Concrete Cone Research Articles

Experimental study of geopolymer used as adhesive in anchorage of steel bars

Abstract Pull-out tests were performed on 42 post-installed steel bars embedded in two large concrete substrates. Three types of adhesive agent, including commercial available organic adhesive (Hilti HiT-Re), inorganic geopolymer paste and geopolymer mortar were used to bond the post-installed reinforce bars, with different embedment length (5d, 8d, 10d, 12d and 15d, where d is the diameter ). Data from the pull-out tests is utilized to compare the bond performance of the three types of adhesive agent and determine the optimum embedment depth of rebars when using geopolymer paste and geopolymer mortar as adhesive. The test results showed that the failure modes of the post-installed rebar system changed from concrete cone failure to combined failure or even rebar fracture failure, with an increase in the rebar embedment depth. When the embedment length of post-installed rebars was less than 10d, the specimens bonded with organic adhesive exhibited the best bond performance, and which were followed by those bonded with geopolymer mortar. And the specimens bonded by geopolymer paste exhibited the lowest bond strength. However, for specimens with rebar embedment depth higher than 10d, the anchoring behavior of three types of adhesive was similar.

Pullout behavior of cast-in-place headed and bonded anchors with different embedment depths

The equipment of French nuclear power plants is fixed on reinforced concrete structures with base plates with headed fasteners. Electricity of France decided to carry out an experimental research program in partnership with Laboratory of Civil and Environmental Engineering in order to optimize the design of the headed fasteners and identify margin. This article introduces the results of static tension tests on an anchorage composed of an anchor plate welded to four ribbed bars or headed smooth studs. The anchors are cast in place in a reinforced concrete block. The experimental campaign is carried out on real size anchors and anchors with reduced embedment depths. Tests on single rod are also carried out in order to analyse the group effects. Following the embedment depth, the collapse of the anchorages is caused by a concrete cone breakout failure, a steel rod failure or a combination failure of bond and concrete cone failure for ribbed bar. For bonded anchors, the group effect involves a decreasing of 30 % of the bond stress. For headed anchors, Eurocode 2 tends to underestimate the ultimate strength for a concrete breakout failure. This experimental campaign will provide a data base enabling the development of numerical models in order to improve the design.

New connection between reinforced concrete building frames and concentric braces: Shaking table tests

Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced concrete frames subjected to lateral loads. These braces may develop high axial tension forces, and transferring them appropriately to the existing beam–column joints is a key challenge. This paper investigates a solution for connecting the end-plate of the steel brace with the frame, using (1) shear-key plates fixed to the concrete with anchor bolts, and (2) a low friction material inserted between the end-plates and the shear-key plates. The presence of the low friction material impedes the development of tension forces in the anchor bolts and ensures that they are basically subjected to shear forces. This prevents brittle types of failure (concrete cone failure, pull-out/pry-out failure), and results in a reduction of the number of anchors required as well as anchorage height. The efficiency and validity of the proposed brace–frame connection is investigated experimentally by means of shaking table tests conducted on a 3×3×3m3 scaled reinforced concrete frame retrofitted with brace-type hysteretic dampers.

Experimental Study on Tension Performance of Anchor Group

The torque-controlled expansion anchors, undercut anchors,bonded anchors and special inverted conical chemical anchors subjected to tension load, which including single anchor, two anchors, four anchors and eight anchors are tested. Failure mode and tension performance of anchor group are investigated, and test value and calculative value of ultimate load are compared. Experimental results show that some anchor group occur the concrete cone failure under tension load, and others occur steel failure under tension load. Test value and calculative value of ultimate load are compared, and the result meets well.

Headed Fastenings Acting in Cooperation with Supplementary Steel Reinforcement

Composite and precast concrete structural systems are becoming the first choice for many construction designers. Headed fastenings are currently a relatively common technique to create joints in such types of structures. Performance of fastenings usually depends on load capacity of the concrete surrounding the fastening. The resistance of the fastening may be increased by using supplementary reinforcement designed in order to prevent concrete cone failure. The background of current design methods and experimental research is discussed in the paper.

