Mechanical Anchorage Research Articles

An integrated experimental and multiscale numerical methodology for modeling pullout of hooked-end steel fiber from cementitious matrix

This work proposes a methodology to translate the experimental pullout results of hooked-end steel fibers from cementitious matrix to a multiscale model with a discrete and explicit representation of steel fibers. The coupling scheme of non-matching meshes used to describe the fiber–matrix interaction is adapted to represent separately and explicitly the anchorage mechanism of hooked-end steel fibers. The difference of the experimental results of pullout tests of hooked-end steel fibers (DramixⓇ 80/60 BN) and straight fibers obtained by cutting the hooked-ends of the fibers is used as input parameters to describe the anchorage mechanism. Pullout tests with one and four fibers aligned to the applied loading and perpendicular to the crack plane are carried out to investigate the effect of instability on the experimental results. The methodology is also coupled with an analytical model for predicting the effect of fibers inclined to the crack surface. Initially, the effect to represent explicitly the anchorage of hooked-end steel fibers in multiscale models is assessed through the simulation of pullout tests. Then, the numerical model is applied to obtain the post-cracking parameters of steel fiber reinforced cementitious composites (SFRCC) through the simulation of flexural three-point-bending test (3-PBT) according to EN 14651, considering the same type of hooked-end steel fibers and a similar matrix strength. Thus, the bond–slip model derived from pullout tests is used together with the amount and orientation of steel fibers obtained from the inductive test carried out. The results demonstrate that the integrated experimental and multiscale methodology may be very useful to link the physical and numerical responses of SFRCC with hooked-end steel fibers, and the numerical tool obtained can contribute for better understanding the failure processes for this type of composite.

P-selectin mobility undergoes a sol-gel transition as it diffuses from exocytosis sites into the cell membrane

In response to vascular damage, P-selectin molecules are secreted onto the surface of cells that line our blood vessels. They then serve as mechanical anchors to capture leucocytes from the blood stream. Here, we track individual P-selectin molecules released at the surface of live endothelial cells following stimulated secretion. We find P-selectin initially shows fast, unrestricted diffusion but within a few minutes, movement becomes increasingly restricted and ~50% of the molecules become completely immobile; a process similar to a sol-gel transition. We find removal of the extracellular C-type lectin domain (ΔCTLD) and/or intracellular cytoplasmic tail domain (ΔCT) has additive effects on diffusive motion while disruption of the adapter complex, AP2, or removal of cell-surface heparan sulphate restores mobility of full-length P-selectin close to that of ΔCT and ΔCTLD respectively. We have found P-selectin spreads rapidly from sites of exocytosis and evenly decorates the cell surface, but then becomes less mobile and better-suited to its mechanical anchoring function.

Effects of natural minor corrosion levels on mechanical property and bond anchorage behavior of CRB600H steel bars

Mechanical property tests and bond anchorage tests of the natural minor corrosion CRB600H steel bars were carried out, and corrosion levels of the steel bars were 0.0%, 1.8%, and 2.1%, respectively. The mechanical property test results showed that the yield strength of the CRB600H steel bars with corrosion levels of 1.8% and 2.1% was approximately 10% and 15% lower than that of intact steel bars, respectively. Still, the strains at the maximum force of the two corrosion levels showed no noticeable change with intact steel bars. The yield strength formula of the natural minor corrosion CRB600H steel bars was regressed. The load-slip curves, failure modes, bond toughness, and bond strength influential factors of natural minor corrosion bond specimens were analysed in the bond anchorage tests. Compared with the control bond anchorage specimens, the bond strength of the specimens with steel bar corrosion levels of 1.8% and 2.1% decreased by 5.4% and 6.3%, respectively. The ultimate bond strength of the natural minor corrosion CRB600H steel bars embedded in concrete was regressed. The development length of the natural minor corrosion CRB600H steel bars satisfying the reliability requirements was calculated using the first-order second-moment method. Based on the calculation results, the calculation formula of the development length for the natural minor corrosion CRB600H steel bars in concrete was regressed.

