Comparison Between Different Design Strategies For Freedam Frames: Push-Overs and Ida Analyses

Smart and simple design of seismic resistant reinforced concrete frame

A general design procedure for failure mechanism control of reinforced concrete frames

Dissipative structural behavior is a common feature of seismic resistant structures. In case of multi-story steel frame structures, the dissipative behavior can be controlled by providing a favorable plastic mechanism, which involves the formation of plastic hinges at predefined locations (e.g., beam ends and/or joints), while rest of the structure behaves essentially elastic. Ensuring the requirements for the development of the plastic mechanism can lead to high strength requirements for non-dissipative elements/components. A modern approach to fulfill these requirements and control the local/global hierarchy criteria is to combine two steel grades, i.e. high strength steels (HSS) in non-dissipative members/components and mild carbon steels (MCS) in dissipative members/components. Used in combination with replaceable dissipative elements, the solution of two steels, called dual-steel solution, is also effective in the recovery phase after an extreme loading, as it eases the retrofit intervention, i.e., creates a more robust and resilient environment. The study presented in the paper is a review of reference works on the practical application of dual-steel systems in multi-story steel building frames.KeywordsHigh strength steelDual-frame systemSeismic resistanceRobustness

Japanese buildings are generally designed as moment‐resistant frames, and beam ends are required to have high bending strength and high plastic deformation capacity. With H‐shaped beams, the contribution of the web to the bending strength is small, so H‐shaped beams with thick flanges and thin webs are used to reduce the amount of steel required for construction. However, H‐shaped beams with thin webs are prone to local buckling at the ends of the beam, resulting in poor plastic deformation performance. The authors have developed a structural system of steel structures in which the ends of beams are reinforced by stiffener plates with the aim of improving the plastic deformation capacity. Especially when these structural systems are applied to a high‐rise building with large‐sized beams, the effect of reducing the amount of steel is high by reducing the thickness of the web. Reducing the amount of steel can be expected to reduce the loads on the environment and the construction cost. In this paper, the simple stiffening method is proposed with stiffeners that can improve factory manufacturability. Secondly, to confirm the plastic deformation capacity of a stiffened steel beam, a series of cyclic loading tests is carried out using 1/2 scale specimens.

Characteristic cyclic plastic deformation in ZK60 magnesium alloy

Outstanding mechanical characteristics make metal matrix composites (MMCs) applicable to many industrial applications. However, the very hard reinforcements that provide such remarkable features for MMCs also cause challenges during the machining process. This paper tries to address these challenges through development of a novel analytical model for prediction of cutting force during machining these composites. The force model is based on calculation of power consumption in different parts of the cutting system. The model considers the plastic deformations, different types of friction at various interfaces and debonding and fracture of reinforcements. The cutting force values predicted by the model are compared with experimental values for various MMCs at different cutting conditions. The close agreement between the results verifies the ability of the model to provide accurate estimation of the cutting force during machining MMCs.

In previous work, stress-strain curves for the atomic lattice of certain metals have been obtained from X-ray diffraction measurements of the lattice dimensions of test specimens under tension or compression, and it has been shown that when the external yield stress is exceeded, there is a systematic departure from Hooke’s Law. It is pointed out in the present paper that this departure indicates that the external applied stress above the yield is no longer balanced primarily by simple displacement of the atoms but also by a new type of secondary internal stress brought about by the process of plastic flow; and that this secondary stress, being of a permanent nature, can be measured by the residual lattice strains exhibited by the lattice after removal of the external stress. These residual strains are measured in various directions to the stress direction for mild steel subjected to tension, and it is shown that the lattice after tension exhibits a longitudinal compression and a transverse expansion in the ratio of 2:1, which means that the density of the material is thereby kept constant. Comparisons of X-ray and mechanical measurements further show that the hysteresis loop exhibited by the external stress-strain curve of mild steel after overstrain can disappear and the linear elastic relation be recovered without any corresponding change in the internal stress, which is therefore a more fundamental physical property. It is also shown that when the elastic range is extended by overstrain in tension, there is no symmetrical increase in the elastic range in subsequent compression, thus confirming the existence and direction of the secondary internal stress. Finally, the lattice stress-strain curves are also obtained for a 0.4 % C steel (partially pearlitic) and a 0.8 % C steel (pearlitic), and by comparison with the results on pure iron and 0.1 % C steel (annealed) it is shown that the maximum residual internal strain developed by the lattice increases markedly with the fineness to which the crystallites can be broken down by the plastic deformation.

Elastic–plastic stress transfer in short fibre-reinforced metal–matrix composites

Experimental and finite element study of high-strength steel framed-tube structures with replaceable shear links under cyclic loading

Hollow aluminium bats were introduced over 30 years ago to provide improved durability over wooden bats. Since their introduction, however, interest in hollow bats has focused almost exclusively around their hitting performance. The aim of this study was to take advantage of the progress that has been made in predicting bat performance using finite elements and apply it to describe bat durability. Accordingly, the plastic deformation from a ball impact of a single-wall aluminum bat was numerically modelled. The bat deformation from the finite-element analysis was then compared with experiment using a high-speed bat test machine. The ball was modelled as an isotropic, homogeneous, viscoelastic sphere. The viscoelastic parameters of the ball model were found from instrumented, high-speed, rigid-wall ball impacts. The rigid-wall ball impacts were modelled numerically and showed good agreement with the experimentally obtained response. The strain response of the combined bat-ball model was verified with a strain-gauged bat at intermediate ball impact speeds in the elastic range. The strain response of the bat-ball model exhibited positive correlation with the experimental measurements. High-speed bat-ball impacts were performed experimentally and simulated numerically at increasing impact speeds which induced correspondingly increased dent sizes in the bat. The plastic deformation from the numerical model found good agreement with experiment provided the aluminium work hardening and strain rate effects were appropriately described. The inclusion of strain rate effects was shown to have a significant effect on the bat deformations produced in the finite-element simulations. They also helped explain the existence of high bat stresses found in many performance models.

