Content Menu
● Introduction to the Gerald Desmond Bridge Replacement Project
● What is a Movable Scaffolding System (MSS)?
● How the MSS Was Used in the Gerald Desmond Bridge Construction
>> 1. Assembly and Lifting into Position
>> 2. Segment Construction Process
>> 3. Integration with Seismic Design
● Benefits of Using the Movable Scaffolding System
● Engineering Challenges and Solutions
● Conclusion
● FAQ
>> 1. What is a Movable Scaffolding System (MSS)?
>> 2. Why was the MSS chosen for the Gerald Desmond Bridge?
>> 3. How heavy is the MSS used in this project?
>> 4. How was the MSS lifted into place on the bridge?
>> 5. What are the seismic design considerations related to the MSS?
● Citations:
The Gerald Desmond Bridge Replacement Project in Long Beach, California, is a landmark infrastructure endeavor that utilized innovative construction techniques to build one of the tallest cable-stayed bridges in the United States. A key technology employed in this project was the Movable Scaffolding System (MSS), a self-launching, traveling steel structure that enabled efficient, safe, and rapid construction of the bridge's approach spans and road deck segments.
Introduction to the Gerald Desmond Bridge Replacement Project
The original Gerald Desmond Bridge, built in the 1960s, served as a critical transportation link at the Port of Long Beach but was no longer adequate for modern traffic and shipping needs. The replacement project began in 2013, aiming to build a new cable-stayed bridge with two 515-foot towers and a main span elevated 205 feet above the water to allow larger ships to pass underneath.
The project involved constructing long approach spans leading to the main cable-stayed section. These approach spans were built at heights ranging from 80 to 150 feet above ground level, presenting significant construction challenges that traditional falsework methods could not efficiently address.
What is a Movable Scaffolding System (MSS)?
The Movable Scaffolding System is a massive, self-launching steel structure designed to support formwork and reinforcement during the casting of concrete bridge segments. Each MSS unit weighs approximately 3.1 million pounds and travels forward along the completed sections of the bridge to support the next segment.
Key Features of the MSS:
- Self-launching: The MSS can move forward on its own without the need for cranes or ground-based falsework.
- Twin Units: Two MSS units were used simultaneously—one on the west approach (orange unit) and one on the east approach (blue unit).
- Supports High Elevation Work: The MSS enabled construction of approach spans 80 to 150 feet above ground, where traditional scaffolding would be impractical.
- Steel Box Girder Structure: The MSS consists of a heavy box girder center section supporting the concrete span and lighter trusses at each end for launching.
How the MSS Was Used in the Gerald Desmond Bridge Construction
1. Assembly and Lifting into Position
The MSS units were assembled on the ground and then lifted into place atop the bridge piers using strand jacks. This lifting process was carefully engineered to raise the 3.1 million-pound structures at a rate of about 20 feet per hour during work shifts.
The MSS was supported on temporary brackets attached to the pier columns. These brackets were lifted using a rigging system with rubber wheels that guided them up the columns, then locked into place with shear lugs and tensioned bars to secure the MSS firmly.
2. Segment Construction Process
Once in place, the MSS supported the formwork and reinforcement for each concrete segment of the bridge deck. Workers installed steel reinforcement and formwork on the MSS platform, then poured concrete to form the box girder segments.
After the concrete cured, the MSS was launched forward on rails or launching wagons to the next span location, where the process repeated. This method allowed continuous, efficient construction of the approach spans without the need for extensive ground-based falsework.
3. Integration with Seismic Design
The bridge design required integral column connections for seismic performance. The MSS construction method was adapted to accommodate these design features, including expansion joints and hinges at quarter-span points to allow for thermal and creep movements while maintaining structural integrity during earthquakes.
Benefits of Using the Movable Scaffolding System
- Efficiency: The MSS allowed rapid construction of long spans with fewer joints and stressing points, reducing construction time.
- Safety: By eliminating the need for extensive falsework and ground scaffolding, the MSS reduced risks to workers and minimized ground impact.
- Cost-Effectiveness: The self-launching nature of the MSS reduced the need for cranes and other heavy equipment, lowering overall costs.
- Minimal Environmental Impact: The MSS minimized disruption to the waterway and port operations by reducing the footprint of construction equipment on the ground and water
Engineering Challenges and Solutions
- Heavy Lifting: Lifting the 3.1 million-pound MSS units required precise engineering and coordination using strand jacks and temporary support frames.
- Overhead Constraints: The MSS obstructed crane access, so the brackets had to be lifted using a marionette-like rigging system with rubber wheels to guide them up the columns.
- Seismic Considerations: The MSS construction sequence was closely coordinated with the bridge's seismic design, ensuring integral pier connections and expansion joints were properly incorporated.
- Weather and Environmental Factors: Construction was planned to minimize impact on port operations and to ensure worker safety in a marine environment.
Conclusion
The use of the Movable Scaffolding System in the Gerald Desmond Bridge Replacement Project represents a significant advancement in bridge construction technology. By enabling the efficient, safe, and economical construction of high-elevation approach spans, the MSS helped deliver a modern, iconic cable-stayed bridge that meets the demands of modern shipping and traffic. This innovative approach not only reduced construction time and costs but also minimized environmental impact and enhanced worker safety. The Gerald Desmond Bridge now stands as a testament to engineering ingenuity and the effective application of movable scaffolding systems in large-scale infrastructure projects.
FAQ
1. What is a Movable Scaffolding System (MSS)?
A Movable Scaffolding System is a large, self-launching steel structure used to support formwork and reinforcement during the casting of concrete bridge segments. It moves forward along the bridge as construction progresses, eliminating the need for ground-based falsework[1][2].
2. Why was the MSS chosen for the Gerald Desmond Bridge?
The MSS was chosen because it allowed efficient construction of approach spans 80 to 150 feet above ground, where traditional scaffolding would be impractical. It also improved safety, reduced construction time, and minimized environmental impact[1][2].
3. How heavy is the MSS used in this project?
Each MSS unit weighs approximately 3.1 million pounds (about 1,400 metric tons)[1][5].
4. How was the MSS lifted into place on the bridge?
The MSS units were lifted using strand jacks supported on temporary frames atop the pier columns. Brackets were also lifted using a rigging system with rubber wheels to guide them up the columns and secure the MSS[2].
5. What are the seismic design considerations related to the MSS?
The bridge design required integral column connections and expansion joints to accommodate seismic forces. The MSS construction sequence was coordinated to ensure these features were properly integrated, maintaining structural integrity during earthquakes[2].
Citations:
[1] https://newgdbridge.com/wp-content/uploads/2018/02/Fact_Sheet_MSS_1-14-16.pdf
[2] https://www.aspirebridge.com/magazine/2021Spring/CBT-MovableScaffoldSystems.pdf
[3] https://newgdbridge.com/almost-done-with-building-east-side-approaches/
[4] https://www.youtube.com/watch?v=U4crdgGDvW4
[5] https://www.roadsbridges.com/bridges/bridge-construction/news/10649981/bridge-construction-massive-scaffolding-installed-at-new-long-beach-bridge-in-california
[6] https://newgdbridge.com/4754-2/
[7] https://www.transport.nsw.gov.au/system/files/media/documents/2023/moveable-span-bridge-study-volume-2-bascule-and-swing-span-bridges-part-1.pdf
[8] https://lbpost.com/news/business/development/video-captures-3-1-million-pound-bridge-builder-moved-during-work-on-gerald-desmond-project/
[9] https://newgdbridge.com/gallery/videos/
[10] https://en.wikipedia.org/wiki/Suspension_bridge
