Steel Strain Research Articles

Influence of Temperature on Low Cycle Fatigue and Ratcheting Behavior of SA333 Gr-6 C-Mn Steel

The aim of this investigation is to study the influence of temperature on the cyclic plastic deformation behavior of SA333 Gr-6 steel at two loading conditions. Strain-controlled cyclic loading experiments were carried out at ± 0.5% total strain amplitude, 1×10-3 s-1 strain rate, and temperature varied from RT to 400°C, whereas stress controlled ratcheting experiments were conducted at fixed mean stress (σm) of 50 MPa and stress amplitude (σa) of 400 MPa, 115 MPa s-1 stress rate, and in the temperature range of RT to 350°C. The investigated steel shows cyclic hardening characteristic at DSA temperature regime in both the loading condition. The steel shows lower fatigue lives at 250°C and 300°C temperatures even though plastic strain amplitude is smaller. The ratcheting life of the steel increases and strain accumulation decreases with the increase in temperature up to 300°C and on further increment in temperature ratcheting life get decreased. The steel shows greater cyclic hardening at both the loading conditions at 300°C.

Extended Tension Chord Model for Boundary Elements of RC Walls Accounting for Anchorage Slip and Lap Splices Presence

This paper presents a mechanical model for the simulation of reinforced concrete (RC) wall boundary elements with lap splices, which builds on the tension chord model. The model is composed of an assembly of components, each one accounting for a different source of deformation. Namely: (i) an anchorage-slip element accounting for the strain penetration of the longitudinal reinforcement into the foundation; (ii) a basic tension chord element evaluating the response outside the lap splice zone; and (iii) a lap splice element describing the behaviour within the lap splice region. For an imposed global displacement, the model provides the steel and concrete stress and strain distributions, the crack distribution and opening, as well as the global resisting axial force. For spliced members, the ultimate displacement is computed through a semi-empirical relationship providing the average lap splice strain at failure. Validation is carried out against a series of uniaxial cyclic tests on RC wall boundary elements featuring both continuous and spliced reinforcement; different lap splice lengths and confining reinforcement are considered. Overall, a good match is obtained between numerical and experimental results in terms of crack width, rebar strain distribution along the splices and ultimate displacement.

The Character of Hydrogen Embrittlement in Mooring Chain Steel

The digital image correlation method has been applied to directly observe the local strain and crack formation in mooring chain steel during tensile tests in air or when simultaneously charging hydrogen in different ways, viz. including/excluding the notch root. Interestingly, hydrogen accumulation promoted crack initiation on the surface when the local strain reached approximately 0.9%, while strain of 19% to 20% was reached in the hydrogen-free specimens before visible crack formation. Even through the stress–strain curves prior to the sudden drop indicate a negligible effect of hydrogen, its presence can greatly reduce the stress-induced crack initiation. In addition, hydrogen introduced while avoiding the notch root can disorganize the regular distribution of strain produced by the notch before crack initiation. Therefore, hydrogen-induced embrittlement below the critical stress criterion can be explained by hydrogen-enhanced localized plasticity, while above the critical stress criterion, hydrogen-enhanced decohesion provides a better explanation.

Investigation on structural behavior of concrete filled stainless steel tubular stub columns

Concrete filled stainless steel tubular (CFSST) Columns have the recognizing feature of high corrosion resistance so that we can directly use in the sea-sand based environments and as well as in normal environments also, we can widely use as structural application without corrosion. This paper presents the finite element analysis and behaviour of short CFSST stub columns of circular cross-sections loaded axially. A finite element model was developed in the ABQUS software and the behaviour of axially loaded s short CFSST stub columns, taking account into the concrete confinement effect and significant effect of stress strain of stainless steel. The computational method outcomes are comparatively verified with the laboratory outcomes and design formula proposed by Liang which is to predict the ultimate strength of short CFSST stub columns of circular columns.

