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The bond behavior between ultra‐high‐performance fibre‐reinforced concrete (UHPFRC) and steel rebars plays an important role in the load‐bearing capacity and serviceability of structural members. A suitable bond–slip model is essential for predicting the load resistance and deformation capacity of members, after cracking of the UHPFRC. This paper studies the bond strength between ribbed steel bars and the surrounding UHPFRC before and after yielding of the steel reinforcement. To determine the corresponding bond–slip relationship, pull‐out tests, with varying embedment lengths of the reinforcement, namely 2 times and 10 times the rebar diameter, and diameter of reinforcing bars ranging from 10 mm to 16 mm were conducted. The bond stress, strain and slip along the embedment length of the steel rebars were measured by strain gauges and displacement transducers. Based on the test data, a bond stress–slip model was derived before (elastic stage) and after (inelastic stage) yielding of the reinforcement. The slip at the yield point is suggested through theoretical equations. The post‐yield bond–slip model is based on yield bond stress and frictional bond stress. The two‐part model was validated through iterative procedures and is able to predict the applied force, bond stress and strain distribution along the reinforcing bar. A comparison between the test data and analytical results demonstrates a good predictive capacity on the bond behavior of reinforcement in UHPFRC both before and after yielding of the reinforcement. [ABSTRACT FROM AUTHOR]

Accelerated bridge construction, with innovative connection details and construction technologies, has been extensively investigated and put into practical application for years. Nowadays, there are three commonly used connection methods of accelerated bridge construction technology, namely, lap‐spliced connection, sleeve connection, and socket connection. Due to the convenience of construction and lower requirements of construction accuracy, the socket connection is more suitable for reconstruction and expansion projects of traffic infrastructure, which could minimize the impact on traffic and accelerate construction progress. According to the structural characteristics of the socket connection, there are some design parameters that may significantly affect the seismic resistance of the structure, such as socket embedment length, fabrication of the shear key, and grouting material strength. To fully study the influence of different design parameters on structural performance, an experiment was carried out to investigate the seismic behavior of the precast pier‐footing socket connections with different design parameters. Five 1:2 scale reinforced concrete precast pier‐footing socket connection specimens with different design parameters were designed and tested under cyclically reversed horizontal loads. The development of hysteresis features, failure mode, load‐bearing capacity, stiffness degradation, structural ductility, energy dissipation capacity, and residual drift are analyzed to reveal the influence of the different design parameters on the seismic behavior of the precast pier‐footing socket connection. The seismic behavior of the precast pier‐footing socket connection was significantly influenced by the embedment length especially when the embedment length was less than 1.0bc. When the embedment length was 0.5bc, the failure mode changed from bending damage at the bottom of the precast pier to the anchorage failure of the precast pier‐footing socket connection. When the embedment length was 1.5bc, the fabrication of the shear key had limited improvement on the seismic performance of the specimen, while reducing the ductility of the specimen. When the embedment length was 1.0bc, the grouting material with a strength grade of C60 could be used in the socket connection between the precast pier and footing. The research presented in this paper provides some design suggestions and a technical basis for evaluating the seismic behavior of precast pier‐footing structures with socket connection. [ABSTRACT FROM AUTHOR]

