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 Permit drawings for the replacement Key Bridge shows the concept main span as a cable stayed bridge design.

A vertical clearance of 230 feet will be provided, greater than before.

The existing collapsed Francis Scott Key Bridge had 185 feet vertical clearance. 2/9

The Francis Scott Key Bridge collapsed after vessel collision from the MV DALI.

This tragedy was entirely avoidable. A small change in course would have prevented ship impact.

All means to control the the motor vessel were unavailable.

A 🧵 about the unseaworthy Dali. 1/9 There were four means available to control the Dali. The propeller, rudder, anchor, and bow thruster.

All of them failed.

The propulsion and steering was lost during two power outages on the motor vessel Dali.

What caused loose electrical wiring and the breakers to trip? 2/9

Bridge collapse in Dresden, Germany.

The Carola Bridge fell into the waters of the Elbe River on September 11.

A 🧵about bridge design.

(1/9) Carola Bridge, also known as Carolabrücke, was a prestressed concrete box girder bridge.

The largest span was 393 ft with a total bridge length of 1,230 ft.

This complex bridge was constructed in 1971 using a span-by-span cast in place concrete on falsework supports.

(2/9)

Bridge design for extreme storms. A 🧵

Two spans of the Phong Chau Bridge in Vietnam collapsed during Typhoon Yagi.

This bridge failure mechanism is one of the most common.

What happened and how is it prevented? (1/10) The water crossing of the Phong Chau Bridge was a three span through truss bridge.

One in water pier collapsed, causing the adjoining two spans to collapse.

The third truss span did not collapse because that was a simply supported span, not a continuous bridge.

(2/10)

The Design Builder has been selected for the rebuild of the Francis Scott Key Bridge!

The design of the replacement bridge begins now. This is what happens next.

A 🧵 about bridge design and construction. (1/12) The winning Design Builder for the project is Kiewit Infrastructure.

They assembled a project team, submitted a technical proposal, and were selected by the Maryland Transportation Authority.

They are now entering Phase 1 of the Progressive Design Build project.

(2/12)

The vertical clearance for the rebuild of the Francis Scott Key Bridge has not been finalized.

Existing bridge had a navigable clearance of 184 feet. Recently built electrical lines now controls at 214 feet.

A 🧵 on construction cost of transportation infrastructure.

1/x The vertical clearance of a bridge affects the entire roadway and is a primary factor in the final construction cost.

As a bridge increases in height, the total bridge length also increases.

This provides distance for vehicles to safely navigate the vertical curve.

2/10

The navigation channel has fully reopened after the collapse of the Francis Scott Key Bridge.

A total of six bridge spans fell after the M/V Dali struck the bridge.

It took 76 days to remove over 50,000 tons of the wreckage.

A 🧵 on next steps to rebuild the Key Bridge. (1/8) Bridge removal has only been of the collapsed spans.

The substructures and foundations that supported the bridge still remain. What happens to them?

The Request for Proposal for the bridge indicates an early works package that will include demolishing the bridge.

(2/8)

How will the Francis Scott Key Bridge be rebuilt?

The Transportation Authority says it will be a Progressive Design Build.

The winning contractor will be chosen by qualifications and the construction cost provided later.

A brief 🧵 about contracts for roads and bridges. 1/10 Let us begin with the Bid-Build method of project delivery.

Here, the contractor uses a completed set of construction documents to provide a bid price. The low bidder wins the project.

This requires final plans for construction, which the new Key Bridge does not have.

2/10

A bridge has partially collapsed after a barge collision with a pier.

The Pelican Island Causeway is the only route on and off the island in Galveston, Texas.

Railroad spans collapsed, causing damage to the vehicular bridge.

A 🧵 about this bridge and next steps. (1/10) The bridge has three different superstructure types.

The channel span is a moveable structure called a bascule, aka a draw bridge.

Steel plate girders extend for several spans, but the barge struck the third type.

Furthest from the channel, a concrete beam span fell. (2/10)

Bridge Analysis to remove the Francis Scott Key Bridge. A 🧵

Extracting the steel at the bottom of the Patapsco River will be complex.

The structural steel arch still has capacity to it, similar to bending a paperclip.

How do you determine the sequence to cut? (1/x) You start with the existing bridge plans.

They will be used to determine the weight of the bridge and the capacity of the steel members.

Lift points will be established to confirm the damaged steel can support itself during removal.

3D survey will be used extensively. (2/x)

The gas and electric utilities in proximity to the Francis Scott Key Bridge Recovery.

What can be considered to enhance safety and facilitate schedule?

Can the electrical transmission lines be de-energized and temporarily removed to enable crane activities on both sides?

1/8 This would be a monumental ask of the Baltimore Gas and Electric company.

Especially because these were only just recently relocated to overhead.

A new temporary directional bore can be done and should take a few months, if accelerated.

This provides a better work zone. 2/8

The collapsed steel spans should not be reused.

When verifying safety for traffic, many members will be compromised due to permanent deformations and other signs of distress.

The continuous bridge was built using temporary towers, this changes the "locked-in" stress.

1/x

https://twitter.com/elonmusk/status/1773931137531810233

Temporary steel towers were used to support the bridge during construction.

Their use and timing of removal dictates when each steel member is fully engaged to support the self weight of the bridge.

If one is removed too soon, or not used at all, this changes everything.

2/x

Bridge design for vessel collision. A🧵

The main span of the Francois Scott Key Bridge is 1300 ft. It also has 185 ft of clearance, making this a massive bridge.

This type of bridge is considered complex.

Baltimore is in for a long haul before replacement. Here is why.

1/x We design modern bridges for ship impact, but this was not always the case.

In 1980 the Sunshine Skyway Bridge also collapsed from vessel strike.

The photo below is the original Skyway. Similar bridges and identical failure.

The Skyway collapse changed bridge design.

2/x