Behaviour of reinforcement in drop tower beam tests

Drop tower tests help to gain understanding about the general behaviour of reinforced concrete members under impact loading and to analyse strains and strain rates occurring within their reinforcement. For this purpose, beam and slab specimens are usually employed. The main advantage of beams compared to slabs is that they are less complex due to the almost two-dimensional instead of three-dimensional wave propagation within them. To investigate the steel strains and strain rates, ten impact tests on beam specimens with various impact energies were performed. The impactor sizes and velocities were varied. The reinforcement bars of the beams were instrumented with semiconductor strain gauges. The measured data suggest that the occurring strains in beam tests are independent of the loading velocity. The same was found for the strain rates. The reason is that higher impact energies mostly influence the concrete damage due to spalling on the impact-facing side which happens after the maximum strains occurred. The strains in the reinforcement bars generally result from the overall deflection because of the impact, the spreading of longitudinal waves in the horizontal direction, and the localized cracking of the concrete due to the formation of a punching cone.

Anchoring the CFRP strengthening of concrete bridge decks: A comparison of methods

Debonding failures are a common problem in concrete bridge decks strengthened with adhesively attached carbon-fibre reinforced polymer (CFRP) strips. Accordingly, in this study, rectangular concrete slabs strengthened with CFRP have been experimentally evaluated to simulate the strengthening of T-beam and box girder slabs. The resulting static load data have been used to compare the effects of four different anchoring methods in terms of crack distribution, deflection, reinforcing steel strain curve, and CFRP strain distribution. The most suitable bridge deck strengthening anchoring method has been then identified and analysed using extant strengthening design methods. The results show that the most practical anchoring method is the use of open CFRP strips attached with concentrated adhesive. The findings of this study indicate that when strengthening T-girder bridges, more than two CFRP anchorage strips should be evenly spaced within the extension of the anchorage length, while for box girder bridges, even more evenly spaced strips should be used. This research and its conclusions can be used as a reference for the improved design of bridge deck strengthening.

Performance of Shear Reinforcement against Punching Shear Loads

This research targets to maximize the ductility and strength of the reinforced concrete flat slabs. However, to be efficient, the shear reinforcement must be anchored well in the tension and compression zones of the slab. The test results on the slab-column connection models which provided with shear reinforcement are introduced in this study. The benefits of using shear reinforcement are to reduce the slab thickness, and to minimize both the cost and the total weight of the structure. Twelve flat slab specimens have been tested to study the effect of different types of steel RFT on the punching shear of the flat slab. The experimental parameters include no shear reinforcement which study the advantage of using tension RFT ONLY against punching shear, no shear reinforcement which study the advantage of using compression RFT against punching shear, shear RFT (Vertical Stirrups) which study the effect of using shear RFT with constant distribution 0.5d, and a new distribution of shear stirrups which study the effect of using new different width & spacing of vertical stirrups. The twelve specimens were loaded with concentrated load at the mid span until failure. The general behavior of the deformation of the tested slab specimens was examined and recorded (cracking, deflection, and strain in both steel and concrete). A comparison established between the experimental and the numericaltheoretical results obtained from applying the punching shear strength formula given in design codes, and finite element modeling analysis; ABAQUS 2017 software package was used for this analysis. A total of six building codes were examined with regard to their provisions concerning the punching shear. A comparison had been made between the research test results and the codes equations to improve the methods of the analysis about the flat slabs. This study aimed to improve the punching shear capacity of flat slab which leads to more accurate results compared with the codes predictions. To achieve this aim, an experimental and numerical study was carried out for this investigation.

Experimental study of prefabricated RC column-foundation assemblies with two different connection methods and using large-diameter reinforcing bars

