Ribbed Steel Research Articles

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.

Ground Characteristic Curve and Convergence Confinement Method - A case study

Ground Characteristic Curve (GCC) describes the relationship between the initial stress of rock mass and the displacement of rock mass on the boundary of tunnels. Another way that indicates the relationship of support pressure and the level of Convergence Confinement of tunnels by percent. The using GCC to design supports in the underground construction has many advantages to ensure full utilization of the loading bearing capacity of rock mass, and release a part of initial stress in the rock mass around tunnels. However, this method is limited in the field of underground mines in Viet Nam. This article analyzed and applied GCC and Convergence Confinement Method (CCM) to design the supports of underground constructions and applied them to the geological conditions of the Nam Mau coal mine - Vinacomin. The research results show that at the geological conditions of the drift at level +125 in Nam Mau coal mine, TH section steel ribs with flange width 124 mm, section depth 108 mm, weight 21 kg/m, maximum support pressure 1.98 MPa, and spacing 700 mm were applied. Results of research in this method can be applied to design rock supports for deep roadways and other drifts in the underground mines in Quang Ninh province of Viet Nam. By a factor of safety, mobilized support pressure, wall displacement of roadways, and convergence of roadways the designation and selection of rock support around roadways will become clearer. Near future this method should be widely applied in the combined protection design in deep roadways in underground mines in Viet Nam. Although the method has great advantages, it is still necessary to have complete and detailed monitoring data of the geological and hydrogeological conditions in the area under consideration.

Stability of steel pile walls and tunnels excavated by shield machines in the urban areas: A case study

Placement of infrastructure and other facilities underground brings superior opportunities for long-term improvements in terms of the environmental impact of urban areas and more efficient use of underground space. However, underground construction in urban areas is a high-risk activity and has been considered a challenging problem for geotechnical and structural designers. Therefore, the evaluation of the stability of underground structures plays a vital role in structural and construction design. This paper presents a case study on analyzing the stability of steel piles walls and tunnels excavated by shield machines in the urban area in Vietnam in terms of the change in internal forces in the structures. The research results show that the excavated stages of the basement influence on the values of internal force in the tunnel lining. In the case of study using composite lining in the tunnel, the thickness of lining concrete 35 cm, steel frame type I-W1000×883 are applied for tunnel excavated before construction of nearby basement, and 30 cm and W1000×350 steel ribs for the opposite side. This research could be applied to evaluate the effects of tunnel excavation near the existing structures in urban such as in the geological conditions in the Ha Noi and Ho Chi Minh City in the near future. However, this analysis also has the disadvantage that it does not consider the construction time as well as the construction sequence of the works during tunnel excavation. The shapes of the tunnel only are circular tunnels and the only type of steel piles in this research. Further study, total evaluation for other types of tunnels and walls of basements should be considered.

Green corrosion inhibition for carbon steel reinforcement in chloride-polluted simulated concrete pore solution using Urtica Dioica extract

In this work, Urtica Dioica (nettles) extract, which contains a variety of organic molecules with N, O and S heteroatoms, was added to provide green corrosion inhibition for carbon steel reinforcements in chloride-polluted (1% NaCl) simulated concrete pore solution. This specific extract had not been previously tested in high alkaline (pH 13.6) solutions. A global analysis was carried out, including electrochemical testing (to assess the inhibition ability of the extract), surface analysis (to check for the presence of organic molecules on the steel surface) and density-functional theory (DFT) quantum chemical calculations (to compute the absorption of inhibitor components on steel exposed to pH 13.6). After 24 h and determined with electrochemical spectroscopy test (EIS), the most efficient dosage (0.075%) of nettles showed that charge transfer resistance (Rct) values for ribbed steel were 4.3 times higher than in non-inhibited solutions, providing an inhibition efficiency of 77%. A similar reduction was determined for current density values from polarization tests. Analysis of the specimen after dipping it in the inhibited alkaline electrolyte via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) revealed the surface adsorption of organic molecules in the nettles extract and their contribution to reinforcing the oxide/hydroxide layer. Moreover, the semi-quantitative carbon amount inside the pits is 9 times higher than on the steel surface. DFT ab-initio calculations indicate that the Urtica Dioica extract can be adsorbed at the Fe2O3 surface with a charge transfer of about −0.028–0.23 e due to binding of N- and O- containing adsorbates. All results suggest the presence of organic molecules related to the nettles extract on steel surfaces under those tested solutions. The nettles extract is able to precipitate on the pits, hindering the development of the anodic reactions. The inhibition efficiency of nettles, their worldwide availability and their environmentally-friendly nature, combined with the readily manufactured extract all point to promising application in this field.

