•A novel system of steel Energy-Dissipative Columns (EDCs) is proposed.•A simplified model of EDC-MF system is established using lumped mass model for MRF and FE model for EDCs.•The effect of storey ...number, stiffness ratio, soft story factor and seismic intensity factor on the mitigation efficiency of EDCs is investigated.•A rational range of lateral stiffness ratios of 0.02–0.2 is recommended for EDC-MF systems.
A novel system of steel Energy-Dissipative Columns (EDCs) is proposed to mitigate seismic responses of reinforced concrete Moment Resisting Frames (MRFs). The EDC-MF dual system aims to not only dissipate seismic energy by replaceable steel strip dampers in EDCs but mitigate inter-story drift concentration to avoid soft/weak-story failure of conventional MRFs. A simplified numerical model of EDC-MF dual system is established by using lumped mass shear model for MRFs and finite element model for EDCs. Parametric studies are conducted to investigate the effect of storey number, stiffness ratio, soft story factor and seismic intensity factor on the mitigation efficiency of EDCs. The results show that the lateral stiffness ratio of EDC to MRF, the story irregularity factor of MRFs, and the ratio of story shear capacity of EDC-MF systems to seismic base shear are the most important parameters. It is found that both the maximum inter-story drift and the inter-story drift concentration can be effectively mitigated due to the presence of EDCs, compared to traditional MRFs. The mitigation efficiency of EDCs increases with increasing lateral stiffness ratio and story irregularity factor under various ground motion intensities. A rational range of lateral stiffness ratios of 0.02–0.2 is recommended for the seismic design of EDC-MF dual systems.
This paper is based on the surface defects of casting billets in the production process of nonoriented silicon steel plates at a steel plant in North China. Taking the parameters of a slab mold in ...the nonoriented silicon steel production process as a prototype, the flow field characteristics of the mold under the same section, different drawing speed and immersion depth were systematically studied by using a LES (large eddy simulation) and VOF (volume of fluid) coupling algorithm. The results show that under the current conditions, when the critical slag entrapment speed increases from 1.0 m/min to 1.2 m/min, the nozzle insertion depth increases linearly with the critical slag entrapment speed, while when the nozzle insertion depth exceeds 130 mm, the increasing effect of further increasing the nozzle insertion depth on the critical slag entrapment speed begins to decrease. When the drawing speed of continuous casting is kept constant at 1.4 m/min, the abnormal fluctuation height of the steel slag interface is significantly improved when the angle of the water nozzle is increased from 15° to 20°, and the proportion of slag entrapment is also reduced from 0.376% to 0.015%. When the nozzle angle is 25°, the slag entrapment ratio is reduced to 0%, and the steel slag interface also ensures a certain activity. The numerical simulation results were applied to the industrial site, and the slag inclusion rate and crack rate of the billet in the continuous casting process of nonoriented silicon steel were obviously improved after the optimization process.
In the present work, the microstructure, phase composition, and temperature dependence of the mechanical properties and fracture micromechanisms of low-carbon steel produced by conventional casting ...and electron beam additive manufacturing have been studied. Regardless of the manufacturing method, the phase composition of steel consists of ferrite with an insignificant fraction of carbides (pearlite grains in both types of steel and single coarse precipitates in the additively fabricated one). It was shown that the studied steels are characterized by a strong temperature dependence on yield strength and ultimate tensile strength. At T = 77 K, both types of steel are characterized by high strength properties, which decrease with increasing test temperatures up to 300 K. In addition, all deformation curves are characterized by the presence of a yield drop and yield plateau over the entire temperature range under study (77 K-300 K). A decrease in test temperature from 300 K to 77 K leads to a change in the fracture micromechanism of the steels from a dimple fracture to a cleavage one. Despite the similar deformation behavior and strength properties, the additively fabricated steel possesses lower elongation to failure at 77 K due to an insignificant fraction of coarse precipitates, which assists the nucleation of brittle cracks.
Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was ...determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.
Blocks from a modified 9Cr-1Mo steel plate used for fast breeder reactor application under normalized and tempered condition were hot-rolled at different temperatures (1050-875 °C) applying same ...amount of deformation, normalized using different austenitizing temperatures (1100-950 °C) and finally tempered at 750 °C. These samples having tempered martensitic microstructures were impact tested over the temperature range of +80 °C to −196 °C. The effect of hierarchical martensitic microstructure with different structural units of varying length scales (i.e. lath, sub-block, block, packet and prior-austenite grain) on the micro-mechanisms of deformation and fracture have been elucidated by studying the propagation of cleavage cracks and the formation of shear cracks within the samples using electron back-scattered diffraction (EBSD) technique and Visco-plastic self-consistent (VPSC) polycrystalline plasticity model. The study indicates strong influence of certain crystallographic variants on the cleavage crack propagation and the ‘martensitic block’ is found to be the ‘effective grain’ controlling the impact toughness at low temperatures. Dynamic fracture at high temperatures was dictated by cracking along the shear bands, evolution of which depend on the size and distribution of prior-austenite grains.
•Role of hierarchical martensitic microstructure on ductile and cleavage fracture is explored.•A model to measure cleavage angle between martensitic variants is presented.•VPSC model used to study dynamic deformation mechanism at high temperature.•Large prior-austenite grain size promotes adiabatic shear bands and associated ductile cracking.•All the block boundaries and some packet boundaries resist cleavage crack propagation.
•A 3D steel frame was analysed to study its resistance to fire-induced progressive collapse.•It is feasible to perform an explicit dynamic analysis for structures in fire by scaling a real fire time ...to seconds.•The uneven load transferring in the two planar direction plays a key role in the collapse modes.•The frame withstands the fire of single columns heated (load ratio of 0.25) but collapses for a higher load ratio of 0.5.•The frame collapses for a corner fire and long edge fire due to the uneven load redistribution.
