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Abstract The stiffness of soils is not constant and it is highly strain dependent. Some nonlinear models such as Fahey's model for sands have been proposed for sands but these models can not be the representative of the behavior of most coarse-grained soils such as alluvial sediments of Tehran. In this paper, firstly some data of deformation modulus of several coarse-grained soils such as Tehran's soil are presented as a function of strain. Then the weakness of nonlinear models such as Fahey's model in predicting the behavior of these kind of geo-materials is presented. In next step, a new proposed model, which is in fact a type of corrected Fahey model, is explained and then a comparison is done for Tehran soil. The foundation of Milad tower is modeled using FLAC software incorporating new model and then calculated settlement is compared with measured one using micro-geodetic method.

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Steel frames with Khorjeeni connections have been widely used in the traditional construction of buildings in Iran during the past decades. In the traditional form of Khorjeeni connections, double section beams are not cut at the intersection with columns, rather they are connected to the column by means of two angles places over the top and bottom of the beam flanges. This type of connection offers advantages for frames, wich carry gravity loads, but it has deficiencies when the frames are subjected to lateral loads. Like other structural frames, there are masonry infills in many frames with Khorjeeni connections. The behavior of composite frames subject to lateral loads differs from that of bare steel frames. In this paper, positive and negative effects of masonry infills were studied on the behavior of steel frames with Khorjeeni connections. Finite element method was used to carry out nonlinear static analysis of subassemblages of this type of frames. Initially, the results of some experiments were utilized to verify the details of the model. Then numerical models of toe span or four span frames with different configuration of bracings and masonry infills were studied. The results showed that infill frames increase the stiffness and strength of frames in the absence of bracing considerably. Even when bracings are present, the increase in stiffness and strength is significant. Simplified compressive strut models proposed in recent guidelines for seismic rehabilitation of existing buildings are also utilized to analyze the models. The results show agreement with the results of more sophisticated FE models. The masonry infills, however, have some negative effects on the behavior of Khorjeeni frames. Parts of the column in the vicinity of connections are prone to plastic damage, particularly when the infills are relatively strong. The Khorjeeni connections are subjected to vertical forces and tortional moments. Due to limited vertical strength of these connections, top stories of this type of frames may suffer when compressive action of strut is mobilized for other bays. This action introduces additional moments, which may damage the connections. Therefore, considering of these negative effects of infills is very important when seismic behavior of the existing frames is assessed, because these effects limit the interstorey drift ratios.

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A large number of buildings in Iran are constructed with masonry infills for functional and architectural reasons. Often, engineers do not consider masonry infill walls in the design process because the final distribution of these elements may be unknown to them, or because masonry walls are regarded as non-structural elements. However, infill walls tend to interact with the frame when the structure is subjected to lateral loads. Masonry infills contribute to the stiffness of the infilled frame under the action of lateral load. This leads to structural response deviating from what is expected in the design. The effects of the infills on the seismic behavior of buildings may be positive or negative, depending on a large number of parameters. Steel frames with Khorjeeni connections have been widely used in the traditional construction of buildings in Iran during the past decades. In the traditional form of Khorjeeni connections, double section beams are not cut at the intersection with columns, rather they are connected to the column by means of two angles places over the top and bottom of the beam flanges. This type of connection offers advantages for frames, wich carry gravity loads, but it has deficiencies when the frames are subjected to lateral loads. Like other structural frames, there are masonry infills in many frames with Khorjeeni connections. The behavior of composite frames subject to lateral loads differs from that of bare steel frames. In this paper, positive and negative effects of masonry infills were studied on the behavior of steel frames with Khorjeeni connections. Finite element method was used to carry out nonlinear static analysis of subassemblages of this type of frames. Initially, the results of some experiments were utilized to verify the details of the model. Then numerical models of toe span or four span frames with different configuration of bracings and masonry infills were studied. The results showed that infill frames increase the stiffness and strength of frames in the absence of bracing considerably. Even when bracings are present, the increase in stiffness and strength is significant. Simplified compressive strut models proposed in recent guidelines for seismic rehabilitation of existing buildings are also utilized to analyze the models. The results show agreement with the results of more sophisticated FE models. The masonry infills, however, have some negative effects on the behavior of Khorjeeni frames. Parts of the column in the vicinity of connections are prone to plastic damage, particularly when the infills are relatively strong. The Khorjeeni connections are subjected to vertical forces and tortional moments. Due to limited vertical strength of these connections, top stories of this type of frames may suffer when compressive action of strut is mobilized for other bays. This action introduces additional moments, which may damage the connections. Therefore, considering of these negative effects of infills is very important when seismic behavior of the existing frames is assessed, because these effects limit the interstorey drift ratios.

