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In the present paper, the withdrawal stiffness of axially loaded threaded rods screwed into timber elements is investigated using theoretical, numerical and experimental methods. The theoretical approach is based on the application of classical Volkersen theory on axially loaded connectors. An experimental investigation of withdrawal of threaded rods from glulam elements is presented. The parameters of this investigation are the embedment length and the angle between the rod axis and the grain direction. The theoretical and numerical estimations are compared to the experimental results. [ABSTRACT FROM AUTHOR]

To investigate bond-slip behavior of reinforcement in high volume fly ash concrete (HVFAC), 189 pull-out specimens are studied under monotonic static load in this paper. The main research variables involve the volume of fly ash, the type and diameter of the steel bars and the water-to-cement ratio (w/c). The tensile loading in this study is applied to steel bar, which increases stably by controlling the gradual increase of steel bar's slip until end of the tests. For each specimen, the complete relationship curve to bond stress and slip are collected. Results indicate that the bond strengths of steel bars increased along with the decrease of the w/c ratio and decreased when the diameter of steel bar increased. Other results also show that the type of steel bar has a significant influence on bond and slip behavior and similar bond-slip relationship curves are presented in HVFAC, compared to conventional concrete (CC). To assess the feasibility of existing bond strength models in HVFAC, predictions from the models are compared with experimental results in the study. Based on the analyses and comparative results, a revised ultimate bond strength model and bond-slip relationship model are proposed to evaluate behavior of deformed steel bar in HVFAC. The first model is affected by the volume of fly ash and could evaluate the bond strengths well, the second one could monitor complete bond-slip curve reasonably. In addition, using the above revisions to the bond behaviors of bar in HVFAC, a simple calculation method for the embedment length of deformed steel bar in the concrete is recommended, because it has a stable design safety reserve. [ABSTRACT FROM AUTHOR]

• Twenty-eight unreinforced UHPFRC cold-joint specimens and 16 reinforced UHPFRC cold-joint specimens are tested using a direct tension test setup. • The effects of the interface roughening method, steel fiber content and length, interfacial reinforcement ratio, and embedment length on the tensile behavior of UHPFRC cold joints are evaluated. • The roughening methods using high-pressure water jet and uneven plastic formwork are highly effective for obtaining good bond performance of UHPFRC cold joints. • The steel fibers distributed at the cold joint interface can enhance the tensile strength and toughness of UHPFRC cold joints. Ultra-high-performance fiber-reinforced concrete (UHPFRC) structures comprise connection joints, which are typically the weakest part. Appropriate joint construction can improve the force-transfer performance of UHPFRC structures. In this study, the effects of the interfacial roughening method, steel fiber content and length, interfacial reinforcement ratio, and embedment length on the tensile behavior of UHPFRC cold joints are investigated via direct tension tests. The test results indicate that the roughening methods using high-pressure water jet and uneven plastic formwork significantly improve the bond performance of UHPFRC cold joints. Moreover, the steel fibers in the cold-joint interface enhance the tensile strength and toughness of these joints. The typical failure mode of the unreinforced UHPFRC cold joint is found to be brittle failure. By contrast, the cracking and failure surfaces shift from the cold joints to the UHPFRC matrix when the UHPFRC cold joint is well-reinforced. Furthermore, an increase in the interfacial reinforcement ratio and embedment length improves the ultimate tensile strength of the reinforced UHPFRC cold-joint specimens, whereas the minimum embedment length decreases with the interfacial reinforcement ratio (should be at least 40 mm). In addition, an equation for the minimum embedment length of reinforcing steel rebars is proposed. The proposed method can be applied to determine the effects of the parameters, tensile strengths of the UHPFRC matrix and cold joint interface, reinforcement ratio, and rebar diameter on the tensile behavior of UHPFRC cold joints. [ABSTRACT FROM AUTHOR]