Analytical solution of the bond strength between ribbed steel bar and engineered cementitious composites considering the fiber bridging effect

AbstractThis paper investigated the analytical solution of the bond strength between ribbed steel bar and engineered cementitious composites (ECC). In this method, ECC cover was regarded as a thick‐walled cylinder subjected to the uniform internal pressure which consisted of an elastic uncracked outer ring and a partially cracked inner ring. For the uncracked outer ring, it can be solved by the elastic mechanics theory. To solve the partially cracked inner ring, two key problems that had to be investigated were the crack width and the tensile stress–crack width relationship of ECC. According to the steady‐state cracking mode, the hoop deformation of ECC was expressed by the equal distribution and then the crack width can be determined. Besides, the fictitious crack model in fracture mechanic was introduced to describe the crack propagation process. Then a trilinear model was applied to reflect the tensile stress–crack width relationship of ECC materials, which considered the combined action of aggregate bridging and fiber bridging on the crack surface. Finally, the comparison between the calculation results and experimental results was carried out to prove the validity of the analytic method of bond strength proposed in this paper. Results indicated that the analytical solution and the experimental data fitted in well with each other. Then parameter analyses were conducted based on the analytical method proposed in this paper.

Rust Distribution of Non-Uniform Steel Corrosion Induced by Impressed Current Method.

The non-uniform corrosion of steel bars is the main factor affecting the durability of concrete. The cracking pattern of concrete due to corrosion is closely related to the distribution of the corrosion products. Research on the thickness distribution of the rust layer and the cracking pattern of concrete under different influencing factors is of great significance in the prediction of the service life of existing reinforced concrete structures and the avoidance of the premature cracking of the reinforced concrete structures to be built. This paper studies the thickness distribution of the rust layer on the surface of single and multiple corroded reinforcements under non-uniform corrosion. The electrochemical analysis of the electrified corrosion process was carried out by using the finite element analysis software, and the distribution of the current density was obtained. The effects of geometric parameters, steel bar position, and steel bar spacing and shape on the corrosion expansion cracking pattern were studied. The results indicated that as the position of the steel bar differed, the crack pattern of the concrete changed, depending on the number of corrosion peaks (i.e., the maximum thickness of the rust layer). In terms of the corner-located steel, the number of corrosion peaks varied in the cases of different geometrical parameters (i.e., the diameter of the steel bar and the distance between the steel bars and the stainless steel wire). Nevertheless, the critical corrosion degrees of the side-located and corner-located steel bars, with respect to the cracking of the outer concrete surface, were basically the same. Additionally, the ribbed steel bar presented a lower critical corrosion degree than that of the plain steel bar, while little influence was exhibited with the varying angles of the rib.