하이브리드 해상풍력 파일 기초 콘크리트 지지구조(MCF) 개발

기존 해상풍력발전 지지구조물의 단점을 보완한 신형식의 파일 기초 하이브리드 지지구조물을 본 연구에서 제안하였다. 이 지지구조는 콘크리트 자중을 이용한 중력식 기초의 개념으로부터 수정되어 4개의 파일로 지지되며, 강재 샤프트와 원추형 콘크리트가 결합된 하이브리드 형식이다. 규모가 크고 두꺼운 콘크리트의 3차원 해석을 위해, 정확한 기하형상 모델링과 응력의 절점 보간이 가능한 솔리드-쉘 입체요소를 개발하였다. 해양구조물 전용 유한요소 프로그램인 XSEA에 탑재된 솔리드-쉘 요소와 Stream Function 파랑 이론을 적용하여, 제안한 하이브리드 지지구조물에 대해 서남해안 지역의 환경조건을 적용한 준정적 해석 및 고유진동수 해석을 실시하였다. 해석결과, 수평변위가 허용변위 이내로 나타났고, 고유진동수 해석을 통해 하이브리드 구조형식의 동적거동에 대한 우수성을 입증하였다. 결과적으로, 파일지지 하이브리드 지지구조물은 우리나라 서남해안 지역과 같이 연약지반에 적용 할 수 있는 충분한 안정성을 가진 것으로 평가 되었고, 각 부재에 대한 최적화 연구를 통해 경제성 확보가 가능한 것으로 검토되었다. This paper proposes a new hybrid support structure by the driven piles which removes disadvantages of the existing type of support structure for offshore wind turbines. The hybrid type of support structure is combined with concrete cone and steel shaft, and is supported not only by gravity type foundations but also by driven piles. For three dimensional analysis of the huge and thick concrete structure, a solid-shell element that is capable of exact modeling and node interpolations of stresses is developed. By applying wave theory of stream function and solid-shell element in XSEA simulation software for fixed offshore wind turbines, a quasi-static analysis and natural frequency analysis of proposed support structure are performed with the environmental condition on Southwest Coast in Korea. In the result, lateral displacement is not exceed allowable displacement and a superiority of dynamic behavior of new hybrid support structure is validated by natural frequency analysis. Consequently, the hybrid support structure presented in this study has a structural stability enough to be applied on real-site condition in Korea. The optimized structures based on the preliminary design concept resulted in an efficient structure, which reasonably reduces fabrication costs.

후 설치 앵커 성능평가와 해석모델

후 설치 앵커인 Set Anchor를 비 균열 콘크리트에 설치하여 앵커의 인발 및 전단 내력에 대하여 고찰 하였다. Torque, 앵커의 직경, 앵커의 삽입 깊이의 변수를 두어 인발 및 전단 실험을 진행 하였으며 인발 하중을 받는 경우에는 Torque, 앵커의 직경 및 삽입 깊이에 영향을 받는 것으로 나타났으며 전단 하중을 받는 경우에는 앵커의 직경 및 삽입 깊이에 영향이 있으나 Torque의 크기에는 영향이 적은 것으로 나타났다. 본 실험에서 앵커와 모재인 콘크리트의 파괴모드는 인발 실험인 경우 앵커 강재 파괴 및 콘크리트 콘 파괴가 발생 하였으며 전단 실험인 경우에는 대부분의 실험에서 앵커의 전단 파괴가 나타났다. 앵커의 인발 내력을 범용 구조해석 프로그램인 ABAQUS를 이용하여 앵커시스템의 해석 시 사용가능한 유한요소 모델링을 도출하여 해석한 결과 콘크리트 구조물에 후 설치 앵커를 사용한 해석대상에 대하여 비교적 정확한 예측이 가능한 것으로 나타났다. The post-installed anchors were installed in non-cracked concrete. And then pullout and shear strength of the anchor were investigated. The test of pullout and shear was conducted torque, diameter and insertion depth of the anchor. If it subjected to pullout load, the performance of it was affected by torque, diameter and insertion of anchor. It it subjected to shear load, the performance of it was affected by diameter and insertion of anchor, but torque was less affected. In failure mode of pull-out test, steel failure of the anchor and concrete cone failure occur. And shear failure mode, most of the tests showed shear failure of the anchor. A commercially available finite element program, ABAQUS, is used in this study, and then the behavior of pull-out of anchor were analyzed. When the interpretation of the available anchor system are derived for finite element modeling of concrete structure, interpreted the resulted with the installation of a target anchor for a relatively accurate prediction was possible.

