In the aftermath of tragedies, like last year’s collapse of the Champlain Towers South condo complex in Surfside Florida, conversations inevitably shift to gleaning some lesson amid the sadness and chaos, a kernel of wisdom that will help to prevent something so horrific from happening again. Given the historic scope of the Surfside collapse, the analysis has been particularly extensive along with calls for systemic change.
But after a year of searching and studying, what have we learned – and can it keep us safe?
Abieyuwa Aghayere, PhD, a professor in Drexel University’s College of Engineering, has been hard at work since that tragic day last June trying to help the public understand what happened. During the days and months following the collapse, Aghayere shared his insight as a structural engineer with reporters trying to find answers. His contributions were included in thousands of stories over the past year, including the coverage that earned a team of reporters at the Miami Herald a Pulitzer Prize.
And in recognition of his thought leadership in the aftermath, he has been an invited keynote speaker at the 2022 Annual Convention of the Structural Engineers Association of California (SEAOC), and delivered a special invited seminar to the National Institute of Standards and Technology (NIST)’s National Construction Safety Team — the federal agency charged with investigating the collapse. He is also an invited panelist in a session at the Smart Cities Connect Fall Conference & Expo later this month.
Aghayere recently took time to share what he’s learned in this past year of studying and thinking about the collapse and what it means for the future of our built environment.
Now that it has been a little over a year since the collapse of the Champlain Towers South condo complex, what have your conversations been like with fellow engineers who are thinking about how this could have happened?
The typical factors that contribute to structural collapses include: design errors, construction errors (e.g. poor workmanship, use of deleterious materials); lack of adequate maintenance, foundation failure; extreme loading (e.g. blast, terrorism, or subjecting a structure to a higher load than it was designed for); external factors, such as adjacent construction vibrations and dewatering or lowering of the water table; and environmental factors, such as seawater infiltration and the presence of salt air moisture.
My discussions with fellow structural engineers have converged on the idea that many of these factors banded together to arrive at this tragic “perfect storm” that was the Champlain Towers South collapse. Many tell-tale signs of serious problems were ignored, even as the building was crying out for help in many ways, such as through cracking and spalling and water leakage.
Has there been any movement or momentum from an inspection/regulatory/code standpoint to institute changes that could prevent something like this from happening again?
Yes, Florida enacted a law in May 2022 for buildings three stories or higher, with the following requirements:
- Structural Integrity Reserve Fund Study Every 10 years:
- Requires visual inspection to determine estimated remaining useful life, and estimated replacement/deferred maintenance cost.
- Phase 1 review: Visual inspection –
- At 25 years for buildings within 3 miles of the coast, and every 10 years thereafter.
- At 30 years for other buildings, and every 10 years thereafter.
- Phase 2 review: Required if “signs of substantial structural deterioration of any building component is found in Phase 1.”
- May involve destructive and non-destructive testing.
- Must report any unsafe condition to the Building Department Official.
A few states and cities already had some periodic inspection regulations in place before the Champlain Tower South collapse for certain structures and structural elements, such as bridges (at least every two years), parking garages, balconies and facades. Some examples of inspection frequencies for structural elements are shown in the table below:
|Parking garages||Exterior Balconies||Façades||Others|
|New York State: Every 3 years||New York City: Every 5 years for 6-stories or more|
|California: SB721 – Every 6 years||Boston: Every 5 years|
|Philadelphia: At 10-year mark and Every 5 years thereafter.||California: Weather-exposed wood exterior elevated elements with impervious floor covering – Every 5 years|
|Chicago: Every 4-12 years depending on building classification|
Note that countries, such as Singapore and Malaysia, have had periodic inspection regulations in place for entire building structures for decades – at least since 1989, in the case of Singapore.
The International Code Council (ICC) has some work in progress with regards to the time intervals for maintenance inspections (occurs annually), periodic inspections, and milestone inspections of buildings, as a function of the risk category of the building and exposure to environmental factors. For example, hospitals, which have a higher risk category than an office or residential building, could have periodic inspections every five years and milestone inspections every 20 years, compared to every 10 years and every 20 years, respectively, for office or residential buildings.
