Short and randomly distributed steel fibres are often used for concrete reinforcement since they offer resistance to crack initiation and, mainly, to crack propagation. In steel fibre reinforced concrete (SFRC) of low fibre volume content, the fibre reinforcement effectiveness is only significant
after matrix cracking , since fibres crossing the crack guarantee a certain level of stress transfer between the faces of the crack, providing to the concrete a residual strength, the magnitude of which depends on the fibre, matrix and fibre-matrix propertie s. The mechanical performance of SFRC is also highly influenced by the fibre dispersion, since the effectivenes s of fibre reinforcement depends on the orientation and arrangement of the fibres within the cement matrix.
The present work resumes the experimental and numerical research carried out for the development of a numerical tool able of simulating the tensile behaviour of steel fibre reinforced self-compacting concrete (SFRSCC). SFRSCC is assumed as a two phase material, where the nonlinear material behaviour of SCC matrix is modelled by a 3D smeared crack model, and steel fibres are assumed as embedded short cables distributed within the SCC matrix according to a Monte Carlo method. The internal forces in the steel fibres are obtained from the stress - slip laws derived from the executed fibre pullout tests. The performance of this numerical strategy was appraised by simulating the tensile tests carried out. The numerical simulations showed a good agreement with the experimental results.
In this paper, an innovative thermally efficient sandwich structural panel is proposed for the
structural walls of a pre-fabricated modular housing system. Traditionally, sandwich concrete panels
consist of conventional reinforced concrete wythes as external layers, polystyrene foam as core
material and steel connectors. However, steel connectors are known to cause thermal bridges on the
building envelope and possibly condensation and mould problems. Furthermore, the possibilities for
thickness reduction/optimization of conventionally reinforced concrete layers are frequently limited by
minimum cover requirements. To overcome these issues, the proposed sandwich panel comprises
Fibre Reinforced Polymer (FRP) connectors and two thin layers of Steel Fibre Reinforced SelfCompacting Concrete (SFRSCC). This paper presents the basic conception of the proposed building
system together with preliminary parametric numerical analyses to define the arrangement and
geometry of the elements that constitute the sandwich panels. Finally, the feasibility of using the
proposed connector and SFRSCC on the external wythes is experimentally investigated through a
series of pull-out tests where failure modes and load capacity of the connections are analysed.
This paper presents a design oriented model to determine the moment-curvature relationship of
elements of rectangular cross section failing in bending, made by strain softening or strain hardening
fibre reinforced concrete (FRC) and reinforced with perfectly bonded pre-stressed steel and fibre
reinforced polymeric (FRP) bars. Since FRP bars are not affected by corrosion, they have the
minimum FRC cover thickness that guaranty proper bond conditions, while steel bars are positioned
with a thicker FRC cover to increase their protection against corrosion. Using the moment-curvature
relationship predicted by the model in an algorithm based on the virtual work method, a numerical
strategy is adopted to evaluate the load-deflection response of statically determinate beams. The
predictive performance of the proposed formulation is assessed by simulating the response of available
experimental results. By using this model, a parametric study is carried out in order to evaluate the
influence of the main parameters that characterize the post cracking behaviour of FRC, and the prestress level applied to FRP and steel bars, on the moment-curvature and load-deflection responses of
this type of structural elements. Finally the shear resistance of this structural system is predicted
The use of twisted stainless steel bars has proven to be effective in scenarios where lateral loads (e. g. earthquakes and winds storms) can cause partial or complete out-of-plane collapse of masonry wall’s outer leaves or separation of wood diaphragms from masonry walls. The particular application of these bars as a dry system in mortar joints, without any binder, brings additional advantages in terms of cost, installation time and weather restrictions. An experimental campaign composed by 60 pull-out tests aimed at characterizing the bond behaviour of twisted stainless steel bars in mortar joints. The influence on bond behaviour of two diameters of the helibar (ϕ8 mm and ϕ10 mm), three different anchorage lengths (8ϕhb, 12ϕhb, and 20ϕhb), and two diameters of the pre-drilled holes (ϕhb–2 mm and ϕhb–4 mm) was studied. Bond strength increased for the tighter pre-drilled hole but decreased for the higher twisted steel bar diameter. Good correlations between bond strength and anchorage length were found for the less tight pre-drilled holes.