• Bond mechanism of steel fiber was experimented using single fiber pull-out test for crimped, 4Dimensional and 5Dimensional steel fiber. • Thermo-mechanically devulcanized recycled crumb rubber powder was used for preparing concrete to identify the bond mechanism of steel fiber with rubber concrete. • Time-dependent loading technique was adopted for single fiber pull-out test to assess the performance of fiber. • Pull-out strength of 5Dimensional steel fiber was found to improve upon effective chemical treatment of fibers with Zinc Phosphate solution and with the provision of additional hooks. Bond mechanism of various types of steel fiber embedded in normal and high strength concrete prepared without and with rubber particles are typically evaluated using single fiber pull-out test. Three distinct types of steel fiber, i.e., crimped (aspect ratio, l/d = 50 and 100), 4D (Double Hooked) and 5D (Triple Hooked) (l/d = 65) fibers embedded in different matrix strengths (M30, M30RC, M60 and M60RC), (RC-rubber concrete) were utilised. The fibers were pre-coated with Zinc Phosphate (ZnPh) in order to enhance the frictional resistance and bond strength between fiber and concrete which portrayed higher peak load than the un-treated fibers. Two different loading rates were adopted such as 1 mm/min (static loading) and 10 mm/min (dynamic loading) for single fiber pull-out test to examine the rate sensitivity on fiber pull-out for various conditions. Crimped fibers failed due to fiber rupture without attaining complete potential in most of the cases, at both loading rates. The pull-out load of 5D fiber was 1.37 times higher than that of 4D fiber at static loading rate. The dynamic increase factor of 4D and 5D fiber was found to be 1.31 and 1.23 respectively at dynamic loading for normal strength concrete, 1.21 and 1.15 respectively for high strength concrete on considering the effect of treatment of fiber. In the case of lesser embedment length, the fiber pulled off from the concrete matrix easily, especially at higher loading rates and in concrete prepared with addition of rubber particles. Performance of 5D steel fiber was found to be better in terms of P max and average shear stress. [ABSTRACT FROM AUTHOR]

In the present paper, the withdrawal capacity of threaded rods embedded in timber elements is investigated using both theoretical and experimental methods. A theoretical approach based on Volkersen theory, assuming a bi-linear constitutive law is developed. Moreover, an experimental investigation of withdrawal of threaded rods from glulam elements is presented. Results for specimens covering a wide range of varying embedment lengths and rod-to-grain angles are provided. The agreement between theoretical estimations and experimental results is good. A nearly linear relation between embedment length and withdrawal capacity, predicted by the theoretical approach, is validated by the experimental results. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive single fiber pull-out experiment on Spirally Deformed Steel Fibers was performed. • An innovative fully hinged fixture was proposed for direct tension tests of dogbone specimens. • Direct tension tests were conducted on dogbone Spirally Deformed Fiber Reinforced Concrete (SDFRC) specimens. • Spiral fibers showed convincing energy absorption capacity during fiber pull-out. • Spiral fibers bridged the main crack of dogbone samples, even at very low fiber percentages. Recent researches indicate promising characteristics of Engineered Spirally Deformed steel Fiber (SDF) for reinforcing cementitious matrixes. However, the available research includes only limited SDF pull-out tests (mostly vertically aligned fibers) and flexural beam tests on Spirally Deformed Fiber Reinforced Concrete (SDFRC). This paper performed a complete single SDF pull-out and several direct tension tests on dog-bone SDFRC specimens with a proposed fully hinged apparatus to fill the research gaps. Various test parameters were considered in the SDF pull-out study, including matrix strength (20 MPa and 30 MPa) as well as fiber embedment length (10 mm, 15 mm, and 20 mm) and inclination angle (0˚, 15˚, 30˚, 45˚, and 60˚) of the fiber. SDFRC strength (20 MPa and 30 MPa) and fiber volume fraction (0.15 % and 0.25 %) were considered in the direct tension tests of SDFRC. Spiral fibers presented promising energy absorption capacity. Consistent with the outcomes of other fiber pull-out studies, the current study found that the matrix strength positively correlates with peak and post-peak pull-out load, while the fiber embedded length and inclination angle correlated inversely with loads. However, unlike other fully deformed fibers, the inverse correlation between the fiber embedded length and loads is considerably less pronounced. The direct tension tests revealed that such a fiber sustains load bearing even in significant cracks (widths ≥ 15 mm). [ABSTRACT FROM AUTHOR]

The bond behavior of reinforcing bars is an important issue in the design of reinforced concrete structures and the use of fiber reinforced polymer (FRP) rebars is a promising solution to handle the problems of steel reinforcement corrosion. This study investigates the bond characteristics of carbon and aramid FRP (CFRP and AFRP) bars embedded in normal strength concrete. A pullout test was performed on 63 normal strength concrete specimens reinforced with FRP and steel rebars with different embedment lengths and bar diameters. The average bond stress versus slip curve is plotted for all specimens and their failure modes are identified. The effects of the embedment length and diameter of an FRP rebar on its bond strength are examined in this work. The bond strengths obtained from the test results are compared with the predictions by the bond strength equation proposed by Okelo and Yuan (2005), and its validity is evaluated. [ABSTRACT FROM AUTHOR]

The recycling of industrial waste such as bottom ash from furnaces is an important issue in construction industry, since it enables reduction in construction cost and has beneficial effect on the environment. In this study, we have investigated the bond characteristics of steel deformed bars embedded in artificial lightweight aggregate concrete which is manufactured from bottom ash. A pullout test was performed on 144 light-weight aggregate concrete specimens to measure the bond strengths. In this test, the parameters included the compressive strength of the concrete and embedment length of rebar. The pullout load vs. slip responses and modes of failure of the specimens were identified during the test. A bond strength equation for lightweight concrete is formulated by performing a regression analysis on the test results and compared with the predictions by the existing equations such as ACI 408, Orangun's, and Darwin's. The comparison shows that the existing bond strength equations cannot be directly applied to the design of lightweight concrete structures and the proposed equation is able to provide a more accurate estimation of the bond strength of lightweight concrete than the existing equations. [ABSTRACT FROM AUTHOR]

