Seismic damage distribution in steel building components with viscoelastic damper

Dissertation for obtaining a master degree

in the field of civil engineering with earthquake tendency

Abstract

Introduction of damage generators is very close to the concept of inelastic behavior and as a result hysteresis energy. Therefore, it can be said that the hysteresis energy at these levels can be a significant criterion for the design or control of the structure. The great dependence of hysteresis energy on the damage of devices has caused this concept and new methods of designing devices to be noticed by researchers and engineers.

In this research, first three steel frames of 4, 8 and 12 floors with a medium bending frame system were designed using the equivalent static method based on the first edition of the 2800 standard and by means of ETABS (Ver. 9.5.0) software, then all the frames were designed under the effect of seven field acceleration maps. Near and seven far field accelerograms have been subjected to nonlinear dynamic analysis by PERFORM3D (Ver.5) software. The purpose of this study is to investigate the distribution of damage, energy, relative displacement, roof displacement and base cutting in the examined frames. Next, the need to use the strengthening method to reduce the relative displacement is described based on the regulations, then viscoelastic dampers are used to strengthen and reduce damage in the investigated frames. The results obtained indicate that despite the uniform distribution of resistance in the height of the floors, the hysteresis and damage energy distribution diagrams do not follow this distribution and the concentration of energy and damage is observed in one or more floors. Therefore, in order to optimally use the maximum capacity of the system, it does not seem reasonable to design structures based on resistance only, and other parameters such as hysteresis energy, which play a major role in the damage of structural members, should be considered in the design process. Also, the effect of using viscoelastic dampers on reducing the damage of high-height frames has been greater, and it shows a good performance in reducing damage under near-field earthquakes.

Key words: hysteresis energy, damage, dynamic analysis, retrofitting, viscoelastic damper

Chapter 1

1-1 Introduction

annually in the world, on average 10,000 people die as a result of the earthquake (Figure (1-1)). UNESCO's studies show that the financial damage caused by earthquakes from 1926 to 1950 was about 10 billion dollars. In this period of time, two cities and 200 villages were destroyed in Central Asia. Since then, several cities including Ashgabat (1948), Agadir (1960), Esco Pih (1963), Managua (1972), Gomona and Tangshan (1976), Mexico City (1985), Spitaka (1988), Kobe (1995), cities in Turkey and Taiwan (1999) and hundreds of villages were razed to the ground due to earthquakes. Historical writings prove the long-standing concern of mankind about the dangers caused by earthquakes [1]. This is the reason why man is trying to deal with this natural phenomenon and has made significant progress in this way. However, due to the excessive complexity of this phenomenon, it has not yet been able to achieve complete safety and security, both in terms of life and material.

Nowadays, it is well known that the structures designed according to the existing regulations will suffer heavy damages against severe earthquakes. However, some earthquake design criteria (especially in the initial design of structures) are still based on elastic analysis and the use of a static force equivalent to an earthquake [2,3]. They enter the structure during an earthquake. The forces used by the earthquake depend on the elastic and plastic characteristics of the structure.

Various researches show that other parameters are also involved in the response of the earthquakes of the structures, and the discussion of force-displacement in elastic or even fully bilinear elastoplastic cannot justify all the behaviors of the earthquakes of the structure. As a result, the researchers are looking to propose a new method in the design of earthquakes of structures. In the same direction and during the last two decades, the energy issue has received a lot of attention.. Because with the progress achieved in this method, many parameters and behaviors mentioned in the seismic design of structures have found the ability to be justified and applied in the design process. Nevertheless, there are still many unknowns and shortcomings in the energy method that prevent it from being presented as a comprehensive method in the form of a reliable regulation. According to the extensive research and researches that are currently being conducted on this issue at the world level, bright futures are predicted for it, and maybe in the near future, the current principles and rules in the regulations will be replaced with the principles and rules of the energy method. which are designed by resistance method and subjected to nonlinear dynamic analysis, it can be seen that in the design based on resistance, despite the uniform distribution of resistance in the floors, this method has weaknesses and cannot be a perfect method for designing buildings, and a concentration of energy and damage is always observed in one or two floors. Studies show that examining structures based on energy concepts can better show the structure's behavior during an earthquake, so in this study, it is tried to examine the structure based on energy concepts.

When an earthquake occurs, a lot of energy enters the structure, the structure must absorb or dissipate this energy in different ways. The members of the structure enter the inelastic range against the earthquake energy, which is a significant amount, so that they can absorb this energy with their deformations. When the members of the structures enter the non-elastic range, permanent deformations occur in the structure, and in order to continue using the structure, those members that have changed their shape too much or are no longer usable should be replaced with new members or strengthened, which is difficult to implement and the cost is high. Therefore, by placing shock absorbers in the structure, these shock absorbers prevent other components of the structure from entering the inelastic range by absorbing the earthquake energy, and as a result, after the earthquake, the various components of the structure still maintain their operability, and they can be replaced or repaired only by visiting the shock absorbers if necessary.

According to the stated information, in this research, the structures to which shock absorbers have been added as a method of strengthening is paid For this purpose, by selecting a number of steel frames with a medium bending frame system that are designed based on the first edition of the 2800 standard [4], we will examine the vulnerability of these frames to earthquakes under different earthquakes in the far and near areas and based on energy concepts, and we will examine parameters such as damage to floors and frames, relative displacement of floors, shearing of the foundation and displacement of the roof, then by controlling the relative displacement values ??based on the regulations, we will explain the necessity of using the retrofitting method to reduce these values. to be For this purpose, viscoelastic dampers are used to reduce relative displacement and damage to the structure. One of the advantages of using viscoelastic dampers is that no external stimulation is needed to activate these dampers, and unlike friction dampers that cannot be activated for less than the sliding force, viscoelastic dampers work in any earthquake and waste energy, thus reducing damage to the structure.

The first chapter contains the introduction, the necessity and objectives of the research and the structure of the thesis.

In the second chapter, the concepts of energy are examined first, and then the damage indicators are introduced, and with regard to the use of dampers in order to strengthen the frames investigated in this research, the vibration controls, especially the types of passive dampers, are reviewed. Due to the use of viscoelastic damper in this research, the dynamic characteristics of this type of damper and its design method are described in detail. The third chapter introduces steel frames as well as different accelerometers of the far and near fields which are scaled according to the 2800 standard method for nonlinear dynamic analysis. Next, Perform-3D software will be introduced and at the end of the chapter, the accuracy of viscoelastic damper modeling in the above software will be examined.