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Possible discontinuities in the subsurface have a major impact on the load‐bearing behavior of post‐installed fastenings. For concrete, the behavior of post‐installed anchors and thus their design can be clearly addressed as concrete is assumed as a homogeneous fastening substrate. This is valid except, for example, in the area of building joints and at joints of precast concrete elements, where the formation of structural joints inevitably occurs and which basically correspond to a separation surface. In contrast, rock mass is characterized by the rock type, but is generally also significantly influenced by its discontinuities. These play a decisive role concerning rock mass stability and show a great impact on the load‐bearing capacity of rock, especially for fasteners with a shallow embedment depth. It is to be assumed that the same also applies to separating surfaces in concrete. Furthermore, the question arises as to the non‐destructive preliminary detectability of such weak zones. For carrying out a comparative study under controlled conditions, artificial interfaces of different geometries were generated in concrete in laboratory tests by inserting PTFE layers at different positions of the test member. Pull‐out tests of post‐installed fastening systems were carried out in their vicinity to determine the load transfer as well as the failure mode. It could be shown that discontinuities have a negative effect on pull‐out loads not only in the rock mass, but also in concrete. However, detection of these by means of a rebound hammer was only possible in the rock mass. [ABSTRACT FROM AUTHOR]

This study analyzes how key factors impact friction rock bolt capacity using standard pull-out tests, focusing on 39 mm diameter, 180 cm long split-tube bolts. We investigate bolt performance dependence on rock mass rating (RMR), time after installation, schistosity orientation, surface roughness, and installation quality. The aim is optimizing bolt design and implementation for enhanced underground stability and safety. Results show RMR strongly exponentially correlates with pull-out resistance; higher quality rock masses increase capacity. Anchorage capacity significantly rises over time, especially for RMR above 70. Increasing angle between bolt axis and rock foliation from 0 to 90° boosts pull-out response. Reducing borehole diameter below bolt diameter grows bolt-ground friction. Empirical models estimate load capacity based on RMR, time, orientation, diameter, roughness and installation quality. These reliably predict bolt performance from site conditions, significantly improving on basic RMR methods. Experiments provide practical friction bolt behavior insights for typical rock masses. The data-driven analysis ensures models are applicable to actual underground scenarios. This enables tailored optimization of bolting configurations and supports. Methodologies presented should improve safety, efficiency and cost-effectiveness of reinforced mining and tunneling. Overall, this study fundamentally furthers friction bolt performance understanding, enabling superior underground support design.

The masonry veneer wall system relies on metal wall ties to connect the outer masonry leaf to the internal frame, ensuring structural stability. In Australia, a masonry veneer wall typically consists of a timber frame that has galvanised wall ties fixed to the side of the timber studs, with a nail or screw, spanned across an air cavity to the external leaf of masonry. This study explores the impact of corrosion on the integrity of these wall ties, emphasising their susceptibility to failure during extreme events. Existing literature highlights tension failure in a veneer wall is the result of nail pull-out from the timber. In the current research, accelerated corrosion of an R2 (Z600) wall tie reveals that tensile strength reduction is due to decreasing tie cross section from corrosion, leading to wall tie fracture rather than nail pull-out. Understanding these failure mechanisms is crucial for building assessment and monitoring strategies for masonry structures, especially in regions prone to extreme wind or seismic activity in combination with corrosion susceptibility, such as coastal environments. [ABSTRACT FROM AUTHOR]

This study explores the bond strength of steel reinforcing bars in normal concrete (NC) and ultra-high-performance concrete (UHPC) with steel fibers, focusing on the behavior of lap-spliced rebars. Key variables such as rebar diameter (D), spacing (s), lap-splice length (L1), and hook length (L2) were evaluated to understand their impact on bond performance. Both NC and UHPC increase in bond strength with greater spacing and lap-splice length, with UHPC demonstrating significantly stronger bond characteristics due to its higher compressive strength. A novel predictive method for calculating bond strength is proposed, offering practical guidance for designing lap-spliced rebars in construction, and includes reduction factors tailored for realistic construction settings. This method achieves an error margin below ±16.5%, providing an accurate approach for practitioners. This rational method incorporates both engineering and economic considerations, particularly valuable for applications in precast concrete structures where enhanced bond performance and durability are essential.

