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In this research, the precision and efficiency of the use of FAM in static nonlinear analysis (pushover analysis) have been compared to the case of using other common element types such as forced-based and displacement-based fiber elements and SAP2000 super elements in nonlinear analysis. In addition, the effects of elastic axial deformation of the members on the performance of the structures, which have not been investigated before using FAM, have also been implemented through analysis by modifying the stiffness matrices of the structural elements. To achieve this goal, a computer code has been developed in MATLAB to analyze the structures using improved FAM. Differences between the FAM and other mentioned methods are revealed through conducting pushover analysis on six 2D steel special moment-resisting frames. The results of pushover curves, base shear forces, and plastic rotation of the critical hinges obtained from all of the methods are compared to demonstrate the accuracy of the FAM. The results indicated that in general, the predictions obtained using the FAM had a good agreement and compatibility with those from other methods of analysis currently used in practice for seismic performance assessment of structures.

Accurate seismic evaluation of buildings requires appropriate nonlinear models in order to capture all possible behaviors of structural elements under different loading conditions. To this aim, various research has been done, and abundance of models have been introduced as well. Notwithstanding the multiplicity of these models, most of them have deficiencies in precise simulating the structural behavior. Thus, the accuracy of a model must be investigated thoroughly to ensure the reliability of the analysis results. At present, the best methodology to scrutinize the capability of the nonlinear models is to verify the model with the results of an existing experiment and performing sensitivity analyses afterwards. This paper focuses on this procedure by comparing three different shell elements which are already developed for RC shear walls in the platform of OpenSEES. The shake-table test of a full-scale 7-Story building slice tested at UC-San Diego is also employed for models' verification. Parameters including mesh size, damping type, and concrete shear retention factor (SRF) were investigated through the nonlinear time-history (NTH) and non-linear static analyses (NSA). It is worth noting that changing these parameters have substantial influence in some cases and therefore appropriate value for each of them must be meticulously selected. The results indicate that the RC shear wall shell models are in an acceptable agreement with the test results.

The occurrence of recent earthquakes with a considerable vertical component has drawn both engineers and researchers attention to the effect of vertical excitations more than the past. Regarding the high vertical to horizontal acceleration ratio of earthquakes which sometimes exceed the unit, the simultaneous effects of these two components cannot be ignored. In addition, the susceptibility of beams' length to vertical ground motions has been evident, yet studies on how the collapse risk of the buildings with various beam length can be affected by vertical excitations are a handful. Thus, in this paper, four 10 and 30-story RC frame-Core wall buildings with 6 and 12-meter beam span are designed, and the nonlinear models of them are developed in the platform of Opensees. Incremental Dynamic Analysis (IDA) in two states, once only under horizontal acceleration (H) and the other under both vertical and horizontal accelerations (H+V) are conducted using a suite of near-field ground motion records. Then, the IDA and the fragility curves are derived, and the collapse probability of the buildings in 1 year and 50 years has been calculated through the integration of seismic hazard and fragility curves in which the derivative of fragility curve is combined with hazard curve using the risk integral. The results indicated that the collapse risk of the buildings with longer beam spans under simultaneous horizontal and vertical excitations are noticeably greater than that of the buildings with 6-meter spans, and the sensitivity of tall buildings to vertical excitations is generally less than mid-rise buildings.

Ever since the nonlinear modelling of the buildings has become a prevalent method to assess the seismic responses, engineers and researchers have been looking for simple and convenient methods. Although the most reliable and accurate behavior is generally obtained from 3D model, in some cases they can be substituted by an equivalent 2D model. This simplicity may be followed by some errors but as long as the errors are quite negligible the incorporating of 2D models will be of interest. Hence, numerous studies have been focusing on how a 3D model can be transformed into a convenient 2D model, such as FEMA P695. Nevertheless, the focus the proposed method in FEMA P695 is on 3D moment frames, while structures including shear walls are remarkably common especially in high-seismicity zones. As regards the lack of any applicable method to transform 3D core wall systems into 2D models, authors of this paper tried to clarify a new simple approach in order to conform a 3D symmetric RC core wall system with a corresponding equivalent 2D model. The proposed procedure can be applied to any symmetric and regular RC core wall systems, regardless of their wall size and thickness, and building height and hence can be considered as a suitable method even for high-rise buildings. To verify this new procedure, first, 3 RC core wall structures were designed in accordance with recent codes. Then, the full 3D and simplified nonlinear planar models of the structures were developed in OpenSEES. Finally, 2D models were adjusted to 3D models through the pushover analysis. The results of modal and pushover analysis indicated that the compatibility of the equivalent planar systems are in a good agreement with the 3D structures.

The geological characteristics of soil materials beneath a site have a significant impact on seismic motion and therefore, affect the seismic performance of the structures. With the aim to reduce the inelastic demand triggered by structural members of frame building during seismic excitations, one of the innovative cost-efficient solutions is the application of friction dampers. However, this type of dampers depend on the story displacements (story drift ratios), and they can be affected by the variation in site properties. Here, the seismic performance of a 10-story intermediate steel damped moment frame is studied under simulated near-fault ground motions for different soil types. Three strong pulse-like records on the bedrock are passed through different soil layers with a linear behavior. Series of nonlinear time-history analyses under simulated records are used to investigate the effect of soil type on seismic performance of structures with friction dampers. The result indicates site soil effect rises input energy to structure; however, dampers are still able to dissipate larger input energy and keep structural elements in the linear stage. Further, soil site effect increases the maximum displacement of structure because it increases the record amplitude.