Thinking About Structural Disasters

Image: US Dept. of Commerce, NIST

The 24 June 2021 collapse of the Champlain Towers South condominium building in Surfside, Florida was as horrific as it was heartbreaking. The disaster ranks among the worst unintentional structural failures in United States history, along with the Kansas City Hyatt Regency walkway collapse almost 40 years earlier and the 1922 roof collapse of the Knickerbocker Theater in Washington, DC. The building collapsed overnight and by the next day, the tragedy was widely covered by local to international news organizations seeking to deliver information to a concerned public in real-time.

The media coverage of a structural disaster is subject to a sort of “fog of war”. In the immediate aftermath, answers are hard to come by. Eye-witness and second-hand accounts, public records and other fragments of information are reported as news organizations receive them. Outside of trade and design professional publications, few media outlets have reporters specializing in construction and the built environment. As a result, reporting on structural failures is often poorly contextualized, contains misnomers and is framed by existing narratives like local government incompetence, “crumbling infrastructure” and effects of climate change, which may be more confusing than clarifying.

For example, early media reports speculated about sinkholes and sea-level rise, latching onto a study that found that the ground around Champlain Towers was settling. The study’s co-author had to caution that the subsidence they observed was not likely related to the collapse. When a three-year-old report by the condominium association’s engineer was made public, media reports emphasized evidence that the pool deck suffered “major structural damage” and had a “major error” in its waterproofing. Descriptions of distress to beams and columns, including exposed and corroded reinforcement in the garage were downplayed. While witnesses observed the pool deck collapsing first, its relation to the collapse, if any, is unclear. Distressed structural beams and columns with exposed and corrosion and reinforcement are clearer signs of trouble. As of yet, there is no smoking gun; but even on the day of the collapse, the tone of certain new stories suggested that this was somehow surprising.

Engineers and architects can be reluctant to publicly discuss structural disasters immediately after the event. Some of this reluctance to speak is based on knowing how much is unknown. As licensed design professionals, they are subject to legal and ethical obligations that require that their public statements be honest and that they make certain disclosures if relevant. A careless statement may imply that the design professional has knowledge that they do not have. [This is where I say that while I am a licensed professional engineer, I do not practice in Florida, I am not involved in investigating the Champlain Towers collapse and that I do not have access to nonpublic information. I am also not going to claim to know the cause of failure.] A few very well-qualified engineers and professional societies have made careful statements discussing how the failures are investigated, and some of the factors that investigators may find to be of interest without claiming to have the answer. However, I have also seen a disappointingly large number of construction products vendors and even a few design professionals suggest that the collapse could have been prevented had their products or services be used.

A shortage of reliable information leaves a void to be filled by unreliable sources who may be biased, uninformed to varying degrees or self-serving, as well as conspiracy theories. Academics may be freer to speak and have the incentive to be viewed as though leaders. But they are often not practitioners themselves and while knowledgeable about theory, they may have little experience with the design and construction process. Contractors, typically not educated in engineering or architecture, may not understand the basis for design decisions, especially if they do not work on similar projects. Lawyers, self-proclaimed experts, elected officials and spokespeople for potentially responsible parties may be more interested in developing business or shaping the coverage than informing the public. The odds of explanation and insight being overcome by noise and misinformation tends to be high. This ill-serves the public.

Structural disasters are complicated and forensic investigations take time. By the time the evidence has been collected, testing and calculations have been performed and hypotheses developed and validated, the media and the public have largely moved on. Incomplete and misleading early information can establish a narrative that prejudices the public’s and policymaker’s understandings of the disaster. For example, recent comments by officials in Florida that building codes should be revised are premature. Not enough is currently known to determine what revisions are needed. Better communication of how and why structures fail would provide the public with more realistic expectations and a basis for thinking about and understanding failures, making it more likely that the right lessons are learned and acted on.

How should the news media and the public understand structural disasters? First, no construction project is perfect; in fact, there has likely never been a project without error. Yet major structural failures are rare and building collapses more so. The reason for this is that structural design is intentionally conservative. For a typical building designed today, the target annual probability of sudden and widespread damage is seven in ten million (0.00007%), exclusive of earthquake hazards, according to the load standard incorporated into many states’ building codes. The probability that the building would survive 40 years without this sort of failure is about 99.7 percent. The probability that it would not collapse is higher.

Older building codes were also intended to be very conservative, according to the standards of the day. Sometimes a hazard that is poorly understood becomes better understood. Codes and standards will be updated to reflect new knowledge and technologies. If an existing building complied with applicable codes when built and is not imminently hazardous, it is usually updated only when substantial alterations are made or the owner wants to mitigate hazards. This avoids the economic and cultural impacts of having to demolish and reconstruct existing buildings as codes change.

