Tension Steel Research Articles

Surface tension of steel at high temperatures

Surface tension is a material property that is needed to describe fluid behaviour, which impacts industrial processes, in which molten material is created, such as thermal cutting, welding and Additive Manufacturing. In particular when using metals, the material properties at high temperatures are often not known. This is partly because of limited possibilities to measure those properties, limitations of temperature measurement methods and a lack of theoretical models that describe the circumstances at such high temperatures sufficiently. When using beam heat sources, such as a laser beam, temperatures far above the melting temperature are reached. Therefore, it is mandatory to know the material properties at such high temperatures in order to describe the material behaviour in models and gain understanding of the occurring effects. Therefore, in this work, an experimental surface wave evaluation method is suggested in combination with thermal measurements in order to derive surface tension values of steel at higher temperatures than reported in literature. The evaluation of gravity-capillary waves in high-speed video recordings shows a steeper decrease of surface tension values than the extrapolation of literature values would predict, while the surface tension values seem not to decrease further above boiling temperature. Using a simplified molecular dynamic model based on pair correlation, a similar tendency of surface values was observed, which indicates that the surface tension is an effect requiring at least two atomic layers. The observed and calculated decreasing trend of the surface tension indicates an exponential relation between surface tension and temperature.

DEFORMABILITY OF STEEL REINFORCEMENT OF DAMAGED CFRP-STRENGTHENED BEAMS UNDER THE ACTION OF CYCLIC LOADING

In the article are presented the main results of experimental studies of deformability of the reinforcement of common damaged and brought, in the course of the previous tests, to the critical state by the 1st group r.c. beams reinforced with carbon fibre (CFRP) sheet in the lower tensioned zone and on the support area. Namely, according to the results of the experiment, using the COMPEX program, adequate mathematical models of the deformations of steel reinforcement of CFRP-strengthened reinforced concrete specimens-beams under the action of low-cycle sign-constant loading were derived, that reflect the influence of these factors both individually and in interaction with each other. Analyzing these models, the features of the development of tensile reinforcement in the specified conditions, were established. In particular, the factors that have the greatest influence on deformations are the relative shear span and the level of low-cycle loading. As compared with the series of tests of ordinary r.c. samples, presence of the external CFRP strengthening reduced deformation of the tensioned steel reinforcement by 1.65 times on the average. There occurs a re-distribution of the tension forces between them

Effect of retrofit type on the blast performance and failure mode of HSC beams retrofitted with UHPFRC

This paper presents a strategy to prevent shear failure and improve the structural performance of existing high-strength concrete (HSC) beams under blast loading. The strategy involves retrofitting with ultra-high performance fiber reinforced concrete (UHPFRC), a novel material which is well-adapted for the blast hardening of concrete structures. Shock-tube air-blast tests are conducted on seven HSC beams which are retrofitted with UHPFRC. The objective was to characterize the effectiveness of various retrofit types on the blast behaviour of both shear-deficient and flexural-dominant HSC members. Three retrofit types were considered: U-jacketing (UJ), full-jacketing (FJ) and a tension-sided (T) overlay. Other parameters included the effects of the concrete substrate roughening method, as well as the tension steel ratio (1.6% or 2.4%) and presence of stirrups in the beams. Both the UJ and FJ retrofits were found to be effective in preventing shear failure in shear-deficient HSC beams having varying shear demands. In addition, both retrofits increased member strength and stiffness, thereby reducing blast-induced displacements and increasing overall blast resistance. Comparing the two retrofits, optimal performance was obtained with full-jacketing due its ability to delay concrete crushing. In HSC beams with sufficient stirrups, both the T-sided and FJ retrofits reduced blast-induced displacements; however, the use of full-jacketing was better able to control damage and increase blast capacity. The roughening method had no substantial effect on the FJ retrofit performance or failure mode, with no debonding observed in the tests.