Reverse cyclic load testing was completed involving four prestressed concrete pile specimens embedded into cast-in-place (CIP) reinforced concrete bent caps. The piles used were 18 in. (457 mm) square x 18 ft (5.5 m) long and were plainly embedded into the bent cap to depths of 18, 22, and 26 in. (457, 560, and 660 mm). The tests were conducted to determine the moment capacity and ductility of the connections along with the slipping stress of the strands. Analytical models were created in which the slipping stress of the strands was calculated using the ACI 318-08 equation for development length. In all cases, the connection achieved more moment than expected due to the confining stress produced from the bent cap, which tends to decrease the development length of the strands. A modified equation that accounts for the beneficial effect of concrete confinement due to shrinkage is introduced. [ABSTRACT FROM AUTHOR]

This study was conducted to examine the bond strength of a beam reinforced with a GFRP (Glass Fiber Reinforced Polymer) rebar through a four-point bending test, adopting the British standard. The variables were made to have a bonding length 5 times (5 d), 10 times (10 d), and 15 times (15 d) that of the nominal diameter of a GFRP rebar. This was done to analyze the relationship between the bonding strength and the slip. The results of the test reveal that pull-out failure was dominant in the 5 d and 10d specimens. Both patterns of the pull-out failure and concrete-splitting failure appeared in the 10 d specimen. On the other hand, the 15d specimen showed only concrete-splitting failure at the end of its bonding length. Therefore, it was proven in this study that the available bonding length of GFRP rebar under a bending condition in a static test is over 15 d. Further research should be conducted on this subject, though, particularly a fatigue bending test and an FEM (Finite Element Method) parameter study, and a bonding model must be developed. [ABSTRACT FROM AUTHOR]

Experimental research was performed to evaluate the applicability of headed bars with small heads in exterior beam-column joints. A total of 12 pullout tests were first performed to examine anchorage behavior of headed bars subjected to monotonic and repeated loading, with test variables such as the head size, shape, and headattaching technique. Reversed cyclic tests of two full-scale exterior beam-column joints were subsequently conducted to assess seismic performance. The pullout test results revealed that all types of heads and head-attaching techniques performed almost equally well, while the seismic test results indicated that the joint using small-headed bars showed better seismic performance than the joint using hooked bars in terms of damage extent, joint behavior, lateral drift capacity, and energy dissipation. In particular, the joint with headed bars generally satisfied ACI 374 acceptance criteria. These experimental results demonstrate that small-headed bars perform well with a development length shorter than that needed for hooked bars, and they can be effectively anchored in exterior beam-column joints under inelastic deformation reversals. [ABSTRACT FROM AUTHOR]

The increase in single-fiber pullout strength usually improves tensile strength and toughness of UHPC. An increase in fiber orientation angle (θ) up to 45° to the direction of pullout load was found to enhance the single-fiber pullout strength. However, such increase in predominant θ value along tensile strength specimens led to a reduction in tensile strength of UHPC. In order to elucidate this controversial observation, analytical models combined with experiments were carried out to assess the key factors influencing the tensile properties of UHPC due to variations of fiber orientation. The test parameters involved the evaluation of the effect of θ (0°–60°) and fiber embedment length (l e) of 5 and 10 mm on the single-fiber pullout performance. The influence of fiber orientation on UHPC tensile performance was also investigated by casting tensile strength samples having predominant θ values of 25°, 30°, 40°, and 50° along the tensile loading direction. Test results indicate that the key factors influencing the tensile properties of UHPC included the fiber-matrix bond strength (τ θ), l e , and fiber number in a given cross section (N f). The highest τ θ was obtained at a θ value of 45°. The increase in θ from 0° to 90° led to a consistent reduction in l e and N f. A simplified model that considers these factors was proposed to assess the effect of each factor on UHPC tensile strength. The model indicates that l e had the greatest influence on tensile strength, followed by N f and τ θ. The decrease of predominant θ in tensile strength specimen from 45° to 25° enhanced l e by 65% and N f by 60%, compared to a 7% reduction in τ θ , thus leading to a net increase in tensile strength of UHPC by 60%. [ABSTRACT FROM AUTHOR]

