Anchor Head Research Articles

Laboratory Model Test Research on Mechanical Characteristics of Anchor in Loess Tunnel under the Action of Pull‐Out Load

The deformation mode of loess surrounding rock of anchor under the action of pull‐out load and the shear stress distribution law of loess anchor and loess interface under the condition of different lengths anchor are studied by using the laboratory self‐made model test chamber and micro anchor pullout instrument. A total of three tests are carried out for the selected test anchor. Three deformation modes of loess surrounding rock under the action of pull‐out load are obtained according to the test results. It is proposed that the maximum shear stress of loess anchor under the action of pull‐out load appears in the section 25 times the anchor diameter from the anchor head, and the shear stress in the middle and rear part of the anchor body can only be brought into full play when the length‐to‐diameter ratio of the anchor body is 110 or more. Based on the displacement solution of Mindlin problem, the drawn conclusion is compared with the theoretical solution of shear stress and axial force of loess anchor under the action of pull‐out load. The results compared are basically consistent, indicating that the conclusion has strong engineering practice, which can provide technical basis for the design and optimization of the system anchor in the sidewall of loess tunnel.

Load transfer on instrumented prestressed ground anchors in sandy soil

abstract: This study evaluates load variations in instrumented prestressed ground anchors installed in a bored pile retaining wall system in sandy soil. Data were collected from instrumentation assembled in the bonded length of three anchors, which were monitored during pullout tests and during different construction phases of the retaining wall system. Instrumentation consisted of electrical resistance strain gauges positioned in five different sections along the bonded length. Skin friction distributions were obtained from the field load measurements. Results showed that the skin friction followed a non-uniform distribution along the anchor bonded length. The mobilized skin friction concentrated more intensely on the bonded length half closest to the unbonded length, while the other half of the bonded length developed very small skin friction. The contribution of the unbonded length skin friction to the overall anchor capacity was significant and this should be accounted for in the interpretation of routine anchor testing results. Displacements applied to the anchor head were sufficient to mobilize the ultimate skin friction on the unbonded length, but not on the bonded length. Performance of loading-unloading stages on the ground anchor intensified the transfer of load from the unbonded length to the bonded length. Long-term monitoring of the anchor after lock-off revealed that the load at the anchor bonded length followed a tendency to reduce with time and was not significantly influenced by the retaining wall construction phases.

RC Structures Strengthened by an Iron-Based Shape Memory Alloy Embedded in a Shotcrete Layer-Nonlinear Finite Element Modeling.

Shape memory alloys (SMAs) have been widely used in civil engineering applications including active and passive control of structures, sensors and actuators and strengthening of reinforced concrete (RC) structures owing to unique features such as the shape memory effect and pseudo-elasticity. Iron-based shape memory alloys (Fe-SMAs) have become popular in recent years. Use of iron-based SMAs for strengthening RC structures has received attention in the recent decade due to the advantages it presents, that is, no ducts or anchor heads are required, friction losses do not occur and no space is needed for a hydraulic device to exert force. Accordingly, Fe-SMAs embedded in a shotcrete layer have been used for pre-stressing RC beams at Empa. The aim of this study is to present an approach to model and analyze the behavior of RC members strengthened and pre-stressed with Fe-SMA rebars embedded in a shotcrete layer. The lack of research on developing finite element models for studying the behavior of concrete structures strengthened by iron-based shape memory alloys is addressed. Three-dimensional finite element models were developed in the commercial finite element code ABAQUS, using the concrete damaged plasticity model to predict the studied beams’ load–displacement response. The results of the finite element analyses show a considerably good agreement with the experimental data in terms of the beams’ cracking load and ultimate load capacity. The effects of different strengthening parameters, including SMA rebar diameter, steel rebar diameter and pre-stressing force level on the beam behavior, were investigated based on the verified finite element models. The results were compared. The load-displacement response of an 18-m concrete girder strengthened and pre-stressed with iron-based SMA bars was examined by the developed finite element model as a case study.

Experimental investigation of concrete edge failure for single stud anchors and anchor groups after fire exposure

In the present study headed stud anchors with single stud, two- and four-stud anchor groups are exposed to various duration of fire and after cooling (cold state) loaded in shear perpendicular to and towards the free edge of concrete member up to failure. The standard ISO 834 fire curve with fire durations of 15 min and 60 min are employed in the experiment. The influence of the number of studs and the duration of fire on the load-bearing behaviour of anchors is experimentally investigated. As expected, the results show that the anchor behaviour is significantly influenced by the fire exposure. Due to the thermally induced damage of concrete the failure pattern is changing from the typical concrete edge failure to a combination of concrete edge failure and pryout failure. For fire duration of only 15 min, the reduction of resistance can be more than 50% of the reference resistance. After 60 min of fire, the reduction factor is approximately corresponding to the reduction factor for 90 min of fire exposure according to current Eurocode 2. Considering concrete capacity method (CC-method), it is demonstrated that simply replacing the compressive strength of concrete at ambient temperature with the reduced compressive strength after fire is not appropriate for predicting the resistance of single stud anchors and anchor groups. However, the projected area ratio of the fracture seems to be valid for predicting the resistance of anchor group based on the reduced resistance of corresponding single stud anchor after fire exposure.

