Anchorage Length Research Articles

Simulating the response of CFRP strengthened shear-keys in composite concrete bridges

The reduction in the integral action between cast-in-situ slab and precast prestressed concrete girders in composite concrete bridges can be attributed to the increase in truck loads; increase in the allowable stress at service loads; exposure to aggressive environments; and the increase in traffic flow. It is a necessity to restore this integral action by strengthening against horizontal shear. In this paper, a finite element analysis (FEA) was performed considering 32 push off specimens using ANSYS software package to evaluate the behavior of shear-keys of composite concrete bridges. The studied parameters include: the concrete compressive strength, spacing of the shear stirrups, the carbon fiber reinforce polymer (CFRP) sheet spacing, and CFRP plate spacing, fiber angle, and anchorage length. The FEA results show that the reduced crack opening and slip in the strengthened shear-keys compared with the control specimen reflect the efficiency of the CFRP strengthening scheme. Moreover, the FEA results indicate that the CFRP composites anchorage length and angle had a notable impact on the longitudinal shear force and corresponding slip, failure mode, stiffness, and toughness. Finally, an empirical model was proposed for predicting the bond-slip behavior of shear-keys based on reliable experimental results available in literature.

Stability of multi-anchor soil walls after loss of toe support

This paper reports the results of a novel experiment in which two nominally identical full-scale steel multi-anchor reinforced soil walls were taken to foundation failure by progressive loss of footing support. The 4-m high walls varied only with respect to reinforcement anchor lengths. The data show that facing displacements at end of construction and at time of foundation failure below the footing were greater for the wall with the shorter reinforcement lengths. Reinforcement loads at end of construction were best estimated using a working stress model proposed by the authors rather than current methods used in Japan and the UK. However, after significant loss of footing support, the Japanese Public Works Research Centre method gave more accurate and safer load predictions. Regardless, both the anchor rods and anchor plates had abundant reserve capacity to provide large margins of safety against internal tensile rupture and pullout modes of failure even after large foundation displacements.

Influence of different peg length in glenoid bone loss: A biomechanical analysis regarding primary stability of the glenoid baseplate in reverse shoulder arthroplasty.

There is no biomechanical basis to determine the influence of different length of the central peg of the baseplate anchored within the native scapula in glenoid defect reconstruction in cases of degenerative or posttraumatic glenoid bone loss in reversed shoulder arthroplasty. The purpose of this study was to analyse the stability of different peg lengths used in glenoid bone loss in reversed shoulder arthroplasty. Different lengths of metaglene pegs with different depths of peg anchorage performed with or without metaglene screws in sawbone foam blocks were loaded in vertical and horizontal directions for differentiating load capacities. Simulated physiological loadings were then applied to the peg implants to determine the limits of loading in each depth of anchorage. The loading capacity of the implant was reduced as less of the peg was anchored. The vertically loaded implants showed a significantly higher stability, in contrast to those loaded horizontally at a corresponding peg length and depth of anchorage (p < 0.05). The tests revealed that the metaglene screws are more essential for primary stability than is the peg particularly in the vertically directed loadings (2/3 anchored: peg contributed to 28% of the stability, 1/3 anchorage: peg contributed to 12%). Under the second test conditions, the lowest depth of peg anchorage (1/3) resulted in 322 Newtons [N] in the long peg with a vertical loading direction, and in 130 N in the long peg with a horizontal loading direction (p < 0.05). The pegs should be anchored as deeply as possible into the native scapula bone stock. The metaglene screws play a major role in the initial stability, in contrast to the peg, and they become more important when the depth of the peg anchorage is reduced. If possible, four metaglene screws should be used in cases of uncontained bone loss to guarantee the highest stability.

