Solving Structural Problems Caused by “Unusual” Suspects

As forensic engineers, Pivot investigates structural and material failures in existing structures. Often, these failures can be attributed to one or more of the “usual suspects” (e.g., corrosion from environmental conditions, overloading, or improper design procedures). However, unexpected deterioration mechanisms can also lead to catastrophic failures and widespread deterioration. In recent investigations, Pivot identified bacterial microorganisms (aka little bugs or, for our purposes, “unusual suspects”) as the primary cause of failures in major infrastructure.

Pivot Engineers Investigate Sudden Failure of Pier

The team at Pivot investigated the sudden?failure of a pier supporting a major highway bridge in Wisconsin. The pier failure resulted in a 2-foot dip in the bridge. Pivot was retained to determine the cause of the failure and develop remediation measures. Pivot’s forensic investigation revealed that the steel piles in the bridge experienced significant loss in section due?microbiologically-induced corrosion (MIC).

Investigating Microbial Corrosion Damage

MIC is a naturally-occurring phenomenon where bacterial cultures grow over the exposed steel surfaces. These bacterial cultures produce acids that cause accelerated corrosion of the steel. This mechanism affects steel elements exposed to nutrient rich environments (e.g., steel piles in soil).

The same microbe-driven mechanism caused an environmental facility to fail. In this case, bacterial cultures attacked the concrete elements, causing loss of concrete cover and severe corrosion of embedded reinforcement.

Investigating microbially-induced deterioration requires good understanding of the biochemical activities occurring at the surface of the structure. Pivot’s evaluations of MIC activity typically include:

• assessment of the exposure conditions to examine the suitability of the environment for bacterial growth.
• biological identification of the microbial species that have grown over the affected structural components. This includes the use of growth culture tests and PCR array evaluations.
• forensic examination of the deteriorated structural elements to confirm that microbial byproducts caused the damage.

At Pivot, our team of experienced engineers examines both the usual and unusual suspects. Our goal is to help our clients reliably identify the probable causes of failures and develop appropriate remediation measures.

Contact us if you want to learn more about fighting “bugs” in steel and concrete.