Mild Steel Bars Research Articles

Hysteretic behavior of precast segmental bridge piers with superelastic shape memory alloy bars

Precast segmental bridge constructions are currently the subject of intensive research in several countries around the world: the USA and Taiwan, amongst others. Especially in the case of post-tensioned (PT) segmental bridge piers, several methods have been suggested to increase the energy dissipation capacity, such as the use of fiber reinforcement, exterior yielding devices at the base segment, and mild steel bars. As a new alternative, in this paper, the use of superelastic shape memory alloy (SMA) bars is suggested in order to improve the hysteretic performance including the energy dissipation capacity of the bridge columns. The use of SMA bars ensures a self-centering capacity to the PT column system. The segments are connected strongly to each other by using rigid links which prevent potential joint openings. Opening at the bottom of the base segment is allowed, leading to the same behavior as that of a single rocking column which is similar to a double-hinged gravity column. Such a column is modeled with a moment–curvature relationship and spread nonlinearity (plasticity) model. Unbonded PT tendons are modeled by a linear spring and the uniaxial behavior of the superelastic SAM bars is modeled with a combination of four springs, namely a post-yielding spring, a hysteretic spring, a slip-lock spring and a gap-closing spring. The SMA model developed provides a good cyclic performance. Considering a segmental bridge pier with 7.5 slenderness, a quasi-static cyclic analysis is carried out to investigate the hysteretic response. The results show that stable energy dissipation, self-centering, and high ductile behavior are achieved with the PT column system.

Dynamic impact characteristics of KN-18 SNF transport cask – Part 1: An advanced numerical simulation and validation technique

Domestic and international regulations for the transportation of radioactive materials strictly prescribe the design requirements for spent nuclear fuel (SNF) transport casks. According to the applicable codes, a transport cask must withstand a free-drop impact of 9 m onto an unyielding surface and a free-drop impact of 1 m onto a mild steel bar. However, the structural performance of a transport cask is not easy to evaluate precisely because the dynamic impact characteristics of the cask, which includes impact limiters to absorb the impact energy, are so complex. In this study, a more advanced and applicable numerical simulation method using the finite element (FE) method via the commercial FE code LS-DYNA is proposed and verified against the experimental results for a 1/3-scale model of the KN-18 SNF transport cask, recently developed in Korea. In addition, the detailed dynamic impact characteristics of the transport cask under free-drop conditions are investigated via the proposed numerical simulation method and actual drop tests to improve the accuracy and optimization of the SNF transport cask design.

Seismic Performance of Face Loaded Unreinforced Masonry Walls Retrofitted Using Post-Tensioning

Out-of-plane flexural testing of three full-scale unreinforced masonry (URM) walls seismically retrofitted using post-tensioning is reported. The selected wall configurations were representative of common URM walls that were vulnerable to out-of-plane failure, and imitated heritage URM construction by using salvaged clay brick masonry and ASTM type O mortar. Varying levels of pre-compression were applied to the test walls using a single mechanically restrained tendon inserted into a cavity at the centre of each test wall. Three different types of tendons were used for post-tensioning of the test walls, being threaded mild steel bar and sheathed greased seven wire strands (with tensile yield strengths of 1300 and 1675 MPa). Behaviour of the post-tensioned URM walls was compared to the response of a non retrofitted URM wall, with the out-of-plane flexural strength of the post-tensioned masonry walls observed to range from 2.9 to 10.3 times the strength of the non retrofitted URM wall. Several aspects pertaining to the seismic behaviour of post-tensioned masonry walls were investigated, including tendon stress variation, damage patterns, force displacement behaviour, initial stiffness and displacement capacity. Test results were compared with equations developed in previous studies, and it was established that the walls that were post-tensioned using seven-wire strands had measured strengths that compared favourably with predicted values, whereas the wall that was post-tensioned using mild steel bar had failed at a lower measured strength than the predicted value.

Smeared Rotating Crack Model for Reinforced Concrete Membrane Elements

This paper presents new constitutive laws for describing the behavior for normal-strength concrete and mild steel bars embedded in concrete. The proposed constitutive laws consider the effect of reinforcement ratio on average stress-strain relationships of cracked concrete and consider the gradual reduction of average stiffness of steel bars embedded in concrete. Equilibrium, compatibility, and constitutive relationships were incorporated into a nonlinear analysis procedure to develop a smeared rotating crack model. The model has the capability of predicting the entire load-deformation response of reinforced concrete membrane elements. Corroboration with data from panel test specimens shows that the model provides good predictions for the entire load-deformation response of elements over a wide range of conditions. Compared to alternative models, the new model was simpler and provided better accuracy in some situations, such as when panels contain heavy amounts of reinforcement in both directions and when panels contain little or no transverse reinforcement.