Performance evaluation of the post-installed anchor for sign structure in South Korea

In this study, numerous experimental tests for post-installed anchor systems used for sign structures in South Korea, drilled in hardened concrete were conducted in order to estimate pull-out and shear strength of the anchor based on three mechanical properties – torque ratio, embedment depth and diameter. In the pull-out tests, the pull-out strength of the anchor system depends significantly on all the three aforementioned parameters while in the shear tests, it was informed that the shear strength is not affected by torque ratio. It was also found that concrete cone failure or damage mechanism was generally observed during and after pull-out tests and in shear strength tests and that the anchor systems fail prior to the failure in the existing primary structural system. Furthermore, 3D finite element model for the anchor systems was created by ABAQUS to validate the experimental results using numerical analysis. It is shown that the formulated finite element model can be used to closely predict the load–displacement relationships as observed in the experimental tests. Further, we also propose a criterion for evaluating limit states to enable reliable design of the anchor systems using probabilistic fragility methodologies.

Multiple Anchor Behavior of Steel-to-Concrete Connections under Reversed Cyclic Loading

Four steel-to-concrete connections with adhesive anchor groups under reversed cyclic loading have been tested. The results showed that anchor steel could reach yield strength before connection failure, generating small shell-shaped concrete cone in the surface of block and the ultimate capacity was governed by strength of anchor. Seismic characteristics of hysteresis curve, rigidity regression, ductility and energy-dissipation were used to draw conclusions that the connections would behave in a ductile manner without significant loss of loading capacity after peak value and visible deformation could develop until failure occurred. Increased embedment depth and added amount of anchors were helpful to improve seismic performance of connections. Only the outer row of most stressed anchors in the tension zone were needed to meet the elliptical interaction of tension and shear capacity requirement during the design process of anchor groups under combined shear and moment loading. In seismic design of steel-to-concrete connections, the predicted capacity by a reduction factor of 0.8 was advised and the comparison of calculated versus observed capacity presented limited variance.

The influence of profiled sheeting thickness and shear connector’s position on strength and ductility of headed shear connector

A three-dimensional finite element model is developed, validated and used in the parametric study to investigate the influence of shear stud’s position and profiled sheeting thickness on the strength, ductility and failure modes of the headed shear stud welded to the modern profiled sheeting. A total of 240 push tests were analysed with different sheeting thicknesses, positions of the shear stud in the trough, concrete strengths and transverse spacings. The results showed that the sheeting thickness influenced the shear connector resistance of studs placed in the unfavourable position more than studs placed in favourable and central positions. The strength of the shear connector placed in the unfavourable position increased by as much as 30% when the sheeting thickness was increased. The shear connector resistance of the unfavourable stud was found to be primarily a function of the strength and the thickness of the profiled sheeting rather than the concrete strength. The strength prediction equations for unfavourable and central studs were also proposed. The results suggested that the strength of the shear connector increased as the distance of the shear stud increased from the mid-height of the deck rib in the load bearing direction of the stud. The load–slip behaviour of the studs in the unfavourable position was more ductile than the studs in the favourable position, with slip of 2–4 times higher. It was found that the increase in sheeting thickness and transverse spacing improved the ductility of the stud in unfavourable position, but had no effect on the stud in the favourable position. The failure modes suggested that the favourable and central studs failed by concrete cone failure and unfavourable studs failed by rib punching together with crushing of the narrow strip of the concrete in front of the stud.

Modeling of anchor bolt pullout in concrete based on a heterogeneous assumption

In this study, numerical simulation of anchor bolt pullout in plain concrete by a heterogeneous numerical model is presented. The heterogeneity of the concrete material was modeled by randomly assigning strength and elastic modulus to the elements according to Weibull's distribution. The ongoing debonding process was obtained, including crack initiation, crack propagation and formation of the concrete cone. The numerical results indicate that there is a strong size effect on failure resistance of the concrete cone. By increasing the anchor head size, peak pullout load and the volume of concrete cone increase. The peak pullout load and the volume of concrete cone also increase with the increasing of embedded length. With this heterogeneous numerical model, the asymmetrical crack patterns and the crack branching observed in tests is obtained. Moreover, asymmetrical crack and crack branching were easy to occur with lower homogeneity index. The numerical results agreed well with the experimental investigations.

