Bar Anchorage Research Articles

Anchorage of steel bars in concrete by geopolymer paste

This paper presents the bonding strength between the embedded rebar and substrate concrete by using geopolymer paste as the bonding agent. The determination of the suitable mix proportions of geopolymer paste as bonding agent was the main interest. Twelve different mix proportions of geopolymer paste by varying the amount of starting binder materials and alkaline concentration were prepared and tested for compressive and bonding strengths. The tested results indicated that both RHBA and SF incorporating with FA could be used in preparation of geopolymer paste. Mixes with SF gave the higher compressive and bonding strengths while the mixes with RHBA required the longer curing time. The bonding strengths of round bar and geopolymer pastes were slightly higher than that of control concrete (1.05–1.12 times) and there were significantly high in case of deformed bars (1.03–1.60 times). The ratios of bonding strength on the compressive strength were also presented. In comparison with commercial repair materials, the bonding strengths of geopolymer paste were higher than those of epoxies about 1.24–1.81 times. These tested results indicated that the bonding strengths using geopolymer paste were high enough and possibly used as bonding material for repair works. The mixtures containing high SF content and high NaOH concentrations were recommended to enhance both compressive and bonding strengths.

Behaviour of Concrete Beams Reinforced with Hybrid Fiber Reinforced Bars

Due to the linear elastic behaviour of FRP bars, the flexural behaviour of FRP reinforced beams exhibits no ductility as occurs in the steel reinforced structures. In this paper, study of the enhancement of the behaviour of concrete beams reinforced with FRP bars was carried out by testing nine beams reinforced with locally produced hybrid fiber reinforced polymer (HFRP) bars. The used hybrid fibers were aramid–glass and carbon–glass. Some of test specimens were reinforced by FRP bars provided with anchorages along the bar length. Crack patterns, cracking and ultimate loads, and deformation were observed and recorded for all tested beams. The effect of using the hybrid fiber reinforced bars and the bar anchorage system were judged by comparing the behaviour of the tested beams by two reference specimens, one reinforced by GFRP bars and the other one reinforced by traditional steel bars. The comparison revealed that HFRP bars provided with the used bars anchorage played a significant role in enhancing the behaviour of concrete beams reinforced with FRP bars.

Finite Element Analysis of Embedded Parts with Big-Diameter Reinforcing Bar under Shear Force

Nowadays embedded parts which connect steel members with concrete structures have frequently emerged in civil engineering; however the existing design code for embedded parts cannot satisfy the increasing demand of engineering as it was derived from limited experiments. In the paper, a finite element study on embedded parts with big-diameter reinforcing bars under shear force is conducted. The aim of the study was to fully investigate the mechanical performances of embedded parts under shear force using a three-dimensional finite element analysis with the help of a commercial software ANSYS. Cross-section internal force of anchor bar, embedded part deformation, interaction force between anchor bar and concrete, and friction force were investigated in order to well know the system response. The results show that the shear capacity of embedded part obtained from finite element analysis is conservative.