Behaviour of UHPFRC-retrofitted RC beams with varying strengthening configurations under single and repeated blast loading

The objective of this study was to characterize the effects of various UHPFRC strengthening configurations on the blast performance of reinforced concrete (RC) beams. The methodology involved blast tests on eight as-built and UHPFRC-retrofitted RC beams using a pneumatically-driven shock-tube. The 150 mm × 200 mm × 2440 mm beams were first cast with 40 MPa concrete and were retrofitted by replacing the 20 mm cover with UHPFRC. The studied parameters included the influence of UHPFRC applied on the tension face, or in the form of U, Full or localized jackets, under single or repeated blast loads. The first set included one as-built beam and three specimens with tension-sided (T), U-jacket (UJ) or full jacket (FJ) retrofits, and were tested under repeated and gradually increasing blast pressures (Pr = 16, 38 and 50 kPa, for Blasts 1, 2 and 3). The second set included one as-built beam and two specimens with full-jacket retrofits applied over the full span (FJ) or in the middle hinge region (FJ-Hinge). The final beam had a hybrid of the T-sided and FJ-Hinge schemes. These beams were tested under single Blast 3 loads, and then tested under static bending to assess their residual capacity. In the first set, all retrofits resulted in reduced displacements (ranging from 30% to 60%) when compared to the as-built beam; however, the repeated blasts ultimately led to crack localization and rupture of the tension steel bars. In the second set, both the full-span and localized hinge schemes led to reductions in damage and displacements (ranging from 20% to 40%), without bar fracture, along with significant residual capacity. Finite element (FE) modelling using LS-DYNA was used to predict the blast behavior of the beams. After validation, the models were used to study the effects of the longitudinal steel ratio and blast load scenario on the behaviour and failure mode of the beams. Increasing the steel ratio was found to be effective in preventing bar rupture, while this failure mode was more likely under repeated blast loading.

Practical temperature calculation and fire-resistant design of special-shaped concrete-filled steel tubular columns

The fire performance of special-shaped concrete-filled steel tubular (SCFST) columns under axial load was investigated in this paper. The ABAQUS based finite element models were conducted for heat transfer and structural analysis. Twelve fire tests on SCFST columns under the ISO-834 standard fire curve by the authors' research were used to verify the model. In addition, heat transfer and fire-resistant mechanism of full-scale SCFST columns were studied; and extensive parametric studies were investigated to examine the influence of fire protection layer thickness, column limb thickness, slenderness ratio and other factors on temperature distribution and fire behavior of SCFST columns. Through the calculation and analysis of temperature field and fire resistance, a simplified temperature calculation method for steel tube, tension reinforcement, and inner steel plate are proposed along with the modularization temperature calculation method for special-shaped concrete sections. Moreover, the ultimate bearing capacity calculation method for SCFST columns under the standard temperature rise curve is proposed allowing for the influence of high temperatures on material properties, which can also be applied to determine fire resistance of SCFST column. Finally, the calculation method for the thickness of fire protection layer and the corresponding fire design is proposed based on the delaying temperature mechanism.

Mechanical and acoustic properties of deformable alloys

The paper is devoted to correlation dependences of ultrasound velocity with characteristics of strength and plasticity in uniaxial tension of Fe18Cr10Ni austenitic stainless steel with a unique set of physical and mechanical properties. Such a successful set of mechanical properties is provided by dislocation slip and twinning, the formation of stacking faults, and martensitic transformation. It should be noted that the assessment of changes in the mechanical characteristics of metals (especially at low temperatures) is a very laborious task and requires the use of non-destructive control methods. Experimental data was obtained using a bench designed to synchronize with recording of the “stress – strain” diagram for determining the values of ultrasound velocity propagation and the attenuation coefficient of the ultrasonic wave as a function of deformation. Measurement of ultrasound velocity propagation was reduced to determining the time of passage of an ultrasonic Rayleigh pulse between transmitting and receiving transducers. Attenuation was determined from the change in pulse shape. The pulses were excited by a piezoelectric transducer at a frequency of 5 MHz. The authors experimentally studied static loading effect on acoustic characteristics and calculated the destruction parameters. The propagation ultrasound velocity in deformable material is an informative feature for analyzing the nature of the processes that control plasticity. The effect of test temperature in the range 180 K ≤ T ≤ 320 K on acoustic and mechanical characteristics of the steel was studied to ensure control of its structural state and mechanical properties by means of non-destructive testing. The temperature range was chosen taking into account the possibility of direct γ → α′ martensitic transformation.

