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Golden Gate Towers Largely Rated 'Good'

Monday, July 30, 2018

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April’s inspection of the towers of San Francisco’s iconic Golden Gate Bridge—the first detailed inspection of the towers in the structure’s 80-year history—revealed steel and concrete in good condition for the age of the span, according to a report to the bridge’s operators.

Golden Gate inspection
Images: Golden Gate Bridge, Highway and Transportation District

Inspectors rapelled down the iconic bridge's towers in April and May for their first detailed inspection in the span's history.

The inspection, performed by workers who rappelled down the towers using ropes, was spurred by new federal regulations requiring increased inspections of many major bridges; it was part of the bridge’s biannual inspection program. Steel below the roadway was inspected in early April, the towers’ concrete foundations in mid-April and the towers above the roadway—the part of the job that got most of the attention given inspectors’ Spider-Man technique—began in late April and lasted into early May.

Fair to Good

The inspectors found paint defects over about 12.5 percent of the south tower’s surface and about 4.5 percent of the north tower. The south tower was found to have corrosion over about 7 percent of its surface—or about 19,000 square feet—while the north tower had rust and structural defects over only 2 percent of its surface.

golden gate inspection

The steel on both towers was rated as "good" or "fair."

All steel on both towers was rated as either “good” condition or “fair.” Good condition is defined as no rust or cracking, and connections that are in place and functioning as intended. Fair is defined as a surface with “freckled rust” and corrosion, but no section loss; cracks that have self-arrested or been stopped by measures taken by maintenance operations; and/or loose (but not missing) fasteners with pack rust.

Any section loss spotted by inspectors was minor, and corrosion, though widespread in certain parts of the south tower (especially south- and west-facing facade plates), was not considered to be especially serious, especially because much of it was on architectural, not structural, components.

Corrosion

Some south- and  west-facing surfaces showed corrosion  and paint defects; the south tower will be blasted and repainted as part of the larger seismic retrofit project that's underway.

Inspectors also deemed the concrete piers to be in a generally good condition, with areas of delamination and spalling, as well as some abrasion and surface weathering on the north pier.

Planned Blasting and Painting

According to the Golden Gate Bridge, Highway and Transportation District, an upcoming phase of the bridge’s seismic retrofit project includes repairs to the facades of both the north and south towers, and the cleaning and repainting of the south tower above and below the roadway. The south tower will be fitted with containment and prepared to bare steel and painted with a three-coat system.

   

Tagged categories: Bridges; concrete; Corrosion; Steel

Comment from Oscar Duyvestyn, (7/30/2018, 7:28 AM)

I'd be interested to see what they are going to do with the rivets, plate edges and other small crevices after the existing coatings have been blasted off.


Comment from Tom Schwerdt, (7/30/2018, 8:43 AM)

Typically one would stripe coat rivets and plate edges, possibly with caulk for crevices.


Comment from Oscar Duyvestyn, (7/31/2018, 1:09 AM)

That's right Tom, typically that's what they do. But will it work? This is always a very challenging aspect of repainting riveted structures. Careful consideration of how to approach this is critical, hence my remark.


Comment from Tom Schwerdt, (8/1/2018, 8:05 AM)

With proper application and inspection, my experience in the field and in the lab is that typically stripe coating does better protect edges.


Comment from Willie Mandeno, (8/6/2018, 6:15 PM)

Will the "three coat system" for the south tower repaint be again be a moisture cure urethane based system, like we also use on the riveted Auckland Harbour Bridge in New Zealand?


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