Sharif Digital Repository

Determination of nonlinear dynamic behavior of structures has always been one of the main goals of both structural and earthquake engineers. One of the newest methods for analyzing seismic behavior of structures is Modal Incremental Dynamic Analysis (MIDA). In fact, this method is an alternative to the Incremental Dynamic Analysis (IDA), which is a difficult and time-consuming method. Despite the MIDA's approximate results, advantages such as adequate accuracy, high speed, and low cost make this method an efficient and appropriate approach. In all the previous studies, the proposed models have had a regularized plan; hence, all the analyses have been carried out on a frame. In this study,... 

Analysis of concrete shallow funicular shells of rectangular plan with simply supported boundary conditions under static loads is performed using the Ritz method. Double Fourier series with the unknown constant coefficients are assumed for the displacement components of the shell and their unknown coefficients are determined such that the potential energy of the shell becomes minimum. The solution is presented in a simple form and is suitable for practical applications. The responses of rectangular-plan concrete shallow funicular shells including deflections, strains, internal forces, internal moments and stresses could be easily determined using the proposed semi-analytical method. The Ritz... 

Analysis of concrete shallow funicular shells of rectangular plan with simply supported boundary conditions under static loads is performed using the Ritz method. Double Fourier series with the unknown constant coefficients are assumed for the displacement components of the shell and their unknown coefficients are determined such that the potential energy of the shell becomes minimum. The solution is presented in a simple form and is suitable for practical applications. The responses of rectangular-plan concrete shallow funicular shells including deflections, strains, internal forces, internal moments and stresses could be easily determined using the proposed semi-analytical method. The Ritz... 

In this paper, an analytical method is presented in order to determine the static bending response of an axisymmetric thin circular/annular plate with different boundary conditions resting on a spatially inhomogeneous Winkler foundation. To this end, infinite power series expansion of the deflection function is exploited to transform the governing differential equation into a new solvable system of recurrence relations. Singular points of the governing equation are effectively treated by applying the Frobenius theorem in the solution, which in turn permits the use of more-general analytical functions to describe the variation of the foundation modulus along the radius of the plate. Moreover,... 

Determination of nonlinear dynamic behavior of structures has always been one of the main goals of both structural and earthquake engineers. One of the newest methods for analyzing seismic behavior of structures is Modal Incremental Dynamic Analysis (MIDA). In fact, this method is an alternative to the Incremental Dynamic Analysis (IDA), which is a difficult and time-consuming method. Despite the MIDA's approximate results, advantages such as adequate accuracy, high speed, and low cost make this method an efficient and appropriate approach. In all the previous studies, the proposed models have had a regularized plan; hence, all the analyses have been carried out on a frame. In this study,... 

Recently, a novel structural system, which is defined as a damped outrigger system, has been proposed to control the dynamic vibration of tall buildings. This paper examines the seismic performance of tall buildings involving multiple outriggers equipped with viscous dampers. In this respect, a dual structural system (braced moment frame) is selected as a bare structure. In addition, the number and position of outriggers are assumed to be variable along the structure height. Nonlinear Response History Analysis (RHA) is performed to evaluate the efficiency of the damped-outrigger system under eight-scaled ground motions. The results are presented based on the average of all ground motions.... 

This paper describes a three-dimensional (3D) finite-element (FE) model developed to assess the seismic behaviour of a novel prefabricated beam-to-beam connection termed a double-bolted flush end-plate beam (DBFEB) splice connection under cyclic loading. The seismic response was analysed and evaluated in terms of the hysteretic behaviour, rigidity, resistance degradation, ductility, energy dissipation capacity and equivalent damping coefficient. It is shown that the required performance can be achieved by controlling the end-plate thickness as well as the bolt grade and diameter; these parameters were therefore chosen as the key geometric variables investigated here for parametric study.... 

The influence of uplift on earthquake response of tall buildings via consideration the horizontal and vertical components of earthquake excitation with and without foundation uplift has been studied. A new finite element modeling method called direct modeling approach are utilized in this study to evaluate the variation of foundation uplift, lateral displacement, base shear and members' forces in each cases. The earthquake response of the models mentioned above, assuming linear behavior was compared to the response in nonlinear behavior. These studies show the importance of uplift foundation on the seismic behavior of tall buildings. The most important results in this study is base shear... 

Most slab-on-girder steel bridges have been designed and constructed without seismic resistance consideration; as a result, their members, connections, and more commonly their substructure are not sized and detailed to provide the required ductile response needed during major earthquakes. A ductile seismic retrofit solution proposed in this investigation consist of converting of existing end diaphragms into ductile end diaphragms and replacing the end cross-frames and the lower lateral-braced panels adjacent to the supports by special ductile diaphragms. Consequently, this creates ductile fuses to protect the rest of the super- and substructure. This paper illustrates the typical seismic... 

Existing design procedures for steel frames have been modified during the last three decades to incorporate the semi-rigid behavior of the connections into the frame design advancement. Knowledge in initial rotational stiffness of a connection is important for the global elastic analysis of frame structures. This paper presents the results of several parametric analyses on the Initial Rotational Stiffness (IRS or Sini) of Bolted Flush End-plate Beam (BFEB) splice connections using Finite Element Modeling (FEM). The FEMs have taken into account material behavior, geometrical discontinuities and large displacements. The analyses have been calibrated to experimental results that are also... 

