Sharif Digital Repository

In this paper, a new base isolation system, namely the sliding concave foundation (SCF), is introduced and the behaviour of the buildings using such a system is theoretically investigated. A building supported on the new system behaves like a compound pendulum during seismic excitation. The pendulum behaviour accompanied by the large radius of foundation curvature shifts the fundamental period of the system to a high value (e.g. more than 8 sec), in a frequency range where none of the previously recorded earthquakes had considerable energy. This results in a large decrease in the structural responses. Since small friction forces are essential on the contact surfaces, PTFE sheets can be used... 

This research explores the effectiveness of the use of stiff diaphragm walls next to a rocking foundation through numerical simulation. This improvement technique is used as a means to increase in subsoil peripheral confinement and reduce rocking-induced settlement. The numerical model was verified by the centrifuge test of rocking shallow foundations on clay under cyclic loading. A parametric study was conducted to explore the effect of three stiff wall shapes on the performance of a rocking system. The general conclusion of the parametric investigation is that the use of stiff diaphragm walls reduced the sinking-dominated settlement response of the rocking system. © 2019 Taylor & Francis... 

The response of a Timoshenko beam with uniform cross-section and infinite length supported by a generalized Pasternak-type viscoelastic foundation subjected to an arbitrary-distributed harmonic moving load is studied in this paper. Governing equations are solved using complex Fourier transformation in conjunction with the residue and convolution integral theorems. The solution is directed to compute the deflection, bending moment and shear force distribution along the beam length. A parametric study is carried out for an elliptical load distribution and influences of the load speed and frequency on the beam responses are investigated. © 2004 Elsevier Ltd. All rights reserved  

Aseismic base isolation is an effective method used to protect structures and their contents against earthquakes. An isolated structure may be designed to remain elastic throughout major ground motions as a result of the efficiency of the isolation systems. In this paper, the equations of motion of two-dimensional elastic structures supported on a new base isolation system called the Sliding Concave Foundation (SCF) are presented and a procedure for their solution is suggested. The responses of a number of structures subjected to different earthquake records are evaluated and the results are compared with those of the same structures supported on two other famous isolation systems and also a... 

Geotechnical design codes have been shifted from classical limit equilibrium analysis toward the performance-based procedures. In foundation design, settlement is the most representative parameter for its performance. Settlement of shallow foundations subjected to earthquake loading and its consequences is one of the most outstanding issues which should be considered in designing different structures. In this study, settlement of shallow footing on two-layered subsoil strata under earthquake loading is of concern. The numerical study presented in this research by means of a 3D dynamic fully coupled u-p analysis, addresses the effect of different parameters on shallow foundation settlement... 

Seismic analysis of complex structures such as concrete dams has been the subject of numerous studies. One of the challenges in seismic analysis of such systems is proper modelling of massed foundation. Since concrete dams’ foundations are usually layered, this makes the homogenous half-space assumption relatively unrealistic. In this paper, the effects of massed layered foundation on seismic response of concrete gravity dams in dam-reservoir-foundation systems are investigated. Seismic finite element analysis of the system carried out using domain reduction method. This approach is compared with another available method named, free-field column. First set of analysis considers the effect of... 

Seismic analysis of complex structures such as concrete dams has been the subject of numerous studies. One of the challenges in seismic analysis of such systems is proper modelling of massed foundation. Since concrete dams’ foundations are usually layered, this makes the homogenous half-space assumption relatively unrealistic. In this paper, the effects of massed layered foundation on seismic response of concrete gravity dams in dam-reservoir-foundation systems are investigated. Seismic finite element analysis of the system carried out using domain reduction method. This approach is compared with another available method named, free-field column. First set of analysis considers the effect of... 

In this paper, the whirling frequencies of simply supported and clamped rotating cylindrical shells surrounded by an elastic foundation are investigated. The Love's shell theory is used along with the Winkler foundation to obtain the governing equations of motion. An exact power series solution is obtained for arbitrary boundary conditions and the results are verified with the literature. Several case studies are performed, and the effect of spinning speed, foundation stiffness, and geometrical dimensions of the cylinder on the whirling frequencies are investigated  

This paper examines the effects of foundation uplift on the dynamic response of steel frames supported by shallow foundations. In order to achieve this goal, the dynamic responses of a number of two-dimensional concentrically braced steel frames with fixed base, flexible base preventing uplift, and flexible base allowing uplift, are compared. The steel frames are modeled by considering material nonlinearities and P-Delta effects, while the soil-foundation system is modeled through the Winkler foundation approach. The dynamic analyses are conducted using 15 far-fault ground-motions with various intensities and different response parameters are monitored. According to the achieved responses,... 

The purpose of this paper is to present efficient and accurate analytical expressions for large amplitude free vibration analysis of single and double tapered beams on elastic foundation. Geometric nonlinearity is considered using the condition of inextensibility of neutral axis. Moreover, the elastic foundation consists of a linear and cubic nonlinear parts together with a shearing layer. The nonlinear governing equation is solved by employing the variational iteration method (VIM). This study shows that the second-order approximation of the VIM leads to highly accurate solutions which are valid for a wide range of vibration amplitudes. The effects of different parameters on the nonlinear... 

