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Current formulas to assess the shear capacity of headed steel stud anchors and post-installed (PI) anchors in case of pryout failure (sometimes known as pull-rear failure) have been derived either based on the indirect-tension resistance model or are fully empirical based on push-out test results. In both cases, the predicted pryout capacity is clearly conservative and underestimates the true pryout capacity of anchorages, especially for stiff anchors with low embedment-to-diameter ratios (hef/d < 4.5). This paper proposes an empirical and a semi-empirical formula to predict the concrete pryout capacity of headed steel studs and PI anchors. They were derived based on an improved indirect-tension model which accounts for the stud diameter and the stud spacing in a group of anchors. Furthermore, a database of 214 monotonic shear tests from the literature, including own tests (push-off and horizontally shear tests), is reevaluated and compared to the provisions of EN1992-4. The scope of this assessment proposal includes single and group of headed steel studs and PI anchors attached to a stiff steel plate as well as shear connectors in composite structures without metal deck embedded in normal-weight concrete.

Chloride-induced corrosion is one of the most important causes of the strength degradation of reinforced concrete (RC) bridges. As the piers of RC bridges are important elements for sustaining lateral loads, corrosion of pier columns may lead to significant degradation of the structure. It is thus necessary to have an appropriate evaluation technique to assess the effect of corrosion on the behaviour of RC columns. Numerical modelling approaches based on a concentrated plastic hinge can predict structural behaviour rapidly and with acceptable accuracy, and are highly regarded by engineers. In this study, a numerical approach was conducted to develop an empirical lumped plasticity model (LPM) for corroded RC column elements. In this study, 13 440 RC column specimens, including corroded and uncorroded columns of both rectangular and circular cross-section, were analysed under monotonic and cyclic loading. The LPM was extracted based on regression of the results of cyclic and monotonic analyses. The calibrated model, valid for corroded and uncorroded columns, was assessed using experimental results and numerical models with data out of the range of those used in the parametric study and was found to have high accuracy. The newly developed plastic hinge model can be used to model and analyse corroded bridge columns rapidly. The results are appropriate for use in further assessments such as fragility or rehabilitation analyses.

Anchorages of non-rectangular configuration, though not covered by current design codes, are often used in practice due to functional or architectural needs. Frequently, such anchor groups are placed close to a concrete edge and are subjected to shear loads. The design of such anchorages requires engineering judgement and no clear rules are given in the codes and standards. In this work, numerical investigations using a nonlinear 3D FE analysis code are carried out on anchor groups with triangular and hexagonal anchor patterns to understand their behavior under shear loads. A microplane model with relaxed kinematic constraint is utilized as the constitutive law for concrete. Two different orientations are considered for both triangular and hexagonal anchor groups while no hole clearance is considered in the analysis. Two loading scenarios are investigated: (i) shear loading applied perpendicular and towards the edge, and (ii) shear loading applied parallel to the edge. The results of the analyses are evaluated in terms of the load-displacement behavior and failure modes. A comparison is made between the results of the numerical simulations and the analytical calculations according to the current approaches. It is found that, similar to the rectangular anchorages, and also for such non-rectangular anchorages without hole clearance, it may be reasonable to calculate the concrete edge breakout capacity by assuming a failure crack from the back anchor row. Furthermore, the failure load of the investigated groups loaded in shear parallel to the edge may be considered as twice the failure load of the corresponding groups loaded in shear perpendicular to the edge.

This paper presents the efficiency of the fiber-reinforced polymer (FRP) composites as internal reinforcement in rescue the structural performance and controlling the mode of failure of the sulfate damaged reinforced concrete (RC) beam-column joint by nonlinear finite element analysis (NLFEA). Firstly, the RC beam-column model was validated against the published experimental results and then was expanded to consider the effect of column axial load level (0%, 25%, 50%, and 75%) and sulfate damage level (without (Level 0), 73 days (Level 1), and 123 days (Level 2)) on the models with and without FRP composites. The structural performance was evaluated in terms of mode of failure, stress distribution, pulling and pushing ultimate load capacity and corresponding displacement, horizontal load–displacement hysteretic loops, horizontal load–displacement envelopes, displacement ductility, energy dissipation, and stiffness degradation. The NLFEA results showed that the internal strengthening of sulfate damaged RC beam-column joint with FRP composite enhanced the cyclic performance (higher load capacity, larger horizontal displacement, higher displacement ductility, higher energy dissipation, and slower secant stiffness degradation) and the efficiency of FRP composite increased with the sulfate damage level. Also, the FRP composite strengthening technique gave the ability to transform the joint-column regions mode of failure from brittle into a ductile mode of failure through the formation of the plastic hinge in the beam only at a higher level of column axial loads of more than 25%. While the application level of column axial loads less than 25% only enhanced just the ultimate axial load capacity and corresponding deflection.

