Pounding of adjacent building have been seen in the moderate and strong earthquakes. There are different methods to model the impact. One of these methods is CONTACT ELEMENTs. CONTACT ELEMENTs include LINEAR and nonLINEAR elastic and VISCOELASTIC and Hertz-damp ELEMENTs. Investigators have generally studied on CONTACT ELEMENTs in elastic structures. In this study, the ability of different CONTACT modelings is added to Opensees software. Validation of modeling is achieved by comparing the numerical result of this study with other investigations' numerical studies. Simulations between analytical modeling and experimental studies show that to conquer displacement, results of different CONTACT ELEMENTs are the same, but velocity and CONTACT force results of ELEMENTs with and without damping have more accuracy. Finally these ELEMENTs are used to model the CONTACT of 5-story building under 6 records, in two left to right and right to left states. As regards, Hertz-damp has the least uncertainty of modeling; therefore results of other ELEMENTs are compared with this ELEMENT. Results generally show that accuracy of nonLINEAR ELEMENTs is more than LINEAR ELEMENTs. This is more obvious in the maximum CONTACT forces.

The tribological aspects of CONTACT systems are greatly affected by the friction and CONTACT pressure distribution throughout the surface of the CONTACT interface. Generally the CONTACT of deformable bodies is a nonLINEAR problem and for the VISCOELASTIC bodies it has a time-dependent response, since their viscous characteristics depends on time. The introduction of friction with its irreversible characteristic in CONTACT surface makes the CONTACT problem more difficult. The objective of this study is to develop a general augmented Lagrangian finite ELEMENT formulation associated with an incremental adaptive procedure which established for analysis of frictional CONTACT problems in VISCOELASTIC systems. The CONTACT behavior has been studied through an improved augmented Lagrangian approach. A generalized Maxwell model has been used to model the VISCOELASTIC constitutive equations in which bulk and shear relaxation functions are represented by the sum of a series of decaying exponential functions of time. Based on the principle of virtual work, an effective finite ELEMENT formulation associated with an incremental relaxation procedure has been developed. As an application of formulation, the numerical example has been presented to evaluate the numerical approach.

The objective of this study is to develop a general finite ELEMENT formulation associated with an incremental adaptive procedure established for the calculation of CONTACT pressure distributions in VISCOELASTIC structures. A generalized Maxwell model has been used to model the VISCOELASTIC constitutive equations in which bulk and shear relaxation functions are represented by sum of a series of decaying exponential functions of time. Based on the principle of virtual work, an effective finite ELEMENT formulation, associated with an incremental relaxation procedure, has been developed. The VISCOELASTIC CONTACT behavior has been studied through an improved augmented Lagrangian approach, based on kinematical conditions of CONTACT bodies. The proper convergence caused by the numerical examples with those obtained from analytical results shows the applicability of presented finite ELEMENT formulation.

In the present paper, dynamic behavior of a multilayer composite plate with VISCOELASTIC structural damping is investigated against a low-velocity impact by a spherical indenter. Hertz CONTACT law is refined to include effect of the lower layers on the stiffness of the CONTACT region and used in a non-LINEAR form. Voltra hierarchical integral is employed for modeling the VISCOELASTIC material and the layerwise theory and non-LINEAR strain-displacement relations are used to model the plate more accurately. To solve the governing integro-differential equations, a combination of the finite ELEMENT method, trapezoidal integration method for the Volterra integrals, and the Newmark numerical time integration method is used. In the results section, effects of the various VISCOELASTICity parameters and the indenter velocity on the time histories of the CONTACT force, indentation, and lateral deflection of the plate are investigated. Results show that due to the damping nature of the VISCOELASTIC materials, the plate rigidity and CONTACT force increase whereas the maximum lateral deflection and the indentation decrease. Furthermore, higher CONTACT forces do not necessarily indicates higher indentations.

Four constitutive equations have been used to describe the behaviour of VISCOELASTIC fluids viz., (i) upper convected Maxwell, (ii) Oldroyd 4-constant, (iii) Bogue-White and (iv) Bird-Carreau. These were modified to improve their ability to predict the observed behaviour of VISCOELASTIC fluids in viscometric and oscillatory shear flows. The fluids used during the experimental work are four different concentrations of polyacrylamide (Separan AP 30) solutions, i.e. 0.6, 0.8, 1.0, and 1.2%, in glycerine / water mixtures. The experimental data are obtained under simple shear and small-amplitude oscillatory shear flow conditions. The viscosity data, obtained from steady shear experiments, and the dynamic viscosity and storage modulus obtained from oscillatory shear experiments have been used to determine the model parameters. The performance of the original and modified models have been studied by comparing their predictions of the viscosities, in steady, and the dynamic viscosities, in oscillatory shear flows. The average root mean square has been used as a criterion for the comparison. Finally, the results of the predictions made by the modified models to the first normal stress coefficients are given to see how they can predict a material function other than those used to determine the model parameters. This may justify the application of these modified models in complex flows such as free coating.

In recent times, earthquake-induced structural pounding has been intensively studied through the use of different impact force models. The numerical results obtained from the previous studies indicate that the LINEAR VISCOELASTIC model is relatively simple and accurate in modeling pounding-involved behavior of structures during earthquakes. The only shortcoming of the model is a negative value of the pounding force occurring just before separation, which has no physical explanation. The aim of the present paper is to verify the effectiveness of the modified LINEAR VISCOELASTIC model, in which the damping term is activated only during the approach period of collision, therefore overcoming this disadvantage. First, the analytical formula between the impact damping ratio and the coefficient of restitution is reassessed in order to satisfy the relation between the post-impact and the prior-impact relative velocities. Then, the performance of the model is checked in a number of comparative analyses, including numerical simulation of pounding-involved response, as well as comparison with the results of the impact experiment and shaking table experiments concerning pounding between two steel towers excited by harmonic waves. The final outcome of this study demonstrates that the results obtained through the modified LINEAR VISCOELASTIC model without the tension force are comparably similar to those found by using the LINEAR VISCOELASTIC model.

A three-dimensional micromechanical finite ELEMENT model is developed to study the VISCOELASTIC behavior of the silica nanoparticle/polyimide nanocomposites. The representative volume ELEMENT (RVE) of the model consists of three phases including silica nanoparticle, polyimide matrix and interphase which surrounds the nanoparticle. The interphase region is created due to the interaction between the silica nanoparticle and the polymer matrix. The effects of different important parameters such as interphase material properties and thickness, silica nanoparticle volume fraction and geometry as well as type of nanoparticles distribution are investigated. It is found that the interphase significantly affects the VISCOELASTIC behavior of the nanocomposites. Also, the results reveal that with decreasing the nanoparticle diameter or increasing volume fraction, the creep strain of the nanocomposite reduces. Moreover, the creep strain of the nanocomposites decreases with the uniform distribution of the nanoparticles inside the polymer matrix. It is shown that for the elastic properties of the nanocomposites, while the predictions without interphase are far from the reality, the predicted mechanical properties with interphase demonstrate very good agreement with experimental data.