Anchorage Bond Research Articles

Experimental investigation and analysis on anchorage performance of 635 MPa hot-rolled ribbed high strength rebars

Due to the rapidly increasing urbanisation in China, the energy consumption of buildings and infrastructures has increased; this has resulted in environmental problems such as excessive carbon emissions. Increasing the strength of steel rebars enables manufacturers to use less steel and save more energy. The micro-alloyed 635 MPa hot-rolled ribbed high strength rebars (HRHSR) offer the advantages of high strength, good ductility, and low costs, compared to ordinary rebars. Bond anchorage is one of the key problems that limits the promotion and application of 635 MPa HRHSRs in practice. In this study, the bond properties of 635 MPa HRHSRs embedded in concrete subjected to monotonic loads were investigated. A total of 120 specimens, which consisted of 60 simple-anchored and 60 hooked-anchored specimens, were subjected to direct pull-out tests to evaluate the effects of anchorage length, hoop ratio, concrete cover, rebar diameter, concrete strength, and anchorage types on the anchorage feature. Meanwhile, the mechanical properties and failure modes of 635 MPa HRHSRs were also analysed. The results demonstrated that the concrete compressive strength, cover size, anchorage length, and stirrups ratio had a positive influence on the ultimate bond strength, whereas the bar size had a negative influence on the ultimate bond strength. Furthermore, four typical failure modes were analysed, including rebar yielding, concrete splitting, concrete crushing, and rebar rupturing, which occurred during the pull-out tests. Thereafter, a modified equation for calculating the ultimate bond strength of 635 MPa HRHSRs in concrete was derived based on the mechanical model and further verified using the test data. This study is expected to be beneficial in promoting the widespread application of 635 MPa HRHSRs and enabling resource savings in the future.

Experimental research on bond anchorage performance of 1860-grade high-strength steel strands and lightweight aggregate concrete

To study the bond anchorage performance of 1860-grade high-strength prestressed steel strands and lightweight aggregate concrete, taking the cover thickness, anchorage length, stirrup spacing and matrix material as characteristic parameters, 10 groups of three specimens – a total of 30 test specimens – were designed and manufactured for pull-out tests. In these tests, the failure modes and the variation of bond strength of specimens were examined, and the influence of the variation of characteristic parameters on the bond anchorage performance of 1860-grade high-strength steel strand and lightweight aggregate concrete was studied. Optimal results were produced with a larger cover thickness and anchorage length, and smaller stirrup spacing. Based on the experimental data, we established the formula of ultimate bond strength and the formula of bond strength when the average slip is 1 mm, and a recommended formula for the anchorage length of components was devised incorporating current building design codes.

Design optimization and experimental validation of a novel wedge-shaped bond anchorage system for prestressed CFRP plates

An efficient anchorage system plays a significant role in the strengthening and repair of existing structures in prestressed carbon fiber reinforced polymer (CFRP) plates. In the present study, a novel wedge-bond anchor was proposed to provide a reliable anchorage load-bearing capacity for the prestressed CFRP plate. Accordingly, interface bond tests were conducted to optimize the anchor parameters. The results revealed that the minimum bond length of the wedge-bond anchor was 100 mm and 120 mm for the adhesives Tc and T1, respectively. After optimization, the weight of the anchor was reduced by 58.3%. A mechanical model was built to analyze the load transfer path and evaluate the anchorage bearing capacity. Based on these, the ultimate anchorage bearing capacity was predicted to be higher than 4.70 GPa and 4.10 GPa for the adhesives Tc and T1, respectively. Tensile tests of the optimized anchor showed that a) the stress in the anchorage zone of the CFRP plate was distributed uniformly, and b) the stress concentration of CFRP in the anchor was avoided, which provided a higher anchorage bearing capacity. The extension applications of wedge-bond anchor were carried out for a larger size of CFRP plates (100 mm × 1.4 mm). Accordingly, it successfully led to CFRP bursting, yet no debonding occurred in the anchor.