Effect of carbon nanotubes on strengthening of RC beams retrofitted with carbon fiber/epoxy composites

The effect of carbon nanotubes (CNTs) in improving the strengthening efficiency of carbon fiber/epoxy composites retrofitted reinforced concrete (RC) beams was investigated. A total of sixteen simply supported RC beams were prepared and tested under four-point loading. The incorporation of CNTs within the systems was done by modifying the epoxy resin using CNTs and/or coating the carbon fiber sheets with CNT enriched sizing agent. The effects of epoxy modification with CNTs, incorporation of CNT enriched sizing agent, anchorage length, and number of retrofitting layers were investigated through crack patterns, failure modes, load-deflection curves, and scanning electron microscopy (SEM) micrographs of fractured surfaces. Experimental results showed that using CNT modified epoxy resin enhanced the ultimate load and stiffness of retrofitted beams. The enhancement efficiency highly depends on the level of dispersion of CNT, anchorage length, and number of retrofitting layers. SEM characterization showed that CNTs could improve the adhesion at the concrete/epoxy interface and carbon fiber/epoxy interface leading to improvement in the load transfer and ultimate load of the strengthened beams.

Modified Push-Off Testing of an Inclined Shear Plane in Reinforced Concrete Strengthened with CFRP Fabric

This study reports the findings of an experimental investigation into the behavior of an inclined shear plane in reinforced concrete, such as a diagonal crack in the web of a beam, strengthened with externally bonded carbon fiber–reinforced polymer (CFRP) fabric. A modified push-off test of novel geometry was developed for this study. This test generates a diagonal failure plane subject to combined shear and tension. Both unwrapped and wrapped tests were conducted, allowing the load sharing and load-displacement behavior of the reinforced concrete, and the reinforced concrete with externally bonded CFRP fabric, to be investigated. Fully wrapped and U-wrapped CFRP fabric configurations were tested. Results indicate that for the arrangement tested, concrete, steel, and CFRP contributions to resistance are not independent, and that effective anchorage lengths given in the United Kingdom and United States guidance for U-wrapped CFRP may not be adequate in some cases.

Bond Behavior between Softwood Glulam and Epoxy Bonded-In Threaded Steel Rod

AbstractThis study aims to develop an improved understanding of the interfacial bond behavior of softwood glulam joints with bonded-in threaded steel rod. A total of 39 glulam joints with bonded-in single-threaded steel rods were tested to failure in the pull-pull configuration. The test results were presented in term of failure modes, load-relative movement response, pullout strength, and the corresponding slip. The distributions of bonded-in rod axial strain, interfacial bond stress, and relative movement were also analyzed to evaluate the local bond stress–relative movement response in the bond line. The results confirmed that the bond-relative movement response is dependent on the locations along the anchorage length, and the bond-relative movement responses located near both the loaded end and the anchorage end were observed to be stiffer than those at other locations. Finally, the predictions for the load capacity of the glulam joints with bonded-in threaded steel rod were carried out based on sever...

Comparison of Bond Behaviour between Reinforcement and UHPC and Ordinary Concrete in Extreme Conditions

The UHPC (Ultra High Performance Concrete) is a promising material suitable for application in special structures. However, the knowledge on performance of this relatively new material is rather limited. The exceptional mechanical properties of UHPC allow for a modification of the design rules, which are applicable in ordinary or high strength concrete. The research executed already in the Czech Republic showed that the anchorage length of ordinary and prestressing steel may be significantly shorter than that which is usually required in code specifications. This paper deals in more detail with impact of thermal stress on bond of prestressing strands and UHPC. Samples were subjected to the cycling heat/frost device and effect of a number of cycles on final bond behaviour of both UHPC and ordinary concrete were investigated. The article describes differences between ordinary concrete and UHPC.

