Performance Of Anchors Research Articles

Experimental Study on Resin Anchoring with Reaming Bottom and Filling in Soft Rock.

This paper deals with the problem of the slippage failure of bolts in supporting soft rock, and the anchoring system being pulled out when conventional anchoring methods are used for bolts. This situation seriously threatens the safety of personnel and efficiency of work at the supporting soft rock. The main goal of this paper is to develop methods that will take full advantage of the potentially great supporting force that can be provided by bolts installed in soft rock. The study discusses the resin anchoring technique with reaming bottom and filling and proposes that replacing soft rock with high strength hard rock is an effective method to improve the anchoring force that prevents slip failure. The results of a comparative analysis of the different maximum diameters of reaming and the anchorage performance of the method using laboratory testing, numerical simulation, mechanics analysis, and field test are described. The results show that when the reaming diameter is less than five times that of the borehole, the anchorage force increases significantly. When the reaming diameter is more than five times that of the borehole, the increasing degree of anchoring force decreases obviously and the trend is gentle. The anchoring force of five times resin anchoring with reaming bottom and filling is 2.8 times that of conventional anchorage. The resin anchoring technique with reaming bottom and filling guarantees that bolts installed in soft rock will provide high supporting forces.

Numerical Simulation of Anchorage Performance of GFRP Bolt and Concrete

We conducted anchoring performance, stress distribution, and full-scale indoor pulling tests on glass-fiber-reinforced polymer (GFRP) bolts. The tests were conducted using finite element software while considering the multi-interface contact and BK criterion by using the cohesive element to simulate the contact relations between the anchor rod body and concrete and building an axial symmetry calculation model of the GRFP bolt and concrete. The results indicated that the finite element model based on cohesive element accurately represents the load–displacement relationship of the GFRP bolt and the distribution law of axial stress along the anchoring length. In addition, the simulation outcomes of the load–displacement relationship were in good agreement with the measured test values. Under the same load, the axial-force-transferred depth of the bolt body was identical regardless of the anchorage length. As anchoring length increases, the pull load on the bolt and the decay rate of axial stress along the anchoring length rises gradually. There is a critical value for the anchorage length of the bolt.

Study on Anchoring Effect of Different CFRP Anchors

Prestressed carbon fiber plate (CFRP) is widely used in the field of bridge reinforcement, but the anchoring ways of CFRP are various, and the anchoring performance of different anchoring forms is also different. In this paper, the anchorage performance, failure form and tension control stress of several common anchorage are studied by experiments, the results show that the anchorage effect is the best when the end of the anchor bearing only tension and no other stresses, which can provide some construction guidance for the selection of anchorage in the future.

Overall pull-out behavior of group anchored steel strands with 90-degree hooked type

The Precast Prestressed Assembled Structural (PPAS) system is a novel prefabricated structure system, which mainly adopts the group anchor technology for 90-degree hooked steel strands in the connection of beam-column members. For this connection, however, the anchorage performance of the group anchored steel strands with 90-degree hooked type has not been fully understood. For this reason, the overall pull-out tests on the 12 test specimens of group anchored 90-degree hooked steel strands were carried out by adopting the overall pull-out test device. The test results indicated that with the increase of the layout quantity of the steel strands in the concrete column from one row of one column (1 steel strand) to three rows of four columns (12 steel strands), the anchorage capacity, anchorage stiffness and energy dissipation capacity of the group anchor specimens were significantly improved, but its anchoring efficiency presents a three-stage change rule of slow attenuation (0.065) - gentle attenuation (0.025) - fast attenuation (0.105). The variation of the anchorage depth of the steel strands in the concrete column has more pronounced effects on the failure mode and pull-out load-overall slip response, indirectly affecting its ultimate anchorage capacity, overall slip, anchorage stiffness, and anchoring efficiency, but hardly affecting its energy dissipation capacity. Additionally, the anchoring efficiency is strongly related to the failure mode of the test specimens. For the failure mode of the steel strand fracture, the anchoring efficiency is always not less than 0.85, which is significantly higher than that of the overall pulling out of the steel strands, always between 0.70 and 0.80. • The overall pull-out tests on the group anchored 90-degree hooked steel strands were successfully carried out. • The multiple 90-degree hooked steel strands with smaller anchorage lengths tended to be overall pulled out. • Increasing the layout quantity of steel strands in the concrete column can effectively improve the anchoring capacity. • Group anchored 90-degree hooked steel strands exhibited higher anchoring efficiency. • The influence of the group anchor effect on its anchorage performance cannot be negligible.