The dynamic response of a Timoshenko beam with immovable ends resting on a nonlinear viscoelastic foundation and subjected to motion of a traveling mass moving with a constant velocity is studied. Primarily, the beam's nonlinear governing coupled PDEs of motion for the lateral and longitudinal displacements as well as the beam's cross-sectional rotation are derived using Hamilton's principle. On deriving these nonlinear coupled PDEs the stretching effect of the beam's neutral axis due to the beam's fixed end conditions in conjunction with the von-Karman strain-displacement relations is considered. To obtain the dynamic responses of the beam under the act of a moving mass, derived nonlinear... 

It is well-known that the behavior of soil-structure systems can be well described using a limited number of nondimensional parameters. This is the outcome of researches based on the premise that the foundation is bonded to the ground. Here, it is shown the concept can be extended to systems with foundation uplift. A set of non-dimensional parameters are introduced which controls the main features of uplifting systems. The effect of foundation uplift on response of soil-structure systems are investigated parametrically through time history analysis for a wide range of systems subjected to ground motions recorded on different soil types. In particular, the effects of uplift on displacement... 

Recent research works demonstrated that the interaction between the loads and the carrying structure's boundary which is related to the inertia of the load is an influential factor on the dynamic response of the structure. Although effects of the inertia in moving loads were considered in many works, very few papers can be found on the inertial effects of the stationary loads on structures. In this paper, an elastodynamic formulation was employed to investigate the dynamic response of a homogeneous isotropic elastic half-space under an inertial strip foundation subjected to a time-harmonic force. Fourier integral transformation was used to solve the system of Poisson-type partial... 

In this paper, nonlinear dynamic analysis of concrete gravity dams was studied. To investigate the effect of dam-reservoir-foundation interaction, a two-dimensional approach was used including the finite element method, and smeared crack approach. The dam-reservoir interaction is solved by staggered solution procedure while the Sharan boundary condition is applied at the reservoir's far-end truncated boundary. The foundation is defined as a part of the structure and some different boundary conditions such as Lysmer, Boulder and damper boundary conditions are applied at its truncated boundaries. Results show that when the nonlinear analysis includes the dam - foundation interaction and the... 

Investigation on the behavior of dams against the seismic loads is a key factor for safety requirement. One of the mostimportant problems in evaluation of seismic behavior of concrete gravity dams is dam-reservoir-foundation interaction. In this paper, we study the effect of dam-reservoir-foundation interaction on nonlinear behavior of concrete gravity dams, a two-dimensional approach was used including the finite element method and smeared crack approach. Effective parameters in the models are physical properties of concrete such as modulus of elasticity, tensile strength and specific fracture energy. Their importance in the nonlinear analysis was investigated in a parametric study.... 

In the present study, free vibrations of single walled carbon nanotubes (SWCNT) on an elastic foundation is investigated by nonlocal theory of elasticity with both beam and shell models. The nonlocal boundary conditions are derived explicitly and effectiveness of nonlocal parameter appearing in nonlocal boundary conditions is studied. Also it is demonstrated that the beam model is comparatively incapable of capturing size effects while shell model captures size effects more precisely. Moreover, the effects of some parameters such as mechanical properties, foundation stiffness, length and radius ratios on the natural frequencies are studied and some conclusions are drawn  

It is first shown that the Dirac's equation in a relativistic frame could be modified to allow discrete time, in agreement to a recently published upper bound. Next, an exact self-adjoint 4 × 4 relativistic time operator for spin-1/2 particles is found and the time eigenstates for the non-relativistic case are obtained and discussed. Results confirm the quantum mechanical speculation that particles can indeed occupy negative energy levels with vanishingly small but non-zero probablity, contrary to the general expectation from classical physics. Hence, Wolfgang Pauli's objection regarding the existence of a self-adjoint time operator is fully resolved. It is shown that using the time... 

In performance-based geotechnical earthquake engineering, the required degree and spatial extent of ground densification for mitigation of liquefaction beneath a structure should be determined based on the acceptable levels of performance of foundation. Currently, there is no solution for evaluation of the amount of settlement and tilt of footings constructed on a densified ground which is surrounded by a liquefiable soil. This implies the need for numerical procedures for simulation of seismic behavior of shallow foundations supported on both liquefiable and densified subsoil. In this paper, the dynamic response of shallow foundations on a densified ground is studied using a 3D fully... 

The dynamics of nonlinear thin plates under influence of relatively heavy moving masses is considered. By expansion of the solution as a series of mode functions, the governing equations of motion are reduced to an ordinary differential equation for time development of vibration amplitude, which is Duffing's oscillator with time varying coefficients. Through the application of Banach's fixed-point theorem, the periodic solutions are predicted. The method presented in this paper is general so that the response of plate to moving force systems can also be considered. © 2002 Published by Elsevier Science Ltd  

An exact solution is established pertaining to the problem of undamped free vibration of a thin circular plate resting on a Winkler foundation with variable subgrade modulus. The solution is performed by applying the infinite power series method. Moreover, the solution procedure is demonstrated through an illustrative example, wherein the general frequency equation is derived for two different boundary conditions. The correctness of the solution is also verified using results available in the literature. Finally, it is shown that the proposed method of solution is directly applicable to the more-general problem of circular plates on a variable-modulus Pasternak-type foundation