Strand Anchors Research Articles

Study on the application of thermal-meltable recovery of CFRP strand anchors

Conventional pressure-type anchoring systems face challenges such as difficulty in recovery, low recovery efficiency, and insufficient durability over long-term use. Although the single-use cost of Carbon Fibre Reinforced Polymer (CFRP) strand anchors is higher than that of conventional steel strands, recovery and reuse can significantly reduce costs. Therefore, this study aims to investigate the bonded anchoring method of CFRP and proposes an innovative thermoplastic CFRP prestressed strand design that combines both anchoring strength and recoverability to address the shortcomings of existing anchoring systems. Two bonding materials, thermosetting resin and thermoplastic resin, were selected for bond strength tests under different conditions. The results indicated that epoxy resin had a bonding force of 280 kN and an anchoring efficiency of approximately 70%, making it the most suitable material. However, the anchoring efficiency still needs improvement. Based on this, an improved design scheme was proposed, which can increase anchoring efficiency to over 95%. Additionally, based on the dispersed bonding anchor system, this study explored a solution that involves adding a positioning plate at the end of the anchor strand and using epoxy resin for anchoring. The anchoring performance tests showed that the tensile strength of the CFRP strand ranged from 2.7–2.8 GPa, with an average anchoring efficiency of 100.5%, demonstrating excellent anchoring performance. Further thermoplastic recovery tests showed that when the temperature increased to 90°C, the maximum recovery force of the strand was 17.2 kN, about 4.4% of the ultimate load. When the temperature increased to 150°C, the maximum recovery force was 7.5 kN. The recovered CFRP strands were clean, with no resin residue, and had no damage, maintaining an intact structure. The proposed thermoplastic CFRP prestressed strand design demonstrates significant advantages in anchoring strength and recoverability. With the improved design, anchoring efficiency can be increased to over 95%, and the high-temperature recovery process shows good feasibility. Compared with traditional anchoring systems, CFRP strands offer higher anchoring efficiency, lower recovery force requirements, better economics, and sustainability, making them a promising solution for engineering applications.

Anchor test and long-term monitoring of grouted anchors instrumented with Fiber Bragg Grating sensing technology

Geotechnical monitoring of anchors provides fundamental data for analysis and evaluation to ensure safe environment. The use of optic fiber sensing technology, especially Fiber Bragg Gratings, brings many advantages of optic fiber sensors, such as high measurement accuracy, real-time continualmonitoring of deformation, on-line access to data and resistance against electromagnetic interferences. This article deals with anchor tests instrumented with FBG deformation gauges of the root and the tendon of the pre-stressed strand anchor in a test field in the Central Bohemian Region. First, the anchor with three optic cables with FBG sensors for measurement of axial deformation was subjected to six loading stages of the anchor test. Most of the sensors measured values of axial deformation less than 200 με and the root mobilisation was observed. Then, the measurement continued by 26-day long-term monitoring and a trend of a small increase of deformations occurred.

Mapping H+ in the Nanoscale (A2C4)2-Ag8 Fluorophore.

When strands of DNA encapsulate silver clusters, supramolecular optical chromophores develop. However, how a particular structure endows a specific spectrum remains poorly understood. Here, we used neutron diffraction to map protonation in (A2C4)2-Ag8, a green-emitting fluorophore with a "Big Dipper" arrangement of silvers. The DNA host has two substructures with distinct protonation patterns. Three cytosines from each strand collectively chelate handle-like array of three silvers, and calorimetry studies suggest Ag+ cross-links. The twisted cytosines are further joined by hydrogen bonds from fully protonated amines. The adenines and their neighboring cytosine from each strand anchor a dipper-like group of five silvers via their deprotonated endo- and exocyclic nitrogens. Typically, exocyclic amines are strongly basic, so their acidification and deprotonation in (A2C4)2-Ag8 suggest that silvers perturb the electron distribution in the aromatic nucleobases. The different protonation states in (A2C4)2-Ag8 suggest that atomic level structures can pinpoint how to control and tune the electronic spectra of these nanoscale chromophores.

Damage-Sequences of Mountain Anchors

Abstract Strand anchors are a perennial problem [1]. In many instances such anchor systems have been in service for decades. Information regarding their construction, composition or manufacturer is often uncertain. In this article the damage to a number of broken strand anchors is investigated. Using relatively simple methods of investigation, it is shown that the main cause of failure encountered is hydrogen-induced stress corrosion cracking.

