Master's thesis in the field of civil engineering, structural orientation
February 1389
Chapter one: Introduction
1-1. General
One of the most important natural events that has always changed people's lives and sometimes destroyed human civilizations by destroying buildings is earthquake. Therefore, humans have always tried to identify and deal with the dangers caused by earthquakes and still have not succeeded in fully controlling this huge energy. Now, even though many researchers have conducted valuable research in the field of safe and appropriate construction, a large number of inhabitants of this earth are still buried under the debris caused by earthquakes every year, and many structures lose their efficiency after the earthquake or collapse. Scientific documentary and observations of the 20th century, it is considered one of the most dangerous regions of the world due to powerful earthquakes. Currently, Iran is at the top of the countries where earthquakes are associated with high casualties, and in recent years, on average, an earthquake has occurred every five years with very high casualties and financial losses in some part of the country. Although it is very difficult to completely prevent damages caused by severe earthquakes, but with the increase in the level of information regarding the country's seismicity, identification and detailed study of the situation. The vulnerability of buildings, their correct and principled safety and strengthening, can reduce losses and damages caused by future earthquakes as much as possible.]1 [
In order to identify and control this phenomenon, researchers have always tried to prepare many regulations around the world for the calculation and construction of earthquake-resistant structures, and many methods for Calculate this force and design structures against it. After calculating the earthquake force, there are methods for designing an earthquake-resistant building, and these methods can be divided into two classical (traditional) and modern categories.
In classical methods, the design is based on the maximum force applied to the building, which is obtained by combining the possible forces stated in various regulations. Each and every component of the structure is designed based on the ultimate strength or maximum force method. But in modern methods, the stability of the structure has also been proposed with the design method based on performance.]2 [
In the system Structural design is usually two very important factors for designers. The first is the safety of the structure and the second is the comfort of the residents against external loads such as wind and earthquakes. To achieve this goal, two factors of displacement and absolute acceleration are effective and must be controlled. In this regard, various systems have been presented that generally change the behavior of the structure in such a way that the incoming energy of the earthquake does not damage the main components of the structure. Due to the fact that non-earthquake-resistant structures are found in our country and due to the fact that the use of additional systems reduces the dynamic response of structures in a very favorable way, therefore, the use of these systems is important in our country. Various factors such as the effect of wind and waves and the movement of cars, without a doubt, one of the types of these dynamic loads that have been most important for structural engineers is the stimulation caused by earthquakes. Of course, the importance of the earthquake issue is partly due to the damage that an earthquake causes in a densely populated area. Since the design of economic structures with various architectures and dimensions that can withstand the forces of a strong earthquake requires a high ability in the art and science of engineering, it seems logical that the field of earthquake engineering as a framework in which the theories and techniques presented in the dynamics of structures andIt will be displayed and used.
The ability of conventional methods of designing and building existing structures is very limited and does not meet the ever-increasing needs of designing new structures. For example, increasing the height of buildings due to the lack of land in big cities and meeting the needs of new architecture with unusual forms are among the problems that show the need for new technologies in construction in our country.
1-2. Necessity of conducting the present research
Different structural systems have been used to deal with the lateral forces caused by earthquakes in steel buildings, which can be referred to as the frame system. Resistant bending, converged harness system and system Divergent braced pointed out. Each of these systems, in turn, has its own merits and demerits, which has been the subject of earthquake engineering research in recent years.
In Iran, the use of convergent bracing systems is very common among structural engineers. Therefore, addressing this issue and stating the disadvantages of these systems and providing practical solutions in the field of eliminating these disadvantages can be of great help in the development of Iran's construction industry in order to make buildings safer. One of the types of convergent brace systems is the buckling resistant brace system or BRB for short This system is one of the most powerful systems in the field of controlling the adverse vibrations of structures against lateral forces, and today in most parts of the world, this system is widely used to dissipate the energy caused by earthquakes.
In this type of braces, the purpose of the brace is to reach the yield point under axial compressive load by preventing the buckling of the member, which is done by an external mechanism. It can be Therefore, the brace will yield both in tension and compression without buckling. Also, since the buckling of braces is not desirable for energy consumption, this system, which has elasto-plastic behavior, is very effective in consuming earthquake energy.]3 [
In the present research, studies have been conducted on buckling-resistant braces as a system resistant to the forces caused by earthquakes. Since the installation of earthquake-resistant systems from the point of view of economy and making them more resistant helps the proper behavior of the structure against dynamic loads, research on these systems is of great importance. The side forces show they give In addition to these advantages, a series of disadvantages have been stated for these braces, which are mentioned below:
The construction of BRB braces is somewhat complicated and expensive and requires modern technology.
Due to the complexity of the construction, the production of BRB braces is the monopoly of certain companies.
If steel with a wide yield range is used as the core of the section, additional forces will be added to the structure. will be applied.]3[
1-3. Research Objectives
The main objective of this study is to research a type of buckling-resistant brace with a new design, which eliminates the disadvantages mentioned for BRB braces in this design. The design of this brace is actually derived from the shape of the buckling-resistant brace proposed by Sridhara[2]. [16] The new brace has a simple manufacturing technology and does not require complex manufacturing technologies. Also, with the modifications considered, this new brace will maintain the stability of the structure more than the current brace in more severe earthquakes. Also, the carrying capacity of the used materials will be used more than the existing models.
In this design, the cross section core is made of thin wall steel The sheath is also designed in such a way that in severe earthquakes, when the reduction in length caused by the compressive force in the core exceeds a certain limit, the section of the sheath can withstand a percentage of the compressive forces of the core as an auxiliary compressive member.