Tetrahedral Profiled Carbon Rovings for Concrete Reinforcements

Textile reinforcements have established themselves as a convincing alternative to conventional steel reinforcements in the building industry. Due to their high load-bearing capacities in addition to a smaller concrete cross section required, the bond between textile and concrete is extremely important. In contrast to ribbed steel bars ensuring a stable mechanical interlock with concrete (form fit), the bond force of carbon rovings has so far been transmitted primarily via the coating of the textile, i.e. by an adhesive bond with the concrete matrix (material fit). However, this material fit must be activated over relatively large yarn areas, which does not allow material-efficient utilization of the mechanical load capacity of the textile reinforcement. Solutions involving profiled rovings promise significant improvements in the bonding behavior by creating an additional mechanical interlock with the concrete matrix. In order to achieve a form-fit effect between roving and concrete, a roving geometry inspired by ribbed steel bars has to be created. For this purpose, an innovative profiling process was developed and implemented.

Structural behavior of expanded rib steel bars used in reinforced concrete beams

Conventional headed rebar is advantageous in reducing embedment depth and simplifying construction; however, they are subject to concentrated stresses at the anchor point which can lead to failure of the structural element. To alleviate the stress concentration and avoid failure, rebars with numerous expanded ribs are proposed herein. The effects of expanded rib bars were investigated by comparing a jointed specimen with an expanded rib bar joint to a specimen with a conventional headed bar and an unjointed continuously reinforced specimen using the four-point bending test. The maximum strength, displacement ductility, cracking analysis, and rebar strain were recorded and analyzed. In terms of structural performance, the expanded rib bars outperformed the conventional headed bars and were equivalent to the unjointed continuously reinforced sections.

Vertical shear capacity of steel-concrete composite deck slabs with steel ribs

The design of steel-concrete composite (SCC) deck slabs is likely governed by the vertical shear under small shear span-depth ratios. This paper aims to propose the calculation method of the vertical shear capacity of the SCC deck slab (Vu). Firstly, Vu is computed as the summation of the contributions of concrete layer (Vc,u) and steel members (Vs,u). Vc,u is treated as the product of the shear capacity of an equivalent reinforced concrete member without web reinforcement and a coefficient that reflects the effects of steel ribs. The formula of Vs,u is developed based on the force equilibrium conditions between the concrete layer and steel members and the section analysis considering the steel-concrete slips. Later, an iterative calculation method is proposed and verified against experiments and finite element (FE) models established via validated simulation techniques. Lastly, an extensive parametric analysis is implemented using the iterative method, from which a simplified calculation method was proposed and proved. Results indicate the iterative method is able to capture the effects of material and geometric parameters, shear span-effective depth ratio, and the degree of steel-concrete interaction. The increases in the heights of concrete layer and steel rib, as well as the rib thickness, can effectively enlarge Vu, while the influences of the steel plate’s thickness and the steel-concrete slips are relatively minor. The iterative method produces accurate predictions with a mean error of 1% and a coefficient of variation of 0.05. The simplified method is more engineer-friendly and yields the average FE/test-predicted ratio being 1.11 as well as the percentage of safe predictions being 95%.

3D meso-scale modelling of the bonding failure between corroded ribbed steel bar and concrete

Subjected to a corrosive environment, the macroscopic behavior of reinforced concrete structures is closely related to the bond property between rebar and concrete. For assessing the material performance and evaluating the nonlinear bond behavior of the interface between corroded ribbed rebar and concrete, and finally revealing the meso-mechanical failure mechanism of the reinforced concrete structure, we propose a 3D mesoscopic model in the current paper. The following elements that may influence the macroscopic behavior of the reinforced concrete are considered in the model: (1) the friction resistance and the mechanical interaction between corroded ribbed rebar, rust and concrete (2) the surface characteristic of threaded ribbed bar. The proposed mesoscopic model allows us to assess the influences of corrosion on the bond performance of corroded reinforced concrete through a two-stage analysis: after considering the expansive behavior of the reinforced concrete in the model, we apply a pull-out force on the corroded rebar to evaluate the bond-slip behavior between the corroded rebar and concrete. For validating our model, we compare the failure patterns and corroded bond stress-slip curves calculated by the model and obtained by experimental means and found a good consistency between them. Finally, a modified model was developed to describe the corroded bond stress-slip relationship. It has been found that when relative slip is applied, the concrete continues to crack along pre-existing cracks caused by corrosion products until the concrete splitting failure accorded. With the increase of corrosion level, the shape of the bond stress-slip curve is similar with a significantly degradation of the bond strength and peak slip, especially at small corrosion levels. Through comparing the proposed modified formula with the existing test data, one can find that the proposed modified formula can effectively characterize the corroded bond stress-slip relationship between deformed rebar and concrete.

