Adhesive Anchors Research Articles

Influence of interfacial characteristics on the shear bond behaviour between concrete and ferrocement

Interfacial bond behaviour between concrete substrate and strengthening materials is crucial for achieving the aims of structural strengthening or repair. This paper presents an experimental investigation on shear bond behaviour between concrete substrate and ferrocement through direct shear tests. Various interfacial characteristics, including surface roughness, type of shear keys and use of wire mesh in the overlay, are considered as test variables. Test results indicate that both surface roughness and shear keys significantly affect the shear bond behaviour between concrete and ferrocement. Specimens with highly roughened concrete surfaces obtained using jet hammer achieve higher shear bond strength and interfacial fracture energy than those with slightly roughened concrete surfaces obtained using needle gun. Installation of shear keys at concrete-ferrocement interfaces can significantly improve the post-peak shear bond behaviour as well as alter the failure mode from brittle to ductile. Shear keys have negligible influence on shear bond strength of specimens with properly roughened surfaces, but can significantly enhance their interfacial fracture energy. As compared with expansive shear keys, adhesive shear keys are more reliable to resist interfacial shear between concrete and ferrocement. Among others, L-shaped or end-extension adhesive anchors are the most effective shear keys for improving interfacial shear bond behaviour between concrete and ferrocement. In addition, the use of wire mesh has negligible influence on shear bond strength but can prevent brittle failure of the overlay. Overall, it is recommended to prepare the concrete substrate with a highly roughened surface and to provide adhesive shear keys with end extension anchored in ferrocement.

Repair of Seismically Damaged RC Bridge Bent with Ductile Steel Bracing

The inclusion of a ductile steel bracing as means of repairing an earthquake-damaged bridge bent is evaluated and experimentally assessed for the purposes of restoring the damaged bent's strength and stiffness and further improving the energy dissipation capacity. The study is focused on substandard reinforced concrete multi-column bridge bents constructed in the 1950 to mid-1970 in the United States. These types of bents have numerous deficiencies making them susceptible to seismic damage. Large-scale experiments were used on a two-column reinforced concrete bent to impose considerable damage of the bent through increasing amplitude cyclic deformations. The damaged bent was then repaired by installing a ductile fuse steel brace in the form of a buckling-restrained brace in a diagonal configuration between the columns and using post-tensioned rods to strengthen the cap beam. The brace was secured to the bent using steel gusset plate brackets and post-installed adhesive anchors. The repaired bent was then subjected to increasing amplitude cyclic deformations to reassess the bent performance. A subassemblage test of a nominally identical steel brace was also conducted in an effort to quantify and isolate the ductile fuse behavior. The experimental data from these large-scale experiments were analyzed in terms of the hysteretic response, observed damage, internal member loads, as well as the overall stiffness and energy dissipation characteristics. The results of this study demonstrated the effectiveness of utilizing ductile steel bracing for restoring the bent and preventing further damage to the columns and cap beams while also improving the stiffness and energy dissipation characteristics.

Time-dependent changes of mechanical properties of polymer-based composite materials for adhesive anchor systems

The long-term performance of adhesive anchor systems is largely determined by the time-dependent mechanical properties. As polymer-based composite materials, the properties of adhesives change during their service life dependent on environmental factors. Therefore, the influence of aging time on Young’s modulus and tensile strength of two different industrially produced materials (epoxy, vinylester) with a high filler content (20–50 vol%) were investigated considering that most literature is focused on neat resins. Mechanical properties of the vinylester based material increased with time and curing temperature. While the strength of the epoxy system increased at higher post-curing temperatures, the modulus slightly decreased, which is in contrast to most literature studies and interpreted as relaxation effect. Changes in the weight of the specimens were monitored. In contrast to other hydrolytic aging studies on submerged specimens a comparably low amount of moisture absorption of the epoxy was found when aged under realistic conditions and desorption of water of the vinylester was observed, which is an uncommon behavior. The reactivity of cement as a filler material was studied by X-ray diffraction (XRD), revealing inert cement phases even at higher temperatures and the presence of water. The results are discussed and compared to available data from literature.

