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Effective Stiffness for Modeling Reinforced Concrete Structures ضرایب ترک خوردگی المان های مختلف سازه ای مقایسه بین آیین نامه های مختلف منبع C-StrucAnalysis-Wong-Jan17-1_EffectiveStiffnessModeling.pdf

EFFECTIVE STIFFNESS MODEL FOR REINFORCED CONCRETE SLABS By Maria Anna Polakl ABSTRACT: A simple procedure for calculating deflections of reinforced concrete two-way slabs is presented in this paper. The material model for reinforced concrete based on the effective stiffness approach has been implemented in a finite-element program incorporating Mindlin-plate-bending elements. Uncracked concrete is treated as an isotropic linear elastic material, and after cracking, the concrete is considered to be an orthotropic material. The reduced stiffness coefficients after cracking are calculated from the effective moments of inertia in the x- and y-directions. These effective moments of inertia are determined using the formula proposed by Branson (1963). The influence of both bending and torsional moments is included in the formulation. The proposed model has been verified by comparisons with results from tests on slabs with various loading and boundary conditions. A study has also been undertaken to check the sensitivity of the proposed formulation when applied to the analysis of slabs with different reinforcement ratios, boundary conditions, and reinforcement orientations. polak1996.pdf

Comparison of plasticity and stiffness of steel shear walls with composite steel plate shear wall Leila Shahryari; Mahdi Esfandiari The steel shear wall and composite steel plate shear wall is introduced in recent three decade and is considered and is spread rapidly. Composite steel plate shear wall which is made of a layer of thin steel sheet with coating of reinforced concrete in one or both sides of steel palate is considered a third generation of resistance shear walls against lateral loads that in addition to increasing the strength, ductility and energy absorption, it is very economical and affordable and it is used in constructing high buildings, retrofitting buildings and tanks. In this paper we have tried to examine the seismic behavior of steel and composite shear walls. For this purpose several models of steel shear and composite walls from one to five stories were constructed and analyzed by Abaqus software. The result show that composite steel plate shear walls has more ability to absorb energy, spread produced stress to different parts of the steel plate and ductile than steel shear walls. The curve hysteresis loop of composite steel palate shear walls is more stable and sustainable than steel shear wall. With increasing the number of stories, the initial strength and stiffness is decreased due to increase in lateral shift but the amount of absorbing energy and ductility is increased. The force tolerance in composite steel plate shear wall models is increased in comparison with steel shear walls منبع دانلود JSEG481443558600.pdf

The Importance of Determining Damage Levels of the Bridges in Non-Linear Dynamic Analysis Original Article, C30 Karimi Moridani K, Khodayari R, Asadpour M. Journal. Civil Eng. Urban. 3(4):191-196. 2013 ABSTRACT:During past earthquakes, different modes of damage were observed in bridges; consequently in seismic evaluation of these structures, various Indexes were used to determine vulnerability of the structures against earthquake vibrations. In this paper, damage indexes of structural elements of bridge are introduced and suggested definitions for structure damage state are stated. Then, a three span bridge is analyzed using OpenSees non-linear analysis software, considering three-dimensional model under earthquake load and non-linear behavior. After calculating necessary outcomes of the elements and nodes, damage indexes of damage at the foundations and columns level were measured. The model is able to calculate responses and damage indexes of supports and joints. Using this model, damage level of bridge structure is determined based on tables, which determine necessity of retrofitting. Based on the result, decisions made based on each criterion are compared. The results show that exact specification of damage indexes for the estimation of the vulnerability of structures (bridges here) is very important. Keywords: OpenSees Model, Bridge, Damage levels, Reinforcement, Stiffness منبع: [Hidden Content] دانلود: [Hidden Content].,30-191-196.pdf J. Civil Eng. Urban.,30-191-196.pdf

An evaluation of impressionableness structural systems under the condition of foundation and bed resistance Original Article, A7 Zare HR, Dehghani M. Journal. Civil Eng. Urban. 2(1): 49-52. 2011. ABSTRACT: The analysis of the structures under the influence of the earthquake load is usually done independent of the conditions and the soil variable under them. In other words, the bed of the structure location is supposed to be rigid. In these conditions seismic excitation in the bed of the structure is conducted in the form of a displacement with acceleration with time (or equivalent force). What happens in reality is that the structure is situated on the soil environment as a flexible bed, and from the view point of dimension as semi-infinite and earthquake vibrations from its source reach the foundation of the structure by passing from this environment which results in soil-structure interaction. The flexibility of the structure foundation and the emission of system energy by the waves in the infinite environment of soil (radiation depreciation) are two important results of soil-structure interaction phenomenon. One of the methods of considering the above-mentioned phenomenon in the analysis of the structure-supposing the elastic linear behavior of the soil environment-is by using SSI equivalents by which we have analyzed frame structures and shear wall frame structures under the earthquake load by considering SSI. By extraction of base shear amounts and displacement of the head of the structures under the influence of different earthquakes quantitative and different results have been obtained in a way that mentioned amounts strong dependence on the stiffness of the structure, stiffness of the soil, the kind of the earthquake ,etc. For this reason, the amount of the base shear and displacement in shear wall frame structures is more different from frame structure system in a way that these variations have twofold decrease or increase in a shear wall frame structure comparison with a frame structure system. This matter and the subsequent results reveal the necessity of paying attention to SSI in analysis and design of important structures from the view point of safety factor economic issues. Keywords: Soil–structure interaction, frame structure, shear wall, stiffness منبع: [Hidden Content] دانلود: [Hidden Content],%20A7,.pdf JCEU, A7,.pdf

8. مهرداد حجازی, پرهام معمارزاده, علی محمدیان, , "Study of the Effect of the Length and Position of Knee Elements on Structural Behavior of Knee-Braced Steel Frames and Comparison with X-Braced Frames", 4th International Conference on Seismic Retrofitting, تبريز, 2012 Abstract In optimum design of steel frames that are resistant to lateral loads it is necessary to provide stiffness and ductility, along with financial considerations. Lateral resistant systems like bending frames or concentric braced frames normally cannot provide liable stiffness and ductility. To solve this problem, it can be helpful to use knee bracing. In a knee bracing system a diagonal member is connected to a knee element that works like a plastic fuse. In this situation, ductility is provided through yielding of the knee element, and stiffness is supplied by a diagonal member. In this study, a number of three-span steel frames with different number of floors have been analysed using nonlinear dynamic method in order to investigate the effect of the length and position of the knee element on the stiffness and ductility of the frames. Obtained results have been compared with those of x-braced steel frames. Keywords : knee bracing, nonlinear dynamic, ductility, stiffness. منبع: [Hidden Content] دانلود: [Hidden Content] PaperC_8873.pdf