In this paper, the effects of irregular mass in height for structures has been investigated. To achieve this goal, two five and ten stories concrete moment resisting frames are modeled using Seismostruct software and subjected to seven different accelerograms. To evaluate the seismic performance of the studied structures, INCREMENTAL DYNAMIC ANALYSIS ((IDA)) has been used. The results reveals that the seismic capacity of the irregularly structures reduced, and therefore, it is suggested that mass irregularity in height be avoided as much as possible.

In first part of this paper, the theory of design of X-braces using different steel grades introduced and its effects on different frames verified using NONLINEAR static analyses. It was found hat using lower grade steel in X-braces increases the stiffness, energy absorption capacity, dampingand ductility of system and decreases its lateral drift. In order to completely investigate behavior of steel structures with X-bracing system in design with different steel grades and consider their DYNAMIC behavior, the frames with different stories studied using advanced NONLINEAR static and INCREMENTAL DYNAMIC Analyses ((IDA)). The results presented as comparative diagrams and tables. The near and far field earthquakes used for DYNAMIC analyse sand their seismic performance studied. Therefore, this research can lead to better investigation of seismic behavior of X-braced systems in design with different steel grades. The proposed theory along with analyses show that building codes and steel seismic design specifications can consider the effects of steel grades in seismic parameters definition of structures. The comparative diagrams and tables show that the seismic behavior of X-braces designed with lower grade steel improves considerably. In addition, the response of structures under near field earthquakes is bigger than related parameters under far field earthquakes.

Today, with the increasing spread of high constructions, as a development symbol, the need for selecting robust and suitable system for bearing optimally loads from earthquakes and wind and with high energy absorption power, has been significantly considered. Steel plate shear walls have been used over four decades as an efficient lateral resistance system. This paper analyzed the over strength factor, Ductility Factor and behavior factor of these system. For this, 7, 15 and 30 floors frames possessing one or two steel plate shear wall spans, have been analyzed in non-linear static, linear DYNAMIC or increasingly DYNAMIC ANALYSIS ((IDA)). For considering inherent uncertainty of earthquake, it was used of increasingly DYNAMIC ANALYSIS and 7 records of the strongest earthquakes have been ever occurred were selected. The results showed that the behavior factor of this system in limit form for high construction is 8 and for short and middle construction is about 9.

INCREMENTAL DYNAMIC ANALYSIS ((IDA)) is a parametric ANALYSIS method that has recently emerged in several different forms to estimate more thoroughly structural performance under seismic loads. It involves subjecting a structural model to one (or more) ground motion record(s), each scaled to multiple levels of intensity, thus producing one (or more) curve(s) of response parameterized versus intensity level. Of great interest in Performance-Based Earthquake Engineering (PBEE) is the accurate estimation of the seismic performance of structures, and in particular, the mean annual frequency (MAF) of exceeding a specified structural demand or a certain limit-state capacity.In this study the behavior of a jacket type offshore platform with different characteristics in its two directions, separately and with 3D modeling considering pile-soil-structure interaction is investigated. By obtaining the (IDA) curves and summarizing the results, the behavior of the jacket is studied.All analyses are performed using OpenSees software. It is observed that the difference of geometry of jacket in two directions due to employing Float Over Deck (FOD) installation method, does not cause similar behavior in both directions and finally in direction with float over installation design requirement is not satisfied.

Recently, the Iranian code is established for the LRFD design of steel structures that consistent with the Iranian seismic design code (2800-4). This study is aimed to compare the performance of steel moment frames (SMF and IMF) in the Near-faults earthquakes designed with the Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD) in a probabilistic framework. After the Static Push over (SPO), new Performance based earthquake engineering (PBEE) approach is INCREMENTAL DYNAMIC ANALYSIS ((IDA)) that can lead to the probabilistic judgment using fragility curves of the structure under the different types of ground motions at different levels of intensity. For the INCREMENTAL DYNAMIC ANALYSIS a large number of NONLINEAR time history ANALYSIS must be carried out. The evaluated steel moment frames are 4-story and 8-story frames. The NONLINEAR models of structures are constructed in the Perform-3D software to perform the NONLINEAR time history ANALYSIS. For the NONLINEAR modelling of beam element, the chord Rotation Model is used that proposed by FEMA and available in the Perform-3D software for the beam elements. This model predict the NONLINEAR behavior of element in the two end region that plastic hinge may be caused duo to the seismic load of earthquake. For the column elements, the fiber element method was employed. In this method, the cross-section of column element is subdivided into some spring elements. Each spring is subjected to axial load, given by the combination of axial force and bending moment acting on the section. This model sometimes is called multi-axial spring model (MS model). The fiber model represents a section at the structural member-end. This modelling can represent the axial-flexural interaction in the column element that their properties of NONLINEAR flexural bearing depends on its axial load in each time step. Nearfield events due to their pulse-like effect are in the spotlight in the last decay. To evaluate their effects on the steel structures that located in the seismic areas of Iran, a number of near-field earthquakes are used in the probabilistic assessment. In the (IDA) curves, the roof drift is used as Damage Measure (DM) and the Spectral Pseudo-Acceleration of the first mode of the structure with 5% modal damping ( 1 (, 5% ) a S T ) is used as Intensity Measure (IM). Also in the probabilistic fragility curves, the direct method is used. It means that the IM is used directly in the fragility curve. To predict the probabilistic function for the different level of performance of structures, the lognormal distribution was used. The study results show that the structures designed by the ASD method have a better seismic performance than the LRFD frames specially in the performance level of Life Safety (LS) and Collapse Prevention (CP). It can be concluded from comparison of the median of collapse functions. For example for the special moment frame (8-story structure), the use of ASD design (instead of LRFD design) leads to a 11% increase in the median of fragility function in the Life Safety (LS) level and 10% increase in the Collapse Prevention (CP) level.