Fiber-reinforced concretes with a high fiber volume fraction — a look in future

Abstract In near future, when the control of the load-bearing capacity of fiber-only-reinforced concrete members will be safely guaranteed, the deletion of the ordinary continuous steel reinforcing bars might be possible. For the time being, it is difficult to change the fiber amount during the casting with today’s techniques. Therefore, the fiber concentration has to be determined by the maximum tensile stress in concrete structural members, resulting in an unnecessary fiber addition in compressed zones. However, if the right amount of fibers could be regulated and added to concrete in real time at the pump outlet, a future vision could be to design and produce a structure by using FEM-controlled equipment. The signals from calculation results could be transmitted to a concrete casting system for addition of a necessary amount of fibers to take care of the actual tensile stresses in the right position in the structure. The casting location could be determined by using a GPS for positioning the pump outlet for targeting the casting location horizontally and a laser vertically. The addition of fibers to concrete at the outlet of a concrete pump and proportioning them there according to the actual needs of the stress situation in a structure, given by a FEM analysis in real time, is a future challenge. The FEM analysis has to be based on material properties of fiber-only-reinforced concrete. This means that the resistance and stiffness of different-strength concrete members with a varying fiber content has to be determined in tests and conveyed to the FEM analysis. The FEM analysis has to be completed before the casting and controlled. Then it can be used as the base for adding a correct amount of fibers to concrete in every part of the structure. Thus, a system for introducing a correct amount of fibers into concrete has to be developed. The fibers have to be added at the outlet of concrete pump. Maybe a system to shotcrete concrete with electronically controlled fiber addition is to be preferred? The target point where the concrete comes to rest into a structure has to be electronically noted and sent to the FEM system. The FEM analysis should then immediately send back the information for the correct amount of fibers at that point. This requires the elaboration of an appropriate signal system, which should not be impossible. An integrated system for the design and production of concrete structures could be developed excluding the heavy and time-consuming work with steel reinforcing bars. The result could be: no evaluation of moments and shear forces from a FEM analysis for determining the bar reinforcement; no bar anchorage requirements and reinforcement detailing; no reinforcement drawings; no reinforcing bars; no heavy work with the reinforcement. Finally, investigations have to be performed concerning the demolition of fiber-reinforced concrete structures and the reuse of the material. The fragments of fiber-reinforced concrete might be sticky and cause problems for nature. The recirculation of material has also to be solved.

SEISMIC RETROFITTING CONNECTION METHOD BY STEEL BRACE WITH ANCHORS

The experimental study on connection method of steel frame with brace is outlined and the structural performance of that is discussed in this paper. The purpose of this study is to develop the new seismic retrofitting system of steel frame with brace.Static loading tests were conducted for a total of five one-bay one-story retrofitted frames with the experimental parameter of connection details between the existing RC frame and the installed steel frame. The results showed that the lateral deformation capacity and the strength of that are controlled by the anchor bars.

Seismic Behavior of Reinforced Concrete Exterior Wide Beam-Column Joints

An experimental and numerical investigation carried out on RC wide beam-column joints when subjected to seismic loads is reported within this paper. The experimental study was conducted by subjecting three full-scale wide exterior beam-column specimens to simulated seismic loads at the Nanyang Technological University of Singapore. Simulations of earthquake loadings were applied on to the specimens via quasistatic load reversals. Seismic performance analysis of the joints were based on the results obtained from the experiment in terms of their general behavior, hysteresis response, and the strain profiles of the longitudinal reinforcement within the specimens. These experimental results were then used to validate a three-dimensional (3D) nonlinear finite-element (FE) model. The behavior of the joints under the influence of critical influencing factors like column axial load, transverse beam, and beam bar anchorage ratio were also analyzed through the parametric studies carried out.

A systematic review of implant‐supported maxillary overdentures after a mean observation period of at least 1 year

The aim of the present systematic review of implant-supported maxillary overdentures was to assess the survival of implants, survival of maxillary overdentures and the condition of surrounding hard and soft tissues after a mean observation period of at least 1 year. MEDLINE (1950-August 2009), EMBASE (1966-August 2009) and CENTRAL (1800-August 2009) were searched to identify eligible studies. Two reviewers independently assessed the articles. Out of 147 primarily selected articles, 31 studies fulfilled the inclusion criteria. A meta-analysis showed an implant survival rate (SR) of 98.2% per year in case of six implants and a bar anchorage. In case of four implants and a bar anchorage, the implant SR was 96.3% per person. In case of four implants and a ball anchorage, the implant SR was 95.2% per year. In all three treatment options, the SR of the implants is more than 95%. The studies included reveal that a maxillary overdenture supported by six dental implants, which are connected with a bar, is the most successful treatment regarding survival of both the implants and overdenture. Second in line is the treatment option with four implants and a bar. The treatment option with four or less implants and a ball attachment system is the least successful.