RESEARCH ON STRUCTURAL PERFORMANCE OF SHEAR WALL OF CLT CONSTRUCTION METHOD WITH STEEL BEAMS AND TENSION MEMBERS

This research proposes a structural system for CLT shear wall that demonstrates high CLT shear performance, high deformation capability, and a method for determining its target performance. CLT shear wall with steel beams, using tensile members prevent the brittle failure occurring at the tensile joint, is proposed. To verify the validity of the proposed method, experiments for full scale CLT shear wall specimens are conducted. Test results are simulated by analysis models. By using material property values that are close to the actual conditions in the experiment, the analysis model is able to accurately reproduce the experiment results.

The analysis of debonding damage between steel tension wire and epoxy resin in flexible end fitting under cyclic loading

Flexible pipe end fitting is a structure connecting flexible pipe and mental flange, which is a transition between flexible structure and rigid structure. Epoxy resin is used to fix tension steel wire in the end fitting. The bonding interface between epoxy resin and tension steel wire is prone to debonding when flexible pipe end fitting is used under cyclic loading. The damage of bonding interface is mainly due to the cumulative effect of cyclic loading. The damage of epoxy resin can cause temperature changes, which can affect the material properties of the resin and then affect the bonding strength. In this paper, the relationships between cycle numbers of epoxy resin and temperature, temperature and elastic modulus are obtained through fatigue analysis and dynamic mechanical analysis (DMA). The fatigue model is established based on the relationship between the modulus of epoxy resin and temperature. Based on the fatigue model, the bonding damage between steel tension wire and epoxy resin is obtained by finite element analysis (FEA). The results show that it is feasible to characterize the fatigue damage between steel tension wire and epoxy resin by temperature. This work provides a new method for predicting the fatigue of tensile steel wire and epoxy resin in end fitting.

Corrosion of galvanized steel in alkaline solution associated with sulfate and chloride ions

Corrosion mitigation strategies for structural steel bridge elements including post tensioned steel components include the use of galvanized steel. The zinc alloy layers and subsequent precipitation of a dense surface oxide in alkaline environments provide beneficial barrier protection to mitigate corrosion. However, severe corrosion of galvanized steel components in contact with sulfate-rich deficient cementitious grout was documented to occur in less than 8 years of bridge service. Electrochemical testing and material characterization showed that the presence of sulfates in alkaline solutions allow for prolonged zinc activity and hindered passivation by the incomplete surface coverage and the precipitation of large sized calcium hydroxy zincate. OCP, LPR, and electrochemical noise (EN) testing showed greater corrosion activity of galvanized steel in chloride and sulfate solutions. EN identified local corrosion activity of the zinc associated to the porous nature of the surface oxide layer.

Neural network approximation of deformation curves under uniaxial tension of steel and silumin specimens

The purpose of the study is developing and testing of the new computational technique for approximation of deformation curves of steel and silumin specimens under uniaxial tension. A scheme of testing steel and silumin specimens for uniaxial tensile is presented. The experiment was carried out in the mechanical testing laboratory of the Department of Applied Mathematics and Mechanics of the Voronezh State Technical University. The experimental deformation curve of a steel specimen was approximated by P. Ludwig’s equation. Prediction of the true stress from the logarithmic strain using a pretrained artificial neural network with a multilayer perceptron architecture is discussed. The neural network model was trained using the RProp (resilient backpropagation) method. The software implementation of the neural network approximation was carried out in a framework of the open source for data analysis — Knime Analytics Platform. A scheme for the implementation of a multilayer perceptron that solves the approximation problem is considered. The simulation results are compared by the values of the mean squared error (MSE) of the approximation. The neural network approximation is turned out to be an order of magnitude more accurate for the steel specimen than the approximation by the P. Ludwig equation. The neural network approximation provided even a smaller MSE value for a silumin specimen than that or a steel specimen. It is revealed that changing the architecture of an artificial neural network affects the quality of modeling. With an increase in the number of hidden layers, the accuracy of the approximation increases. Neural network approximation is an effective approach to solving the problem of the analytical description of experimental deformation curves and leaves the possibility of using a universal technique for a variety of materials and different types of tests.

