Steel-concrete Bond Research Articles

Prediction of ultimate bearing capacity of RC beams after fire: data-driven method

The ultimate bearing capacity of reinforced concrete (RC) beams after exposure to fire was investigated using numerical simulations, regression fitting and machine learning techniques to examine the thermal and mechanical properties of the beams after high-temperature exposure. A series of fire and static load tests was conducted on seven RC T-beams. Based on the experimental observations and considering the effects of high-temperature concrete spalling and steel–concrete bond degradation, a numerical model was developed to simulate the temperature distribution and structural behaviour of RC T-beams. The accuracy of the numerical model was validated by comparing the cross-sectional temperature profiles and ultimate bearing capacities after fire exposure with experimental results. A dataset of 500 samples was established, with variables including fire exposure time, depth of concrete spalling, spalling area ratio and loading conditions. Regression fitting and machine learning techniques were used to establish predictive formulas and models for estimating the ultimate bearing capacity of RC T-beams after fire exposure. The accuracy of both methods was found to be within 10%.

Characterization of different longitudinal shear transfer mechanisms for profiles embedded in concrete walls

Concrete walls or columns reinforced by one or multiple embedded steel profiles have gained popularity due to their improved strength, ductility and energy dissipation capacity. However, certain gaps in information are remaining in the available standards regarding the design of such non-conventional reinforced concrete systems. In particular, a proper characterization of the longitudinal shear transfer properties at the steel-concrete interface is required for a reliable design. Although sufficient information is available regarding mechanical connectors like shear studs, detailed information is required for any other types of mechanical connectors such as welded steel plates or for configuration without mechanical connectors. Moreover, even for cases with mechanical connectors, the orientation of the profile – and hence the distance to the face of the concrete – and the tying system can have a significant influence on the load transfer mechanisms. To this purpose, this article presents the outcomes of a set of push-out tests with the objective of comparing the force transfer mechanisms from the steel profile to the surrounding concrete wall for different types of interfaces. 13 tests specimens are investigated, with flexible (shear studs) and/or rigid (steel plates) shear connectors, considering different orientations of the profile and tying mechanisms, as well as a comparison with profiles without mechanical connectors. Based on the test results and subsequent analytical assessment, relevant conclusions are drawn regarding the longitudinal shear transfer at the steel-concrete interface. If necessary provisions are followed, welded steel plates prove to be an effective alternative to the shear stud connectors in terms of connector strength. The orientation of the embedded steel profile, consequent position of the mechanical connectors and their distance to the concrete face are observed to have a significant influence on the compression strut evolution, which therefore dictates the necessity (or not) of horizontal confinement or ties. Furthermore, combining the shear strength offered by different types of mechanical connectors and the steel-concrete bond offer a precise estimate of the longitudinal shear strength and therefore indicates towards the conservative nature of the design provisions suggested by the available standards.

Steel-Concrete Bond versus Primary Crack Opening in Reinforced Concrete Beams

Steel-Concrete Bond versus Primary Crack Opening in Reinforced Concrete Beams

Corrosion effects on bond strength in reinforced concrete with fly ash

Reinforcing steel bars provides additional strength and ductility to concrete by forming a strong bond with the concrete matrix. Corrosion of steel bars can significantly reduce the bonding effect between the steel bar and concrete, which can compromise the structural integrity and durability of reinforced concrete structures. An experimental investigation was performed to examine the influence of fly ash (FA) and corrosion on concrete–steel bond behavior. The accelerated corrosion method was employed to obtain the desired level of corrosion. The FA content, corrosion percentage, and presence of stirrups were considered significant factors influencing bond behavior. The bond–slip curves and bond toughness were used to discuss bond behaviors. The findings indicated that mild corrosion (below 2.5%) can enhance concrete–steel bond performance, and the addition of 20% FA leads to higher ultimate bond strength (τu ), significantly mitigating the decrease in bond strength caused by severe rebar corrosion. Also, this study analyzed the influence of stirrups on the bond strength of FA concrete and had a nearly insignificant effect compared to regular concrete. The results and discussions of the present study carry significant importance in the establishment of a bond–slip constitutive model under multifactor coupling conditions. Furthermore, it offers valuable insights into the design of engineering structures.

