Progressive deformation (ratcheting) can occur as a response to variable loads as soon as the elastic limit is exceeded. If this is the case, strains and displacements accumulate in the event of cyclic loading in each load cycle.Widely known as triggers for ratcheting and already being considered in some design codes are configurations, in which a structure is subjected to at least two different types of load, namely a constant load (the primary load) and a superimposed cyclic load. In this paper, another mechanism that generates ratcheting is introduced. It can be attributed solely to the effect of a single load. In the simplest case, this can be explained by the successive activation of (an infinite number of) plastic hinges if a load of constant magnitude is moved in space. The increments of strains and displacements can decrease or increase from cycle to cycle, when the material is hardening, or if elastic foundation is present, or if the equilibrium condition is formulated for the deformed system (second-order theory) or if ‘‘large’’ rotations are taken into account (third-order theory).

Dynamic ratcheting (DR) is a phenomenon that occurs in nonlinear systems and one aspect of complicated nonlinear dynamic behaviors. DR behavior have a strong effect on the magnitude of plastic deformation in single-degree of freedom (SDOF) hysteretic damping systems, therefore there is need to precisely examine this phenomenon caused by earthquake excitations. DR-inducing frequencies of ground excitation are called "active frequencies". A new method is proposed in this study to identify active frequencies of DR-inducing ground excitation using wavelet transform. The identification method is based on a reduced dimensionality and filtered frequency content of original record according to closeness of displacement time history of SDOF system under both original and modified record. The objective of this study is divided into two main parts: In the first part of this study, applying the proposed method for a DR- inducing ground motion and it was an example that how the method could be utilized to identify active frequencies of DR- inducing ground motion. The second part of this study is devoted to identify the DR- inducing ground motions between a set of ground motions records, containing 504 records up to the year 2012, in Iran. The reduced representation of ground motion is a useful technique for extracting active frequencies from ground motion.

The present study aimed to introduce a numerical method to study ratcheting strains of rectangular plates. A new numerical analysis was conducted by development of dynamic relaxation method combined with MATLAB software to evaluate the ratcheting behavior of the thin steel plate under mentioned loading condition. In order to verify the results, experimental tests were performed under stress-controlled conditions by a zwick/roell amsler HB100 machine and bending ratcheting of CK45 steel plate at room temperature was studied. Under stress-controlled conditions with non-zero mean stress, ratcheting behavior occurred on thin plate. Moreover, a finite element analysis was carried out by Abaqus using nonlinear isotropic/kinematic (combined) hardening model. The results showed that the rate of ratcheting strain decreased with an increase in cycle number. It was found that the hysteresis loops were wider in experimental method than those of other methods because of more energy dissipation. The numerical results are in a good agreement with the simulation and experimental data. Comparison of errors between these methods obviously demonstrate high accuracy of the new introduced method.

Dynamic Ratcheting (DR) is a nonlinear dynamic phenomenon occurring in hysteretic damping systems. It means the structural plastic deformation increases asymmetrically in successive cycles under an earthquake excitation. Although it is generally recognized that DR is closely related to the frequency contents of an earthquake excitation applied to the structure, no targeted analysis has been conducted on the influence of time-varying frequency content on occurrence and development of DR. This manuscript aims to analyze the influence of time evolution of DR-inducing ground motion frequency content on developed DR phenomenon in the Single Degree-Of-Freedom (SDOF) system with the Elastic-Perfectly-Plastic (EPP) hysteretic behavior. To survey the influence of time evolution of ground motion frequency content on the developed DR: In the first step, the three DR-inducing ground motion records were selected as excitations input of EPP SDOF systems. In the second step, time-varying frequency of ground motions were changed by shifting their frequency content forward or backward in time using wavelet transform to produce altered versions records. In the final step, the displacement responses of EPP SDOF systems under selected records and their altered versions were compared. By analyzing the displacement response of EPP SDOF systems excited by selected ground motions and their altered versions, it can be found that the time-varying frequency content considerably influences the developed DR behavior in SDOF systems. In the selection of records for dynamic analysis of structures, time-varying frequency content could be further considered as an important characteristic variable for ground motion records.

In this paper, accumulation of plastic deformation of AISI 1045 steel plates with circular cutouts under cyclic axial loading is studied. Loading was applied under force-control conditions. Experimental tests were performed using a Zwick/Roell servo hydraulic machine. Under force-control loading with nonzero mean force, plastic strain was accumulated in continuous cycles called ratcheting. Numerical analysis was carried out by ABAQUS software using nonlinear isotropic/kinematic hardening model. The results of the numerical simulations were compared to experimental data. The results demonstrated that the ratcheting response of plates with circular cutouts could be numerically simulated with a reasonable accuracy. It was observed that the local and global plastic deformation increase with increasing the notch diameter. Also, maximum principal stress was the main parameter for initiation of crack around the notch. Based on numerical results, at notch root, both ratcheting strain and local mean stress relaxation was occur simultaneously and due to relaxation of local mean stress, plastic shakedown was occurred.