Assessment and Rehabilitation Solutions for an Industrial Hall Affected by Extreme Actions

The original structure of the industrial hall consisted of longitudinal reinforced concrete frames with columns and beams and 133 timber roof trusses (33.5 m span each), which were supported on longitudinal beams. Owing to the extreme action of snow, many trusses in the timber roof crashed down and fell onto the auxiliary structure. This led to the occurrence of a 200 mm distance between two elements in the bottom flange connection area, a 150 mm displacement in the upper part of the reinforced concrete (RC) columns, and many transversal cracks. The main causes that led to the collapse of the timber roof trusses were the high level of stress applied on the structure by snow loads in December 2018, as compared with the provisions of the Romanian code, the fact that the structure was designed for a rigid transversal frame instead of a deformable structure, and the insufficient dimensions of the cleats used on the bottom flange. The rehabilitation solution chosen consisted in lifting the timber roof trusses, after their crashing down, to near their initial level. The degraded structure was strengthened by: (1) consolidating each timber roof truss using a steel tension rod at the bottom flange of the truss, with the timber truss anchored at both ends by being inclined and perforated; and (2) for the RC columns, the strengthening solution was based on carbon fiber reinforced polymer (CFRP) lamellas and wraps.

An experimental and numerical study of twin dowel type shear connector

The hunger for a better, more effective, more economic, easier for construction, and overall more sustainable bridge design is enormous nowadays. One of the solutions for the problems described is a steel-concrete composite structure with embedded continuous shear connectors. Such structure uses advantages of both materials (concrete in compression and steel in tension) while lowering the overall height of the structure and time of the construction. This paper presents a new design of the connector of twin dowel type, with clothoid dowel, where two dowel connectors are welded longitudinally by flanges to create one twin connector. Its geometrical attributes are closely described and the design origin is explained. The study of the proposed shear connector consists of experimental and numerical part. In experimental study, the experiments performed—four push-out tests—and their setup, instrumentation and material characteristics are described and their results in a form of load-slip curves are presented and analyzed. In numerical study the finite element model developed in ABAQUS software is presented with a detailed description of the modeling process. In results and discussions the results of the numerical study are compared with results from the experimental study and the resistance of the proposed shear connector is briefly compared to shear connectors from chosen studies.

NSM GFRP Strengthening of Reinforced Concrete Beams after Exposure to Fire: Experiments and Theoretical Model

The effectiveness of near-surface mounted glass fiber–reinforced polymer (NSM GFRP) retrofitting of reinforced concrete (RC) beams after exposure to fire is investigated in this study both experimentally and analytically. Experiments were performed on nine RC beams: one beam was not exposed to fire (control specimen) and eight beams were divided into two groups exposed to fire for 30 and 60 min. In each group, one beam was not retrofitted, whereas the other three beams were retrofitted using NSM GFRP. After retrofitting, all beams were loaded until failure. The experimental results confirmed that the retrofitting technique effectively recovered the strengths of postfire RC beams. The failure mode of the GFRP retrofitted beams was the peeling-off of concrete cover, whereas that of the control and unretrofitted postfire beams was flexural failure via the yielding of tension steel. The NSM GFRP retrofitting fully recovered or significantly increased the yield and ultimate strengths of postfire RC beams by up to 39%. The yield deflection capacity of the NSM GFRP retrofitted postfire beams was much higher than that of the control beam; however, the ultimate deflection capacity of these beams significantly decreased. Consequently, the GFRP retrofitted postfire beams were of low ductility because of the peeling-off of the concrete cover. NSM GFRP retrofitting slightly improved but did not completely recover the yield stiffness reduced by fire, whereas it increased the plastic stiffness significantly by up to threefold. An analytical model for estimating the yield moment of postfire RC beams without/with NSM GFRP retrofitting was proposed, considering the very limited information, for example, fire duration obtained from actual fire events. The practicality and reasonable accuracy of the proposed model render it beneficial for structural engineers.