Transfer columns are the essential elements in a building frame structure wherein some stories are constructed with steel-reinforced concrete (RC) columns and others with RC columns. The stories with transfer columns may suffer severe damage due to sudden changes in strength and stiffness along their heights. This study investigates the structural behavior of transfer columns subjected to axial compressive loading and bending about major/minor axes. Forty transfer columns are modeled in the finite element software ABAQUS to study their failure mechanism, lateral bearing capacity, and ductility ratios. The parameters investigated are the levels of embedment length of the structural steel, and the detailing of lateral ties and the base plate at the truncation zone in the column. It is concluded that hybrid columns have higher lateral strengths than the RC columns but exhibit limited ductility due to the sudden shear failure. The specimen with structural steel extended by 50–60% of clear column height exhibited improved ductility. The precipitous failure of the transfer column is alleviated with the provision of a base plate and anchor bolts at the end of the structural steel section. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Grouted Sleeve Connections (GSC) play an important role in assembly of structural members for precast concrete structures. With many experimental work and parametric study have been done on the tension load-slip behavior of GSC, the mechanical behavior for the tension load-slip responses of GSC should also be studied and explained. The failure modes for GSC in tensile tests with different material properties are firstly analyzed here by investigations on 326 GSC specimens. To study the mechanism of the failure modes, a partial-interaction numerical model is introduced to simulate the load-slip responses of GSC with provided bond-slip characteristics. The different boundary conditions for long and short embedment lengths are described respectively. More than 400 data points in load-slip responses are collected from tensile tests of GSC. The verification between theoretical results with test results shows good agreement. Hence, with the partial-interaction numerical model, the corresponding GSC load-slip responses could be obtained by given material and dimensional properties. Furthermore, parametric study shows that load-slip responses of GSC in tensile behavior change with embedment lengths of reinforcing bars. The CT scan results also show that embedment lengths for reinforcement are suggested to be longer than the designed size by considering the original defects of the sleeves and the eccentricity of reinforcement in construction.

Basalt fibers have been adopted as reinforcements to improve mechanical performance of concrete materials and structures due to their excellent corrosion resistance, affordable cost, and environmental-friendly nature. While the reinforcing efficiency is significantly dependent on fiber-matrix interfacial properties, there is a lack of studies focusing on the bonding behavior of basalt fibers in the mortar matrix. In this paper, a series of experiments were carried out to investigate the characteristics of single basalt fiber pulled out from the mortar matrix. Three embedment lengths and three types of mortar strength were considered. As references, the pull-out behavior of single polyvinyl alcohol (PVA) fiber and glass fiber in mortar matrix were also tested for comparison. Results from the pull-out test revealed that the average bonding strength is more effective than the equivalent shear bonding strength to illustrate the interfacial bond behavior of single basalt fiber in mortar matrix, which can be improved by either longer embedment length or the stronger mortar matrix. Finally, the tensile and compressive strengths of basalt/PVA/glass fiber-reinforced concrete (FRC) were measured to investigate the influence of interfacial shear bonding strengths. It was shown that, while PVA fiber developed the highest shear bonding strength with mortar, the basalt fiber exhibited the best reinforcing efficiency of FRC.

Important aspects of foundation design include developing an understanding of the behaviour of enlarged base piles and aiming to predict their capacities when subjected to uplift loads. On single enlarged base piles implanted in cohesionless soil and subjected to pure tension loading, model experiments have been done. In a steel soil tank, the tests were carried out on straight-shafted vertical steel piles with an outside diameter (Do) of 25mm and inner diameter (Di) of 19mm, base diameter (Db) of 50mm and base angle (θ) of (45◦). The embedment length-to-base diameter ratios (L/Db) of the studied piles are 5, 6, 8, and 12. The relative density of 30%, 50%, and 80% are used to prepare the sand bed. The effect of pile embedment depth and relative soil density on the uplift loads is examined. The investigation showed that the behaviour of single enlarged base piles under uplift loading is mostly determined by the ratio of pile embedment length to base diameter and soil parameters. Using the base at the end of piles significantly increases their uplift capacity, according to the study's findings.

Three-dimensional concrete printing (3DCP) faces challenges in determining and ensuring adequate bond strength between reinforcement and printed concrete. Traditional methods for predicting bond performance are merely deterministic without considering potential uncertainty, which would lead to risks for structural safety. To address this issue, this paper develops a trustworthy machine learning based prediction model for bond strength in reinforced printed concrete (RPC) structures using Natural Gradient Boosting algorithm. This developed model provides both scalar bond strength predictions and corresponding standard deviations, and in the test, it achieved a 94.5% safety rate and outperformed empirical formulas and deterministic approaches. Instructive guidance can be offered for structural engineers and designers in determining reinforcement embedment lengths for 3D-printed concrete during constructions. This probabilistic prediction approach can further enhance the safety and efficiency of digitally fabricated concrete structures, potentially extending its application to other critical parameters in printed concrete. • A probabilistic machine learning (ML) based prediction model for bond strength between reinforcement and printed concrete. • Higher safety rate by proposed model in comparison with previous ones. • A trustworthy approach for optimal embedment length design in printed concrete. • Ensuring safety rather than statistical indexes is more critical for applying ML. [ABSTRACT FROM AUTHOR]