Concrete is a heterogeneous material with a wide variety of usage in structural design. Concrete under tension exhibits strain softening, i.e., a negative slope in the stress-deformation diagrams. Different softening curves have been proposed in the literature to interpret this phenomenon. In current research, a new softening curve for concrete has been proposed by using the newly introduced concept of fractal geometry. This new softening curve is denominated a 'Quasi-fractal' softening curve and consists of two parts, a linear portion at the beginning and an exponential portion in the rest of the curve. A comparison of a "Quasi-fractal" softening curve with a set of proposed experimental... 

In this article, a particular off-center bracing system is introduced. In this system, the tensile diagonal strut is not straight. When the load is applied, the original geometry changes and thus causes the system to harden. Based on this behavior, a step-by-step analytical method is developed. Using this method, a Geometrically Nonlinear Analysis Program (GNAP) is designed to analyze the elastic force-displacement relation. Extension of this program to dynamic analysis led to a Dynamic Nonlinear Analysis Program (DNAP). The object of this article is to show that such bracing systems will lead to less seismic force on such structures compared to classic concentric bracing systems. On the... 

This paper is concerned with the development of buckling-restrained knee bracing frames for seismic design and retrofit of steel frame structures. Analytical models based on the new nonlinear finite element modeling of the system for the moment and shear yielding mode were developed in a structure with buckling-restrained knee-braces. Parametric study was performed with new and practical parameters of the system describing the specification of the system in elastic and inelastic behavior; and the results are shown in form of the appropriate graphs and charts. This study makes an offer to a simple design technique for this type of structure with a bilinear approach, using a nonlinear finite... 

An approximate method is presented that can be used to determine the nonlinear behavior of a new structural bracing system called the 'Chevron Knee Bracing' (CKB). In this framing system, an especial form of diagonal brace connected to a knee element instead of a beam-column joint is investigated. The diagonal element provides lateral stiffness during a moderate earthquake. However, the knee element is designed to have three plastic joints or two yielded specimens in flexural and shear yielding mode, respectively, for dissipation of the energy caused by a strong earthquake. This article demonstrates the transformation of a complex problem into a new, practical set of design charts and... 

Many of heterogeneous structural materials, like concrete, have different behavior under tensile stresses in comparison to their behavior under compressive stresses. The aim of this paper is to interpret behavior of such materials subjected to tensile stresses, by using newly introduced concept of fractal geometry. In the first part of this paper, tensile behavior of granular composites has been studied by using fractal geometry. It is shown that the fractality of the cross section in this kind of composites can be used to interpret the size effect on tensile strength. In fact, this work is a modification with innovations on the previous studies on fractal based size effect. This hypothesis... 

The latest research studies on Steel Plate Shear Walls (SPSWs) suggest that the use of large-sized openings in infill plates calls for the use of heavy stiffeners or special measures for ensuring system stability. This study explores the effect of introduction of large unstiffened openings in SPSWs. A number of single story SPSWs with solid infill plates and their corresponding models with unstiffened openings are designed and analyzed numerically. In addition, this study provides a comparison of the experimental and numerical results obtained from the finite element models of SPSWs with openings. The results indicate the acceptable behavior of the specimens even at high levels of drift in... 

This paper investigates the influence of an opening in the infill steel plate on the behavior of steel trapezoidal corrugated infill panels. Two specimens of steel trapezoidal corrugated shear walls were constructed and tested under cyclic loading. One specimen had a single rectangular opening, while the other one had two rectangular openings. In addition, the percentage of opening in both specimens was 18%. The initial stiffness, ultimate strength, ductility ratio and energy dissipation capacity of the two tested specimens are compared to a specimen without opening. The experimental results indicate that the existence of an opening has the greatest effect on the initial stiffness of the... 

In this paper, a new analytical approach is proposed for free vibration and buckling analysis of a rectangular Mindlin plate resting on the Winkler–Pasternak foundation of varying stiffness. According to Mindlin theory, there are three independent governing differential equations. Thus, three Fourier series expansions along with auxiliary polynomial functions are employed to represent the plate's deflection and rotation angle functions. The process of making a set of equations is then completed satisfying the corresponding equilibrium equations and boundary conditions. The proposed method incorporates general elastic supports for all plate's edges, and subsequently can deal with all possible... 

This study deals with the geometrically non-linear vibration analysis of concrete shallow funicular shells of rectangular plan with four clamped edges under impulse loads. The shape of a concrete funicular shell is such that the shell is subjected to pure compression under its dead weight. Following the existing method presented for the linear vibration analysis, the geometrically non-linear vibration analysis is considered through the use of non-linear shallow shells theory. Each displacement component is expanded in a double Fourier series and the kinetic energy, the elastic strain energy and the virtual work done by external forces are calculated in terms of the displacement components.... 

A special type of shell structure - a concrete shallow funicular shell of circular plan - is considered in this paper. Funicular shells carry their dead weight only by in-plane compression forces. Numerical analysis of funicular shells was performed using the non-linear finite-element method, considering both geometric and material non-linearities. A circular-plan concrete funicular shell unit was also constructed and its ultimate central concentrated load is determined. The ultimate load of the shell unit predicted by the numerical model was very close to the experimentally determined ultimate load, thus confirming the validity of the numerical model. The numerical results revealed the...