NSM GFRP Strengthening of Reinforced Concrete Beams after Exposure to Fire: Experiments and Theoretical Model

The effectiveness of near-surface mounted glass fiber–reinforced polymer (NSM GFRP) retrofitting of reinforced concrete (RC) beams after exposure to fire is investigated in this study both experimentally and analytically. Experiments were performed on nine RC beams: one beam was not exposed to fire (control specimen) and eight beams were divided into two groups exposed to fire for 30 and 60 min. In each group, one beam was not retrofitted, whereas the other three beams were retrofitted using NSM GFRP. After retrofitting, all beams were loaded until failure. The experimental results confirmed that the retrofitting technique effectively recovered the strengths of postfire RC beams. The failure mode of the GFRP retrofitted beams was the peeling-off of concrete cover, whereas that of the control and unretrofitted postfire beams was flexural failure via the yielding of tension steel. The NSM GFRP retrofitting fully recovered or significantly increased the yield and ultimate strengths of postfire RC beams by up to 39%. The yield deflection capacity of the NSM GFRP retrofitted postfire beams was much higher than that of the control beam; however, the ultimate deflection capacity of these beams significantly decreased. Consequently, the GFRP retrofitted postfire beams were of low ductility because of the peeling-off of the concrete cover. NSM GFRP retrofitting slightly improved but did not completely recover the yield stiffness reduced by fire, whereas it increased the plastic stiffness significantly by up to threefold. An analytical model for estimating the yield moment of postfire RC beams without/with NSM GFRP retrofitting was proposed, considering the very limited information, for example, fire duration obtained from actual fire events. The practicality and reasonable accuracy of the proposed model render it beneficial for structural engineers.

The Structural Behaviour of Tension Steel Rods Strengthened with Carbon-Fiber-Reinforced Composite Materials

Strengthening can increase or recover the bearing capacity of steel constructions of buildings and structures in operation. Besides well-known strengthening techniques, including an increase in the sectional area by means of attaching steel plates, angles, channels, pipes etc. to a strengthened element, other methods, that involve the use of carbon fiber-reinforced composite materials, have strong prospects. So far, the structural behaviour of steel constructions, strengthened with carbon fiber-reinforced composite materials, is understudied, and this fact restrains the practical application of this strengthening method. The article presents the results of complex experimental, theoretical and numerical studies of the features of the operation of steel-stretched elements reinforced with glued carbon fiber. The emphasis is on the load-bearing capacity of the reinforced element, and not on the mechanism of destruction of the glue. This is due to the use of an adhesive joint performed using the glue and gluing technology recommended by the manufacturer of carbon fiber. It has been experimentally established that, in this case, the stresses in carbon fiber cannot exceed a certain value. Theoretical dependences for the calculation of CFRP-reinforced steel stretched elements are proposed. The scientific novelty of this research project is a set of basic principles and methods, developed to identify the bearing capacity of steel rods, strengthened with carbon fiber-reinforced composite materials, taking into account the joint strength performance of a steel rod and adhesively bonded carbon-fiber-reinforced composite material, as well as the new findings thus obtained, such as the theoretical dependencies needed to identify the bearing capacity of steel rods strengthened with carbon-fiber-reinforced composite materials; experimental data on the joint strength performance of carbon-fiber-reinforced composite lamellas attached to a steel rod by an adhesive; experimental data on the performance and the bearing capacity of steel rods strengthened with carbon-fiber-reinforced composite lamellas; development of finite element models of steel rods strengthened with carbon-fiber-reinforced composite materials, and computational studies of steel rods strengthened with carbon fiber-reinforced composite materials.