With so much conservatism in structural design, something must go very wrong for a building to collapse. Or more likely multiple things must go very wrong. The potential causes of a failure are numerous: design errors, construction errors, deficient materials, natural disasters not contemplated by design, negligent overloading, unexpected subsurface conditions, deterioration, improper maintenance, and even intentional acts. Larger failures are usually more complicated and forensic investigators must sort through potential contributing factors and determine – if possible – which particular combination of causes is most likely to have caused the failure.

Consider a mid-rise apartment building. Large buildings are subject to larger loads from their weight and occupancy, and larger effects from wind and earthquakes. Buildings like this are often made of reinforced concrete, a material that varies in properties to a degree from batch to batch, develops strength with time, and requires a high degree of quality control. Reinforcing details can be complicated and subject to interpretation, and are not easily observable after the concrete is poured. A lot can go wrong. In addition, most structures are less stable during construction than upon completion. Design and construction errors often manifest as distress and failures as the structure is loaded for the first time by its own weight during construction. Therefore, most structural failures occur during construction. Among failures during construction, a substantial proportion affects concrete elements and structures.

Since the occurrence of a structural failure often requires multiple causes, failures are more likely to initiate where loads or parts of the structure are more complicated, like connections and slender compression elements. Similarly, failures are more likely when more hazards are present, such as during storms and earthquakes. For a failure to begin, some proximate cause must be present without which the failure would not occur. That may be a load, a defect or some change in the condition of the structure. Since Champlain Towers had been in service for many years, one of the fundamental questions is what changed that could have initiated the collapse at the particular time it happened. There may never be a consensus on what that initiating event was, but investigators will narrow down the possibilities.

In addition to engineering, construction and environmental causes, structural failures are often organizational failures. Like designs and constructed works, all organizations are imperfect. Design and construction are collaborative, but also semi-adversarial, resulting in opportunities to detect and remedy errors early. For example, checking calculations is a fundamental step in the structural design process. Coordination by the project’s architect provides an opportunity to discover and resolve conflicts between design disciplines before they occur in the field. Governments require that permit applicants submit construction documents to demonstrate that plans for the project exist and are reasonably complete. Critical aspects of structural work are subject to code-required special inspection to confirm that the contractor is executing the work properly. When these and other checks and balances are omitted or parties fail to fulfill their responsibilities, the risk of failure increases. Often a failure of a party within the overall organization of the project is due to an organizational failure internal to that party.

The Champlain Towers South collapse will be thoroughly investigated like few structural disasters in history. These investigations will take years to complete. With such a catastrophic loss, precise apportioning of liability among the potentially responsible parties is worth huge sums of money to their insurers. As lawsuits begin, parties to the litigation will retain structural engineering consultants and other experts to evaluate the evidence and develop theories of causation. These experts, having different perspectives according to their education and experience, and usually being asked to answer different questions salient to their particular clients, will not likely agree about all of the facts of the case and their implications. Much of the litigation will be settled and the work of the experts may never be public.

Fortunately, the National Institute of Standards and Technology (NIST) is investigating the cause of the collapse as they have other major structural failures such as the destruction of the World Trade Center. Their investigation will produce a public report identifying the likely cause(s) of failure and offering recommendations of how design and construction practice, building codes and standards, and other regulations can be improved to prevent similar failures. However, the implementation of those recommendations will be up to government agencies, code-writing organizations and industry and professional groups that promulgate design and construction standards.

When NIST’s report is released, the public and their representatives must pay attention and organize to see that necessary policy changes are made. If the interests harmed by changes make their objections known, but the interests benefited by the changes fail to show up, it is likely that the changes will be delayed or never enacted at all. Since the public and even some in the architecture, engineering and construction community are often unaware of the reason behind proposed code changes, they may work to defeat them or ignore them when they are enacted. Some contractors and building officials are still unaware of the wood frame connection requirements that arose from lessons learned after Hurricane Andrew in 1992 and have been in the codes for several cycles. Understanding how the lessons learned from failures are used to improve construction practice helps those improvements to occur.

Public officials and news organizations, as well as the architects and engineers, need to better communicate the nature of structural failures, what they mean and how the long process of investigating and learning from failures leads to better construction in the future. Improperly understanding and communicating about structural disasters has consequences. The mix of incomplete, misleading, and even false information available immediately after the event can set the narrative into which later information will be contextualized. If this fosters prejudicial and inaccurate mythology in the minds of the public, lessons from the failure will not be learned and policy and practice changes will not be made to prevent similar disasters in the future.

The information and statements in this document are for information purposes only and do not comprise the professional advice of the author or create a professional relationship between reader and author.