The 3D/4D model includes fabrication and delivery of deck and tower sections for the self-anchored suspension portion of the bridge.
With nearly 300,000 vehicles crossing the San Francisco-Oakland Bay Bridge (SFOBB) daily, it is one of the busiest bridges in the nation. Following the 1989 Loma Prieta earthquake, the California Department of Transportation (Caltrans) decided to replace the east span of the Bay Bridge with a new structure and to seismically retrofit the west span while it remains open to traffic. When completed, this project will be among the largest public works projects in state history, costing $6.3 billion, and will feature the world’s largest self-anchored suspension span.
One of Caltrans’ original mandates was to keep the bridge open to traffic during the retrofit projects. But the agency realized that with a robust communication plan, closing the bridge in extreme cases was a possibility. But some of the detours and construction operations were so complex and radical that conveying them demanded a new communications method. Consequently, with the start of construction, Caltrans demanded a new, more dynamic outreach and information strategy to inform the public and project stakeholders about construction activities and impacts.
On Labor Day weekend of 2007, project team members, including representatives from public agencies, contractors, and consultants working on the seismic retrofit of the bridge’s east span, took part in an unprecedented engineering event—demolition and replacement of a 300-foot section of the original concrete viaduct connecting the east span to the Yerba Buena Island tunnel. The new viaduct would be rolled in on rails to replace the old structure, requiring closure of the bridge for three days. A radical and proactive communication campaign was required to head off a potential traffic and public relations nightmare.
Not since the 1989 Loma Prieta earthquake had the bridge been closed for this length of time. The planned closure would have a major impact on the economic and social functionality of the entire Bay area. The challenge for Caltrans was to communicate its intentions to close the bridge and the reasons for the closure in a manner that the public could understand and support. To do this, it was critical to show the construction activities that would require bridge closure in realistic, sequential renderings. The level of detail in the simulation would not have been possible without development of a sophisticated 3D/4D model.
A key component of the communications plan for construction of the new viaduct was development of accurate, photo-realistic construction sequence simulations of the roll-in. Design visualizations and animations based on a 3D/4D model of the bridge were used to explain construction activities leading up to and including the roll-in of the new structure during the three-day Labor Day weekend in 2007. These illustrations provided for stakeholders an easy-to-follow picture that detailed the following:
- construction staging adjacent to the viaduct before bridge closure;
- complex demolition stages during bridge closure;
- various pieces of equipment and their locations during the process; and
- "snapshots" of the area depicting the effects of the project during the most intense phases of construction.
The media campaign was so successful that the roads and highways on both sides of the bridge were unusually quiet and traffic-free for the entire three-day weekend closure. Media stories ran statewide. On the evening before the closure, traffic was so light that the bridge closed 40 minutes earlier than scheduled. Use of the photo-realistic construction sequence simulation in the outreach campaign allowed audiences to understand the message better.
The project won the 2007 California Transportation Foundation’s Tranny Award. Caltrans will continue to use this method of public outreach and education for other large-scale closures of critical arteries because it can rely on this efficient means of communication to affect motorists’ behavior.
Design visualizations and animations based on a 3D/4D model of the bridge were used to explain construction activities, including the roll-in of the new viaduct during the three-day Labor Day weekend in 2007.
Although initially developed as an outreach tool to inform the public about complicated construction activities and to garner public acceptance and support, the 4D construction sequencing visualizations have proved to be an invaluable tool for the client, design team, and contractors to resolve design issues and comprehend the challenges of working on numerous components in a tightly confined area and on an accelerated schedule.
|Renderings show the construction sequence for the self-anchored suspension section of the bridge.|
Based on successful delivery of 3D model renderings of the new bridge during the environmental approval phase, Caltrans requested that Parsons Brinckerhoff (PB) develop an updated 3D model of the entire span to reflect the completed design for use in its new outreach strategy under separate contract with the Bay Area Toll Authority (BATA). Under the BATA contract, PB produced a 3D digital model of the entire east span corridor that included the existing bridge, temporary structures, and the future new span.
For more than 10 years, Parsons Brinckerhoff (PB) has been involved in the East Span Retrofit project under a contract with Caltrans. In total, the project comprises six major construction contracts with a total construction cost of more than $6 billion. PB is the designer of record for the civil design and also led development of the approved Environmental Impact Report for the project. Currently, three of the contracts are under construction, and three are still in design.
To add value for the client, PB leveraged the 3D model work by using it to create a 4D model. Using Autodesk Navisworks Manage 2009, individual components of the 3D model were linked to their associated construction activities in the various contracts’ schedules in Primavera software to produce a 4D simulation of the entire project that shows construction activities over time in a highly effective and realistic way. The 4D model was a tool not previously used by BATA, but the client instantly grasped the visualization benefits during review and, as a result, supported the effort to develop a more detailed 4D model for the project. The model was then updated as construction planning progressed and the schedules evolved.
The 4D model depicts multiple contractors’ construction activities occurring simultaneously in the same work area. This helps resolve the issues of fitting these activities in a confined area with limited access, such as on Yerba Buena Island. Multiple activities can be shown together for any day during the life of the project. The 4D model is being embraced by clients and team members at every level of the project, from the Caltrans scheduler to the Toll Bridge Program Oversight Committee, the executive committee responsible for making the big decisions on the project.
As more uses for the 4D model present themselves, the detail and complexity of the Bay Bridge 4D model has expanded. The model has been extended to include fabrication and delivery of deck and tower sections for the self-anchored suspension portion of the bridge, which are critical activities for overall construction scheduling. Now the model links to more than 3,000 construction activities in the multiple contracts, and the model itself has grown to more than 800 million polygons.
The 3D/4D models and the visualizations based on them accomplish the following goals:
- inform the design and construction teams about planned construction processes;
- communicate to decision-makers when certain activities will take place and how key milestones affect timing;
- foster collaboration among project partners and stakeholders;
- show the public what the project will look like during construction; and
- facilitate media campaigns, leveraging visualizations (such as that done for the Labor Day 2007 closure) to help communicate information about all future closures and traffic detours.
The project work has created many new opportunities for Caltrans and BATA to explain the project to non-technical stakeholders, and has made stakeholder communication easier and more comprehensive. Caltrans and BATA have committed to the continued use of visualization and 4D modeling to illustrate construction sequencing for several more key components of the new bridge, including a detailed visualization of the construction of the self-anchored suspension portion of the bridge. The client has also requested that the structural and MEP components for the bridge be modeled in 3D and then compared for potential errors or conflicts between the two construction document packages being developed in parallel. The technology used on this project has led to discussions by Caltrans’ leadership on the inclusion of 4D modeling and digital prototyping as standard components of their project development process for large infrastructure projects.
PB’s visualization and 4D modeling work has effectively demonstrated the value of 3D digital prototyping and, in particular, 4D schedule-driven simulations for communicating complex construction activities on large infrastructure projects. The process has fostered better collaboration among the project partners and stakeholders since all have contributed to the integrated project model, and every component of the final project is represented in this integrated project visualization. This project represents another significant step toward true virtual design and construction.
Brady Nadell, P.E., is project manager and supervising engineer for Parsons Brinckerhoff. He can be contacted at firstname.lastname@example.org. Kevin Gilson is senior professional associate, project manager, and director of visualization for Parsons Brinckerhoff. He can be contacted at email@example.com.