Evaluation of the Low-Cycle Fatigue Life in ASTM A706 and A615 Grade 60 Steel Reinforcing Bars

The low-cycle fatigue behavior of ASTM A706 and A615 Grade 60 (420 MPa) deformed reinforcing steel bars were evaluated experimentally. Although this study was initiated to evaluate the low-cycle fatigue of reinforcing bars in precast hybrid frame connections, the conclusions presented here may also apply to other relevant applications. Laboratory tests were performed under strain-controlled cyclic axial loading with nonzero mean strains. The deformed bars were subjected to constant-amplitude sinusoidal strains ranging from zero to peak strains that varied between 2 and 8% in different tests. All tests were performed on unmachined bar specimens. The experimental data were analyzed and compared with existing low-cycle fatigue models. Such models relate the total and plastic strain ranges to the number of cycles to failure. Relationships for calculating the tensile and compressive stresses corresponding to maximum strains are proposed based on the experimental results. Equations that relate dissipated energy to strain amplitudes and the number of cycles to failure are developed. This study demonstrates that the low-cycle fatigue responses of ASTM A706 and A615 mild steel bars are similar even though their monotonic ductility ratios are very different. The proposed low-cycle fatigue relationships for both ASTM A706 and A615 mild steel bars can be used to calculate maximum permissible strains in applications such as the precast/prestressed hybrid frames. The prediction of bar fracture due to low-cycle fatigue is an important consideration in the seismic design of reinforced and precast/prestressed concrete structures.

Nonlinear finite element analysis and modeling of a precast hybrid beam–column connection subjected to cyclic loads

In this work, a detailed three-dimensional (3D) nonlinear finite element model is developed to study the response and predict the behavior of precast hybrid beam–column connection subjected to cyclic loads that was tested at the National Institute of Standards and Technology (NIST) laboratory. The precast joint is modeled using 3D solid elements and surface-to-surface contact elements between the beam/column faces and interface grout in the vicinity of the connection. The model takes into account the pre-tension effect in the post-tensioning strand and the nonlinear material behavior of concrete. The model response is compared with experimental test results and yielded good agreement at all stages of loading. Fracture of the mild-steel bars resulted in the failure of the connection. In order to predict this failure mode, stress and strain fields in the mild-steel bars at the beam–column interface were generated from the analyzed model. Such fields of stresses and strains are hard to measure in experimental testing. In addition, the magnitude of the force developed in the post-tensioning steel tendon was also monitored and it was observed that it did not yield during the entire loading history. Successful finite element modeling will provide a practical and economical tool to investigate the behavior of such connections.

Corrosion of Bare and Galvanized Mild Steel in Arabian Gulf Environment

Corrosion performance of bare and galvanized mild steel in atmospheric, soil and splash zone exposure conditions was evaluated at a Khaleej Mardumah test station (KMTS) in Jubail Industrial City (JIC) located at Arabian Gulf coast. The samples were exposed for a period of 15 months. During the exposure, the environmental conditions were periodically monitored by analysis of air, soil, groundwater, and seawater samples. The corroded mild steel and galvanized steel samples were examined by SEM, XRD and XRF to identify the corrosion products and study their surface morphology. Weight loss method was employed to determine the corrosion rates. The experimental results showed that intense temperature and humidity variations as well as high chloride and sulfate concentrations in the region result in severe corrosion of bare mild steel especially under the splash zone conditions. A comparison with the corrosion data for other parts of the world shows that atmospheric and soil environments at the selected test site are significantly corrosive to mild steel. The splash zone, on the other hand, is much more corrosive to mild and galvanized steel than the other parts of the world.

