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۱NONLINEAR FINITE ELEMENT ANALYSIS OF FLANGED RC SHEAR WALLS BASED ON MULTI–LAYER SHELL ELEMENT
نویسنده(ها): ، ،
اطلاعات انتشار: سومین کنفرانس بین المللی بتن و توسعه، سال
تعداد صفحات: ۱۰
Nonlinear simulations for structures under earthquakes have been widely focused on in recent years. However, precise modeling for the nonlinear behavior of reinforced concrete shear walls, which are the major lateral–force–resistant structural member in high–rise R.C. buildings, still has many items to be investigated. In this paper, based on the principles of composite material mechanics, a multi–layer shell element model is proposed to simulate the in–plane bending and the coupled in–plane bending–shear nonlinear behaviors of RC shear wall. The multi–layer shell element is made up of many layers with different layers of thickness, and different material models (concrete or rebar) are assigned to various layers so that the structural performance of the shear wall can be directly connected with the material constitutive law. Besides the traditional elasto–plasticfracture constitutive model for concrete, which is efficient but does not give satisfying performance for concrete under complicated stress condition, a novel concrete constitutive model, referred as microplane model, which is originally proposed by Bazant et al., is developed to provide a better simulation for concrete in shear wall under complicated stress conditions and stress histories. Three flanged shear walls under static push–over load were analyzed with the proposed
shear wall model for demonstration. The simulation results show that the multilayer shell elements can correctly simulate the in–plane bending failure for tall flanged walls and the coupled in–plane bending–shear failure for short flanged walls. In addition, with microplane concrete constitutive law, the behavior and the damage accumulation of flanged shear wall can be appropriately modeled, which is
very important for the performance–based design of structures under disaster loads.<\div>

۲SEISMIC BEHAVIOR OF SHORT COLUMNS IN RC STRUCTURESq
نویسنده(ها): ،
اطلاعات انتشار: سومین کنفرانس بین المللی بتن و توسعه، سال
تعداد صفحات: ۱۳
Civil engineering structures as well as office or apartment building are affected by earthquakes. A common cause of failure seems to be shear stress. The earthquake forces developed at different floor levels in a building need to be brought down along the height to the ground by the shortest path. Short column phenomenan is one of the effective causes of buildings failure in past earthquakes. This destructive phenomenon is due to column heighf difference in a story level that is predominantly because of localing building on sloppy ground. These buildings have unequal height columns along the slope, which causes ill effects like twisting and damage in shorter columns. In some buildings, few or no walls are provided at the first story (pilot). In the structures with difference in story level, major
problems is due to discontinuity of floor diaphragm that causes significant changes in period, stiffness distribution of earthquake force and seismic loading of structures . In this research, at first, seismic behavior of short column phenomenon is determined, then, nonlinear behavior of reinforced concrete short columns in 4, 8 and 10 story structures with story level difference is investigated. Short columns
and mentioned structures are analysed under the earthquake record of Elcentro with different peak ground acceleration with IDARC software which is nonlinear dynamic analysis program. In this investigation, the results of maximum response, base shear, global damage index and displacement time history and effect of short column in structural failure is evaluated.<\div>

۳NONLINEAR ANALYSIS OF DIFFERENT SHAPE OF FLANGE SHEAR WALLS
نویسنده(ها): ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۷
The reinforced concrete shear walls are effective elements against lateral loads. This lateral resisting system absorbs shear and also controls the displacement of structure. But past analyses show that structure behavior would improve if shear wall have been flanged. Five models in the form of T, U, H, Z and I shapes wall used in this study for investigation of nonlinear behavior of flanged shear walls. Walls had been modeled and meshed by using nonlinear finite element software. Analytical results show that shear absorption of T shape shear wall is more than other shapes. In this study, the lateral load in T shape shear wall is 10 percent more than that of Z shape. Also study of shear walls ductility show that I shape shear wall has been able to undergo horizontal displacement after yielding more than other models. This is equal to 7 percent more than U shape shear wall. The analytical results of shear wall also show when flange is in pressure, shear absorption is 5 percent more than flange under tension. Finally, the ultimate resistant of shear walls with web of connect in center of flange (T shape) could be increased up to 10 percent versus shear walls with web of connect in corner of flange (U shape).<\div>

