Progressive Collapse of Buildings
Presentation for Seminar in 3rd Semester By:- Manthan Shah (140080720012) B.V.M ENGINEERING COLLEGE, Vallabh Vidyanagar
Back Ground •
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On May 16, 1968, in Newham, east London, Ivy Hodge a tenant on the 18th floor of the 22-story Ronan Point apartment, struck a match in her kitchen. The match set off a gas explosion that knocked out load-bearing precast concrete panels near the corner of the building. The loss of support at the 18th floor caused the floors above to collapse. The impact of these collapsing floors set off a chain reaction of collapses all the way to the ground. The corner bay of the building collapsed from top to bottom. Mrs. Hodge survived but four others died.
What it is...! • • •
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This was not a largest building disaster, but the magnitude of the collapse was completely out of proportion to the triggering event. This type of sequential, domino-effect failure was labelled “progressive Collapse.” This term is used to describe the spread of an initial local failure in a manner analogous to a chain reaction that leads to partial or total collapse of a building. In progressive Collapse, the final state of failure is disproportionately greater than the failure that initiated the collapse. In general, the total damage to a building due to abnormal loading event may be in proportion to the local damage caused by event or may be disproportionate to it. If the total damage is highly disproportionate to the local damage, it may lead to a Progressive Collapse.
What it is...! •
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The disproportionate refers to the situation in which failure of one member causes a major collapse, with a magnitude disproportionate to the initial event. Thus, “progressive collapse” is an incremental type of failure wherein the total damage is out of proportion to the initial cause. Progressive collapse is a catastrophic structural phenomenon that can occur because of human-made and natural hazards. It is similar to successive fall of cycles, in a cycle stand, when the first one is pushed. There are number of cases of progressive collapse of buildings during construction also.
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Generally, buildings are not designed for gas explosions, bomb explosions, vehicular collisions, aircraft collisions, tornados etc. Thus, when buildings are subjected to such abnormal loads, they may sustain extensive damage. Hence a designer should ensure safety at two levels, at “local level” and at “global level”. The local level safety can be ensured by designing the key structural elements for abnormal loads, whereas global level safety can be ensured by providing alternate load path in the structural system. Examples of man made progressive collapse:
Definitions • •
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Progressive collapse can be defined as collapse of all or a large part of a structure collapsed by failure or damage of a relatively small part of it. The General Services Administration (GSA, 2003b) offers a specific description of the phenomenon: “Progressive collapse is a situation where local failure of a primary structural component leads to the collapse of adjoining members which, in turn, leads to additional collapse.” Based on ASCE 2005: progressive collapse is: “The spread of local damage, from an initiating event, from element to element resulting, eventually, in the collapse of an entire structure or a disproportionately large part of it; also known as disproportionate collapse.” Progressive collapse can simulated to the collapse of the Card House.
Causes of Progressive Collapse • • •
Progressive collapse of the building generally occurs under the abnormal loads. Abnormal loads usually act over a relatively short period of time in comparison with ordinary design loads. The potential abnormal loads that can trigger the progressive collapse can be categorized as: Uncontrolled Fire Pressure Loads • Internal gas explosions • Blast • Wind over pressure • Extreme values of environmental loads
Causes of Progressive Collapse Impact Loads • Aircraft impact • Vehicular collision • Earthquake • Design and construction errors • Overload due to occupant misuse • Storage of hazardous materials
The Mechanism •
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Progressive collapse occurs when a structure has its loading pattern or boundary conditions changed such that structural elements are loaded beyond their capacity and fail. Progressive collapse of building structures is initiated when one or more vertical load carrying members (typically columns) are collapsed. Once a column is failed the building's weight (gravity load) transfers to neighbouring members in the structure. If these members are not properly designed to resist and redistribute the additional load that part of the structure fails. The vertical load carrying elements of the structure continue to fail until the additional loading is stabilized. As a result, a substantial part of the structure may collapse, causing greater damage to the structure than the initial impact as Shown in Figure.
The Mechanism
Progressive Collapse Mechanism of Building Collapse Due to Blast Load with Mechanism
Types of Progressive Collapse •
There are six different types of progressive collapse with different types of mechanisms. 1. Pancake-type collapse 2. Zipper type collapse 3. Domino Type Collapse 4. Section type collapse 5. Instability type collapse 6. Mixed type collapse
Methods of Prevention •
In general, there are three alternative approaches to designing structures to reduce susceptibility to disproportionate collapse: 1. Redundancy or alternate load paths • In this approach, the structure is designed such that if any one component fails, alternate paths are available for the load in that component, preventing a general collapse from occurring. • In its most common application, design for redundancy requires that a building structure be able to tolerate loss of any one column without collapse. 2. Local resistance • Designing particular members for higher loads. • In this approach, critical components that are potential subjects for attack and that are susceptible to progressive or disproportionate collapse are provided with additional resistance.
Methods of Prevention 3.
Interconnection or continuity • This approach is a improvisation of the previous ones where, the connections are provided more attention. • Studies of recent building collapses show that failure could have been avoided or at least reduced in scale at little additional cost if structural components had been interconnected more effectively.
Design to Resist Progressive Collapse •
The two most frequently used design approaches intended to address the issue of progressive collapse are: 1. Providing tying capacity • This ensures that beams, columns, connections and floor can act together to provide a specified minimum level of horizontal tying resistance. • The elements are designed with some more attention to provide tying and interconnection. 2. Checking alternate load paths • It presumes the instantaneous loss of a single column and then requires that the load is carried by an alternate paths. • These alternate paths should be analysed in advance.
Some Rendered Models From Physics Simulations by Mody Motion on YouTube.com
References • • • • •
Progressive Collapse Basics; by R. Shankar Nair, Ph.D., P. E., S. E. Best Practices for Reducing the Potential for Progressive Collapse in Buildings; US Design of Building Structures to Improve their Resistance to Progressive Collapse; D A Nethercot PROGRESSIVE COLLAPSE ANALYSIS OF R.C. BUILDINGS; By Digesh D. Joshi a dissertation thesis https://www.youtube.com/channel/UCdiTXx3e55HrQepgWj2Tt3w
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