Sharif Digital Repository

Recent research in the field of earthquake engineering has seen the development of a number of different displacement-based seismic design (DBD) methods. Such methods aim to overcome limitations with the force-based design methods incorporated in current codes, and the most developed DBD method currently available is the Direct DBD approach, presented by Priestley. The objective of this work is to investigate the performance of the Direct DBD design procedure for steel moment-resisting frame structures. For this purpose, a series of regular steel MRF frames, varying from 4 to 20 stories in height are designed based on DDBD approach and utilizing displacement design spectrum of the Iranian... 

Heavy damage developed from near field earthquake in resent years cause serious attention to this problem. Investigation shows that these records include large energy pulse, unlike far field earthquake. Overall effect of near field earthquakes ignored in the most building codes. The purpose of this investigation to find effect of near field earthquake on reinforced concrete moment frames. To achieve this goal Erduran damage index is efficient way to calculate damage. Two 4th and 8th story reinforcement concrete moment frame buildinges with moderate and high ductility designed by strength criterion. Seven pairs of near field earthquakes and seven pairs of far field earthquakes scaled and use... 

Concrete has long been considered by engineers as one of the most used constructional materials. Therefore, recognition of mechanical behavior of concrete materials is of particular importance. So, extensive studies have been undertaken to understand and analyze its behavior under different loading conditions. Based on these studies, many models for describing the behavior of concrete are presented. Of these, many models are based on the combination of plastic theory and damage mechanics, and by using them, significant success has been achieved in the correct modeling of concrete materials. On the other hand, one of the important loading conditions encountered by concrete structures is in... 

Although the moment frame can show deformable behavior against seismic loads, but its flexibility and low stiffness, especially in tall structures, cause the governance criterion to be designed. The use of eccentrically braced frames was able to solve the displacement problem to some extent, because it has the characteristics of both flexural frame systems and conccentric bracing. Different methods have been proposed to eliminate residual displacements in this type of system, one of which is the use of post tensioned cables. The aim of this study was to investigate the seismic behavior of a steel structure with a eccentrically braced frame system with post tension cable.The cables are anchor... 

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... 

The seismic performance of a low-rise nonductile reinforced concrete (RC) building rehabilitated using eccentric steel bracing is investigated. At first three-story building was Modeled using sap 2000 computer program then analyzed and getting the results. The effectiveness of the eccentric steel bracing in rehabilitating the building was examined. The effect of distributing the steel bracing over the height of the RC frame on the seismic performance of the rehabilitated building was studied. The behavior of the nonductile RC frame members is represented by a beam–column element capable of modeling the strength deterioration and the effect of the axial force on the yield moment and the... 

Actin filaments are the most abundant component of the cellular cytoskeleton and provide shape for the most eukaryotic cells. Actin constitutes 1-10% of the total protein in most cells and is present at even higher concentrations in muscle cells. The functions of actin are directly connected to its mechanical properties, therefore both experimental and computational understanding of the mechanical properties of actin filaments are essential to elucidate their functions in cells and muscles. Actin exists in two forms, actin monomers (G-actin) and actin filaments (F-actin), which have continuous polymerization and depolymerization processes. In the polymerization process, different... 

This thesis investigates the performance of concentrically braced frames through numerical simulation approaches. During a moderate to severe earthquake, the bracing members and their connections are expected to undergo significant inelastic deformations into the post-buckling range. Recently, provisions for special concentrically braced frames (SCBFs) were developed to exhibit stable and ductile behavior in the event of a major earthquake. Special Concentrically Braced Frames (SCBFs) are distinguished from Ordinary Braced Frames in that they possess improved post-buckling capacity. Performance based evaluation of SCBF system as well as ordinary concentrically braced frame (OCBF) system... 

The use of unbonded post-tensioned precast concrete walls with horizontal joints as the primary lateral load resisting system in seismic zones has been considered in several previous studies. These walls are constructed by post-tensioning precast wall panels across horizontal joints using post-tensioning steel which is not bonded to the concrete. The behavior of the unbounded post-tensioned precast structural wall under lateral loads strongly depends on base panel geometry and concrete confinement properties. In this research an analytical parametric investigation on base panel design parameters is conducted using DRAIN-2DX software. Fiber beam-column elements are used to represent the... 

This study presents a modified Microplane model in two-dimensional space which is capable of modeling anisotropic materials accurately. The main idea of Microplane model is to write constitutive equations in terms of vectors rather than tensors. Material constitutive laws are written for planes of every possible orientation to calculate the response of each plane to a given loading. Then the results of all the planes, called microplanes, are added up using Principle of Virtual Work (PVW) to form together the macroscopic response of the material. Microplane model with kinematic constraint is used in this study. Kinematic constraint states that microscopic (local) strain vector acting on each... 