Abstract The factors influencing geogrid–soil interface characteristics are critical design parameters in some geotechnical designs. This study describes pull-out tests performed on gravelly soils commonly encountered in the Xinjiang region and reinforced with two types of geogrids. The factors affecting the geogrid–gravelly soil interface properties are investigated with different experimental loading methods (pull-out velocity, normal stress), geogrid types, and soil particle size distributions and water contents. The ultimate pull-out force increases with the normal stress and pull-out velocity. Furthermore, with increasing coarse particle content and water content, the ultimate pull-out force increases and then decreases sharply. Based on these research results, this paper provides reasonable parameters and recommendations for the design and pull-out testing of reinforced soil in engineering structures. In reinforced soil structure design, the grid depth should be increased appropriately, and the coarse particle content of the overlying soil should be between 30 and 40%. During construction, the gravelly soil should be compacted to the maximum compaction at the optimal water content, and the structure should have a reasonable waterproofing system. According to the calculation results of the interface strength parameters, the uniaxial geogrid–gravelly soil interface has a high cohesive force c sg, which should not be ignored in reinforced soil structure design.

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In this study, the bond-slip behavior between textile reinforced concrete (TRC)-confined concrete and rebars both at ambient temperature and after ISO 834 standard fire was investigated experimentally through pull-out tests. The failure modes, ultimate load, average ultimate bonding stress and energy consumption were obtained and discussed. Effects of rebar diameters (12 mm, 14 mm and 16 mm), bonding lengths (2.5d, 5d and 7.5d) and high-temperature exposure durations (30 min and 60 min) on the bonding behavior between TRC-confined concrete and rebars were examined emphatically. It was observed that the damage modes of specimens changed from pull-out failure at ambient temperature into splitting failure for both TRC-confined specimens and companion unconfined specimens exposed to high temperatures. The results obtained demonstrated that both the ultimate load and the average ultimate bonding stress can be significantly improved by the utilization of TRC jackets after 30 min exposure, and the increment of the average ultimate bonding stress can reach up to 90% as compared to those unconfined specimens. However, the enhancement of TRC jackets became unobvious after 60 min. Finally, based on test results and Prigogine's dissipative structure theory, the energy analysis of bond-slip curves was evaluated to verify the enhancement of TRC jackets quantitatively. [ABSTRACT FROM AUTHOR]

Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior, yet only a few experimental works and analytical models have been reported, most of which are based on the global rock bolt response evaluated in pull-out tests. This paper presents a laboratory experimental setup aiming to capture the rock formation effect, while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level. It is shown that the behavior along the sample itself varies, with certain points exhibiting stress drops with crack formation. Some edge effects related to the kinematic freedom of the grout to dilate are also observed. Regardless, it was found that the mid-level response is quite similar to the average response along the sample. The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations. The paper also offers a plasticity-based hardening load transfer function, representing a ''slice'' of the anchor. The paper describes in detail the development of the model and the calibration/determination of its parameters. The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.

Rebar‐to‐concrete bond is a fundamental aspect of the behavior of reinforced concrete structures. The characterization of the interface response is challenging due to the complexity of the physical phenomena and the large number of factors involved. Locally, the response is characterized by the bond–slip relationship, which is typically obtained experimentally from pull‐out tests with short bonded lengths. The behavior of longer anchorages in structural members differs significantly from short tests as the bond stress distribution is not uniform. In this context, this paper presents the results of a comprehensive research aiming to establish a better relationship between the local bond–slip response from short pull‐out tests and the response of medium‐length anchorages. The results of an experimental program are presented, including the effect of some parameters commonly found in structural applications, such as casting conditions, clear cover, rib geometry, and rib orientation. A local bond–slip relationship for well‐confined conditions is proposed on the basis of the tests performed by the authors and on the examination of a database on short pull‐out tests from the literature. Based on this relationship and some mechanical considerations, the local bond–slip relationship for unconfined conditions can satisfactorily be formulated based on crack‐width measurements from the concrete surface. This can be useful for the assessment of existing structures and can be seen as a step forward in the development of a consistent mechanical model for bond. [ABSTRACT FROM AUTHOR]