During earthquakes, buildings are subjected to loads well beyond their usual demands, resulting in high stresses in the structural components and additional inertial forces coming from the non-structural elements. When post-installed anchors are used to form the connection between non-structural or structural members and the primary reinforced concrete structure, these anchors are also subjected to high seismic demands. To determine whether a post-installed anchor is suitable for such applications, it is assessed for its performance under seismic demands. In this review paper, the current European approach for testing and qualification of post-installed anchors under seismic actions is reviewed and discussed in the context of structural applications where anchors are used to form the connection between structural members that participate in the load-transfer mechanism against seismic loads. The first part of this paper provides a description of the testing procedures and the criteria against which the anchor performance is assessed. The procedures and assessment criteria are discussed regarding the suitability in the case of the above-described structural applications. In the second part, the qualification of anchors under seismic actions is discussed in the light of an upcoming performance-based design approach for anchors. In such an approach, information on the displacement and hysteretic behavior of an anchor in a broader range of the load–displacement curve is of vital importance. Therefore, additional testing approaches might be required in order to supplement the information on anchor performance provided in the current testing procedures. One such testing approach for pulsating tension load is reported.

In der Ingenieurpraxis steigt die Nachfrage nach Befestigungsmitteln im stahlfaserverstärkten Beton (Steel Fibre Reinforced Concrete: SFRC), was ein tiefes Verständnis über das Tragverhalten erfordert. Zu typischen Anwendungen zählen Fußpunktkonstruktionen von Schwerlastregalsystemen, Schwermaschinen in Industrieböden, Stahlbetonfertigteilbau, Industrie- und Hochbau. Die teilweise widersprüchlichen Versuchsergebnisse aus verschiedenen Literaturstellen deuten auf die Notwendigkeit für tiefergehende Auswertungen hin, um die sichere Anwendung der Befestigungen in SFRC sicherzustellen. In diesem Aufsatz wurden alle relevanten Literaturergebnisse aus den letzten Jahren zusammengefasst. Aus den einzelnen Versuchsergebnissen wurde eine Datenbank erstellt, die 274 Versuchsergebnisse an unterschiedlichen Befestigungsmitteln unter Zug-, und Querbeanspruchung in Normalbeton (99 Versuche) und in SFRC (175 Versuche) umfasst. Auf Basis der Auswertung der bis 2018 veröffentlichten Ergebnisse wurde ein Bemessungsansatz in Tóth et al. 2019 entwickelt, der den Einfluss des tatsächlichen Stahlfasergehaltes auf den Widerstand von Dübeln und Kopfbolzen bei Betonausbruch und Betonkantenbruch berücksichtigt. In diesem Paper werden die verfügbaren Versuchsergebnisse diesem Ansatz gegenübergestellt und ausführlich diskutiert.

The current recommendations given in the codes and guidelines for design of anchorages to concrete are limited in scope to rectangular and regular anchor groups with a maximum of three anchors in a row. Furthermore, several assumptions are made, which may render the designs conservative but may also lead to unconservative results such as the required base plate thickness and the cracked concrete assumption. The aim of this experimental study was to investigate the load-displacement behaviour of tension loaded anchor group configurations that are either only partly covered or not covered by the current design provisions. Furthermore, this work aimed to generate an experimental database on the concrete cone failure of anchor groups under tension loading. The results of a comprehensive experimental program carried out on diverse anchor group configurations within and beyond the scope of the European Standard EN1992-4 are discussed focusing on several aspects such as (i) different geometric configurations, (ii) varying stiffness of the base plate, and (iii) influence of eccentricity. The experimental program contains tests on single anchors and on anchor groups in normal- and high-strength concrete. The testing concept, test setup and the test results are discussed in detail in this paper. Based on the evaluation of the test results presented here, a new analytical model is being developed for the concrete cone failure mode of tension loaded anchor groups that will be presented in a future paper.