Uncertainty analysis of the power law extrapolation techniques for adhesive anchors

Modern construction industry is increasingly utilizing postinstalled adhesive anchors as an alternative to traditional mechanical anchors. Although the application of adhesive anchors under sustained load offers many advantages, the associated approval guidelines based on a power law extrapolation technique have a number of ambiguities and limitations, which are shortly reviewed in this paper and subjected to uncertainty quantification and sensitivity analyses. Some of the observations presented may be considered as specific to the available experimental database of sustained load test, while some recommendations are universal, as they relate to the underlying creep phenomena and robust measures in regression. It is further shown, how a regression based safety factor could be derived from an experimental database and a possibilistic set of plausible choices.

Experimental results on mechanical behaviour of metal anchors in historic stone masonry

Ancient buildings constructed in stone masonry often deteriorate and partially collapse, with only their façades and/or lateral walls remaining. This work provides a study of the mechanical behaviour of anchors used as connections between existing walls and new members, for purpose of strengthening of historic stone masonry buildings. The paper addresses a comparative analysis between an experimental campaign and analytical formulations for ultimate load prediction. To obtain practical results, pull-out tests were carried out with adhesive and mechanical metallic anchors in stone masonry walls constructed in laboratory. The results allow conclusions on the most efficient connections in terms of adhesion.

Adhesion strength test with change in temperature as a parameter at post-installed adhesive anchor with acrylic adhesive

Adhesion strength test with change in temperature as a parameter at post-installed adhesive anchor with acrylic adhesive

トルク管理型接着系あと施工アンカーの引抜き挙動

トルク管理型接着系あと施工アンカーの引抜き挙動

A blueprint for robust crosslinking of mobile species in biogels with weakly adhesive molecular anchors

Biopolymeric matrices can impede transport of nanoparticulates and pathogens by entropic or direct adhesive interactions, or by harnessing “third-party” molecular anchors to crosslink nanoparticulates to matrix constituents. The trapping potency of anchors is dictated by association rates and affinities to both nanoparticulates and matrix; the popular dogma is that long-lived, high-affinity bonds to both species facilitate optimal trapping. Here we present a contrasting paradigm combining experimental evidence (using IgG antibodies and Matrigel®), a theoretical framework (based on multiple timescale analysis), and computational modeling. Anchors that bind and unbind rapidly from matrix accumulate on nanoparticulates much more quickly than anchors that form high-affinity, long-lived bonds with matrix, leading to markedly greater trapping potency of multiple invading species without saturating matrix trapping capacity. Our results provide a blueprint for engineering molecular anchors with finely tuned affinities to effectively enhance the barrier properties of biogels against diverse nanoparticulate species.

Mechanical behavior of adhesive anchors under high temperature exposure: Experimental investigation

The improvement in mechanical and adhesion properties of polymer resins have allowed to progressively substitute cast-in place rebars by polymer-based anchors in some applications, by providing equivalent or even higher mechanical properties at ambient temperature. However, a temperature increase has the effect of weakening the bond and leads to a significant decay in the bearing capacity of the adhesive anchors.This paper presents a study of the phenomena that occur at high temperature in an adhesive anchor when exposed to high temperatures by means of two pull-out test procedures and by thermomechanical characterization of the polymer resin. Results showed that the resin glass transition is the responsible for the decay in the fire resistance of adhesive anchors. The paper highlights the non-conservative aspect of the current design method used to calculate the fire resistance of chemical anchors and proposes to consider the pull-out curves as input data.

Shear strengthening of damaged reinforced concrete beams with Hybrid Composite Plates

This paper aims to evaluate experimentally the potentialities of Hybrid Composite Plates (HCPs) technique for the shear strengthening and repairing of reinforced concrete (RC) beams. HCP is a thin plate of Strain Hardening Cementitious Composite (SHCC) reinforced with Carbon Fiber Reinforced Polymer (CFRP) laminates. For this purpose, an experimental program composed of four Rectangular and five T-cross section beams was executed to assess the strengthening efficiency of HCPs technique. There were two control beams without any type of shear reinforcement, and seven beams strengthened with HCPs. The HCPs were applied to the lateral faces of the beams by using a combination of epoxy adhesive and mechanical anchors. The bolts were applied with a certain torque in order to increase the concrete confinement. To have a better understanding of the shear behavior of SHCC material, Iosipescu shear tests were carried out, and the results were used to derive their fracture mode II parameters.To further explore the potentialities of the HCPs technique for the shear strengthening, the experimental tests were simulated numerically by a FEM-based computer program considering the material properties obtained experimentally. After demonstration of the good predictive performance of the numerical model, a parametric study was executed to investigate the influence of some parameters on the load carrying capacity of the strengthened beams, namely: i) Use a mortar instead of the SHCC; ii) application of different applied torque level to the mechanical anchors; iii) different bond condition between HCPs and concrete substrate.

