A Parking Structure collapse is a rare but alarming failure that often results from multiple contributing factors. In northern North America, parking structures face unique stresses from harsh weather and heavy use. Appropriate engineering can ensure that these stresses are handled effectively, so why do parking structures collapse?
A combination of structural deficiencies, environmental influences (like snow, ice, and freeze-thaw cycles), and maintenance lapses can all work together to undermine a garage’s integrity.
This article examines the common causes behind such collapses, highlights notable case studies in the region, analyzes frequent failure points, and recommends best practices to prevent future incidents.
Common Factors That Lead to Structural Issues
Structural Design Inducing Tension (Hogging Moments)
Concrete is excellent in compression but weak in tension. Parking structures experience hogging moments—areas of negative bending where the top of the slab is in tension. These tension forces cause cracking, particularly over beams and tees, which are common structural elements in parking garages.
Once cracks form, water infiltration increases, compounding the effects of freeze-thaw damage. Cracks in tension zones do not self-heal and require costly repairs to prevent long-term degradation. When not properly mitigated, cracked concrete accelerates all other failure mechanisms, making the structure more vulnerable to long-term deterioration.
This is why the Kiwi CarPark system was designed to relieve tension overtop of the galvanized steel beams. This structural approach eliminates tension from the top surface of the concrete.
Structural failures due to concrete in tension (hogging moments) have been documented in various cases. The Tropicana Casino Garage Collapse (New Jersey, 2003) was a notable example where improper reinforcement at critical connection points caused catastrophic failure during construction. Tropicana Casino Garage Collapse (2003).
Ensuring proper reinforcement and designing to eliminate unnecessary tension forces is key to preventing such failures.
Environmental Influences (Weather and Climate)
Northern North America’s climate introduces severe environmental stresses on parking structures. Freeze-thaw cycles and de-icing salts infiltrate concrete, corroding steel reinforcement. Water and salt carried by vehicles seep into cracks, and when the temperature drops, the water expands, widening cracks further. Salt significantly accelerates the corrosion of steel, leading to spalling and weakening the structure internally Freeze-Thaw and De-Icing Salt Effects.
Heavy snowfall and ice accumulation pose another risk, adding extreme loads. Garages must be designed for snow load, but excessive accumulation or poor snow removal practices can overwhelm structures. Thermal expansion and contraction can induce stress cracks if not properly accounted for with expansion joints, increasing structural vulnerability. The Bayshore Mall Parking Garage Collapse (Wisconsin, 2023) was partially attributed to excessive snow loads that caused sections of the structure to fail under unanticipated stress. Bayshore Mall Parking Garage Collapse (2023).
Carbonation and pH Reduction
Even without direct water exposure, chemical reactions within the concrete can weaken the structure over time. Carbon dioxide (CO₂) from the air reacts with calcium hydroxide inside the concrete, lowering the pH. Once the pH drops below 9, the passive protective layer around the rebar breaks down, making it vulnerable to corrosion—even in dry conditions.
Older parking structures or those with highly porous concrete are especially at risk. Carbonation Contamination in Concrete.
Construction Inconsistencies and Material Variability
The quality of construction significantly impacts parking structure longevity. Cast-in-place concrete is prone to inconsistencies, including improper curing, mix variations, and human error. On-site weather conditions can affect concrete strength and durability. Poor workmanship can result in honeycombing, cold joints, and uneven reinforcement placement, all of which create weak points in the structure.
Using precast, factory-controlled concrete components significantly reduces variability and improves structural reliability, as these elements are produced under controlled conditions to ensure uniform quality.
Corroded Steel Supports and Connectors
Reinforcing steel and connections embedded in concrete (beams, columns, or precast connections) often suffer hidden corrosion. Rusting steel loses cross-section and bond to concrete, reducing structural strength. Corroded connections—such as beam-to-column joints or weld plates—are especially dangerous, as their failure can bring down entire sections of the structure.
Investigations into the Ann Street Parking Garage Collapse (New York, 2023) revealed long-standing corrosion in key load-bearing columns and connections, exacerbated by unchecked deterioration over time Ann Street Parking Garage Collapse (2023).
Overstressed Structural Elements
Deck slabs and columns can experience overload due to excessive snow, too many vehicles in one area, or additional weight beyond design capacity. Such overstressing can lead to punching shear failures, flexural failures, and column collapses.
In the Downtown Ottawa Parkade Collapse (Ottawa, 2025), the weight of accumulated snow caused structural failure in key support columns that had already suffered from cracking and degradation due to exposure to moisture and salts.