Experimental Investigation on Bond Behavior of Cement-Matrix–Based Composites for Strengthening of Masonry Structures

Fabric-reinforced cementitious matrices have raised a great interest for the external strengthening of historical masonries, representing a valid alternative to fiber-reinforced polymers. As the effectiveness of an external reinforcement firstly depends on the bond performance, this paper presents an experimental investigation, through double-shear tests, on the bond behavior of cement-matrix-based composites reinforced with three different textiles, namely, carbon, polybenzoxazole (PBO), and glass. Textiles and matrix specimens were experimentally tested to correlate mechanical properties of the constituent materials with the global response of the composites. The results of bond tests highlighted that PBO-fiber- and glass-fiber-based composites better exploit the mechanical properties of the textile. Observation of the failure mechanisms highlighted that debonding phenomena occur at the fiber–matrix interface. Furthermore, the effective anchorage lengths were estimated. The values of fracture energy were determined by a fracture-mechanics approach, using the experimental values of debonding loads. Finally, the values of fracture energy were correlated with the mechanical characteristics of the constituent materials.

Support of 25 m deep excavation using ground anchors in Russia

The paper describes the design, construction and testing of some 3600 temporary single-bore multiple anchors used to support the deep basement that formed part of the foundation support system for the Kuntsevo Plaza, a pedestrian-oriented, mixed-use development in the Kuntsevo district of south-western Moscow, Russia. Single-bore multiple-anchor technology was used effectively to provide support for a 45 m deep diaphragm wall constructed to support a 25 m deep excavation in the geotechnically challenging Moscow mixed soils, comprising combinations of low-strength clays, sands and silts. Previous attempts to sustain the required workloads of up 600 kN in the anchors had failed due to unacceptable creep. However, an understanding of the concept of progressive debonding, and the use of this knowledge in the design of efficient fixed anchor lengths, proved highly effective. Also, the introduction of fixed anchor enhancement techniques such as end-of-casing grouting in granular soils and post-grouting in cohesive soils enabled anchor capacities more than double those previously achieved in the prevailing ground conditions. Also described is the extensive programme of investigation tests conducted to establish important parameters regarding the behaviour of the ground and the performance data relating to the ground anchors that effectively limited wall displacements; this was a crucial requirement due to the sensitivity of adjacent underground services.

Effect of Interface Morphology on Charge Transport

Molecular devices are a promising candidate for new technology nowadays. Great effort has been devoted recently to understand the charge transport at the interfaces in nano junctions and the role of bond length on the transport properties of molecular junctions. However, these studies have been largely based on the analysis of the low-bias conductance, which does not allow elucidating the exact influence of the symmetry in both the electronic structure and transport characteristics of the interfaces. In this work we had presented a theoretical study of the charge transport, and how conductance changes with varying the bond length of end group anchor (thiol group) on both sides of anthracene molecule to the extreme limits beyond these either the bond broke or it got overlapped with another consecutive bond. Further we rotated (along Z axis) the molecule under observation (anthracene di-thiol) and measured the effect of the rotation on the current and conductance. We have performed first principles calculations of the transport properties of these molecules using a combination of density functional theory and non-equilibrium Green's function techniques.

Experimental and Numerical Analysis on the Bonding Performance of GFRP Bolts

By pull-out tests between GFRP bolts and concrete, the influence of the diameter and surface shape of GFRP bolts on the bonding performance was studied. By ANSYS analysis, the effects of anchorage length, diameter, geotechnical parameters and prestress on the bonding performance were studied. The experimental and numerical analysis results show that: with the increase of bolt diameter, the bonding strength of bolts decrease and the slippages increase. The bigger the parameters of rock-soil like modulus of elasticity, cohesion strength and internal friction angle are, the better is the bond behavior and the smaller is the slippage. The prestress plays an important role in the rock stability and the restriction of deformation. With the enhancement of the prestress of bolts, the peak shear stress increases but the effective anchorage length nearly stays the same.

