Year:2005 | Volume:39 | Issue:3 (91)|Papers Count:15

In this paper, first, the von Karman nonlinear theory of plate is used to present the differential equations of large deformation of thin plates in terms of the in-plane forces and out-of-plane displacement and moment sum. Then, the Galerkin integrated formulation of problem is presented. The independent variable of this equation includes the displacement u, v, w and the moment sum M. As a basic step of the Galerkin method all variables are independent in terms of the basic functions which are given in area coordinate system and the generalized coordinates. The integrated equations for each problem are solved by Newton-Raphson to drive the generalized coordinates. Several examples are solved including isocel and right-angled triangular plates under uniform distributed load and compared with results obtained by other researchers.

Frequent earthquakes with different magnitude yearly occur in the country especially in areas with high seism city causing serious casualty and damage. Among those areas, Qazvin has experienced strong earthquakes like 1962 Boin -Zahra and 1990 Manjil in its history. The objective of this research is to seismically evaluate existing buildings in Qazvin, such that while studying the current situation and seismic evaluation of these building structures, general guidelines are investigated to improve existing conditions. In this paper with a short reference to geo-seismology and seismically, after reviewing different methods for seismic evaluation of buildings, applying relevant modification, aria qualitative method was selected due to building systems in the area and field visits information. Then using the modified Aria method, seismic evaluation of visited building was discussed. Based on the obtained conclusions, most unreinforced masonry buildings particularly in No.1 municipality area and some steel & concrete structures are seriously vulnerable to damage during moderate and strong earthquakes, and thus need special attention for seismic retrofit.

Khorjini (saddle) frame is one of typical structural systems in Iran and needs seismic retrofit based on previous research reports. In this paper, a sort of hysteresis dampers called buckling restrained braces (BRB) is considered and its behavior and design procedure are investigated to study its effect on seismic performance of steel frames. Finally, a typical khorjini (saddle) frame has been seismically retrofitted and was analytically subjected to the time-histories of the Naghan, Tabas and Northridge earthquakes. Numerical results showed that BRBs have high capability in seismic design of new structures and seismic retrofit of existing structures as well.

Some analytical investigations are done on the arrangement and orientation of fibers in steel fiber reinforced concrete (SFRC) specimens incorporating various volume fractions of fibers. The distribution functions of fiber location variables are investigated to produce an analytic model for the prediction of the mechanical properties of SFRC. Considering the effect of surrounding boundaries and distribution function, theoretical expressions are derived for the number of fibers per unit cross sectional area the orientation factor of fibers in SFRC. Finally a comparison between empirical and analytical results are made to confirm the analytical results

In recent years, some authors have investigated the problem of seismic bearing capacity by limit state procedures. In these studies, the inertia forces developed within the soil volume which were ignored in previous studies were considered.In this paper, the effect of the soil mass underneath a footing on its bearing capacity is studied using upper bound limit analysis method and considering rigid blocks. It is shown that the consideration of inertia forces within the soil is responsible for a decrease in the bearing capacity and its effects decreases as the internal friction of the soil increases.

In this paper an exact solution of dynamic analysis of dam-reservoir interaction in time-domain is considered. The radiation condition of the infinite reservoir and flexibility of dam structure are included in formulation so the interaction problem is solved in closed-form. Problem is proposed by simplifying dam as a tapered beam. Dam thickness is assumed variable. The proposed method is used for analyzing the interactive behavior of dam-reservoir with different geometric properties, which is demonstrated by numerical examples when the system is subjected to Elcentro and Taft earthquakes. Dam displacement and hydrodynamic pressure is compared with empty and full reservoirs with those of various researchers and EAGD-84 (Fenves & Chopra) program and good performance of the method is demonstrated

Wavelet Transform is a new tool for signal analysis which can perform a simultaneous signal time and frequency representations. Under Multi Resolution Analysis (MRA), one can quickly determine details for signals and their properties using Fast Wavelet Transform (FWT) Algorithms.In this paper, for a better physical understanding of a signal and its basic algorithms, Multi Resolution Analysis together with wavelet transforms in a form of Digital Signal Processing (DSP) will be discussed. For a Seismic Signal Processing (SSP), sets of Orthonormal Daubechies Wavelets (ODW) are suggested. When dealing with the application of wavelets in SSP, one may discuss about denoising from the signal and Data Compression existed in the signal, which is important in seismic signal data processing. Using these techniques, El-Centro and Nagan signals were remodeled with a 25% of total points, resulted in a satisfactory results with an acceptable error drift. Thus a total of 1559 and 2500 points for El Centro and Nagan seismic curves each, were reduced to 389 and 625 points respectively, with a very reasonable error drift, details of which are recorded in the paper. Finally, the future progress in signal processing, based on wavelet theory will be appointed

