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.

The present study investigates the seismic performance of reinforced concrete moment frame SYSTEM retrofitted with different steel BRACING SYSTEMs. Two types of structural combinations including concentric steel BRACING SYSTEM and steel mega BRACING SYSTEM were used in two types of structures with different numbers of stories. These two structures which are designed by 5 and 10 story reinforced concrete moment frame SYSTEM have poor lateral stiffness. They were considered to compensate for the limitations of drift regulations in areas with high seismic risk and life safety performance level. Then, these frames are improved by concentric steel BRACING SYSTEM and mega BRACING SYSTEM. In this study, the nonlinear static (pushover) analysis was used to evaluate the performance of the structure under the influence of ground motions. Also chord rotation, story drift and base shear were used to compare the response of the improved structure. It was shown that the steel mega BRACING SYSTEM and the concentric steel BRACING SYSTEM are respectively the best types of steel BRACING SYSTEMs for upgrading and retrofitting the structures in terms of drift control regulations, the amount of base shear, the number of plastic hinges, the number of collapse elements and the economic issues.

In the Eccentric braced frames (EBFs), which one end of the link beam is connected to a column, the safety of the link-to-column connection is a requirement for the ductile and safe performance of the EBF. But among of the tests that have been implemented on this connection yet, because of the intensity of forces on vulnerable region of the link-to-column connection, the tested specimens were confronted with brittle and sudden failures. So it seems that the reduced beam section ((RBS)) can be a suitable solution for raising this problem, by concentrating flexural stresses at a location away from the connection, in flexural yielding link beams. Therefore in this paper, the possibility of keeping the plastic hinge away from the location of link-to-column connection, in the meanwhile achieving the required plastic rotation of link beam, by using the (RBS) connection, were investigated. This evaluation was done by using a finite element program ETABS and with nonlinear static analysis (pushover) for a dual SYSTEM of special moment frame and special eccentric braced frame. According to the present work, the models with (RBS) by earlier developing the hinge at the (RBS) region, delay yielding occurrence of link at the column face. So the yielding does not occur at the column face, at least prior to achieving the moment at the location of (RBS) region to 1.1 times of its expected plastic moment capacity.

In this paper, the problem of layout optimization for X-BRACING of steel frames is studied using the ant SYSTEM (AS). A new design method is employed to share the gravity and the lateral loads between the main frame and the BRACINGs according to the requirements of the IBC2006 code. An algorithm is developed which is called optimum steel designer (OSD). An optimization method based on an approximate analysis is also developed for layout optimization of braced frames. This method is called the approximate optimum steel designer (AOSD) and uses a simple deterministic optimization algorithm leading to the optimum patterns and it is much faster than the OSD. Several numerical examples are treated by the proposed methods. Efficiency and accuracy of the methods are then discussed. A comparison is also made with Genetic algorithm for one of the frames.

The current design philosophy for buildings located in zones with high seismic risks is that the buildings must have sufficient strength and stiffness to remain elastic and serviceable under moderate but frequently occurring earthquakes and to have sufficient ductility to prevent collapse under extreme earthquake loading. Conventional structural steel framing SYSTEMs such as moment resisting frames (MRFs), concentrically braced frames (CBFs), and eccentrically braced frames (EBFs), are extensively used in seismically active areas. Each of the previously mentioned structural SYSTEMs has different advantages and disadvantages. In this study, response modification factor of ordinary inverted V-braced frames and specially inverted V-braced frames are evaluated, result confirm that the proposed height for buildings with ordinary inverted braced frames in the ASCE7, can be increased up to 10. 7 meter. In addition, results indicate that by using ordinary inverted V-BRACING SYSTEMs in buildings their height can be increased up to 6 stories or 20 meters. Using special inverted V-braced SYSTEMs can have saving about 0 to 30 present on used materials for frames from 1 story to 16 stories. According to the results of this study, the response modification factor proposed by Iranian seismic design code (2800 standard fourth edition), (R=5. 5), is more logical than the one which is proposed by ASCE7, (R=6). Unfortunately, in special inverted V-braced frames, and when the story of the frames increases up to 12 stories, expected ductility demand cannot be achieved, so as a result, for frames that are more than 12 stories tall, lower response modification factor should be used. In addition, frames taller than 12 story height don’ t experience specified target displacement and collapse before getting to preferred mechanism. This phenomenon shows the necessity of using different response modification factor for frames taller than 12 stories.