In this work, the residual bond performance of reinforcement in concrete under elevated temperatures is experimentally investigated using the cuboidal (square prismatic) concrete specimens. The test reinforcement was placed at different cover distances with an aim to study the influence of elevated temperature on bond pullout and bond splitting behavior. It was found that under ambient conditions as well as after exposure to elevated temperature, concrete cover has a strong influence on the absolute value of the bond strength and failure mode. The thermal degradation of bond strength is found to be similar to that of compressive or tensile strength of concrete for pure bond or splitting failure respectively. The level of confinement provided by the concrete cover to the rebar reduces with increasing temperature, while the width of splitting cracks increases with increasing temperature. The bond stiffness gradually reduces with the increase in exposure temperature for both pullout and splitting failure. The details and the results of the experimental investigations are reported in this paper.

A large number of studies confirm the beneficial effects of the steel fiber reinforcement in concrete structures. The addition of steel fibers to the concrete mix leads to better mechanical and physical concrete properties including higher fracture energy, reduced crack widths, higher impact and abrasion resistance, increased durability. Due to the increasing popularity of using anchorages in steel fiber reinforced concrete (SFRC), it is essential to understand the behavior of anchorages in SFRC and to validate the applicability of the current provisions for the design of anchorages for use in structural concrete. However, there is only little research available on the behavior of anchorages in SFRC. This paper presents the results of experimental investigations on tension and shear loaded steel anchors in normal-strength plain concrete (PC) and in SFRC. The comprehensive test program includes 62 pull-out and shear loading tests on single anchors and on anchor groups. The test results are discussed in detail to emphasize the influence of steel fiber reinforcement on the load-displacement behavior of fastening systems. The results indicate that the fiber content has a positive effect on the load-displacement behavior of the anchorages, in general. A better utilization of fastening systems can be attained due to the more ductile behavior and due to the crack bridging mechanism of the SFRC. Furthermore, in certain applications and parameter combinations the ultimate load in case of concrete failure may be higher in SFRC compared to PC.

Zusammenfassung Die Bemessung von zugbeanspruchten Befestigungen in Beton nach den aktuellsten Normen und Richtlinien weist viele grundlegende Einschränkungen zur Anwendung der Konzepte auf. Sie beschränkt sich beispielsweise auf rechteckige Dübelanordnungen und setzt die Verwendung einer ausreichend steifen Ankerplatte voraus. Definitionen und Regelungen zur Bestimmung einer ausreichend steifen Ankerplatte sind in den derzeitig gültigen Vorschriften nicht enthalten. Aufgrund von technischen, funktionellen oder baulichen Anforderungen werden jedoch auch solche Befestigungen in der Baupraxis ausgeführt, für die die Bemessung durch die aktuellen Vorschriften nicht abgedeckt ist. Dieser Beitrag stellt ein neuartiges Bemessungskonzept vor, das einen federmodellbasierten Ansatz mit einem 3D-Finite-Elemente-Solver kombiniert. Dadurch steht eine Softwarelösung für die Bemessung und Bewertung von zugbeanspruchten Gruppenbefestigungen in Beton zur Verfügung, die die wesentlichen Einschränkungen der aktuellen Bemessungsnormen behebt. Das Konzept des nicht-linearen Federmodells, das in einer benutzerfreundlichen Dübelbemessungssoftware implementiert ist, basiert auf der Annahme, dass innerhalb einer Gruppenbefestigung die Zugkräfte von den Befestigungsmitteln aufgenommen werden, während die Druckkräfte direkt durch das Anbauteil in den Beton eingeleitet werden. Zur Modellierung des Dübelverhaltens werden nicht-lineare Federn verwendet. Um den Einfluss des Bauteilrandes und der benachbarten Befestigungen zu berücksichtigen, wird ein Ansatz für die Flächenaufteilung angewendet, der auf der Grundlage einer Vielzahl von experimentellen Untersuchungen der Autoren entwickelt wurde, Bokor et al. [25]. Die Ankerplatte wird mit finiten Solid-Elementen modelliert, um die Steifigkeit der Ankerplatte und Lastumlagerungen zwischen den Befestigungen einschließlich möglicher Versteifungen der Ankerplatte realistisch zu betrachten.

