Sharif Digital Repository

Attitude control of a novel regional truss-braced wing (TBW) aircraft with low stability characteristics is addressed in this paper using Reinforcement Learning (RL). In recent years, RL has been increasingly employed in challenging applications, particularly, autonomous flight control. However, a significant predicament confronting discrete RL algorithms is the dimension limitation of the state-action table and difficulties in defining the elements of the RL environment. To address these issues, in this paper, a detailed mathematical model of the mentioned aircraft is first developed to shape an RL environment. Subsequently, Q-learning, the most prevalent discrete RL algorithm, will be... 

Concentrically braced structures are one of the most common resistant systems in steel structures due to their high stiffness and lateral strength. However, when these structures are subjected to moderate and severe earthquakes, their compression member begins to buckle. Also, buckling of compression members in Concentrically Braced Frames (CBFs) decreases ductility and degradation of the hysteresis curve. Numerous studies have been performed to improve the behavior of CBFs. Using steel dampers is considered one of the appropriate ways to improve the behavior of CBFs. Although steel dampers improve the hysteretic behavior of the CBFs, they impose additional costs on structures. Therefore, in... 

Recent studies have indicated the need of considering aftershocks in the seismic design/assessment of structures. This article investigates the effect of sequential mainshock and aftershock earthquakes on eccentrically braced steel frames with vertical energy-absorbing links. To achieve this, 4, 8 and 12-storey frame buildings are modelled in Perform3D® software considering non-linear behaviour of materials and components. The frames are subjected to a set of 12 main earthquake records corresponding to the required hazard level, and then subsequent aftershocks are applied using incremental dynamic analysis (IDA). To reduce the computational cost, an alternative approach is also adopted by... 

Buckling-restrained braces (BRBs) have been spread widely, especially in high seismic hazard zones due to their excellent energy absorption capacity. BRBs are composed of a main load-carrying steel core restrained with other elements mostly made of concrete and steel casing to preserve it from buckling. Although BRBs provide excellent cyclic behavior, a problem is with their heaviness, which leads to difficulties such as installation and transportation. This study presents a numerical and experimental investigation on a BRB with a new proposed restraining system composed of concrete panels confined with partially carbon fiber reinforced polymer (CFRP) strips to reduce the weight of the... 

In many earthquake prone regions in developing countries, substandard steel moment resisting frame (SMRF) systems pose a profound danger to people and economy in the case of a strong seismic event. Eccentric bracing systems with replaceable vertical links can be utilized as an efficient and practical seismic retrofitting technique to reduce future earthquake damages to such structures. This paper aims, for the first time, to demonstrate the efficiency of eccentric bracing systems with vertical links as a seismic retrofitting technique for the SMRF structures with WCSB and to develop fragility curves for such structures. To achieve this aim, first, the effect of the vertical links on the... 

The eccentric bracing system equipped with vertical links is capable of providing high levels of stiffness, strength and ductility, and therefore, can be efficiently used for seismic retrofit of existing structures. This study aims to investigate the seismic reliability of steel moment-resisting frames retrofitted by this system using a novel combined series–parallel system approach. The seismic response of 4, 8 and 12-storey steel moment-resisting frames (MRFs) are evaluated under a set of design basis earthquakes (DBE) before and after retrofitting intervention. Adopting an engineering demand parameter approach (EDP-Based) for reliability assessment and development of analytical models for... 

The tension-only braced frames (TOBFs) are widely used as a lateral force resisting system (LFRS) in low-rise steel buildings due to their simplicity and economic advantage. However, the system has poor seismic energy dissipation capacity and pinched hysteresis behavior caused by early buckling of slender bracing members. The main concern in utilizing the TOBF system is the determination of appropriate performance factors for seismic design. A formalized approach to quantify the seismic performance factor (SPF) based on determining an acceptable margin of safety against collapse is introduced by FEMA P695. The methodology is applied in this paper to assess the SPFs of the TOBF systems. For... 

Nonlinear behavior of jacket platforms is important in both design and rehabilitation issues that depends on the bracing arrangement. Both ductility and strength of the structures derived from pushover analysis are highly related to configuration of the braces. Considering a suitable criterion such as constant weight or constant stiffness and period of the structure in all arrangement cases, one can compare the capacity curves and find the best configuration. In this paper a simple logical method for investigating the strength and ductility of the jacket structure is presented, it is shown that global geometry and configuration of the braces are very important and effective in both strength... 

In this paper, earthquake-induced economic loss of buildings with the eccentrically braced frame as the lateral load resisting system is investigated. Economic loss in this paper includes collapse loss, demolition loss, and structural and nonstructural repair loss. A simplified probabilistic story-based loss estimation procedure is employed for this purpose. A thorough study is conducted on the verification of shear link response with experimental results as shear link is the main source of nonlinearity in eccentrically braced frames. Nonlinear response history analyses are conducted on four, eight and sixteen story prototype models and engineering demand parameters such as story drift... 

The seismic performance of diagrids equipped with buckling restrained braces (BRBs) is investigated. In that regard, the effects of BRBs on the seismic performance characteristics of diagrids such as response modification factor, R, overstrength factor, Ω0, ductility ratio, μ, and median collapse capacity, S^CT, are evaluated. To this end, 6 three dimensional diagrid structures with various heights and diagonal angles are modeled using OpenSees program and are equipped with BRBs in a novel arrangement. Utilizing nonlinear static analysis, the seismic performance factors of models are evaluated. Subsequently, the median collapse capacity (S^CT) of the models are determined by performing... 

