Structural Defects in Garage Highlight Need for Structural Analysis and Concrete Testing

Structural Defects in Garage Highlight Need for Structural Analysis and Concrete Testing

A disintegrating parking garage in Manhattan temporarily shut down service between two Amtrak stations – but it could have been much worse were it not for a recently passed law that led to the issues being discovered.

The 107-space parking garage is in the Hell’s Kitchen neighborhood of Manhattan, where it sits on a platform built atop two Amtrack lines running from Penn Station north through Westchester County.

According to an Engineering News-Record article, an engineer initially discovered structural issues in the garage in early November 2023. The problems were so bad, the engineer called 911 to report them.

This led to city officials issuing a vacate order. Subsequent investigations conducted by the NYC Dept. of Buildings and Amtrack led to the discovery of two small holes, each several inches across, in the concrete on the entrance ramp of the garage and a ramp to the lower level.

It was eventually determined that all levels of the garage were defective with exposed rebar and cracks. City and Amtrack engineers initially believed they could install overhead protection above the tracks so trains could continue to run while repairs to the garage were undertaken. However, additional structural issues at the roof of the tunnel below the garage were discovered by workers while they were installing this protection.

Caution cones around a hole in concrete.
(Photo credit: ENR, via NYC Dept. of Buildings) Structural damage like this was found throughout a parking garage in Manhattan in late 2023. The issues necessitated a temporary closure of the Amtrak lines that run beneath the garage while repairs were completed.

A bulging masonry façade above one of the garage entrances, and a crumbling concrete retaining wall were also discovered on site.

City engineers ultimately determined the Amtrak lines needed to be closed until repairs were completed.

These defects were visible to the naked eye – no specialized investigative technology was required to see the issues which led to the temporary closure of the garage and the lines.

The garage sits next to a 38-story residential building and a school, but according to the ENR article, city officials said these buildings were not impacted by the structural defects as they were “contained to the area below the garage.”

In 2021, New York City passed a law that added new requirements for parking structure owners to hire an engineer to inspect their properties at least once every six years.

The NYC law went into effect January 1, 2022, requiring owners of parking structures to hire a NYS licensed and registered professional engineer to inspect the structure at least once every six years and file a report with the Department of Buildings documenting the results of the inspection that include buildings, or portions of a building, used for parking or storing motor vehicles, including space inside or under a building, and open parking garages and enclosed parking garages as define din the NYC Building Code.

Those who fail to comply with the law may be subject to hefty fines.

This law is why an engineer was evaluating the Hell’s Kitchen garage in the first place. Had the defects not been identified and the proper precautions taken, the situation could have easily devolved into something like what occurred in lower Manhattan in April, where the collapse of a 65-year-old, three-story parking garage claimed the life of one person and injured several others.

The issue of deteriorating concrete structures is not limited to parking structures, as evidenced by the tragic 2021 collapse of the Champlain Tower condominiums in Surfside, Florida, that claimed the lives of 98 people.

Both the Surfside and Manhattan stories highlight the need for routine structural analysis and concrete testing of these structures, so defects and damage can be identified and repaired before the unthinkable happens.

Qualified technicians use non-destructive technologies such as Ultrasonic Pulse Velocity (UPV) testing and Tomography to evaluate the integrity of concrete structures.

When problems are identified, precision concrete scanning tools like ground penetrating radar (GPR) and electromagnetic (EM) locating help find and map post-tension cable and rebar that may require repair, and items like embedded utilities that need to be avoided.

GPRS Project Managers conduct ground penetrating radar scans in a parking garage.
Ground penetrating radar scanning helps detect potential issues such as voids that can compromise the structural integrity of concrete structures.

Tools of the Trade

Ultrasonic Pulse Velocity (UPV) testing is the simplest non-destructive method of evaluating a concrete slab for structural defects. UPV involves placing a transmitter on one side of a concrete slab, and a receiver on the other. The transmitter emits a series of ultrasonic pulses, or “taps,” through the concrete and to the receiver, which measures the amount of time it takes for the pulse to travel through the slab.