Experimental investigation on the anchorage performance of hooked high-strength steel strands for beam-to-column connection

To explore the anchorage performance of hooked steel strands used in the beam-to-column connection of the precast prestressed assembled structural (PPAS) system, considering the influence of the various research variables, such as anchorage length and the length of the vertical segment of the steel strand, 16 specimens were designed and tested under the pull-out loading. The failure modes, pull-out load-slip curves, peak point loads, and the corresponding slips of the tested specimens were obtained accordingly. Besides, by means of portable X-ray detection technology, the shape evolution of hooked steel strands in the concrete columns under various pull-out loads were imaged and compared, and the anchorage failure mechanism of hooked steel strands was further clarified. The test results demonstrated that three failure modes were observed in all test specimens. Besides, the hooked steel strands can significantly improve its ultimate anchorage capacity and material strength utilization efficiency. When the anchorage length is not less than 500 mm, and the length of the vertical segment is 5d, 10d and 15d, the conical fracture failure of the steel strand always occurs in the test specimens, and the material strength utilization efficiency is always not less than 90 %, far higher than that of the straight steel strands. In addition, the relative slip at the loaded end is obviously related to the anchorage parameters of the steel strands. In details, whether the length of the vertical segment is 5d, 10d or 15d, the relative slip of the hooked steel strand is significantly lower than that of the straight steel strand, which is strongly related to the unique anchoring mechanism of hooked steel strand. However, the necessary anchorage length is needed for hooked steel strands to achieve the ideal anchorage effect, which should generally not be less than 500 mm.

Bond and anchorage performance of beam flexural bars in beam-column joints using slag-based geopolymer concrete and their effect on seismic performance

An available study on the bond and anchorage performance of beam flexural bars in beam-column joints using slag-based geopolymer concrete (GC) is limited. The applicability of current design codes to beam flexural bars design in GC beam-column joints is unknown. In this study, to investigate the bond and anchorage performance of beam rebars at the GC beam-column joints and their effect on seismic performance, cyclic loading tests were performed on 2 reinforced GC interior beam-column joints and 6 reinforced GC exterior beam-column joints. The test results showed that the increase in column depth-to-beam rebar diameter ratio (hc/db) from 21 to 25 improved the bond performance of the beam flexural bars in the reinforced GC interior beam-column joints, which significantly improved the energy dissipation capacity. The limits of hc/db larger than 20 in GB50010-2010 (except seismic grade I that requires hc/db ≥ 25) and ACI 318-19 were not safe for reinforced GC interior beam-column joints. The limits of hc/db in Eurocode 8 and NZS3101 for low-strength concrete (fc′ ≤ 30 MPa) were applicable. In reinforced GC exterior beam-column joints, the bond and anchorage performance of 90˚ hooked bars was superior to that of the corresponding headed bars. Regardless of the anchorage details, the bond and anchorage performance of the reinforced GC exterior beam-column joints increased with the increase of the development length of beam flexural bars. In reinforced GC exterior beam-column joint design, the bar development length requirement of GB50010-2010 was applicable to both 90˚ hooked bars and headed bars. Eurocode 8, NZS3101, and ACI 318-19 were applicable to the development length of 90˚ hooked bars.