Corrosion Protection of Embedded Steel Reinforcement Using Canarium Schweinfurthiia Exudate for Coastal Concrete Structures

This experimental study evaluated the effects of corrosion on the bond behavior and structural integrity of reinforced concrete. A total of 36 concrete cube specimens containing reinforcing steel bars were divided into control, uncoated, and Canarium schweinfurthiia exudate/resin coated groups and immersed in 5% NaCl solution for 360 days. Periodic tests were conducted to analyze corrosion levels, bond strength, steel bar properties, and failure loads. Results showed the control specimens exhibited little corrosion while uncoated bars experienced significant corrosion after exposure. In contrast, exudate/resin coated bars demonstrated a substantial reduction in corrosion, indicating the coating's inhibitory effects. Pull-out bond strength and maximum slip tests consistently revealed lower strengths and higher slips in corroded samples compared to controls. However, coated specimens maintained higher bond capacities and lower displacements, validating the coating's protective performance. Measurement of bar diameters, cross-sectional areas, and weights before and after corrosion highlighted the proportional losses associated with the corrosion process. Dimensions and masses of corroded reinforcements decreased by 2-7% on average from initial values. In comparison, controls showed minimal variations. Failure load analyses found controls withstood the highest loads, while corroded members exhibited reduced capacities. Overall, the study demonstrated corrosion negatively impacts the critical steel-concrete bond and undermines composite action essential for structural integrity. Exposure to NaCl solutions markedly increased corrosion and decomposition of unprotected bars. However, natural Canarium schweinfurthiia exudate/resin coatings were highly effective at mitigating corrosion effects by preserving bond strength, slip resistance, steel geometries and load capacities close to uncorroded levels. The findings validate protective coatings as a viable solution for durable reinforced concrete design in marine environments. Proper corrosion prevention through coatings or inhibitors can help ensure structures withstand service loads over their design life.

Effect of self-compacting concrete placement technology on the load-bearing capacity of the concrete-concrete and steel-concrete bond in layered elements

The article presents a study on the technology of layered execution in self-compacting concrete structures. The research focused on 800×480×160 mm panel elements, cast in two layers from a single mix casting point. Three different delay times for delivering the second layer of mix were considered: 15, 30 and 60 minutes. Two technological variants of mix application were analysed: from the top and from the bottom of the mould. The study investigated the influence of the placement technology on the load bearing capacity of the concrete layer-to-layer joint and the rebar-to-concrete joint. The load-bearing capacity of the concrete layer-to-layer joint was determined through a splitting tensile strength test on core specimens extracted from panel elements. Notably, existing literature has primarily explored the load-bearing capacity of the concrete layer-to-layer joint on smaller elements and has not accounted for mix placing technologies diverging from the traditional one. A test of the rebar-to-concrete bond at the layer interface was conducted using the pull-out method. Substantial differences were identified in the mixing pattern of concrete layers, contingent on the placing technology employed. Top-down casting led to a reduction in the load-bearing capacity of the concrete layer-to-layer interface, coupled with decreased stiffness and bond strength of the rebar-to-concrete connection as the delay time of the second layer increased. Conversely, bottom-up concreting maintained the load-bearing capacity of the combined concrete layers at 90% of the strength of the monolithic specimen throughout the entire test range. The article recommends the utilization of bottom-up placing technology for executing elements in the multilayer casting of self-compacting concrete.

