Investigation of progressive rupture in braced steel frames based on Iran's seismic design criteria

Dissertation

Master's degree

Department: Civil Engineering, Structural Orientation

Abstract

One of the phenomena that can occur during the design, implementation and operation of buildings is the phenomenon of progressive rupture. This phenomenon is defined as the spread of failure in a structure from one element to another so that it eventually leads to the failure of the entire structure and a major part of it. One of the methods to evaluate the potential of progressive rupture is the APM method, which is done through the column removal scenario and directly by removing one or more columns. In this study, progressive rupture in steel frames designed according to Iran's seismic design criteria has been investigated. For this purpose, the progressive rupture potential of three steel buildings with double bracing system and bending frame of 4, 8 and 10 floors was studied with the help of ABAQUS finite element software using APM method. The results show that the columns that are connected to the removed column through the beam have the largest share in the redistribution of the forces in the structure, and in the meantime, the effect of the adjacent columns is more compared to other columns, and it is considered that the presence of excess capacity in the columns that are located in the vicinity of the column plays a very important role in preventing progressive failure. Bending - Abnormal loads

Chapter one:

Introduction and generalities

Research

Introduction

Since the first time the term progressive rupture[1] entered the structural design literature, not more than 50 years have passed. In this half century, three big events have caused engineers to pay attention to this type of damage. In the first incident that happened in 1968, an entire opening of Ronan's apartment building was destroyed. In the second incident, the P. Morera Federal Building suffered massive destruction due to a bomb explosion in 1995, and the last incident occurred on September 11, 2001, during which the two northern and southern towers of the World Trade Center in New York were completely destroyed due to the collision of two planes. These three events may seem different at first glance, but in fact, all three have one similarity, and that is that, in general, the removal of one or more primary members has led to the destruction of all or a large part of the structure [1]. The collapses and damages that have occurred in buildings in recent years have highlighted the issue of progressive rupture. In fact, in this type of rupture, which is also called disproportionate rupture, the ratio of initial damage to final damage is high, and local damage in the structure can lead to progressive damage in the entire structure or a large part of it. Various factors can cause local damage and eventually progressive rupture in structures. The most important of these factors are design or construction errors, fires, explosions, accidental overloads, vehicle accidents, bomb explosions, etc. During this half century, various regulations and standards tried to cover this issue, but most of them were satisfied with expressing qualitative expressions and provided less practical solutions. In recent years, two institutes have tried to provide methods for resistant design in progressive upheaval, these two institutes prepared standards under the title of GSA [2] and DOD [3], which were welcomed by engineers [2 and 3].

Structural safety has always been a key issue for engineers in the design of civil engineering projects. Progressive destruction is a relatively rare event in which unconventional loads cause local damage and the structure spreads the damage due to the lack of continuity, ductility and uncertainty. If the structure has the necessary continuity and ductility against the expansion of progressive rupture, only local failure can occur, but otherwise, the progressive rupture is general and can include the entire structure. In many cases where progressive rupture has spread, it has been observed that the loss of life that occurs during the phenomenon of progressive rupture is much more than the casualties that occur during the application of the initial abnormal load to the structure [4]. The weakness of structural research in the country is noticeable.. The importance of this issue doubles due to the poor quality of construction of most buildings and the use of old construction methods in Iran. Looking at the history of collapses and sudden failures of important and high-ranking structures around the world, it can be seen that the cause of the destruction of many of them was the partial failure of a part of the structure due to an accident such as explosion, overloading, collision of air and ground vehicles and its spread to the entire structure. The interesting thing to note is that all these collapses have one thing in common, and that is that in all of them, a part of the structure was subjected to a type of loading that could not be predicted by the structural designer at the design stage. The repetition of these almost similar collapses made the design engineers look at such collapses as one of the design concerns and try to consider them in the structure design process. In this regard, extensive research has been conducted by structural researchers in the world and its results have been presented in the form of guidelines and regulations in industrialized countries. On the other hand, due to technological advances, the science of structural engineering is progressing and expanding at a high speed, which results in lighter, more durable buildings and more complex architecture than before. On the other hand, the existence of computers has made it possible to analyze structures with appropriate approximations to reality. In modern regulations, there is a constant attempt to reduce the margin of confidence and, as a result, the additional strength required during the life of the structure. While this development can have many advantages, including the economic issues of projects, it will also bring disadvantages. Among other things, due to the longer life of the structure, it has become more difficult for the design engineer to predict the operating conditions or possible accidents during its life. This is where the rapid development of technology has become a factor against the assurance of the design engineer.

The possibility that buildings will be exposed to natural or man-made threats during their lifetime is very high. Engineering knowledge about the threats of natural phenomena such as wind, earthquake, etc. And how these phenomena affect buildings, as well as the reaction of structural and non-structural elements of buildings against these phenomena has been expanded. On the other hand, during the increasing man-made threats, especially in recent decades, different countries have faced terror attacks and extensive urban wars, and in most cases, explosions have caused the destruction of buildings or high casualties. Therefore, the officials in many countries decided to pay attention to the research to formulate the rules for the design of buildings under such explosions. On the other hand, due to the fact that the performance of the structures during the period of use is very important, it is necessary to investigate the behavior of the structures under the effect of unusual loads such as vehicle collisions, explosions, implementation and design errors. . Meanwhile, the use of braced steel buildings is very common. The evaluation of the behavior of these structures against the lateral forces caused by the earthquake has been evaluated. Due to the great importance of progressive rupture and the resulting losses in buildings, the need to accurately evaluate the behavior of these structures against progressive rupture is felt. Therefore, in this research, the investigation of progressive rupture in braced steel frames based on the seismic design criteria of Iran is addressed. 1-3- An overview of incidents leading to progressive rupture. The progressive changes that have occurred in the last few decades will be investigated and pointed out, and the factors causing them will be explained.  

1-3-1-Progressive rupture in Ronan Point building

It can be said that the history of progressive rupture problem as an engineering problem has its roots in the demolition of Ronan Point building in 1968 in the east of London. Ronan Point was a new 22-story building consisting of prefabricated load-bearing panels bolted together. Shortly after the residents settled in the building, due to the natural gas explosion on the 18th floor, only one of the load-bearing wall panels on that floor was destroyed. This destruction led to the loss of the support of the roof above it and subsequently caused the upper ceilings to fall on the floors of the lower floors in the form of a progressive destruction and continued to the lower level of the building. This incident led to important changes in the construction laws of England.