NONLINEAR DYNAMIC inversion is one of the well-known methods in the field of DYNAMIC flight control, which its development refers to the INCREMENTAL NONLINEAR DYNAMIC Inversion (INDI). Based on this, in this paper, the non-linear slow and fast modes of the aircraft is separated into two parts. Then, a distinct control is designed for each part. In the outer and inner loops, the PID and the sliding mode controller are designed, respectively. In addition stability ANALYSIS, the simulation results for Boeing 747 are presented and compared with the reference model modes and the conventional INDI. NONLINEAR DYNAMIC inversion is one of the well-known methods in the field of DYNAMIC flight control, which its development refers to the INCREMENTAL NONLINEAR DYNAMIC Inversion (INDI). Based on this, in this paper, the non-linear slow and fast modes of the aircraft is separated into two parts. Then, a distinct control is designed for each part. In the outer and inner loops, the PID and the sliding mode controller are designed, respectively. In addition stability ANALYSIS, the simulation results for Boeing 747 are presented and compared with the reference model modes and the conventional INDI.

In knee braced frames, the braces are attached to the knee element rather than the intersection of beams and columns. This bracing system is widely used and preferred over the other commonly used systems for reasons such as having lateral stiffness while having adequate ductility, damage concentration on the second degree convenience of repairing and replacing of these elements after Earthquake. The lateral stiffness of this system is supplied by the bracing member and the ductility of the frame attached to the knee length is supplied through the bending or shear yield of the knee member. In this paper, the NONLINEAR seismic behavior of knee braced frame systems has been investigated using INCREMENTAL DYNAMIC ANALYSIS ((IDA)) and the effects of the number of stories in a building, length and the moment of inertia of the knee member on the seismic behavior, elastic stiffness, ductility and the probability of failure of these systems has been determined. In the INCREMENTAL DYNAMIC ANALYSIS, after plotting the (IDA) diagrams of the accelerograms, the collapse diagrams in the limit states are determined. These diagrams yield that for a constant knee length with reduced moment of inertia, the probability of collapse in limit states heightens and also for a constant knee moment of inertia with increasing length, the probability of collapse in limit states increases.

In this paper, the application of Endurance Time (ET) method to the seismic ANALYSIS of bridges is elaborated. ET method is a novel seismic ANALYSIS method based on time history ANALYSIS in which a structure is subjected to a predefined intensifying acceleration function. First, six concrete bridges were modeled in this study. Three Endurance Time Acceleration Functions (ETAFs) were applied to the models, and the average of responses was calculated. Next, the time history ANALYSIS was conducted using seven real accelerograms that are scaled using the method recommended by Federal Highway Administration (FHWA) to be compatible with the design spectrum of American Association of State Highway and Transportation Offcials (AASHTO) guideline for a site with soil type C in Berkeley, California. The average of the responses of these analyses is considered as a reference. By scaling the mentioned accelerograms over a wide range of hazard levels, INCREMENTAL DYNAMIC ANALYSIS ((IDA)) is performed. Finally, the comparison of the response of ET ANALYSIS and time history ANALYSIS and also the comparison of Endurance Time ANALYSIS (ETA) and (IDA) curves revealed good agreement. The major advantage of ET method over time history and (IDA) methods is the need for less computational effort for performing the ANALYSIS. Such time effciency was achieved due to the possibility of predicting responses by a smaller number of analyses despite maintaining the necessary accuracy.

Structural walls commonly used as efficient structural elements to resist lateral and vertical loads. Diverse performance of bearing wall system in past earthquakes, motivates investigation on the adequacy of current seismic design provision for these walls. This study considers seismic performance of model walls of bearing wall and building frame systems designed as ordinary and special structural walls. Performance of the model walls are evaluated through static pushover and INCREMENTAL DYNAMIC analyses. Results show superior performance of the bearing wall system, which is in odd with small response modification factor given in the current design codes.