Anchoring of a retaining structure with glass fibre strand anchors

In Copenhagen, Denmark, a large construction pit has been designed to facilitate the excavation for the basement of a new district in the city called “Postgrunden”. The retaining wall is constructed by sheet piles installed into the Copenhagen Limestone with the use of pre-drilling and with ground anchors in two levels. The construction pit as well as the anchors are temporary, however, both parts are left in the ground after construction of the basement has been concluded. Most of the anchors were constructed as normal steel strand anchors, however, at one location glass fibre anchors were found to be the best solution due to restrictions concerning installation under third party property. Therefore 82 ground anchors with glass fibre strands were installed. These anchors were the first of their type used in production in Denmark. However, in Denmark there is no Eurocode or National Annex on composite materials at the time of the design and therefore the designers had no direct standard to design by. The design of the glass fibre anchors was therefore based on the index of safety method from Eurocode 0 along with a set of fracture tests made in a laboratory. The tests were used for a statistical analysis that along with a required index of safety gave the characteristic ultimate resistance of the strands and the elastic modulus. During installation the contractor had to consider the different material behaviour of the glass fibre strands compared to the traditional steel strands, e.g. the brittle shear tolerance, that dictates the assembly of the glass fibre strands to steel strand couplers to allow for testing and prestressing of the anchors. Further, the glass fibre anchors are not as heavy and stiff as the traditional steel anchors, which added an extra challenge during installation below the ground water table. Anchor testing was performed using traditional anchor testing equipment. The hollow plunger jacks were chosen in respect to the long piston stroke required for the extra elongation of glass fibre strands due to a low modulus of elasticity. All anchors were tested with either suitability or acceptance test to a factor of 1.43 or 1.30 above the design load, respectively.

Comparison of the Performance of Self-Drilled Hollow Bar and Strand Anchors in Soft Soil: A field Study

Hollow bars are used increasingly for anchorage applications and have become popular in soil improvement of projects over the use of traditional strand anchors because of their lower construction cost and time. Main factor for soil reinforced with anchors is the pullout resistance. Because little work has been done to investigate the load-deformation behaviour of hollow bar anchors, their bond characteristics in comparison with strand anchors is pending both for developing design codes and construction methods. This study presents a comparison of hollow-bar and strand anchor load-deformation behaviour. A field study was performed by installing full-scale hollow-bars and strand anchors in loose silty sand and subjecting them to pullout testing. The observed load–displacement behaviour indicated that the induced bond diameter of the hollow bar anchors was greater than theoretical calculations and the bond strength estimated for them was larger than the values proposed by existing codes. At a unique bonded and unbonded length, the hollow-bar anchors recorded higher ultimate load than the strand anchors. The bond strength for the hollow-bar anchors was 65–100% greater than for the strand anchors.

Comparison between Chinese and British Standards for Strand Anchor Structure Design

In this paper, the relevant provisions regarding the classification, safety factor, strand anchor structure design and corrosion protection design are compared between the British standard BS EN 1537:2013, BS 08081:2015 and the Chinese national standard GB 50086-2015, the main differences of the strand anchor design are summarized, which can be used as reference for other strand anchor designers and researchers.

Case study on the maintenance of various anchored retaining walls in the Austrian high‐speed road network

AbstractAnchored retaining structures demand detailed preliminary investigations for appropriate and economic repair and upgrading. However, due to the complex constraints and insufficient data basis, it is often necessary to investigate the basis for the design of repair works in advance. The article described two anchored constructions. The first is a bored pile wall to dowel a slope. In addition to the repair of corrosion damage to the strand anchors, repair of the uphill drainage system is an essential part of the refurbishment concept. The second example is a retaining structure about 40 years old, in which several rod anchors show corrosion to their heads. Since there is a lack of information about the ground conditions for the assessment of structural safety and design of repair works, additional investigation boreholes were drilled.

Development of Under–anchorage Effective Prestress Detecting Instrument and Engineering Application

For detecting under–anchorage effective prestress of steel strand by lift–off test convenient. Revealing the testing principle of lift–off text and developing the testing in strument. The instrument consists of data acquisition card, oil pressure sensor, high precision displacement sensor and electric oil pump. Based on the graphical software platform LabVIEW, the test program is compiled by using G language. And further gives the program source code. Integrating the texting instrument (LTF 1.0) of under–anchorage effective prestress based on the software and hardware. So the engineering application is carried out. The research results show that the instrument can detect the under-anchorage effective prestress effectively by the load–displacement curve. Meanwhile it has the advantages of high precision, good safety and convenient operation. Through field application, the effective prestress of prestressed steel strand anchor was increased from 54.4% to 94.7%, and same strand dispersion was reduced from 10.2% to 1.7%.

Stability of the human polymerase δ holoenzyme and its implications in lagging strand DNA synthesis

In eukaryotes, DNA polymerase δ (pol δ) is responsible for replicating the lagging strand template and anchors to the proliferating cell nuclear antigen (PCNA) sliding clamp to form a holoenzyme. The stability of this complex is integral to every aspect of lagging strand replication. Most of our understanding comes from Saccharomyces cerevisae where the extreme stability of the pol δ holoenzyme ensures that every nucleobase within an Okazaki fragment is faithfully duplicated before dissociation but also necessitates an active displacement mechanism for polymerase recycling and exchange. However, the stability of the human pol δ holoenzyme is unknown. We designed unique kinetic assays to analyze the processivity and stability of the pol δ holoenzyme. Surprisingly, the results indicate that human pol δ maintains a loose association with PCNA while replicating DNA. Such behavior has profound implications on Okazaki fragment synthesis in humans as it limits the processivity of pol δ on undamaged DNA and promotes the rapid dissociation of pol δ from PCNA on stalling at a DNA lesion.