Pullout Performance of Fully and Partially Bonded Retrofit Anchors in Low-Strength Concrete

Although steel reinforcing bars can be used as post-installed anchors to integrate new structural members to the existing structural system in the seismic retrofit of reinforced concrete structures, premature cone-type concrete failure can reduce the bars’ efficiency when they are anchored into low-strength concrete. This study investigates pullout behaviors of fully and partially bonded chemical anchors post-installed in low-strength concrete. The test parameters are the embedment length, the bonded length of the anchors, and the humidity and dust surface conditions of the anchor holes. The pullout behavior is examined through the load-displacement curves, modes of failure, and anchorage strengths of specimens. The results show that the pullout performance of partially bonded, post-installed chemical anchors embedded in low-strength concrete is significantly better than conventional fully bonded post-installed chemical anchors, which suggests that partially bonded anchoring of deformed bars could be useful for anchorages in seismic retrofit applications. A model is proposed for predicting the pullout strength of anchors that fail due to a combination of concrete cone and bond failures. A good correlation is found between the model predictions and test results from this study compared with previously-published experimental findings.

PULL-OUT TEST OF ANCHOR BOLT FOR FASTENING LEAD DAMPER TO CONCRETE FOUNDATION

Pull-out tests on anchor bolts for fastening lead damper to concrete foundation were conducted to evaluate factors affecting pull-out behavior of anchor bolts. The main parameters were type of anchor bolt commonly used for anchorage of lead damper and layout of reinforcements around anchor bolt. The following results were obtained : (1) Vertical reinforcements arranged around anchor bolt contribute to increase in concrete breakout strength. (2) For long nut type anchor bolt, long nut length covered anchor bolt must be treated with enough care to avoid slipping anchor bolt. Because slipping failure lead to decrease in tensile strength and increase in pull-out displacement at failure. (3) The slope of the concrete cone was much flatter than 45 degree assuming in design procedure, regardless of the embedment depth, anchor type and reinforcement pattern. (4) Based on test results, simple concrete failure model was proposed. Using this model, effective radius of projected area were assessed 0.81le - 0.96le. These values were close to effective radius 1.0 le in existing design formula according to AIJ.

Analytical Method for Failure of Anchor-Grout-Concrete Anchorage due to Concrete Cone Failure and Interfacial Debonding

Depending on the relevant material properties, failure of grouted anchor anchorage to concrete can result from pullout of concrete cones, debonding at either anchor-grout or grout-concrete interface, fracture of anchor, and combination of some of these failure modes. The intention of the present study is to present an analytical method for analyzing the concrete cone failure during the process of interfacial debonding by using deformation compatibility conditions at the anchor-grout and grout-concrete interfaces. The tensile stress in the anchor and interfacial stresses at the two interfaces are formulated at different loading stages. It is assumed that interfacial debonding modeled as an interfacial shear crack only appears at the anchor-grout interface and is initiated from the loaded end. The concrete cone and interfacial debonding failures are analyzed according to the sizes and material properties of the anchorage. Three different failure modes are considered, including concrete cone failure at the unloaded end without interfacial debonding, interfacial debonding plus concrete cone failure at the same height as the interfacial shear crack tip, and interfacial debonding plus concrete cone failure at the unloaded end. In each case, the load for the initiation of the concrete cone failure, and the cone angle are determined analytically. Subsequently, material and structural parameters are adopted to study their influences on the failure modes and calculated results. It is found that if the embedment length is relatively long, the concrete cone failure occurs within a local scope. If the concrete diameter is large enough, the failure mode is the interfacial debonding without concrete cone failure. The conclusions provide useful references for engineering practice such as designing grouted anchor anchorage to concrete in light of different needs and failure modes.