There are many factors that may affect the concrete-strand and concrete-duct bond behavior in post-tensioned (PT) concrete slabs and beams. The importance of bond strength is to ensure a proper transfer of stresses from strands and ducts to the surrounding concrete. This research focused on bonded post-tensioned (PT) concrete elements, which includes the use of grout and ducts to provide the link between the strand and the concrete. The strength of the grout, the type and geometry of the ducts, and the embedment length of both strands and ducts were investigated through an experimental testing program to disclose the average interface shear stress within the embedded length of PT elements. This work helped in a better understanding of the bond behavior and the corresponding related parameters involved in the design process.

Laboratory pull-out tests were conducted on the following rock bolts and cable bolts: steel rebars, smooth steel bars, fiberglass reinforced polymer threaded bolts, flexible cable bolts, IR5/IN special cable bolts and Mini-cage cable bolts. The diameter of the tested bolts was between 16 mm and 26 mm. The bolts were grouted in a sandstone sample using resin or cement grouts. The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample. In most tests, the rate of displacement was about 0.02 mm/s. The tests were performed using a pull-out bench that allows testing a wide range of parameters. This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response (rock bolts and cable bolts). It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole, which cannot be neglected when the test results are used to assess the bolt-grout or the grout–rock interface.

The embedment length influences the adhesion between the cast iron material and the concrete. The concrete's compression strength also contributes to an increase in bond strength. Therefore, this research aims to determine the maximum pullout force on each variation of the anchor and the optimal embedment length. A gauge is modeled as a rod-type with a diameter of 16 mm, and the embedment lengths used are 5D, 10D, and 15D, while the compressive strengths include fc’ 20, 30, 40, 50, and 60 MPa. Furthermore, a finite element-based application was utilized with the ANSYS Workbench student version. The result showed that the concrete with strengths of 20, 30, 40, 50, and 60 MPa has maximum pullout forces of 27.011, 53.536, 68.657, 68.970, and 84.407 kN, respectively at an embedment length of 15D. It was observed that the failure pattern obtained starts from the defect in the concrete cone and ends with the breakage of reinforcement or steel failure at each variation of concrete strength. A combination of two non-parametric techniques was used in this research, which includes Kruskal Wallis and U-Mann Whitney test. The first technique revealed that the chi-square value for strengths 20, 40, 50, and 60 MPa is 9.486, while that of 30 MPa is 9.881. The second test employed showed a significance value below 0.05. In conclusion, the embedment length affected the value of pullout force, and 15D was the optimum embedment length for each variation of concrete strength. The enhancement in tensile strength increases with the strength of the concrete.

This comprehensive experimental study aimed to determine the bond performance of basalt fiber reinforced polymer (BFRP) bars in geopolymer concrete (GC). The study examined the bond performance of BFRP bars and GC by considering several parameters, including bar diameters of 8, 10, and 12 mm, embedment lengths of 4, 8, and 12 db mm (where db is the diameter of the bar), concrete covers of 20, 40, and 70 mm and compressive strengths of 21.7 and 34.4 MPa. The study also compared the effect of the bar surface and bar type on GC bond performance. Eventually, the results were compared with ordinary concrete (OC). The obtained results indicated that an increase in the BFRP bar diameter results in a decrease in the average bond stress. Similarly, an increase in the length of the bond leads to a reduction in the bond stress. The specimen possessing a short embedment length failed due to bar pullout, while the specimens with a longer embedment length failed as a result of concrete splitting. The outcomes also showed that the strength of bond increases with an increase in compressive strength and cover thickness. Furthermore, the results also indicated that BFRP-reinforced GC has comparable bond performance to steel-reinforced GC and BFRP-reinforced OC and performed better than OC. Last, Comparisons between the existing bond-slip models were offered to demonstrate the best bond stress-slip model for FRP bars and GC for ascending branch up to ultimate bond stress of the bond slip curves and for whole curves. [ABSTRACT FROM AUTHOR]