Numerical Simulation Analysis of Mechanical Properties and Application of Large Deformation Cable with Constant Resistance

Large deformation cable with constant resistance present super-mechanical characteristics of high constant resistance, large deformation, energy absorption and impact resistance compared to traditional anchor cable. These have been successfully applied in geotechnical engineering and tunnel engineering. In order to effectively solve the technical problems of the cable-stay breaking and the anchor head fall off, due to the large deformation of the traditional reinforcement cable of the slope of the Tonglushan ancient copper mine relics in Daye City, Hubei Province. In this paper, the finite element structure nonlinear analysis model of large deformation cable with constant resistance was established through finite element software ANSYS. Following, combined with the indoor test for comparative analysis, proved the reliability of the numerical simulation analysis model. Finally, the depth of the potential weak sliding zone (surface) of the slope was determined by the finite element analysis and strength reduction method. This provided a theoretical basis for the construction of deep mechanics monitoring and early warning system based on NPR anchor cable, and realizes the integrated control objectives of the reinforcement, monitoring and early warning of the site slope.

Seismic Design of Precast Component Beam-Column Joints using Headed Anchors

Precast construction system ensures high degree of quality, safety, and accelerated construction practice in R.C structures. It is well established in non-seismic conditions where gravity loads are predominated. But it is hesitated to implement during seismic conditions by the effect of lateral loads. Most of structural failures in precast framed structures are associated with beam-column joints as the integrated joint system experience high shear, and moments by cyclic action of seismic loads. In this context, researchers found that the joint distortions in precast system is well associated with its location of beam-column sub-assemblage. In beam-column joints the connections are attributed to locate in D-regions (D:Discrete) and B-regions (B:Beam) where the force transfer mechanism follows by strut - tie method (STM) or flexure beam theory(FBT) respectively. This paper analyzed the seismic performance of “Component Based Precast Joints”[CBPJ] located in D& B regions. To meet the convergence requirements, the connection systems are detailed by mechanical couplers and headed anchors. Five numerical models of exterior beam-column joints representing two models (BM1,BM2) of B-region and three models (DM1,DM2,DM3) of D-region are developed and verified their seismic performance with monolithic joint system by non-linear finite element analysis using ABAQUS software .The results indicated that the use of headed anchors in precast joints are effectively contributed to seismic requirements of shear, ductility, stiffness and energy dissipation. Also the precast joints located in D & B regions resembling good performance of joint sustainability during moderate seismic conditions as monolithic system.

Damage‐sensitive impedance sensor placement on multi‐strand anchorage based on local stress variation analysis

An important issue in impedance-based damage monitoring is to deploy sensors in proper positions in which damage-sensitive impedance responses can be captured effectively. In this study, a full-scale multi-strand anchorage is analyzed to determine optimal locations of piezoelectric sensors for impedance-based monitoring of locally damaged strands. First, stress variations of the multi-strand anchorage are experimentally measured to estimate the anchorage behavior under the effect of locally damaged strands. Strain signals are examined for axial, circumferential, and radial stress components under the variation of prestress forces. Second, a finite element analysis is made on the multi-strand anchorage to back up the experimental findings. Third, a damage-sensitive structural model is interpreted for the local strand breakage. Finally, impedance responses sensitive to local strand breakage are experimentally examined for a few scenarios simulated in the anchorage system. PZT (lead zirconate titanate) sensors deployed on the anchor head and the bearing plate are evaluated to comparatively determine ideal regions of interest for impedance monitoring. The results show that the greater stress variation yields the greater variations in impedance responses and the near-top and near-anchor heads are ideal regions of interest for damage-sensitive impedance monitoring.

STRUCTURAL PERFORMANCE OF POST-INSTALLED REBAR ANCHOR PART 2: ANCHOR PERFORMANCE OF POST-INSTALLED REBAR WITH SMALL PLATE

In the case of repair and reinforcement of an R/C structural frame, and installation of new members for extension and reconstruction, it is necessary to anchor such as main bars and wall reinforcement bars of new members to the existing frame. In this case, the anchor is required to reliably transfer the tension of the rebar to the existing frame. The purpose of this research is to propose a post-installed headed rebar anchor method with high reliability both in structural performance and workability, and to evaluate the anchorage performance of the method.

