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.

By locating a steel shear panel at the intersection point of the X-braces, concentrically or eccentrically braced shear panel (CBFSP and EBFSP) is formed. In this paper, to perform parametric study, 1-story CBFSP and EBFSP models with span length greater or less than height are considered. Using linear static analyses, the effects of size and location of the shear panel on the lateral stiffness of the frame with respect to the moment resisting frame with the same member sections are investigated. Next, for 1- and 3-story models, maximum displacement along with base shear and the ratio between the dissipated energy and input energy are examined under 4 ground motion records. Behavior of the truss elements in cross-strip model for nonlinear dynamic analyses is validated based on a performed experimental program. The findings show that the optimum state is achieved by decreasing size of the shear panel and situating it at the middle of the frame or to some extent upper. Furthermore, in this study, tentative values of the over-strength, deflection amplification and response modification FACTORS, which are estimated by pushover curves, are proposed. Using linear regression, an equation is obtained for estimation of the fundamental period of CBFSP and EBFSP.

The theoretical best-possible resolution can be predicted using Beylkin's formula. This formula gives answers to the effect on resolution of frequency, aperture, offset, and acquisition geometry. In this paper, for each 3-D single-fold data seta spatial wavelet is obtained from migration of an event that attributed to diffraction. Then the width of the spatial wavelet is compared to the resolution predicted by Beylkin's formula. The measured widths confirmed the theoretical predictions (i.e. zero-offset data produces the best possible resolution; 3-D shot records produces the worst resolution, and common-offset gathers and cross-spreads producing the intermediate resolution. It is shown that the effects of sampling and fold cannot be derived directly from Beylkin's formula; these 79 effects are analyzed by looking at the migration noise rather than width of the spatial wavelet. Our results indicated that random coarse sampling may produce somewhat less migration noise than regular coarse sampling, though it cannot be as good as regular dense sampling. Generally speaking, increasing fold does not improve the theoretically best possible resolution. However, as noise always has a detrimental effect on the resolvability of events, fold by reducing noise will improve resolution in practice. Required algorithms were written by authors in MATLAB environment.

In this paper a new ribbed bracing system (RBS) is proposed capable of performing as a variable stiffness system that can be used for controlling structural deformations and frequency shifting to compensate SEISMIC energy. RBS has two important advantages. Because of ribbed system, the compressive member is rigidly moved like a piston and a cylinder and therefore it is a buckling prevented system. Also it is possible to use this system as a semi-active system by considering the story drifts and global structural damage and control the system if it is necessary to be open or closed based on the operational criteria assigned in the system. RBS has no need to any actuator and large power supply, but just a battery-size power supply to switch the ribbed mechanism to be on or off. RBS is composed of a ribbed supplemental part and a normal wind-bracing on each floor. Considering an appropriate criterion based on the storey drift, minimum number of bracing systems will be active on the height of structure during earthquake. In contrast with completely closed RBS (CC-RBS) by on-off bracing system arranged along the height of the building cause period shifting of the structure to the larger value. Three stages are considered in the numerical studies: conventional bracing frame (CBF), CC-RBS and semi-active RBS (SA-RBS). Damage indices and Fourier transforms are calculated in order to discuss on the efficiency of the proposed system. Nonlinear dynamic analysis of system has been carried out and structural behaviour has been investigated.Numerical results show the efficiency of CC-RBS in reducing structural damage and improving SEISMIC energy. Also base shear is reduced when SA-RBS is used and structural damage is more uniform in this case.

One way to reduce SEISMIC force is to use knee bracing systems. In this method, the diagonal limbs of the brace are connected to the knee joint. The duty of the brace is to create stiffness and the duty of knee member is to create ductility like a yielding damper. In this method, some novel results are achieved by combining Y type bracing with the knee members. In this regard, three samples of the proposed frame were tested in the laboratory of structure based on the ATC24 loading protocol. The results show that this SEISMIC system has a good PERFORMANCE in energy absorption and stability. At lower frame displacements, the knee element begins the absorb energy process faster. The use of a knee bracing system can be a good alternative to the brace system due to its ease of replacement. The behavior of the hysteresis (force-displacement) curves obtained from the experimental tests show good results in force balancing. Moreover, due to relatively lower initial stiffness and strength, the proposed frame will perform well in low-intensity earthquakes. It was observed that the failure mechanism of the structure has an acceptable ductility in the plastic part of the system. In addition, it was shown that by moving the middle node towards the corner of the frame and increasing the eccentricity of this point, the stiffness of the frame decreases and as a result, the natural vibration period and system displacement increases under constant load.