One of the major aspects of retrofitting or strengthening of existing concrete structures is to install rebars using chemical adhesives. In a view to lighten the disturbance of existing structures by reducing the number of holes, high strength rebars (80 grade; nominal yield strength of 550 MPa) are more preferable for repairing and strengthening structural components. Here, a total of 108 specimens were prepared to evaluate the performance of post-installed high strength deformed rebar (PIHSDR) in concrete using pull-out tests. Test parameters included concrete compressive strength (fc' ), rebar diameter, embedment length of rebar into concrete and concrete cover to rebar diameter ratio (c/db) to investigate the bond behaviors of PIHSDR at the epoxy-concrete interface. Bond stress-slip relationships for PIHSDR were obtained, investigated, and hence compared with previous research and available codes. It was observed that most of the specimens showed concrete rapture, splitting, or rebar rapture failure and none of them showed pull-out failure which indicates that the epoxy resins are very much effective as bonding chemicals for retrofitting concrete structures in the steel-concrete interface. Besides, regression analyses were performed using the experimental data to obtain a closed-form equation for predicting the bond strength for PIHSDR. The predicted bond strengths were observed close to the actual test data with a high coefficient of determination (R2 = 0.99) and very low root mean square error (0.078).

Bond strength of steel reinforcement embedded in ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) plays a vital role in the post‐cracking behavior of reinforced UHPFRC members in flexure or tension. This paper presents an analytical study on the bond strength of steel reinforcement in UHPFRC. Three different bond‐slip models, namely the modified fib model, Marchand model and the proposed model are compared in the analytical method and explicit equations are also proposed. Comparisons with test data suggest that the proposed model and explicit equations can evaluate the bond‐slip behavior of reinforcement with good accuracy. Marchand model shows similar predictions of bond‐slip behavior to the proposed model at different load levels, whereas the modified fib model is accurate only when the reinforcement nearly yields in tension. The embedment length required for embedded reinforcement to develop its yield and ultimate strengths can also be calculated from the analytical method and explicit equations. [ABSTRACT FROM AUTHOR]

As a novel civil engineering material, Engineered Cementitious Composite (ECC) has attracted more and more attention due to its strain-hardening characteristics, good post-cracking resistance and its unique properties. Bonding between Engineered Cementitious Composite (ECC) and rebar has a great effect on the mechanical behavior of structural members. In this paper, direct pull-out tests were conducted to understand the bond behavior between the ECC and rebar. The test parameters included rebar diameter and type, cover layer thickness, embedment length and fiber volume content. Bond-slip curves, failure and cracking pattern and bond strength were compared and discussed. The test results indicated that the bond strength decreased with the increase of embedded length. Through regression analysis with the test data, the functional relationships between bond strength and cover layer thickness and rebar diameter were fitted well. According to the positive and negative signs of the fitting parameters m and n, the relationship between the bond strength and the cover layer thickness and the rebar diameter could be determined. The bond strength increased obviously with the increase of fiber content. When the fiber volume content was 1, 1.5 and 2%, the bond strength of these specimens were 1.5, 2.5 and 3.1 times that of specimens without polyvinyl alcohol (PVA) fiber.

Rock bolts are one of the main measures used to reinforce unstable blocks in a rock mass. The embedment length of fully grouted bolts in the stable and competent rock stratum behind the unstable rock blocks is an important parameter in determining overall bolt length. It is required that the bolt section in the stable stratum must be longer than the critical embedment length to ensure the bolt will not slip when loaded. Several series of pull tests were carried out on fully grouted rebar bolts to evaluate the pull-out mechanics of the bolts. Bolt specimens with different embedment lengths and water/cement ratios were installed in either a concrete block of one cubic meter or in steel cylinders. Load displacement was recorded during testing. For some of the bolts loaded beyond the yield load, permanent plastic steel deformation was also recorded. Based on the test results, three types of failure mechanisms were identified, corresponding to three loading conditions: (1) pull-out below the yield strength of the bolt steel; (2) pull-out between the yield and ultimate loads, that is, during strain hardening of the steel; and (3) steel failure at the ultimate load. For failure mechanisms 2 and 3, it was found that the critical embedment length of the bolt included three components: an elastic deformation length, a plastic deformation length and a completely debonded length due to the formation of a failure cone at the borehole collar. [ABSTRACT FROM AUTHOR]