Analysis of Multi-Tendon Friction-Based Composite Anchorage Device for CFRP Cables and Its Anchorage Mechanism

Carbon fiber-reinforced polymer (CFRP) cables are anticipated to be employed in larger, longer, and more durable structures in the engineering field. However, its anchorage devices and mechanism should be appropriately developed and improved. At present, mainly relying on the adhesive force, most anchorage devices may lose their efficiency because of adhesive aging and failure or the slip of an individual tendon. A friction-based composite anchorage device with an integrated bearing of inner cone filler (i.e., load transfer media (LTM)) bonding and a single extruding anchor is proposed, and the anchorage mechanism is examined for Φ7 CFRP cables of strength 2400 MPa. Firstly, sufficient conditions for anti-slip failure of CFRP tendons in the anchorage zone are derived by assuming uniform LTM bonding. The obtained results reveal that the smaller inner pore size of the barrel leads to higher efficiency. Additionally, the maximum efficiency depends on the friction coefficient of the contact surface, the inner cone angle of the barrel, and the diameter and quantity of the CFRP tendons. The necessary conditions for the safety of the CFRP tendon anchorage zone are carefully obtained based on the Tsai–Wu failure criterion. It is concluded that the compressive stress of CFRP tendons in the anchorage zone should gradually increase from the load-bearing end to the no-loading end. Additionally, the relations among the anchorage efficiency coefficient and the CFRP tendon diameter d, the anchorage length l, the dip angle of LTM external conical surface α, and the friction angle β are derived based on the equivalent failure principle. The CFRP cables of four specifications (i.e., with Φ12, Φ19, Φ37, and Φ121 tendons) are designed under theoretical guidance, and eight static tests are carried out for more verification studies. The test results indicate that the anchorage efficiency coefficient of designed anchorage devices can be over 90%, and even up to 96.8%. Further, the failure modes are divergent destruction, which verifies the reliability of friction-based anchorage devices and provides a solid theoretical foundation for the design and engineering applications of CFRP cables.

Blast retrofit of one-way reinforced concrete members using externally bonded FRP and FRP anchorage

This paper presents the results of nine as-built and carbon fiber reinforced polymer (CFRP) retrofitted reinforced concrete panels subjected to simulated blast loading using a pneumatically operated shock tube. The objective of the study was to characterize the blast response of CFRP retrofitted reinforced concrete panels, with and without supplemental mechanical anchorage applied to the CFRP. The results indicate that retrofitting can significantly increase the strength and stiffness of reinforced concrete flexure members and greatly enhance the displacement time-history response over non-retrofitted members. Debonding of the externally bonded CFRP was the failure mode for all retrofitted members. FRP anchors, designed to prevent or delay debonding failures through mechanical end-anchorage, were found to substantially enhance the performance of panels experiencing critical diagonal crack debonding. However, the FRP anchors were found to have no substantial effect on retrofit performance for the case plate-end interfacial debonding failures. In addition, the displacement time-histories for as-built and FRP retrofitted panel obtained through detail single degree of freedom analysis were found correlate well with those obtained experimentally. Finally, a discussion on the practical considerations of using externally bonded FRP retrofits to resist blast loads and recommendations for protective design are presented.

Self-Calibration Technique with Lightweight Algorithm for Thermal Drift Compensation in MEMS Accelerometers.

Capacitive MEMS accelerometers have a high thermal sensitivity that drifts the output when subjected to changes in temperature. To improve their performance in applications with thermal variations, it is necessary to compensate for these effects. These drifts can be compensated using a lightweight algorithm by knowing the characteristic thermal parameters of the accelerometer (Temperature Drift of Bias and Temperature Drift of Scale Factor). These parameters vary in each accelerometer and axis, making an individual calibration necessary. In this work, a simple and fast calibration method that allows the characteristic parameters of the three axes to be obtained simultaneously through a single test is proposed. This method is based on the study of two specific orientations, each at two temperatures. By means of the suitable selection of the orientations and the temperature points, the data obtained can be extrapolated to the entire working range of the accelerometer. Only a mechanical anchor and a heat source are required to perform the calibration. This technique can be scaled to calibrate multiple accelerometers simultaneously. A lightweight algorithm is used to analyze the test data and obtain the compensation parameters. This algorithm stores only the most relevant data, reducing memory and computing power requirements. This allows it to be run in real time on a low-cost microcontroller during testing to obtain compensation parameters immediately. This method is aimed at mass factory calibration, where individual calibration with traditional methods may not be an adequate option. The proposed method has been compared with a traditional calibration using a six tests in orthogonal directions and a thermal chamber with a relative error difference of 0.3%.