Novel wedge-shaped bond anchorage system for pultruded CFRP plates

Prestressed strengthening with carbon fiber reinforced polymer (CFRP) plates has gained attention for the rehabilitation of existing structures. In this study, a novel wedge-shaped bond anchorage system was developed. The wedge-shaped adhesive in the bond zones exerted a high pressure on the CFRP plate when the CFRP plate was subjected to tension. The shear force along the fiber direction resisted the tension force of the CFRP plate, realizing reliable anchorage. The shear stress in the anchorage zone was distributed uniformly, owing to the deformation of the low-modulus adhesive. Therefore, the stress concentration was reduced, which generally occurs for traditional CFRP anchors and causes premature failure of the CFRP plate. The stress distribution in the anchorage zone was obtained by mechanical analysis, and the maximum anchorage-bearing capacity was calculated based on the critical bond-slip criterion of the CFRP plate and epoxy adhesive. The effects of the adhesive properties on the anchorage efficiency were also investigated. A test was performed to validate the effectiveness of the proposed anchorage system.

Research on the Bond Anchorage Properties of Alkali-Activated Slag Cementitious Material

By bond-anchorage property tests at 20°C ∼500°C, the distribution of shear stress between carbon fiber sheets and concrete at all levels of loading and anchorage lengths were measured, which means the bond lengths during CFRP sheets are pulled off at the same time when the concrete is torn and stripped were gotten. The failure modes were obtained. In addition, the failure loads were measured, and the calculated formulas of anchorage lengths were identified by fitting at high temperature. It can be seen that the anchorage lengths of carbon fiber sheets increase with increasing temperature at 20°C ∼100°C, the anchorage lengths of carbon fiber sheets decrease with increasing temperature at 100°C ∼500°C. Tests prove that AASCM has favorable high-temperature resistant and bond anchorage properties.

Simulation Analysis of Chemically Bonded Anchors in ABAQUS

At present, the finite element analysis has been an effective method to study the mechanical properties of steel bar drawing. In this paper, finite element analysis of the influence of bond strength on anchorage performance with concrete plastic damage model based on nonlinear analysis in ABAQUS was carried out. The finite-element analysis model of the single bar was established by using the finite element software ABAQUS. The Spring2 nonlinear spring element was introduced to simulate the interface of concrete and adhesive. Chemical anchorage bond slip constitutive model was determined by Spring2 element real constants. The nonlinear characteristics of concrete materials under the single reinforcement drawing could be described with the combination of the concrete plastic damage constitutive mode and nonlinear finite element methods. The nonlinear behavior of concrete under uniaxial tension of the action, especially the crack and stress distribution, could be accurately described. In order to study the influence of adhesive bond strength of chemically-bonded rebar mechanical properties, the constitutive relation of the bonded rebar slip of test results was referenced. The nonlinear property of spring was assigned by the bond slip relationship, embodied in the F-D curve of the spring. In order to analysis the influence of bond strength on anchorage performance, the slope of linear growth stage and the peak of nonlinear growth stage in bond slip relationship curve were changed.

Anchorage length and bond stress-slip model of an untensioned wire strand placed at the interface between a half-PC beam and topping concrete

The purpose of this research is to obtain the anchorage length and the bond stress-slip relationship of an untensioned seven-wire strand placed at the interface between a half-precast beam and topping concrete, applied to the precast concrete beam-column joint developed recently. From a pullout test with various embedment lengths, the anchorage lengths were determined for strands of diameters 12.7 and 15.2 mm, and also for a bundle of two 12.7 mm strands. Additionally, the bond stress-slip model was established by means of a numerical algorithm applying the strand strains measured in the pullout test. The anchorage lengths estimated numerically using the bond stress-slip model agreed well with the test results. For the interface between a half-precast concrete beam and topping concrete, a new bond condition coefficient $$\eta_{2} = 0.875$$ was proposed for use in the design equation for the basic anchorage length suggested in the CEB FIP Model Code.

Experimental and numerical study of strengthening non-ductile RC columns with and without lap splice by Carbon Fiber Reinforced Polymer (CFRP) jacketing

This paper presents an effective method for strengthening non-ductile reinforced concrete columns by applying an externally bonded Carbon Fiber Reinforced Polymer (CFRP) fabrics to enhance the shear capacity and confinement. Six rectangular reinforced concrete columns designed for gravity load only were tested under quasi-static cyclic loading. Three columns were provided with short lap-splice length of longitudinal reinforcements at the plastic hinge location to study the effect of lap splice. The experimental results indicate that, by means of CFRP jacketing, the shear strength under reversed cyclic loading is significantly improved as compared to the un-strengthened columns tested in the previous studies. In addition, owing to the confinement from CFRP, the columns exhibit a dramatically improved displacement capability. The nonlinear analysis of columns is also conducted by means of nonlinear fiber section frame element. The key attribute of the nonlinear analysis is to include the effect of lap splice of longitudinal reinforcement through the lap-spring spring model formulated according to the tri-uniform bond stress model. By combining the stress-strain models of concrete, steel reinforcement, lap-splice’s bond model, anchorage bond slip and nonlinear shear spring into the fiber section frame element, the numerical results shows a good agreement with experimental ones.