The monopile is the most common form of foundation employed in offshore wind turbines. These foundations are subjected to millions of repeated load cycles, owing to wind and wave action. In this study, a series of six cyclic lateral load tests and two monotonic tests were performed on an aluminum model pipe pile with an outer diameter of 63.5 mm and a wall thickness of 2.5 mm. A model monopile was embedded in medium dense sand (Dr = 55%) and subjected to asymmetric two-way cyclic loading. From the experimental investigations, the effects of embedded length and the asymmetric two-way cyclic loads on the lateral pile head displacements and the cyclic secant stiffness of the soil–pile system were studied. Linear regression analysis was also performed to fit the conventional degradation parameters using the minimum number of critical constraints, which included the loading conditions and the flexibility parameters of the soil–pile system. From the test results, it was observed that asymmetric two-way loading causes a reversal of accumulated displacement for a pile embedded at a greater depth (L > 1.91T) under relatively lower amplitudes (ζb < 0.37). The cyclic secant stiffness was observed to increase at a relatively constant rate (Aκ) with the logarithm of the number of cycles. The study also revealed that the magnitude of initial cyclic secant stiffness, in comparison with the monotonic stiffness, exhibited a critical drop near the specific load character, ζc = −0.38. [ABSTRACT FROM AUTHOR]

The effect of rust of the reinforcement bars on the bond and slip behavior between the rebars and the surrounding concrete is still under research judgement. This paper, investigated the effect of ranges of rebar rusting (0, 30-50% and 70-90%) of the limits of losing in mass that specified in the ASTM standard (6% of bar nominal mass) combined with other main parameters that affect the bond and slip behavior. A number of 72 pullout prepared specimens were tested. The studied parameters were using normal and high strength concrete (31 MPa and 76 MPa), different bars diameters (12, 16 and 25 mm), the change of embedment length (150 and 300 mm) and the using of bond epoxy coating for embedded length of reinforcing bars. The results showed that the rust within certain amount of permissible losing of mass (about 50%) led to increase the bond strength and decrease the slip between reinforcement bars and concrete. However, increasing rusting above 50% but within the permissible losing in mass would slightly decrease the bond strength and increase the slip comparing with zero rusting case for all tested bar sizes with and without using the bond improvement factors. The main recommendation of the study is to use the same criterion of acceptance of losing in mass specified by ASTM as the acceptance criterion of the amount of rust in the reinforcement bars and using one of the studied improvement factors when the rust amount exceed 50% of the permissible limit of losing in mass.

Direct pull-out method was conducted to explore the bond stress-slip response of ribbed basalt fiber reinforced polymer (BFRP) bars embedded in ecological high ductility cementitious composites (Eco-HDCCs). The effects of the embedment length and cover thickness on the bond properties between Eco-HDCCs and the bars were described. Results indicate that the failure characteristics of the specimens depend on the embedment length and cover thickness of the BFRP bars. As the embedment lengths of the bars increase, the ultimate bond stress decreases while the ultimate slip increases. Besides, both the ultimate bond stress and ultimate slip show an increasing trend if the specimen has a cover thickness of less than 45 mm, while the increasing trend is slower if the specimen has a cover thickness of more than 45 mm. In addition, the strain of the specimen surface depends on the cover thickness, and the strain increases when the cover thickness is in a range of15 mm–35 mm. Moreover, certain embedment lengths and cover thicknesses of the BFRP bars are recommended in the structural design of bridge deck link slabs. The bond stress-slip relationship models of the BFRP bars in Eco-HDCCs are proposed based on the test results. [ABSTRACT FROM AUTHOR]