Direct Tension Pullout Bond Test: Experimental Results

Results from 50 bond tests conducted using the so-called direct tension pullout specimen type are presented. Anchorages of steel bars with machined deformations were tested so as to enable a targeted study of the effect of rib height and related rib area on bond behavior; tests were conducted with or without the combined presence of external confinement over the embedded length. The novel specimen form presented in the paper was designed to simulate the state of stress arising in usual bar anchorages in the tension zones of flexural members (where both cover concrete and bar are stressed in tension). This development was motivated by the need to eliminate spurious influences of the test setup on specimen behavior, which are known to interfere with bond mechanics in conventional bond tests leading to unconservative estimates of bond strength and misleading interpretations as to the true parametric dependencies of the bond problem. Additional parameters studied in the experimental program were the development length, the cover thickness, the effect of confinement, and the tensile strength of concrete. Data reduction (local bond strength and slip estimates) was possible by fitting the exact solution of the differential equations describing the state of stress along the anchorage to the test measurements, while accounting for important phenomena such as yield penetration or debonding, and bond plastification. Next, the obtained values for local bond strength were used for calibration of the frictional analog for bond strength (a Mohr-Coulomb failure criterion). Milestone values for bond and slip were estimated with reference to the code limit-state model for bond.

Strain Measurement Using Embedded Fiber Bragg Grating Sensors Inside an Anchored Carbon Fiber Polymer Reinforcement Prestressing Rod for Structural Monitoring

Results are reported from a study carried out using a series of Bragg grating-based optical fiber sensors written into a very short length (60 mm) optical fiber network and integrated into carbon fiber polymer reinforcement (CFPR) rod. Such rods are used as reinforcements in concrete structures and in tests were subjected to strain through a series of cycles of pulling tests, with applied forces of up to 30 kN. The results show that effective strain measurements can be obtained from the different sensors mounted along the rod. Additionally, the tests show that close agreement with the results obtained from the calibrated force applied by the pulling machine and from a conventional resistive strain gauge mounted on the rod itself is obtained. Calculations from strain to shear stress show a relatively uniform stress distribution along the bar anchor used. The results give confidence to results from various methods of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> monitoring of strains on such CFRP rods when used in different engineering structures.

Seismic Retrofit of Reinforced Concrete Building Structures with Prestressed Braces

A prestressed concrete brace system was first proposed in 2001 to dramatically simplify seismic strengthening procedures. Since the proposed system does not necessitate any steel bar anchorage, the construction period is shorter and the construction cost is lower. The system has been revised in terms of its aesthetics, materials, and construction methods since the first proposal of the system. This paper introduces a series of prestressed concrete brace system and discusses their interesting features. Design procedures and some examples are also introduced with experimental results.

Effect of Construction Details on the Bond Performance of NSM FRP Bars in Concrete

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement has proven effective for strengthening reinforced concrete structures and is gaining increasing attention. The NSM reinforcement is installed by grooving the surface of the member to be strengthened and embedding FRP bars or strips in the grooves with an appropriate binder. This paper reports the results of an investigation designed to evaluate the influence of some construction parameters on the bond performance of NSM FRP round bars. These parameters include the groove depth and width-to-depth ratio, the groove distance from the edge of the member, the mechanical properties of the groove-filling epoxy, and the use of transverse FRP sheets for confinement of the joint. During the tests, conducted with a direct shear setup, the loaded-end and free-end slips and the strain distributions along the reinforcement and in the transverse plane were monitored. Tests were conducted on both short and long NSM bar anchorages. Results are here reported and analyzed to determine the effect of the test variables on local bond-slip behavior and development capacity. The local bond-slip curves obtained from the tests with short bond length are modelled analytically and used to predict the capacity of the specimens having long bond length and the same other test variables.