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In this paper, the results of a statistical study on inelastic displacement ratio for structures subjected to pulse like near fault ground motions were presented. This study is important because, the results can used for evaluating inelastic displacement demand of structures with known lateral stiffness and strength subjected to near fault ground motions. Inelastic displacement ratio were computed from the response of single-degree-of-freedom systems having 6 level of strength reduction factor when subjected to 61 pulse like near fault records. The influence of period of vibration normalized by period of peak spectral displacement, strength reduction factor, period associated with velocity pulse TP, earthquake magnitude and distance to the source, post-yield stiffness and hysteresis behavior of structure on inelastic displacement are evaluated. Results indicate that strength and stiffness degrading in short period region increase inelastic displacement demands. Finally, a simply equation for estimate the mean of the inelastic displacement ratio for structures subjected to pulse like near fault ground motions is proposed.

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In this paper, the results of a statistical study on inelastic displacement ratio for structures subjected to pulse like near fault ground motions are presented. This study is important because the results can be used for evaluating inelastic displacement demand of structures with known lateral stiffness and strength subjected to near fault ground motions. Inelastic displacement ratio is computed from the response of single-degree-of-freedom systems having 6 level of strength reduction factor subjected to 61- pulselike near fault records. The influence of period of vibration normalized by period of peak spectral displacement, strength reduction factor, period associated with velocity pulse TP, earthquake magnitude and distance to the source, post-yield stiffness and hysteresis behavior of a structure on inelastic displacement ratiois investigated.For more study on the strength and the stiffness degradation effects on inelastic displacement, three type of hysteresis behavior have been considered. The first type iselasto-plastic behavior. Elasto-plastic behavior is generally used to represent the non-degrading hysteretic behavior. Second and the third typesarethe stiffness degrading and the strength-stiffness degrading hysteretic behavior.Results indicate that strength and stiffness degrading in short period region increases inelastic displacement demands. Further the period associated with velocity pulse plays a main role in inelastic displacement and has a significant effect on it. It is found that strain hardening can reduce inelastic displacement relative to system with perfectly elasto-plastic hysteresis behavior. Magnitude and source to site distance have little effects on inelastic displacement. Finally, a simple equation is proposed for estimating the mean inelastic displacement ratio for structures subjected to pulse like near fault ground motions.