Installing reinforcement piles is an effective method to mitigate ground movement in liquefied soils. In this study, the effectiveness of the pile-reinforcement method is evaluated using an advanced finite element program OpenSeesPL. Parametric studies are conducted to investigate key parameters in the mitigation model, including pile area replacement ratio, pile diameters and pile-embedment length. The effectiveness of pile reinforcement to reduce large flow deformation in the liquefied ground is significantly influenced by the pileembedment condition. It is recommended the embedment length is at least 1 m or 2 m if the underlying soil is a dense or a medium sand. [ABSTRACT FROM AUTHOR]

Laboratory pull-out tests were conducted on the following rock bolts and cable bolts: steel rebars, smooth steel bars, fiberglass reinforced polymer threaded bolts, flexible cable bolts, IR5/IN special cable bolts and Mini-cage cable bolts. The diameter of the tested bolts was between 16 mm and 26 mm. The bolts were grouted in a sandstone sample using resin or cement grouts. The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample. In most tests, the rate of displacement was about 0.02 mm/s. The tests were performed using a pull-out bench that allows testing a wide range of parameters. This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response (rock bolts and cable bolts). It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole, which cannot be neglected when the test results are used to assess the bolt-grout or the grout–rock interface.

• A new CFFT beam-column connection is investigated experimentally and analytically. • The experimental optimal embedded depth is two times the depth of the CFFT beam. • The flexural capacity of CFFT and failure mode were estimated using design equations. • Bond-stress distribution approach is proposed to estimate the optimal embedded depth. • The calculated optimal embedded depth was in a good agreement with the experimental. Researchers have extensively investigated the behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) as beams or columns individually, while the beam-column connections of such elements remain to be investigated. The current study is focused at developing and investigating a simple and practical CFFT beam-column connection. The proposed connection is made of a steel connection to connect the CFFT beam to the CFFT column. The steel connection is attached to the CFFT beam using a high-performance epoxy cement-grout between the HSS tubing and the CFFT beam. The steel connection is fixed to the CFFT columns using eight high-strength bolts. Four different lengths of the steel connection are tested to study the required embedment length of the CFFT beams inside the HSS tubing. The experimental results show that the optimal embedment length required to induce flexural failure of the CFFT beam is two times the depth of the CFFT beam (i.e. FRP tube depth). Analytical equations are developed to calculate the flexural capacity of the CFFT beam and estimate the optimal embedment length required to achieve its nominal flexural capacity. [ABSTRACT FROM AUTHOR]

Given that current code provisions do not include a detailed design method for either precast or monolithic concrete walls with steel coupling beams, experimental and analytical studies of precast concrete (PC) wall-steel coupling beam systems were carried out. For the experimental part, large-scale cyclic tests of PC wallsteel beam connection subassemblies were performed with a test parameter of reinforcement details in the PC wall and all the same other design parameters such as the embedment length of steel section in the PC wall and the size and end connection details of the steel coupling beam. The overall design methodology for the said systems was first discussed; the seismic behavior of each test specimen with different reinforcement details was investigated; and using the test results and analytical methods, adequate seismic details were finally proposed. The test results indicate that the reinforcement details in the PC wall had a substantial effect on the seismic behavior of the tested specimens, and that the suggested reinforcement details performed very well under reversed cyclic inelastic deformations. [ABSTRACT FROM AUTHOR]

Abstract Ultra-high-strength concrete (UHSC) has attracted attention from engineers because of its great capability on reducing the size of reinforced concrete columns. However, the bond performance of steel rebar embedded in UHSC has not been examined enough yet, although it is a fundamental information for structural design. So, this study comprehensively investigates the bond performance of deformed steel rebar embedded in high-strength concrete (HSC), very-high-strength concrete (VHSC), and UHSC with compressive strengths ranging from 80 to 180 MPa. Different bar diameters (12.7, 15.9, and 19.1 mm), embedment lengths (0.5, 1.0, and 1.5 × bar diameter), cover depths (1, 2, and 3 × bar diameter and center), steel fiber volume fractions (0, 0.5, 1.0, and 1.5%), and yield strengths of steel rebar (normal-strength vs. high-strength) were all considered. Test results indicate that the average bond strength increased significantly with an increase in the compressive strength of the concrete and decreased slightly with an increase in the bar diameter. Average bond strengths of steel rebars in HSC, VHSC, and UHSC were all increased by increasing the embedment length. The cover depth marginally influenced the bond strength when pullout failure was generated, and it significantly increased the bond strength when splitting failure occurred. The incorporation of steel fibers most effectively increased the bond strength in the UHSC mixture, compared with the HSC and VHSC mixtures. Lastly, the widely used prediction models for average bond strength were not accurate for concrete with a compressive strength greater than 80 MPa; thus, a new, appropriate model needs to be proposed in the near future. [ABSTRACT FROM AUTHOR]