Numerical Study on Anchor Head Shapes for Lodging Anchors on Debris Structures for Capturing Space Debris

Numerical Study on Anchor Head Shapes for Lodging Anchors on Debris Structures for Capturing Space Debris

Numerical and experimental study on anchor head shapes for lodging anchors on debris structures

Numerical and experimental study on anchor head shapes for lodging anchors on debris structures

English

English

Monotonic shear strength of headed studs in reinforced infill walls

Headed studs are key components of structures which facilitate composite behavior between steel and concrete elements. In steel building structures, reinforced concrete infill walls surrounded by a stiff steel frame is a common example of a composite structure used to resist horizontal loads such as those produced by earthquakes or wind. To this end, these types of concrete walls need to be anchored to the steel frame with headed studs which must withstand shear and tensile forces (AISC 360). To properly design headed stud anchors in concrete walls, it is first necessary to understand their behavior when subjected to monotonic shear forces considering edge conditions and reinforcing details that may influence the stud strength.Few tests have examined headed studs subjected to monotonic shear with typical boundary effects in reinforced infill walls, so a new experimental study on 17 specimens explores the behavior of headed studs exposed to monotonic shear loading with group effects. The experiments showed that the strength of studs installed in infill walls with edge conditions is well predicted (average error in prediction is smaller than 10%) by ACI 318, AISC 360 and EC-4. However, when group effects of anchors are included in the analysis of infill walls, only the ACI 318 is able to predict the behavior.

Pryout capacity of headed stud anchor groups with stiff base plate: 3D finite element analysis

AbstractConcrete pryout failure mode of a group of relatively shallow embedded anchors welded to a steel base plate has not been extensively investigated in the past. Therefore, the failure mechanism and resistance of such anchor groups needs to be clarified. In this paper a three‐dimensional (3D) finite element parametric study for quadruple (2 × 2) anchor groups loaded in shear with no influence of edges is carried out. In the study, embedment depth of anchors and anchor spacing in both directions are varied. The results show that the increase of anchor spacing perpendicular to the shear load direction has no major influence on the concrete pryout capacity, whereas the increase in anchor spacing parallel to the loading direction significantly increases the pryout capacity. For anchor spacing greater than a particular threshold value, the pryout resistance of a group of anchors is approximately equal to the resistance of a single anchor multiplied by the number of anchors. Based on the results of the study, a design formula for anchor group failing in pryout is proposed and compared with the current design code recommendations.

Review of existing designs of drill-and-injection anchor piles

Introduction. The paper examines the main types of anchor piles used in geotechnical construction are examined in terms of their design variants, the scope of their application, advantages and disadvantages, designs and types of drill bits depending on the type of soil foundation. The aim of the study is the search for and analysis of existing domestic and foreign designs of drill-and-injection anchor piles used for strengthening existing foundations and bases, for dowel reinforcing landslide slopes and different installations such as caissons, retaining walls, masts, towers and pillars bearing pull out loads as well as discovering new, previously little-known anchor designs. The objectives of the study are to perform a patent search and a literary review of existing designs of drill-and-injection anchor piles.
 Materials and methods. Systematization, structural, comparative and contrastive analyses. The paper also utilized the theoretical generalization of the data obtained in the detailed analysis of literature and patent data containing information about the previously developed and applied designs of anchor piles were used in the search and selection of relevant literature.
 Results. The application of the anchor piles is of great importance in modern foreign and domestic geotechnical practice. The need for their application is connected with ensuring the safety of construction, reducing the period of foundation work execution, and the economic efficiency of approved engineering solutions.
 Conclusions. It was found that despite a large number of anchor pile types, all of them, as a rule, are made the using technology of the company Bauer. It is revealed that commonly the anchor design consists of three main parts: a head (supporting element), a rod (element transferring the load from the anchor head to its root) and an anchor root (element transferring the load from reinforced structure to ground and foundation soil).

Safety reduction in anchor groups due to uneven crack distribution

In the present paper, the safety reduction in anchor groups composed of cast-in place headed anchors was experimentally investigated. In particular, groups of two anchors were installed in concrete members designed such that one of the anchors was located in a crack and the other one in plain concrete. The samples were loaded in tension, thus simulating a connection with clamped rotation under both monotonic and cyclic conditions. The results are commented and discussed demonstrating how the presence of uneven crack distribution could lead to a safety reduction, which should be properly taken into account in the design of anchor groups.

