As rescue crews, officials and investigators continue to search for answers in the aftermath of last month’s tragic condo collapse in Surfside, Florida, engineers have already been deployed to inspect other buildings in the area in hopes of preventing another catastrophic structural failure. While crises of this magnitude often occur as the result of a tragic-but-relatively-rare set of coincidental circumstances, they can also expose pervasive weaknesses in the systems that are intended to protect us.
Abieyuwa Aghayere, PhD, a professor in Drexel’s College of Engineering and expert in structural failure analysis, has been closely following developments with the Champlain Tower collapse and has provided his insights on the matter to a number of national media outlets, including CNN, The New York Times and the Wall Street Journal. Aghayere suggests that the failures that resulted in the collapse could have been detected with the proper inspection procedures. In a conversation with the Drexel News Blog, he projects that more frequent and rigorous inspections will be just one of a number of building design, engineering and inspection policy changes likely to be instituted in the aftermath of this historic disaster.
Where does this tragedy fit into the historic context of disasters involving building collapses in America?
Not including the Twin Towers collapse in New York City in 2001 and the Alfred P. Murrah Federal Building collapse in 1995 – both of which were caused by terrorist acts, this tragedy ranks as the second worst building failure disaster in the history of the United States. Currently, the worst building failure disaster in United States history is the 1981 Kansas City Hyatt Regency Walkway collapse where 114 people lost their lives, and 200 more were injured.
What aspects of this collapse set it apart from others that have happened before?
This building was in a highly corrosive environment with the saltwater ingress into the building and the salty air environment that has led to ongoing concrete deterioration for decades.
Based on current available information, repairs of the concrete in this building have been going on since at least 1996, yet it appears that no testing of the concrete cores were done to ascertain the in-situ concrete (in place) compressive strength and properties of the concrete, such as the chloride ion concentration. Furthermore, no rebar scans appear to have been done.
One other tragic aspect of this collapse was the fact that most of the occupants of the building were asleep at the time the collapse occurred, leaving those innocent folks no time to react or try to escape from the building.
The multiplicity of factors that appear to be involved in this failure, and the fact that this building collapse happened in spite of the number of professionals that have reviewed and inspected the building over many decades is a unique aspect of this failure. Furthermore, it appears that no review or verification of the original design had been reported in all the previous reviews of the building.
How have previous events contributed to creating or changing codes and laws intended to prevent tragedies like this?
There are a number of examples of this throughout history, here are a few of the prominent ones:
- Alfred P. Murrah Federal Building collapse in Oklahoma in 1995:
After this collapse – caused by a terrorist act, the General Services Administration (GSA) published guidelines in 2000 (revised in 2003) to prevent progressive collapse. The GSA defines progressive collapse as follows:
“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. Hence the total damage is disproportionate to the original cause.”
The structural integrity reinforcement provisions in the American Concrete Institute (ACI 318) Code specifies the detailing of the rebar in the perimeter and interior beams and girders to prevent progressive collapse and improve the ductility (i.e., the ability of a structure to continue to dissipate energy and deflect under constant load) and redundancy (i.e., the ability to support loads in multiple ways) of structures – so that any resulting damage to the structure will be localized.
- The Tacoma Narrows Bridge Collapse, 1940:
The lessons learned from this failure led to a better understanding of the impact of aerodynamic forces on large slender structures, which has influenced wind design of structures in the United States.
- Kansas City Hyatt Regency Walkway Collapse, 1981:
This failure drew attention to how steel connections were previously designed in the building construction industry where steel fabricators often designed steel connections. It led to the practice of steel connections being designed by either the structural engineer of record or by a licensed engineer engaged by the steel fabricator. This failure also brought into focus the need for better communication between design engineers and steel fabricators, as well as reinforce the imperative to prevent progressive collapse in structural designs.
- New York City Local Law 11/Façade Inspection Safety Program (1998): Deaths of pedestrians in 1979 and 1982 from pieces of facades falling onto sidewalks and a rash of façade failures led to Law 11 in 1998, since replaced by the Façade Inspection and Safety Program (FISP). This law requires that all buildings in New York City taller than six stories must have their facades inspected by a licensed structural engineer or architect every 5 years.