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Abstract: Steel frames with Khorjeeni connections have been widely used in the traditional construction of buildings in Iran during the past decades. In the traditional form of Khorjeeni connections, double section beams are not cut at the intersection with columns, rather they are connected to the column by means of two angles placed over the top and under bottom of the beam flanges. This type of connection offers advantages for frames, which carry gravity loads, but it has deficiencies when the frames are subjected to lateral loads. Like other structural frames, there are masonry infills in many frames with Khorjeeni connections. The behavior of composite frames subject to lateral loads differs from that of bare steel frames. In this paper, positive and negative effects of masonry infills, when strengthed by reinforced shotcrete, are studied on the behavior of steel frames with Khorjeeni connections. Finite element method was used to carry out nonlinear static analysis of subassemblages of this type of frames. Initially, the results of some experiments were utilized to verify the details of the model. Then numerical models of two span or four span frames with different configuration of bracings and masonry infills and characteristics of shotcrete were studied. The results showed that infills increase the stiffness and strength of frames in the absence of bracing considerably. Even when bracings are present, the increase in stiffness and strength is significant. When the infills are strengthened, their effects on stiffness and strength of composite frames increase. However if the steel frames are not strong enough, their strength limit the effects of infills. The masonry infills, however, have some negative effects on the behavior of Khorjeeni frames. Parts of the column in the vicinity of connections are prone to plastic damage, particularly when the infills are relatively strong. The Khorjeeni connections are subjected to vertical forces and tortional moments. Due to limited vertical strength of these connections, top stories of this type of frames may suffer when compressive action of strut is mobilized. For other bays, this action introduces additional moments, which may damage the connections. Therefore, considering these negative effects of infills is very important when seismic behavior of the existing frames is assessed. When the infills are strenghted by shotcrete, these negative effects become even more important and the inter story drift rations need to be limited in order to avoid failure in conections.

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Grid stiffened composite shells are one of the most important structures in aerospace industries. In this study critical buckling load of these structures with diamond shape stiffeners under axial loading based on smeared method is presented. The effect of shell thickness, angle of fibers in shell and the direction of stiffeners into the buckling load is determined. First-order shear deformation theory based upon the Ritz method is used to calculation of critical buckling load of these structures. In the use of FSDT theory, transverse shear forces in stiffeners have been considered. The results are compared with FEM solution with clamped boundary condition.

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The main purpose of the present research is analytical and numerical analyses of graphene/epoxy nanocomposites with a random distribution of nanoparticles. For this purpose, by combining the molecular dynamics and micromechanics methods, a new approach is presented. The molecular dynamics method is used to model the stiffness of the graphene/epoxy nanocomposites containing one layer of nano graphene embedded in epoxy resin. A multi-scale modeling strategy from macro to meso, then from meso to micro and finally from micro to nano scales is introduced. A representative volume element (RVE) is selected and for a nanocomposite having a single monolayer graphene embedded in epoxy resin, the longitudinal (E11), transverse (E22) and normal (E33) stiffnesses for three RVEs with arbitary graphene size are simulated. The best curve is fitted to each stiffness diagram and stiffnesses of the RVE in three directions with true graphene size are investigated. In order to consider the effect of randomly graphene sheets distribution in epoxy resin, micromechanical approach is used. Finally, the stiffness of the nanocomposites with randomly distributed graphene is calculated. For evaluation of the present approach in this research an experimental program is conducted. The result of the modeling is well agreed with the experimental data.

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Hydraulic engine mounts are applied to the automotive applications to isolate the frame from the high frequency noise and vibration produced by the engine. It also designs to reduce the engine shake motions from the road distribution usually occurred at low frequencies. This implies that the stiffness and damping properties of the engine mount should be amplitude- and frequency- dependent. In the semi-active engine mounts this task will be done by changing the mount parameters such as stiffness and damping. Magneto-rheological fluids are used in the mounts to change their damping by applying the magnetic field. When the current is applied to the electromagnet and the magnetic field is present, the behavior of the magneto-rheological mount is changed by the magneto-rheological effects. In this paper, a prototype magneto-rheological mount was built and experimentally evaluated. Also, the mathematical model of the mount was developed to represent the dynamic behavior of the engine mount system. The model was numerically solved based on the prototype parameters and simulated in MATLAB. The experimental results were used to verify the model in predicting the mount characteristics.