Transient response of plates to travelling loads with application to slamming damage

Magnetic domain motion has been widely studied in the fields of spintronics, nanowires, and thin films. However, there is a lack of such studies on industrial steels, especially for domain motion under the action of varying stress. Understanding domain motion under stress is helpful for the improvement of evaluation accuracy and the establishment of theoretical models of passive, nondestructive testing technology. This paper presents the influence of varying tensile stresses on the magnetic domain motion of silicon steel sheets. Magnetic domain rotation and domain wall displacement were characterized using magnetic domain images, and their motion mechanisms under elastic and plastic stresses are presented. The results show that the domain rotation under stress involves reversible and irreversible changes. The effect of material rearrangement on domain rotation and domain wall displacement after plastic deformation is discussed. Based on the motion mechanism, a threshold stress value (TSV) required for the complete disappearance of the supplementary domains in the elastic range is proposed, enabling the classification of the elastic stress ranges in which the reversible and irreversible domain rotations occur. In addition, the effect of microstructure on TSV is also discussed, and the results show that the regions far away from the grain boundary need larger stresses to complete an irreversible domain rotation. Additionally, the domain width and orientation also affect the TSV. These findings regarding the domain motion mechanism and TSV can help to explain the sequence of domain rotation under stress and modify the stress assessment under dynamic loads in electromagnetic nondestructive evaluation, especially in the magnetic memory method.

Ductile materials fail through mechanisms of void nucleation and coalescence. A tensile test of a ductile metal begins with reversible elastic deformation, proceeds through permanent plastic deformation, and ends with rupture. Dislocations in the grains of a metal do not slip in the elastic range but begin moving in the plastic range. As the dislocations interact with grain boundaries and each other, they cause increasing resistance to plastic deformation, termed work hardening. The applied load and the true stress rise together during this process. When the dislocations have no room to move, voids open up in the material. As these voids coalesce into cracks, the true stress rises rapidly and the sustained load decreases. Rupture occurs when the cracks propagate through the specimen and it loses all load-carrying capacity. The complexity of the ductile fracture phenomenon continues to attract substantial attention from researchers. Sharp objects in a production environment can puncture fragile components made from ductile metals. Non-linear dynamic simulations help engineers to plan processes such that these components do not fail when an accident happens. The projectile is termed a probe, and the component is the target. The surface of the probe that contacts the target may be sharp, blunt, or flat. Probes are typically cylindrical for simplicity, but other shapes that exist in the production environment are equally applicable.

In an earlier study of the phenomena of dynamic buckling of shells in the elastic range using a 48 degree-offreedom doubly curved quadrilateral imperfect thin-shell finite element, the interesting destabilizing effects of initial imperfections on a spherical shell, a spherical cap, and a hemispherical shell were found. The formulation was based on the Kirchhoff-Love shell theory with geometric imperfections. In this study, the earlier formulation is extended to include the effect of plasticity in tensor form so that a wide range of practical problems can be considered in order to study more completely the effects of dynamics, amplitude of imperfection, and plasticity. The effect of viscous damping is also considered by using the Rayleigh damping concept. Examples include static and dynamic buckling analyses of 1) axisymmetrically imperfect spherical shells, 2) axisymmetrically imperfect spherical caps, and 3) asymmetrically imperfect spherical caps, all in both elastic and elastic-plastic ranges. For case 3, there seems to be no previous results available for comparison. From the wide variety of examples studied, the previous conclusions for shells with axisymmetric imperfections were reconfirmed for shells with asymmetric imperfections, i.e., dynamic effect, imperfection, and plastic deformation, which all have the effect of reducing the buckling load to various degrees. On the contrary, the viscous damping has the effect of increasing the dynamic buckling load. Such an effect is quantified in two examples.

The unstiffened extended end-plate connection exhibits different behavioral characteristics and energy dissipation capacities depending on the thickness of the end-plate and the change in the gauge distance of the high-strength bolts. In particular, the energy dissipation capacity of the unstiffened extended end-plate connection is affected by the failure modes of the connection: the beam failure mode and the connection failure mode. That is, the energy dissipation capacity varies depending on the case, where the failure is caused by the occurrence of plastic hinges acting like fuses in the beam ends, and the failure results from the plastic deformation after the flexural yielding of the end-plate. This study was conducted to design and construct the connection in such a way that it could provide sufficient strength, stiffness, and energy dissipation capacity in response to the fracture of the connection that may occur in case of an emergency, by inducing a position where the plastic hinge fuse occurs in the end-plate of the connection. For the evaluation of the energy dissipation capacity of the connection, a three-dimensional nonlinear finite-element analysis of the unstiffened extended end-plate connection was performed by changing the thickness of the end-plates. The finite-element analysis results showed that the energy dissipation capacity increased when the thickness of each end-plate decreased, and that the residual deformation did not occur when an SMA end-plate was installed instead of the end-plate with the conventional SN steel applied.