Refractory castables, i.e., refractory aggregates and ultra-fine particle mixtures with calcium aluminate cement (CAC) and deflocculants, were created 40 years ago for the metallurgy and petrochemical industries. These materials demonstrate outstanding performance even over 1000 °C. Typically, they have no structural reinforcement, resisting compression stresses because of the combination of temperature and mechanical loads. This study is a part of the research project that develops high-temperature resistance composite material suitable for fire and explosion protection of building structures. However, this application is impossible without structural reinforcement, and the bond performance problem becomes essential under high temperatures. This experimental work conducts pull-out tests of austenitic stainless 304 steel bars and typical structural S500 steel bars embedded in refractory castables after high-temperature treatments. This study includes plain and ribbed bars and considers two castable materials designed with 25 wt% CAC content for 50 MPa compressive strength after drying (typical design) and 100 MPa strength (modified with 2.5 wt% microsilica). This test program includes 115 samples for pull-out tests and 88 specimens for compression. As expected, the tests demonstrated the plain bars' inability to resist the bond stresses already at 400 °C; on the contrary, ribbed bars, even made of structural steel, could ensure a mechanical bond with cement matrix up to 1000 °C. However, only stainless steel bars formed a reliable bond with the high-performance castable, determining a promising object for high-temperature applications. Still, the scatter of the test results did not ensure a reliable bonding model. In addition, the castable strength might not be optimal to ensure maximum bond performance. Thus, the test results clarified the research objectives for further developing the reinforced composite. [ABSTRACT FROM AUTHOR]

In this paper, we address the relatively underexplored topic of the bond behavior between various carbon rebars and high-strength concrete. This research aims to bridge the knowledge gap in understanding how different manufacturing processes and surface profiles of carbon fiber rods influence their bond strength with concrete. Through experimental bond tests comparing different carbon fiber rebars with varied surface profiles and manufacturing methods, we observed that the achievable bond stresses are significantly influenced by these factors. One carbon rebar variant was selected based on preliminary investigations for detailed analysis. Extensive investigations were conducted on the preferred carbon rebar. Factors such as concrete strength, bond length, and testing speed were experimentally explored. The results not only corroborate many findings from traditional reinforced concrete construction but also reveal new phenomena unique to carbon rebars. These insights are crucial for advancing the application of carbon rebars in modern construction, offering a potential solution to challenges faced in conventional concrete construction. [ABSTRACT FROM AUTHOR]

In the last two decades blind‐bolted connections have been developed to allow bolting of open section beams (e.g, I‐beam) to steel hollow section (SHS) columns where access from all sides of the column is not possible. Filling the tubular column with concrete in the vicinity of the beam‐to‐column connection has been shown to improve the anchoring mechanism of the blind‐bolted connection thereby increasing the strength and stiffness of the connection and reducing the column face deformation, however it adversely affects the joint ductility. This study introduces polyurethane foam filled steel tubular columns in combination with a new anchoring arrangement employing hollo‐bolts to develop a novel connection between the SHS columns and open section beams that provides a better combination of stiffness, strength and ductility. To investigate the behaviour of the proposed arrangement, monotonic pull‐out tests of blind bolted T‐stub connections anchored to foam‐filled steel tubular (FFT) and concrete‐filled steel tubular (CFT) columns using holloBolts were conducted. Benchmark tests on unfilled SHS columns were also conducted for comparison. The FFT in conjunction with the proposed anchoring mechanism was shown to provide a good stiffness as the CFT columns, and almost similar ductility to that of the unfilled steel tube blind‐bolted connection. Hence it is concluded that employing foam instead of concrete as an infill leads to favourable combination of strength and ductility, thus rendering FFT an attractive light alternative to CFT sections when ductility of the joint is an important design consideration. [ABSTRACT FROM AUTHOR]

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant. [ABSTRACT FROM AUTHOR]