Prefabricated reinforced concrete (RC) column-to-foundation connections are typically located at the critical region of the columns and are subjected to a combination of large compression and bending deformation under earthquake actions. The seismic behaviour of these connections affects the structural behaviour of precast concrete frames as a whole. The prefabricated column-to-foundation connections using grouted sleeves (PC-S) and grouted corrugated ducts (PC-C) were two typical connections. However, up to now the researches on the seismic performance of the two typical connections are mainly concentrated on small-diameter reinforcing bars used in the connections. The use of large-diameter high-strength reinforcing bars in the large size precast columns has clear advantages in precast structures as it helps improve the construction efficiency due to a reduced number of connected longitudinal bars and less congestion of the reinforcing bars. In this study, two full-scale prefabricated column-foundation assemblies with different connection methods, designated as PC-S and PC-C, respectively, along with one cast-in-place reference specimen, were prepared and tested under quasi-static cyclic loading. In all three specimens, large-diameter high-strength reinforcing bars were adopted as the longitudinal reinforcing bars. The test results showed that both types of connections exhibited similar strength as compared to the cast-in-place specimen. In specimen PC-S, buckling of the longitudinal bars and rupture of stirrups at the top of the grouted sleeves were observed, and this led to lower ductility with an ultimate lateral drift ratio of 4.5%. In specimen PC-C, a more pronounced pinching behaviour was observed after a lateral drift ratio of 2%, which was due to significant bond-slip displacements of large-diameter high-strength longitudinal bars in the overlap region. The three specimens exhibited different plastic hinge mechanisms at the column bases as demonstrated from the measured steel strains, cracking patterns and failure modes. Based on the experimental results, further improvements of using large-diameter high-strength reinforcing bars in the two types of prefabricated column-to-foundation connections are recommended.

AN ASSESSMENT OF THE EFFECT OF CONSTRUCTION ERRORS DURING THE IMPLEMENTATION OF RC T-BEAMS

This paper investigates the effects of construction errors during the implementation of reinforced concrete T-beams. These errors are classified into two main sections. The first focuses on the position and ratio of reinforcing bars, while the other is related to the concrete strength. A total of ten specimens of T-beams were tested to assess the effect of the possible defects in the construction sites, viz. impact of misplacement of slab reinforcement, irregular arrangement of slab reinforcement, the change in bar diameter of slab reinforcement and the effect of casting method of concrete on the structural behavior of T-beam sections. The results indicated that the faulty placement of slab reinforcement leads to a lower bending moment capacity of the slab (brittle behavior) and the steel strain of slab decreases as the height of slab reinforcement decreases. The irregularity of the reinforcing bars in concrete slab affects the ultimate load carrying capacity of the slab. Also, it was found out that well-arranged distribution of reinforcement improves the ductile behavior of the slab and reduces the corresponding deflections.

Study on the interfacial bond slip constitutive relation of I-section steel and fully recycled aggregate concrete

17 standard push-out specimens which are designed to study the interfacial bond-slip behavior of I-section steel and reinforced recycled concrete with 100% replacement ratio of coarse aggregate (SRRC). The parameters of test are strength of recycled aggregate concrete, thickness of I-section steel protective layer, embedded length of I-section steel and ratio of stirrups. The test results show that the strain and stress of the I-section steel at the interface of SRRC distribute exponentially, and the four test parameters have a certain influence on the interfacial bond strength of SRRC. Based on the analysis of the test data, the calculation formulas of the interfacial bond strength of SRRC are established. The constitutive relations of the bond-slip at the loading end are established, and the multistage linear results are more satisfied with the test results than power-type. Finally, the position function of the bond-slip F(x) and the bond stress G(x) are introduced, and the bond-slip constitutive relation with changes of position are established, which provides a reference for related specification design and engineering construction.

Numerical simulation of SHPB test of ultra-high performance fiber reinforced concrete with meso-scale model

<p indent="0mm">Ultra-high performance steel fiber-reinforced concrete is an innovative cement-based composite material with excellent mechanical properties and outstanding potential in resisting extreme loads. In this study, a meso model of ultra-high performance steel fiber-reinforced concrete specimen, which consists of cement mortar and fibers, is developed to numerically simulate Split Hopkinson pressure bar (SHPB) tests for investigation of behavior of ultra-high performance steel fiber-reinforced concrete material under impact loading. The software LS_DYNA is used to perform the numerical simulation of dynamic tests. A good agreement is observed between the simulated results and experimental results. After the meso model is validated with static compression and split tension tests, SHPB tests are numerically modelled and the stress-strain history is interpreted in the meso-scale level. The influence of fiber on ultra-high performance steel fiber-reinforced concrete in dynamic tests is investigated. Within a reasonable range of steel fiber volume ratio (optimum volume ratio ranges from 0%–2.5% for micro steel fiber), the dynamic strength of ultra-high performance steel fiber-reinforced concrete increases significantly with the increase of steel fiber volume ratio, however, the contributions of fibers to Dynamic Increase Factors (DIF) of ultra-high performance steel fiber-reinforced concrete are constantly lower than those of conventional concrete material. The proposed model qualitatively and quantitatively predicts the material static and dynamic behaviors, and also gives insights on the fiber reinforcement effect in the concrete matrix. In this study, the dynamic constitutive relationships of ultra-high performance fiber-reinforced concrete are derived for predicting the dynamic strength of ultra-high performance fiber-reinforced concrete with different steel fiber volume ratios and strain rates.