A new shear strengthening technique, designated as embedded through section (ETS), has been
developed to retrofit existing reinforced concrete (RC) elements. This technique calls for holes to be
drilled through the beam section; then bars of steel or FRP materials are introduced into these holes
and bonded with adhesives to the surrounding concrete. When concrete cover has not the bond and
strength requisites to guarantee a strengthening effectiveness for the Externally Bonded and Near Surface
Mounted techniques, ETS strategy can be a competitive alternative since it mobilizes the beam’s concrete
core which is, generally, free of damage. To explore the potentialities of the ETS technique for the shear
strengthening of RC beams, an experimental program was carried out, composed of RC T-cross section
beams shear strengthened by using steel bars. The influence on the shear strengthening efficiency of
the inclination and shear strengthening ratio of ETS configurations was evaluated; the study also
examined the interaction of ETS bars and existing steel stirrups. An increase of shear capacity up to
109% and 136% in the beams with and without internal stirrups, respectively, was obtained. Inclined
ETS bars provided higher increase of shear resistance than vertical ones.
This work presents a numerical study of the behaviour of stainless steel I-beams subjected to lateral–torsional buckling in case of fire and compares the obtained results with the beam design curves
of Eurocode 3.
New formulae for lateral–torsional buckling, that approximate better the real behaviour of stainless steel structural elements in case of fire are proposed. These new formulae were based on numerical simulations using the program SAFIR, which was modified to take into account the material properties of the stainless steel.
Numerical modelling of the lateral–torsional buckling of steel beams at elevated temperature has shown that the beam design curve
from EN 1993-1-2 is over-conservative in the case of non-uniform bending. Based on the newly proposed methodology for cold design
from the EN 1993-1-1, an improved proposal for the lateral–torsional buckling of unrestrained steel beams subjected to fire is presented
in this paper that addresses the issue of the influence of the loading type, the steel grade, the pattern of the residual stresses (hot-rolled or
welded sections) and the ratio h/b, between the depth h and the width b of the cross-section on the resistance of the beam, achieving better
agreement with the numerical behaviour while maintaining safety. The proposal is found to be safe and accurate through an extensive
comparison with the results of FEM numerical simulations of more than 5000 beams. A statistical study of the results is performed,
showing the accuracy of the improved proposal presented in this paper.
The influence of ethanol, sulfuric acid and chloride on the corrosion resistance of 316L stainless steel was investigated by means of polarization curves and electrochemical impedance spectroscopy measurements. Over the studied range, the steel corrosion potential was independent of H2SO4 and NaCl concentrations in aqueous solution. On the other hand, in solution containing 65 wt.% ethanol and 35 wt.% water, the corrosion potentials were higher than those obtained in aqueous solution. Besides, the steel corrosion potential was affected by the addition of H2SO4 and NaCl in solution. In solutions with and without ethanol, plus 0.35 wt.% NaCl, the presence of 1 wt.% H2SO4 inhibited the appearance of pitting corrosion.
This study focuses on the behavior of galvanized steel in a corrosive marine environment and on the runoff process for the same material occurring in Valparaiso, Chile. The corrosion potential and corrosion rate evaluated via mass loss were used to determine the corrosion damage to the galvanized steel. The compositions of the corrosion products were determined using X-ray diffractometry (XRD), and their morphology through scanning electron microscopy (SEM). The runoff solutions collected after rainfall were analyzed to determine the pH value, and Cl-, SO4(2 -) and Zn2+ ion concentrations. The results after 15 months show that the corrosion potential of the galvanized steel increases over time, indicating the formation of a protective film that consists of zinc corrosion products. These products were identified as zincite and simonkolleite. The pH values obtained for the runoff solutions are similar to those of the reference rainwater samples, and the chloride concentrations of the runoff solutions are approximately twice those of the rainwater.