Effect of plasma surface treatment on mechanical and corrosion protection properties of UV-curable sol-gel based GPTS-ZrO2 coatings on mild steel

Abstract Hybrid sol-gel based nanocomposite coatings derived from hydrolysis and condensation of a photopolymerizable silane precursor 3-Glycidoxypropyltrimethoxy silane in combination with zirconium-n-propoxide were deposited on mild steel substrates by a dip coating technique. In some cases, substrates were subjected to an atmospheric air–plasma surface pre-treatment prior to coating deposition. The coatings were subsequently densified by exposure to ultraviolet radiation followed by a thermal treatment at 250 °C. Characterization of the coatings with respect to thickness, water contact angle, pencil scratch hardness, adhesion and abrasion resistance was carried out. Corrosion testing was carried out on the coatings for a 1 h exposure to a 3.5% NaCl solution by electrochemical polarization and impedance measurements. The hybrid sol-gel coatings were found to improve the mechanical properties and corrosion resistance of mild steel. Plasma surface pre-treatment was found to improve the adhesion of coatings significantly and decreased the corrosion rate from 0.2652 mpy obtained for coatings without any surface pre-treatment to 0.0015 mpy, which was nearly 600 times lower than that of bare mild steel.

Evaluation of corrosion and wear resistance titanium nitride (TiN) coated on mild steel (MS) with brush plated nickel interlayer

Titanium nitride (TiN) coatings were deposited on mild steel (MS) by direct current reactive magnetron sputtering. With the aim of improving the corrosion resistance of TiN, an additional nickel interlayer was brush plated on the steel substrates before TiN film formation. The phases have been identified with X-ray diffraction analysis. The hardness values of TiN layers were found to increase with the increase in thickness of the Ni interlayer. The wear track investigations of TiN layers showed that the TiN/MS system was worn out by abrasive wear mechanism while on the film with Ni interlayer is by adhesive wear. It was found that the TiN/Ni/MS stack had a weaker tendency towards corrosion and higher corrosion resistance in 3·5%NaCl than the bare MS substrate, Ni/MS and TiN/MS specimen.

Large-Scale Experimental Study of Precast Segmental Unbonded Posttensioned Concrete Bridge Columns for Seismic Regions

The seismic behavior of the proposed precast segmental unbonded posttensioned concrete bridge columns for use in regions of high seismicity was investigated experimentally. Posttensioning tendons were placed in the hollow core of the columns and left unbonded with the surrounding concrete to decrease prestress loss during earthquakes. Bonded mild steel bars continuous across the segment joints, also referred to as energy dissipation (ED) bars, were used to enhance the seismic resistance of the columns. The bars were unbonded at the critical joint to avoid premature low cycle fatigue failure. The objectives of this study were to (1) verify the proposed construction method and seismic detailing for the ED bars and (2) investigate the seismic behavior of the columns with different ED bar ratios and posttensioning forces. Four large-scale specimens were designed and tested with lateral cyclic loading. Test results showed that the proposed construction method and seismic detailing for the ED bars were effectiv...

Mechanical behaviour of Zn–Fe alloy coated mild steel

Zinc alloy coatings containing various amounts of Fe were deposited by electrodeposition technique on a mild steel substrate. The concentration of Fe in the produced alloy coatings ranged from 0 to 14 wt.%, whereas the thickness of the coatings was about 50 μm. Structural and metallurgical characterization of the produced coatings was performed with the aid of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. This study aims in investigating the mechanical behaviour of Zn–Fe coated mild steel specimens, as no research investigation concerning the tensile behaviour of Zn alloy coated ferrous alloys has been reported in the past. The experimental results indicated that the ultimate tensile strength of the Zn–Fe coated mild steel was lower than the bare mild steel. In addition, the ductility of the Zn–Fe coated mild steel was found to decrease significantly with increasing Fe content in the coating.

A Non-Linear 3D FEM to Simulate Un-Bonded Steel Reinforcement Bars under Axial and Bending Loads

This paper presents development of 3D non-linear finite element model to simulate the response and predict the behavior of un-bonded mild steel bars under axial and bending loading. The models were successfully analyzed with the finite element software ANSYS, taking into account the nonlinear material properties of the reinforced mild steel bars. A bending strain relationship is derived based on a parametric study involving multiple nonlinear finite element models. A mild steel fracture criterion based on low-cycle fatigue models is proposed to control the total (elastic and plastic) strains in the mild steel bar below a maximum permissible limit. In addition, FE predictions of bar elongation due to strain penetration reasonably agreed with a proposed empirical equation by Raynor and Lehman. It was concluded that the equation proposed by Raynor and Lehman is considered valid for estimating the additional unbounded length and can be used in both analysis and design.