Experimental Investigation on Flexural Performance of Masonry Wallettes Strengthened with Cementitious Matrix Grid

A large experimental study was conducted at IIT Patna, India to evaluate the effectiveness of different types of cementitious matrix grids (CMGs) in improving the flexural performance of unreinforced masonry specimens. Four types of masonry wallettes: brick-lime mortar, brick-cement mortar, brick-mud mortar and autoclaved aerated concrete (AAC) block masonry were prepared in the laboratory. In this study, eleven different CMG comprising of glass fabric and steel wire meshes embedded in the five different grades of cementitious matrix were used to strengthen the masonry assemblages. The aim of this study is to understand the role of various parameters such as tensile strength of CMG, compressive strength of masonry and cementitious matrix in influencing the efficiency of the strengthening scheme. In total 130 specimens with failure plane-parallel and perpendicular to the bed joint were prepared and tested under quasi-static displacement control loading. Considering the ease of installation, the fabric was directly placed on the masonry wallette using mechanical anchors and then covered with a thick layer of cementitious matrix.Test results highlights that all strengthening schemes are effective and can significantly enhance the flexural moment capacity in the range of 2.5 - 63.0 times the flexural moment of the respective control specimens. These strengthening schemes effectively mitigate the brittle behaviour of masonry wallettes and improved the deformation capacity by 1.2 - 18.1 times when compared to the respective control specimens. The study also illustrated that the strength of cementitious matrix can play an important role in contributing to the strength and deformability of the masonry specimens strengthened with CMG. For low strength cementitious matrix, debonding failure was commonly observed, whereas, for high strength cementitious matrix, the failure/rupture of reinforcement was noticed. In addition, the shear failure of masonry or debonding failure of reinforcing mesh was observed for specimens in which CMG had higher percentage of reinforcement.

Experimental Database on pullout bond performance of steel fiber embedded in ultra-high-strength concrete

The bond strength between the steel fiber and the ultra-high performance concrete (UHPC) matrix plays a significant role in improving the behavior of plain UHPC. This paper compiles the existing experimental research database on the pullout bond performance of steel fibers embedded in UHPC. The variations of key parameters in the database are the steel fiber type and geometry, fiber volume fractions, and fiber embedded length. The effects of these parameters are analyzed and discussed in detail. Based on the analysis of the results, it was found that the deformed steel fibers, i.e., the hooked-end, half-hooked-end, and twisted steel fibers clearly provided higher average bond strengths than that straight fibers. The average pullout bond strength was obtained by increasing of fiber volume fraction in the UHPC matrix up to 2% (11.21MPa) with an increment of 20.4%. When the steel fiber volume fractions increase beyond 2%, the average bond strength decreases. Additionally, it was also found that using smaller embedded lengths in deformed steel fibers could result in the improvement of bond strength. This could be due to the fact that the bond is controlled by the mechanical anchorage of the end-hook rather than the physio-chemical bond in the straight portion. Conversely, increasing the embedded length of steel fiber could greatly contribute to the enhancement of pullout resistance resulting in increased bond strength between the UHPC matrix and steel fibers.