Deformation Characteristics of Mono Strand Anchor Head

This paper investigates experimentally the deformation characteristics of the mono strand anchor head used in prestressed concrete bridge. Since the strains measurable in the anchor head are the axial and hoop strains, the deformation characteristics of the anchor head are examined by measuring these strains at various positions and according to the jacking force exerted on the pre-stressing strand. Moreover, the possibility to estimate the jacking force acting in the tendon based upon the measured strains and the corresponding error are evaluated.

The search for the ideal tendon repair in zone 2: strand number, anchor points and suture thickness

This review article examines the mechanical factors involved in tendon repair by sutures. The repair strength, repair stiffness and gap resistance can be increased by increasing the number of core strands and anchor points, by increased anchor point efficiency and the use of peripheral sutures, and by using thicker sutures. In the future, laboratory tests could be standardized to a specific animal model and to a defined cyclic motion programme. Clinical studies support the use of multi-strand core and peripheral sutures, but two-strand core sutures are not adequate to ensure consistently good clinical results. Training surgeons in complex tendon repair techniques is essential.

Llyn Alaw reservoir post-tensioned anchor installation

As a result of leakage along the downstream face of the dam, a section 10 inspection carried out in February 2006 contained a recommendation for a study to be undertaken into the uplift pressures and stability of the concrete gravity dam impounding Llyn Alaw reservoir. The study was subsequently carried out and showed the dam to have inadequate factors of safety for stability during an extreme seismic event. Dwr Cymru Welsh Water awarded a contract to undertake the design and supervision of works to ensure the stability of the structure. The selected method of stabilising the structure was to install 44 no. post-tensioned strand anchors along the length of the dam, vertically through the crest and into the bedrock foundation. This paper describes the stages of the project from feasibility studies and design through to construction of the scheme, which was completed in mid-2013.

Corrosion susceptibility of potential rock bolts in aerated multi-ionic simulated concentrated water

Rock bolts used for the reinforcement of underground mines, tunnels and nuclear waste repositories are made up of low and medium carbon steels, and high strength low alloy steels. Typical rock bolt systems used for rock reinforcement are mechanically anchored bolts, grout anchored, frictional rock stabilizers and strand anchors. For nuclear waste repository sites such as Yucca Mountain (YM) as well as for mines and tunnels, in addition to mechanical properties, corrosion properties are also important due to potential seepage of water through the fractures or pores in the rock. During temporary rock support period of 50–100 years, the temperature of the tunnel at YM should be maintained at ambient conditions. For any reason if the rock bolts are exposed to YM waters and high temperatures in the tunnel then there is a chance of corrosion of steel rock bolts. In this study an attempt was made to study the corrosion properties of various potential rock bolts for YM tunnel support via the aid of electrochemical corrosion testing. At ambient temperature (25 °C) all the rock bolts that were studied showed good corrosion resistance in these waters. At higher temperatures, 60 °C and 90 °C, corrosion resistance of rock bolts decreased, but due to special stress relief heat treatment of one of the frictional rock stabilizers (Swellex Mn 24) the corrosion rates were lower than all other tested rock bolts. Note: Swellex, Split set and Williams are the proprietary names of Atlas Copco, International Roll Forms, Inc. and Williams Form Engineering Corp, respectively.

Verankerung der Stützmauer Entschigtal / Anchorage of the Sustaining Wall Entschigtal

Abstract Structural design and the position of the sustaining wall Entschigtal were at the origin of corrosion of the back layer of reinforcement. A drecrease of the load bearing section was observed in 1995. The assessment of the actual state of the reinforcement turned out to be a complex task in the context of the inspection of the structure. It was the combination of different test methods which finally led to reliable results concerning the extent and the position of corrosion of reinforcement. In order to restore the load bearing capacity for the remaining required service- life consolidation measures werde necessary. Permanent strand anchors have been placed to strengthen the wall.

Investigation of different types of flexible anchor tendons (rock bolts) for stabilization of rock masses

1. On the basis of tests, several types of flexible prestressed anchor tendons with tensions of 100–190 tons and embedment lengths of up to 40 m were recommended and experimentally justified for strengthening potentially unstable rock. Their basic constructional and technical parameters were determined, and their economic indices were calculated. 2. The most promising type of anchor is the flexible prestressed anchor tendon made from a bundle of parallel high-strength 5-mm diameter wires, which develop a maximum force in the hole. The strand and rope anchor tendons require a smaller volume of labor, but the wires in the strands and ropes undergo torsional and bending forces which cause large stress losses. Stabilization of the stresses in a cable requires a long time, making it necessary to apply either tensioning or preliminary elongation. 3. Further improvement in the different types of prestressed anchor tendons should be carried out by using high-strength wires 7–8 mm in diameter, with a strength of 170–200 kg/mm2, which are being produced now on an industrial scale. It is necessary to enlarge the tendons, thus increasing their capacity, and to improve the techniques for their fabrication and for the mechanization of their installation.