Forty-five pull-out tests were carried out to investigate the bond behavior between recycled aggregate concrete (RAC) and ultrahigh-strength steel bars (UHSSBs) with spiral grooves. Bond performance influencing factors were taken into account to analyze the ultimate bond stress and slip, bond energy absorption, bond stiffness and residual bond stress, including UHSSB corrosion levels from 0 to 11%, recycled coarse aggregate (RCA) replacement ratios from 0 to 100%, stirrup ratios from 0.51 to 1.03%, UHSSB embedded length from 10d to 20d, concrete cover thickness from 30 to 70 mm, and anti-rust coating. Pull-out failure was observed in all specimens, and the experimental results showed that the bond strength and bond stiffness initially increased when the corrosion level was no more than 1.5% and then decreased with increasing corrosion levels. Corrosion-induced bond degradation decreased with increasing stirrup ratios and concrete cover thickness, and bond strength decreased with increasing embedded length of UHSSB and RCA replacement ratios. The anti-rust coating can effectively prevent UHSSBs from rusting but can lead to a decrease in bond strength by 37.3%. A bond strength model was proposed considering the corrosion levels of UHSSBs and RCA replacement ratios with presented predictions for the bond stress–slip relationship, which provided a reference for engineering design. [ABSTRACT FROM AUTHOR]

In this paper, we address the relatively underexplored topic of the bond behavior between various carbon rebars and high-strength concrete. This research aims to bridge the knowledge gap in understanding how different manufacturing processes and surface profiles of carbon fiber rods influence their bond strength with concrete. Through experimental bond tests comparing different carbon fiber rebars with varied surface profiles and manufacturing methods, we observed that the achievable bond stresses are significantly influenced by these factors. One carbon rebar variant was selected based on preliminary investigations for detailed analysis. Extensive investigations were conducted on the preferred carbon rebar. Factors such as concrete strength, bond length, and testing speed were experimentally explored. The results not only corroborate many findings from traditional reinforced concrete construction but also reveal new phenomena unique to carbon rebars. These insights are crucial for advancing the application of carbon rebars in modern construction, offering a potential solution to challenges faced in conventional concrete construction.

Ribbed bars are known for their enhanced bond to concrete. Their ribs make bar section variable along the axis and the strain profile is variable as well, under any given applied force. Such variable strain profile has not been measured so far, thus the stress profile and its effect on the global behavior of the bar cannot be determined. Though optical fibers are an effective means to measure the strains in structural members, their application to the study of bond behavior is still in its infancy. Such an application is the objective of this research project. Specially manufactured partly smooth and partly ribbed bars with optical fibers were tested in pure tension (bare bars) and in the pullout from concrete to investigate the strain profile variability. In the bare bars, the strain measured in the smooth part was constant (as expected), while in the ribbed part higher strains were measured but no localized effects were detected, and the location of the ribs was not identified. Similar behavior was obtained by 3D finite‐element analysis, which merely yielded slight ups and downs at ribs' locations, with an average strain that is similar to the measured strain. However, in the pull‐out tests, the strains were constant in the unbonded smooth part and exhibited an undulating profile in the bonded ribbed part, where the peaks were related to the locations of the ribs. Such promising results motivate further studies to improve the resolution of the proposed technique. [ABSTRACT FROM AUTHOR]

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant.

This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results. A database was created combining published experimental data with in-house tests. By means of a comprehensive framework, a Coulomb-type failure criterion accounting for friction mobilization was defined. During the elastic phase, in which the interface joint is not yet created, the proposed model provides zero radial displacement, and once the interface joint is created, interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints. The results predicted by the proposed model are in good agreement with experimental results. The model has been implemented in a finite element method (FEM) code and numerical simulations have been performed at the elementary and the structural scales. The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.

Understanding mechanical interactions at the root-soil interface is essential to predict the erosion of vegetated slopes. Recently, the shear strength of vegetatedil under changing hydraulic conditions has been measured and modeled; however, root-soil interfaces have not been investigated under changing hydraulic conditions. This paper proposes (1) a novel pullout apparatus to measure the shear strength at the root-soil interface under changing suction, (2) a Mohr-Coulomb-Vilar (MCV) shear strength model of root-soil interfaces, and (3) a numerical simulation using Node-To-Segment (NTS) approach along with Finite Element Method (FEM). The pullout tests were verified using the numerical simulation, and the results showed that the combination of the MCV model and NTS/FEM approach can accurately predict the shear behavior of root-soil interfaces under changing suction. In addition, we experimentally evaluated the pullout problem of roots and showed that the present method provides reasonably predicts root-pullout problems even when the suction is changed during the pullout process. The current method, therefore, can be used for predicting root-soil interface dynamics under varying suction and soil pressure by only adding two additional parameters of the Vilar model.