The effect of rock hardness and integrity on the failure mechanism of mortar bolt composite structure in a jointed rock mass

The appearance of joints in the rock tunnels makes the rock mass show obvious anisotropy and discontinuity in physical and mechanical properties, which has a significant influence on the rock mass stability. As one of the normally used support structures in tunnel construction, Mortar bolts will inevitably pass through the joints during the process. Both rock hardness and rock mass integrity will directly affect the anchorage performance of mortar bolts in joint rock. Considering this, this paper designs a mortar bolt pull-out experiment to investigate the joint rock failure modes and bolt-grout composite structure failure modes under different conditions of rock hardness and rock mass integrity. By taking the two influencing factors of rock hardness and integrity into account, the calculation formulas of ultimate pull-out load and ultimate displacement of mortar bolts in joint rock are established and proposed.

Experimental Research on Bonded Anchorage of Carbon Fiber Reinforced Polymer Prestressed Strands.

Aiming at the problems of a large number of corrosion and fatigue damage of the current prestressed steel strands, this paper adopts carbon fiber-reinforced composite (CFRP) strand with better corrosion resistance and fatigue resistance and uses it in concrete structures. The bond anchorage is usually used to anchor CFRP tension members, which bonds the CFRP through the binding medium. Through experimental research on the CFRP strand bond anchorage, the inner taper of the CFRP prestressed strand cone was anchored and the influence of different anchor lengths and bonding media on the anchorage performance was determined. The test results demonstrate that the taper of the conical anchorage described in this paper is a key factor affecting its anchorage performance and increasing the inner taper within a certain range is beneficial to improving the anchorage performance of the conical anchorage. The bonded anchorage of the CFRP prestressed strand with a 200 mm anchor is the most reliable and efficient, as the taper of the 200 mm anchor is the largest. The average anchoring efficiency coefficient of the 200 mm anchor was 96.4%, which is 3.7% and 2.6% higher than the average anchoring efficiency coefficient of 220 mm and 250 mm anchors, respectively. The anchoring efficiency of the anchor is also high (94.1%) when the epoxy resin mortar is used as the bonding medium. Moreover, after an appropriate amount of quartz sand is added to the epoxy resin, the overall comprehensive performance of the anchor can be improved to a certain extent and the stress of the CFRP strand can be improved. The coupling between ultra-high-performance concrete dry mix (UHPC-GJL) and CFRP strand materials is not suitable for UHPC-GJL being used, as its binding medium as the average anchoring efficiency coefficient is only 44.5% when UHPC-GJL is used as the anchor bonding medium.

Anchorage performance of straight rebars in UHPC with strain-hardening property

Bond and anchorage are the basis to conduct performance analysis on reinforced-concrete structures. The strain-hardening property makes the bond-slip behaviour of rebars in ultra-high-performance concrete (UHPC) different from that in ordinary concrete. This study investigates the anchorage performance of straight rebars in UHPC based on its material properties. First, the anchorage failure process is revealed using pull-out test combined with computed tomography scanning. Thereafter, a finite element model is established to analyze the effects of strain-hardening property on failure mechanism and anchorage performance. The regularity of bond stress distribution along the rebar is also obtained. Subsequently, parametric analyses are developed to analyze the effects on bond stress, including the embedded rebar length, concrete cover thickness, and tensile strength and ductility of UHPC. Expressions for the non-uniform distribution of bond stress are established. Finally, a calculation formula is proposed for the anchorage-bearing capacity considering the strain-hardening property of UHPC material.

