Matt Dursh

Thanks for reading my 🧵. I am a Professional Engineer, Bridge Designer, and Design-Build Project Manager.

Designing and building bridges over water is my career specialty.

I will continue to provide updates on the rebuild of the Francis Scott Key Bridge in Baltimore, MD. 7/7

The Francis Scott Key Bridge rebuild is being done as a Progressive Design-Build method of project delivery.

The project is in the Preconstruction phase which advances the design, determines the full scope of work, and agrees on a Guaranteed Maximum Price for the work.

6/7

Demolition work to remove the remaining Francis Scott Key Bridge will begin later in the Spring.

Work is for a turn key contract for on-land demolition, meaning one contractor will deliver the full services on land.

Over water demolition is subcontracted in segments. 5/7

Land surveying will obtain topography and elevations of the project site.

An underwater survey called bathymetric will be done using sonar tech to map the mudline.

This photo is a side scan sonar of the collapsed Francis Scott Key Bridge after the Dali hit the bridge. 4/7

Soil is carefully collected from the sampler, visually classified, and then sent to a lab to test it's properties.

The blow counts and properties will be used by the Francis Scott Key Bridge Geotechnical and Structural Engineers to design foundations for the new bridge.

3/7

A soil investigation will be performed to determine the characteristics of soil to support the Key bridge.

Samples are collected using a Standard Penetration Test (SPT).

A heavy weight is dropped from a height to push the sampler into the ground while counting blow counts. 2/7

Site work for the rebuild of the collapsed Francis Scott Key Bridge finally begins next week.

This 🧵 overviews the what will occur next on the reconstruction of the Key Bridge.

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Many such cases when contractors underestimate form pressure from wet concrete.

Concrete is 2.5 times denser than water.

Rebar is artwork buried in concrete.

The fire started the morning of November 1st, 2024 in Cincinnati, Ohio.

The bridge is currently stabilized and demolition of the damaged spans will begin after Thanksgiving.

Will need to do a 🧵 on this one in the future.

The Daniel Carter Beard Bridge was severely damaged in a fire.

The fire originated from a wooden playground with a rubber flooring underneath the bridge.

The highly combustible material burned with such intensity that it separated the steel bridge beams from the concrete deck.

Francis Scott Key Bridge rebuild and bridge design update.

This 🧵 overviews the bridge type, span lengths, pier protection, and how the replacement Francis Scott Key Bridge will be constructed. 1/9

The Francis Scott Key Bridge fell after the MV DALI lost power and struck a channel pier.

The pier column was hollow.

In this 🧵 details about the reinforced concrete pier design of the Key Bridge. 1/9

Bridge design and the rebuild of the Francis Scott Key Bridge.

A brief 🧵 about foundations for bridge structures and info on the upcoming Early Works construction of the replacement Key Bridge.

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The engineers of the Francis Scott Key Bridge can determine pile capacity in various ways.

While pile driving the capacity, stresses, and more info is calculated in real time.

After driving, a static load test can be done to verify the actual capacity of the steel pile.

4/4

A Test Pile program verifies the soil that supports a bridge provides the necessary capacity to resist the loads from the structure.

The Francis Scott Key Bridge rebuild will use a Load Test Monitoring Geotechnical Consultant to determine capacity of the driven steel piles.

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Bridges are supported on deep foundations that transfer loads from the structure to earth.

The Francis Scott Key Bridge rebuild will use driven steel piles as the deep foundation.

Early Works construction for the Test Pile Program includes welders and rolled steel shapes.

2/4

Bridge design and the rebuild of the Francis Scott Key Bridge.

A brief 🧵 about foundations for bridge structures and info on the upcoming Early Works construction of the replacement Key Bridge.

1/4

Reconstruction of I-26 over the Nolichuky River in Tennessee is making progress after being destroyed by Hurricane Helene.

The bridge abutment has been rebuilt and new prestressed concrete girders have been installed.

The other bridge on the left is open to one lane each way.

You are welcome. Thanks for the comment.

I will continue to post details about the collapse of the Francis Scott Key Bridge and the upcoming rebuild of the Key Bridge.

I am bridge designer, Professional Engineer, and design-build design manager of heavy civil infrastructure projects.

Thanks for reading my 🧵. 9/9

The rebuild of the Francis Scott Key Bridge is also likely to use a hollow reinforced concrete column as the pier substructure.

The channel piers of the replacement Key Bridge will be protected against vessel collision.

Anticipate the use of rock islands and dolphins. 8/9

Would the Francis Scott Key Bridge still be standing if Pier 17 was solid?

No, the forces caused by the allision far exceeded the column's capacity.

To protect bridges against vessels the size of M/V Dali a pier protection system is used to run aground the ship first. 7/9

Tension is resisted by the rebar. The further away the steel is from the concrete face, the more structural capacity it offers.

The reinforcing steel "works best" when it is near the outside of the section.

This is the fundamentals of reinforced concrete design. 6/9

Concrete works well in compression, but has little tension capacity.

The hollow section provided enough area of concrete to resist the maximum compression loads.

By using a hollow pier section, the Key Bridge engineers reduced the weight of the column legs by about 50%. 5/9

Hollow columns, found on the existing Francis Scott Key Bridge and many other structures, are used as a structurally efficient reinforced concrete design.

It lessens the weight of the pier. This saves on concrete materials and reduces the loads resisted by foundations. 4/9

The outer dimensions of the Key Bridge's square columns is 14 feet by 14 feet.

The wall thickness of the column is 2 feet with a 4 feet thick slab that encloses a ~19' hollow void.

Hollow columns are commonly used for large bridges.
Why do this and how does it work? 3/9

The Dali struck Pier 17 of the Francis Scott Key Bridge, causing the bridge to collapse.

Pier 17 was a reinforced concrete column with a hollow square cross section.

In hollow columns, the middle of the column is not filled with concrete. 2/9

The Francis Scott Key Bridge fell after the MV DALI lost power and struck a channel pier.

The pier column was hollow.

In this 🧵 details about the reinforced concrete pier design of the Key Bridge. 1/9

Agree.