The objective of this investigation is to assess the effectiveness of hybrid fiber reinforced polymer (FRP) strengthening on the overall behavioral improvement of reinforced concrete (RC) beams under flexure . Eight square RC beams were cast and strengthened using different FRP techniques including (i) near surface mounting (NSM), (ii) external bonding (EB) and (iii) hybrid strengthening using a combination of NSM carbon FRP laminates and EB CFRP fabric . Peak moment capacity was calculated analytically by enforcing the sectional equilibrium using the strain compatibility procedure. A micro plane based nonlinear three-dimensional finite element (FE) model was developed to simulate the behavior of the RC beams with and without FRP strengthening. Experimental results revealed that hybrid FRP strengthening could increase the strength by 160%. Moreover, the ultimate displacement of hybrid FRP strengthened beams improved significantly when compared to only the NSM technique. Only NSM strengthening improved the peak strength by 85% but had a brittle bond failure. Only EB strengthening improved the ductility of the flexural members due to confinement but did not significantly increase the strength. Predictions of the FE model correlated well with the experimental results and revealed that minimum edge distance for NSM laminates has to be ensured for preventing premature edge de-bonding failures.

This paper investigates the axial compression and bending interaction behavior of reinforced concrete (RC) columns repaired and strengthened with different FRP (Fiber Reinforced Polymer) techniques after severe damage. The columns were initially damaged under different axial compression to bending load ratios. The loads were applied at different eccentricity (e) to depth (h) ratios to have (i) pure compression (e/h = 0), (ii) eccentric compression (e/h = 0.63) and (iii) pure flexure (e/h = ∞). After initial damage, the specimens underwent severe concrete core degradation with the main steel reinforcement reaching its yield strain. Later, the specimens were repaired using high strength cement grout (HSCG) and further strengthened using (i) near surface mounting (NSM) of carbon FRP (CFRP) laminates and (ii) hybrid FRP technique with a combination of NSM laminates and external bonded (EB) fabrics. After that, the columns were loaded again until failure. An axial compression (P) – bending moment (M) interaction diagram was developed experimentally for the severely damaged columns. Also, the interaction curves were developed analytically using strain compatibility procedure with the modified constitutive models. Experimental results reveal that the specimens repaired and strengthened using hybrid FRP technique can effectively restore the original capacity under different eccentric load levels. The analytical predictions showed a close match when compared to the experimental observations.

In recent years, the use of post-installed anchors to connect the haunch elements with the structural members has been investigated proficiently. It represents a promising alternative for strengthening of joints of existing reinforce concrete (RC) structures (moment resisting frames) with low invasion. The efficacy of the fully-fastened-haunch-retrofit (FFHR) solution has been proven by past works for two-dimensional RC beam-to-column joints, subjected to cyclic loading, without transverse beam and slab. In these cases, the presence of the haunch, providing a suitable design of the anchoring system, modifies the strength hierarchy shifting the mode of failure from joint’s shear breakout to the formation of the plastic hinge in the beam. However, due to the presence of the slab and transverse beam, as the authors discussed elsewhere, an increase both (i) in the joint resistance and (ii) in the beam flexural resistance must be expected, but particular care must be taken to the non-symmetric behavior. In this regard, results obtained for two RC beam-to-column sub-assemblies with transverse beam and slab retrofitted using FFHR are presented. The structural behavior under cyclic load is compared with the as-built identical specimen. The applicability of the FFHR to existing RC structures, is confirmed but, at high level of ductility demand, both anchorage break-down and reduced displacement capacity are observed.

Anchor channels are cast in concrete and allow the connection of components using channel bolts. In recent years, the design to value resulted in ever thinner concrete elements, which often cannot accommodate the required embedment depth of standard anchor channels. For this reason, channels may be fitted with short anchors. While existing design provisions allow for the calculation of the tension capacity also for shallow embedded anchor channels, tests are required to determine product-specific parameters for the economic shear loads design. The presented study investigated the performance of shallow embedded anchor channels tested in shear. The detailed evaluation of the test data demonstrates that testing of the minimum embedment is conservative and that the load-displacement behavior of channels with welded I-sections is comparable to that of channels with forged headed studs. In addition, a new evaluation approach is proposed.