Simulation of Tests on Cast-In and Postinstalled Column-to-Foundation Connections to Quantify the Effect of Cyclic Loading

AbstractAdditional columns are often used as a retrofitting solution for reinforced concrete structures, particularly in seismic regions. These columns require postinstalled starter bars that inhibit the detailing of the anchorage with hooks. Often, the anchorage length of straight starter bars cannot be accommodated in foundations, which are generally short. For this reason, reductions of the large anchorage length, which are required according to the design codes, are desirable. The aim of the study presented in this paper was to quantify the adverse effect of cyclic loading on the capacity of connections with reduced starter bar anchorage lengths. To this end, finite-element analysis employing bond elements was realistically carried out to simulate seismic tests on column-to-foundation connections. The analysis allowed the study of the effect of cyclic loading on global performance and local behavior in terms of tensile and bond stresses along the starter bar. An equation to take into account the effec...

An Optimization Model of Tunnel Support Parameters

An optimization model was developed to obtain the ideal values of the primary support parameters of tunnels, which are wide-ranging in high-speed railway design codes when the surrounding rocks are at the III, IV, and V levels. First, several sets of experiments were designed and simulated using the FLAC 3D software under an orthogonal experimental design. Six factors, namely, level of surrounding rock, buried depth of tunnel, lateral pressure coefficient, anchor spacing, anchor length, and shotcrete thickness, were considered. Second, a regression equation was generated by conducting a multiple linear regression analysis following the analysis of the simulation results. Finally, the optimization model of support parameters was obtained by solving the regression equation using the least squares method. In practical projects, the optimized values of support parameters could be obtained by integrating known parameters into the proposed model. In this work, the proposed model was verified on the basis of the Liuyang River Tunnel Project. Results show that the optimization model significantly reduces related costs. The proposed model can also be used as a reliable reference for other high-speed railway tunnels.

The Influence of Age and Temperature on the Bond Behaviour between Prestressing Strands and UHPC

Applications of precast elements made of UHPC have been increasing in recent years. Also in the Czech Republic, UHPC can be found as a structural material in first applications in both, buildings and transport structural engineering. Structures made from this modern material required experimental programs verification of material properties and also for determination of behaviour of structural elements. In previous research of the bond of UHPC and various types of reinforcement was proven to be very good, which makes it possible to reduce radically anchorage lengths. This paper deals in more detail with determination of the bond of prestressing strands and UHPC, during the first week after casting, in particular. For prestressing of precast elements, there are very important short-time strengths and short-time bond is showing to be a decisive factor for optimum prestressing time. Second part of the paper is focused on impact of thermal stress on bond of prestressing strands and UHPC. Samples were subjected to the cycling heat/frost and effect of a number of cycles on final bond behaviour of both UHPC and ordinary concrete were investigated. The article describes differences between ordinary concrete and UHPC.

Effect of Lightweight Concrete Density on Bond Strength

The main objective of this paper is connected with the search of an optimal anchorage length of reinforcement in lightweight and ultra-lightweight concretes. Experimentally obtained values of the bond stress between lightweight concrete and reinforcing bars are presented. The density classes of lightweight concrete were D1,0, D1,2 and D1,4. The results are compared with equal ones of normal density concrete. The tests with ordinary reinforcement and with non-metallic hybrid reinforcement C-GFPR (30% portion of carbon fibres) were conducted.

Concrete Design Guide. No. 5: How to calculate anchorage and lap lengths to Eurocode 2

This article discusses how to calculate an anchorage and lap length for steel ribbed reinforcement subjected to predominantly static loading using the information in Section 8 of Eurocode 2. Coated steel bars (e.g. coated with paint, epoxy or zinc) are not considered. The rules are applicable to normal buildings and bridges.