• The numerical test of pull-out based on continuous-discontinuous coupling was established. • The deformation coordination law between optical fiber and soil was analyzed. • The deformation coupling performance between fiber and soil was quantified. The application of distributed fiber optic strain sensing technology in soil settlement deformation monitoring is becoming increasingly widespread, and the interface coupling characteristics between fiber optic cables and soil directly affect the accuracy of the monitoring system. This article designs an indoor pull-out experiment of fiber optic cables in soil and studies the effects of cover layer pressure and fiber anchorage diameter on the interface coupling characteristics during the pull-out process. Based on the continuous discrete coupling simulation method, a numerical model for the pull-out test was established consistent with the experiment. Through experimental verification, the pull-out test's numerical results accurately and intuitively reflect the coupling interface between the optical cable and the soil. The results show that increasing the cover layer pressure and anchoring diameter can enhance the optical cable and soil coupling effect. The continuous discrete coupling model method can effectively simulate and analyze the coupling effect between fiber optic cables and soil, providing new means and valuable insights for the practical application of fiber optic monitoring in soil deformation. [ABSTRACT FROM AUTHOR]

The realistic consideration of reusability of a fire effected RC structure or structural member relies on the accurate estimation of post-fire structural capacity. Bond between steel and concrete play a vital part in the structural analysis of RC. This paper presents a study on bond behaviour of RC structural members exposed to fire employing ISO-834 fire scenario and using beam-end test specimens to take into account the realistic boundary conditions of a flexural member. The study is a continuation of the previous work done by authors. The focus of this paper is to understand the residual bond behaviour considering various concrete covers and the presence of transverse reinforcement for various fire durations. Two different fire exposure scenarios are considered, namely one-sided heating, where only the surface with the minimum concrete cover is exposed to fire and three-sided heating, where two side surfaces along with the surface with minimum cover are exposed to fire. The beam-end specimens were exposed to fire for a desired fire exposure duration, followed by a natural cooling to room temperature. An unconfined pull-out test was performed thereafter to obtain residual behaviour. The results show that although concrete cover and presence of transverse reinforcement do have an influence on the absolute values of the residual bond splitting strength after fire, the relative values of bond degradation due to fire are not very strongly influenced by these parameters. • Post-fire bond behavior of reinforcement in concrete is experimentally investigated considering real fire scenarios. • Different concrete cover and transverse reinforcement in the bonded zone are considered. • Modified beam-end specimen is used in the experimental investigations. • Specimens are subjected to ISO834 fire scenarios for different fire exposure durations with one- or three- sided exposure. • Severe reduction in post-fire bond capacity and stiffness is observed for all the investigated cases. [ABSTRACT FROM AUTHOR]

This article presents results of an investigation that focuses on assessing bondline strength of carbon/epoxy fiber reinforced polymeric (CFRP) precured strips embedded in concrete for near‐surface‐mounting (NSM) strengthening applications. In this study, experimental evaluation and nonlinear numerical analysis of CFRP/concrete interfacial bond behavior are investigated. In this study, 15 pull‐out tests were performed on different reinforced concrete (RC) U‐shaped column specimens with different NSM groove configurations to evaluate the effect of groove size, groove depth, and adhesive bondline thickness on overall performance of the CFRP‐NSM system and to identify the optimum groove dimensions. Experimental results indicated that changing groove geometries of the NSM‐FRP reinforcements significantly affect bondline strength and associated mode of failures of NSM‐CFRP system. It was also shown that increasing bondline length lead to an increase in ultimate failure load and CFRP rupture strain. Based on results of this study, NSM materials with lower longitudinal moduli and higher rupture strains (e.g., E‐glass/epoxy or basalt/epoxy), may increase toughness and enhance performance of the NSM strengthening system. [ABSTRACT FROM AUTHOR]