The most prevalent way to deal with lateral loads in steel structures is using common BRACING SYSTEMs like concentric BRACING SYSTEMs. One of the major drawbacks of this SYSTEM is the buckling when the compression force exceeds the elastic buckling strength, thereby being unstable before reaching the yield limit. In other words, the behavior of these braces is asymmetric under tension/compression forces leading to reduce the ability of the SYSTEM to absorption of the most exciting energy and can lead to additional structural and non-structural damages due to the change in the direction of the inertial forces. To tackle these problems and to improve the performance of BRACING SYSTEMs, in this work for the first time, a new BRACING SYSTEM called a fan BRACING SYSTEM has been introduced. Fan brace enhances the ductility and energy absorption of the SYSTEM by removing harmful buckling effects byreplacing axial deformations with flexural ones, which tends to make the SYSTEM softer and thus increase the natural vibration period of the structure and reduce the earthquake shear force. In this study, the proposed brace is studied using numerical modeling under affecting cyclic excitation based on the loading protocol of ATC-24. The advantages of this SYSTEM include the symmetrical behavior even in the large cyclic deformations, as well as high energy absorption and lighter weight in comparison with the buckling-restrained brace (BRB).

This paper examines a newly developed seismic force-resisting SYSTEM. To achieve improved seismic performance, the strongback SYSTEM combines aspects of a traditional concentric braced frame with a mast to form a hybrid SYSTEM. The mast acts like a strongback to help resist the tendency of concentric braced frames to concentrate damage in one or a few stories during severe seismic excitations. The purpose of the strongback SYSTEM is to promote uniform story drifts over the height of a structure. For this purpose, in this paper, the design principles for achieving the desired goal, along with a new relationship for controlling the amount of story drift uniform index for this SYSTEM is presented and the nonlinear dynamic behavior of structures 3, 6 and 12 stories with three seismic force-resisting SYSTEM with different configuration at the intersection of the braces to the beam under seven acceleration of far and seven acceleration of near field for achieving the correctness of the design principles and comparing the effects of the near and far field earthquakes has been studied. The strongback BRACING SYSTEM is specifically designed to prevent the uniform story drift and alleviate the soft-story mechanism [2]. The design procedure is such to keep strong-back aspects elastic and stress ratio less than 0. 5. Although the seismic codes specify limits for story stiffness and resistance ratio, this limitation does not guarantee to avoid damage concentration. It should be noted that the concept of uniformity is a relative concept and all stories can never have equal and uniform drift in a structure under earthquake. However, a structure can be designed such that the drifts are distributed uniformly in all stories approximately. For uniform story drift and prevention of soft-story in this SYSTEM, it is not just enough to keep the stress ratio less than 0. 5 so as to completely design this SYSTEM, and the necessary examinations were carried out to reach a relation between conventional braces and aspects of strongback. In addition, studies by Lai and Mahin [2] show that the simple design strategy used does not result in adequate member sizes near the top of the strongback SYSTEMs and limited yielding of the strongback spine occurs at these levels. According to the ratio of the braces length and Dimensions of their sections, when the stress ratio in strongback should be less than 0. 5, this result was obtained some limitation must be considered about conventional braces stiffness ratio and the aspects of strongback. Therefore, by considering the issue of elastic state of the components of strongback in earthquakes, conventional braces were designed for code earthquakes force and stiffness ratio of strongback braces to conventional braces is in each story equal to or more than 2. 5 and section of strongback zipper member was considered equal to section of strongback brace member in the story. During these tests, which were performed using the trial and error method, various earthquakes were used to perform the nonlinear time history analysis and various values were considered for the stiffness ratio of strongback braces to conventional braces and were evaluated, which revealed that the stiffness ratio of 2. 5 would cause a more uniform distribution of drift along the height of the structure and was the basis for the design of the braces of this SYSTEM. Results show that the proposed design principles, which are proportional to the stiffness ratio of BRACING, are presented by providing an index of uniformity distribution error in structures 3, 6 and 12 stories, which occurred less than 6, 4. 8 and 8. 6 respectively. Also by creating a difference of 0. 5% between the maximum and minimum of the story drift ratio in most of the structures studied, it has been able to hold the strongback truss in elastic to nonlinear analysis, reduce the concentration of deformations and prevent the creation of a soft story structure.

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.

According to researches, oil and gas projects generally and upstream projects of them especially include a lot of complexities and uncertainties, which lead to an increase in the risk of these field investments. Despite, using risk management methods and techniques, with applying hardware and software developments, has become more popular, recent researches have not been able to provide the comprehensive view of oil and gas upstream risks. As respects to the important role of these projects for Iran economy and necessity of mass investments in the oil and gas upstream sector, it is necessary to identify, assess and prioritize the oil and gas upstream risks methodically and structurally. In this study, with using risk break down structure framework based on Project Management Body of Knowledge (PMBOK) and PEST Classification, the oil and gas upstream risks would identify and classify with a documentary method. The study identifies 60 risks and classifies them into four classes, which have been used in next step for prioritizing by TOPSIS technique. The results with prioritizing based on third risk breakdown structure level, show that as well as the diversity of and variety of upstream project’s risks, there are the heterogeneous risks from first and the second risk breakdown structure level. These results emphasize on selecting precise and appropriate tools to the management of risks.