Behavior of two-way RC slab with different reinforcement orientation layouts of tension steel under drop load impact

In this research work, dynamic nonlinear incremental finite element analysis is conducted in ABAQUS software with an inbuilt explicit module to study the impact response of a two-way singly reinforced concrete slab, 1000 mm × 1000 mm × 75 mm, with different flexural tension steel reinforcement orientation layouts subjected to low-velocity falling-weight impact loading by cylindroconical impactor with a flat nose of 40 mm diameter having overall mass 105 kg from 2500 mm drop height. Computational findings are found in consonance with experimental results of Sadraie et al. (2019) on an isotopically reinforced concrete slab of the same dimensions with flexural tension steel in two layers i.e., one at 90-degree and the other at 180-degree orientations, subjected to the same impact load. Local damage in the form of punching occurs in the immediate vicinity of the impacted region. Overall deformation and cracking reflect the global behavior of the slab. The slab reinforcement is improvised by providing the same tension steel (0.88 %) in three layers: the first- and third- layer having orientation layouts of (a) 30- & 150-degree, (b) 45- & 135-degree, (c) 60- & 120-degree, and (d) 75- & 105-degree; the second layer is common with 90-degree orientation, and analyses are carried out under the same impact load. The Concrete Damage Plasticity and Johnson-Cook models, respectively, including the strain rate effects, are chosen to define concrete and steel materials’ response under impulsive impact loading. Computational results are discussed and presented in terms of displacement–time plots, stress distribution in the concrete and reinforcing bars, damage dissipation energy, and damage profiles. The tension steel in three layers and its orientation is found to have a noteworthy influence on the response of the slab and reduces the damage severity under impact loading.

Role of shear reinforcements on the punching shear resistance of two-way RC slab subjected to impact loading

• Numerical analysis of punching shear resistance of RC slab subjected to impact loading. • Impact test setup is modeled in ABAQUS/Explicit computer code. • Computational results compared with the experimental ones from literature. • Parametric study to analyze the effect of stirrups’ width, spacing, and the number of compression reinforcement bars. • Shear reinforcement was able to improve the impact resistance of slab against punching. The possibility of acting impulsive loads such as blast and impact on gravity load-carrying structural members such as slabs during their construction and service life cannot be ruled out. Studies on the response of RC slabs under impact loading are available in the literature. However, the role of the shear reinforcements in the slab under impact is not fully understood and therefore needs further investigation. The slab subjected to concentrated impact loading in the form of falling construction equipment, landslip hazards, and other similar events may cause damage through punching or perforation. Under quasi-static concentrated loading, the design parameters that contribute to the shear resistance against punching are (1) concrete strength, (2) flexural steel, and (3) shear stirrups. In this work, a three-dimensional finite element model of a square concrete slab of normal strength concrete (30.10 MPa), 1000 mm × 1000 mm × 75 mm, with tension reinforcement only (0.88 %) subjected to low-velocity drop-weight impulsive impact is developed in ABAQUS/Explicit computer code considering Concrete Damage Plasticity and Johnson-Cook models with strain rate effects and validated with the experimental results in the open literature. The nonlinear interaction between the concrete and steel reinforcements is taken into account. The drop weight is a hard steel cone frustum-headed striker/impactor with a flat impact face of a total mass of 105 kg allowed to fall from 2500 mm height, impacting the slab at its centroid. To study the effect of the shear reinforcement on the impact resistance of the slab, the shear reinforcement has been varied by varying the stirrups’ width, spacing, and the number of compression reinforcement bars while keeping the impact load and other design parameters such as concrete/steel strength, support conditions, slab thickness, span, and flexural tension steel constant. Numerical simulations are executed and the outcomes are presented in terms of displacement–time plots, damage/stress profiles, damage modes, and damage dissipation energy. The results so extracted are discussed and compared. It has been found that the increase in shear reinforcement by decreasing the spacing of the stirrups improves the impact resistance of the slab against punching.

Impact response prediction of square RC slab of normal strength concrete strengthened with (1) laminates of (i) mild-steel and (ii) C-FRP, and (2) strips of C-FRP under falling-weight load