The bond between concrete and fiber-reinforced polymer (FRP) bars is severely degraded when the glass transition temperature of the FRP (set mainly by the polymeric matrix, typically a thermosetting resin) is approached, and therefore long development lengths are required to enable a proper anchorage in cooler zones of FRP–reinforced concrete (RC) members exposed to fire. In spite of the potential of bent bars to shorten such lengths, and thereby improve the fire resistance of FRP–RC members, very few studies have addressed the effects of elevated temperatures on the bond performance of bent FRP reinforcement. This paper presents experimental and numerical investigations concerning the bond behavior of straight and 90°-bent glass-FRP (GFRP) bars at elevated temperatures. Steady-state pull-out tests were first carried out on bent ribbed bars, from 20°C up to 300°C, and the results were compared with those previously obtained from straight bars. The experiments showed that the hook effect provided by the bend and tail lengths of the bars enabled bond-strength increases of between 30% and 90% compared with straight bars. Three-dimensional finite-element models were then developed to: (1) simulate the pull-out tests; and (2) perform design-oriented parametric studies, aimed at assessing the influence of elevated temperatures on the anchorage strength of straight bars with different surface finishes (sand-coated and ribbed), and of 90°-bent ribbed bars with varying tail and straight development lengths. Temperature-dependent local bond stress versus slip laws were implemented in the models in order to describe the bond interaction along the straight and bent lengths of the bars. The models provided a good agreement with the test data, in terms of load versus slip response, and a reduction in pull-out load and bond stiffness with temperature. The findings were that: (1) the adoption of 90°-bent anchorages with appropriate tail lengths is an effective and practical approach for improving the bond strength of GFRP bars at both ambient and elevated temperatures; and (2) at elevated temperatures, to mobilize the tensile strength of GFRP bars, the development lengths of straight and bent bars designed for ambient temperature must be significantly increased. Finally, optimal anchorage lengths are proposed, as a function of temperature, for beam and slab applications. [ABSTRACT FROM AUTHOR]

Due to the combined action of chloride ion corrosion and freeze-thaw cycle, the bonding performance between steel bars and concrete will deteriorate, and even lead to premature failure of structures. In order to analyze the change law of bonding performance between geopolymer concrete and steel bars under the coupling action of freeze-thaw cycle and chloride ion corrosion, the bonding performance between geopolymer concrete and steel bars under the environment was studied by pull-out tests. The influences of the cover thickness of geopolymer concrete, the concentration of salt solution and the number of freeze, thaw cycles on the ultimate bond strength and bond-slip curve of the specimens were analyzed. At the same time, the decaying rule of splitting tensile property of geopolymer concrete in deicer-frosting environment was summarized. The results show that the failure mode of the specimens in deicer-frosting cycles and water-freezing cycle is the same as that of the specimens without freeze-thaw cycle. However, the ultimate bond strength is generally lower than that of the without freezing specimens. After 50 freeze-thaw cycles, the ultimate bond strength of deicer-frosting cycle and water-freezing cycle specimens is about 56% ~ 67% and 80% of that of without freezing specimens. Finally, in order to providing reference for engineering application of concrete structures, a fitting formula for the splitting tensile strength and ultimate bond strength of geopolymer concrete considering the number of freeze, thaw cycles and salt solution concentration is proposed. [ABSTRACT FROM AUTHOR]

This paper focuses on the FE analysis of the mechanical behavior of glued composite fiber-reinforced polymer (FRP) rods into glulam timber, using a 3D-continuum damage mechanics. The application of FRP to the glulam timber beams, despite the fact of limited investigations to date, offers an interesting and economic solution for strengthening in timber construction. In particular, the use of glued-in FRP rods for timber connections instead of steel is of great interest, due to the improved durability of the joint systems compared to their equivalent counterparts made of steel rods. For pull-out tests, the estimation of the mechanical response of glued FRP rods into glulam timber is very complex because of the combination of the three different materials: FRP rods, epoxy resin and glulam timber as well as the complexity of the expected brittle modes of failure of the timber. On the other hand, the existing prescriptive approaches (standard design codes) did not cover all the modes of failure expected within timber material and their predictivity is highly depending on the loading direction and on the rod material. There is, therefore, still a need to establish a general and predictive FE model to simulate accurately and cost-effectively the glued-in rod timber connections. In this study, a FE model combining 3D continuum damage mechanics (CDM) and cohesive zone modeling approaches is presented and its effectiveness was verified by comparison to experimental results available in the literature. [ABSTRACT FROM AUTHOR]

