Progressive+Collapse+Overview

= Progressive Collapse: Overview and Lessons Learned = toc

//Brian Brunnet, B.A.E., Penn State, 2012//

Abstract
Progressive collapse is one of the most devastating types of building failures, most often leading to costly damages, multiple injuries, and possible loss of life. Factors such as construction errors, miscommunication, poor inspections, or design flaws contribute to these progressive collapses, which have lead to many changes in building codes throughout the nation. This post provides a tentative overview of the cause and effects of progressive collapse, prevention techniques that are used today, and cites specific infamous building failure cases that were the result of progressive collapse.

Key Terms
progressive collapse, prevention, floor collapse, disproportionate collapse, domino effect

Definition
The term progressive collapse is defined as the collapse of all or a large part of a structure precipitated by damage or failure of a relatively small part of it. ("Disproportionate Collapse", Oct. 2011, 1) It is sometimes also called a disproportionate collapse, which is defined as a structural collapse disproportionate to the cause of the collapse. As the small structural element fails, it initiates a chain reaction that causes other structural elements to fail in a domino effect, creating a larger and more destructive collapse of the structure. A good example of progressive collapse is a house of cards; if one card falls near the top, it causes multiple cards to fall below it due to the impact of the first card, resulting in a full collapse of the house of cards. Cases such as Skyline Plaza or the Tropacana Casino Parking Garage clearly show this domino effect because you can physically see how the collapse of one floor above overloads the strength capabilities of the floors below, causing each floor to collapse onto the ones below it. Figure 1 on the right shows the devastating aftermath of a large progressive collapse of one of the World Trade Center towers after the attacks on September 11, 2001.

Causes of Progressive Collapse
There are usually multiple factors that take place in order to initiate a progressive collapse. Often, these collapses will take place during the construction phase of a building, as in the case of Skyline Plaza and 2000 Commonwealth Avenue. Miscommunication between contractors and engineering documents can cause a progressive collapse. In this case, workers may improperly install specific structural elements that can lead to weakened structural members throughout the building. Some contractors may be pressed for time to where they may improperly address key connections or finishing techniques to adequately install the structure. Construction technology may also fail, as it did in many cases where buildings used lift-slab technology to construct the building, such as in the L'Ambiance Plaza case. Improper inspection or overlooking structural issues also leads to factors that initiate a progressive collapse. In some cases proper inspection may find a faulty member or connection yet may not properly document it or resolve the issue do to poor miscommunication. Another root cause of progressive collapse takes place in the design phase of a building. If structures go for years without receiving proper maintenance, rust or other material failures can occur which weaken the structure and make it more susceptible to a progressive collapse. Engineers may under-design specific elements because of an underestimation of loads or load paths which in turn cause higher stresses on specific structural elements. Often times engineers design for a specific live load or construction load that is exceeded on the job site due to storage of materials.

Representative Progressive Collapse Case Studies
Progressive collapses can be initiated by many different factors, and usually lead to large damages and loss of life. In this section, a few of the more well known specific cases will be described, in which each case can provide a separate view on the initiation, prevention, and lessons learned behind progressive collapse. Many of these cases remind the reader that good communication, proper design, and proper installation could have possibly prevented these horrific tragedies from occurring. Below is a list of some specific progressive collapse cases. The title of each case provides a link to a more detailed case study of that specific progressive collapse case:

Skyline Plaza
In Bailey's Crossroads, VA, a large apartment complex called Skyline Plaza was under construction. Workers were busy pouring concrete on an apartment building in the complex and at 2:30pm on March 2, 1973, a large progressive collapse occurred in the center of the building, collapsing each floor from the top down. The root cause of the problem is said to be due to the premature removal of forms and shoring for slabs in the vicinity and specific columns on the 23rd floor. Four key concrete columns along with the concrete slab did not reach their desired strength and failed, causing the floor above to collapse onto the floor below, bringing a large center portion of the structure to the ground. Figure 2 below shows the portion of the building that collapsed and Figure 3 provides a detailed image of the devastation after the collapse.

Ronan Point Apartments
On May 16, 1968, a gas explosion occurred in a kitchen on the 17th floor of a 22 story apartment building in London, England. The explosion blew the load bearing walls of the kitchen outward, causing the floors above to collapse onto the 17th floor, which in turn was overburdened by the weight of those floors, leading to a progressive collapse of the floors below. Upon further investigation, it was found that the apartment complex was flawed in both design and construction. This collapse lead to a vast amount of changes to building codes at the time. Figure 4 below shows the collapse of each floor onto the ones below in a progressive collapse manner. (Pearson, "Ronan Point", 2005, 1) ===2000 Commonwealth Avenue=== In January 25, 1971, a punching shear failure led to a progressive collapse of the eastern side of the 2000 Commonwealth Avenue building in Boston, MA. As the building was being constructed, a punching shear failure occurred on the 16th story which was believed to be caused by multiple issues such as improper shoring of floors, low concrete strength, improper concrete detailing, and confusion over responsibilities. As the failure took place, the floor above collapsed onto the floor below, which initiated a chain reaction causing the eastern half of the building to progressively collapse to the ground. (Delatte, "Commonwealth Ave", 2004, 1)

Harbour Cay Condominiums
Around 3:00pm on March 27, 1981, workers were busy constructing condominiums in Cocoa Beach, FL. During construction, a punching shear failure occurred which led to a progressive collapse of the entire structure. Upon further review, it was found that construction errors such as improper installation of reinforcement and inadequate shoring had led up to this collapse. Significant design errors such as an under-designed slab thickness were also accredited to the collapse of the Harbour Cay Condominiums. (AP, "Florida License", 1981, 1)