Reinforced concrete (RC) slab is an indispensable component of all kinds of structures to carry gravity loads in general. Quite often than not, the slabs are subjected to impact loads from accidental mishaps, falling construction equipment, and falling boulders and rocks which are not considered in the structural design. Design codes of practice for RC structures permit the structural design based on the experimental investigation which is not viable because of constraints such as experimental facilities, materials, and time requirements. However, current advancements in the computational techniques available make it possible to obtain the comprehensive response of the slabs subjected to impact loadings. In the present research work, different strength-enhancing techniques such as steel/C-FRP sheet laminates and C-FRP strips are considered for impact resistance enhancement of two-way normal strength concrete slab, 1000 mm × 1000 mm × 75 mm, with 0.88 % conventional tension steel reinforcement subjected to a free-falling concentrated load of 1035 N. For this purpose, a 3-D finite element model of impacting test setup is formed in ABAQUS-v.6.15 explicit commercial computer code. Computational analyses and simulations of free-fall impact are carried out on the validated ABAQUS model by allowing a 105 kg steel weight (impactor) from a height of 2500 mm with an initial impacting velocity of 7 m/ sec on the top surface of the slab at its centroid. The Concrete Damage Plasticity model is implored for nonlinear elastic and inelastic behaviors, degradation of stiffness, and loading rate effect on concrete. The nonlinear behavior of the reinforcing bars is taken into account. Steel is idealized with the Johnson-Cook model but the C-FRP laminate is defined or modeled with ABAQUS Hashin’s criterion. It is found that the used strengthening techniques improve the response of the slab in terms of displacement and damage severity, and alter the mode of failure.

Experimental and numerical study of the effect of steel Tie-rods on load-bearing capacity of Persian brick arches

Arches are a fundamental feature of traditional Persian architecture. In Iran, arched structures have been used for centuries to cover expansive areas. They are typically made of wooden or steel tension members, called “tie-rods”. Tie-rods are essential in controlling and restraining horizontal forces caused by external loads occurring in arches and vaults. The current experimental study aims to assess the effect of steel tie-rods and their connection to the piers on the load-bearing capacity of Persian brick arches with three common geometries (semicircular, ordinary-four-centered, and ordinary pointed) subjected to a static gravity load. After experimentally determining the mechanical properties of the materials, a numerical model for arches using a nonlinear material behavior approach and the Willam-Warnke failure criterion was developed in ANSYS finite element code. The experimental results were subsequently compared to the numerical results. The results indicated that the type of tie-rod-pier connection and the arch’s geometry could affect the load-bearing capacity of arch-shaped structures subjected to static gravity loads. Finally, the performance of tie-rod-pier connections for different geometries of Persian arches was evaluated, especially for ancient structure restoration projects, and recommendations regarding tie-rod connections in different geometries of Persian arches were offered.

Minimization of dynamic changes in the tension of long products behind the outlet cage in rolling stock production in coils

Purpose. Justification of technical solutions as to the reduction of the amplitude and reduction of the dynamic change duration in the tension of the rolling stock at the exit of the output cage when moving to winding a new layer to an acceptable level in terms of its effect on the resulting profile of the rolled product through the control of the rotation frequency of an output cage. Methodology. The conducted research was based on a complex model of the process of rolled steel winding with a Garrett-type winder and the tension of rolled steel in the area of the exit cage-winder. To control the actual amount of tension at the output cage exit, it is suggested to use the amount of free deflection of the rolled steel directly behind the cage. The research was carried out by simulating the process of rolled steel winding according to the basic control scheme and control schemes that predict the influence on both drives, i.e. the winder drive and the output cage drive according to the actual value of tension, in various combinations with further analysis and comparison of the obtained results. Findings. It was established that the correction for the deviation of the actual rolling tension in the finishing cage-winder area from the specified value of the winding current of the winder electric drive does not eliminate rolling tension when switching to the next layer winding and the oscillating form of the transition process, which are characteristic of the basic rolling winding scheme. In turn, the correction of the rotation frequency of the output cage rolls drive reduces the amplitude of the roll tension jerk by almost half with a simultaneous reduction in the time of the transition process and readjustment when switching to a new layer winding. Originality. It has been shown for the first time that the introduction of the roll tension control circuit by correcting the high-speed rolling mode of the output cage ensures minimization of dynamic changes in the rolled steel tension when switching to a new layer winding and reduces the probability of local tightening of rolled steel profile. Practical value. The use of the described technical solutions in the control system of the section of rolled products winding of the small-grade wire mill DSDS 250/150-6 PJSC ArcelorMittal Kryvyi Rih ensures the improvement of the commercial properties of the winding of rolled products produced on the rolling mill.