Anchorage performance of group anchored 1860-grade high-strength steel strands for beam-column connection

• An overall pull-out test device for group anchored steel strands is developed. • The influence law of the layout quantity of steel strands on the pull-out load and average bond stress is analyzed. • The influence law of the embedment length of steel strands on the pull-out load and average bond stress is investigated. • The calculation formula for the critical anchorage length of the group anchored steel strands embedded in the concrete column is also proposed. • The difference of stress development of steel strands at different positions in group anchor specimens is revealed. To determine the rational anchorage form of group anchored 1860-grade high-strength steel strands adopted in the beam-column connection of the Precast Prestressed Assembled Structural (PPAS) system frame, the overall pull-out test was carried out to investigate the influence of the anchorage type, embedment length and arrangement form (layout quantity) of steel strands on the overall pull-out behavior of group anchored steel strands. Test results indicated that the influence of the interaction of multiple steel strands in concrete columns (i.e., group anchor effect) on the anchorage performance should be taken into consideration. The layout quantity and embedment length of the steel strands have a significant influence on the anchorage performance of group anchored steel strands, such as the overall slip, ultimate anchorage capacity, and average bond stress at each characteristic point, but the influencing law is different obviously. In addition, a calculation formula for critical anchorage length of the group anchored steel strands embedded in the concrete column was also proposed, and relevant design suggestions for anchorage length were recommended for various arrangement forms of steel strands. The bond properties of the steel strands in concrete columns vary with their positions in group anchor specimens, which indirectly affects the anchorage performance of the group anchored steel strands, but its influence degree is strongly related to the stress development level of steel strands at that position.

Experimental study on spatial mechanical properties of grout anchor lap joints

To study the anchoring performance of non-concentric and multi-medium lap joints of grout anchors, pull-out experiments of 18 groups of specimens were implemented. The main focus of this study is the influence of steel bar diameter and anchorage length on the bond and anchorage performance when the diameter of metal bellows and spacing of spiral stirrups are fixed. Qualitative and quantitative analyses are conducted to experimentally ascertain the mechanical safety of structures. The finite element method is employed to replicate crack development and mechanically simulate the segment model. The simulation results are analyzed and compared with experimental data. When the anchorage length is 35d–40d (where d is the diameter of the embedded steel bar), no component is damaged, indicating that the anchorage length is stable and reliable. However, when the anchorage length is less than 15d, slip failure occurs. In this work, a comprehensive description of the mutual restriction and force transmission variation law of each component of the node under the action of stress based on the strain distribution analysis of the multi-media coupling model is provided. Moreover, optimization suggestions for the structure are proposed. The results of this study provide experimental support for the application of this type of joint in prefabricated building structures.

Experimental and finite element studies of prefabricated timber-concrete composite structures with glued perforated steel plate connections

To evaluate the feasibility of adopting glued perforated steel plate (GSP) connections in prefabricated timber-concrete composite (PTCC) structures, two series of tests were conducted in this study: push-out tests on prefabricated GSP (PGSP) connections and bending tests on PTCC beams. The same experimental programmes on cast-in-situ timber-concrete composite (TCC) structures with this type of connection were also performed. For validation, the three-dimensional finite element (FE) models considering the orthotropic elastic–plastic damage behavior of the timber, damage plasticity characteristics of the concrete, fracture of the adhesive, and the nonlinear shear-slip behavior of the connections were developed. The test results demonstrated that the glued perforated steel plate connections have excellent slip stiffness and shearing capacity but low ductility due to the brittle fracture of the adhesive. Owing to the high anchorage performance of the grouting cements and low shrinkage behavior of the dry construction method, the connection stiffness and load-carrying capacity of PGSP are higher than those of GSP. The PTCC beams showed better bending performance than the cast-in-situ TCC beams as a result of the higher slip stiffness of PGSP than that of GSP. Additionally, the FE numerical results are in good agreement with the test results in terms of the failure modes, shear-slip behavior of the connections, and bending performance of the composite beams.

Investigating the anchorage performance of full-grouted anchor bolts with a modified numerical simulation method

To reveal the failure mechanism of full-grouted bolting system, revised Pile elements were selected to numerically reveal the anchoring performance of full-grouted anchor bolts. A tri-linear bond-slip model was embedded in the Pile elements. A three-dimensional mining stope was created. A rectangular main roadway reinforced with full-grouted anchor bolts was simulated. Then, the retreat mining method was used to exploit the coal seam. The impact of buried depth, pillar size and shearing strength of the grout/rock contact surface was studied. It showed that the coal seam’s burial depth significantly influenced the anchorage performance of the anchor bolts. Moreover, increasing the shearing strength of the grout/rock contact surface was conductive to improving the anchorage performance of anchor bolts and preventing roadway convergence. Simulation results were compared against experimental laboratory test and in-situ observation outcome. It was conductive to revealing the anchorage mechanism of full-grouted anchor bolts under the in-situ condition.

