Sharif Digital Repository

In this thesis, finite element (FE) models were developed to study hysteresis behavior of pipe braces subjected to cyclic loading. Thus steel braces previously tested by other investigators are used. The results of the analysis are in good agreement with the experiments. Besides, the FE analysis could also simulate both the overall and local buckling. As a result, a sharp growth in plastic strains is followed by geometric changes at the mid-span due to local buckling. The sharp growth of plastic strains is entitled as strain rises. In fact, the local buckling triggers rupture of braces at the mid-span. The local buckling initiation is identified by the sharp growth in plastic strains.... 

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... 

Bracing Systems are usually a set of inclined members that are embedded in structures to resist lateral forces and control lateral displacements. There are different types and behaviors for Bracing Systems depending on the way of assembling and locating them in the structure. Braced Frames, such as Concentrically Braced Frames (CBFs), generally have high stiffness and low ductility. Another Type of Braced Frames is Eccentrically Braced Frames (EBFs) which improves CBFs by establishing suitable ductility as well as stiffness. Inelastic behavior of Links involved with EBFs caused this in EBFs. Nevertheless, these systems have no efficiency in next earthquake, because links are parts of beams... 

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... 

In this Thesis Project the Behavior of Multi-story Steel Frames Equipped with Yielding elements has been investigated and analyzed. These elements act against severe earthquakes like fuse and cause dissipation in main part of input energy of structure. The position of these elements are at the cross point of braces. The most advantages of yielding elements in steel frames are ease to use and ability to replace after earthquake The main idea in this research is the effect of number of stories in buildings which are equipped with yielding elements.3,7 and 10-story steel frames with 3 bays and 15,20 and 25-story steel frames with 5 bays are the models for this investigation. At the first part... 

This research discusses the delay in strengthening projects by shear wall and steel bracing. It studied importance of causes and effects of delay in such projects. Forty-four causes were identified and classified by source into nine groups. Eleven negative effects of delay were known in this research. A field survey was conducted through a structured questionnaire including 22 owners, 40 contractors, 40 university's professors who have a PhD degree in structural or earthquake engineering, 35 consultant engineers, and 37 supervisor engineers in Mazandaran and Tehran. Relative Importance Index technique ... 

In this study, HSS and double angle braces subjected to cyclic loading in order to study the buckling and post buckling behavior have been investigated by Finite Element method. The results of FE analysis are fairly in good agreement with experiments. Analysis demonstrate that when local buckling occurs in middle span, subsequently, strain rises severely. Accordingly, this strain jumping causes early fracture in braces. Therefore, local buckling can be one of the primary reasons of fracture in braces. As a result, local buckling must be considered one of the primary limit state of Performance-Based design of steel braces. In addition, finding a way to predict local buckling can help us to... 

In this Thesis, the behaviour of stell brace was studied in finite element models. In this section, a comparison between the results of these models and the results of experimental models which were done in past years, was carried out. It shows that these result is in good agreement with each other, Moreover it has been found that the primary cause of failure in the sample is local bucking and then change in the geometry of sample which will be followed by strain jumping in next cycles which shows the importance of local buckling due to the proximity of this event to strain jumps and can be accepted as braces limit state design.Finally, we try to predict the time of failure of samples with... 

In this study the behavior of steel bracings under cyclic loading, is modeled with finite element method. Analysis have shown that after local buckling in plastic mid-span position, due to the severe geometry change, the strain grows rapidly, The sharp growth of plastic strains is entitled as strain rises. Geometry change created will cause the collapse brace speeding up. In fact, the main local buckling can be used as a determinative factor in performance base design for steel braces. So the thesis has been investigated, using the parameters fracture life to quantify local buckling and fracture. Also with using the CVGM model, the fracture of the brace could be predicted. The analytical... 

This study examines the safety and economics concerns in seismic design of column splices in steel concentrically braced frames. The importance of column splices in steel frames is that in structures with high columns, due to the limited length of existing profiles or economic issues, we have to use column splices. Error in the design and implementation of the column splice can affect the stability and overall performance of the structure. In this regard, the Seismic Provisions for Structural Steel Buildings has provided rules for designing column splices in the braced frame. The purpose of this research is to evaluate the criteria presented in the regulation and obtain seismic demand and... 

Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced concrete frames subjected to lateral loads. These braces may develop High axial tension forces, and transferring them appropriately to the existing beam– Column joints is a key challenge. This paper investigates a solution for connecting the end-plate of the steel brace with the frame, using shear-key plates fixed to the concrete with anchor bolts, and a low friction material inserted between the end-plates and the shear-key plates. The presence of the low friction material impedes the development of tension forces in the anchor bolts and ensures that they are basically subjected to shear forces.... 

Studying the performance of irregular structures in past earthquakes reveals that due to their severe vulnerability, we need to accurately assess the behavioral characteristics of such structures. On the other hand, all existing seismic codes recommend the use of response modification factor to determine the base shear, design forces of the members, and the design drift ratios, which seem to have limited comprehensiveness. Moreover, the response modification factor for a structural system is discussed in a general manner and the effect of factors such as number of bays, number of stories, span length, story height and irregularities are not considered. In this research, the effects of... 

The response modification factor (coefficient of behavior) of structures (R) is a parameter that is used during their design using the linear static analysis method to account for the effects of the non-linear response of the structure considered. Therefore, the existing seismic codes consider it necessary to use the R factor during the design process. In addition, for each family of structural systems, the Codes propose a specific R factor in a very general manner. In this project, an effort has been made to obtain and propose a correct, relatively accurate, and logical coefficient of behavior for two-dimensional steel frames equipped with a special type of bracing. In this regard, the... 

In recent years, due to urban expansion and population growth, number of floors and excavations depth has increased. Stabilization of excavations is one of the most important issues in geotechnical engineering. Today, one of the most widely used methods that is used in deep excavations is brace soil by steels and pretension them. In this thesis tries to evaluate static behavior of flexible supporting structures with pretension anchors by using PLAXIS2D, FLAC3D and GEOSTUDIO softwares. The objective of this modeling is better understanding the static behavior of walls, comparing the two and three dimensional modeling and the effect of corners of excavation on deformation. The results shows... 

In this thesis, the behavior of cold-form steel (CFS) frames equipped with various configurations of steel sheathing and K-shaped braces is experimentally investigated. Low lateral resistance is the main deficiency of the CFS shear walls. Despite their advantages, such as being lightweight, ease of fabrication, and an environmentally friendly system, their lack of adequate lateral strength prevents engineers from widely using them, especially in areas with medium to high seismicity or in mid-rise buildings. In this regard, a total of seven full-scale specimens with different configurations of steel sheathing and k-braced, with and without cladding, were tested to investigate their seismic...