Current regulations for tests on construction site for plastic anchors in concrete Tests on construction site in the base material concrete are regulated at the European level and in Germany only for approved plastic anchors. In September 2019 the Deutsches Institut für Bautechnik (DIBt) published the technical rule „Durchführung und Auswertung von Versuchen am Bau für Kunststoffdübel in Beton und Mauerwerk mit ETA ...". The Deutsche Ausschuss für Mauerwerk e.V. (DAfM) puplished in 2020 issue 4 of the series of puplications „(Dübel‐) Versuche am Bauwerk in Mauerwerk – Aktuelle Regelungen für Kunststoffdübel und Metall‐Injektionsanker zur Verankerung im Mauerwerk" for the practical implementation of this technical rule for anchorages in masonry. This article summarizes the essential contents of the DIBt technical rule for anchorages in concrete and shows the slight deviations from the regulations in the base material masonry. [ABSTRACT FROM AUTHOR]

The bond performance between steel bar and cement-based materials was the prerequisite for the two materials to work together, and previous studies showed that the bond behavior of the steel bars and cement-based materials will vary with the kinds of cement-based materials. For this reason, this paper adopted 12 direct pullout test specimens including three types of concrete and two types of steel bars. The strain of the steel bar at six measuring points was measured with a strain gauge. Based on the measured strain and free end slip of the steel bars, the distribution of steel stress, bond stress, and relative slip and the bond slip relation along the anchorage length were obtained and analyzed for different concrete and different steel bars. Based on these test results of steel strain and relative slip at six measuring points, the anchorage position function could be established in consideration of anchorage position, which was conducive to the establishment of an accurate bond–slip relationship. In addition, the anchorage length of the steel bar in Engineered Cementitious Composites (ECC) calculated from the equilibrium equation of critical limit state is only half of the anchorage length calculated in the current Code for Design of Concrete Structures (GB 50010-2010) in China. It is suggested to establish the critical anchorage length formula suitable for ECC in future studies.

Mussel‐inspiration is extensively utilized for multifunctional modification on the surface of universal materials. Polyphenols are more and more exploited for mussel‐inspired chemistry to replace polydopamine owing to their ubiquitousness and inexpensiveness. Herein, to explore the interfacial properties between fully drawn yarn (FDY) polyester fiber‐bundle and epoxy matrix, codeposition of polyethyleneimine/catechol (PEI/CCh) is used to modify FDY polyester fiber‐bundles by mussel‐inspired method. The orthogonal experiments are performed to obtain the optimum formula which is 2 g L−1 PEI, 1 g L−1 CCh, and 24 h codeposition time. The results of surface structure characterization measured via Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscope, and energy dispersive X‐ray indicate that PEI/CCh aggregates are uniformly coated on fiber surface to fabricate continuously lamellar structures. The surface hydrophilicity and water infiltration rate constant are acquired by water contact angle. These results elucidated that FDY fiber surface is successfully endowed with polyethyleneimine/catechol aggregates and surface hydrophilicity greatly improved. Single fiber‐bundle pull‐out tests are conducted to evaluate the interfacial strength. Compared to pure fiber‐bundle specimens, there are 67.57%, 57.63%, and 45.07% increase of initial debonding load, peak load, and interfacial shear strength, respectively. [ABSTRACT FROM AUTHOR]

