Non-destructive Concrete Structural Analysis Could Mitigate Liability In Florida Condominiums

Non-destructive Concrete Structural Analysis Could Mitigate Liability In Florida Condominiums

Structural engineers, architects, and concrete restoration companies in Florida have a very big job in front of them. The engineers and architects have to certify the structural integrity of every high-rise condominium building in the state by providing “Milestone Inspections” that must be completed by December of 2024, and updated every 10 years after that.

If the estimated 54,000 licensed professionals fail to locate a structural fault that leads to significant damage, collapse, injury, or death, they could be held accountable by the condo homeowners association (HOA) who hired them, according to a new statewide law.  

In May of 2022 the Florida State Legislature unanimously passed a bill that expands Miami-Dade County’s high-rise condominium building codes to the entire state, and puts the existence of condo associations on the line by imposing both penalties ($500 or 60 days in jail per violation) and the oversight of local building authorities who may impose additional penalties if the Milestone Inspections are not completed by the end of 2024. Additional penalties can be handed down if the necessary concrete repairs found by inspections are not completed and certified in a timely manner.

Known as “The Surfside Bill,” CS-SB 5-D (in conjunction with SB 4-D) gives precise guidelines for inspecting and certifying the structural integrity of high-rise buildings (anything three stories or above) in Florida. It became knowns as the Surfside Bill after the tragic 2021 collapse of the Champlain Tower condominiums in Surfside, Florida that claimed the lives of 98 people.

Specifically, the new law lays out strict deadlines for Milestone Inspections to be conducted within 30 years of the date of the issuance of the Certificate of Occupancy(CO). If the building is within three miles of the coastline, the milestone inspection must be conducted within 25 years from the issue date of the CO. Once the initial inspection is complete, the HOA must recertify the structural integrity of their building with a Structural Integrity Reserve Study every 10 years.  

The responsibility for certifying the structural integrity of these thousands of concrete high-rises rests on their condo associations, and in turn, the structural engineers and architects those associations employ. Any repairs required by the milestone certification or recertification assessments will be the responsibility of the HOA, who in most cases will contract with a concrete restoration company to complete. Those repairs must also be certified.

Florida has 44,000 licensed engineers on record, and 10,917 architects were licensed to practice in the state in 2020. That means perhaps 54,000 people will have to certify, in writing, the structural integrity of Florida’s 1.52 million condominiums. At least one major contractor in the area reports a back log of over 100 milestone inspections waiting to be scheduled, and we are only at the beginning of the process.  

How Do You Conduct A Milestone Inspection?

The Milestone Inspection as laid out in the law consists of two phases. Phase One requires a licensed architect or engineer to visually inspect all habitable and non-habitable areas of a building, including the major structural components, and to provide a written assessment of the conditions. If the inspector determines that there is no substantial structural deterioration, then a Phase Two inspection is not required.

The Phase Two inspection must be performed if substantial structural deterioration is assessed during a Phase One inspection. Phase Two requires the engineer or architect to utilize additional methods – often destructive in nature, like coring or cutting – to determine if the structure is sound and safe for its inhabitants. They must also recommend a plan to fully assess and repair damaged and distressed portions of the building. However, the law also states they are to attempt to conduct these additional inspections in areas and in ways that cause the least disruption and damage to the structure, and are “easily repairable.”

This presents several potential issues for inspectors as stated in Architect Magazine in 2021.

“Although visual inspections can reveal signs of trouble, evidence like spalling and exposed rebar often suggest along-established problem. Core samples can be drilled before such symptoms present themselves, but invasive techniques have obvious drawbacks and can create new vulnerabilities. Non-invasive forensic methods, on the other hand, offer the best opportunity to catch concrete cancer before it is too late.”

The standard way to determine the structural integrity of a concrete slab is still what’s known as the “3-iron test,”“hammer test,” or sounding. An engineer or architect will walk through a building, applying a metal rod, a rebound hammer, or an actual golf club to the concrete to “sound” for defects like honeycombing, delamination, cracks, and voids.

A rebound hammer, also called a Schmidt hammer, being applied to a concrete wall.
A rebound hammer, also called a Schmidt hammer, being applied to a concrete wall.

The specially designed rebound hammer, or Schmidt hammer, can be employed to test the hardness based on the measured distance of the rebound, but in many cases, the inspector will simply knock a piece of metal against the concrete wall, floor, or ceiling to test for a variance in acoustics. A hollow sound means you have a void, but cannot define what kind: honeycombing, cracking, delamination, etc.

This method, while efficient in the short term, leaves you with many unanswered questions, and a lot of potential liability. This “swiss cheese” method of investigation and detection could give a condominium HOA a clean bill of health because the hammer or rod wasn’t applied directly to the area of the defect. The association would never know, until it was too late.

That is actually the industry standard – in 2022. Amazing, isn’t it?

What is Concrete Cancer & How Do You Find It Before A Building Collapses?

“Concrete cancer” refers to the invasion and expansion of water damage in the slab, sometimes brought on by the deterioration of the rebar that was placed to reinforce it as it was poured. The term was popularized in the book Concrete Planet and is an apt metaphor especially when you can visualize what interior concrete slab deterioration looks like.

The results of a UPV test on a concrete pillar
The results of a UPV test on a concrete pillar showing unseen structural integrity issues. UPV is the most cost-effective NDT approach for structural analysis.