This study presents the experimental investigation of half-scale, one-story, one-bay pinned frames equipped with a ribbed bracing system (RBS). The RBS is a newly developed passive control system designed to eliminate buckling and enhance the seismic behavior of structures. Here, mechanical models of this bracing system were designed and constructed. Pinned frames equipped with the RBS were cyclically tested. The hysteretic behavior and energy absorbing capacities of the frames were evaluated. Based on the results, the full plastic capacity of the brace was achieved and no buckling occurred. The RBS frame illustrated proper hysteretic behavior and energy dissipation capacity up to 4% story... 

Purpose: This paper aims to study the lateral behavior of cold-formed steel walls with K-shaped bracing by finite element modeling. Design/methodology/approach: The braces which have the same section as those for studs and tracks are connected to the frame by screw connections. By pushover analysis, lateral performance of two frame categories, with different dimensions and bracing arrangements, is examined, and the force-displacement diagram and the ultimate strength of walls are extracted. Probable failure modes during lateral loading including distortional buckling of studs, buckling in braces and failure of connections are simulated in the numerical model, and some strengthening... 

Some existing platforms may have some problems with probable extreme future loads such as earthquake. From economic point of view, it is preferable to retrofit and continue using of existing jackets in many cases, in comparison to a new installation. Two efficient rehabilitation methods of friction damper device and buckling restrained braces are presented and investigated numerically for seismic loads from far-fault and near-fault earthquakes. As an example, an existing four-leg service platform placed in the Persian Gulf (Ressalat) is considered and the results are presented. Because of low redundancy in jacket platforms (after buckling of compression members), it is important to... 

The objective of this study is to develop analytical fragility curves for an ensemble of existing 3-to 6-story residential steel buildings with concentrically braced frames in 2 directions, designed during 2010 to 2015 in Qazvin, Iran. The buildings were modeled three-dimensionally in OpenSees considering braces buckling behavior. Maximum Inter-story Drift Ratio (.MIDR) and spectral acceleration at. fundamental period of the structure with 5% viscous damping (Sa(7,5%)) were considered as Damage Index (DI) and Intensity Measure (/M), respectively. Limit states were specified as discussed in FEMA 356. Ground motion record selection and uncertainties assessment were carried out based on FEMA... 

Considering the interaction of flexural moment and shear force in the steel frames with haunch or intermediate beam length and eccentrically braced frames with intermediate link length is a major concern of the structural analysis and design. This article contains two stages. In the first stage, to investigate the moment–shear interaction for the highly ductile steel I-sections, a study is carried out using finite element analysis and a simple and practical relationship is developed. In the second stage, a simple approach based on virtual work method for assemblage of interconnected rigid bodies is employed to consider collapse mechanisms with mixed hinges. Using this approach, the... 

Passive steel dampers have shown favorable performance in last earthquakes, numerical and experimental studies. Although steel dampers are more affordable than other types of damper, they are not economically justified for ordinary buildings. Therefore, in this paper, an innovative steel damper with shear yielding mechanism is introduced, which is easy to fabricate also can be easily replaced after sever earthquakes. The main goal of implementing such a mechanism is to control the possible damage in the damper and to ensure the elastic behavior of other structural components. The numerical results indicate an enhancement of the hysteretic behavior of the concentrically braced frames... 

The objective of this study is to develop analytical fragility curves for an ensemble of existing 3-to 6-story residential steel buildings with concentrically braced frames in 2 directions, designed during 2010 to 2015 in Qazvin, Iran. The buildings were modeled three-dimensionally in OpenSees considering braces buckling behavior. Maximum Inter-story Drift Ratio (.MIDR) and spectral acceleration at. fundamental period of the structure with 5% viscous damping (Sa(7,5%)) were considered as Damage Index (DI) and Intensity Measure (/M), respectively. Limit states were specified as discussed in FEMA 356. Ground motion record selection and uncertainties assessment were carried out based on FEMA... 

In this investigation, seismic behavior and design coefficients of the ribbed bracing system (RBS) are evaluated by considering various archetypes that reflect configuration variability. RBS is a lateral bracing system with a unique mechanics that prevents buckling-induced damage by allowing free deformation of brace under compression. After successful experimental validation and numerical evaluation of RBS specimens in previous studies, FEMA P695 methodology is adopted in this study to subject 48 archetype structures to incremental dynamic analysis (IDA) procedure. Evaluation of the probabilistic collapse capacity of the archetypes against the code requirements reveals that RBS system can... 

Ribbed bracing system (RBS) is an innovative structural system designed to eliminate the buckling of braces and enhance the behavior of structures under seismic loads. In this study, a collaborative performance of 2 RBS devices bracing a frame was assessed numerically and experimentally. In the numerical phase, the collaboration of ribbed braces at various stages of reversal loading was elaborated mathematically and was used for representing the system using finite element modeling. In the next phase, the numerically observed behavior was validated experimentally by conducting cyclic quasistatic tests of the proposed configurations. Two alternative RBS configurations—called completely closed... 

This article evaluates the seismic performance of structures equipped with a ribbed bracing system (RBS). RBS uses ribbed faces that freely slide under compression, however, interlock under tensile forces. Two RBS mechanisms; Completely-closed RBS (CC-RBS) and Improved-centering RBS (IC-RBS), were proposed and successfully tested for eliminating compressive buckling of braces. CC-RBS and IC-RBS provide high energy dissipation capacity and small residual story drifts, respectively. Here, these mechanisms were employed for design and modeling of three structures with varying heights. The models were then subjected to incremental dynamic analysis (IDA), and their seismic performance was...