Source: https://www.constructiondive.com, August 1, 2018
By: Kim Slowey

In the second of three reports, Nelson Forensics has determined that the cracks in the McKinney High School football stadium, according to The Dallas Morning News, were caused by: too much water in the concrete mix, which caused the concrete to shrink more than it should have while it dried; not enough concrete in the cross-section along pier lines; and too little steel reinforcing to control shrinkage cracking.

Nelson said that the stadium’s design was not at issue but rather that construction was not carried out in accordance to the project documents.

The company reiterated its position that the cracks did not pose safety concerns, only durability concerns. However, Nelson said that while cracking at the visitor concourse did not affect the structural integrity of the slabs, if the cracks are left unrepaired, they could widen and become a tripping hazard. Water intrusion could also corrode reinforcing steel.

McKinney Independent School District told NBC 5 that it is withholding payment from Manhattan Construction and Stantec Architecture until repairs are complete. An upcoming third report from Nelson will focus on the lower bowl of the stadium.

Dive Brief:

• Manhattan Construction Co. and Stantec Architecture, contractor and designer, respectively, for an approximately $70 million high school football stadium under construction in McKinney, Texas, both told the school district’s board of trustees at its monthly meeting on May 29 that they would work to find the cause of significant concrete cracks and, if either is at fault, pay to fix them, according to a McKinney Independent School District news release.
• School district officials noticed cracks at both the visitor and home concourses, as well as at the lower bowl wall, in January, and one member of the board expressed concern that the issue hasn’t been rectified. The school district has hired investigative and forensic engineering firm Nelson Forensics to work with Manhattan and Stantec to uncover the reason behind the cracks. The district anticipates being able to provide the board an update at its next regular meeting later this month.
• The 12,000-seat arena is one of the most expensive high school stadiums in the country, according to The Dallas Morning News, and is scheduled for completion in time for this fall’s football season. Construction of the stadium is being financed as part of a $220 million voter-approved bond package.

Dive Insight:

While cracks in concrete can signal problems with structural integrity, they can also sometimes be simply cosmetic issues that do not undermine safety.

When crews were performing repair work on the failed Oroville Dam spillway in Oroville, California, last November, the Federal Energy Regulatory Commission expressed concern over small cracks that appeared in new concrete slabs. The agency, however, and the California Department of Water Resources, came to agree that the cracks did not affect the integrity of the concrete, and both the existing work and concrete mix for future slabs were left unchanged.

And then there are cracks that could indicate a more serious issue.

During an investigation to determine the cause of a deadly pedestrian bridge collapse at Florida International University in Miami, Florida, the National Transportation Safety Board discovered, according to the Miami Herald, that cracks appeared in the bridge’s span as early as February 24, about 19 days before it fell, and then in a diagonal support prior to installation. The bridge was built offsite then installed over the course of a weekend, raising questions as to whether the stress of installation was a factor in the bridge’s failure or post-installation tightening of steel rods was to blame. The investigation is still ongoing, and no cause has yet been officially determined.