Safety evaluation and the static-dynamic coupling analysis of counter-arched slab in plunge pool

The stability of plunge pool slab of drainage structure is crucial to energy dissipation, but the working conditions of counter-arched slab are very complex and its stress procedure is considerably nonlinear and coupling. Therefore, a nonlinear static and dynamic coupling method to analyze the counter-arched slab configuration is put forward, which can reflect the coupling of dynamic loads, slab, anchor bars, groundwork and abutment as well as the dynamic procedure of instability. Various nonlinear factors and static-dynamic coupling are taken into consideration, and the working conditions, stress mechanism, dynamic instability procedure and influential instability factors are revealed. The proposed method thus provides a comprehensive safety evaluation method of plunge pool, which further provides an important theoretical basis for engineering design of counter-arched slab in plunge pool.

Evaluation of Load Transfer and Strut Strength of Deep Beams with Short Longitudinal Bar Anchorages

This paper examines the behavior of struts and nodes in deep beams fabricated using short longitudinal bar anchorages. Laboratory tests were conducted of 12 deep beams in which the longitudinal reinforcement was anchored into the support using short straight bar anchorages. The shortest anchorage lengths provided were below 50% of those required by ACI 318-08 Chapter 12 provisions. Four different specimen groups were constructed using three different shear span-depth ratios (a/d) and two longitudinal bar sizes. Most of the beams failed by strut crushing after yielding of the main longitudinal reinforcement at midspan. Only those specimens with the shortest anchorage length in each group developed concrete splitting failures along the anchorage region. The effect of a/d and anchorage length on strut strength and load transfer mechanism observed in the tests is presented and discussed. Test results indicate that a significant portion of the applied shear force may be transferred through truss action even in beams with low a/d. Short anchorage length affected the load transfer characteristics of the deep beams. These findings can be used in better understanding the merits of different strut-and-tie models for design of deep beams.

Anchorage of Large-Diameter Reinforcing Bars in Ducts

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Cyclic Response of Exterior Beam-Column Joints with Different Anchorage Methods

This paper presents the cyclic response of six exterior beam-column joints with or without eccentricity to evaluate the use of mechanical anchorages in place of hooked bar anchorages. In high seismic zones, the hooked beam bars often cause steel congestion in a joint at building comers. From previous tests of beam-column joints, the use of mechanical anchorages in place of hooked bar anchorages provides a promising solution for steel congestion, but it has not been verified in eccentric beam-column joints. The presented experimental program demonstrates that eccentric beam-column joints with mechanical anchorages can exhibit satisfactory performance and adequate anchorage capacity for a limiting drift ratio. Extending ACI design methods to cover the use of mechanical anchorages for eccentric beam-column joints is an appropriate code modification. Test results also indicate that the cyclic behavior of exterior beam-column joints can be significantly improved by attaching double mechanical devices on each beam bar within the joint.

Bond Tests of Short NSM-FRP and Steel Bar Anchorages

Performance of near-surface mounted (NSM) bars as additional reinforcement in strengthening of existing reinforced-concrete construction largely depends on the development capacity of the bar inside the groove. This is controlled primarily by the surface characteristics of the bar and its interaction with the surrounding groove filler and the cover concrete. In this paper, the bond strength of short NSM-bar anchorages is explored experimentally, using a modified eccentric pullout test specimen designed to alleviate some of the deficiencies associated with bond testing. A total of 45 tests were conducted to study the influence of the most important technological parameters of this upgrading method, namely the groove dimensions, the embedment length, and the surface pattern of the bars. NSM bars were 12 mm diameter rods: CFRP bars used had a sandblasted surface and winding helical lengthwise indentations. Steel bars were either standard deformed bars or smooth reinforcement. The variety of bar type consider...