Soft computing models for assessing bond performance of reinforcing bars in concrete at high temperatures

The bond between steel and concrete in reinforced concrete structures is a multifaceted and intricate phenomenon that plays a vital role in the design and overall performance of such structures. It refers to the adhesion and mechanical interlock between the steel reinforcement bars and the surrounding concrete matrix. Under elevated temperatures, the bond is more complex under higher temperatures, yet having an accurate estimate is an important factor in design. Therefore, this paper focuses on using data-driven models to explore the performance of the concrete-steel bond under high temperatures using a Gene Expression Programming (GEP) soft computing model. The GEP models are developed to simulate the bond performance in order to understand the effect of high temperatures on the concrete-steel bond. The results were compared to the multi-objective evolutionary polynomial regression analysis (MOGA-EPR) models for different input variables. The new model would help the designers with strength predictions of the bond in fire. The dataset used for the model was obtained from experiments conducted in a laboratory setting that gathered a 316-point database to investigate concrete bond strength at a range of temperatures and with different fibre contents. This study also investigates the impact of the different variables on the equation using sensitivity analysis. The results show that the GEP models are able to predict bond performance with different input variables accurately. This study provides a useful tool for engineers to better understand the concrete-steel bond behaviour under high temperatures and predict concrete-steel bond performance under high temperatures.

Steel–concrete bond deterioration in reinforced concrete tension members due to primary cracks

Primary cracks in reinforced concrete tension members lead to the deterioration of the steel–concrete bond. This study aims to investigate this bond deterioration by establishing a novel relationship between the bond force and slips near the cracks. The descending part of this relationship represents the bond deterioration, with its parameters determined by the structural responses. An iterative algorithm is proposed based on this relationship to analyze the bond behaviors of tension members. The effectiveness of the proposed method is validated using reinforced concrete tension members from experiments in the literature. The results demonstrate a gradual decrease in bond forces from local maximum to zero near the cracks, indicating the presence of the descending part of the bond–slip relationship. The length, slope, and characteristic points of the descending part vary with crack spacing and slips at the cracks, leading to nonlinearity in steel strains. In comparison to existing methods assuming constant length or slope, the proposed method accurately predicts these variable parameters, and provide precise estimations of bond force.

Experimental study, numerical simulation and GRNN model for predicting the flexural loading capacity of corroded reinforced concrete beams

The present article is an effort to quantify the flexural strength of corroded reinforced concrete (RC) beams. Eight RC beams with dimensions of 150 × 200 × 2200 mm were tested in four-point bending, including six beams corroded in a chloride environment with average corrosion of longitudinal reinforcement in the range of 5% to 15%. The remaining two beams were used as control beams. The ultimate strength, failure mode and particularly the relationship between crack width and corrosion level are analyzed and discussed. A two-dimensional non-linear finite element model has been presented to simulate the steel bar corrosion considering the deterioration of concrete strength and steel-concrete bond stress. The generalised regression neural network (GRNN)-based model for the ultimate flexural strength of corroded RC beams has been established based on 123 experimental data collected from previous studies. The experimental results were used to separately validate the non-linear finite element model and novel GRNN model. Experimental results indicate that if the overall corrosion rate is used, the corrosion crack width can be a function of the percentage of section loss. The GRNN model provides superior predictive results compared to previous empirical methods with the highest correlation coefficient (r), and the smallest normalised root mean square error.

Steel-concrete bond behaviour of concrete mixes with wood waste: pull-out and bending tests of full-scale beams and columns

The present work intends to encourage a more widespread application of concrete mixes containing wood waste by investigating the steel–concrete bond of ordinary steel reinforcement bars and prestressed strands to assess the feasibility of using these composites in structural applications.After a set of preliminary tests, two mixes were selected in which aggregate was partially replaced by wood chip and sawdust. The effect of the steel–concrete bond length and reinforcement diameter on the shear strength was evaluated for steel bars and two-wire strands.The incorporation of wood appears to create a better mechanical interaction by increasing the component of friction as a resistance mechanism. In the case of the strands, the bond resistance is significantly higher (above 2.3 MPa) than the reference (0.9 MPa), regardless of the wood-concrete composites and the bond length. Additional tests have been performed to evaluate a possible creep effect. The specimens were subjected for 120 h to a constant tensile load corresponding to 50% of the mean results of the pull-out test. Results show that incorporating wood does not enhance the creep for this load level.Full-scale structural elements were also constructed to assess the feasibility of using these composites in structural applications. Bending and bending plus fatigue tests were performed to determine the behaviour under static and dynamic loads. It was concluded that the reference concrete without wood incorporation cracked for lower loads (26.0 kN) than the composites with wood (above 38.8 kN) and presented much higher bending stiffness (27835 kN.m2) than the wood-concrete composites (below 8544 kN.m2). The wood concrete with sawdust resisted fatigue tests without cracking.