Analytical study on one-way reinforced concrete beam-slab sub-structures under compressive arch action and catenary action

In case of accidental loading, compressive arch action and catenary action in beams and slabs can be mobilised to resist progressive collapse of reinforced concrete structures. Analytical models have been proposed for reinforced concrete beam-column sub-assemblages under compressive arch action and catenary action. Nonetheless, the effects of the slab on load resistance and deformation capacity of one-way beam-slab sub-structures have not been fully investigated. This paper presents a study on the structural behaviour of one-way beam-slab sub-structures subjected to compressive arch action and subsequent catenary action. In the study, an analytical model is developed to predict the load-displacement relationship and the axial force-displacement relationship of sub-structures. The model is developed in accordance with rigid-plastic assumption. Compatibility, equilibrium and constitutive models for steel reinforcement and concrete are taken into account in the model. Hogging and sagging moments are calculated by taking moments about the plastic centres of beam-slab sub-structures. The model is validated against published test data and reasonably good accuracy is obtained in terms of the load resistances under compressive arch action and catenary action. The variation of bending moments, neutral axis depths and steel strains can also be obtained through the analytical model. The model is then used for parametric study of the effects of longitudinal reinforcement, slab width, and thickness on compressive arch action and catenary action. The parametric study shows that the cross-sectional area of longitudinal reinforcement in the slab affects the catenary action capacity and the width and thickness of the slab affects the deformation capacity of one-way beam-slab sub-structures. Finally, conclusions are drawn from the analytical study which can be used in the design of one-way beam-slab sub-structures against progressive collapse.

Robustness evaluation of CSMM based finite element for simulation of shear critical hollow RC bridge piers

PurposeThe purpose of this study is to evaluate the effectiveness of two-dimensional (2D) cyclic softened membrane model (CSMM)-based non-linear finite element (NLFE) model in predicting the complete non-linear response of shear critical bridge piers (with walls having aspect ratios greater than 2.5) under combined axial and reversed cyclic uniaxial bending loads. The effectiveness of the 2D CSMM-based NLFE model has been compared with the widely used one-dimensional (1D) fiber-based NLFE models.Design/methodology/approachThree reinforced concrete (RC) hollow rectangular bridge piers tested under reversed cyclic uniaxial bending and sustained axial loads at the National Centre for Research on Earthquake Engineering (NCREE) Taiwan have been simulated using both 1D and 2D models in the present study. The non-linear behavior of the bridge piers has been studied through various parameters such as hysteretic loops, energy dissipation, residual drift, yield load and corresponding drift, peak load and corresponding drift, ultimate loads, ductility, specimen stiffness and critical strains in concrete and steel. The results obtained from CSMM-based NLFE model have been critically compared with the test results and results obtained from the 1D fiber-based NLFE models.FindingsIt has been observed from the analysis results that both 1D and 2D simulation models performed well in predicting the response of flexure critical bridge pier. However, in the case of shear critical bridge piers, predictions from 2D CSMM-based NLFE simulation model are more accurate. It has, thus, been concluded that CSMM-based NLFE model is more accurate and robust to simulate the complete non-linear behavior of shear critical RC hollow rectangular bridge piers.Originality/valueIn this study, a novel attempt has been made to provide a rational and robust FE model for analyzing shear critical hollow RC bridge piers (with walls having aspect ratios greater than 2.5).