Conformity assessment model for mechanical coupling devices and anchors for reinforcing steel for use in concrete structure

The use of mechanical coupling devices and anchors for reinforcing steel for use in concrete structures can simplify the design and construction of reinforced concrete and reduce the amount of reinforcement required. Technical Approvals of these products by suitably qualified organisations are acceptable under Building Regulations and by major specifiers as the appropriate way of assessing non-standard or new and innovative products. Specifiers, manufacturers, traders, and customers increasingly demand certainty in the quality management of mechanical coupling devices and anchors entering the supply chain. The supply chain is extremely complex. The weak traceability systems and pressure on the supply chain to reduce cost have created the environment where risks increase. This unique and comprehensive model describes the technical and assessment requirements for the conformity of mechanical coupling devices and anchors. It covers all stages in the supply chain from the production, assembly, product performance and evaluation of mechanical properties including tensile strength, ductility, permanent elongation (slip), cyclic loading performance and fatigue performance. The essential elements of the quality management system combined with additional requirements on process control, product testing and robust installation methodology are essential and agreed by all relevant sectors of industry.

A New Augmentation Method for Improved Screw Fixation in Fragile Bone.

Pertrochanteric fractures (TF) due to osteoporosis constitute nearly half of all proximal femur fractures. TFs are treated with a surgical approach and fracture fixation is achieved using metallic fixation devices. Poor quality cancellous bone in osteoporotic patients makes anchorage of a fixation device challenging, which can lead to failure of the fracture fixation. Methods to reinforce the bone-implant interface using bone cement (PMMA) and other calcium phosphate cements in TFs have been described earlier but a clear evidence on the advantage of using such biomaterials for augmentation is weak. Furthermore, there is no standardized technique for delivering these biomaterials at the bone-implant interface. In this study, we firstly describe a method to deliver a calcium sulphate/hydroxyapatite (CaS/HA) based biomaterial for the augmentation of a lag-screw commonly used for TF fixation. We then used an osteoporotic Sawbones model to study the consequence of CaS/HA augmentation on the immediate mechanical anchorage of the lag-screw to osteoporotic bone. Finally, as a proof-of-concept, the method of delivering the CaS/HA biomaterial at the bone-implant interface as well as spreading of the CaS/HA material at this interface was tested in patients undergoing treatment for TF as well as in donated femoral heads. The mechanical testing results indicated that the CaS/HA based biomaterial increased the peak extraction force of the lag-screw by 4 times compared with un-augmented lag-screws and the results were at par with PMMA. The X-ray images from the patient series showed that it was possible to inject the CaS/HA material at the bone-implant interface without applying additional pressure and the CaS/HA material spreading was observed at the interface of the lag-screw threads and the bone. Finally, the spreading of the CaS/HA material was also verified on donated femoral heads and micro-CT imaging indicated that the entire length of the lag-screw threads was covered with the CaS/HA biomaterial. In conclusion, we present a novel method for augmenting a lag-screw in TFs, which could potentially reduce the risk of fracture fixation failure and reoperation in fragile osteoporotic patients.

Experimental study of fibre-reinforced TRC shear strengthening applications on non-stirrup reinforced concrete T-beams

Textile Reinforced Concrete (TRC) materials have proven to be not only a viable solution, but also an effective one when used to strengthen Reinforced Concrete (RC) structures. The main drawbacks associated with this type of composites is mainly related to the low tensile strength of the cementitious matrix. To overcome such limitation, an improved class of such materials, named Fibre/Textile Reinforced Concrete (F/TRC) and consisting in the addition of short dispersed fibres to the cementitious matrix, was recently developed. An experimental campaign aimed at assessing and comparing of both TRC and F/TRC strengthening solutions upon the shear strength of real-scale RC beams was performed. Different parameters were investigated, including shape and number of textile layers, presence of short dispersed steel fibres, and presence of mechanical anchorages. The results show how the different parameters influence the overall behaviour of the tested specimens and highlight the strong increase in performance achievable using F/TRC materials compared to normal TRC.

Design of Multipanel CLT Shear Walls with Bidirectional Mechanical Anchors Following Capacity-Based Design Principle

AbstractThe applicability of the capacity-based design approach to buildings consisting of cross-laminated timber (CLT) shear walls has lacked analytical expressions that depend on the structural t...

