Progressive Collapse Analysis of Structures

Numerical Codes and Applications

Daigoro Isobe

• Publisher: Butterworth-Heinemann
• Year: 2017
• Print ISBN: 9780128129753
• eBook ISBN: 9780128130421
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Provides a new method for analysing collapse behaviours of buildings under various scenarios, such as impact, fire, blast demolition, earthquake, and tsunami.The analysis of the vulnerability of buildings against progressive collapse is a challenging task. Progressive Collapse of Structures: Numerical Codes and Applications provides a variety of numerical analysis tools and methods which allow engineers to simulate structural collapse behavior during all stages of the process.This book covers methods such as adaptively shifted integration (ASI) and ASI-Gauss techniques. Algorithms are supplied to simulate member fracture and contact behaviors. The author also supplies various numerical examples including case studies from the World Trade Center (WTC) towers in New York City, Nuevo Leon buildings in Mexico, and the collapse of the Canterbury Television (CTV) building in New Zealand.- Discusses algorithms for simulating fracture and contact behaviors of structural members- Covers fire-induced progressive collapse analyses of high-rise towers, seismic pounding analysis of adjacent buildings, blast demolition analysis of steel-framed structures, and many more- Includes numerical codes that supply highly accurate solutions with less memory use and small computational cost

Chapter One

Introduction

Abstract

This book is aimed to introduce basic theories of a numerical code, which enable one to simulate progressive collapse behaviors of structures. Moreover, some applications of the numerical code, arranged in the order of disastrous events, are shown to help the readers understand the validity and utility of the code. The source program of the numerical code is also shown in the appendix to help students and beginners to understand the basic structure of finite-element simulations. This book can be used as a textbook for such classes as “structural analysis,” “structural mechanics,” “computational mechanics,” and so on.

Keywords

Aims and scope; Finite-element method (FEM); Progressive collapse; Simulation; Structures

1.1. Aims and Scope

Mankind has developed strong and artistic structures over many years. Unfortunately, pleasant occasions with these man-made structures are subjected to change due to natural or man-made disasters. Events such as earthquakes, tsunamis, big fire, terrorist attacks, and poor construction works are a few examples of these disasters. The main aim and scope of this book is to make a contribution to disaster reduction and mitigation. It can be achieved by simulating the collapse behaviors of structures during such disastrous events, by a low-cost, highly accurate, finite-element code which can be used in any low-configuration personal computer.

This book is particularly aimed to explain the basic theories of a numerical code, which enables one to simulate progressive collapse behaviors of structures. Moreover, some applications of the numerical code arranged in the order of disastrous events are also shown to help the readers understand the validity and utility of the code.

Chapter 2 introduces adaptively shifted integration (ASI) technique, which is a basic technique implemented in the numerical code. First, the basic beam theory and incremental finite-element formulation of a linear Timoshenko beam element utilized in this technique is described. Then, the basic theory of the original ASI technique, including a shifting technique of a numerical integration point and its relation to a stress evaluation point, is described. Furthermore, a time-integration scheme for incremental equation of motion based on the updated Lagrangian formulation, along with a formulation to analyze structures under seismic excitation, is also described.

Chapter 3 introduces an ASI-Gauss technique, which is a revised ASI technique, and a main structure utilized in the numerical code for analyzing collapse behaviors of buildings. First, a general idea to increase more accuracy than the original ASI technique is explained in this chapter. Then verification of the code was conducted by comparing the numerical results with the ones obtained by conventional finite-element method (FEM) and the original ASI technique. Furthermore, the results obtained by the ASI-Gauss code was verified and validated by a detailed analysis performed by a supercomputer and an experiment conducted using a three-dimensional shake table.

Chapter 4 introduces member fracture, contact, and contact-release algorithms which play a key role to simulate the collapse behaviors of buildings. Member fracture was considered by applying the shifting process used in the ASI and ASI-Gauss techniques, and contact and release between members were considered by adopting gap elements and their nodal displacement information to keep the computational cost lower. The member fracture algorithm, an outline of gap elements, flow of elemental contact and release, and simple numerical examples are discussed in this chapter.

Chapter 5 introduces one of the applications of the numerical code; an aircraft impact analysis of the World Trade Center tower, which simulated the events occurred during the 9/11 terrorist attacks. The simulation was conducted to examine the damage and the dynamic unloading phenomena, a so-called “spring-back phenomena,” that occurred in the core columns of the towers during impact.

Chapter 6 introduces a fire-induced progressive collapse analysis of high-rise buildings with outrigger truss systems conducted to qualitatively demonstrate the effects of fire and structural parameters on the progressive collapse behaviors of buildings. The effects of fire and structural parameters on the redundant strengths were surveyed by observing the collapse initiation time: the duration from the beginning of the fire until collapse initiation.

