Anchorage Bond Research Articles

Mechanism analysis of helical and twisted reinforcement

Although helical and twisted reinforcement has been used to reinforce concrete for more than two decades, its rationale still remains unclear. With a brief review of current researches on the helical and twisted reinforcement properties, this paper describes some new phenomenon of the helical and twisted reinforcement in concrete and other matrix by experimental studies, and then discusses on mechanism of “helical effect of strengthening”. This paper also discusses the mechanism of “accessional helical effect of strengthening” and its significance in industrial practice. Extensive tests indicate that twisting is the most effective way to improve reinforcement mechanical properties. The main results are: (1) They can greatly enhance bond anchorage in base material. In some pull-out tests, the pull-out resistance increases with reinforcement slip within the specimens, which results not only in a higher pull-out load but also a larger slip up to 70%–80% of reinforcement embedded length. (2) Concrete reinforced by twisted bars demonstrates certain ductility at failure. (3) The bond strength depends on the pitch space directly. (4) The twisted effect on material strengthening is from a three-dimensional interlocking force which is formed from material untwisting when they were pulled out from base specimens.

Comparative performance of sub-standard interior reinforced concrete beam–column connection with various joint reinforcing details

This paper discusses the effect of some important parameters on cyclic behavior of sub-substandard interior beam–column connection. The objective is to investigate the effect of joint shear stress, anchorage bond of longitudinal beam bar within the joint and horizontal joint reinforcements on the joint performance. The experiment consisted of five half-scale beam–column specimens. The control specimen (J1) represented a typical non-ductile beam–column joint in mid-rise RC buildings constructed in low seismic zone. In specimen J2, the bond between concrete and longitudinal bars was completely removed initially. In specimen J3A and J3B, a substantial amount of horizontal joint reinforcement was provided in joint core. In specimen J4, the column size was enlarged to reduce shear stress in joint. The experimental result demonstrated brittle joint shear failure in control specimen (J1), specimens J3A and J3B, beam splitting failure in specimen J2 and ductile flexural failure in specimen J4. Based on experimental results, it was found that the initial lost of bond did not cause a substantial reduction in joint capacity. Moreover, provision of substantial horizontal joint reinforcements in specimen J3A and J3B did not produce a comparable improvement in the seismic performance. With increased column size in specimen J4, the energy dissipation characteristics were greatly improved as indicated by large spindle-shaped cyclic loops.

Effect of Fiber-Reinforced Polymer Confinement on Bond Strength of Reinforcement in Beam Anchorage Specimens

This paper reports on the fourth phase of a multiphase study undertaken at the American University of Beirut (AUB) to examine the effect of fiber-reinforced polymer (FRP) sheets in confining bond-critical regions in reinforced concrete beams. Results of the first three phases showed that glass- and carbon-fiber-reinforced polymer (GFRP and CFRP) sheets were effective in increasing the bond strength and improving the ductility of the mode of failure of tension lap splices in high-strength concrete (HSC) and normal-strength concrete (NSC) beams. The main objective of the fourth phase of the AUB study was to assess the effect of CFRP sheets in improving the serviceability and ultimate response of beam anchorage specimens. The added experimental data and the improved knowledge of the bond behavior of FRP confined concrete members will encourage the use of FRP technology to strengthen and retrofit bond anchorage zones. Ten beam anchorage specimens were tested in positive bending in two series. The variables we...

Bond strength of reinforcing steel bars milled from scrap metals

In many poor developing countries, reinforcing steel bars are milled using scrap metal from obsolete vehicle parts and machinery. In Ghana, these bars which are classified as mild steel, are normally milled with ribbed surfaces similar to standard high-yield steel bars to enhance their bond with concrete. Hitherto there has been inadequate information on the actual physical behaviour including the bond properties of these reinforcing steel bars, which are already in use in structural concrete. This paper presents a description of the experimental investigation of the anchorage bond resistance and slip characteristics of the steel bars in beams and pull-out specimens. The results of the study have shown that the average anchorage bond strength of the bars developed at ultimate steel stresses is higher than that of mild steel but close to standard high-yield deformed bars. The beam tests gave lower values of bond strength at relatively lower steel stresses, and averaged about 50% of the pull-out bond results. The large difference in the results of the beam and pull-out tests is due to the different concrete covers to the steel bars and the absence of concrete confinement usually developed by shear reinforcement in beams. Bond failure was mostly caused by the splitting of concrete.