In concrete which is a quasi-brittle material failure initially occurs between aggregate and mortars. Fibers of all orientations, randomly embedded in FRC, serve to restrict and delay the coalescence of micro-cracks, micro-voids and micro-slips into wide continuous cracks. While the fibers increase the uniaxial tensile and compressive strength only moderately, they are very effective for enhancing the ductility and energy absorption capability. This elevates structure resistance to impact, ground-shock and blast. One of the most successful efforts toward reaching a macroscopic model which can take micromechanical properties into account is the Microplane model. In this microscopic... 

In recent years, composite systems comprised of reinforced concrete columns and steel beams, have taken consideration. This system took its own advantages both from steel and concrete systems. Joints of this system categorized into through-beam-type and through-column-type. In this research, after reviewing past studies, two kinds of the joints were modeled in ABAQUS finite element program and seismic performance of these two joints were evaluated. These two selected joints were tested by Chin-Tun Chen and Cheng-Chih Chen ( ) and also Hiroshi Kuramoto and Isao Nishiyama ( ). After verifying the finite element model with the experimental studies, a parametric study were conducted on the steel... 

In the 1994 Northridge earthquake, connections in the resistant steel moment frames sustained unexpected brittle fractures in the beam to column connection region. One of the strategies to decrease the vulnerability of connections is reducing the beam section in a region, near the column face. Because to reach the plastic hinge in this region and decrease deformation in other region, like beam end, panel zone and columns. Reducing in beam section is caused some differences in seismic performance of steel frame. Although extensive numerical and experimental studies have conducted on this type of connection but limited studies have performed on the moment frame with reduced beam section... 

Light cold formed steel structures have a wide use in building constructions and industrial projects due to their economical advantages, rapid erection and installation and capability for industrial mass production. The main objective of this thesis is to investigate the seismic behavior and to study the seismic requirements for design of Light steel frames (LSF) structures. The cold forming technique, and the basic concepts of cold formed steel members design have been investigated and the basic concepts of seismic design of light cold formed steel structures is discussed. In order to investigate the performance of steel strap framed wall systems and estimate its response modification... 

Concrete as a heterogeneous, quasibrittle and practical material has always been a challenging material for modeling. Although numerous models have been proposed since now, many of them have some deficits. Microplane is a multiscale model which introduces some micro-planes as interaction planes between concete and aggregates. To generate concrete behavior, stress-strain relations are established on these micro-planes. In the present study, two prominent microplane models, M2 and M4, has been used in 2D and 3D Finite element framework. M2 model has been applied and developed to produce FRC behavior for uniaxial tension and compression under static and cyclic loading. To better optimize M2... 

Concrete structures may become weak and damage due to different reasons and need retrofitting or strengthening. Strengthening means increasing strength and resistance of members that injured to resist the design loads. The weakness of these structures may due to change in the design code provisions, administrative error, change in the usage of the building and damage caused by different events. In the last decade substantial research has been conducted on this field most of which were on the upgrading of RC beams under different loading. There are few studies in strengthening works of RC beams under static loads of torsion. Most researchers in this field have been used polymer fibers to... 

Composite Reinforced Concrete-Steel (RCS) frames which have reinforced concrete columns and steel beams attracted a lot of attention in recent years. They take advantage from the benefits of both reinforced concrete and steel frames thorough using the optimum combination of concrete and steel structural elements. In this research six structures including three 3-story, and three 6-story buildings are designed in a region with very high seismicity risk. These structures include composite RCS moment frames, special steel moment frames, and reinforced concrete special moment frames. RCS moment frames which are designed they not only have reinforced concrete columns similar to reinforced... 

These days steel frames are among the most widespread structural systems, and apart from this, tendency for using slender members in these frames, shows the need for study of effects of axial force and in other words stability of the structure and its members. When secondary effects due to axial gravity forces which results in lateral displacement of the structure come in action, they will reduce strength significantly; as a consequent ductility demand with raise. If this decreased strength exceeds the existing redundant strength, displacements will increase significantly and cause instability of the structure and its collapse. AISC 360-10 has introduced 3 methods for analyzing stability of... 

Composite systems consisting of concrete columns and steel beams are introduces as structural systems in recent years. These structural systems enjoy merits of both steel and concrete frames by efficiently combining the advantages of them. This study is allocated to lateral force resistance system using armed concrete and structural steel. Advantages of composite structures rather to those of two other conventional ones are among performance characteristics under ultimate loads, economical conservation, and higher speed of construction.In this research the aim is to study these frame under earthquake induced loads. The seismic performances of these composite frames with through column beams,... 

The use of steel as one of the most widely used materials in the construction of structures is accompanied by problems and among them the problem of establishing stability in structure is important. To provide stability in the structure as a whole and for each of its elements, the new edition of the American Specification for Structural Steel Buildings, has introduced three general methods based on the elastic analysis. It includes, direct analysis method, effective length method and first-order analysis method. Each method has advantages and disadvantages. The present study is divided into two parts. The first part gives an overview of the behavior of structures and methods of determining...