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... 

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... 

Regarding the numerous casualties and financial losses due to intense earthquakes, the ductility is considered of the main importance in addition to stability, stiffness, and strength criteria of the structure’s connections. In order to enhance the seismic behavior of the structures in such severe earthquakes, design codes for steel structures have suggested special types of connections. Among them, bolted end plate connection is considered a conventional type of connection used for creating ductile semi-rigid connection.In this study, in order to simulate the behavior of this joint, a 3-D finite element model is developed in Abaqus software, in which the inelastic behavior of the materials... 

Progressive collapse in the structures can be happened as a result of many events such as terrorist attack, planes or vehicle collision to the structures and etc. Researchers’ attention to this phenomenon after occurring progressive collapse in Ronan Point building attracted and by happening terroristic attacks in Alfred P. Murrah and WTC buildings, studies in this field has developed extensively, meanwhile some of the codes, including UFC 4-023-03 or GSA, have proposed general instructions and analytical methods for increasing the strength of the structure against progressive collapse. If the structure in this analysis, does not meet the acceptance criteria of the code, the structure must... 

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... 

In this thesis the performance of anew energy dissipative device, slit steel damper (SSD) is investigated. The slit steel damper is manufactured with I-shaped, wide flange H-shaped profiles with a number of slits cut from the web. The device is installed between beam and chevron brace and fastened by four bolts on each side, which enables the replacement of the device due to strong earthquake.A numerical study is conducted to studythe nonlinear behavior of the SSD systems by using a nonlinear FE program. It is found that the numerical modeling results have a good agreement with the existing test results.In the next step a parametric study is performed to study the effects of the number of... 

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... 

Fiber Reinforced Polymer (FRP) tendons are suitable to be used in concrete beams exposed to aggressive environments. This study proceeds the design and it presents the flexural capacity (in relation to the moment-curvature) for composite sections (reinforced with steel bars and pre-stressed FRP) rectangular, T-section which has been bent and broken. The failure is in attending with strain softening, stress hardening of fiber reinforced concrete (FRC) and reinforcing with steel bars and polymer. Using the predicted moment-curvature relationship, a numerical method is used to estimate the load deflection response at sample beams under concentrated and uniform loads. A parametric study will be... 

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... 

This study deals with the monotonic behavior of reinforced concrete membranes. In the first step, small reinforced concrete membrane panels were studied. Examining the available test results on reinforced concrete panels, a new set of stress-strain relations for normal strength concrete and mild steel bars embedded in concrete. The salient features of the proposed constitutive laws are: 1) considering the effect of reinforcement ratio on average stress-strain relationships of cracked concrete; and 2) considering the gradual reduction of average stiffness of steel bars embedded in concrete. Equilibrium, compatibility, and constitutive relationships were incorporated into an algorithm to... 

Cold-formed steel sections are lightweight materials and suitable for building construction owing to their high structural performance. Conventionally, they are used as purlins and side rails in the building envelopes of industrial buildings. The most common sections are lipped C and Z sections, and the thickness typically ranges from 1.2 to 3.2 mm, and sections with yield strengths at 280, 350 and 450 MPa are commonly available. For connection design, codes of practice for design of cold-formed steel structures only provide design rules for the load carrying capacities of individual fastenings with bolts, screws and welds while no guidance on the structural behavior of connectors such as... 

Grillage structures are used at roofs of some buildings and community halls and shopping centers and airports, or structures that used as bowers. The grillages is constructed with steel or concrete beams. In most of the carried out Researchs the twisting effect on these structures has been ignored. In this research the behavior of such structures with considering regulation and softwares limits by some simple programable assumptions is simulated. So with using MATLAB software a program extracted for grillages nonlinear analysis and its results was compared with common engineering software. In This approach in addition to pure bending, bending – torsion interaction is considered too and I... 

Because of mistakes in the design and calculation, incoherence between construction and design, structural changes, changes in loads and also damages caused by the passage of the time, concrete structures need to be improved and strengthened. Polymeric sheets reinforced by fibers (FRP), according to their appropriate characteristic, are more efficient for strengthening concrete structures. Most studies on confined columns refers to confined RC columns with FRP and less mentioned about prestressed columns. In this study, the behavior of prestressed columns is analyzed by modeling a case of prestressed column in a nonlinear analysis software. Samples of confined concrete columns with CFRP and... 

Prestressed concrete structures are used all around the world widely; especially for elements which are under the effects of bending like prestressed concrete slabs. In these sorts of elements the aim of designing is to control the tensional stresses and the cracks delivering higher strength. This can improve the capabilities of the structure, architecturally and economically. Seismic design of structures is based on horizontal component of ground motions. In recent years, it has been observed that the vertical component of ground motion could be stronger than horizontal one especially for those which have happened in near field sources. In these kinds of earthquakes the importance of... 

Steel Concentrically Braced Frames are common lateral load resisting frames. Poor design of this system can lead it to premature failure of braces. This failure may be due to non-elastic buckling of brace members or their connections. Design Codes divide Concentrically Braced frames into two groups: Ordinary Concentrically Braced Frames and Special Concentrically Braced Frames and for each, specific limitations have been determined for width to thickness ration and slenderness. Many of these limitation have been obtained on the basis of experimental tests. In this thesis steel braces behavior under cyclic loading is studied. For parametric investigation, Finite Element Method is used. Abaqus... 

The purpose of this thesis is assessment of seismic performance of self-centering concentric braced frames (SC-CBF). In this structures, the column under tension can uplift from the foundation at a specified level of lateral loading and by using some methods such as post-tensioning (PT) bars or tendons, the structure is able to self-center after severe Earthquakes. In this systems, PT bars and energy dissipation elements resist column uplift. The effect of energy dissipation ratio and initial stress in PT bars was investigated in design and performance of four four-story analytical models. Nonlinear static and dynamic analyses were conducted to compare some parameters in these four models... 

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... 

Including control systems structures against lateral forces such as dynamic loads, earthquakes etc. are viscoelastic damper, that their use in recent years on the structure had positive results. Although the use of dampers improve certain behavioral characteristics, such as relative displacement, but can increase the structural acceleration and energy absorption structures. Passive damper performance depends on several factors such as temperature, time, frequency, stiffness of bracing and structures, type of loading that should any of these uncertain in the optimal design of controlled structures taken into account. Common method of achieve proper placement pattern of passive dampers, which... 

Structural system identification from vibration data is one of the most interesting research topics in the structural health monitoring area. Recently, realization and detection of the effects of damage when a structure is subjected to strong ground motion has become a great concern in earthquake and structural engineering communities. Seismic signal processing is one of the most reliable methods of detecting the structural damage during earthquakes. The structural responses during earthquakes are nonstationary with respect to both amplitude and frequency. The state-of-the-art time-frequency distributions when applied to vibration records were studied. Different methods of analysis for... 

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,...