Experimental study on influencing factors of anchorage performance of concrete bonded rebars

Hilti re-100 structural adhesive is used to plant reinforcement in concrete, and the factors affecting the anchorage performance of planted reinforcement are analyzed. The Planting reinforcement of the concrete specimen and the specimen with reinforcement anchored in concrete in advance are compared. A total of 36 groups of tests were carried out, including 27 groups of embedded reinforcement tests and 9 groups of embedded reinforcement tests. The test mainly analyzes the influence of concrete strength, reinforcement diameter and planting depth on the anchorage performance of planting reinforcement. There are three failure modes in the test, which are the separation failure of reinforcement and structural adhesive, the tensile failure of reinforcement and the separation failure of reinforcement and concrete. Through the analysis of the test data, the bond slip data curve is obtained.

Anchorage performance of a modified cable anchor subjected to different joint opening conditions

In tunnelling engineering, the cable anchor is usually used to reinforce the surrounding rock mass. Site observation shows that the cable anchor may be subjected to different joint opening conditions. However, little study has been launched to study the influence of the joint opening on the anchorage performance of cable anchors. This paper conducted the laboratory Short Encapsulation Pulling Test (SEPT) to study the anchorage performance of a modified cable anchor subjected to different joint opening conditions. During the test, the joint opening was simulated with the bearing plate whose central diameter was different. The results showed that when the joint opening size increases, the maximum load-carrying capacity of cable anchors decreases. This was observed under both unconfined and confined boundary conditions. Moreover, under the confined condition, there was a threshold for the joint opening size. Once the joint opening size was beyond that threshold, further increasing the joint opening size had marginal effect on the capacity of cable anchors. Additionally, under the confined condition, the maximum load-carrying capacity of cable anchors was apparently higher. Furthermore, under the confined condition, cable anchors showed apparent residual load-carrying capacity in the post-failure stage. By contrast, under the unconfined condition, after the peak, the load-carrying capacity of cable anchors dropped dramatically. This leaded to negligible residual load-carrying capacity.

Roof Bolting Anchoring Performance Research on the Entry under the Gob of Close-Distance Coal Seam

Seam spacing plays a crucial role in selecting roof bolting of the close-distance coal seam. This work utilized three methods to determine the minimum roof bolting seam spacing of the lower coal seam (LCS) entry after the upper coal seam (UCS) mining. Based on the entry of the No.3-2 coal seam (LCS) in Chaili Coal Mine in China, theoretical analysis, pull-out bolt test, and numerical simulation were performed to calculate the maximum floor failure depth of the UCS and to determine the minimum seam spacing of the roof bolting. The maximum floor failure depth of the UCS determined through theoretical analysis and numerical simulation is 3.2 m and 3.3 m, respectively. In general, the anchorage length of rock bolting is less than 2.4 m, so the minimum seam spacing is 5.6 m or 5.7 m. To further determine the anchorage performance of the roof, the pull-out test was employed on the entry roof of the LCS. When the seam spacing is no less than 6 m, the test results show that the pull-out force of the bolt is more significant than 30kN; in addition, the numerical simulation results indicate that the roof-to-floor and rib-to-rib convergence are relatively small. Therefore, the LCS entry’s minimum roof bolting seam spacing can be determined as 6 m. This study could be used to select and design roof bolting under similar close-distance coal seam conditions.

Engineering Properties of New Claw Connectors for Alkali-Resistant Glass-Fiber-Reinforced Plastics.