The influence of coarse aggregate and reinforcement on the anchorage bond strength of laterized concrete

Many factors are known to affect the anchorage bond stress of laterized concrete. Laterized concrete is concrete in which some, or all, of the fine aggregate is from lateritic soils. The effect of types of coarse aggregate and reinforcement on the anchorage bond stress of laterized concrete was investigated in this study. The punching test method was used to determine the anchorage bond stress characteristics of laterized concrete specimens cured for 28 days. The results have shown that for the crushed granite and the dug-up aggregates (“dug-up aggregate” refers to aggregates obtained from natural sources and have almost the same size range with the crushed granite), the values of anchorage bond stress obtained compare well with those of the ordinary concrete but higher than that of the lightweight concrete. The anchorage bond stress values obtained for specimens made of dug-up aggregates are higher than those obtained for crushed granite. Higher anchorage bond stress values were obtained for laterized concrete specimens containing deformed bar reinforcement than those containing plain bar reinforcement. Laterized concrete specimens having higher cement content produced higher anchorage bond stress.

Factors Affecting Anchorage Bond Strength in High-Performance Concrete

The objective of this investigation was to observe the effect of the compressive strength of concrete, reinforcing bar size, thickness of concrete cover, and amount of web reinforcement on the anchorage bond strength and on the bond behavior of reinforced high-performance concrete. For this purpose, eccentric pullout bond tests were conducted under monotonic loading on high-performance concrete specimens. Some of the specimens were reinforced by one and some by two deformed steel bars. Results indicated that the bond strength between reinforcement and concrete increased with increasing concrete strength, cover thickness, and amount of web reinforcement, while it decreased with increasing bar size. Using the test data, the variation in the average bond strength with respect to each of the stated parameters is formulated. The trend of variation for each parameter is compared with the associated trends inherent in the development length expressions of the American Concrete Institute Building Code and the Eurocode 2. An expression for the required development length, enveloping all the tested specimens, is presented.

Bond Anchorage of Pretensioned FRP Tendon at Force Release

The anchorage of fiber‐reinforced plastic (FRP) tendons in pretensioned prestressed concrete (PC) members may cause the formation of cracks as a result of tendon wedge effect and mechanical interlocking during prestress force transfer. This paper presents experimental results obtained with a braided epoxy‐impregnated aramid FRP tendon having a 16‐mm nominal diameter and initial prestress force of 125.6 kN. Minimum concrete cover was 52 mm. End‐zone reinforcement and tendon partial blanketing were used to determine their effect on concrete stress field intensity and on cracking due to prestress force transfer. It was found that steel stirrups do not prevent cracking, but they limit its propagation. A carbon FRP coil of small pitch inhibits crack formation, but the concrete tensile strain remains high. Partial blanketing is the most effective solution, causing only a limited increase in transfer length (approximately 20%). An analytical solution to the experiment was obtained by using the finite element met...

Effect of mix proportion and reinforcement size on the anchorage bond stress of laterized concrete

Lateritic soils, being locally available, have been one of the major building materials in Nigeria, and in most tropical countries in general. This paper reports the results of investigations carried out on the effect of mix proportion and size of plain round steel reinforcement on the anchorage bond stress characteristics of laterized concrete specimens. Laterized concrete is concrete in which some, or all, of the fine aggregate is from lateritic soils. Sieve analysis of both the lateritic soils and the coarse aggregates used was carried out. Seven different bar sizes ( 6, 8, 10, 12, 16, 20 and 25 mm) which were cut into pieces 170 mm long to fit into the 150 cube mould were used. Also, three different mix proportions ( 1:1:2; 1:1 1 2 :3 and 1:2:4) were used for the study. The results have shown that both the mix proportion and the size of reinforcement have a significant effect on the anchorage bond stress of laterized concrete specimens. The richer, in terms of cement content, the mix proportion, the higher the anchorage bond stress of laterized concrete. Also, the anchorage bond stress between plain round steel reinforcement and laterized concrete increases with increase in the size of reinforcement used.

