the load amplitude decreases after 10, 30, and 100 cycles. On the contrary, C2 category tests increase the amplitude within 75 or 59 cycles, depending on the test. Constant loading tests apply when the anchors are installed in cracked concrete. In contrast to the mentioned patterns, this study observes the behaviour of the adhesive anchors when the amplitude of each cycle is increased by 5 % until the anchor fails. Standard short‐term pull‐out tests are carried out to determine the load increments. Various parameters such as the embedment depth, bond line thickness, hole cleaning, wet concrete, and elevated temperatures are studied. Confined and unconfined tests are performed. Overall, the reference short‐term failure loads are higher than those in the tests with incremental and cyclic loading. The anchors installed with reduced hole cleaning, in wet concrete or subjected to elevated temperatures have a lower failure load compared to the reference series. Two additional bond line thicknesses are used for comparison. The increase in the thickness influenced the failure load differently for confined and unconfined test setups.

Numerical Investigation on the Mechanical Properties of Vault Void Lining and Steel Plate Strengthening.

To study the mechanism of vault lining under different void heights and verify the strengthening effect of the attached steel plate, a CDP (concrete-damaged plasticity) model and the XFEM (extended finite element method) were used to construct the local numerical model of the vault void, and an experiment was carried out for verification. The strengthened structure of the steel plate was assembled with a combination of a two-component epoxy adhesive and chemical anchor bolts. Five lining models with various void thicknesses, together with their strengthened models, were evaluated. The results of the established numerical model were compared with the experimental results in terms of failure mode, vertical displacement, and load-deformation results. The results of the two numerical models were in good agreement with the experimental results, revealing the failure mechanism of the vault lining. The rigidity of the specimen after steel plate strengthening was significantly improved. When the void height was one-fourth of the secondary lining thickness, the lining cracks were reduced from 14 to 4, and the distribution width of the cracks was also reduced from 1.047 to 0.091 m after steel plate strengthening. The level of damage caused by cracking was significantly reduced, which proves the effectiveness of the surface-sticking method for steel plate strengthening.

Analytical study on fracture mechanisms ruling resistant load of post‐installed adhesive anchor

AbstractExperimental and FEM‐based analytical studies revealed the following aspects regarding post‐installed adhesive anchors set with epoxy or UHPFRC adhesive. The experimental and FEM results agreed in regard to maximum load, load–displacement curve, crack pattern, failure mode, and the location of failure. The load‐bearing mechanisms were discussed employing a model with a conic surface and an interface layer below it, which revealed the contribution of a conic surface to the maximum load was low, and that of an interface layer was very high. The mechanisms of combined failure with cone‐shaped fracture of concrete and interface slipping were also discussed.

既存壁式鉄筋コンクリート造建築物において下階壁面内に施工される接着系あと施工アンカーの引張特性に関する実験的研究

For the renovation of the reinforced concrete boxed-wall building, a new opening would be constructed on multi-story wall frame, and local retrofit with post-installed adhesive anchors would be applied. In this study, evaluation method of tensile strength for a post-installed adhesive anchor embedded in wall plane was proposed. The non-fixed bond-tensile test of anchor specimens embedded in wall-slab specimen was conducted. The parameter of specimens are embedment length of anchors, wall thickness, and wall shapes. Tensile strength of the anchors could be evaluated due to previous formula with the assumption of the effect of local retrofit on bottom floor wall and floor slab.

Mortar cure-dependent effects on adhesive anchor systems loaded in tension

This paper presents a large experimental campaign and the corresponding analysis quantifying mortar curing effects on the pull-out performance of bonded anchor systems. Standard confined pull-out tests were performed on two commonly used adhesive anchor systems. The two investigated bonded anchor systems were based on different materials, where the mortar of the first bonded anchor system (BAS-VE) was a vinyl-ester based product and the second bonded anchor system (BAS-EP) contained an epoxy-based mortar. In order to isolate the mortar curing effects on the anchor performance, a mature concrete was used as base material minimizing well-known aging and curing effects related to the substrate, concrete. In total, 93 pull-out tests were performed for various curing times in order to characterize influences on bond strength, stiffness, and peak displacement. Depending on the product specifications and corresponding approval documents, tests were carried out in a time-range of a few minutes up to three months after the anchor installations. Measured temperature (and humidity histories) of the environment have been utilized for predicting the mortars’ degree of cure for each structural anchor test. The results show a cure-dependent behavior in BAS-VE and BAS-EP. Although the bond strength fails to increase significantly after reaching the manufacturer approved minimum curing time, the stiffness shows an increase for longer cured anchors.

Elastic solutions for stresses in compliance-tailored adhesive anchors

Joining of structures via adhesive anchors is of theoretical and practical engineering importance, including anchors that support concrete ceilings in urban infrastructure. Such anchors typically fail due to stress concentrations at the loaded and/or embedded ends, captured by the well-known ‘shear-lag’ model. Herein, such anchors are revisited by considering elastic properties variation of the adhesive along the embedment length in discrete steps, to reduce critical stress concentrations, and thereby minimize the propensity of failure. Initially, a closed-form solution is developed for a system with single-step variation in adhesive compliance along the embedment length (henceforth referred to as double-adhesive bondline), which agrees well with Finite Element simulations. The simplest double-adhesive tailoring is found to reduce the maximum shear stress by 43% while maintaining the super-critical bondlength characteristics of such designs. The theoretical framework thus developed is extended to systems comprising an arbitrary number of discrete adhesives along the embedment length considering, fixed and free boundary conditions of the embedded-end, to allow for parametric evaluation of the adhesive compliance tailoring for optimal stress reduction (maximum shear stress reduces by 46% for triple-adhesive bondline) while maintaining critical-length characteristics. The adhesive tailoring could be effectively applied to anchors with critical-length characteristics by employing a facile double-adhesive bondline with the compliant adhesive near the loaded-end and stiffer adhesive near the embedded-end. The particular case of the well-known Boston tunnel anchor problem is analyzed as an exemplary demonstration of the approach.