Copyright of Tikrit Journal of Engineering Sciences is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For using amorphous steel fibers (ASF) in Portland cement composites, the performance of ASF was evaluated by a pullout test and compared to that of a hooked-end steel fiber (HSF). The embedment length of the fiber (5.0, 8.0, and 12.5 mm), compressive strength of the mortar, and number of fibers were considered the test variables. The results showed that a single ASF had a greater maximum applied load ( P max ) than a single HSF; however, at a mortar compressive strength of 30–42 MPa, its bond strength ( τ max ) and pullout energy ( E f ) decreased by 40.9–55.8% and 16.9–79.7%, respectively, compared to those of a single HSF. Furthermore, in the pullout failure mode, the E f of 4 ASFs, which have a volume fraction equivalent to a single HSF, was 2.10–3.04 times higher than that of a single HSF. Based on the E f of ASFs, an embedment length of 5–8 mm is recommended to provide the most effective ASF reinforcement effect to a mortar with a compressive strength of up to 40 MPa. [ABSTRACT FROM AUTHOR]

The single fibre pull-out response of macro synthetic fibre from concrete matrix has been investigated and reported in this study. Particular attention has been given to the response of the interfacial shear resistance between the matrix and fibre to loading rate at different fibre embedment length. One mix design and one fibre type have been used throughout the experiment while four orders of magnitude of loading rate and three embedment lengths are the variables evaluated. The effect of loading rate on the tensile strength of the macro synthetic fibre under four order of magnitude of loading rates is also reported. All tests were conducted in a controlled climate room at a temperature of 23 ± 1 °C and a relative humidity of 65 ± 5%. Experimental test results have shown that the ultimate tensile strength of the fibres is dependent on the loading rates. Pull-out behaviour from concrete matrix is shown to be slip softening and sensitive to loading rate and embedment length. All fibres pulled out of the concrete matrix without fracturing. Pull-out load increases as the loading rate and the embedment length increases. [ABSTRACT FROM AUTHOR]

A series of rock bolt pull tests were carried out in the laboratory to determine the critical embedment length of a specific type of fully cement-grouted rebar bolt. The rebar bolt is 20 mm in diameter, and it is widely used in underground excavations in Norway. Three water-cement (w/c) ratios were used in the tests. It was discovered that the critical embedment length of the rock bolts was approximately 25 cm for the water-cement ratio 0.40 (the corresponding uniaxial compressive strength (UCS) of the grout is 37 MPa), 32 cm for the ratio 0.46 (UCS 32 MPa), and 36 cm for the ratio 0.50 (UCS 28 MPa), for the specific type of cement, Rescon zinc rock bolt cement. It was found that the bond strength of the rock bolt is not a constant but is related to the embedment length. The bond strength was linearly proportional to the UCS of the grout. [ABSTRACT FROM AUTHOR]

Flexural bond failure and anchorage failure, which are combined with shear failure at simple supports or near cutoff points, are investigated for bar detailing of positive and negative moment reinforcement in terms of development length and additional embedment length beyond the point of zero moment. The flexural bond requirement for safe bar development and the shear reinforcement necessary for the anchorage forces of cutoff flexural reinforcement at critical sections are drawn by consideration of the bond strength along straight or hook bars and its additional embedment length beyond zero moment. The proposed design equations and failure mode diagrams lead to safe bar detailing of reinforced concrete beams with inherent discontinuities of flexural reinforcement. [ABSTRACT FROM AUTHOR]