Effectiveness of basalt FRP tendons for strengthening of RC beams through the external prestressing technique

This paper investigates the feasibility of newly developed basalt fiber reinforced polymer (BFRP) as prestressing material and the structural behavior of reinforced concrete (RC) beams strengthened with externally prestressing BFRP tendons. Three main factors potential controlling structural strengthening effects, including tension stresses, bending angles and anchorages of the tendons, were first discussed based on literature review and finite element (FE) simulation. In the structural experiment, the effects of tension stresses and the tendon profiles on the flexural behavior of RC beams were discussed and the evaluation on the ultimate bearing capacity, cracking moment, crack width and deflection of strengthened beams was conducted by theoretical calculation and experimental results. The results show that the prestressing level of BFRP tendon can be determined to be 0.50fu and 0.38fu (fu is the tensile strength) according to creep rupture limit. The bending angle at the deviator is optimized to be 2° and the bond anchorage with resin epoxy was adopted to maximize strength utilization. For strengthening behavior, the second-order effect of the externally prestressed beam can be effectively relieved by using proper deviators, which is demonstrated by enhanced ultimate capacity. All of the strengthened RC beams are failed by concrete crushing, with satisfactory crack patterns and superior ductility compared to the control beam, which demonstrates the simultaneous working of internal steel reinforcements and external prestressing BFRP tendons during loading. The evaluation on mechanical behavior of strengthened RC beams indicates theoretical calculation according to several existing standards can well predict strengthening effect.

Feasibility of Using Palmyrah Strips as Reinforcing Material in Cost Effective Houses

Construction of cost effective houses is a dilemma among the impoverished population in developing countries. The ever increasing price of traditional building materials results in high capital investments for residential buildings. Palmyrah is a significant economic resource, widely spread all over the northeast region of Sri Lanka. This research explores the technical feasibility of using heartwood of Palmyrah as a reinforcing member in lightly loaded concrete elements. Initially, mechanical properties of Palmyrah were examined through static bending, tensile, and compressive tests. Percentages of water absorption, dimensional stability, and anchorage bond strength were investigated to envisage the suitability of Palmyrah as reinforcement. Next, several short span slabs and beams reinforced with Palmyrah strips were subjected to tests. It was observed that Palmyrah reinforcement enhanced the moment capacity of the slabs and beams compared to unreinforced sections. Experimental failure loads of slabs and beams were higher than theoretically predicted values with Palmyrah reinforcement. Further, Palmyrah reinforced beams and slabs underwent flexural failures. Thus, it is concluded that heartwood of Palmyrah has the potential to be used as reinforcement in lightly loaded slabs and beams. Further research is recommended to investigate the durability and serviceability issues.

Influence of concrete composition on anchorage bond behavior of prestressing reinforcement

An experimental research addressing the effects of concrete composition and strength on anchorage bond behavior of prestressing reinforcement is presented to clarify the effect of material properties that have appeared contradictory in previous literature. Bond stresses and anchorage lengths have been obtained in twelve concrete mixes made up of different cement contents (C) – 350 to 500kg/m3 – and water/cement (w/c) ratios – 0.3 to 0.5 – with compressive strength at 24h ranging from 24 to 55MPa. A testing technique based on measuring the prestressing force in specimens with different embedment lengths has been used. The results show that anchorage length increases when w/c increases, more significantly when C is higher; the effect of C reveals different trends based on w/c. The obtained anchorage bond stresses are greater for higher concrete compressive strength, and their average ratio of 1.45 with respect to transmission bond stresses implies a potential bond capacity.