Refined nickel nucleation and plated metal adhesion induced by pulsed light-induced plating on picosecond laser-ablated silicon solar cells

This study reports the impact of pulsed Ni light-induced plating (LIP), compared to the commonly used galvanostatic Ni LIP, on the initial Ni nucleation and subsequently plated busbar adhesion of Cu-plated laser-ablated p-type passivated emitter and rear Si solar cells. Initial Ni nucleate sizes decreased from 27.8 ± 9.1 to 25.4 ± 7.9 nm when the pulse-on current density during pulsed Ni LIP was increased from 50 to 178 mA cm−2, and were smaller than the 30.4 ± 9.7 nm nucleates observed with galvanostatic plating at 25 mA cm−2 after the same charge had been delivered to the surface. The density of Ni nucleation was also increased for pulsed LIP. This increased density of smaller Ni nucleates was attributed to the higher pulse-on currents inducing a larger surface potential which favoured nucleation over Volmer Weber 3D island growth of Ni. It also led to a greater density of adhesive anchor points along busbars which contributed to more adhesive plated contacts with busbar pull forces as high as 3 N mm−1 being measured when the pulse-on current density was 100 mA cm−2. However, it is shown that higher pulse-on current densities can result in unintended parasitic reactions, such as H2 evolution, and reduced busbar adhesion.

Anti-explosion and reinforcement effects on a cavern with a new prestressed anchor cable

Traditional cavity reinforcement technology is difficult to effectively protect the cavity from damage caused by modern large-yield explosions, and the anti-explosion performance of prestressed anchor cables needs to be improved urgently. The design of a new prestressed high-elastic fully adhesive anchor cable for the enhancement of the anti-explosion effects of the anchor cable is presented in this paper. A constitutive model of the anchor cable is established in FLAC 3D and used to restore an equal scale field anti-explosion test. The reinforcement effects of the new anchor cable are compared with the conventional one’s. Results show that the stresses of the anchor cables differ at different locations: the anchor cable at the arch crown of the cavern is the one mainly under pressure with the compressive strain of the new anchor cable reduced by 25 %; while the anchor cable at the arch foot of the cavern is the one mainly under tension and the tensile strain of the new anchor cable is reduced by 26.3 %. The vertical displacement of the arch crown is reduced by 16.2 % with the reinforcement of the new anchor cable. The new anchor cable performs much better on the reinforcement of the cavern than the conventional one in the aspects of stress, strain and displacement, which provides a basis for the design of new anchor cables and their applications in engineering.

Design and strength reduction factors calibration of adhesive anchors embedded in thin concrete members

This study presents and evaluates the safety level in the design procedure proposed for adhesive anchors in thin concrete members with full embedment depth under tensile and shear loads, to help in adopting the design models in building codes. In addition, the study provides calibration for the strength reduction factors. Based on the results of a comprehensive reliability analysis using the First-order reliability method (FORM) and a 3.5 selected reliability index threshold, strength reduction factors (ϕ) of 0.65, 0.60, and 0.55 are proposed for adhesive anchors under tensile loading for anchors class I, II, and III respectively. An Anchor class represents the anchor tensile capacity sensitivity for installation as per ACI 318-19. The study also proposes ϕ factor of 0.75 for adhesive anchors under shear load. The FORM results and the adequacy of the proposed strength reduction factors are verified using Monte Carlo-based reliability analysis. The results indicate that the current ACI 318-19 strength reduction factors can be safely used for the design of adhesive anchors in thin concrete members as they result in a slightly higher reliability index than the proposed ϕ factors in this study.

Fracture behavior of multiple adhesive postinstalled anchors subjected to shear force

In this study, experiments were conducted on post-installed anchors subjected to shear force in order to enhance applicability when post-installed anchors were used for seismic reinforcement. Furthermore, since there were a large number of post-installed anchors when they were actually used, an experiment was conducted in which aăshear force was simultaneously applied to one to four anchors. In this study, it was focused on number and pitch of anchors. Major findings of this study were summarized as follows: in case of 22.46 (N/mm2) for concrete compressive strength, shear strength of anchors was not double, triple, and quadruple as number of those increased to 2, 3, and 4, and that gradually decreased as number of those increased, the boundary condition between anchor shear rupture and pry-out failure was found that concrete compressive strength was 25.12 (N/mm2) or less and anchor pitch was 30 to 50 mm, and anchor was tensile strength over SD390.

目荒らしと接着系アンカーを併用した耐震補強接合部の組み合わせ応力下における力学挙動

目荒らしと接着系アンカーを併用した耐震補強接合部の組み合わせ応力下における力学挙動