Best Practices for Prevention
Load Management and Snow Load Planning
Proper load management is essential for ensuring the long-term structural integrity of parking garages, particularly in regions with heavy snowfall. Studies have shown that excessive and uneven snow loads can create critical stress points in structures, leading to premature deterioration or failure. Excessive loading, whether from vehicles, snow accumulation, or storage of materials, can put undue stress on structural elements, leading to premature deterioration or even collapse.
One key strategy is to designate specific snow loading areas on the roof level to prevent uneven distribution of weight. If snow accumulates excessively in one section, it can cause localized overloading, increasing the risk of structural failure. Snow removal procedures should be carefully planned to ensure even weight distribution and avoid adding excess loads to already stressed areas.
Additionally, defining clear snow removal processes is critical. Using improper removal techniques, such as allowing plowed snow to build up along perimeter walls or failing to remove excess weight in a timely manner, can compromise the structure. Engineers should incorporate redundancy into the design, ensuring that if one structural element is overstressed or fails, others can compensate and prevent progressive collapse.
By integrating proactive load management strategies and prioritizing structural redundancy, owners can significantly reduce the risk of overload-induced failures and extend the lifespan of their parking structures.
Use Ultra-High Performance Concrete (UHPC) for Deck Slabs
One of the most effective ways to improve the longevity of parking structures is by using Ultra-High Performance Concrete (UHPC) for deck slabs. Unlike traditional concrete, which is prone to cracking, water infiltration, and freeze-thaw deterioration, UHPC offers an exceptionally dense microstructure that significantly limits chloride diffusion. This prevents water and salt from reaching embedded rebar, eliminating one of the primary causes of reinforcement corrosion. Traditional concrete, while durable, is prone to cracking, water infiltration, and freeze-thaw deterioration. UHPC addresses these weaknesses with its exceptionally low permeability, high compressive strength, and enhanced durability.
UHPC has a compressive strength exceeding 25,000 psi, making it far more resistant to cracking and surface wear than conventional concrete. Because of its extreme density, UHPC does not require an additional topping membrane to protect against water infiltration. This eliminates a major long-term maintenance cost while ensuring the structure remains durable for decades. Its dense microstructure prevents water penetration, protecting reinforcement from corrosion. Additionally, using precast UHPC panels ensures consistent quality, eliminating on-site construction inconsistencies that often lead to early structural failure.
By incorporating UHPC into parking structure design, owners can benefit from a longer-lasting, low-maintenance solution that resists environmental stressors and eliminates the need for costly waterproofing treatments. This translates to significant long-term savings while ensuring a more durable, corrosion-resistant structure that outperforms traditional concrete decks. The Kiwi CarPark modular parking structure system developed by Kiwi Newton uses UHPC precast panels that stay completely in compression and avoids concrete tension.
Keep Concrete in Compression – Eliminating Tension Cracks
Another very effective way to extend the lifespan of a parking structure is to keep the concrete in compression, preventing cracks from forming in the first place. Infact, concrete in compression can selfheal microcracks. Traditional parking garages often experience hogging moments (A hogging moment produces tension on the top and compression on the bottom), where certain areas of the slab are forced into tension, leading to cracks that allow water infiltration and corrosion. Over time, these cracks worsen, accelerating deterioration and reducing structural integrity.
A better approach is to design with simply supported precast UHPC deck panels, which remain in bi-axial compression under normal loading conditions. By eliminating tension zones, this design prevents:
- Tension cracks that weaken concrete over time.
- Water infiltration into structural elements, which can accelerate freeze-thaw damage and corrosion.
By keeping the concrete in a constant state of compression, engineers can dramatically increase durability, reduce long-term maintenance costs, and prevent the structural weaknesses that lead to costly failures.
Use Galvanized Steel for Structural Elements
Corrosion is one of the biggest threats to parking structures, often weakening critical support elements hidden inside concrete. Traditional rebar, embedded within the concrete, corrodes over time as moisture and de-icing salts infiltrate cracks, leading to unpredictable failures that are difficult to detect until it’s too late.
A more durable approach is to use galvanized steel beams and columns, which remain fully visible and easier to inspect for signs of wear. Hot-dipped galvanization protects steel elements by forming a corrosion-resistant barrier, extending their lifespan beyond 90 years before requiring maintenance (not failure, just the time to first maintenance). Unlike rebar that deteriorates unseen within concrete, galvanized steel allows for predictable, gradual degradation, reducing the risk of sudden structural failure.