The role of lintels and parapets on the mechanical performance of multi-storey cross laminated timber shearwalls with openings

The current study presents the results of an extensive numerical analysis using a validated Finite Element model and aims at investigating the influence of the geometrical and mechanical properties of lintel beams and parapets on the stiffness and strength of multi-storey cross laminated timber (CLT) symmetric shearwalls with either door or window openings. The influence of construction techniques, where the opening is cut out of the panel or constructed using separate elements is investigated. The results of the analysis show that in general, monolithic models resulted in significantly higher strength and stiffness values compared to those obtained from models assuming segmented shearwalls. The assumptions associated with the connectivity between the various structural components in the wall may have a very significant effect on the internal forces and efficiency of the design. The study also particularly highlights the importance of the parapet on the overall behaviour and failure mechanism, even though no structural function is typically associated with it. The lintel height seemed to only play a significant role when no parapet is present, i.e. in the case of door openings, where height of the lintel was observed to directly influence the failure mechanism, with intermediate lintel heights leading to failure in the wood elements, while for relatively small or large values, the failure occurred in the mechanical anchors.

Experimental study on flexural behaviour of reinforced concrete beams strengthened with passive and active CFRP strips using a novel anchorage system

The paper presents the research on reinforced concrete (RC) beams strengthened with carbon fibre reinforced polymer (CFRP) strips with various configurations in terms of anchoring and tensioning. The five full-scale RC beams with the total length of 6.0 m were strengthened with passive strips, without and with mechanical anchorages at their ends, as well as with strips tensioned by the novel prestressing system with three various prestressing levels ranging from 30 to 50% of the CFRP tensile strength. All RC beams were tested under static flexural load up to failure and they were investigated in a full range of flexural behaviour, including the post-debonding phase. The main parameters considered in this study include the use of mechanical anchorages, the effect of tensioning the strips and the influence of the various prestressing levels. Several performance indicators have been established to evaluate the beams’ behaviour. The study revealed that the RC beams strengthened using tensioned CFRP strips exhibited a higher cracking, yielding and ultimate moments as compared to the beams with passively bonded CFRP strips. Moreover, increasing the beams’ prestressing level has a significant positive influence on the performance of strengthened beams. However, it did not affect the ultimate load-bearing capacity of the beams. The optimal prestressing level for the novel system has been determined as 60% of CFRP tensile strength.

Functionalization of screw implants with superelastic structured Nitinol anchoring elements

BackgroundDemographic change is leading to an increase in the number of osteoporotic patients, so a rethink is required in implantology in order to be able to guarantee adequate anchoring stability in the bone. The functional modification of conventional standard screw implants using superelastic, structured Ti6Al4V anchoring elements promises great potential for increasing anchoring stability.MethodsFor this purpose, conventional screw implants were mechanically machined and extended so that structured-superelastic-positionable-Ti6Al4V anchoring elements could be used. The novel implants were investigated with three tests. The setup of the anchoring elements was investigated in CT studies in an artificial bone. In a subsequent simplified handling test, the handling of the functional samples was evaluated under surgical conditions. The anchorage stability compared to standard screw implants was investigated in a final pullout test according to ASTM F543—the international for the standard specification and test methods for metallic medical bone screws.ResultsThe functionalization of conventional screw implants with structured superelastic Ti6Al4V anchoring elements is technically realizable. It was demonstrated that the anchoring elements can be set up in the artificial bone without any problems. The anchorage mechanism is easy to handle under operating conditions. The first simplified handling test showed that at the current point of the investigations, the anchoring elements have no negative influence on the surgical procedure (especially under the focus of screw implantation). Compared to conventional standard screws, more mechanical work is required to remove the functional patterns completely from the bone.ConclusionIn summary, it was shown that conventional standard screw implants can be functionalized with Ti6Al4V-structured NiTi anchoring elements and the new type of screws are suitable for orthopedic and neurosurgical use. A first biomechanical test showed that the anchoring stability could be increased by the anchoring elements.