Experimental Study on the Behavior of a Novel Stiffened Hexagonal CFDST Stub Column under Axial Load

A concrete-filled double skin tube (CFDST) consists of an outer steel tube, an inner steel tube, and the space between them filled with concrete. Existing studies have shown that the buckling of steel tubes can be significant in noncircular CFDST for nonuniform confinement or a large width-thickness ratio. Stiffening of the steel tubes is necessary to fully utilize the strength and improve the load-carrying capacity of CFDST. Against this background, the author proposed a novel stiffened hexagonal CFDST column with steel strips welded on both the inner tube and outer tube to form several closed cavities. This paper presents an experimental study on the axial compressive behavior of this new type of CFDST column. The experimental program consisted of five stiffened hexagonal CFDST specimens and two reference specimens for comparison, and the test variables were the hollow ratio and rib width. The test results showed that the ultimate bearing capacity and ductility of the CFDST specimens were greatly enhanced by the steel strips and ribs. Moreover, the finite-element (FE) method was used to develop a three-dimensional model of the CFDST column subjected to axial loading and validated against the experiment. The average error of the FE analysis when predicting the column bearing capacity was 0.029 compared with experimental results. Based on the FE model, a parametric study was conducted to analyze further the effect of each parameter on the axial behavior. Furthermore, a strength design formula was developed to estimate the compressive strength of the novel hexagonal CFDST column.

Experimental and analytical studies on mechanical performance of innovative energy-dissipating hold-down for CLT structures

Connection is the most important part in cross-laminated timber (CLT) buildings as it guarantees necessary strength, stiffness, ductility, and integrality for the whole CLT structure. This paper proposes an innovative energy-dissipating hold-down connection for CLT structures, which combines the advantages of the soft-steel bracket and high-damping rubber for providing great energy-dissipating capacity and high ductility. A series of tests were performed under quasi-static monotonic and reversed cyclic loading to investigate the failure mechanisms and mechanical properties of the novel hold-down connection. Test results demonstrate that the connections can continue to work as a whole even after the occurrence of preliminary failures of steel ribs rupture and weld fracture. Final failure modes, including debonding between the rubber and steel plates, rupture of the front steel plate and breakage of screws, caused the invalidation of the connection. Meanwhile, load–displacement curves of the connections usually exhibit a bi-linear form, and the connection’s yielding is caused by the yielding of steel ribs. All the tested specimens exhibited stable energy-dissipating capacity in the working stage and were all classified as highly ductile. Furthermore, efforts were made to develop a simplified analytical model for estimating the basic mechanical properties of the novel hold-down connections. Comparison with test results shows that the analytical model can provide reasonable estimations of the initial stiffness, post-yield stiffness, yield force and failure force. The test results and analyses presented herein provide useful technical bases for supporting future studies and practical applications of the novel hold-down connection for CLT buildings.

Bond of Ribbed Steel Bar in High-Performance Steel Fiber Reinforced Expanded-Shale Lightweight Concrete