Fire safety is a critical performance aspect of construction products, and post-installed anchors and rebars are no exemption in that regard. During their service life, anchors and rebars are subjected to different kinds of load actions, so they have to be qualified and designed for critical safety performance. While the qualification guidelines for static and seismic loading have matured to conclusive requirements over the past two decades, the requirements for determining the resistance to fire are just about to consolidate. This contribution strives to provide clarity on the fire rating of post-installed anchors and rebars. For this, the current status of the regulations, as well as the underlying background, is reviewed after a brief introduction. Typical examples of fire ratings in the field of post-installed anchors and rebars are given, and recent research undertaken to close the last regulative gaps is briefly presented.

Use of organic resins such as epoxy and vinyl esters as bonding materials in fibre reinforced polymer (FRP) strengthening of concrete members is widely accepted. However, the performance of organic resins is compromised when exposed to high temperature and extreme weather conditions leading to reduced durability of the strengthened systems. The present study attempts to evaluate the effectiveness of inorganic (cement mortar and geopolymer mortar) bonding materials for shear strengthening of prestressed concrete (PSC) beams using the near-surface mounting (NSM) technique. Different types of bonding materials are used in this study for NSM shear strengthening including: (i) epoxy resin, (ii) high strength cement grout (HSCG) and (iii) geopolymer mortar. Bond tests were first conducted to evaluate the pull-out/bond strength of different bonding materials. Bond tests revealed that epoxy resin had the highest bond strength followed by geopolymer mortar and HSCG. Sixteen full-scale PSC beams were cast with and without stirrups. The beams were strengthened using NSM CFRP laminates oriented at 45-degree configuration and then tested under a three-point bending configuration. Experimental results revealed that the performance of high strength cement grout and geopolymer mortar was similar but with a lesser efficiency compared to the epoxy resin.

This paper presents the results of nonlinear finite element (FE) analysis of fiber-reinforced polymer (FRP)-strengthened reinforced concrete (RC) columns under different combinations of axial compression (P) and bending (M) loads. Three-dimensional FE models of RC columns were analyzed for different eccentricity (e) to depth (h) ratios as: a) axial loading (e/h = 0); b) uniaxial eccentric loading (e/h = 0.15 and 0.63); and c) pure bending (e/h = ∞). Three different strengthening schemes-namely, 1) near-surface mounting (NSM); 2) external bonding (EB); and 3) hybrid strengthening. were considered. The load-displacement curves, P-M interaction diagram, and failure modes from FE analysis and experiments compared quite well. The validated FE modeling approach was used for performing parametric investigation to evaluate the influence of: 1) concrete strength; 2) carbon FRP (CFRP) laminate ratio in NSM strengthening; 3) CFRP fabric ratio in EB technique; and 4) CFRP ratios in hybrid strengthening.

In the present study different single headed stud anchors are exposed to various durations of fire and loaded in shear perpendicular to and towards the free concrete edge up to failure after cooling. The effects of concrete edge distance, nominal diameter, embedment depth and concrete compressive strength on the load-bearing behaviour of the anchors at various durations of fire are experimentally investigated. The standard fire curves ISO-834 with the corresponding durations of 15 min and 60 min are employed to study the effect of fire on the residual capacities of the anchors. Even more than expected, the results demonstrate that the anchor behaviour is significantly influenced by the fire exposure. Under ambient conditions, the influence of the edge distance on anchor resistance is very strong while the influence of the anchor diameter and the embedment depth is relatively weak. However, after fire exposure the influence of the edge distance reduces and the influence of the diameter and the embedment depth on the shear resistance increases. The influence of fire exposure is significant on the concrete edge capacity of the anchors. After only 15 min of fire duration, the reduction of more than 50% of the reference value is reported.

The paper presents and discusses the results of a numerical study on post-fire (residual) behavior of reinforced concrete (RC) beams with critical tension lap splices . It is based on the experimental findings and the validation of the numerical approach in the accompanying paper and further analyzes the residual performance by varying most influencing parameters such as bond length, fire duration and concrete cover to the spliced reinforcing steel. Three-dimensional numerical (FE) analysis is performed employing the temperature dependent microplane model for concrete in the framework of the smeared crack approach. The numerical results show that the exposure to fire can change the strength hierarchy of the flexural member such that the splice lengths required to develop the bar under ambient (unheated) conditions may not be sufficient to develop the bar in residual (post-fire) conditions due to the preceding bond splitting failure. It is further found that increased concrete cover does not significantly enhance the post-fire flexural capacity . In closing, a design concept for the determination of the required bond length in case of fire loads is presented.