In the last few decades, steel plate shear walls have been introduced as primary lateral load resisting elements in several buildings around the world. The system consists of vertical steel infill plates, one story high and one bay wide connected to the surrounding beams and columns. Experimental testing was conducted on various specimens, under cyclic quasi-static loading. Good energy dissipation and ductility capacities were achieved. In this concept, the post-buckling strength of the none-stiffened thin steel plate shear wall is relied upon for most of the frame shear resistance, similar to the slender web of plate girder. In this paper, a nonlinear finite element model that includes both geometric and material nonlinearity for steel plate shear walls was developed. Another analytical method is presented that is useful for the prediction of cyclic monotonic behavior. The models gave good prediction of the specimen behavior. In order to understanding the behavior of steel plate shear walls, nonlinear time-history analysis and parametric study was done.

The application of composite cylindrical shell is greatly increased in aerospace and marine structures. The present paper investigates the stability analysis of ring-stiffened cylinders. Incorporating pre-buckling deformation, buckling load is calculated through geometrically non-linear analysis. The cinematic relations of shell, based on Sanders non-linear theory by including first order shear deformation (FOSD) are manipulated. The appropriate traditional Fourier series functions are selected to express the corresponding displacements and rotations of cylindrical shell and ring stiffeners. The shell is subjected to both axial and external pressure. The study is based on Ritz method and the load-deflection and load-interaction forces curves are obtained by mixed Newton-Raphson iteration and arc-length method. The results are presented in terms of buckling and post-buckling response for different shell and stiffeners lay-ups. Also the effect of stiffened shell stacking sequences on interaction forces is investigated

In this paper, a numerical model of reinforced concrete structure based on a combined finite discrete element method has been proposed. Using this approach, it is possible to model various phenomena such as projectile impact and penetration, progressive cracking, strain softening of concrete and contact features of post cracking. Rankin failure criterion has been used for concrete. The behavior of cracked parts is governed by principles of the discrete element method and contact mechanics. The discrete element method idealizes the whole medium into an assemblage of individual bodies, which in addition to their own deformable response, interact with each other (through a contact type interaction) to perform the same response as the medium. Finally, several concrete and reinforced concrete structures have been simulated and compared with experimental results.

A numerical method is developed for 3D delamination modeling in composites based on fundamentals of computational plasticity, computational contact mechanics and fracture mechanics. Composite plies are modeled with 3D solid and pentahedral discrete/finite elements and the interlaminar behavior of plies is considered using combination of an anisotropic bilinear strain-softening plasticity model and the Penalty method. Numerical examples are investigated to assess the ability and performance of the method.

To assess seismic vulnerability of existing reinforced concrete buildings in Iran, cyclic and monotonic load test on six beams was carried out. Three of the specimens represented semi-engineered buildings and three of them represented well designed buildings that have been designed according to the seismic provisions of ACI318-99. Seismic provisions and standard detailing requirements are not met adequately in the semi-engineered buildings. The semi-engineered and standard specimens had similar span length and identical seismic demand in the buildings, but they differ in dimensions of the section, amount and arrangement of both longitudinal and lateral reinforcement, and concrete strength. All the specimens were half-scale and had 1250 mm length and 150 to 200 mm width. The aim was to determine seismic characteristics in terms of energy absorption capacity, ductility, and vulnerability of the beams under strong cyclic and monotonic motion. Based on the test results, parametric idealized curves for cyclic response and backbone curve of both standard and semi-engineered beams were established. The idealized curves could be used for numerical simulation of the existing buildings under seismic load. During the tests, the semi-engineered specimens showed much less strength, ductility, and energy dissipation capacity in comparison to the standard ones. The reduction in strength, ductility, and energy capacity was in average about 50, 40, and 70%, respectively. The standard specimens, that were detailed according to the intermediate ductility provisions and that is commonly applied in Iran, demonstrated relatively good cyclic capacity, but the provision of using at least 1/3rd of the main longitudinal reinforcement in the opposite side of the section seems insufficient and it is recommended to be increased to 1/2nd

Soil nailing is an in-situ soil reinforcement technique which has been used during the past two decades to retain excavations or stabilize slopes. In Europe, the French and German methods and in United States, the Davis method, are the design methods that have been most commonly used. These methods only control the global stability of the wall and pull out of the nails. In this paper a design approach which provides a rational estimate of maximum tension and deflection of nails is introduced. To evaluate these forces and deflections a user friendly computer code (soiln) has been written. Examples of applications of this program are provided and the results are compared with those obtained from other methods.