Thanks to new technologies and applications, it is possible to “see” inside a post-tension slab and assess everything from honeycombing to cold joints in seconds, without drilling, cutting, or sounding.

Non-invasive and non-destructive structural analysis tools like Ultrasonic Pulse Velocity (UPV) and Tomography have a much higher accuracy rate in finding and identifying the exact type of concrete deterioration occurring in a building, cause no additional damage, and provide a clear, concise pathway to recommended repairs because they allow you to actually see what is going on inside the concrete.

How Does Ultrasonic Pulse Velocity Testing Work?

The simplest non-destructive testing option for concrete slab is Ultrasonic Pulse Velocity or UPV testing. UPV operates on the same underlying principle as sounding, by measuring the distance or velocity of a sound wave. It takes the “3-iron test”to a whole new, hyper-accurate level of visualization that is vastly superior when deployed by a trained and experienced operator and causes zero damage to the structure.

To use UPV on a slab the Project Manager places the transmitter on one side of the slab and the receiver on the other. Then, the transmitter sends a series of ultrasonic pulses, known as “taps,” through the concrete, where the receiver picks up the taps to measure the amount of time it took for the pulse to travel through the slab. The denser the concrete, the longer it takes for the pulse to travel, making it a simple job to find the interruptions occurring within.

The formula for calculating Pulse Velocity is V = L/T

V = Pulse velocity in meters per second

L = Distance between the transmitter and receiver centers

T = Transmit time in seconds

V =L/T

It takes a trained and experienced technician to ensure the precise data collection required to accurately calculate the UPV measurements and findings. The standards for how to nondestructively test and determine pulse velocity readings through concrete are provided by ASTM C597, 180/902-7, and EN 12504-4and EN 13791.

The ultrasonic wave forms and data points can be integrated to create maps that show the variations in pulse velocity that may point to potential structural issues.

UPV can locate the location and approximate size of:

  • Honeycombing
  • Inclusions
  • Cracks
  • Cold Joints
  • Overall Uniformity
  • Correlated Strength of the Slab
  • Changes Over Time

UPV is a cost-effective solution for non-invasive concrete imaging that can provide specific strength and structural integrity data as part of a Milestone Investigation or a recertification. There are, however, additional tools available to provide a more comprehensive picture of what is happening underneath the surface of a concrete slab that can confirm the UPV findings quickly.

How Tomography Can Supplement UPV Imaging For Structural Analysis

Tomography, also known as Ultrasonic Tomography can be used to both confirm UPV results, and to provide clear 3D tomographic imaging of the interior of the slab. Tomography is potentially more informative than a UPV test result because it maps the interior and provides a color-coded three-dimensional map – much like a 3D heat map – that shows in detail any insertions, cavities, cracks, holes, honeycombing, foreign inclusions, and other flaws. The warmer the color (red, orange, etc.), the more serious the structural defect.

Unlike UPV which needs a transmitter and receiver, each placed on opposing sides of the slab to determine the speed of pulse dispersion, Tomography allows for complete imaging from only one exposed surface because each of the tomograph’s multiple transducers both transmit and receive. Further, because tomography utilizes shear wave reflections instead of taps, its data processing provides more informative imaging that is instantly readable: solid concrete shows up as blue with 0% void, and damaged concrete with a 100% void like a hole, shows as red. Color variances between the red and blue extremes are interpolations of the data and shear wave reflections and provide provide an accurate assessment of the strength, depth of any defect detected, and structural integrity of the slab.

It is important to note that Ultrasonic Tomography requires more specialized training than UPV, and while UPV is less costly, Tomographic imagery provides the most precise internal strength and structural integrity measurements.

You are never left wondering what got missed due to human error because the entire interior of the slab is visualized in three dimensions and color, so you can immediately locate defects and deterioration, and their severity. This allows everyone from the architect to the HOA President to the individual condo owner to understand the condition of the structure easily, and also allows for an easier process for future Structural Integrity Reserve Studies by pin pointing areas of concern before they become significant.

How Drone Photogrammetry Can Aid High-Rise Visual Inspections

Because Phase One inspections require a visual inspection and complete assessment of all “habitable and non-habitable” locations of a structure, it is vital to be able to see the façade up close. However, when you’re inspecting a high-rise, it can be almost impossible to properly view the balcony on the 19th floor without significant time, equipment, and expense.

Façade inspection is where the aid of a UAV (unmanned aerial vehicle) or drone can prove invaluable. A drone outfitted with a high-resolution camera can capture point-in-time visuals to allow for up-close assessment of difficult exterior high-rise spaces, and even roofs, for Phase One Milestone Inspections. Those images can be rectified to provide a geolocated orthomosiac image of the entire façade for reference purposes.

Drone photogrammetry makes the 10-year Structural Integrity Reserve Study inspection and analysis much easier because the inspector can refer to previous images to immediately recognize significant structural changes. The images can be delivered in either RGB or FLIR formats.

GPRS is the only company that employs highly trained and specialized Project Managers who can provide UPV inspections and imaging, Tomography, drone photogrammetry, ground penetrating radar, and even 3D laser scanning services to completely visualize and assess any concrete structure with accuracy and evidence, so that necessary Milestone Inspections and recertifications can be completed with confidence.

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