Structure, mechanical and corrosion properties of DC reactive magnetron sputtered aluminum nitride (AlN) hard coatings on mild steel substrates

Aluminum nitride (AlN) coatings of about 2 μm thick were deposited on mild steel (MS) by means of direct current (DC) reactive magnetron sputtering. AlN coatings were prepared in an Ar + N2 gas mixture and their crystal structure, microstructure, and topography were analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. XRD revealed that the films are polycrystalline in nature and have a hexagonal wurtzite structure with a predominant peak observed along the (002) plane. SEM and AFM images showed the presence of continuously covered pebble like spherical grains on the surface. These coatings showed lower coefficient of friction and excellent wear resistance compared to the bare MS substrate. The potentiodynamic polarization studies showed lower corrosion current density and higher polarization resistance for the AlN/MS structure than the uncoated MS substrate.

ULTIMATE SHEAR STRENGTH OF PRESTRESSED CONCRETE MEMBERS CONSIDERING BOND STRESS OF PRESTRESSING STEEL

Analytical methods based on truss and arch mechanisms were proposed to predict the ultimate shear strength of prestressed concrete members. Yielding of longitudinal mild steel bars and prestressing tendons were taken into account. Bond capacity of prestressing tendons was also included in the analyses. Test results from 119 prestressed concrete beams and columns in the past literature were compared with the analytical results in terms of the ultimate shear capacity. The proposed methods gave a better and more accurate estimation of the ultimate shear capacity than the method provided in the standard for design and construction of prestressed concrete structures published by Architectural Institute of Japan. The accuracy did not depend on the experimental parameters such as shear reinforcement ratio, axial force level, shear span ratio and concrete compressive strength specified for the specimens.

HI-STAR 100 spent fuel transport cask analytical evaluation for drop events

The US Nuclear Regulatory Commission (NRC) is responsible for licensing commercial spent nuclear fuel transported in casks certified by NRC under the Code of Federal Regulations (CFR), Title 10, Part 71. Both the International Atomic Energy Agency (IAEA) regulations for transporting radioactive materials (Ref. 2, paragraph 727) and 10 CFR 71·73 require casks to be evaluated for hypothetical accident conditions, which includes a 9 m (30 feet) drop impact event on a flat, essentially unyielding, horizontal surface, in the most damaging orientation. The present paper examines the behaviour of one of the NRC certified transportation casks, the HI-STAR 100, for drop impact events. The specific area examined is the behaviour of the bolted connections in the 'overpack' top flange and the closure plate, which are significantly loaded during the hypothetical drop impact event. The term 'overpack' refers to the cask that receives and contains a sealed multipurpose canister (MPC) containing spent nuclear fuel. The analytical work to evaluate the NRC certified HI-STAR 100 spent fuel transport cask for a 9 m (30 feet) drop impact event on a flat, unyielding, horizontal surface, was performed using the ANSYS and LS-DYNA finite element analysis codes. The models were sufficiently detailed, in the areas of bolt closure interfaces and containment boundaries, to evaluate the structural integrity of the bolted connections under 9 m (30 feet) free drop hypothetical accident conditions, as specified in 10 CFR 71·73. Evaluation of the cask for puncture, caused by a free drop through a distance of 1 m (40 inch) onto a mild steel bar mounted on a flat, essentially unyielding, horizontal surface, required by 10 CFR 71·73, was not included in the current work. Based on the analyses performed to date, it is concluded that, even though brief separation of the flange and the closure plate surfaces may occur, the seals would close at the end of the drop events, because the materials remain elastic during the duration of the event.

Bond performance of polystyrene aggregate concrete (PAC) reinforced with glass-fibre-reinforced polymer (GFRP) bars

This paper concerns the bond performance of GFRP bars in polystyrene aggregate concrete (PAC) by the proposed concentric pullout test. Identical specimens reinforced with mild steel bars were used for comparison. The bond performance including the mode of failure and bond strength was studied with varying polystyrene aggregate content, concrete strength, embedment length, shape and surface treatment of the bars. Empirical formulae were developed for the estimation of development length on the basis of the pullout test results. The bond development length ( l d ) determined according to ACI Building Code was used for comparison. Considering the bond performance, the sand-coated GFRP bar gave the most promising results with the highest bond strength attained. In particular, the bond strength was found increased with the compressive strength and concrete density of PAC. Besides, the bond development length for PAC reinforced with GFRP bars can be predicted satisfactorily using the ACI equation.