Comparison of Stress Distribution in Surrounding Bone during Insertion of Dental Implants on Four Implant Threads under the Effect of an Impact: A Finite Element Study

The design of an implant thread plays a fundamental role in the osseointegration process, particularly in low-density bone. It has been postulated that design features that maximize the surface area available for contact may improve mechanical anchorage and stability in cancellous bone. The primary stability of a dental implant is determined by the mechanical engagement between the implant and bone at the time of implant insertion. The contact area of implant-bone interfaces and the concentrated stresses on the marginal bones are principal concerns of implant designers. Numerous factors influence load transfer at the bone-implant interface, for example, the type of loading, surface structure, amount of surrounding bone, material properties of the implant and implant design. The purpose of this study was to investigate the effects of the impact two different projectile of implant threads on stress distribution in the jawbone using three-dimensional finite element analysis.

Effect of Ti rolling process on the enhanced interfacial adhesion between TiO2 and underlying Ti substrate

TiO2 nanotube arrays (TNAs) prepared by the traditional methods are prone to peeling off from the underlying titanium due to the weak interfacial adhesion between the nanotube layers and Ti substrates, which greatly restricts their applications. Here, 2.5 mm titanium plates are cold rolled to the Ti sheets of various thicknesses by controlling the cold-rolling reduction process. Ti sheets are then anodized in an electrolyte that was composed of water, NH4F, and ethylene glycol. It is discovered that after the cold-rolling process, not only are the pore sizes of the nanotubes smaller, but also the tube length is longer, indicating different growth behavior for the rolled Ti sheets. The results of XRD, EBSD, and metallographic microstructure analysis revealed mechanical anchorage at grain boundaries and decreased F contents, which leads to release stress at the TNAs/Ti interface. Most probably the released stress, finer grain sizes and increased dislocation density are responsible for the improved adhesion.

NONLINEAR FINITE ELEMENT ANALYSIS OF MECHANICALLY ANCHORED REINFORCED STEEL I BEAMS

Aim: Steel structural elements can lose their strength in vehicle crashes, fire, fatigue, decay, humidity, etc. Consequently, their load-bearing capacities reduce considerably. A widely used strengthening method for steel beams is fiber-reinforced polymer strips or plates. One of the most important problems for this practice is sudden end-strip debonding due to the high normal and shear stress concentration. In this study, the structural behavior of deformed steel I-beams strengthened by carbon composites under bending was studied numerically. Using a commercial nonlinear finite element program (ABAQUS), a finite element model verified with the formerly executed experimental study was presented. To examine the effect of Mechanical Anchorage on large samples, a parametric study was carried out with the verified finite element model. In the parametric study, mainly three parameters were considered. Flange slenderness ratio (Bf/tf), web slenderness ratio (H/tw), and length to cross-sectional depth ratio (L/bf). Results derived from the nonlinear analysis revealed that the employment of the bolt anchorage increases the load capacity of the deformed elements and sustains the elements to resist more loads. However, the behavior and strengthening capacity of this practice is accordingly dependent on the flange slenderness ratio and web slenderness ratio of the proposed beam. Obtained results also indicate that the efficiency of mechanical anchorage in short-span beams is higher compared to the long-span beams.

Achieving Excellent Interfacial Bonding of Qp980 Steel to Cfrtp by Laser Joining Via Carbon Fiber Reinforced Mechanical Anchorage

Achieving Excellent Interfacial Bonding of Qp980 Steel to Cfrtp by Laser Joining Via Carbon Fiber Reinforced Mechanical Anchorage

Experimental Study on Physical Model of Prestressed Anchorage Mechanism of Fractured Rock Slope

In view of some problems in the application of prestressed anchoring technology in broken rock slope, this study, combined with the prestressed anchoring project of K+276 broken rock slope of Chengdu-Chongqing Expressway (CCE), based on the field geological survey and key data monitoring, adopts physical model test to study the diffusion mode of prestressed anchor cable. The concrete influence of rock mass quality, anchor cable tensioning tonnage and other factors on the stress and deformation of broken rock slope is analyzed, and the application mechanism of prestressed anchorage technology in the reinforcement of broken rock slope is discussed.