Post-fire behaviour of high-strength quenched and tempered steel under various heating conditions

Quenching and tempering (QT) are common procedures in manufacturing high strength steel for building applications to achieve structural, economic and architectural benefits. However, the tempered martensitic microstructure of QT steel can change dramatically when exposing to high temperatures, leading to significant deterioration in mechanical properties. This paper investigates the post-fire mechanical properties of two types of QT steel with nominal yield stresses of 690 MPa and 1070 MPa, respectively. The main test variables include the exposure temperature (100–1200 °C), heat soak time (0.5–4 h), and cooling method (cooled in furnace, air or water). It is found that the heat soak time has obvious influence on the residual mechanical properties of QT steel, when the exposure temperature is above 500 °C. The cooling method, however, only severely affects the residual properties at a temperature above the phase change temperature (around 724 °C). It is also found that QT steel with a higher yield stress experiences more severe strength deterioration after exposure to a temperature of over 300 °C. When the exposure temperature is higher than 500 °C, however, the residual properties of the two types of steel become similar. Based on the test data in this paper and the literature, empirical equations are proposed to predict the residual elastic modulus, yield stress, ultimate strength, and ultimate strain of QT steel after exposure to elevated temperatures.

Investigation of the interior RC beam-column joints under monotonic antisymmetrical load

The paper presents numerical findings of reinforced concrete interior beam-column joints under monotonic antisymmetrical load. The finite element models considered compression and tension damage were calibrated by test results in terms of the load-displacement, failure modes, and strains of longitudinal steel. The emphasis was put on studying the effects of hoop reinforcement ratio in joint core and the axial compression ratio on the responses of the joints. The results show that, in addition to the truss and strut-and-tie mechanisms, the confinement mechanism also existed in the joint core. A certain amount of stirrup is not only able to enhance the confinement in joint core, undertake a part of shear force and thus to increase the shear capacity, prevent the outward buckling of steel bars in column, improve the stress distribution in joint core, delay cracking and restrain the propagation of cracks, but also to increase the yield load, decrease the yield displacement of beam and improve the joint ductility. However, excessive horizontal stirrups contribute little to the joint performance. In a certain range, larger axial compression ratio is beneficial for the joint mechanical behavior, while it is negative when axial compression ratio is too large.

Residual drift mitigation for bridges retrofitted with buckling restrained braces or self centering energy dissipation devices

A three-column reinforced concrete bridge bent that did not have reinforcement details necessary to provide adequate load capacity and displacement ductility was evaluated under seismic excitations. Two retrofit methods for improving its seismic performance were examined: (i) Buckling Restrained Braces (BRBs), and (ii) Self Centering Energy Dissipation devices (SCEDs). The numerical model of the bridge bent was validated with previous in-situ quasi-static experiments of a full-scale bent. The BRB inelastic behavior was modeled using isotropic and kinematic strain hardening properties. Flag-shaped hysteresis with slip deformation and bearing were used to model the SCED. The numerical models of the BRB and SCED were validated with full-scale experiments of the brace members. Nonlinear time-history analysis was carried out using far-field and pulse-type ground motion sets to evaluate the seismic performance of the as-built and retrofitted bridge bents in the transverse direction. The performance limit states were defined using HAZUS criteria. Incremental dynamic analysis (IDA) was implemented to evaluate the performance of the two retrofit methods up to the collapse limit state. The results show that a retrofit with either BRBs or SCEDs improves the seismic performance of the bridge bent by decreasing drift ratio demands, and reducing the maximum steel and concrete column strains. The BRB and SCED braces reduce damage to the concrete columns by dissipating a significant portion of the input seismic energy. SCED retrofit reduces the bridge bent residual drift ratio under strong earthquakes to acceptable levels; this improves post-earthquake serviceability, increases bridge resilience and keeps repair costs low. Bridge bent peak and residual drift ratio demands were found to be higher under far-field ground motions compared to pulse-type ground motions.