By using galvanized steel beams and columns in parking structure designs, engineers can improve inspection accessibility, reduce long-term repair costs, and enhance structural reliability, ultimately preventing failures caused by hidden corrosion issues. This is why the Kiwi CarPark system for design-build of parking structures uses hot-dipped galvanized steel columns and beams.
Long-Term Warranties with Structural Inspection Responsibility
When investing in a parking structure, owners should look beyond just the initial design and construction—long-term durability and maintenance should be a top priority. One of the best ways to ensure a structure remains safe and reliable over time is to partner with a design-builder who offers long-term warranties and takes responsibility for ongoing structural inspections and cleaning.
Choosing a firm that provides 20, 30, or even 50-year warranties ensures that the structure is built with longevity in mind. More importantly, these warranties should include routine structural inspections, corrosion protection measures, and scheduled cleaning to prevent deterioration from environmental factors like de-icing salts and freeze-thaw cycles.
By shifting the responsibility for maintenance and inspections to the design-builder, owners can avoid unexpected repair costs and reduce liability risks. A proactive approach to upkeep, ensured through a well-structured warranty, can extend the life of a parking structure, preserving both safety and long-term value.
Kiwi Newton is one of the only design-builders that offers long-term warranties for the parking structures that they build. This displays our confidence with our construction methods and our commitment to quality.
Case Studies of Notable Collapses
Downtown Ottawa Parkade Collapse (Ottawa, Ontario, 2025)
Snow load and structural degradation led to a partial collapse of a six-story parking structure in downtown Ottawa in February 2025. Early one morning, the top level of this 1989-built open parking garage gave way, shearing off several concrete columns and sending a section of deck down onto the level below. Fortunately, because it happened before rush hour, no injuries occurred even though about 50 vehicles were damaged. Ottawa’s fire department structural collapse team found that a heavy snow load on the roof deck likely contributed to the failure. The region had accumulated significant snowfall, and firefighters observed five to six large concrete girders on the top level were visibly sagging under the weight. Upon closer examination, multiple reinforced concrete columns were cracked or broken at the upper levels, suggesting a sudden column failure. The collapse left a gaping hole in the top deck (as seen in the image with cars teetering on the broken slab) and prompted an emergency demolition of parts of the structure. City officials noted that no formal structural inspection of the garage had been conducted since its construction in 1989, meaning it was solely up to the owner to perform maintenance over 35+ years. This raised questions about whether undetected deterioration (such as corrosion in the column reinforcing steel or damage from freeze-thaw cycles) had reduced the structure’s capacity. While a full investigation is ongoing, the Ottawa incident echoes others where an older parking structure, subjected to heavy snow and lacking recent structural evaluation, suffered a failure. It underlines the need for periodic inspections on such garages and diligent removal of heavy snow accumulation, in addition to robust original design.
Source:
Algo Centre Mall Roof Collapse (Elliot Lake, Ontario, 2012)
The Algo Centre Mall in Elliot Lake, Ontario, suffered a deadly roof collapse on June 23, 2012, when a portion of its rooftop parking deck caved in. The collapse sent concrete and cars crashing into the shopping mall below, killing two people. Investigations found that the primary cause was severe corrosion of the steel support beams holding up the parking deck. For decades, water leakage through the roof (which doubled as the parking surface) allowed rain and winter salt to seep onto the steel structure.
The building’s waterproofing had been flawed since construction in 1979, and a proper membrane was never effectively installed. As a result, every winter salt-laden slush leaked into the joints, and over time the steel connector in one critical area rusted away, losing most of its load-carrying capacity. The fatal collapse was triggered when a vehicle drove over this weakened spot, applying stress that the rusted connection could no longer hold. Equally troubling was the lack of maintenance action despite obvious signs: the roof had been leaking for years (shoppers routinely saw buckets catching drips inside the mall) and engineers had warned of structural issues, yet only superficial patchwork repairs were done.
An inquiry later noted that the problem was “never fully addressed” and was repeatedly downplayed or deferred by successive owners. This tragedy exemplifies how environmental factors (water and salt) plus maintenance neglect can lead to a structural failure. The lessons from Elliot Lake prompted calls for stricter inspection regimes and enforcement of repair orders to prevent such long-term neglect.