This paper numerically investigates progressive collapse resistance of three-dimensional steel frames with reinforced concrete slabs exposed to localized fire using LS-DYNA. An explicit dynamic analysis is carried out and the real fire time is scaled down to save the computational cost. The prototype of the model is based on the eight-storey building in Cardington tests. The scenario of heating individual columns on the ground floor is first studied followed by a sever case of simultaneously heating four columns in one compartment. The collapse modes and load redistribution scheme of the frame subjected to different load ratios and fire locations are investigated. The modelling parameters such as mesh size, initial imperfection, timescale are first studied by validating against the fire test data. It is found that the mesh size has little influence on the responses of members at elevated temperature. The initial imperfection has significant effect on the load-bearing capacity of columns. The quasi-static behaviour of structures under a fire duration of hours can be simulated in a dynamic analysis by being scaled to seconds without causing oscillation of responses. The numerical results of the 3D frame show that the frame does not collapse in the case of single column heated for a fire design load (load ratio of 0.25 for columns). By increasing the load ratio to 0.5 as for the ambient design, progressive collapse occurs. For a fire of four columns heated, the frame collapses for the corner bay fire and long edge bay fire but withstands for the internal and short edge bay fires. The collapse modes are dominated by the uneven load redistribution in the two horizontal directions and the fire location, which cannot be simulated by a 2D model. The loads previously sustained by the buckled heated column are transferred more along the short span than the long span. The critical temperature of a column in a frame is significantly lower than that given in EC3, due to the fact that the translational and rotational restraint increase its load ratio and reduce its effective length, respectively. The critical temperature for the global collapse of the frame is about 50–100°C higher than that of individual heated columns.
•The steel ribs applied for soil-steel bridge do not cause significant advantages in reducing stresses of the shell.•Application of shell model without steel ribs do not exceed the allowable stresses ...and displacements in the shell.•Obtained results show that the application of the ribs in CSP shell is not necessary from the practical point of view.•The CHBDC standard gives values that are closer to the FEM results.
Soil-steel bridges are becoming increasingly popular in various parts of the world, and are often built with a span of 3–25 m. Those with a span greater than 12 m are usually equipped with additional stiffening elements, e.g. ribs, relieving slabs, longitudinal beams, steel ribs and steel ribs filled with concrete. This paper examines the necessity of using these additional stiffening elements, using the example of a soil-steel bridge with a span of over 17 m. Stiffening steel ribs filled with concrete were used in this bridge, and the behaviour of the corrugated steel shell of the bridge was then analysed under backfilling loads. The DIANA program with the finite element method was used for the numerical analysis. The maximum displacements, bending moments and axial forces for the three numerical models of corrugated steel shell were considered, and the displacements obtained from numerical calculations were compared with measured results. In addition, the bending moments and axial forces obtained using finite element analysis were compared with results based on the relevant standards and design methods.
•Concrete with fibre reinforcement shows better strength and ductility.•Hybrid steel wire mesh and steel fibre reinforcement improves beam shear capacity.•Beam with hybrid reinforcement shows ...exceptional energy absorption capacity.•Slab with hybrid reinforcement survives 12kg TNT detonation at 1.5m standoff distance.•Numerical model confirms the charge shape effect in the blast tests.
Structural responses and damages under blast loading environments are critical to structural and personnel safety. The blast scenarios involving close-in detonations are attracting increasingly more attentions over the last few decades due to the rising of terrorism. Under close-in detonations, structural elements tend to fail in a brittle mode including shear, concrete crater and spall. In such loading scenarios, the structural designated loading capacity which is usually based on flexural deformation assumption is not fully developed. To provide high-level structural protection, high performance concretes with varying fibre additions are now widely investigated and used in blast resistance designs. In the present study, field blast tests results on reinforced concrete slabs under close-in detonations are presented. Performances of slabs made of normal strength concrete and steel fibre reinforced concrete are compared and discussed. Besides conventional steel rebar reinforcement, new reinforcement scheme i.e. hybrid steel wire mesh-micro steel fibre reinforcement is investigated through the laboratory static tests and field blast tests. Furthermore, a numerical study based on Multi-Material ALE and Lagrangian algorithm is carried out to further investigate the field tests’ phenomenon.
•Categorical gradient Boosting (CatBoost) is presented to predict the strength of concrete-filled steel tubular columns.•A total of 3103 tests, which is divided in four datasets, is collected to ...train and test the learners•The comparison of the present results and those from the code predictions shows very high prediction accuracy•The coefficient of determination (R2), which is the lowest value (R2 = 0.964) for Dataset 2 and the highest one (R2 = 0.996) for Dataset 1.
Due to complexities from the interaction between steel tube and concrete filling of concrete-filled steel tubular (CFST) columns, their strengths are very complicated, which is a highly nonlinear relation with material strengths and geometry. Categorical gradient Boosting (CatBoost), which is advanced boosting machine, is presented to solve the problems. A total of 3103 tests, which is divided in four datasets, is trained and tested the learners to determine the ultimate axial strength as the output variable while the strength of materials (concrete and steel) and geometry (e.g., diameters/width/heights, thickness, effective length, eccentricities) are the input ones. The comparison of the present results from 10-fold cross validation and those from the code predictions (AISC 360-16, Eurocode 4 and AS/NZS 2327) and previous study shows very high prediction accuracy in terms of coefficient of determination (R2), which is the lowest value (R2 = 0.964) for Dataset 2 and the highest one (R2 = 0.996) for Dataset 1. While the predictions from three codes beyond material limit and slenderness are less conservative than those within it, CatBoost provides nearly similar experiment results with the mean values as unity without any limits. This algorithm can be used to predict an accurate strength of CFST columns.