Crack widths near reinforcement bars for beams in bending

Earlier research performed on axially loaded concrete prisms shows that crack widths close to reinforcement are smaller and less dependent on concrete cover than crack widths at the concrete surface. To check practical applicability of these results a similar experimental investigation of cracking behaviour has been undertaken for beams loaded in bending. The influence of steel stress and concrete cover on crack widths close to the reinforcement and at the concrete surface has been investigated. The results show that the main features of cracking behaviour for axially loaded prisms and beams are similar. Beams resemble axially loaded prisms in that cone-shaped concrete failure occurs in the bond zone where the bar meets a crack. At higher steel stresses this concrete cone follows the displacement. For this reason crack widths close to the bar are significantly smaller and much less affected by the thickness of concrete cover than at the concrete surface. Surface crack widths consequently are poor indicato...

Testing of anchorages in concrete under dynamic tensile loading

The tensile dynamic behaviour of anchors in concrete has been experimentally investigated by employing Hopkinson bar techniques. Dynamic pull-out tests with two anchor size diameters have been performed, concrete cone breakout failure has been predominantly induced, and full force-displacement curves have been obtained.

Influence of loading rate on concrete cone failure

Three different effects control the influence of the loading rate on structural response: creep of bulk material, rate dependency of growing microcracks and structural inertia. The first effect is important only at extremely slow loading rates whereas the second and third effects dominate at higher loading rates. In the present paper, a rate sensitive model, which is based on the energy activation theory of bond rupture, and its implementation into the microplane model for concrete are discussed. It is first demonstrated that the model realistically predicts the influence of the loading rate on the uniaxial compressive behaviour of concrete. The rate sensitive microplane model is then applied in a 3D finite element analysis of the pull-out of headed stud anchors from a concrete block. In the study, the influence of the loading rate on the pull-out capacity and on the size effect is investigated. To investigate the importance of the rate of the growing microcracks and the influence of structural inertia, static and dynamic analyses were carried out. The results show that with an increase of the loading rate the pull-out resistance increases. For moderate loading rates, the rate of the microcrack growth controls the structural response and the results of static and dynamic analysis are similar. For very higher loading rates, however, the structural inertia dominates. The influence of structural inertia increases with the increase of the embedment depth. It is shown that for moderately high-loading rates the size effect becomes stronger when the loading rate increases. However, for very high-loading rate the size effect on the nominal pull-out strength vanishes and the nominal resistance increases with an increase of the embedment depth. This is due to the effect of structural inertia.

3D FE analysis of anchor bolts with large embedment depths

In the present paper the results of a finite element study of single headed stud anchors loaded in tension (concrete cone failure) are discussed. Anchors with extremely large embedment depths (up to 1500 mm) for which few experimental data is available are investigated. Many such anchors are used in engineering practice, therefore, the aim of the study was to investigate their safety. The numerical analysis is performed using a three-dimensional finite element code based on the microplane model. Calculated concrete cone capacity for large anchors with small heads shows good agreement with the current LEFM based design formula for anchors. The numerical study and the available test data show that the ultimate strength of anchors with larger heads is higher than predicted by the design code formula. Furthermore, the size effect on the ultimate load of these anchors is less pronounced. It is shown that the current design formula is conservative for anchors with large heads. A correction factor is proposed to account for the effect of the size of the headed stud and to improve design formula. Further theoretical, experimental and numerical work is needed to investigate the performance of large single anchors and anchor groups and to verify and improve current design recommendations.

Size effect on the concrete cone pull-out load

In the present paper the failure mechanism and size effect of the concrete cone resistance is reviewed and studied. The influence of material and geometrical parameters on the failure mode and size effect is investigated. In the numerical studies the smeared crack finite element analysis, based on the microplane material model for concrete, was used. Both, experimental and numerical results show that there is a strong size effect on the nominal concrete cone pull-out strength. It is demonstrated that besides the embedment depth the scaling of the head of the stud as well as the scaling of the concrete member influence the nominal strength.

Anchors to Concrete under Tension - a Probabilistic Approach

A stochastic model for single anchors in uncracked concrete under centric tension is proposed. The corresponding limit state functions for concrete cone and steel failure are formulated and their variables defined. By way of an example, a probabilistic analysis for a typical anchor is performed. Furthermore, it is demonstrated that the safety index of an anchor is governed by the stochastic definition of the applied loads.