Designers of the $1 billion Ship Channel Bridge project made faulty assumptions about the soil around the bridge’s critical supports above and below ground, did not properly account for winds on the stability of the supports and failed to factor in the weight of two-way traffic on the southbound span while the northbound structure is built, according to engineers hired by the county to review the plan.

The structural and design issues were among 21 “significant concerns” raised by COWI, an international consulting and engineering firm brought on by Harris County Commissioners Court earlier this year to review the design by FIGG Bridge Group.

Others issues include pylons, pillars and support cables that do not meet the county’s specifications in various ways and possible changes to how construction should proceed on the bridge that carries the Sam Houston Tollway across the Houston Ship Channel. The tollway is owned and managed by the Harris County Toll Road Authority, which began designing the bridge in 2014. Construction started in April 2018.

Construction on the span was halted in early January when some of the more serious concerns cited by COWI were raised. Work on the approaches to the bridge continues.

In its summary, COWI said solving the issues would require revisions to yet-to-be-built bridge components and corrections to some components that already have been constructed. In some cases, additional study would be needed to determine “whether the potential consequences of leaving certain already constructed components as-is would be acceptable even though this review has identified that they do not conform to the project standards.”

COWI’s report is scheduled to be discussed Tuesday by Commissioners Court.

“I am glad I did this study and pushed for a non-Harris County and non-Texas firm,” Precinct 2 Commissioner Adrian Garcia said. “If these findings are significant, we will deal with it.”

Toll authority and county leaders said they were withholding judgment on the severity of the concerns until FIGG and COWI could work through the matters. Though COWI relied on some of FIGG’s documentation, the two companies intentionally did not communicate.

“To have a fully independent review meant they had to have that wall between them,” said Peter Key, interim executive director of the toll road authority.

County officials, at Garcia’s request, hired COWI early last year to review the Ship Channel Bridge work following the collapse of a pedestrian bridge in Florida designed by FIGG. Though the pedestrian bridge was designed by a different team of engineers, Harris County officials said they wanted a re-evaluation out of an abundance of caution.

Garcia said the county already is $300 million into the project and it remains a priority despite the delay.

“Our economy needs it and our mobility needs it, but I need to make sure so we can say we have done everything humanly possible that this bridge is safe.”

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The companies will have a lengthy list of matters to discuss. In their final report, the COWI evaluators detail their concerns with the bridge’s design, including worries that:

Parts of the massive pillars meant to hold up the cable stay bridge do not meet the county’s specifications

Pylons sunk into the boggy ground along Buffalo Bayou do not meet the county’s set design standards, along with inadequate structural capacity for the base of the towers

Curves along the giant towers do not meet capacity requirements for carrying the load

C ables that support the bridge and thread through the massive towers do not meet the project’s standards for avoiding slight movements.

Combined, the issues raised by COWI affect nearly every major facet of the design and construction of the bridge, from below ground to high above the roadway where the towers will rise to 514 feet.

FIGG officials, in a statement, said they look forward to working through COWI’s findings.

“Reviews are common in the bridge engineering profession, and it is typical for engineering analyses from two companies to have differences,” officials said. “It was fully expected that there would be some comments to address.”

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Key said the first step will be to let the companies work through the concerns. Only then, he said, can Harris County “determine how significant a time impact and how significant a financial impact” the project faces.

He said toll road officials hope to update the commissioners on the project “as soon as practical, which may mean about four weeks’ time.”

“We know we have to move on it,” Key said.

After early discussions with COWI and FIGG about the pylon design, officials opted to halt work. At the time, HCTRA’s leadership said they expected a three-week delay.

The bridge, which HCTRA has planned for more than a decade, replaces the existing steep and stressed bridge, which was built in 1982. Work started with the southbound span. Once the southbound bridge is completed, crews will tear down the current bridge and build a northbound twin. Work was expected to take until 2024, though the recent delays push that back.

Cables strung through the towers will support the roadway built from pre-cast concrete segments that will be installed as workers move away from the pylons. The road will remain about 175 feet above the ship channel, around the height of the current bridge, but the distance between the two towers will be far greater at more than 1,300 feet, compared with 750 feet today.

The added space will allow for deepening the ship channel and will give ships more room to maneuver — a priority for Port of Houston officials — while giving the tollway capacity. Officials expect use of the tollway to swell to about 158,000 vehicles daily by 2035, up from around 60,000 now.

The Ship Channel Bridge is not the only span slowed by questions related to FIGG’s designs. The Texas Department of Transportation stopped work on the Harbor Bridge in Corpus Christi in November and dropped FIGG from the project in January.

The work on both bridges came into question following the collapse of a pedestrian bridge at at Florida International University in March 2018, killing six people. FIGG and its consultants were held responsible for the collapse after a review by the National Transportation Safety Board. FIGG disputed some of those findings, saying the collapse was “the result of a complex series of events and failings by parties at multiple stages of the project.”

Garcia said however the concerns are addressed, that is precisely what he wants to avoid on one of the busiest truck routes in the region across the Houston Ship Channel, the main artery of commerce in the area.

“We are going to close the books on the independent review and begin the process of allowing the two firms to talk,” Garcia said. “Hopefully, it becomes a lot of nothing.”

dug.begley@chron.com