Now that more is known about what caused the collapse in Surfside, Florida, are you noticing new inspection techniques being employed, or efforts/strategies to retrofit older buildings?
What I have noticed is increased activity within building departments — especially in Florida — to get older buildings inspected and reviewed well before the 40-year mark, which used to be the threshold age for recertification review. Some condominium buildings have been evacuated in Florida — and one in South Carolina — due to structural deficiencies.
Structural engineers reviewing a condominium building in Florida recently called for evacuation of the building due to excessive deflections and post shoring of the underground parking garage “roof” slab was provided in another condominium building. So, I have noticed that structural engineers have not hesitated to act when they have noticed problems.
There are a number of existing inspection techniques (e.g., impact echo, ground penetrating radar – GPR) that if used in the Champlain Towers South condominium could have provided information about the internal condition of the concrete in the slabs and columns, and the rebar within. I suspect we will see an increased use of these technologies going forward.
There have been a number of other notable structural failures in the year since Champlain Towers, including bridge collapses in Pennsylvania and California and a number of smaller building collapses around the country. With new federal funding for infrastructure becoming available in the near future, what changes would you like to see that could help shore up our built environment in the near- and long-term?
Repair the structurally deficient elements in bridges with ratings of 4 or lower. Shore up and retrofit these bridges and replace any lost section due to corrosion to prevent sudden and brittle-type collapse like what happened in Pittsburgh.
The Fern Hollow Bridge in Pittsburgh was built in 1970 with a rigid steel K-frame superstructure system and had a September 2021 inspection rating of “poor,” or 4. It collapsed in January 2022, and apparently, no repair or retrofitting work had been done on the bridge since the September 2021 “poor” rating.
Many such bridges with “poor” ratings should be replaced, but they remain in service because of lack of adequate funding for bridge maintenance, repair, and replacement. There are more than 3,000 bridges rated in “poor” or structural deficient condition in Pennsylvania out of about 25,000 state-owned highway bridges.
Repair or replace all bridges with ratings of 4 (i.e., a “poor” rating) or lower.
Rather than relying on just visual inspection which occurs at fairly long intervals (e.g., two years for bridges), use remote monitoring technology, such as accelerometers and fiber optic sensor networks, to continuously measure and monitor critical structural parameters, including frequency and amplitude of vibration and displacements, in buildings and bridges with the help of a data acquisition system and data analysis software.
The data obtained can be translated into structural parameters, which can be used as an early warning alert system of any imminent structural problems if certain thresholds are exceeded, just like the data from the sensors in airplanes. The use of such technology, in bridges for example, will create a database of structural parameters that can be helpful to bridge owners in prioritizing the repair and maintenance of their bridges.
There are usually not enough financial resources to repair or replace all structurally deficient bridges, but with the recent infrastructure funding, hopefully the repair and replacement of more bridges will become possible.
What changes might still need to be made in support of greater safety?
In general, the municipal building departments in smaller jurisdictions, like the town of Surfside, should either employ competent and licensed structural engineers to review the drawings that are submitted for building or construction permits. If they cannot afford this, they should contract out the reviews to private structural engineering firms.
In the case of Champlain Towers South, I would have expected the Building Department review of the structural drawings to have detected the glaring design errors pertaining to the concrete cover to the rebar in the exposed concrete slabs and the congested or overcrowded vertical rebar in the concrete columns in the East Tower. Those design errors should have been easily identified.
More specifically, here are a few suggestions based on lessons we learned from the Champlain Towers South collapse, that could help to prevent similar tragedies in the future:
- In structural reviews for building recertification or milestone inspections, the original design of the critical gravity and lateral load resisting elements should be checked.
Do not rely on the assumption that the structure has been “time-tested.” The I-35W Mississippi River bridge in Minneapolis – built in 1967 – collapsed after 40 years in 2007 due to an inadequately designed gusset plate!