Numerical models for the dynamic response of submerged floating tunnels under seismic loading

AbstractThe modeling of tethering elements of seabed anchored floating structures is addressed, with particular reference to the so‐called Archimedes Bridge (submerged floating tunnel, SFT) solution for deep water crossing; attention is devoted to the design solution encompassing slender bars as anchor elements. Two numerical tools are proposed: firstly, a geometrically nonlinear finite element (NWB model), developed in previous work, has been refined in order to capture the effect of higher flexural modes of anchor bars. Secondly, a 3D beam element, based on the classical corotational formulation (CR model), has been developed and coded. Both elements are implemented in a numerical procedure for the dynamic time domain step‐by‐step analysis of nonlinear discretized systems; seismic loading is introduced by generating artificial time histories of spatially variable seismic motion. An example of application of the NWB element is shown regarding the behavior of the dynamic model of a complete SFT. The model was subjected to extreme multiple‐support seismic loading. The seismic behavior is here illustrated and commented, especially in light of the effect of higher local vibration modes of the anchor bars. Finally, a comparison between the performances of the two modeling approaches is presented. Both harmonic and seismic excitations are considered in the test; the results justify the use of the simpler NWB approach, especially in the SFT design phase. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Strength and ductility of stiffened thin-walled hollow steel structural stub columns filled with concrete

It is generally expected that inner-welded longitudinal stiffeners can be used to improve the structural performance of thin-walled hollow steel structural stub columns filled with concrete. Thirty-six specimens, including 30 stiffened stub columns and six unstiffened ones, were tested to investigate the improvement of ductile behaviour of such stiffened composite stub columns with various methods. The involved methods include increasing stiffener height, increasing stiffener number on each tube face, using saw-shaped stiffeners, welding binding or anchor bars on stiffeners, and adding steel fibres to concrete. It has been found that adding steel fibres to concrete is the most effective method in enhancing the ductility capacity, while the construction cost and difficulty will not be increased significantly.

Reinforced concrete beam–column joints with crossed inclined bars under cyclic deformations

AbstractThis experimental study investigates the effectiveness of crossed inclined bars (X‐bars) as joint shear reinforcement in exterior reinforced concrete beam–column connections under cyclic deformations. Test results of 20 joint subassemblages with various reinforcement ratios and arrangements including X‐bars in the joint area are presented. The X‐type, non‐conventional reinforcement is examined as the only joint reinforcement and in combination with common stirrups or vertical bars. The experimental results reported herein include full loading cycle curves, energy dissipation values and a categorization of the observed damage modes. Based on the comparisons between the overall hysteretic responses of the tested specimens, it is deduced that joints with X‐bars exhibited enhanced cyclic performance and improved damage mode since a distinct flexural hinge was developed in the beam–joint interface. Further, the combination of crossed inclined bars and stirrups in joint area resulted in enhanced hysteretic response and excellent performance capabilities of the specimens. However, in some specimens with X‐bars as the only joint shear reinforcement, the deformations of the bent anchorage of the beam's bars caused considerable damages at the back of the joint area. Discussion for a potential replacement of the joint stirrups with X‐type reinforcement in some cases of exterior joints is also included. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Monolithic and Cyclic Behavior of Deep Beams Designed Using Strut-and-Tie Models

This paper presents findings from experiments on four simply supported deep beams subjected to monotonic and reversed cyclic loads. The adequacy of using a strut-and-tie model for seismic design also was assessed. Deep beams subjected to monotonic loading were compared with similar beams tested under reversed cyclic loads. Other variables besides the loading regime were the development length of the main flexural reinforcement and the amount of stirrup reinforcement used for confinement of bar anchorage above the supports. Results were examined against design provisions given in Appendix A of ACI 318-05 and in the 1996 Federation Internationale de la Precontrainte Recommendations. The results show that the performance of all 4 beams exceeded expectations in terms of strength, stiffness and deformation capacity, thus verifying the reliability of the strut-and-tie model for structural members subject to either monotonic or reversed cyclic loads. Current provisions for strut-and-tie models appear adequate for seismic design.