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In this paper, a cable actuated robot is introduced as a new rehabilitation approach. The quality improvement of human and machine interface has led to create a new device in this area. The interface between the robots with the physical characteristics of body can improve the interaction forces and the patient safety. Considering the joint compliance during the motion range can make the patient feel better and thus, bring success for the rehabilitation program. The key element "cable" makes the possibility of force transmission in this mechanism. Cable actuator is used in this project in order to achieve to maximum adaptation with elbow operation Moreover in the design of rehabilitation device, some advantages are regarded like the low-cost and light weight, smooth joint motion with adjustable stiffness, motor size reduction. The dynamic parameters related to the elbow behavior are described with amplitude and frequency investigating. The performance of the elbow rehabilitation device is examined. Stiffness variation of robot joint is effectively compatible with the elbow joint stiffness according to rehabilitation protocols. As the presented mechanism able to simulate elbow rehabilitation, it can be used more widely in the field of medical robotics.

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Orthopedic plates are currently used in bone healing process. However they cause density loss because of the change in natural stress patterns.The aim of this study was to evaluate a newly developed bone plate using functional graded material in term of stress pattern. In the present study, 3D finite element models of tibial bone plate with variable stiffness of a graded material and traditional bone plates made of stainless steel and Ti alloy have been developed by using the ABAQUS software. Effects on the predicted stresses at the fracture site in the presence of a distance between the plate and fractured bone were also studied. For this purpose, a 3D model of tibia was created with the exact geometry of the real bone geometry by using CT scan images of a human left leg. Results showed that the bone plate with graded material offers less stress-shielding to the bone, providing a higher compressive stress at bone to induce accelerated healing in comparison with Ti alloy and stainless-steel bone plate. Results also showed that the use of non-contact plates provide a favorable mechanical environment for the following fracture healing.

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Nowadays, composite materials are used in different applications. Some of these applications involve components subject to cyclic loading. Fatigue is the dominant failure mechanism for structures under this type of loading. Hence, proper prediction of fatigue life is essential for safe design and operation of structures, maintenance, repair and replacement of components. Many of the existing models in this field have not assessed the degradation of material properties such as stiffness and strength during fatigue damage. In this paper, a stiffness-based model is initially evaluated for fatigue damage analysis of composite structures. The model is validated with two sets of experimental data. A residual strength model is coupled to the choice model and a modified model is developed. Then, residual fatigue life of fiber reinforced polymeric composites is predicted for three sets of experimental data under two-stage loading. The results demonstrate that the proposed model has an improvement on accuracy in the estimation of residual fatigue lives. For better evaluation of the developed model, experimental results and some existing models are compared with the present study predictions. It is concluded that in most cases, the predicted values by the proposed model is closer to experimental values in comparison with other models.

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The application of wing and stabilizer in aerospace vehicle is most important to stability and flight motion. Nonlinear 2D wing is estimated. Nonlinear damping and stiffness with freeplay in plunging and pitching motion is assumed. 2nd order Damping nonlinearity and 3rd order stiffness nonlinearity in pitching and plunging motion is assumed. Fully nonlinear structure with nonlinear 3rd order piston theory aerodynamic is assumed for the first time and result evaluated with different references. The equations are defined with Hamilton principle with the use of kinetic and potential energy and virtual work. They are solved in the state space via the ruge-kuta numerical method to determine chaotic and limit cycle oscillation motion of supersonic airfoil. The result show that as the speed increases, the behavior of 2D wing is softening type with the use of nonlinear rotational stiffness. But, It shows hardening type with the use of transversal nonlinear stiffness. The effect of transversal and rotational freeplay is more complicated than other parameters and increases instability in low speed. In other hand the stability increases with freeplay in high speed. As shown, increase velocity decrease damping effect in post flutter behavior.