Sustained Load Performance of Adhesive Anchor Systems in Concrete

Sustained Load Performance of Adhesive Anchor Systems in Concrete

Spatially-degraded adhesive anchors under material uncertainty

The classic problem of stress transfer in a cylinder through shear to a surrounding medium, is analyzed here in the context of pullout of an anchor under material uncertainty. Assuming a log-normal distribution for the random shear stiffness field of the adhesive, the stochastic differential equation (SDE) is formulated for spatially-tailored/degraded adhesive anchors. The stochastic shear stress distribution in the adhesive is presented for various embedment lengths and adhesive thicknesses clearly demarcating the regime over which failure would initiate. The stochastic variation of maximum shear stress of the adhesive as a function of embedment length and adhesive thickness is also presented. It is observed that the mean maximum shear stresses in the degraded adhesive for both fixed and free embedded-end cases converge and the influence of boundary condition at the embedded-end on shear stress field disappears as the embedment length is increased. For the parameters considered here, about 45% longer embedment length is required compared to an intact bondline for shear-dominated load transfer, suggesting that the design of adhesive anchors should adequately account for likely in-service damage that causes material uncertainty to avoid premature failure.

Creep and damage of an adhesive anchor system by accelerated testing and modeling

An accelerated testing and modeling method was proposed and implemented to predict the long-term performance through short-term pullout tests of a cylindrical anchor core by tensile loading at different elevated testing temperatures. Dimensional analysis was conducted to predict the creep behavior of adhesive anchor systems by small-scale tests. By using the frequency-temperature superposition principle, the master curves of the complex and storage moduli were generated in the Prony series form. By performing inverse numerical Laplace transformation, the creep compliance of the adhesive in the time domain was calculated and then used in the viscoelastic analysis of the adhesive anchor system. To validate the model, six adhesive anchor samples with different sizes of hole diameter and depth were fabricated and creep tests were then conducted at different temperatures. Overall, the test results agree well with the theoretical ones using the adhesive’s viscoelastic properties. An accelerated test protocol was further established for the long-term performance analysis of the adhesive anchor systems. The error sources of the experiments were discussed. Because of the generality of the formulation and testing mechanism, the present test method is applicable to the design and analysis of different types and sizes of adhesive anchor systems.

A blueprint for robust crosslinking of mobile species in biogels with weakly adhesive molecular anchors

A blueprint for robust crosslinking of mobile species in biogels with weakly adhesive molecular anchors

Non-contact alignment-free soundness evaluation of adhesive anchors by exciting/detecting longitudinal bolt vibrations using electromagnetic acoustic waves

Non-contact alignment-free soundness evaluation of adhesive anchors by exciting/detecting longitudinal bolt vibrations using electromagnetic acoustic waves

Pull-Out Behavior of Adhesive Connections in Unreinforced Masonry Walls

The connections between walls of unreinforced masonry (URM) buildings and flexible timber diaphragms are critical building components that must perform adequately before desirable earthquake response of URM buildings may be achieved. Field observations made during the initial reconnaissance and the subsequent damage surveys of clay brick URM buildings following the 2010/2011 Canterbury, New Zealand, earthquakes revealed numerous cases where anchor connections joining masonry walls or parapets with roof or floor diaphragms appeared to have failed prematurely. These observations were more frequent for adhesive anchor connections than for through-bolt connections (i.e., anchorages having plates on the exterior facade of the masonry walls). Subsequently, an in-field test program was undertaken in an attempt to evaluate the performance of adhesive anchor connections between unreinforced clay brick URM walls and roof or floor diaphragm. The study consisted of a total of almost 400 anchor tests conducted in eleven existing URM buildings located in Christchurch, Whanganui and Auckland. Specific objectives of the study included the identification of failure modes of adhesive anchors in existing URM walls and the influence of the following variables on anchor load-displacement response: adhesive type, strength of the masonry materials (brick and mortar), anchor embedment depth, anchor rod diameter, overburden level, anchor rod type, quality of installation, and the use of metal mesh sleeves. In addition, the comparative performance of bent anchors (installed at an angle of minimum 22.5° to the perpendicular projection from the wall surface) and anchors positioned horizontally was investigated. Observations on the performance of wall-to-diaphragm connections in the 2010/2011 Canterbury earthquakes, a summary of the performed experimental program and test results, and a proposed pull-out capacity relationship for adhesive anchors installed into multi-leaf clay brick masonry are presented herein.