To optimize the engineering properties of connectors, a new claw-shaped alkali-resistant glass-fiber-composite-reinforced connection member was designed in this study. Tensile, shear, and durability tests were conducted on the joint. Moreover, numerical analysis was performed, and the performance of the proposed connector was verified in engineering applications. Hence, the following conclusions hold: (1) At the same shear diameter and anchorage depth, the anchorage performance and shear resistance of claw connectors are better than those of rod connectors. (2) Claw connectors with an anchorage depth of 3.5 cm and a hollow joint with an outer diameter of 14 mm exhibit an excellent overall performance. (3) Alkali-resistant glass-fiber-reinforced plastics exhibit good durability. (4) The ANSYS numerical model can be used to accurately predict the load–displacement variation law of the pull-out and shear of the connectors. (5) Through research, it has been proven that claw-shaped connectors have good pull-out resistance, shear resistance, and durability, and the structure has good stability in engineering applications. Therefore, the structure can provide a significant reference for similar projects.

Anchorage Performance of Geopolymer-Grouted Rock Bolts

Anchorage Performance of Geopolymer-Grouted Rock Bolts

Improvement of Anchorage Performance of Carbon Fiber-Reinforced Polymer Cables.

Prestressed concrete composed of steel materials is increasingly used in various social infrastructures, such as bridges (cables), nuclear containment structures, liquefied natural gas (LNG) tanks, and structural reinforcements. This study aimed to substitute the steel in bridge cables with fiber-reinforced polymers (FRPs) to prevent the damage caused by the performance degradation of corroded prestressed steel. An optimized single-anchorage system was derived by applying multiple variables, such as the surface treatment, number of insert layers, and sleeve processing companies, to improve the maximum load and bonding with the anchorage system sleeve using the carbon FRP (CFRP) cable. The B-L-4 specimen (sleeve specifications of company B, longitudinal surface treatment, and four insert layers) was determined to be the optimized single-anchorage system. When the tensile test was conducted after applying the optimized single-anchorage system to the three- and seven-multi-anchorage systems, the tensile performances of B-L-4 were 100 and 95% of the one-multi-anchorage system, respectively. Considering that the problems associated with the construction of three- and seven-multi-anchorage systems have been addressed, these systems can be applied to actual bridges in the future, and can significantly benefit their maintenance.

Anchorage performance of grouted corrugated duct connection under monotonic loading: Experimental and numerical investigation

The grouted corrugated duct connection (GCDC) has wide applications in column-to-cap beam and column-to-footing joint of precast bridges. The anchorage performance of GCDC has received more attention due to the lack of understanding. In this study, a two-phase experimental program was conducted to investigate the anchorage performance of GCDC. The pull-out tests of 40 specimens in Phase Ⅰ mainly focused on the effects of various factors on anchorage requirement of GCDC, in which factors such as anchorage length, duct-to-rebar diameter ratio were considered. Test results indicate that the failure modes of GCDC and the proposed equivalent bond stiffness are mainly governed by the anchorage length and duct-to-rebar diameter ratio. The anchorage length of 10–15 times rebar diameter and duct-to-rebar diameter ratio of 2.5–3.5 are recommended to ensure bond strength. In Phase Ⅱ, 40 design specimens were pulled out to investigate the bond-slip constitutive relationship of GCDC. The variation law of ultimate bond strength was analyzed with the variation of the anchorage length and duct-to-rebar diameter ratio. Based on experimental results, basic bond stress-slip relationship and bond stress distribution function were obtained through curve fitting, which were in good agreement with test results. Finally, the comprehensive bond-slip constitutive model incorporating location function was developed. The refined finite element model considering bond-slip constitutive relationship was established to investigate and verify the pull-out test results. Therefore, the anchorage requirement recommended can provide reference for the selection of anchorage length duct-to-rebar diameter ratio for engineering application of GCDC. Furthermore, the bond-slip constitutive model developed is the theoretical basis for finite element analysis of GCDC.