Effects of Different Coatings, Primers, and Additives on Corrosion of Steel Rebars

In this research, methods of increasing the corrosion resistance of reinforced concrete were experimentally investigated. The study used silica fume and fly ash at optimized percentages of 10 and 25% by cement weight, polypropylene fibers at a ratio of 2.5% by volume of concrete, and a commercial corrosion inhibitor, 2-dimethylaminoethanol (Ferrogard 901), at 3% by cement weight. The corrosion resistance of three types of reinforcements, mild steel (STt37), AISI 304 stainless steel, and AISI 316 stainless steel, was investigated. The effects of various coatings, including hot-dip galvanizing, alkyd-based primer, zinc-rich epoxy primer, alkyd top coating, polyamide epoxy top coating, polyamide epoxy primer, polyurethane coatings, a double layer of alkyd primer and alkyd top coating, and a double layer of epoxy primer and alkyd top coating, were evaluated on the reinforcement surface. The corrosion rate of the reinforced concrete was determined through results of accelerated corrosion and pullout tests of steel-concrete bond joints and stereographic microscope images. The samples containing pozzolanic materials, the corrosion inhibitor, and a combination of the two showed significant improvement in corrosion resistance by 7.0, 11.4, and 11.9 times, respectively, compared to the control samples. The corrosion rate of mild steel, AISI 304, and AISI 316 decreased by 1.4, 2.4, and 2.9 times, respectively, compared to the control sample; however, the presence of polypropylene fibers reduced the corrosion resistance by 2.4 times compared to the control.

Bonding of Steel Bars in Concrete with the Addition of Carbon Nanotubes: A Systematic Review of the Literature

Advances and innovations in science and engineering have been increasingly supported by nanotechnology, and the modification of cementitious materials by nanoengineering is an expanding field. With this perspective, this paper aims to elucidate the behavior of steel bars in concrete with the addition of carbon nanotubes (CNTs) as a function of the characteristics of the cement-based material, the dispersion techniques and dosage of CNTs, the bond tests and specimen geometry, and the rebar characteristics. To reach this proposed goal, the ProKnow-C methodology was applied to select the most relevant publications from the last ten years, and then seven articles were fully analyzed. The results of the present systematic review of the literature revealed both consolidated knowledge and gaps to be filled in future research, as the need to study the chemical effect of adding these nanomaterials for improving steel–concrete adhesion, the bonding of thin bars in concrete, and the real influence of anchorage length on the steel–concrete bond, regardless of the use of CNTs, is vital.

Experimental study on the effect of grouting volume on the tensile performance of offset semi-grouted couplers

Research results have shown that the mechanical properties of sleeve grouting connections are related to the diameter of the rebar, the sleeve, the grout, the temperature and the loading method, but research on the factor of grout volume needs to be further developed. Therefore, this paper considers the effects of three grouting volumes (50%, 75% grouting and 100% full grouting) on the tensile properties of the joint under the offset condition of the rebar. A total of 22 uniaxial tensile tests on semi-grouted steel sleeve connection specimens were carried out, mainly to study the damage morphology, load-displacement relationship, stiffness and the strain change law on the surface of the rebar and the sleeve under different grouting amount, etc. The stress mechanism of the specimens in the tensile condition was analysed, and the effective bond length calculation model was proposed with reference to the steel-concrete bond strength research theory, and the formula for calculating the maximum bond stress related to the effective anchorage length was obtained. Studies have shown that the grouting amount affects the load bearing capacity and stiffness, and that the quality of the specimen joint is reliable when the grouting volume reaches more than 75% of the design grouting volume.