Integrity evaluation of adhesive anchors using electromagnetic acoustic transducer

The aging of social infrastructures has recently become a serious problem. The high efficiency of the testing is required to handle increased inspection demand. There is interest in testing the soundness of adhesive anchors. Bolts are connected to a concrete using holes filled with adhesive materials. Since anchor bolts is inspected by skilled workers manually, it is difficult to improve the efficiency. Several sensing methods have been proposed, but these measurements require a precision alignment or contact. We propose a non-contact evaluation method of adhesive anchors using an electromagnetic acoustic transducer (EMAT). An EMAT is a transducer for non-contact vibration generation and reception based on electromagnetic mechanisms. A neodymium ring magnet and two coils were used as an EMAT. We used 100 mm long M8 and M12 steel bolts mounted with epoxy resin in 70 mm depth holes in concrete. The EMAT which was placed around the bolt excited longitudinal vibrations of bolt by burst waves. Vibration signals were received after the excitation. The relationships between the resin amount and the resonance characteristics of the vibrations are evaluated for pursuing the applicability of this method to the on-site inspection. Resonance frequencies and quality factors are utilized for health monitoring of adhesive anchors.

Full scale flexural test of jointed concrete members strengthened with post-tension tendons with internal anchorage

A new strengthening system, which embeds a post-tensioned PC bar tendon into the wedge-shaped anchorage of an existing concrete member, was developed. Previously, the adequate load-bearing capacity of the prestressing tendon anchorage was confirmed on simple element specimens. In the present study, the developed system is applied to the addition of new concrete members to old concrete structures. The strengthening effect of the system was examined in a loading test on jointed full-scale concrete members. The saltwater permeability at the joint was also examined. The flexural properties of the jointed members were compared to those of concrete beams jointed with conventional post-installed adhesive anchors. The concrete beams jointed by the proposed system exhibited superior crack-resistance and load-carrying capacity, and their joints were strongly water-impermeable.

Cyclic behavior of reinforced concrete bridge bent retrofitted with buckling restrained braces

The cyclic behavior of a deficient reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was experimentally evaluated using large scale experiments and quasi-static cyclic loading that reflected subduction zone earthquake demands. The retrofitted reinforced concrete bent specimen consisted of two circular cross section columns, a rectangular cap beam and a buckling restrained brace in a diagonal configuration. The brace was secured to the bent using steel gusset plates and post-installed adhesive anchors. The retrofitted bent was designed to perform elastically or with minor damage under different seismic hazards design levels. Two BRB designs were considered in an effort to assess the influence of the BRB design on the overall bent performance. The data from these large-scale experiments were analyzed considering bent hysteretic response, observed damage, component curvatures, internal member loads, as well as the overall stiffness and energy dissipation characteristics. The results successfully demonstrated the effectiveness of utilizing buckling restrained braces for achieving high displacement ductility of the retrofitted structure, while also controlling the damage of the existing vulnerable reinforced concrete bent. No damage was observed in the connection regions of the brace throughout the loading history, leaving the potential for rapid replaceability of the sacrificial BRB element.

A shear-lag model for functionally graded adhesive anchors

A shear-lag model for stress transfer through an adhesive layer of variable stiffness joining an anchor rod and the concrete is presented and the effect of such an inhomogeneous bondline on interfacial shear stress distribution in comparison with that of a homogeneous bondline anchor subjected to monotonic axial tension is investigated. A closed-form solution is presented for arbitrary distribution of shear stiffness of the bondline considering both bonded and debonded embedded-end conditions of the anchor. Subsequently, the specific cases of linear and constant distribution of stiffness are discussed in detail, and it is shown how the general solution can be simplified for these examples. For validation, the distribution of shear stress along the bondline for the aforementioned cases is compared with that of equivalent axisymmetric Finite Element (FE) models and the results are found to be in good agreement. The theoretical solution developed can be readily used to evaluate the pull-out performance of post-installed adhesive anchors. Variable stiffness adhesive interfaces deserve an interest in practical applications either to estimate the effect of loss of interface stiffness, due to degradation of the adhesive material, or to engineer the interface with optimum distribution of stiffness so as to maximize the structural performance of bonded systems.