Sharif Digital Repository

In this thesis, the nonlinear seismic behavior of typical Iranian building is evaluated. The evaluation results indicated that these building, which were designed, based on first edition of 2800 standard and before, due to ductility and stiffness deficiency, don’t satisfy the 3th edition of 2800 standard and FEMA356 requirements, then retrofit of the most old structures is recommended. Selected samples include ordinary moment resistant concrete frames. The effectiveness of three retrofit schemes, concentric steel bracing (CBF), Eccentric steel bracing (EBF) and buckling restrained bracing, are studied and compared. The results of investigation indicated that although CBF retrofit scheme is... 

Structures having buckling restrained braces (BRB) as earthquake resisting system, have the qualities of high lateral stiffness and the ability to damp the energy coming from earthquake, at the same time.In addition to new structures, these braces can also be used in rehabilitating old steel or concrete buildings. By using this kind of resisting system, smaller sections are needed in design of buildings and also the cost of repair after earthquake can be highly reduced.The most important advantage of buckling restrained braces is their equal behavior and capacity in both tention and compression, that causes high energy absorption as a result of symmetric and stable cyclic behavior. All these... 

One of the most common failure modes of structures in earthquakes is soft story failure which causes by discontinuity of lateral force resisting elements like braces. so the ground floor acts as a soft floor. In this case columns are imposed to large deformation and plastic hinges are formed at top and bottom of the columns. This case is named as story mechanism (severe drift of the story). In most of this case building collapsed or going to collapse. To resolve this problem, different solutions are presented. One of the strategies under section (2-10) 2800 code is increase of designed load in columns of the soft floor. This measure cause to Significant increases in the sections of the... 

Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. In the conventional bracing systems, it is assumed that the braces buckle under compressive forces; but Buckling Restrained Brace (BRB) does not buckle under pressure. In this study performance of BRB in jacket platform, with a case study of Resalat platform, has been investigated under earthquake load and powerful wave. The modeling of jacket equipped with this brace has been done in Abaqus software, and results... 

Buckling-Restrained Braced Frame system (BRBFs) are a new type of steel seismic-load-resisting system that has found use in several countries because of its efficiency and its promise of seismic performance far superior to that of conventional braced frames. The system is addressed in the 2005 edition of the AISC Seismic Provisions for Structural Steel Buildings, also a set of design provisions has been developed by NEHRP. This thesis illustrates the seismic design of buckling-restrained braced frames and compares its seismic performance with the performance of ordinary bracing systems. This work investigates the advantage and disadvantages of this new type of seismic resisting. By having... 

By constraining the steel members against lateral buckling, buckling-restrained braces (BRB’s) show similar load-deformation behaviors and energy absorption capacities in both tension and compression. As a result, BRB’s demonstrate significant energy dissipation capacity compared to ordinary braces. On the other hand, the relatively small post-yield stiffness of BRB’s usually leads to significant residual drifts, which may render the structure unusable. In recent decades, significant research has been put into improving the performance of structures equipped with BRB’s. In this project, the current methods to enhance the performance of the BRB’s are explored, and novel approaches are... 

In many structures, using long span girders due to architectural reasons is evitable. Studies show that in this situations, using plate girders is not only a non-economical choice, but also it reduces the structure performance, because of plastic hinges which would be formed in columns instead of beams, due to higher stiffness of girders. To overcome this difficulties, Truss girders or open-web ones are good choices for substitution. Recently, a novel lateral loading system named “truss bending moment system” equipped with buckling restrained braces (BRB) is also proposed. In this research, some structures with usual configurations are designed with both mentioned systems. In each case,... 

Recent earthquakes indicate the importance of retrofitting existing structures to achieve an acceptable level of performance. Use of bracing systems is a cost-effective method for seismic retrofitting of existing steel frames. In particular, Buckling Restrained Braces (BRBs) and Special Concentrically Bracing systems (SCB) are practical choices to be used because of their large energy dissipation capacity especially under moderate to severe earthquakes. Buckling restrained braces which yield in both tension and compression, exhibits stable and predictable hysteretic behavior. In this study several existing steel frames, which are designed based on older versions of the building codes, have... 

In this study, seismic performance of steel diagrid structures is investigated using far-field earthquake records and their seismic performance factors, such as overstrength factor (Ω_0), ductility ratio (µ_T) and response modification coefficient (R) are evaluated according to the FEMA P695. To meet this objective, 12 archetype 3-D models of diagrid structure with two different height of 8 and 12 stories and three different diagonal angles of 45, 63.4 and 71.5 degrees are designed according to the ASCE 7-10 and using response modification factor R=3.6. With regard to the main horizontal beam connections with the diagrid system, equal number of models with pin and rigid type of connections... 

This project aims to determine seismic performance coefficients of Off-Center Braced lateral load resisting system (OBS) equipped with Buckling-Restrained Braces (BRBs), along with comparing its seismic performance in extreme seismicity level with those of Special Moment Frame (SMF). For this intent, the structural design of 24 regular-in-height residential OBS-BRB models was first carried out following ASCE7-16. Then, Static (Pushover) and Incremental Dynamic Analysis (IDA) were performed on the models using the methodology of FEMA P-695 to obtain the target coefficients. Furthermore, the coefficients were used for Pushover and IDA analysis of 27 irregular-in-height OBS-BRB models with soft... 

In today’s world, the use of lateral load-bearing systems, such as bracings, has become a pretty common practice. Often showing axial deformation behavior, these members exhibit proper performance under tensile loads but tend to become unstable under compressive loads. In contrast to common bracing systems, the buckling-restrained bracing (BRB) systems perform well under not only tensile loads but also compressive loads. Recent studies have paid greater deals of attention to the application of short-core BRB systems in different structures. The bracing core has been shortened to increase the core deformation and hence the energy dissipation capacity of the bracing system. In this condition,... 

This investigation is intended to assess the behavior of SCBFs in the presence of typical brace members, which buckles in compression, and BRBs joining by yielding elements. While braces play a role in providing stiffness for structure, central yielding elements will act as energy-absorbing fuses. In this frame type, energy dissipation will mainly be undertaken by BRBs and yielding elements. The mentioned yielding elements do this by initiating plastic hinges in each corner of the central frame. As it is clear, designing a structure that includes the stated lateral-load-resisting system necessitates seismic performance parameters to be evaluated. Hence, by pursuing the FEMA P695 methodology,... 

This study proposes an efficient risk-targeted framework for integrated optimal seismic design and quantifying target safety of steel Special Moment-Resisting Frames (steel SMRFs) with and without various passive damping devices such as Buckling-Restrained Braces (BRBs), Friction Dampers (FDs), and Fluid Viscous Dampers (FVDs). This framework provides an automated design procedure formulated as a constrained single-objective optimization problem to achieve the minimum Life Cycle Cost (LCC) within the Particle Swarm Optimization (PSO) algorithm and can be the basis of current seismic codes for target safety calibration. LCC includes initial construction cost and lifetime seismic losses such...