Nonlinear steel strains in cracked RC beams based on bond-stress profiles

Steel–concrete bond is instrumental in transferring tensile forces to the concrete via the bond stresses, whose values and distribution along a steel bar vary with the level of the load applied to the reinforcement. To study the profile of the strains in the reinforcement, the variation of the bond-stress distribution is considered and the bond stresses are introduced according to Model Code 2010. The transfer length where the bond stresses are active is shown to be a function of the slip in the cracked sections. This slip can be evaluated from the concrete strains based on the plane-section hypothesis to take care of the strain compatibility between the concrete and the reinforcement. The equilibrium of the internal forces, the constitutive laws of the materials and the bond stress-slip law make it possible to model the kinematic interaction between the concrete and the reinforcement. An iterative algorithm is proposed to calculate the steel strains, and the effectiveness of the numerical procedure is checked against the test data coming from simply-supported RC beams tested in this research project or available in the literature. The results show that the nonlinear evolution of steel–concrete slip close to the cracks may increase the transfer length of the bond stresses by 50% under increasing loads, and the steel strains by up to 90% along the bonded length. As a result, the steel-strain profile becomes a slightly-nonlinear function of the load, which is also markedly affected by the crack pattern.

Bond behavior between steel bars and 3D printed concrete: Effect of concrete rheological property, steel bar diameter and paste coating

• The effects of the rheological property on the steel–concrete bond behavior of printed and cast samples were investigated. • The porosity at the steel–concrete interface is related to the bond strength. • The bond strength values of 3D printed samples with ribbed bars of different diameters were compared. • The rheological properties of fresh concrete for 3D printing are very significant to control the quality of reinforced 3D printed concrete. Due to the unique layer by layer deposition process of extrusion-based 3D printed concrete (3DPC), the bonding of steel bars with 3DPC differs from that with traditional cast concrete. To understand the steel-printed concrete bond behavior, this paper mainly explored the effect of preparation technologies, concrete rheological properties, steel bar diameter and paste coating on steel bars on the bond behavior between ribbed steel bars and concrete. According to pull-out test and X-ray computed tomography test, the results showed that bond strengths between 3DPC and steel bars were obviously lower than those between steel bars and cast concrete. The rheological properties of fresh concrete show significant impact on the bond behavior of reinforced 3D printed samples. Lower yield stress and plastic viscosity can narrow the bond strength gap between printed samples and cast samples. The utilization of surface coated steel bar with fresh cement paste can effectively enhance the steel-3DPC bond strength. The variations in steel–concrete bond strengths can be explained via pore structure at steel–concrete interface. The results suggest that it is of great importance to control the quality of reinforced 3D printed concrete by optimizing the rheological properties of fresh concrete for 3D printing.

Investigação dos mecanismos de resistência ao cisalhamento direto em peças de concreto com fibras de aço e PVA

Some mechanical properties of concrete can be improved with the addition of other materials, such as the incorporation of fibers, which results in increased tensile strength and toughness, presenting post-cracking behavior that significantly contributes to the transfer of shear stresses, especially in planes that are propitious to the formation of cracks. To evaluate the effects of the addition of fibers to concrete, in terms of the ultimate shear strength and the mechanisms that constitute it, such as cohesion between the component materials, aggregate interlock, friction and dowel action, an experimental program was carried out. Two mixtures were produced from a conventional concrete mix, with the addition of 0.5% steel fibers and 0.2% synthetic polyvinyl alcohol, PVA fibers. Specimens for direct shear testing, push-off type, were molded, with and without transverse shear reinforcement, and a steel-concrete bond condition was set as a variable. The results showed that the addition of steel fibers results in a significant increase in the shear strength of concrete, na effect not observed with PVA fibers. The aggregate interlock and cohesion mechanisms were responsible for approximately 70% of the ultimate shear strength in all the concrete tested, while the rest was attributed to friction and the dowel effect.

Bond Behavior of Concrete-Filled Steel Tube Mega Columns with Different Connectors.