For the structural application of high-performance Steel Fiber Reinforced Expanded-shale Lightweight Concrete (SFRELC), a reliable bond of ribbed steel bar should be ensured. In this paper, an experimental study was carried out on the bond properties of ribbed steel bar embedded in SFRELC by the direct pull-out test. The SFRELC was produced with a strength grade of 35 MPa and a volume fraction of steel fiber as 0%, 0.8%, 1.2%, 1.6% and 2.0%, respectively. Fifteen groups of specimens were made with a central placed steel bar with diameter of 14 mm, 20 mm and 28 mm, respectively. Complete bond stress-slip curves were determined for each group of specimens, and the characteristic values of bond-stress and slip at key points of the curves were ascertained. Results show that the bond strength, peak-slip and residual bond strength increased with the increase of the volume fraction of steel fiber. With the increase of steel bar diameter, bond strength decreased while the peak-slip increased, and the descending curves became sharp with a decreased residual bond strength. Formulas for calculating the bond strength and peak-slip were proposed. The relationships were determined for the splitting bond strength, residual bond strength with the bond strength, the splitting bond slip and residual bond slip with the peak-slip. Combined with rational fitting analyses of bond strength and slip, a constitutive model was selected for predicting the bond stress-slip of ribbed steel bar in SFRELC.

Mechanical Properties of Hot Rolled Ribbed and Plain Steel Rods

This study focuses on microstructure and mechanical behaviour of 3PS (Semi-killed mild steel) hot rolled ribbed and plain carbon steel. 3PS billet steel samples and hot rolled ribbed and plain steel rods of different heat numbers and profiles were characterized for its chemical composition, microstructure, and tensile behaviour. The composition analysis of 5 (five) 3PS billet samples shows that there was no appreciable variation in chemical composition of the hot-rolled plain and ribbed steel rods. The microstructures of as-received steel billet (3PS) examination revealed large grains of ferrite and pearlite while those of hot-rolled 3 PS mild steel samples of different heat numbers contain smaller grains of ferrite and some amount of pearlite. The results also indicated that yield and ultimate tensile strength reach maximum values (492 and 361 N/mm2) at 0.31% elongation for heat number 43 while maximum values for heat number 56 (478 and 362 N/mm2) at 0.33 % respectively. The ribbed steel rod of the same diameter as plain steel exhibit slightly better mechanical properties with higher values of yield and ultimate tensile strength. There is consistency in the chemical composition of the as-received billet and the hot rolled products.

STUDY ON BONDING PROPERTY OF POLYURETHANE CEMENT (PUC) TO STEEL BAR

The pull-out test of the bar and PUC is carried out in this paper, the effects of protective layer thickness, reinforcement anchorage length, diameter and shape of reinforcement on bonding properties were studied. The results show that the bond strength between reinforcement and PUC material increases with the increase of the thickness of the protective layer, but decreases with the increase of the anchorage length and diameter of reinforcement. The bond strength of bare round steel is significantly lower than that of ribbed steel, and the maximum bond strength is about 47.4% of ribbed steel. By analyzing the bond slip curve obtained from the pull-out test, the stress process of bond anchorage between reinforcement bar and PUC material is mainly summarized into three stages: the rising stage, the falling stage and the residual stage. The characteristics of the curve, the stress process and the failure mode of specimen at each stage are analyzed.

Influence of high temperatures on the bond between carbon Fibre-Reinforced polymer bars and concrete

The effect of corrosion on reinforced concrete structures can lead to significant economic losses. Therefore, steel bars used in the concrete structures must be replaced with a different material that can withstand water contact without causing corrosion and can ensure the safe operation of the structure during its lifespan, even in adverse weather. Carbon-fibre-reinforced polymer (CFRP) bars are one of the materials that can replace steel bars and they have already been applied as a substitute previously. This study analyses the bonding of these bars with concrete at high temperatures and for longer time periods. It presents an experimental plan that involves a series of pullout trials at different ages, days, and thermal conditions in CFRP rods either treated with ribbed steel bars or that underwent sand-ribbed surface treatment. Some compression tests for each mixture were performed at the same ages and temperatures as the experimental plan in pullout to determine the influence of high temperatures on concrete. The study completed with some complementary tests on the CFRP rods using optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM), from the evaluated pullout samples. The high temperature significantly affected the ribbed CFRP bars by diminishing their bond stress and did not affect the sanded CFRP bars. This uneven behaviour and the influence of high temperature on concrete resistance at the age of 180 d is justified.