Analysis of Bond and Anchorage Performances of Helical and Twisted Reinforcement Material

The performance of helical-effect of the helical and twisted material is elaborated in this paper. Through analyzing the parameter of the helical and twisted material, a mechanism model based on the bond of anchorage is built. Furthermore the fundamental derivation formula is done and the sensitivity is analyzed. Based on systematic study of bond anchorage performance of helical and twisted reinforcement material, the mechanical of the helical-effect was theoretically analyzed and quantitatively studied. The relationship between pullout and bond slip was studied by mechanical analysis and mathematical modeling stage by stage, the formula was established and derived. As a result, theoretical understanding of the helical-effect was deepened, providing the theoretical basis for optimization of material properties, geometry parameters and developing new materials.

Experimental Study on Compressive Bond Anchorage Properties of 500 MPa Steel Bars in Concrete

Few studies on the anchorage of reinforcing bars under the compressive conditions have been undertaken. This paper reports the results of 99 pushout tests done to investigate the compressive bond anchorage properties of 500 MPa steel bars in concrete. The precise slip values have been measured using a laser displacement sensor with high resolution, allowing the complete force-slip curves to be obtained. The influence of concrete strength, bar diameter, concrete cover, embedded length, and transverse reinforcement on the bond properties under compressive conditions is investigated. A new formula for calculating the compressive bond strength for 500 MPa reinforcing bars in concrete is proposed based on the test results.

Tensile bond anchorage properties of Australian 500N steel bars in concrete

In order to investigate the tensile bond anchorage properties of Australian 500N steel bars in concrete, 111 pullout tests were conducted. The precise bond slip values have been gained by using the laser displacement sensor with high resolution, including the complete bond-slip curves. How the main anchorage factors such as concrete strength, bar diameter (8, 10, 12, 16, 20, 24, 28, 32 and 36 mm) the concrete covered, embedded length and transverse reinforcement influencing the bond anchorage properties was studied under tensile condition. The process of the tensile force-slip failure for Australian 500N reinforcing steel can be divided into five stages: elastic stage, local slip stage, slip in ascent stage, slip in descent stage and remnant stage. The formula for calculating the tensile bond strength of Australian 500N reinforcing bar in concrete was proposed according to the test results, including the consistent model for tensile bond-slip relationship.

Shear behaviour of reinforced phyllite concrete beams

The shear behaviour of concrete beams made from phyllite aggregates subjected to monotonic and cyclic loading is reported. First diagonal shear crack load of beams with and without shear reinforcement was between 42–58% and 42–92% of the failure loads respectively. The phyllite concrete beams without shear links had lower post-diagonal cracking shear resistance compared to corresponding phyllite beams with shear links. As a result of hysteretic energy dissipation, limited cyclic loading affected the stiffness, strength and deformation of the phyllite beams with shear reinforcement. Generally, beams with and without shear reinforcement showed anchorage bond failure in addition to the shear failure due to high stress concentration near the supports. The ACI, BS and EC codes are conservative for the prediction of phyllite concrete beams without shear reinforcement but they all overestimate the shear strength of phyllite concrete beams with shear reinforcement. It is recommended that the predicted shear capacity of phyllite beams reinforced with steel stirrups be modified by a reduction factor of 0.7 in order to specify a high enough safety factor on their ultimate strength. It is also recommended that susceptibility of phyllite concrete beams to undergo anchorage bond failure is averted in design by the provision of greater anchorage lengths than usually permitted.

Long anchorage bond–slip formulation for modeling of r.c. elements and joints

In this paper a bond–slip relationship for long anchored bar has been proposed for modeling the structural behavior of r.c. elements and joints, able to take into account the interaction phenomena between ribbed bars and concrete also in condition of highly-stressed reinforcement. In such conditions some factors play a key role in modifying maximum tangential stress which can be transferred, for example the variation of the section area of the bar due to the Poisson’s effect, as well as the modification of the geometry of the ribs due to yielding. The proposed formulation has been developed by considering mean parameters, in order to obtain a tool usable also with general-purpose finite element codes. A first series of validation tests have been carried out by means of FE simulations of experimental pull-out tests on long anchored bars. Then the proposed formulation has been applied to simulate the well-known experimental tests carried out by Leonhardt and Walter on beams and finally to reproduce the cyclic response of a beam-column joint highly affected by the bond conditions of the longitudinal reinforcement.