Effect of Loading Rate on Anchorage Bond and Beam-Column Joints

Small scale reinforced concrete specimens subjected to cyclic loading were tested at rates varying from 0.0025 to 2.0 Hz to investigate the effects of several variables including loading rate, shear-span-to-depth ration a/d, and stirrup spacing. This study's primary objective was to investigate the rate effect of cyclic loading on bond in reinforced concrete structures. Several different parameters such as stiffness degradation, energy dissipation, failure mode, strain and bond-stress distributions along the bar were examined to evaluate the differences due to the rate of loading.

Bond of deformed bars in steel fibre reinforced concrete under cyclic loading

The bond between reinforcing steel and steel fibre reinforced concrete under reversed cyclic loading was studied. This loading simulates the conditions that may occur at an interior beam-column joint of a concrete frame structure during an earthquake. An analytical study was carried out, which included an assessment of the stresses and deformations in both the concrete and the steel. The results of an extensive experimental programme indicated that the behaviour of specimens under reversed cyclic loading was quite different from that under monotonic loading. In addition, under reversed cyclic loading, specimens containing steel fibres exhibited much better anchorage bond characteristics and a decreased rate of crack development as compared to specimens without fibres.

The influence of lateral pressure upon anchorage bond

Synopsis This paper examines the effect of lateral pressure upon the anchorage bond behaviour of both plain and deformed reinforcing bars in lightweight-aggregate concrete. Two common bond tests, the cube pull-out and the semi-beam tests, were modified that lateral pressures could be applied to the bond specimens. The major variables studied were the magnitude of the lateral pressure, the bar diameter. the length of embedment and the concrete strength. The results of over 200 bond tests show that for plain bars the application of lateral pressure can result in an increase in pull-out load of over 250%, whilst for deformed bars of similar size the corresponding increase is about 75%. The different bond mechanisms for plain and deformed bars were highlighted by the failure modes of the bond specimens; this difference in behaviour is rejected in the theoretical work by a frictional bond strength criterion for plain bars and a splitting or shearing criterion f or deformed bars.

Bond stress along lapped reinforcing bars

Synopsis The state of stress along a lapped splice in reinforced concrete can be determined by using the modulus of displacement theory. The theory is based on actual displacement or local deformations in the bond zone near the surface of the reinforcement. The stresses along the anchorage length can also be estimated with moment cracks taken into account. Special attention must be paid to cracks in the cover along the reinforcement. In practice, however, the simpler equations with the concrete acting just as an adhesive between the lapped bars gives reasonable results. By using this theory, formulae can also be evaluated for other types of bond anchorage.

Bond strength in steel fibre-reinforced concrete: Tattersall, G. H. and Urbanowicz, C.R. Magazine of Concrete Research, Vol 26 No 87 (June 1974) p 105

Test results are presented to show that the Anchorage bond strength of deformed bars is 40% higher in steel fibre concrete than in plain concrete. The fibres were most effective in controlling cracking and failure of the test specimens. It is suggested that a steel fibre tensile skin can substantially improve the stiffness and serviceability conditions of conventionally reinforced structural members. The experimental work consisted of several pull-out tests on 10mm, 12mm, 16mm, 20mm and 25mm diameter bars embedded in steel fibre and plain unreinforced concrete. All the reinforcing steel were hot-rolled, high-yield deformed bars with a characteristic strength of 410 n/mm2 and were embedded either vertically or horizontally within the concrete. /TRRL/

A limit state anchorage bond test for reinforcement in concrete

A new standard anchorage bond test for steel reinforcement in concrete has been developed in accordance with limit state principles. The basis of the test is non-failure of the anchorage.

Bond Strength between Reinforcing Bars and Lightweight Aggregate Concrete

It is the main purpose of this study to obtain information on bond strength of reinforcing bars for lightweight concrete as compared with that for normal river sand and gravel concrete. The influences of surface characteristic of reinforcing bars and methods of test were also investigated. Four types of bars were tested and three kinds of methods of test (pullout test, tension test and long prism test) were chosen.From the tests the following results were obtained and conclusions drawn:(1) The test date show no difference in bond strength between lightweight concrete and normal concrete, so far as both the kinds of concrete are equal in compressive strength.(2) There is correlation among the test results by three different test methods.(3) The pullout test gives the most reasonable measure to evaluate the relative effectiveness of reinforcing bars in respect of the anchorage bond.(4) The long prism test serves to evaluate the effectiveness of the bars for controlling cracks.