This paper addresses the load-deflection behavior of adhesive and grouted anchors embedded in both plain and steel fiber-reinforced normal- and high-strength concretes. Both 12 and 16 mm-diameter adhesive anchors were tested at embedment depths ranging from 40 to 160 mm, while grouted anchors of 16 mm diameter were tested at 80, 120, and 160 mm embedment depths. A total of 57 anchors (39 adhesive and 18 grouted anchors) were tested under monotonic tension loading. Test results showed that pullout capacities of the anchors were not significantly affected by the addition of steel fibers into the concrete. The ultimate deflection and toughness, however, were greatly improved provided that the anchor failed through concrete breakout. Current design methods (ACI 349-85 and concrete capacity design [CCD]) overpredicted the pullout capacity as governed by concrete failure. The overprediction increased with increasing concrete strength, but slightly decreased with the addition of steel fibers for a given concrete strength. [ABSTRACT FROM AUTHOR]

• 96 samples were tested to investigate the bond behavior of reinforcing bars in UHPC. • The minimum development lengths for different concrete cover were recommended. • A theoretical bond strength model using fiber–matrix discrete concept was proposed. • The proposed model was in good agreement with 343 test data collected from literature. The study provided an experimental and theoretical investigation on the bond behavior of reinforcing bars in ultra-high performance concrete (UHPC) via a series of pullout tests. Test parameters included depth of concrete cover, bar embedment length and bar diameter. Failure mode, crack pattern and load-slip response were recorded and discussed under different test parameters. Test results indicated that inadequate concrete cover depth led to splitting failure while short embedment length resulted in concrete cone failure, corresponding to lower bond strengths. The bond strength increased up to 229.8% and the pullout energy increased 401.4% as the concrete cover depth increased from 0.5 d to 2 d. The development lengths were recommended to be 6 d and 8 d corresponding to the concrete cover depth of 2 d , 1.5 d , respectively. A theoretical bond strength model using fiber–matrix discrete concept was proposed and validated by comparing the calculated values with the test results and 343 test data collected from literature. The average ratios of the calculated results to the test results and collected data were 0.996 and 1.039, with a standard deviation of 0.255 and 0.252. The proposed model established the connection between the meso -scale bond property of fibers and matrix and the macro-scale bond strength of steel bars and UHPC, offering an alternative perspective in understanding the bond performance of steel bars in UHPC. [ABSTRACT FROM AUTHOR]

• A novel beam-column connection in the Precast Prestressed Assembled Structural (PPAS) system frame structure is proposed. • The pull-out behavior of the steel strands in the concrete column is experimentally accessed. • The influence of anchorage form, anchorage position, and embedment length is investigated. • The force transmission mechanism of the steel strand with different anchorage forms in concrete column was revealed. The Precast Prestressed Assembled Structural (PPAS) system frame structure has been gradually applied in building and storage structures. In this building system, the 15.2-mm high-strength steel strands are used as the bottom longitudinal reinforcement of the precast beam, and a certain length of non-prestressed steel strands reserved at the beam ends are anchored into the concrete column to form a novel beam-to-column connection. For a reliable design of the connection joint, the mechanical behavior of this connection should be taken into account. This paper summarized the results obtained in the pull-out tests of the steel strands with different research variables, including anchorage form, anchorage position, and embedment length, and it was found that the use of the steel strand with 90-degree hooked anchorage form in the concrete column significantly affected the pull-out behavior of steel strand, such as failure mode, pull-out load versus slip curve, and ultimate load, etc. In particular, compared to the specimens of steel strands with straight-line form, the specimens having steel strands with 90-degree hooked form shows a 62% increase in ultimate load in average. [ABSTRACT FROM AUTHOR]

• Socketed pier to pile cap can achieve comparable seismic performance as CIP one. • Reduced embedded length (0.5D) is verified reliable under lateral cyclic loading. • Embedment length greatly affects the numerically calculated stress of socket wall. • Minimum embedment length is proposed based on the allowable grouting stress. Socket connections are recommended to connect precast members in accelerated bridge construction (ABC) due to their advantages over other connecting methods. The primary objectives of this study are to evaluate the seismic behavior of socketed piers with different embedment lengths, and explore the minimum embedment length for designing pier-pile cap socket connections. The numerical analysis suggested that the stress distribution of the socket wall was greatly influenced by the embedment length, and proposed a way to estimate the minimum embedment length based on the allowable stress of grouting. Accordingly, specimens were designed and tested under lateral cyclic loading with a constant vertical load. The experimental results showed the seismic behavior of all specimens were comparable. That is, different embedment lengths could reach the same expected flexural failure mode, i.e., the plastic hinge region formed at the bottom of the pier above the pile cap. And the results also verified that the embedment length for socketed piers into pile caps can be reduced due to a different load mechanism as compared to that of a spread footing. Considering the strength degradation of bonding grout for the real bridge practices, the minimum embedment length should be multiplied a safe factor. [ABSTRACT FROM AUTHOR]