- Structural review reports should include a check of the critical failure modes for all the structural systems (e.g., check punching shear failure for a flat plate floor system). In all the prior structural review reports for Champlain Towers South, I noticed that there was no mention of punching shear, which should have been the first failure mode to be checked given the flat plate floor system used in the pool deck and in the main building.
- Be specific about the structural condition of the building in the structural review report and indicate whether the building is safe or is in imminent danger of collapse, or whether the building should be shored or evacuated.
- Investigate the internal conditions of deteriorated structural elements and evaluate the need for post shoring of the structural members, especially for flat plate/flat slab structures.
- Monitor the effects of vibrations from adjacent construction on nearby existing structures before, during, and after construction, and conduct pre-construction and post-construction condition assessment of adjacent existing structures.
- The use of Structural Health Monitoring (SHM) systems in buildings, which has been largely confined to seismic monitoring and evaluation, could lend itself for use as an early warning alert system in high-rise buildings for impending structural collapse.
- Provide redundancy in the lateral-force-resisting-systems for buildings. For an irregular L-shaped building like Champlain Towers South, provide independent East-West and North-South shear walls in each leg to ensure lateral stability of each segment of the building.
- Flat plate and flat slab floor systems that are lightly reinforced should be checked for flexure-induced punching failure. This type of slab failure occurs at a lower load than the typical punching shear failure and it occurs suddenly and in a brittle fashion.
- Indicate clearly on the structural drawings the elements that are necessary to resist lateral loads – such as chords and drag strut (or collector) element or reinforcement and any shear friction reinforcement – to ensure an adequate lateral load path for the transfer of in-plane forces from the concrete floors/roof or diaphragms into the shear walls.
- The engineer should use drag struts or collector reinforcements that lie within the plane of each floor or roof along the shear wall lines and help to drag or push the lateral wind and seismic load at each floor/roof level into the shear walls. They should also use chords which are structural elements or reinforcement along the edges of the floors and roof, perpendicular to the shear walls. They should be inspected and the reviewing engineer should check that these elements are shown on the drawings.
- Provide adequate slope for drainage for exposed slabs, and the architect or waterproofing consultant should specify waterproofing for all exterior slabs.
- For structural elements exposed to salt air moisture and seawater intrusion, use the concrete cover prescribed in ACI 357.3R-14, Guide for Design and Construction of Waterfront and Coastal Marine Structures. This standard requires 2.5-inch concrete cover instead of the 1.5 inch required in the ACI 318 Code for concrete members exposed to salt spray. Note that only ¾ inch concrete cover to the rebar was specified for the exposed slabs in Champlain Towers South, which results in quicker and easier infiltration of seawater into the concrete slab.
- Avoid structural systems that can lead to progressive collapse, as was the case in Champlain Towers South, where the failure of the pool deck and the step beams led to the failure of the entire East Tower. Separating the pool deck from the lobby slab with an expansion joint and providing an independent lateral force resisting system for the pool deck could have prevented the spread of the pool deck collapse.
- For slab-to-shear wall connections, provide dowel reinforcement to tie the wall to the slab and to resist lateral forces parallel to, and perpendicular to, the plane of the shear wall.
- For flat plate or flat slab pool deck-to-basement wall connections, provide dowel reinforcement to tie the wall to the slab and to resist lateral forces parallel to, and perpendicular to, the plane of the basement wall.
- Provide adequately designed hydrostatic slabs for buildings with basement slabs where the Base Flood Elevation (BFE) is higher than the bottom of the basement floor slab; and provide moisture barrier below the hydrostatic slab on top of the subgrade and protect the moisture barrier from damage during construction. Ensure that vertical dowel reinforcement is provided between the hydrostatic slab and the pile caps below.
- There is a need for mandatory periodic reserve fund studies for condominiums to ensure that adequate funds are available for the proper maintenance and repair of the buildings.
- There is a need for periodic and milestone inspection regulations for existing high-rise buildings.
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