Seismic Risk Assessment of a 42-Story Reinforced Concrete Dual-System Building Considering Mainshock and Aftershock Hazard

A seismic risk assessment of a 42-story reinforced concrete dual-system building considering mainshock and aftershock hazard is presented. Sequential nonlinear response history analyses are performed using as-recorded mainshock-aftershock sequences. Aftershock assessment describes the case where the mainshock has occurred, and the associated damaged state of the building is known. A Markov process model is used to integrate the increase in vulnerability of the mainshock-damaged building with the time-dependent aftershock hazard. Aftershock risk is quantified as the probability of exceeding the structural response demand limits used in performance-based seismic design of tall buildings at different instants in time following the mainshock. The same metric is used to quantify mainshock-aftershock risk; however, for this type of assessment, the uncertainty in the intensity and damage caused by both the mainshock and aftershock is considered. The results of mainshock-only, aftershock, and mainshock-aftershock assessment show that the coupling beam rotation demand limit generally has the highest probability of exceedance compared with the peak transient and residual story drift ratios, frame beam rotations, and compressive and tensile strain in boundary element concrete and steel, respectively. The implied 50-year exceedance probabilities of the demand limits currently used for the collapse prevention performance level were found to vary significantly across the various response parameters.

Effects of crumb rubber aggregate on the static and fatigue performance of reinforced concrete slabs

The utilization of crumb rubber concrete (CRC) is a sustainable solution for dealing with waste tyres. The aim of this work is to investigate the effects of rubber instead of fine aggregates on the static and fatigue performance of reinforced concrete slabs. Based on a series of experiments conducted to determine the material properties of rubberized concrete, a total of eight one-way reinforced concrete slabs were cast, including six CRC slabs and two normal slabs as control specimens according to rubber content and load type, and then were tested under four-point bending loads. The deflection, concrete strain, steel strain and load-bearing capacity of the reinforced CRC slab with different rubber content under monotonic loading were firstly investigated. And then, the effect of rubber incorporation on the failure behavior of reinforced concrete slab was examined, including the fatigue damage evolution, failure mode and fatigue life. The results indicate that rubberized concrete with appropriate mix proportions has the potential to be used in structural members. However, a high rubber content may result in the over-reinforcement of the RC slab, and could be also detrimental to its fatigue life. High fatigue stress can degrade the bonding between the rubber and paste, suggesting that the advantages of rubber that facilitate energy absorption cannot be utilized. For the safe design of rubber as a replacement for fine aggregates, the content of rubber in RC slab is suggested to be no more than 10%.

A Behaviour of Axially Loaded Steel Concrete Composite Long Columns with Basalt Fiber

Composite sections have numerous favorable circumstances over unadulterated steel and solid segments. From the past examinations, it has been demonstrated that the yield strain of the high-quality steel is more prominent than a definitive compressive strain of the solid when exposed to stacking. Consequently, this investigation is centered around the impact of early solid pounding on the conduct of the composite sections.In order to maximize the contribution of the concrete to prevent early crushing of the concrete, the concrete reinforced with basalt fiber was considered. In this project, there are twenty one column specimens were casted to study the mechanical behavior in detail. The impact of basalt fiber on the quality and disappointment conduct of composite sections were wanted to explore. For the structure of composite sections, the standard Eurocode-4 plan strategy has been pursued. To ponder the test execution of the proposed composite sections, the two closures with stuck help condition and hub stacking tests were considered

Ratcheting assessment of pressurized pipelines under cyclic axial loading: Experimental and numerical investigations

The present study aimed to study ratcheting strains of pressurized stainless steel (UNS S32750) pipes with cyclic axial loading conditions. To this aim, some experiments were performed for the tubes involving cyclic axial loading under internal pressure. All specimens were analyzed with a finite element code. Ohno-Wang hardening model was employed in numerical analysis to calculate the ratcheting of the tubes. By using this hardening model, all predicted ratcheting results were consistent with those of the experimental ones. In this study, the effect of pre-compressed strain, internal pressure and stress amplitude were evaluated experimentally and the numerical results were compared with the results. Finally, the tubes collapsed at about the same strain level as it did under monotonic loading. The number of cycles to collapse and the ratcheting strain rate of the pressurized pipelines depend on the different parameters such as cyclic loading parameters, pre-strain and internal pressure. The results show that an increase of pre-strain, internal pressure and cyclic loading parameters leads to increase ratcheting strain rate of pipelines in both axial and circumferential directions.