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Structural damage identification can be considered as the main step in Structural Health Monitoring (SHM). We can find many different methods which use structural dynamic responses for damage prognosis. Although some of them are concentrated on solving an inverse problem for damage identification, others suggest a direct procedure for defect detection. Despite the good performance of these methods in damage identification, researchers are attempting to find efficient and simple methods for damage identification with high level of accuracy. This paper presents a reference-free method for structural damage identification under earthquake excitation. Damages are defined as some changes in the special instants during an earthquake occurrence and structural time history responses are used as an input signal for discrete wavelet analysis. Finally the “detail coefficients” are inspected for determining the damage characteristics, such as the appearance, the time sequence, and the location of damage(s). Although the peak values in the detail coefficients can show the existence and time sequence of damage, for determining damage location we should inspect these peaks for finding the maximum value. As a result, the associated element with a signal which has maximum peak, can be considered as the damaged element. The applicability of the presented method is demonstrated by studying three numerical examples. First example is devoted for damage identification in a four-story shear frame. It is assumed that we have equipped all of the stories by sensors for recording structural responses. Three different damage scenarios with single and multiple damage cases under two samples of earthquake records, namely El-Centro (1940), and Northridge (1994) earthquakes, are studied. In addition, we study the effect of using different wavelet mother functions and different input signals, such as displacement and velocity responses. All of the obtained results emphasize the applicability of the presented method in damage identification. In second example, we consider a concrete simple beam with ten elements by simulating two different damage scenarios. In this case, we inspect the applicability of the method by considering only the transitional degrees of freedom (DOF) as the equipped DOFs by sensors. This can be interpreted as using limited number of sensors. In addition we use the displacement time histories for damage identification. For having a clear strategy in damage localization, we propose two rules for judging about elements’ health which are based on seeking maximum values of the wavelet coefficients in the damaged instants. Obtained results show the good performance of the presented method in finding time sequence of damage occurrence and damage location. In the third example, we investigate the applicability of the presented method in the presence of complex models of damages by defining bilinear stiffness reduction. In this case, although damage can cause some reduction in the effective stiffness of damaged structure, this reduction is different in positive and negative displacements. Two different damage scenarios are simulated on a single DOF structure under different excitations, namely earthquake excitations and generated White Noise excitation. Obtained results reveal the robustness of the presented method in damage prognosis in the presence of complex damage models.

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The Assessment of strain accumulation due to nonlinear events like creep, plasticity or ratcheting phenomenon has gained importance, since it causes an increase in creep and fatigue damage of materials. Some factors like the magnitude of loading, constitutive equations or the elastic regions around the nonlinear events have effect on the rate of strain accumulation. The elastic follow-up can explain the mechanism of strain accumulation. This phenomenon may occur when a mechanical structure with elastic manner is connected to non-linear events and they are subjected to a displacement load. In these cases, the high rigidity portion of elastic region of mechanical structure may enhance the force to the regions with low rigidity. So in the local non-linear portion, the strain is accumulated. This phenomenon is proposed as an important instruction in mechanical assessment codes. In this study, the effects of Elastic Follow-up phenomenon on strain accumulation due to elastic-plastic and local creep are investigated. So the Elastic Follow-up parameter is defined by the methods which are described in high temperature assessment procedures (R5). The results revealed that the strain accumulation depends on the elastic region in structures which is described by the Elastic Follow-up phenomenon.

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Pulse wave velocity often used as an indicator clinically for diagnosis of cardiovascular diseases. This assumption is well grounded in the physics of pulsatile flow of an incompressible fluid where it is fully established that a pulse wave travels faster in a tube of stiffer wall, the wave speed becoming infinite in the mathematical limit of a rigid wall. in this paper we point out that pulse wave velocity in a stiffer tube is strictly valid only when the wall is free from outside constraints, Which is used as the outer boundary condition (tethering: the degree to which the vessel wall is surrounded by tissue). In this paper, using the equations of blood fluid and vessel walls and using analytical solutions and the use of tethering as outer boundary conditions pulse wave velocity is investigated. In previous research pulse wave velocity has been obtained just for the tethering zero and one, But in the study pulse wave velocity investigated for tethering different degrees of tethering and for three different material wall viscoelastic, elastic and stiff. With this research, it is clear the changes of pulse wave velocity with change of degrees of tethering and change of material wall ,This results is a great help for use of pulse wave velocity as an clinical index to predict arterial stiffness.