۴PUSHOVER ANALYSIS OF STEEL MOMENT FRAME ACCOMPANIED WITH RC SHEAR WALL OR STEEL BRACING
نویسنده(ها): ، ، ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۱۰
In this paper, the nonlinear behavior of dual structural systems in forms of steel moment resisting frames accompanied with reinforced concrete shear walls and steel moment resisting frames accompanied with concentrically braced frames, have been studied. Some parameters such as ductility factor of structure (μ), over–strength factor (Rs) and response modification factor (R) for the mentioned structures have been under assessment. To achieve these objectives, the 10–story buildings containing such structural systems used to perform the pushover analyses having different load patterns. These analyses are displacement based pushovers and modal pushover. Analytical results show that the steel moment resisting frames accompanied with concentrically braced frames system have higher ductility factor than the other one. However, the response modification factor for both systems is equal. And so it is demonstrated to achieve appropriate seismic performance, using the steel moment resisting frames accompanied with concentrically braced frames system can have more advantages than the other one. Regarding to the results, it appears that the Cd factor for the mentioned structural systems is more than the values which are in Iranian Seismic Code.<\div>

۵SEISMIC EVALUATION OF AVAILABLE RETROFITTING METHODS FOR NON–DUCTILE RC FRAMES USING ANNS
نویسنده(ها): ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
reinforced concrete frames buit with out seismic provisions do not satisfy the minimum requirements of the capacity design pholosophy. These frames possess a number of structural deficiencies including inadequate shear capacity poorly reinforced joints deficient lap splice lengths and insufficient buckling and confinement reinforcement. these frames are characterized by inadequate ductility which is one of the key performance indicators in seismic design of RC structures. as a consequence of poor reinforcement detailing lack of transverse reinforcement in the joint region as well as absence of any capacity design principles brittle failure mechanisms are expected.<\div>

۶Evaluating the Performance of Steel Ring in Special Bracing Frame
نویسنده(ها): ، ، ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
one of the appropriate procedures to reduce damages in structures is to increase dissipation of seismic energy by the structure to achieve this goal , in the last decade several researchers attempted to introduce various solutions . One of the significant methods regarding this is implementing ductile elements in some point of structure in order to dissipate the energy of an earthquake this element plays the role of a sacrificing element for the structure. this prevents other structural members from getting damaged<\div>

۷Investigating the Seismic Design Lateral Force Distribution of a Tall Steel Moment Frame Building Based on Inelastic Behaviour
اطلاعات انتشار: نهمین کنگره بین المللی مهندسی عمران، سال
تعداد صفحات: ۶
In recent earthquakes, most of the observed collapses have been related to inappropriate distributions of strength and stiffness of structural elements. Since most building structures designed according to currentcode procedures are expected to undergo large deformations in the inelastic range when subjected to major earthquakes, lateral force distributions can be quite different from those given by the code formulas. One of the essential elements of performance–based seismic design of structures should be touse more realistic design lateral force distribution, which represents peak lateral force distribution in astructure in the inelastic state and includes the higher mode effects. In this paper, design lateral force distribution of the 20–story steel moment resistant frames located in Los Angeles, which was the subject of an extensive analytical study as part of the SAC project, has been investigated using dynamic timehistory analyses results. The maximum story shear at each level, under twenty ground motion records at 10% and twenty at 2% probability of exceedance in 50 years, obtained from nonlinear time history dynamic analyses, and compared with the code lateral load pattern. OpenSees software has been used in this paper for modeling and performing analyses. It is concluded that code lateral force distribution does not able to accurately predict deformation and force demands that may be induced during nonlinear phase; causing structures to behave in a rather unpredictable and undesirable manner<\div>

۸An Investigation on the Effect of Core on Shear Lag in Tubular Structures
نویسنده(ها): ، ،
اطلاعات انتشار: نهمین کنگره بین المللی مهندسی عمران، سال
تعداد صفحات: ۸
In the recent years, there have been many new skyscrapers built which soar into new heights. The most efficient building system for high rises has been the framed tube system. However, the framed tube buildings suffer from shear lag effect which causes a nonlinear distribution of axial stresses along the face of the building. In the present study, the effect of core on shear lag phenomenon in tubular structures is investigated. Three different tubular structure models including model without core, model wit centralcore and model with central core but eliminated in last 15 stories have been analyzed. A shear lag index isdefined for evaluating these models. From examination of the results, the effective influence of core for improving the behavior of framed tube structures has been concluded. The influence of core in reduction of shear lag in first story is estimated by 5%.Investigating the shear lag phenomenon of columns on webframe, it could be revealed that in top story the positive and negative shear lag phenomena have been occurred simultaneously.<\div>
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