The electrochemical behavior of low-carbon steel in 0.10 mol L-1 KNO3 aqueous solutions and 0.10 mol L-1 tetraethyl ammonium chloride ethanolic solutions was studied in absence and with different concentrations of linalyl acetate (LA). Electrochemical techniques such as potentiometry, cyclic voltammetry, chronoamperometry, Tafel polarization and electrochemical impedance spectroscopy were used in order to comprehend the interaction between the organic compound and electrode surface. Experiments involving weight loss measurements were performed. LA adsorbs on the low-carbon steel surface even in the presence of a large amount of water or ethanol. The adsorption energy for this process was -25.98 kJ mol-1 for aqueous solutions and -26.71 kJ mol-1 for ethanolic solutions. It was also detected that the adsorbed species on metal surface decreases the anodic current density values as well as the weight loss of the metal species. This effect allows us to classify the linalyl acetate as a green corrosion inhibitor of low-carbon steel in aqueous and ethanol medium.
The process of passivation of carbon steel when experiencing plastic deformation in simulated pore solution has been studied using electrochemical tests and atomic force microscopy (AFM). The polarization results show that the activity of the carbon steel increased with increasing degree of deformation. Before the passive films were ruptured, the heavily deformed samples presented a high open circuit potential (OCP). On the other hand, the pitting incubation time decreased with increasing plastic deformation. The Mott-Schottky results suggested that the high deformation caused the passive films to be heavily doped. In addition, the space charge layers of passive films were thinned when the plastic deformation increased. The AFM observations indicated that the passive films become more inhomogeneous as the deformation increased. These results demonstrate that passive films on the deformed carbon steel become unstable when the plastic deformation increases.
An experimental and theoretical study on the inhibition corrosion efficiencies of twenty three compounds in hydrochloric acid (15% w/v) on 13% Cr modified stainless steel (martensitic) has been carried out. This inhibitor set includes amines, thiourea derivatives and acetylenic alcohols. Experimental weight losses at 60ºC were correlated with group and quantum AM1 descriptors obtained from QSPR analysis. Such data, for a large set of molecules, offer a unique opportunity for searching for correlations between inhibition corrosion efficiency and molecular properties. Calculations based on three different statistical methodologies were carried out. The first method, using calibration procedures, employs an ordinary least squares (OLS) methodology with a simple descriptor selection based on R² values. From this procedure, we obtained a model, Y15, having a R² value of 0,979 and a Q² value of 0.786. The second method employs a descriptor selection based on the second-order cross-validation OLS procedure (SOCV-OLS). In this process, the variables are chosen according to their ability to predict molecular inhibition efficiencies. The best model obtained using this methodology, Q5, had R² and Q² values of 0.859 and 0.785, respectively. The third method...
Hot dip galvanizing is very effective means of protection against corrosion. Some recommendation concerning the steel quality are generally known and accepted. The process consists of cleaning (pickling or sand blasting) and dipping the structures or pieces into liquid zinc bath. The case study of hot dip galvanized steels is presented. Some recent failures of hot dip galvanized welded structures and hot dip galvanized high strength steel screws are presented. Structures were made of S355 grade steel and MIG/MAG process was applied for welding. Large cracks were observed in the vicinity of welds after hot dip galvanizing process. The presence of both hydrogen and liquid metal embrittlement was identified and associated mainly with higher hardness of HAZ or the quenched and tempered steels. Possible cracking mechanisms are discussed. The influence of chemical composition and production process (welding, heat treatment) was analyzed according to data published in literature. The solutions and recommendations for avoiding the failure in hot dip galvanized structures are proposed.
The objective of this paper is to provide a review of the calibration procedure of the resistance factor for a target reliability index. Resistance factors for cold-formed steel columns are calculated with a first order second moment reliability approach. A test database of 323 cold-formed steel columns concentrically loaded with plain and lipped C-section was assembled, and test-to-predicted statistics were obtained for the three design methods available in Brazilian cold-formed steel code: the Effective Width Method (EWM), the Effective Section Method (ESM) and the Direct Strength Method (DSM). For the normal load combination, dead-to-live load ratio of 1/3, and target reliability index or = 2.5, the calculated resistance factors, g, for the three methods are consistent with current value specified by Brazilian code. For all methods, with target reliability index or = 3.0, the calculated resistance factors, g, are higher than the current value used in Brazilian code.