L'Ambiance Plaza
On April 23, 1987 in Bridgeport, CT, L'Ambiance Plaza underwent a progressive collapse during construction leading to multiple deaths and injury. The building used lift-slab technology to construct each floor and then jack them upward into place. The exact cause of the collapse is unconfirmed and led to much debate, however there are multiple theories as to what had caused the progressive collapse, such as the belief of a jacking rod and lifting nut slipped out due to deformed angle weld. Other possible theories are an instability of the wedges supporting the 12th floor and roof package or possibly inadequate welds and connection details were the root cause of the collapse. Finally, the collapse could have been initiated due to a combination of several of these theories. (Peraza, "L'Ambiance", 1995, 1)

Tropacana Casino Parking Garage
On October 20, 2003 in Atlantic City, NJ, a section of the top floor of a parking garage at Tropacana Casino progressively collapsed during construction while workers were pouring concrete above. It is believed that a slight movement in the structure caused the form-work and shoring below to fail. Multiple other construction issues such as improper reinforcement placement caused the top floor to shear away from the outer wall. The added weight from the floor collapsing above caused four other floors below to collapse as well.

World Trade Center Towers
On September 11, 2001 in New York City, NY, two hijacked commercial airliners were intentionally flown into World Trade Center Towers 1 and 2. The buildings were actually designed to withstand an impact from an airplane using an exterior facade that could shed and redistribute loads around an opening in the building if an impact were to occur. However, both buildings experienced a progressive collapse of the entire structure primarily due to heat generated damage from the resulting fires to the steel framing. The buildings used spray fire-protection material (SFPM), gypsum wall board, or a mix of the two as the primary form of fire protection, however the impact broke that level of protection allowing fire to grow out of control and weaken the steel substructure of the building. Once fire weakened the steel structure, the massive weight of the structure above exceeded its plastic strength causing both buildings to progressively collapse to the ground. (Seffen, "World Trade Center", 2008, 1)

== ==

Prevention Techniques
====

Since a multitude of factors usually cause progressive collapses, there are several ways to prevent a progressive collapse from occurring. Many engineers use structural software and load path analysis to design for progressive collapse, where building elements are designed to shed load to other members. Studies have been done to help understand progressive collapse, such as in

the event of a sudden removal of a column. (Herrmann, "Mechanisms", 2010, 1) In the case of the World Trade Center Towers collapse, the design of each tower used interlocking facade pieces which allowed for this distribution of loads. (Seffen, "World Trade Center", 2008, 1) This change in load path can give adequate warning before a collapse can occur. Review any designs and calculations using computer programs or multiple engineers to ensure that a mistake wasn't made. Most of the collapse cases occurred during construction. With this in mind, adequate communication with the contractors and engineers should be made to ensure that these structural elements are installed properly. Engineers can do this by making construction plans clear and easy to read so that contractors in the field can understand how to properly install the structure they have intended. Proper inspection of structural members is necessary to ensure the structure is erected according to plan.

Lessons Learned
Some lessons to be learned are that buildings should be designed with redundancy including the ability to transfer load to nearby members in the case where a structural member fails or is removed from the structure. This redirection of loads allows the building to remain standing if a column or set of columns are taken out such as in a terrorist attack or a failure due to a large compressive load. (Gross, "Resistant Design", 1983, 1) Exiting and egress strategies have been redeveloped throughout codes to reduce travel distances and provide multiple exits in the event of an emergency. (Wright, "Progressive Collapse", 2003, 1) Other lessons to be learned are that during construction, comprehensive inspections should be maintained on a project to catch any mistakes made on the structural system, including inspections of proper erection techniques. Additionally, many times high strength cables will be strung between columns in a floor slab to help distribute loads in the event that a column would fail. (Wright, "Progressive Collapse", 2003, 1) As in the L'Ambiance Plaza case, ASCE created a committee to observe and study lift slab technology and constitute proper lifting techniques for lift slab construction. (Peraza, "L'Ambiance", 1995, 1) Safety should be the main goal on any job site, and if any situation or connection seems unsafe, proper notification should be taken to ensure that an accident doesn't occur. Many of these progressive collapses are due to overloading of members due to excessive construction loads or other mistakes during construction.

Conclusion
In conclusion, progressive collapse is a devastating and deadly failure that is usually caused by a range of factors. These collapses often cause multiple injuries or even death and have costly consequences. Many of these collapses take place during the construction phase, however some occur due to maintenance issues, terrorism, or other causes. This form of collapse can be prevented if proper inspection, design, and installation are maintained.

Additional References

 * Gurley, Colin (01/01/2008). “Progressive Collapse and Earthquake Resistance”. //Practice Periodical on Structural Design and Construction//. ASCE. (1084-0680), 13 (1), p. 19.
 * **ASCE Journal Article**: This article from ASCE describes the progressive collapse case at Ronan Point, while also giving details about the importance of tie requirements. It also provides details about lost support analysis in progressive collapse design.


 * Osborn, Andrew E. (01/01/2006). “Progressive Collapse – An Implosion Contractor’s Stock in Trade”. //Journal of Performance of Constructed Facilities//. ASCE. (0887-3828), 20 (4), p. 391.
 * **ASCE Journal Article**: This article from ASCE describes how progressive collapse is viewed from a different perspective, from the eyes of an implosion contractor. These workers create controlled progressive collapses used to demolish a building. The article gives insight on techniques used to demolish a building by a controlled progressive collapse.


 * Sagiroglu, Serkan (01/01/2008). “Progressive Collapse of Reinforced Concrete Structures: A Multihazard Perspective”. //ACI Structural Journal//. (0889-3241), 105 (1), p. 96.
 * **ACI Journal Article**: This article from ACI describes how the vulnerability of reinforced concrete structures against progressive collapse caused by man-made hazards depend heavily on their resistance to natural hazards.