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Evolutionary structural optimization (ESO) is based on the simple concept of systematically removing inefficient material from the structure after each finite element analysis, so that the resulting design is gradually evolved to an optimum. The bidirectional evolutionary structural optimization (BESO) method is a new version of the ESO method in which simultaneously removing and adding elements is allowed. Due to the importance of nonlinear structural analysis, in this study the BESO approach is used for nonlinear analysis of structures. The problems nonlinearity is assumed for the geometry, for the material, and for both geometry and material. In the first example, the BESO is applied to maximize the stiffness of a cantilever beam with a time dependent loading. Next, the BESO is applied to optimize the stiffness of a plate with the material nonlinearity. The results show that the nonlinear analysis leads to a much stiffer design. In the third example, a cantilever beam with both material and geometry nonlinearity is considered. The beam is also to be optimized for stiffness. The optimized shapes are compared for linear and nonlinear analysis against the SIMP.
Furthermore, effectiveness of the ESO is proved by applying them to some shape optimization problems. The aim is to find the best fillet and notch shape so that it possesses a lower stress concentration factor. Design boundary has been set with some control points and optimization process is only applied to these points. First a square plate with a circular hole at its center is optimized for minimizing the stress concentration. The obtained results for linear and nonlinear analysis using ESO are compared with the results obtained using the biological growth method. Then, a square plate with a rhombus hole is optimized for stress concentration. It is concluded that using ESO, the maximum stress concentration around the boundary of the hole can be significantly decreased with linear analysis and the ESO is a powerful alternative for the biological growth method. The ESO method is finally used for shape optimization of geometrically different fillet for minimization the stress concentration. The material is assumed nonlinear while there is geometrical nonlinearity for loading. The results are compared with that of Wu who has used the fully stressed design criterion. The results show that using the ESO, the stress concentration factor is significantly redused and in this case it is reduced by 22%. In this way, the optimum shapes have completely uniform stress in the boundary of the fillet. The results show that the ESO has a superior capability for shape optimization of fillets of nonlinear structures and in this case the maximum stress is reduced by 7.7%.
Furthermore, effectiveness of the ESO is proved by applying them to some shape optimization problems. The aim is to find the best fillet and notch shape so that it possesses a lower stress concentration factor. Design boundary has been set with some control points and optimization process is only applied to these points. First a square plate with a circular hole at its center is optimized for minimizing the stress concentration. The obtained results for linear and nonlinear analysis using ESO are compared with the results obtained using the biological growth method. Then, a square plate with a rhombus hole is optimized for stress concentration. It is concluded that using ESO, the maximum stress concentration around the boundary of the hole can be significantly decreased with linear analysis and the ESO is a powerful alternative for the biological growth method. The ESO method is finally used for shape optimization of geometrically different fillet for minimization the stress concentration. The material is assumed nonlinear while there is geometrical nonlinearity for loading. The results are compared with that of Wu who has used the fully stressed design criterion. The results show that using the ESO, the stress concentration factor is significantly redused and in this case it is reduced by 22%. In this way, the optimum shapes have completely uniform stress in the boundary of the fillet. The results show that the ESO has a superior capability for shape optimization of fillets of nonlinear structures and in this case the maximum stress is reduced by 7.7%.

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The composite conical lattice structure in this paper made of helical ribs and thin outer skin. In this research, free vibrations of these structures with and without outer skin were investigated. A smeared method is employed to obtain the coefficients of stiffness of conical shell. Theoretical formulations are based on sander thin theory of shell. For verification of the analytically obtained results, using ANSYS software the 3D finite element model of composite lattice conical shell is built and analyzed. To verify the accuracy of this method, comparison of the results are made with numerical results from ANSYS Software and show a good agreement between them. Also, some special cases as influences of the semi vertex angle and thickness of the outer skin on the natural frequencies of the conical shell are studied. It is concluded that, the increasing of the semi vertex angle leads to increasing the natural frequencies of conical shell. Moreover for outer shell thicknesses greater than a specific value, the increment of the thickness of the outer skin leads to decreasing the natural frequencies. Because of few researchers investigated merely vibrational behavior of the composite lattice cylindrical shell, the obtained results of this paper have novelty and can be used for further and future researches.