The data from UPV testing can be used to create maps illustrating the variations in pulse velocity that may point to potential structural issues, including honeycombing, inclusions, cracks, and cold joints.

Tomography, or Ultrasonic Tomography, can be used to both confirm UPV results and to provide clear 3D tomographic imaging of the interior of the slab. It not only maps the interior of a concrete slab; it also provides a color-coded, three-dimensional image detailing any insertions, cavities, cracks, holes, honeycombing, foreign inclusions, and other flaws.

Ground penetrating radar complements UPV as the most accurate, versatile tool for seeing what’s inside a concrete slab without physically penetrating it.

GPR scanners emit radio waves that interact with any subsurface material they may encounter. Those interactions, sometimes referred to as “bounces,” are picked up by the GPR receiver, and displayed on a reading as a series of hyperbolas that vary in shape and size depending on the type of material encountered. A skilled GPR technician can interpret this data to provide a highly accurate picture of the subsurface infrastructure embedded in that concrete slab.

EM locating compliments GPR scanning by detecting the electromagnetic signals radiating from metallic pipes and cables.

These signals can come from the EM locator’s transmitter, which applies current to the pipe, or from current flow in a live electrical cable. They can also result from a conductive pipe acting as an antenna and re-radiating signals from stray electrical fields (detected by the EM locator functioning in Power Mode) and communications transmissions (Radio Mode). Signals are created by the current flowing from the transmitter which travels along the conductor (line/cable/pipe) and back to the transmitter. The current typically uses a ground to complete the current. A ground stake is used to complete the circuit through the ground.

By using GPR and EM locating in conjunction, qualified concrete scanning technicians can identify and map everything buried in or just beneath a concrete slab. This ensures safe concrete cutting and drilling and assists in concrete structural analysis by indicating the presence of voids and other defects.

Let GPRS Help You!

GPRS concrete scanning services assist in the evaluation of concrete structures by visualizing the subsurface infrastructure embedded in the concrete slab*.

Our mission is 100% subsurface damage prevention. By hiring a professional concrete scanning company like GPRS to visualize what’s inside your concrete before you cut or core it, you ensure you avoid costly and potentially dangerous subsurface damage.

From skyscrapers to sewer lines, GPRS Intelligently Visualizes The Built World® to keep your projects on time and on budget, and your people safe.

What can we help you visualize? Click the links below to schedule a service or request a quote today!

Frequently Asked Questions

Can GPR determine the difference between rebar and electrical conduit?

Yes, ground penetrating radar can accurately differentiate between rebar and electrical conduit in most cases. We have an extremely high success rate in identifying electrical lines in supported slabs or slabs-on-grade before saw cutting or core drilling.

Additionally, GPRS can use EM locators to determine the location of conduits in the concrete. If we can transmit a signal onto the metal conduit, we can locate it with pinpoint accuracy. We can also find the conduit passively if a live electrical conduit runs through it.

How is GPR used to identify tendons vs. rebar in a post-tensioned slab?

In post-tensioned structures, we typically find one mat of support rebar near the base of the slab. This mat is generally consistently spaced and remains at a constant elevation. Post-tension cables are generally found above this support mat and “draped” throughout the rest of the structure. The elevation of the cable is usually high near the beams and column lines and drapes lower through the span between beams and column lines. Knowledge of these structural differences allows us to accurately differentiate between components. Our Project Managers will leave you feeling confident in our findings and in your ability to drill or cut without issue.

Why do I need concrete scanning?

When you’re excavating for a new structure or renovating an old building, there are countless subsurface hazards that need to be accounted for prior to excavation, core drilling or saw cutting.

Cutting or drilling without first having the concrete scanned could be detrimental to your job site and company, and it could lead to subsurface damage that costs tens of thousands of dollars to repair and endangers everyone on the project.

*GPRS does not provide concrete testing services, and we provide structural analysis on a limited basis when required by the scope of the work.