Cyclic stress development in substandard beam–column joint

This paper investigates the failure, bond, strain and stress development of steel bars in a cyclically loaded substandard reinforced concrete beam–column joint. A seismic assessment of 17 existing buildings in a low seismic zone was conducted to study correlations among column size, column depth to bar diameter ratio, bond index and column tributary area. Four half-scale specimens, representing beam–column joints in buildings with various column tributary areas, were tested under quasi-static cyclic loading. The test results reveal brittle joint shear failure in specimens with small and medium column tributary areas and beam flexural failure in specimens with a large column tributary area. By unbonding longitudinal beam bars in the joint, joint shear failure can be prevented. Local pull-out bond and anchorage bond were also studied. All the specimens studied demonstrated the existence of anchorage bond, but local pull-out slip cannot be prevented in all specimens regardless of column depth to bar diameter ratio.

Behaviour and analysis of beam–column joint strengthened by cast-in-situ expansion

This paper presents a joint strengthening method using cast-in-situ expansion. The objective of cast-in-situ expansion is to make a joint stronger than adjoining beams and change failure from brittle joint shear to ductile beam flexure. In this method, cast-in-situ expansions are fabricated around corners of the joint. The cast-in-situ expansion increases joint shear capacity through increased effective joint area and increases anchorage bond capacity of beam bars passing through the joint through increased apparent column depth. An experimental programme is conducted. Four half-scale beam–column specimens were tested under quasi-static cyclic load. The specimens were strengthened with triangular and square expansions. Test results indicated brittle joint shear failure in the control specimen and beam flexural failure in the strengthened specimens. The strength, stiffness and energy dissipation of strengthened specimens were increased. The experiment is supplemented by non-linear finite-element analysis to investigate the flow of stresses in the joint panel and the expansion. The non-linear finite-element analysis applies the fixed smeared crack concept to simulate distributed cracks in the beam, column and joint panel. A one-dimensional discrete joint element is applied to represent the interfacial contact between beam and column and between expansions and members where local non-linearity such as bar pull-out and interface shear may occur. Both experiment and finite-element analyses demonstrate parallel cracks along the edge of expansion, indicating a diagonal compressive strut. Based on the principal stress plot, the finite-element method reveals two load-bearing mechanisms. In addition to the primary diagonal compressive strut in the joint panel, the expansion provides the secondary strut mechanism along the edge of the opposite expansions. The size of expansion has a direct influence on the capacity of the secondary strut. The failure of the strengthened specimens depends on the relative bending capacity of beam sections and the combined capacity of the primary and secondary joint strut mechanism.

Prediction of tensile capacity based on cohesive zone model of bond anchorage for fiber-reinforce dpolymer tendon

In this paper, analytical solutions based on a cohesive zone model (CZM) are developed for the bond fiber-reinforce dpolymer (FRP) tendon anchorage under axial load. With bilinear cohesive laws, the analytical solutions of tensile capacity of anchorages are derived. The concept of the minimum relative interface displacement s m is introduced and used as the fundamental variable to express all other parameters, such as external tensile load. Experimental and analytical results show that the thickness of the anchoring material is main factor affecting tensile capacity. The characteristic bond strength depends mainly on the properties of the bonding agent-anchoring material, the geometry and surface conditions of the tendon, and the radial stiffness of the confining medium. A comparison of the calculated and experimental results showed good agreement. Formulas based on fracture energy of the tension load capacity derived in the present work can be directly used in the design of FRP tendon anchorage.

Seismic retrofit of substandard beam-column joint by planar joint expansion

A seismic retrofit technique for existing reinforced concrete beam-column connections using planar joint expansion is proposed. The method is based on a two-dimensional expansion of beam-column joint using cast in-situ concrete and dowel bars. The method is economical and architecturally acceptable. Three half-scale sub-standard beam-column specimens were tested under quasi-static cyclic loading. One was control specimen and the other two were retrofitted specimens with triangular and square joint expansion. According to test results, the control specimen showed brittle joint shear failure while retrofitted specimens showed beam flexural failure. The strength, stiffness, energy dissipation and ductility of retrofitted specimens were greatly improved. The planar joint expansion is effective to reduce joint shear stress and improve anchorage bond of beam bar within the joint. The plastic hinge formation can be moved away from column face, thus preventing joint shear failure. The triangular and square expansions perform almost equally well. The construction joints formed at the interfaces between specimen and joint expansion do not produce an adverse effect in cyclic behavior.