Source:
Bayshore Mall Parking Garage Collapse (Glendale, Wisconsin, 2023)
Heavy snow accumulation contributed to the collapse of a parking garage at Bayshore Mall in Glendale, Wisconsin (February 2023). This multi-level garage suffered a partial collapse when a section of the third level pancaked down onto lower levels around noon, fortunately with no injuries reported. Investigators quickly pointed to an unusually heavy snowfall as a likely trigger. The Milwaukee area had received a wet, dense snow/sleet mix the night before, and a large pile of snow remained on the top deck of the garage. The fire chief noted that snow “was one of the main factors behind the collapse”, given the considerable weight added by the roughly 2 inches of heavy snow collected on the structure. The snow load may have overstressed one bay of the deck, causing it to give way and drop onto the level below in a chain reaction. Photos of the aftermath show broken concrete slabs and a mound of snow in the collapsed area. Initial inspections suggested no fundamental design flaw in this relatively modern garage; instead, weather overload combined with perhaps an uneven distribution of plowed snow led to failure. This case underscores that even in properly designed garages, extreme snow loads (especially when snow is not evenly cleared) can precipitate a collapse. It also highlights the importance of monitoring and removing heavy snow from parking structures to stay within safe load limits.
Sources:
- Bayshore parking garage collapse, chief ‘confident’ of no injuries | FOX 9 Minneapolis-St. Paul
- Portion of Bayshore Parking Garage Collapses » Urban Milwaukee
Ann Street Parking Garage Collapse (Manhattan, New York, 2023)
A four-story parking garage at 57 Ann Street in Lower Manhattan suddenly collapsed on April 18, 2023, killing one garage employee and injuring several. This structure was a nearly 100-year-old concrete frame building that had been repurposed as a parking facility for decades. Preliminary findings indicate the collapse was likely due to overloading and deterioration in an aging structure. At the time of failure, roughly 80–90 vehicles were parked on the roof level, an enormous weight (estimated around 250,000 lbs in total) that may have exceeded the deck’s capacity.
City officials noted that the sheer mass of so many cars on the top deck “might have been enough to trigger the collapse,” especially given the building’s advanced age. Compounding the issue, evidence has surfaced that the garage had long-standing structural problems that went unaddressed. Inspections after the collapse – and a prior investigative report – revealed extensive concrete spalling, rusted support beams, and even missing or corroded columns in the garage and others like it. In fact, this garage had a 2003 violation for hazardous cracked concrete that was never fully remedied. It was also cited in 2009 for exceeding its rated capacity, after which the owners installed car stackers (lifts) to add more vehicles – further increasing the load on the structure.
These factors indicate a pattern of overuse and poor maintenance. The collapse likely initiated at a failed column or connection on an upper level (where the overload was highest), and the deck then fell in a pancake fashion. In the aftermath, New York City launched emergency inspections of similar parking garages citywide, shutting down several that were found in unsafe condition. The Ann Street collapse demonstrates the danger posed by cumulative neglect in an old garage: when years of corrosion and cracking meet an overload condition, the structure’s margin of safety can quickly evaporate.
Sources:
- NYC parking garage collapse: 2 factors eyed in deadly Lower Manhattan incident; building considered unstable – ABC7 New York
- Better Buildings Blog | RAND Engineering& Architecture, DPC
Lessons Learned – Build Better
Parking structure collapses in northern North America typically result from an intersection of factors: underlying structural weaknesses, aggressive environmental conditions, and lapses in maintenance or oversight.
Case histories from Ontario to Wisconsin to New York show how design or construction flaws, if coupled with years of corrosion or an extreme weather load, can push a garage past its tipping point. The consequences of a collapse are high – risking lives, causing financial loss, and eroding public confidence in infrastructure.
Fortunately, the engineering and management practices to prevent such failures are well understood. By learning from past collapses, stakeholders are increasingly emphasizing rigorous inspections, durable design, and proactive maintenance as the norm for parking structures. Ultimately, treating parking garages not as forgettable concrete slabs but as critical structures that demand care will help ensure they remain safe and standing even under the toughest conditions.
For all of these reasons and more, Kiwi Newton pioneered a new approach to building parkign structures in North America. A “Prefabricated Panel and Beam” approach to parking structure construction. This approach has learned from the failures of the past, and innovated a construction method that is more durable, reduces maintenance costs, and costs less to construct than traditional methods.
With the Kiwi Carpark System you can build parking structures that:
- Reduce construction costs
- Reduce maintenance costs by 90%
- Increase driver & pedestrian safety
- Streamline construction schedule
- Have a 100+ year lifespan
Contact us today to learn more.