Chapter 7 introduces a trial to estimate the risk of progressive collapse of buildings by investigating the relation between a key element index, which indicates the contribution of a structural column to the vertical capacity of the structure, and the scale of progressive collapse. The numerical results on various models with different structural strengths indicated an increase of risk of progressive collapse as the sum of key element index values became larger.

Chapter 8 introduces a blast demolition analysis of buildings, which is another useful application of the numerical code. In this chapter, the code was verified and validated by comparing the predicted result with that of an experimental one. A demolition planning tool utilizing the key element index is also developed and the methods of selecting specific columns to efficiently demolish the whole structure are demonstrated.

Chapter 9 introduces a seismic pounding analysis of adjacent buildings, in which the phenomena are expected to occur mainly during long-period ground motion. An analysis was performed on a simulated model of the Nuevo Leon buildings of Mexico City, which consisted of three similar buildings built consecutively with narrow expansion joints between the buildings, and except one building, collapsed completely in the 1985 Mexican earthquake. It can be seen from the numerical results that the difference of natural periods between the adjacent buildings caused by previous earthquakes may have had triggered the collisions and the collapse.

Chapter 10 introduces a seismic collapse analysis of the CTV building, which collapsed during the Lyttelton aftershock on February 22, 2011, in New Zealand. The result showed its unbalanced strengths in the EW and NS directions because of its biased distribution of anti-seismic walls. Moreover, the collapse behavior was observed with a clear twist-mode vibration around the north wall complex.

Chapter 11 introduces a debris impact analysis of a steel-framed building in tsunami, which was conducted by applying seismic ground motion, fluid forces, and debris collision, continuously in a single simulation. The story drift angle of the building and the drag force applied to the building during the sequence were both investigated and compared between models with and without a wall placed under the water line.

Summaries of the developed numerical code, applications, and the future works are described in Chapter 12.

Appendix A introduces a source program of the ASI-Gauss code to help students and beginners to understand the basic structure of finite-element simulations. Only the essences of the program are shown in the appendix; however, the application files can be downloaded freely from the author's website if required.

Appendix B introduces another version of the ASI technique, which utilizes Bernoulli–Euler beam elements. Although this technique cannot be used in collapse analysis of structures, highly accurate solutions can be obtained with only one element subdivision per member in usual non-collapse analysis. Basic theories with some numerical examples of elastic and elasto-plastic analysis under static and dynamic loadings are shown in this appendix. The code can also be downloaded from the author's website.

Appendix C introduces a different type of collapse analysis, which was not carried out on buildings but on nonstructural components; the ceilings of a gymnasium. According to the numerical result, the collapse of the ceilings progressed owing to the detachment of clips that connected the ceiling joists to the ceiling joist receivers, and eventually led to a large-scale collapse.

Appendix D introduces another application besides collapse analysis of buildings—a motion behavior analysis of furniture during earthquakes. Some furniture were modeled with beam elements and the motion behavior analyses were conducted using the ASI-Gauss code with a contact algorithm based on sophisticated penalty method. The results were compared with the experimental results performed on a shake table.

1.2. Definition and Recognition of Progressive Collapse

The term progressive collapse is defined by Ellingwood et al. (2006) as “Spread of local damage, from an initiating event, from element to element resulting, eventually, in the collapse of an entire structure of a disproportionately large part of it; also known as disproportionate collapse (ASCE 7-05).” The phenomenon was first officially reported when the Ronan Point tower, London, UK, collapsed due to a gas explosion in 1968 (Ministry of Housing and Local Government, 1968). Total collapse of the World Trade Center towers during the 9/11 terrorist attacks in 2001 made the term more popular (ASCE/FEMA, 2002).

1.3. Numerical Methods to Simulate Progressive Collapse Behaviors

The progressive collapse phenomenon is, of course, very d...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• About the Author
• Preface
• Acknowledgements
• Recommendation Letter
• Chapter One. Introduction
• Chapter Two. Adaptively Shifted Integration Technique
• Chapter Three. ASI-Gauss Technique
• Chapter Four. Member-Fracture, Contact, and Contact-Release Algorithms
• Chapter Five. Aircraft-Impact Analysis of the World Trade Center Tower
• Chapter Six. Fire-induced Progressive Collapse Analysis of High-rise Buildings
• Chapter Seven. Risk Estimation for Progressive Collapse of Buildings
• Chapter Eight. Blast Demolition Analysis of Buildings
• Chapter Nine. Seismic Pounding Analysis of Adjacent Buildings
• Chapter Ten. Seismic Collapse Analysis of the CTV Building
• Chapter Eleven. Debris-Impact Analysis of Steel-Framed Building in Tsunami
• Chapter Twelve. Conclusions
• Appendix A. Source Program of the ASI-Gauss Code
• Appendix B. ASI Technique Utilizing Bernoulli–Euler Beam Elements
• Appendix C. Ceiling Collapse Analysis of a Gymnasium
• Appendix D. Motion-Behavior Analysis of Furniture During Earthquakes
• Index