NONLINEAR STATIC procedure (NSP) is a common technique to predict seismic demands on various building structures by subjecting a monotonically increasing horizontal loading (pushover) to the structure. Therefore, the pushover ANALYSIS is an important part of each NSP. Accordingly, the current paper aims at investigating the efficiency of various algorithms of lateral load patterns applied to the structure in NSPs. In recent years, fundamental advances have been made in the NSPs to enhance the response of NSPs toward NONLINEAR time history ANALYSIS (NTHA). Among the NSPs, the philosophy of "adaptive procedures" has been focused by many researchers. In the case of utilizing adaptive procedures, the use of incremental force vector considering the effects of higher modes of vibration and stiffness deteriorations is possible and seems that it can lead to a good prediction of seismic response of structures. In this study, a new adaptive procedure called energy-based adaptive pushover ANALYSIS (EAPA) is implemented based on the work done by modal forces in each level of the structure during the ANALYSIS and is examined for steel moment resisting frames (SMRFs). EAPA is inspired by force-based adaptive pushover (FAP) and story shear-based adaptive pushover (SSAP). FAP has applied modal forces directly into load patterns; SSAP, on the other hand, has implemented the energy method in system`s capacity curve for measuring the equivalent movement. EAPA has enforced the concept of energy directly in load pattern; so that by using the modal forces-movements an energy-based adaptive algorithm is obtained. Hence, the effects of higher modes, deterioration in stiffness and strength, and characteristics of a specific site are incorporated and reflected in applied forces on the structure. Results obtained from the method proposed a desirable accordance with the extracted results from NTHA over the height of the structure.

Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of concentrically braced dual systems with steel moment-resisting frames was assessed under seismic loads through pushover ANALYSIS using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the NONLINEAR STATIC alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.

Design sensitivity ANALYSIS is a necessary task for optimization of structures. Methods of sensitivity ANALYSIS for linear systems have been developed and well documented in the literature; however there are a few such research works for NONLINEAR systems. NONLINEAR sensitivity ANALYSIS of structures under seismic loading is very complicated. This paper presents an analytical sensitivity technique for Reinforcement Concrete Moment Resisting Frames (RCMRF) that accounts for both material and geometric NONLINEARity under pushover ANALYSIS. The results of proposed method are compared with the results of finite difference method. A three-story, two bays moment frame example is used to illustrate the efficiency of the method. This technique can be very useful and efficient for optimal performance-based design of RC buildings.

The NONLINEAR STATIC pushover ANALYSIS technique is mostly used in the performance-based design of structures and it is favored over NONLINEAR response history ANALYSIS. However, the pushover ANALYSIS with FEMA load distributions losses its accuracy in estimating seismic responses of long period structures when higher mode effects are important. Some procedures have been offered to consider this effect. FEMA and Modal pushover ANALYSIS (MPA) are addressed in the current study and compared with inelastic response history ANALYSIS. These procedures are applied to medium high-rise (10 and 15 storey) and high-rise (20 and 30 storey) frames; efficiency and limitations of them are elaborated. MPA procedure present significant advantage over FEMA load distributions in predicting storey drifts, but the both are thoroughly unsuccessful to predict hinge plastic rotations with acceptable accuracy. It is demonstrated that the seismic demands determined with MPA procedure will be unsatisfactory in NONLINEAR systems subjected to individual ground motions which inelastic SDF systems related to significant modes of the buildings respond beyond the elastic limit. Therefore, it’s inevitable to avoid evaluating seismic demands of the buildings based on individual ground motion with MPA procedure.

In this paper, the effect of the deterioration behavior of hysteretic cycles in NONLINEAR STATIC ANALYSIS (pushover) has been studied. One of the deficiencies of this method is that the deterioration of hysteretic cycles for structural elements is approximately considered in this ANALYSIS. To evaluate this effect, nine special moment resisting frames have been used and loaded, based on the Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No.2800, 3rd Edition). These frames have been analyzed and designed by ETABS software. The modified Takeda and non-degrading Clough models have been used in inelastic dynamic ANALYSIS. The two latter models have been successfully used in the past to analytically reproduce the hysteretic behavior of well-detailed flexural-controlled reinforced concrete elements. The inelastic dynamic ANALYSIS of the reinforced concrete structures program, IDARC, is used for NONLINEAR STATIC and dynamic ANALYSIS, which considers damage ANALYSIS by using the Park & Ang damage model. The maximum displacement amounts obtained from NONLINEAR dynamic ANALYSIS are compared with those obtained from NONLINEAR STATIC ANALYSIS. Results show that the average amounts of maximum displacement increase 4% and 9%, respectively; with considering deterioration effects at different seismic hazard levels (0.2g and 0.25g), rather than target displacements of a pushover ANALYSIS. In addition, in the modified Takeda model that considers deterioration effects, the damage index for a seismic hazard level of 0.2g, increases by 53% more than that of the bilinear model. This ratio is 81% for a seismic hazard level of 0.25g.

In this paper, the seismic behavior of three intermediate moment-resisting concrete space frames with unsymmetrical plan in five, seven and ten stories are evaluated by using pushover ANALYSIS. In each of these frames, both projections of the structure beyond a reentrant corner are greater than 33 percent of the plan dimension of the structure in the given direction. The performance of these buildings has been investigated using the pushover ANALYSIS. Results have been compared with those obtained from non-linear dynamic ANALYSIS.

Pushover ANALYSIS is a simplified NONLINEAR ANALYSIS technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the so-called dynamic pushover ANALYSIS, i.e. a dynamic time history ANALYSIS of an equivalent single degree of freedom model of the original system, as well as other available approximate STATIC methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover curves. In a so-called dynamic pushover ANALYSIS, the bi-linear and tri-linear approximations of these pushover curves were used to assess the target displacements by performing dynamic NONLINEAR time history analyses. The results obtained for five different special moment resisting steel frames, using five earthquake records were compared with those resulted from the time history ANALYSIS of the original system. It is shown that the dynamic pushover ANALYSIS approach, specially, with the tri-linear approximation of the pushover curves, proves to have a better accuracy in assessing the target displacements. On the other hand, when NONLINEAR STATIC procedure seems adequate, no specific preference is observed in using more complicated STATIC procedures (proposed by codes) compared to the simple first mode target displacement assessment.

In the conventional design and ANALYSIS methods affecting parameters (loads, materials' strength, etc) are not set as probable variables. Safety factors in the current Codes and Standards are usually obtained on the basis of judgment and experience, which may be improper or uneconomical. In technical literature, a method based on NONLINEAR STATIC ANALYSIS is suggested to set Reliability Index on strength of structural systems. In this paper, a method based on NONLINEAR Dynamic ANALYSIS with rising acceleration (or Incremental Dynamic ANALYSIS) is introduced, the results of which are compared with those of the previous (STATIC Pushover ANALYSIS) method and two concepts namely Redundancy Strength and Redundancy Variations are proposed as an index to these impacts. The Redundancy Variation Factor and Redundancy Strength Factor indices for reinforced concrete frames with varying number of bays and stories and different ductility potentials are computed and ultimately, Reliability Index is determined using these two indices.