Capacity of dynamically installed anchors as assessed through field testing and three-dimensional large-deformation finite element analyses

The capacity of dynamically installed anchors in soft normally consolidated clay was examined experimentally through a series of field tests on a 1:20 reduced-scale anchor. The anchors were installed through free fall in water, achieving tip embedment of 1.5–2.6 times the anchor length, before being loaded under undrained conditions at various load inclinations. Vertical anchor capacities were between 2.4 and 4.1 times the anchor dry weight and were satisfactorily predicted using the American Petroleum Institute approach for driven piles. Anchor capacity under inclined loading increased as the load inclination approached horizontal; the field data indicated this increase to be up to 30% for the minimum achievable inclination of about 20° to the horizontal. Corresponding large-deformation finite element analyses showed a similar response, with the maximum capacity occurring at a load inclination between 30° and 45° to the horizontal. The finite element results demonstrate that, for the anchor geometry considered, an inclined load at the anchor padeye could be decomposed into ultimate vertical and moment loading at the anchor centroid. The establishment of a vertical and moment loading yield envelope for the geometry investigated forms the basis of a simple design procedure presented in the paper.

Force Analysis of an Anchored Inshore Pipeline

ABSTRACT Zhang, S.; Liu, L., and Zhang, Q., 2015. Force analysis of anchored inshore pipeline. This paper mainly analyzes the optimal anchorage length of a straight-laid inshore pipeline. To begin with, several ways of how to fix a pipe are ticked off, and the way with discontinuous anchor is chosen for the specific analysis. Mathematical model is built to analyze the stress state of the pipeline, which is fixed with the screw anchor, and the main failure mode of pipeline-excessive-yield-failure mode-is checked; thus we gain the maximum anchorage distance of the pipeline. To get a more exact result, a finite element model of the pipeline is built. With the software ANSYS, the model is analyzed under wave conditions. The results reveal that the maximum anchorage distance differ in different determinants, namely distance, stress and strain; the stress of the pipeline first exceeds the allowable range when anchorage distance increases.

Bond behaviour of normal‐ and high‐strength recycled aggregate concrete

AbstractThe effect of concrete grade on the bond between 12 mm diameter deformed steel bars and recycled aggregate concrete (RAC) has been investigated with the help of 45 pullout tests with concentric rebar placement for coarse recycled concrete aggregate (RCA) replacement levels of 25, 50, 75 and 100%. For all the three concrete grades, the measured bond‐slip relationships indicate similar mechanisms of bond resistance in the RAC and the natural aggregate (NA) concrete. The most accurate and least conservative predictions of the measured bond strengths were obtained from the local bond‐slip model in the fib Model Code for Concrete Structures 2010. Bond strength normalized to fc(3/4) resulted in an improved match with test data and increased with an increase in the RCA replacement levels and decreased with an increase in compressive strength. An attempt to explain this behaviour has been sought in terms of brittleness index, an analogous parameter from rock mechanics. An empirical bond stress versus slip relationship has been proposed for the 12 mm diameter bar and it is conservatively suggested that similar anchorage lengths for this bar in all three concrete grades can be adopted for the RAC and the NA concretes.

콘크리트 강도별 매입 철근의 유형별 부착력 측정실험

Many construction equipment or supporting structure should be installed in a field without appropriate anchorage to cause a collapse of those. Anchor length, anchor diameter, hooked or non hooked will be made and tested in the study. This one will be analyzed and compared with the previous study in order to find out some difference, strength by strength, based on this study. Embedded re-bar and the resistant capacity against pulled out force of re bar have been tested and analyzed by concrete design strength and rebar diameter in the study. 21Mpa and 24MPa compressive strength which are used in construction practice have been applied as variables. Those rebars are composed of D13, D16. D22 which are mostly used at construction sites. The followings are summarized as conclusions.1) ductility is not increased as rebar diameter becomes larger under the condition of non-hooked anchorage.2) those are two times of displacement difference between small diameter of rebar and large one with hooked anchorage of rebar while being 1/10 times difference with non-hooked condition but, only 10% difference of maximum load are shown, not conspicuously between hooked and non-hooked condition.3) displacement related to ductility can be three(3) times decreased if only concrete compressive strength and rebar diameter become larger with heavy support weight.