The oxide layer formed on the surface of a grain oriented silicon steel was characterized by SEM and EDS. 3% Si steel substrates were coated by two types of slurries: one formed by MgO and water and other formed by MgO, water and SrSO4. The ceramic films were evaluated by SEM, EDS and X-ray diffraction. Depth profiles of Fe, Si and Mg were obtained by GDS. The magnetic core losses (at 1.7 Tesla, 60 Hz) of the coated steel samples were evaluated as well. The use of MgO containing strontium reduced the volume fraction of forsterite particles beneath the outermost ceramic layer. It was observed a reduced magnetic core loss with the use of the slurry with MgO containing strontium.
Zirconia/stainless steel composites have been prepared by a wet processing method with metal volume concentration ranging from 15% to 30%. The composites were characterized by electrical and mechanical measurements. The dependence of the electrical properties of these composites with the metal concentration presents a percolative behaviour with a metal-insulator transition, in addition to an increment of the capacity in the neighbourhood of a critical volume concentration. This value was found to be f c = 0.285, which is much higher than the theoretical value for randomly dispersed 3D composites (f c = 0.16). It has been found that the incorporation of stainless steel particles to zirconia matrix, increases the toughness and decreases both the hardness and the flexural strength. The enhancement of toughness is attributed to a crack deflection mechanism as a consequence of a weak ZrO2/stainless steel interface.
Superduplex stainless steel has been frequently employed in new sites of Brazilian Pre-Salt. In these environments, chloride concentration, temperature and carbon dioxide are normally present in higher levels than those at sea water at room temperature. In these conditions, it is expected that the passive films of stainless steel also show modifications. To better understand such modifications, samples of superduplex stainless steel UNS S32750 were submitted to electrochemical impedance measurements in brine media, at two temperatures and under presence/absence of carbon dioxide. The electrochemical impedance results were initially tested using the Kramers-Kronig transform and subsequently fitted by equivalent circuit employing constant phase elements - CPE. Moreover, to quantify the effect of each factor (temperature, chloride, carbon dioxide and microstructure) on the equivalent circuit, their parameters were tested applying statistical analysis. Significant effect of carbon dioxide and temperature was found on related parameters of passive film for heat-treated samples.
For good performance of electrical steels it is necessary a high magnetic induction and a low power loss when submitted to cyclic magnetization. A fine dispersion of precipitates is a key requirement in the manufacturing process of Fe- 3%Si grain oriented electrical steel. In the production of high permeability grain oriented steel precipitate particles of copper and manganese sulphides and aluminium nitride delay normal grain growth during primary recrystallization, causing preferential growth of grains with Goss orientation during secondary recrystallization. The sulphides precipitate during the hot rolling process. The aluminium nitride particles are formed during hot rolling and the hot band annealing process. In this work AlN precipitation during hot deformation of a high permeability grain oriented 3%Si steel is examined. In the study, transfer bar samples were submitted to controlled heating, compression and cooling treatments in order to simulate a reversible hot rolling finishing. The samples were analyzed using the transmission electron microscope (TEM) in order to identify the precipitates and characterize size distribution. Precipitate extraction by dissolution method and analyses by inductively coupled plasma optical emission spectrometry (ICP-OES) were used to quantify the precipitation. The results allowed to describe the precipitation kinetics by a precipitation-time-temperature (PTT) diagram for AlN formation during hot rolling.
The present study focuses on the effect of various degrees of plastic deformation generated by cold radial forging on the mechanical properties and the fracture morphology of 32 CDV 13 steel. The cold forging percentage was evaluated for 17.45, 33.30, 42.0 and 46.47 %. The microstructural analysis of the steel shows tempered martensite. The tensile strength, yield strength and hardness were found to increase with the increase of cold forging percentage due to the energy stored in the material during cold forging. For higher cold forging percentage, the toughness of the material was decreased according to the reduction of absorbed energy obtained during deformation. Fractography of the Charpy impact specimens shows a surface roughness and dimple pattern for the steel as was acquired and for 17.45 and 33.3 % of cold forging; while for 42 and 46.47 % of cold forging a cleavage fracture pattern was observed.