Anilinium 5-sulfosalicylate electropolymerization on mild steel from an aqueous solution of sodium 5-sulfosalicylate/disodium 5-sulfosalicylate

Aniline is electropolymerized on bare and chemically pretreated mild steel from an aqueous solution of 0.10 M anilinium 5-sulfosalicylate in 0.20 M sodium 5-sulfosalicylate/0.20 M disodium 5-sulfosalicylate buffer as the supporting electrolyte, at room temperature. At constant anodic potential black poly(anilinium 5-sulfosalicylate) (PANISSA) films are obtained on bare mild steel and characterized by IR spectroscopy, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). IR spectroscopic analysis confirms typical polyaniline structure with 1,4-disubstituted aromatic nuclei and incorporation of sulfosalicylate anions as dopants. Adhesion of PANISSA films is significantly improved when the mild steel electrode surface is chemically pretreated by 0.10 M ammonium peroxydisulfate aqueous solution. The IR spectra of the films obtained on chemically pretreated mild steel surface indicate an interaction between PANISSA and products of the mild steel oxidation by peroxydisulfate. The SEM images show differences in morphology between PANISSA films synthesized on bare and chemically pretreated mild steel surface. The efficient anticorrosion behavior of adherent PANISSA film on chemically pretreated mild steel is proved by EIS.

Mechanical testing of steel/aluminium–silicon interfaces by pushout

The functionality of structural light alloy castings can be improved by inserting into them, upon moulding, local iron base reinforcements. To acquire a better knowledge of such bimetallic assemblies, samples were prepared by immersing a mild steel bar (5 mm in diameter) in aluminium base Al–Si alloy melts held at 730 °C. After melt solidification, the bimetallic samples were cut into 5 mm thick slices and pushout testing was performed on these slices. Characterization of damaging corresponding to different load level before complete debonding allows the determination of the failure mode. Crack initiation occurs at the specimen bottom face in the intermetallic reaction layer, important damage occurs before complete debonding and no brittle failure is observed. The results highlight the necessity of analysing pushout tests with a more integrated approach taking into account shear stress distribution along the interface such as interfacial crack growth.

Local reinforcement of magnesium base castings with mild steel inserts

The functionality of structural light alloy castings can be considerably improved by inserting into them upon moulding iron base local reinforcements. A necessary condition to obtain tight joints with good load transfer is that a sound metallurgical bond is formed at the insert/alloy interface. However, many physical–chemical factors play an important part in the mechanical behaviour of the joint. To acquire a better insight into this issue, bimetallic samples were prepared by immersing a mild steel bar (5 mm in diameter) in magnesium base Mg–Al alloy melts held at 650–750 °C in a graphite crucible (mean diameter 19 mm). Different processing conditions were used to vary the degree of chemical interaction at the insert/alloy interface. After melt solidification, the bimetallic samples were cut into slices (2–10 mm thick) and push out testing was performed on these slices. Attempts have been made to relate the main features of the load–displacement curves thus obtained with the nature and extent of the transition zones formed at the insert/alloy interface.

Shear strength of concrete beams reinforced with steel bars milled from scrap metals

The paper reports a study on the shear resistance of concrete beams reinforced with mild steel bars that are milled from scrap metal such as old vehicle parts and obsolete machinery. It has been previously reported that because the chemical compositions of carbon, sulphur and phosphorus in these reinforcing steel bars exceed the maximum allowable limits, the characteristic tensile strengths are too high and ductility too low for standard mild steel. Concrete beams reinforced with such bars to resist flexural tensile and shear stresses were tested under a two-point loading system to provide a central constant moment region and outer shear spans. Tested beams exhibited little deflection and very low ductility prior to collapse. Experimental failure loads for the beams averaged 123% of the theoretical failure load, which was generally governed by either shear or yielding of the tension steel. Shear failure was mostly initiated by diagonal tension cracks, followed by either crushing of the concrete, or splitting of the concrete over the longitudinal tensile bars near the supports. Failure of the beams was brittle and the post-cracking strain energy absorption averaged 357.9 Nm. At failure the maximum crack width in the beams ranged from 1.12 to 5.0 mm, the largest sizes forming in the diagonal shear cracks.