Engineering geological investigations for designs of excavation method and support system of diversion tunnel at Bulango Ulu Dam, Indonesia

This paper presents engineering geological investigations for designs of excavation method and support system of a diversion tunnel at Bulango Ulu Dam, Indonesia. Evaluation of drill cores along the tunnel was carried out to determine the geological engineering conditions. Classifications of rock masses were carried out based on the Central Research Institute of Electric Power Industry (CRIEPI) and Rock Mass Rating (RMR) to analyze the excavation method and support system. The rock masses along the tunnel were classified into D, CL, and CM classes based on the CRIEPI and poor, fair, and good quality based on the RMR. The tunnel portals consisted of poor quality rock masses, while the main tunnel section consisted of good quality rock masses. The excavation method of full-face was proposed for the main tunnel section, while top heading and bench were proposed for the tunnel portals and main tunnel section having fair quality rock masses. The support system recommended for tunnel portals were 4-5 m long, 1-1.5 m spaced systematic bolts, 100-150 mm thick shotcrete, and 1.5 m spaced steel ribs. Meanwhile, the support system proposed for the main tunnel section was 3 m long, 2.5m spaced bolts, and 50mm thick shotcrete in the crown.

Rock mass classification for design of excavation method and support system of tunnel 1 Sigli-Aceh toll road, Indonesia

This paper presents an empirical design of the excavation method and the support system of tunnel 1 of the Sigli-Aceh toll road, Indonesia, based on the rock mass quality of Rock Mass Rating (RMR) and the Japan Society of Civil Engineers (JSCE). The results showed that the tunnel route consisted of fair to good quality calcarenite interlayered by sandstone and D II to C II rock categories based on the RMR and JSCE. Based on the RMR, recommended excavation method for the tunnel section having fair to good quality rock mass is the full-face, top heading and bench methods. The recommended support system is a rock bolt with a length of 3 - 4 m, spacing 1.5-2.5 m, shotcrete thickness 5 - 10 cm. Meanwhile, the recommended excavation method based on the JSCE classification with rock categories DII and CII is bench cut, and full-face methods with auxiliary bench cut. The recommended support system is a rock bolt with a length of 3 - 4 m, spacing 1.2 m, shotcrete thickness 10 - 20 cm, steel ribs H-125 -H-150, spacing 1-1.2 m, and lining 30 cm on the wall and 40 - 50 cm on the floor.

Investigation of cold drawing process of thin-walled ribbed steel tube

Cladding tube is an important part of nuclear power components. This paper presents a simulation and experimental study on the cold drawing process of one kind of cladding tubes, namely thin-walled ribbed steel tube. Three kinds of drawing processes are studied: single pass drawing, tube sinking and fixed-plug combined drawing process, and two pass fixed-plug drawing process. The finite element (FE) simulation model considering Johnson-Cook constitutive equation is established to analyze the effective stress, effective plastic strain, and contact force in different drawing processes. Different out diameter (OD) and wall thickness (WT) 316L stainless steel (SS) tubes are used to investigate the forming process of the ribbed tube. Furthermore, experiments with the same parameter settings are compared with the simulations. It is found that the simulation and experimental results are in good agreement, the ribs height highly depends on the tube OD and WT. The results show that the formation of tube ribs is caused by the extrusion of the drawing die. In addition, during the forming of the tube ribs, inner grooves will be formed on the inner wall of tube, and the fixed-plug drawing process can effectively reduce the depth of the inner groove. Finally, the microstructure and hardness of the ribbed tube at different position are investigated. This work provides a reference for the integrated forming process of the ribbed tube.

Effect of steel–FRP ratio and FRP wrapping layers on tensile properties of glass FRP-wrapped ribbed steel reinforcing bars

Effect of steel–FRP ratio and FRP wrapping layers on tensile properties of glass FRP-wrapped ribbed steel reinforcing bars