Francis Scott Key Bridge (I-695) complete collapse after large ship hits it

[Beltway]

Why? They were built before the 1991 AASHTO vulnerability guidelines. They have no current vessel impact risk calculation using modern standards. The NTSB emphasized that inclusion on the list doesn't mean imminent collapse -- but it does mean unknown risk.

So because we don't know if they're vulnerable or not, that means they definitely are vulnerable. Gotcha.

It means what it says -- they were listed by the NTSB among 68 U.S. bridges requiring a vulnerability assessment for ship strike collapse risk.  I think you could say that means they are vulnerable.

No, you can't.  Not until an assessment concludes such.

" We also urge the owners of the 68 identified bridges to calculate whether
the probability of a bridge collapse from a vessel collision is above the acceptable
risk threshold established by AASHTO. If so, we urge them to develop and implement
a risk reduction plan that includes input from the interdisciplinary team, identifies
short- and long-term strategies to reduce risk, and considers the safety of the vessels
and structures in the waterways."

https://www.ntsb.gov/investigations/AccidentReports/Reports/MIR2510.pdf
March 18, 2025

Appendix B: US Bridges [68] Over Navigable Waterways Frequented by
Ocean-Going Vessels with Unknown Levels of Risk of Collapse from
a Vessel Collision
. . . . .

If it is still unknown for a bridge, then why?

Getting to the Key Bridge proposal, why has this not been done before design approval?

[Rothman]

Why? They were built before the 1991 AASHTO vulnerability guidelines. They have no current vessel impact risk calculation using modern standards. The NTSB emphasized that inclusion on the list doesn't mean imminent collapse -- but it does mean unknown risk.

So because we don't know if they're vulnerable or not, that means they definitely are vulnerable. Gotcha.

It means what it says -- they were listed by the NTSB among 68 U.S. bridges requiring a vulnerability assessment for ship strike collapse risk.  I think you could say that means they are vulnerable.

No, you can't.  Not until an assessment concludes such.

" We also urge the owners of the 68 identified bridges to calculate whether
the probability of a bridge collapse from a vessel collision is above the acceptable
risk threshold established by AASHTO. If so, we urge them to develop and implement
a risk reduction plan that includes input from the interdisciplinary team, identifies
short- and long-term strategies to reduce risk, and considers the safety of the vessels
and structures in the waterways."

https://www.ntsb.gov/investigations/AccidentReports/Reports/MIR2510.pdf
March 18, 2025

Appendix B: US Bridges [68] Over Navigable Waterways Frequented by
Ocean-Going Vessels with Unknown Levels of Risk of Collapse from
a Vessel Collision
. . . . .

If it is still unknown for a bridge, then why?

Getting to the Key Bridge proposal, why has this not been done before design approval?

The NTSB report doesn't address the new Key Bridge proposal, only the problems with the old one.

Looks like the new design does include measures to mitigate collision risk, so the assertion that design approval that it ignored it altogether doesn't seem supported.

https://www.enr.com/articles/60258-new-design-for-francis-scott-key-bridge-replacement-unveiled

[Beltway]

The NTSB report doesn't address the new Key Bridge proposal, only the problems with the old one.
Looks like the new design does include measures to mitigate collision risk, so the assertion that design approval that it ignored it altogether doesn't seem supported.
https://www.enr.com/articles/60258-new-design-for-francis-scott-key-bridge-replacement-unveiled

"The original 1.7-mile steel bridge, which collapsed after being struck by the disabled neo-Panamax container vessel M/V Dali in the early morning hours of March 26, 2024, provided only 1,209 ft of horizontal clearance between the main spans, and 185 ft of vertical clearance above the channel. The new bridge's cable-stayed main span will exceed 3,300 ft, an increase of more than 600 ft over the original continuous truss span length."

Not sure what they are thinking there; the proposed main span is 1,600 feet.
. . . . .
"the original bridge included four large dolphins to protect the pylons supporting the central through-truss spans. Each dolphin was composed of 25-ft-diameter sheet pile filled with tremie concrete and capped with reinforced concrete. The dolphins were fitted with 17-ft-long rubber fenders at various locations. Each of the main pylons also was surrounded by a 100-x-84.5-ft crushable concrete box and timber fender system."

That looks accurate, and refutes the critics that said there were no dolphins.
. . . .

The only thing they say about protection is this, and there is no engineering detailed about what they are proposing --

"Maryland officials say that the structure also will feature the latest in pier protection technology — the absence of which on the original Key Bridge may have contributed to the structure's collapse. "

[Rothman]

The NTSB report doesn't address the new Key Bridge proposal, only the problems with the old one.
Looks like the new design does include measures to mitigate collision risk, so the assertion that design approval that it ignored it altogether doesn't seem supported.
https://www.enr.com/articles/60258-new-design-for-francis-scott-key-bridge-replacement-unveiled

"The original 1.7-mile steel bridge, which collapsed after being struck by the disabled neo-Panamax container vessel M/V Dali in the early morning hours of March 26, 2024, provided only 1,209 ft of horizontal clearance between the main spans, and 185 ft of vertical clearance above the channel. The new bridge's cable-stayed main span will exceed 3,300 ft, an increase of more than 600 ft over the original continuous truss span length."

Not sure what they are thinking there; the proposed main span is 1,600 feet.
. . . . .
"the original bridge included four large dolphins to protect the pylons supporting the central through-truss spans. Each dolphin was composed of 25-ft-diameter sheet pile filled with tremie concrete and capped with reinforced concrete. The dolphins were fitted with 17-ft-long rubber fenders at various locations. Each of the main pylons also was surrounded by a 100-x-84.5-ft crushable concrete box and timber fender system."

That looks accurate, and refutes the critics that said there were no dolphins.
. . . .

The only thing they say about protection is this, and there is no engineering detailed about what they are proposing --

"Maryland officials say that the structure also will feature the latest in pier protection technology — the absence of which on the original Key Bridge may have contributed to the structure's collapse. "

Well, it was a third-party report rather than an actual design approval document.

Nice that it softened your tone.