This study examines the flexural performance of six 9-m full-scale two-span Nail-Laminated Timber Concrete (NLTC) composite slabs. The slabs were made with lumber beams edge-joined with double nailing, end-joined with butt joints, and the reinforced concrete topping connected with a set of notches, inclined screws, or a combination of both. The multi-span configuration of slabs reduces their deflections simply and effectively. Five-point monotonic bending tests were considered for all slabs. Before full-scale slabs, compressive and tensile pull-out tests of Timber-Concrete Composite (TCC) shear connections were performed, including notches and inclined screws. Tensile pull-out tests of shear connections were also included to emulate the negative bending moments that occur in the middle of the slabs. Failure modes, load–mid-span deflection relation, bending stiffness, and timber-concrete slip were evaluated for all slabs. A detailed 3D micro-Finite Element (FE) model of the shear connections was built in ANSYS software, whereas a macro-FE model of NLTC slabs was made in SAP2000, demonstrating a good fit for the timber-concrete interaction and the load-carrying capacity of the composite slab at the serviceability range. Moreover, an analytical elastic TCC beam with the Girhammar method was assessed and demonstrated as more precise than the traditional γ -method. Finally, an accurate prediction of the numerical and analytical (Girhammar) models for the bending stiffness at service loads up to 30% of capacity is observed, with errors in a range of 2–23% and 9–74%, respectively. • Testing of six 9-m two-span Nail-Laminated Timber Concrete (NLTC) slabs. • Notched, screwed, and mixed timber-concrete connections are tested and used. • Analytical slab model with the Girhammar method is accurate for these multi-span slabs. • Numerical and analytical slab models are accurate for loads up to 30% of capacity. • Multi-span NLTC slabs can be a promising solution to cover large spans. [ABSTRACT FROM AUTHOR]

The phenomena associated with the consolidation of fresh concrete (bleeding and plastic settlement) are commonly considered significant for the bond performance of reinforcement. However, rules to take care of such influence for design are not consistent amongst design recommendations and may lead to notable differences. With this respect, two failure modes generally govern the bond failure, namely the spalling of the concrete cover (also called splitting failure) and the pull‐out of the reinforcement. In this paper, a detailed investigation is presented on the influence of bleeding and plastic settlement on both failures modes, in an effort to understand their conceptual differences and to clarify how shall consistent design recommendations be formulated. Such investigation is based on a comprehensive experimental programme, comprising 137 pull‐out tests on specimens with different casting conditions, embedment lengths, loading arrangements and concrete covers. On the basis of the test results, the phenomenological differences between pull‐out and spalling failures are clarified, as well as the main influencing phenomena (particularly the potential presence of cracks and voids under the reinforcement and the mechanical properties of concrete). On this basis, a physically‐consistent approach is presented to consider the casting conditions on the bond performance and failure modes. [ABSTRACT FROM AUTHOR]

Active connectors for components of carbon reinforced concrete – development of a compact connector made of thermal shape memory alloys The implementation of a modular, prefabricated construction method as well as the extensive use of lightweight elements made of carbon or textile reinforced concrete requires new types of connection elements. Component parts made of carbon reinforced concrete can be made much slimmer than comparable reinforced concrete elements. In addition to the geometric conditions for the connection of such thin‐walled carbon reinforced concrete components, the force transmission in such thin elements creates great challenges for the planner and the executing staff. In connection with the simplest possible assembly on the construction site, these seem to be insurmountable hurdles. As part of a research project, new and innovative connections that work on the basis of shape memory alloys (SMA) were developed for this specific application. The newly developed connection concepts aim to significantly simplify assembly on the construction site. By using memory steel as an active connection element, mechanical accessibility for connection can be dispensed with. In this article the primary field of application of the SMA connectors as well as the first concepts and developments are shown. [ABSTRACT FROM AUTHOR]

Understanding mechanical interactions at the root-soil interface is essential to predict the erosion of vegetated slopes. Recently, the shear strength of vegetatedil under changing hydraulic conditions has been measured and modeled; however, root-soil interfaces have not been investigated under changing hydraulic conditions. This paper proposes (1) a novel pullout apparatus to measure the shear strength at the root-soil interface under changing suction, (2) a Mohr-Coulomb-Vilar (MCV) shear strength model of root-soil interfaces, and (3) a numerical simulation using Node-To-Segment (NTS) approach along with Finite Element Method (FEM). The pullout tests were verified using the numerical simulation, and the results showed that the combination of the MCV model and NTS/FEM approach can accurately predict the shear behavior of root-soil interfaces under changing suction. In addition, we experimentally evaluated the pullout problem of roots and showed that the present method provides reasonably predicts root-pullout problems even when the suction is changed during the pullout process. The current method, therefore, can be used for predicting root-soil interface dynamics under varying suction and soil pressure by only adding two additional parameters of the Vilar model. [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.

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