- San Francisco’s “Leaning Tower”: After construction in 2009, significant sinking or settlement (exceeding 16 inches by 2015) and leaning started occurring in San Francisco’s Millennium Tower. The 58-story, 645 feet tall concrete condominium building was supported on a concrete mat foundation, which in turn was supported on precast, prestressed concrete piles – which transfers the building loads through friction between the piles and the dense, silty sand layer 50 to 85 feet below the ground surface. Friction piles had previously been used as the foundation system for many other tall buildings in San Francisco, but due to the settlement issues with the Millennium Tower, all tall building development in San Francisco after 2009 utilize piles that extend down into the bedrock, which is approximately 250 feet or more below the ground surface. In addition, the San Francisco Building Code now requires all new buildings taller than 240 feet to undergo independent geotechnical engineering peer review. The Millennium Tower is currently undergoing an extensive underpinning operation to correct the tilt and to minimize any further differential settlement.
In the aftermath of the collapse there has been a surge in inspections and repairs of other buildings in the area of Champlain Towers. What are these engineers looking for? And how might these differ from those that were already required by law?
These inspections will focus more on the structural and geotechnical engineering aspects of the buildings looking for issues that could lead to total collapse of a structure, rather than the less critical aspects of the building, which, though they might be important, will not lead to a total building failure like we saw in Surfside, Florida. My hope is that these inspections will also involve checking the original design of the structure to verify that it is adequate and conforms to the Code.
It seems like a number of obstacles might have prevented inspectors from noticing the extent of the degradation at Champlain Towers prior to the collapse. What are some of the challenges that engineers face, in general, when inspecting buildings or other built structures? What legal responsibility do engineers bear when they notice serious structural damage or degradation?
Some of the challenges include the scope of work that is dictated by the client. If the structural engineer, for example, recommends checking the original design of the project including the foundations, the owners would often object due to the attendant cost. Their thinking is that because the building has been standing for all these years, all must be well with the building.
Other challenges include the fees that structural engineers are paid for these and other design services, which are not always commensurate with the level of risk and liability that they take on.
The engineer’s first and foremost duty is public welfare and safety, so they are duty bound to report to the client whatever issues they might have found in their structure. However, whether structural engineers are mandated to report their findings about the safety of a structure to the jurisdictional authorities would depend on the regulations in place within the jurisdiction.
I believe that structural engineers should be empowered to report any unsafe structural conditions to the jurisdictional authorities — not just only to the client.
What, if any, far-reaching changes do you anticipate that we might see to building codes and laws related to construction as a result of this tragedy?
The questions that come to mind with regards to this tragedy are: How should older buildings conform to the new codes? Should older buildings be made to conform to new provisions in the codes and who pays for the retrofit, or should they continue to be permitted to go without upgrading to comply with the new code? Should there be structural peer reviews for building structures taller than say six stories? Should there be a mandate to inspect existing buildings periodically? Should there be a mandate for structures that are exposed to the elements to be inspected and maintained periodically?
I think we could see a few changes come about because of this, including:
- Some jurisdictions may pass regulations to ensure regular periodic inspections and maintenance of existing structures, say every 10 to 15 years.
- Some jurisdictions may pass regulations for regular periodic inspections and maintenance of structures and structural elements that are exposed to the natural elements – such as parking garages, exterior balconies and balcony railings, and exposed slab roofs over underground parking garages, say every three to five years.
- Some jurisdictions may mandate structural and geotechnical engineering peer reviews for buildings above a certain height – especially those in coastal areas.
- With the scrutiny that has resulted from the tragic collapse of the Champlain Towers South building in Surfside, Florida, the department of buildings and inspections in various jurisdictions will become more proactive with their inspection programs and that may lead to safer buildings.
Aghayere has authored a number of textbooks on structural design and analysis of buildings. His books “Structural Steel Design” (3rd edition), “Reinforced Concrete Design” (9th edition) and “Structural Wood Design” (2nd edition) are considered definitive texts on these subjects.
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