Concrete-filled steel tubes (CFSTs) are widely used in construction. To achieve composite action and take full advantage of the two materials, strain continuity at the steel–concrete interface is essential. When the concrete core and steel tube are not loaded simultaneously in regions such as beam or brace connections to the steel tubes of a CFST column, the steel–concrete bond plays a crucial role in load transfer. This study uses a validated finite-element model to investigate the bond-slip behavior between the steel tube and concrete in square CFST mega columns through a push-out analysis of eleven 1.2- × 1.2-m mega columns. The bond-slip behavior of CFST mega columns with and without mechanical connectors, including shear studs, rib plates, and connecting plates, is studied. The finite-element results indicate that the mechanical connectors substantially increased the maximum bond stress. Among the analyzed CFST mega columns, those with closely spaced shear studs and rib plate connectors with circular holes exhibited the highest bond stress, followed by plate connectors and widely spaced shear stud connectors. In the case of shear stud connectors, the stud diameter and spacing influenced the bond behavior more than the stud length. As the stud spacing decreased, the failure mode shifted from studs shearing off to outward buckling of the steel tube.

Study on flexural behavior of spliced shallow composite beams with different shear connectors

The flexural behavior of spliced shallow composite beams with different shear connectors including steel–concrete bond force and slotted webs were experimentally studied in detail. Finite element models by using spring element to consider the bond-slip behavior between steel beam and concrete slab are developed and validated against the test results. The prediction formula for the flexural capacity of the beams is deduced and validated. The analysis results show that compared with the beam using slotted web shear connectors, the beam relying on steel–concrete bond force shows better flexural capacity and ductility. Both the beams failed in ductile failure mode. The shallow composite beams with partial shear connection have the excellent ability of stress redistribution which would be improved by decreasing the shear transfer coefficient. Through the comparison with the experimental results and numerical results, the prediction formula proposed in this paper for the flexural capacity of the composite beam with partial shear connection shows better accuracy than Eurocode.

Study of Attapulgite as an Additive in Reinforced Concrete by Substitution of Cement and Its Effects on the Durability Properties of Hardened Concrete

The valorization of Senegalese attapulgite clay in concrete, as a solution against the exhaustion of the cement deposits was studied. In that purpose, attapulgite was first calcined at 800°C to make it reactive and added in concrete by substitution of Portland cement (CEM I 52.5N) at contents of 0, 5 and 10% by conserving a constant water/cement ratio value of 0.65. The effects of the partial replacement of cement by attapulgite on the physicochemical and mechanical properties of the concrete as well as on the steel-concrete bond were examined. For this purpose, the water porosity, the intrinsic permeability and the density of the clay-based concrete were evaluated. Compression, tensile and pull-out tests were carried out to determine the impact of clay on the Young modulus, the compressive and tensile strengths and the steel-concrete bond. This study was completed by a characterization of the pozzolanic reactivity of calcined attapulgite. All the results of these studies were compared with those of Portland cement as a reference. The substitution of cement by attapulgite up to 10% in concrete has only a small influence on its porosity and permeability and confers to the concrete gain in compressive strength of 11%. However, it caused a loss of steel-concrete bond of 10%.

INVESTIGATION OF THE EXPERIMENTAL AND NUMERICAL FLEXURAL BEHAVIOR OF INNOVATIVE TOTALLY ENCASED COMPOSITE BEAMS

Composite steel-concrete beams have been widely used in long span construction and high rise buildings due to their favorable behavior in terms of high strength, stiffness, and ductility. In this research, the flexural behavior of an innovative steel-concrete composite section is investigated experimentally and verified numerically using ABAQUS software. The studied section is composed of steel tubular specimen or steel hollow pipe totally encased in concrete in the absence of any flexural or shear reinforcement. Instead, steel mesh wraps are used around the tubular steel specimen to provide sufficient steel-concrete bond. All of the studied beams have the same 3m length and T-section dimensions to provide adequate comparison of results. The influence of using different percentages of steel mesh wraps around the steel specimen and the structural steel shape effect on the failure mode and ultimate flexural capacity were investigated. It was found that the ABAQUS model has provided excellent simulation of the flexural response of the studied beams with acceptable difference in results as compared to those obtained from experimental testing. Besides, the presence of steel mesh wraps at highly compressive damaged locations have prevented concrete spalling and crushing in these zones by ensuring sufficient steel-concrete bond.