In a core-wall structure with buckling restrained braces (BRB) outrigger, locations of the plastic hinges are influenced by the outrigger action. Therefore, the designer should consider the issue and use suitable details in the plastic hinge area. The essential questions that arise here are the plastic hinge location and the design moment demand used for design of this kind of structure. In this paper, responses of the core-wall buildings with BRB outrigger designed by using the traditional response spectrum analysis procedure are assessed by implementing the nonlinear time history analysis. The result demonstrates that the plasticity can extend over anywhere within the core-walls specially, at the base and above or below the outrigger levels. Formation of three plastic hinges in the core-wall is recognized suitable for the system. To control the plasticity extension in the core-wall, it is recommended that a new modal combination method be applied to calculate the moment strength of the three plastic hinges over the height. A capacity design concept is used to design other regions of the core-wall where the plasticity does not extend to. The proposed procedure improves behavior of the system by restricting the plasticity extension to the predefined plastic hinge regions. levels in the first case. Therefore, placement of the outrigger at 0.5H is not recommended according to the displacement demand.
CAPACITY DESIGN APPROACHThe philosophy of capacity design in structural seismic engineering ensures that during an earthquake, the structure responds in a favorable ductile manner. This is achieved by pre-selecting an appropriate plastic mechanism and then providing special detailing to the plastic hinge regions. Providing enough ductility in these regions leads to energy dissipation under severe earthquakes (Park and Paulay, 1975;Paulay and Priestley, 1992). Capacity design approach can keep the large portion of the core-walls elastic and facilitate the detailing of the reinforcement there. The ease of detailing and reduction in Figure 11. Average of the (a) curvature ductility, (b) moment, (c) shear, (d) inter-story drift ratio and (e) lateral displacement envelop, in 40-story core-wall.
One way for decreasing the effect of pounding is to set the separation gap between two adjacent buildings. On the one hand, earthquakes in earthquake-prone zones often occur as a chain of successive earth movements in the form of foreshock, mainshock and aftershock. On the other hand, the existence of soft story in the lowest story of the structure is the most common type of irregularity in lateral stiffness. This paper investigates the effect of seismic sequences to estimate the separation gap at the highest collision level of two adjacent structures. For this purpose, 335 adjacent combinations of regular and irregular steel moment-resisting frames are evaluated which have a soft story on the first story. Separation gap demand is calculated using dynamic analysis of nonlinear time history under a set of seismic sequences which are a combination of the mainshock and aftershock. Results of the total of analysis done show the seismic sequence effects are significant and should be considered in the process of determining the normal separation gap (here after, NSG). Finally, based on the done studies, an empirical relationship is presented to estimate the seismic sequence effects on separation gap of two regular and irregular adjacent structures.
One of the most important members of steel structure's connection region is beam-to-column connection. Rigid connection in steel moment frame has special role in the behavior of these structures and the fire resistance of these connections can be important. In this paper the behaviors of three common types of rigid connections in Iran under the effect of heat were studied by the use of numerical finite element methods through ABAQUS software. The models were verified by the use of an experimental model through elastic and plastic amplitudes up to collapse and during numerical results, and the effect of large deformation in the nonlinear region has also been considered. The results show that the connection with the end plate had a better performance against heat than other connections. Also reduced stiffness and lateral buckling in this connection were less than other connections.
In seismic codes, the force strength reduction factor is proposed to transform elastic to inelastic strength. The ductility reduction factor, R l , plays a key role on R factor if no overstrength is present. The R l is determined by SDOF systems. But the higher mode (HM) and Multi-Degreeof-Freedom (MDOF) effects need to be considered to extract the R factor. These effects are studied by proposing a v-MDOF via at least 1764 Nonlinear dynamic Analysis of 2D-frames. Also a sensitivity study has been performed on R l and a v-MDOF . Results obtained from studies conducted on the frames, indicate that HM and MDOF effects have a considerable influence on the base shear. Also the a v-MDOF is typically higher than unity both for ordinary and for near-field earthquakes and it is affected by period, span number and ductility level. These effects are remarkable for near-field motions. Finally, a simplified practical expression is proposed to estimate the a v-MDOF . Ó 2015 Faculty of Engineering, Ain Shams University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
The most important feature of the behavior factor is that it allows the structural designer to be able to evaluate the structural seismic demand, using an elastic analysis, based on force-based principles quickly. In most seismic codes, this coefficient is merely dependent on the type of lateral resistance system and is introduced with a fixed number. However, there is a relationship between the behavior factor, ductility (performance level), structural geometric properties, and type of earthquake (near and far). In this paper, a new and accurate correlation is attempted to predict the behavior factor (q) of EBF steel frames, under near-fault earthquakes, using the genetic algorithm (GA). For this purpose, a databank consisting of 12960 data is created. To establish different geometrical properties of models, 3−, 6−, 9−, 12−, 15, and 20− story steel EBF frames were considered with 3 different types of link beam, 3 different types of column stiffness, and 3 different types of brace slenderness. Using nonlinear time history under 20 near-fault earthquake, all models were analyzed to reach 4 different performance levels. 6769 data were used as GA training data. Moreover, to validate the correlation, 2257 data were used as test data for calculating mean squared error (MSE) and correlation coefficient (R) between the predicted values of (q) and the real values. In addition, the MSE and R were calculated for correlation in the train and test data. Also, the comparison of the response of maximum inelastic displacement of 5 stories EBF from the proposed correlation and the mean inelastic time-history analysis confirms the accuracy of the estimate relationship.
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