Setback in elevation of a structure is a special irregularity with considerable effect on its SEISMIC PERFORMANCE. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian SEISMIC code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the SEISMIC PERFORMANCE is done based on both global and local criteria.Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.

Different and to some extent poor SEISMIC PERFORMANCE of structural systems under various types of near-field earthquake excitation, made re-assess and re-evaluation of “SEISMIC PERFORMANCE FACTORS” used in building codes, an inevitable important task. In this paper, SEISMIC PERFORMANCE of special moment resisting steel frame system (SMRSF) under near-Field (with and without pulse) and far-field record excitation is investigated through FEMA P695 methodology. In order to cover the “design space” of the selected structural system, archetypes consisted of 1, 2, 3, 5, 8 and 15 story buildings with 4 and 8 meters bay are selected and designed based on Iran’s national building codes for a “very high SEISMIC” region. Corresponding non-linear models are built based on most recent advances in structural components modeling using OpenSees software. At first by performing non-linear static analysis, overstrength factor and period-based ductility are evaluated and quality of non-linear models is controlled. Afterwards, incremental dynamic analyses (IDA) are performed using far-field, near-field pulse like and non pulse like records. Finally, by using IDA results, “adjusted collapse margin ratio (ACMR)” of the models are calculated and compared to “allowable collapse margin ratio (ACMRallowable)”. Therefore, SEISMIC PERFORMANCE of the models are evaluated and “response modification coefficient” (R) for the system is investigated and compared with this factor under different types of ground motion records. Results indicated that except for 15 story buildings, proposed “response modification coefficient” and “over-strength factor “for SMRSF system are adequate under far-field records. However under pulse like near field ground motions, it was observed that short period structures are to some extent vulnerable. For long period structures, in contrast with far-field records, SEISMIC PERFORMANCE of structures designed by prescriptive provisions has adequate PERFORMANCE under near-field pulse like motions.

Construction of welded moment resisting connection is common. These connections have high potential for brittle failure of welds if quality of welding is not controlled. In this research new bolted bracket connection similar to Kaiser bolted bracket connection is introduced. Kaiser connection has invention patent so construction society can’t utilize them without authority. Proposed connection of this paper can be manufactured by both casting and welding methods and can eliminate patent problems. In this evaluation connection PERFORMANCE, pretention force of bolts, height of bracket, number of bolts and length of bracket have been evaluated. In modeling of connection in order to accuracy of results between different connected area and bolts faces contact elements were created. The standard cyclic history was selected for loading of specimens. The results shows that proposed connection can be accepted by connection code for using in special moment resisting frames from both ductility and strength aspects. Findings are extended as hysteresis curves, released energy of connection, rupture index indicators and slip of bolts.

The current Iranian SEISMIC Code, for SEISMIC loading and analysis of structures, (Standard no.2800) considers linear elastic analysis to be adequate for structural and SEISMIC response prediction for a majority of structures.In this regulation, an importance factor, I, is considered to improve the PERFORMANCE of buildings based on their importance. Linear analysis is inadequate for observing structural PERFORMANCE during earthquakes, because proper SEISMIC behavior and the stability of structures are not just governed by strength; structures need to resist determined amounts of force and should be able to displace determined amounts of displacements. On this basis, it is expected that by using importance factor, I, in linear analysis, the structures will behave properly, and after earthquakes, will present a desired level of PERFORMANCE.New SEISMIC regulations, such as FEMA 356 and the Iranian SEISMIC Rehabilitation Guideline, use a PERFORMANCE-based design method; nonlinear analysis methods are the main tools of these codes. Also, the main objective of this research is to evaluate the SEISMIC PERFORMANCE of buildings, with different importance levels, designed according to the Iranian SEISMIC Code, using the Iranian SEISMIC Rehabilitation Guideline.In this research, a set of structures, with different categories of occupancy and different numbers of stories, are designed according to the Iranian SEISMIC Code. The SEISMIC PERFORMANCE levels of the mentioned structures are evaluated using nonlinear static analysis (pushover), based on the Iranian SEISMIC Rehabilitation Guideline.The results show that the low- and medium-rise buildings behave to a life safety (LS) PERFORMANCE level. In high-rise buildings, with medium importance, the required PERFORMANCE level (LS) is not achieved, and in very high importance (essential) buildings, the required PERFORMANCE level (IO) is not achieved. Therefore, increasing the importance factor, I, does not necessarily lead to improvement in PERFORMANCE levels, but leads to an increase in structural weight; this could be a noneconomic decision. By using non-linear analysis in parts of the structure, in which PERFORMANCE level is not met, the structure would be strengthened and achieve the required level of PERFORMANCE.