Effect of edge distance on shear friction capacity of steel plates anchored with reinforcing bars in comparison with headed bolts

The shear friction capacity calculated using clauses 11.6.4 to 11.6.10 in ACI 318-14 or clauses 11.5.1 to 11.5.6 in CSA-A23.3-14 do not take into consideration the effect of edge distance on the shear friction capacity. The main objectives of this research are to study the effect of edge distance on the shear friction capacity by means of a specifically designed experimental program, to determine the minimum edge distance to develop the shear friction capacity, and to derive an expression for reduction of shear friction capacity for edge distances less than the minimum edge distance. The study involved testing eight specimens. In four specimens, a steel plate was anchored using welded reinforcing steel bars, and in the other four specimens the steel plate was anchored using headed concrete anchors (bolts) (HCA). The steel plates were tested under shear load at edge distances of 75, 150, 225, and 300 mm (3.0, 6.0, 9.0, and 12.0 in), for the two types of anchorage. The results were compared to design values according to ACI 318-14 and CAN/CSA-A23.3-14 standards. An equation is derived to compute the minimum edge distance after which the full shear friction capacity is developed. Another equation is derived to compute the proposed shear capacity for reinforcing bar anchors for edge distances less than the minimum edge distance.

Experimental investigation of forces along anchors subjected to dynamic loading under tension and compression in field tests

Full-scale field tests of dynamic rockfall have been performed on a flexible SPIDER Avalanche system to study the dynamic force distribution along the foundations under dynamic loading. Therefore, an anchor to measure dynamic tensile forces and a pile to measure dynamic compressive forces were each equipped with strain gauges. Furthermore, a static pull loading test with load steps of 1 min duration was performed on the anchor to highlight the difference between dynamic and static loading. Effective kinetic energies applied on the net of the SPIDER Avalanche system range from 25 to 492 kJ with impact velocities between 17 and 25 m/s. The results show that the dynamic forces close to the pile- and anchor head are higher and that they are decreasing with increasing distance of pile and anchor. However, the dynamic tensile force distribution is nonlinear over the length of the anchor, whereas the dynamic compressive force distribution is linear along the pile length. The comparison of static and dynamic tensile forces shows that dynamic tensile forces are depleted within a shorter distance of the anchor compared to the static tensile forces. Dynamic tensile forces present 25% less in value than the static tensile forces.

A Refined Model for Predicting Concrete-Related Failure Load of Tension Loaded Cast-in-Place Headed Anchors in Uncracked Concrete

Abstract Current theoretical models for predicting the concrete cone breakout capacity of tension loaded headed anchors do not consider the influence of member thickness, size of anchor head, and orthogonal surface reinforcement. In the present study, the influence of the aforementioned parameters was studied both numerically and experimentally. Both the numerical and experimental results showed that the tensile resistance of headed anchors increases by increasing the member thickness or if orthogonal surface reinforcement is present. In addition, the anchorage capacity further increases with increase of the anchor head size. The current model for predicting the concrete cone failure load of tension loaded headed anchors were refined and extended by incorporating three modification factors to account for the influence of the member thickness, size of anchor head, and orthogonal surface reinforcement. The accuracy of the proposed model was verified based on the results of 124 tests on single headed anchors from literature.

Aggregate effect on concrete cone capacity

Recently, a large experimental campaign was completed that attempted to establish a link between petrography of the coarse aggregate, the concrete material properties and the system response in terms of concrete cone capacity. The investigation focused on three normal strength concretes having different coarse aggregate types (quartz, limestone, basalt) but otherwise similar mix design. All specimens of each concrete were cast from the same batch, carefully cured following three sets of curing protocols, and systematically characterized. The investigation comprised aggregate and concrete characterization, and structural tests performed at two ages on cast-in headed stud anchors under tensile loading. The aggregate characterization included the determination of Los Angeles coefficient, hardness and Young’s modulus. In order to characterize the concretes, standard compression and indirect tension tests, were performed together with fracture tests. The experimentally obtained material and structural data finally served for the evaluation of current predictive models in terms of concrete compressive strength or concrete fracture properties as well as a correlation study. Aided by photogrammetric analysis, the concrete cone shape was determined for each individual test and analyzed to uncover possible dependencies on the coarse aggregate type.

Investigations of rock anchor corrosion and its influence factors by exhumations in four typical field sites

With the abundance application of rock and soil anchors in high slope and underground projects, more concerns have been paid to the working condition and durability of the anchorage system. To effectively evaluate the corrosion of anchors in service and the influence factors, field exhumations were performed in four typical application sites and tests of samples were conducted in laboratory. Chemical composition, metallurgical structure and mechanical performance of anchors are tested. Microstructure and component of corrosion byproducts and grout were analyzed. The environmental influence factors are also assessed. The results demonstrate that the anchor head is most liable to corrode in comparing to other section of the anchor. Presence of damaging ions can accelerate the initiation and development of corrosion. Chemical and mechanical properties of anchors remain basically unchanged after 1.5 to 20 years' service. Groundwater and stray currents in the underground do not induce noticeable influence on the corrosion of anchors. This research accomplished a set of evaluation methods of influencing factors and the general law of anchors' corrosion in field environments, which may provide a reference framework for evaluating the environmental effects, durability and service life of rock anchors.