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Precise Prismatic actuators are one of the most important actuators used in robotic industry and the main base of parallel robots as 6PUS Stewart-Gough robot. Because of bearing large axial forces by this actuators, elastic deformations are inevitable in the main parts of them. This results in elongation and compression of the piston and ball screw, which deteriorates the dynamic linear positioning accuracy of these actuators. The existence of accurate dynamic equations can seriously help to control these errors. Most of the dynamic models which have been used for these actuators based on lumped parameter approach have one DOF for rigid and two or three DOF for flexible state and the stiffness of parts are considered as constant. In this study, the direct dynamic equations of a rotating prismatic actuator which has three DOF in axial direction and ball screw drive system, are proposed using the Lagrange method. In addition to the flexibility of the moving piston, the ball screw is considered with variable stiffness. The important point of this study is the variability of ball screw stiffness. As the nut moves along the shaft, the active length and stiffness of the shaft change; which is very similar to the reality. In addition to the analytical method, the actuator is modeled in the finite element software, ABAQUS and the results of the analytical method and the finite element method are compared.

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Precast concrete structures have been widely used since the last century. Fast production, quick erection, higher quality, economical aspects, lower labor costs etc. are of noticeable advantages of such structures compared to that of in-situ concrete structures. Considering frame structures, connections play a vital rule in local and global behavior of precast concrete structures. Catastrophic failures and losses are incurred globally due to failure in connection regions, so connections are considered to be the weak spots in precast concrete structures. Consequently, a great amount of attention and care is required in designing and forming connections, especially in precast concrete structures. In addition, compared to monolithic structures, it is relatively more difficult and more time consuming to achieve rigidity in connections due to the nature of precasting. Plus, difficulties arising from construction and structural details will neutralize inherent characteristics of precasting. Thus, obtaining a connection with details that are simple enough to be constructed easily on site, which, of course, satisfies demanding mechanical characteristic, can be of great importance. In this paper, two new types of beam to column connections are proposed. These connections are designed, modeled and analyzed numerically using nonlinear finite element software, ABAQUS. Main goal of the research was to achieve constructible and easily erectable connection detail which can provide satisfactory lateral strength, stiffness, ductility and energy absorption.
Embedded steel corbels are used as members which transmit tension due to imposed positive moment and shear in negative moment in addition to their role as seating in initial stages of construction. Continuity is provided with bolting or welding of bottom bars to the corbel and then connection area is filled completely with expansive grout. Eccentricity of transmitted forces is a decisive factor especially in dynamic loadings, thus, in design, it is minimized by adjusting bar and corbel size and position and welding locations, size and shapes. Top bars are passed through holes, previously cast into the precast concrete column and are embedded in in-situ concrete of slabs. T shaped assemblies of the connections are modeled and laterally loaded until ultimate concrete strain is reached. In terms of strength, both connections were capable of achieving 95 percent of equivalent monolithic assembly. Considering lateral stiffness, proposed connections were able to provide initial stiffness of more than 80 percent of equivalent monolithic connection. Precast connections were 20 to 30 percent less ductile than their monolithic counterpart. Noticing relative geometric complexity and difference in force transmission mechanisms of connections, lower ductile behavior of connections is justifiable. Effects of axial column load are studied on response of the assemblies. Compressive axial load relatively improves lateral stiffness and energy absorption of the connections. By imposing axial tension on column, lateral stiffness and strength is significantly reduced.
Comparing before mentioned mechanical characteristics of proposed connections with their equivalent monolithic assembly, satisfactory response under lateral monotonic loading is observed. Based upon results derived from this study, proposed connections may be used as semi rigid beam to column connections in precast concrete frames, instead of fully rigid connections.