Leveraging History for the I-40 Bridge Design and Rehabilitation

: Ground level image looking up at a highway bridge with two spans featuring a stone façade.

Leveraging History for the I-40 Bridge Design and Rehabilitation

September 4, 2022
Eric “Rick” Nelson, PE

Looking up from underneath two highway bridges on I-40 during our firm’s bridge rehabilitation project with the completed substructure work (foreground) and existing substructure (background).

Historic bridges offer a snapshot of the past, exemplifying the design, engineering, and construction project methods of their era. Bridges can be iconic because of their aesthetic appeal, as connections in important transportation routes, or serve at critical junctions in major urban areas. Some bridges, such as the Brooklyn Bridge and the Golden Gate Bridge, are recognized as historic landmarks.

Historic bridges are often old enough to warrant more frequent inspection, maintenance, and repair than newer bridges. In some cases, complete rehabilitation or replacement may be necessary. Preserving and restoring historic bridges necessitates maintaining visual appearance and aesthetic appeal while ensuring structural integrity and functionality.

The design process for historic bridge restoration typically follows these key steps:

1. Documentation and Assessment

In this step, surveys, visual inspections, and research about the bridge’s history are conducted to establish how the bridge was designed and constructed, what modifications may have been made to the bridge, and its current condition. Engineers should collaborate with the client or bridge owner, regulatory agencies such as transportation departments and historic preservation offices, other professionals on the planning and design team (e.g., urban planners), and additional project stakeholders (e.g., community members and organizations) to establish the bridge’s status.

2. Preservation Planning

Preservation planning is the second phase and refers to setting the bridge rehabilitation project’s goals and objectives. This phase involves determining the required level of restoration, the desired appearance, and any functional changes required to help ensure the bridge meets modern standards while preserving its historic integrity.

3. Ensuring Historical Accuracy

Historic bridge restoration strives to preserve the structure’s original appearance and character. Planning relies on historical documentation, photographs, and drawings to determine the bridge’s original design and materials. Reasonable architectural features such as parapets, piers, railings, guardrails, and decorative lighting should be conserved or replicated if it is missing or deteriorated beyond repair.

4. Structural Upgrades

While preserving historic materials is a key aspect of the restoration, the bridge may need structural upgrades to bring it up to modern standards, physically reinforce it, and prevent hazards. Engineers examine the bridge’s load capacity, general stability, and, as applicable, its resilience against seismic activity, wind, and flooding. Potential approaches may include strengthening the bridge by adding structural elements, repairing and replacing damaged pieces, and performing foundation reinforcement checks.

5. Materials and Techniques

Engineers attempt to conserve as much of the original design as possible while maintaining the bridge’s historic appearance. Sometimes, the additional support and safety equipment are hidden from view. Whether a historic bridge project uses the original design or simply maintains the historic appearance, the bridge’s configuration must meet engineering design standards. Materials are crucial in historic restoration, so wherever possible, engineers use the original elements. When a new component is required, the use of original types of materials and fabrication techniques are first considered. If they are not available or appropriate for modern use, then materials and techniques replicating the original appearance are sought.

6. Collaboration and Approvals

In the case of a historic bridge restoration, architects, engineers, preservation specialists, and historians usually collaborate on the project. Local authorities should also be involved in obtaining necessary permits and approvals. The restored bridge must meet regulatory agencies’ preservation and design standards, as well as applicable building codes and other requirements.

7. Long-Term Maintenance

After the restoration, a long-term maintenance plan should be developed to maintain the bridge’s condition and lifespan. Inspections, repairs, and protective measures such as painting and corrosion control should be conducted regularly to keep the bridge safe.

I-40 Historic Bridge Rehabilitation

Interstate 40 is a primary east/west corridor in the U.S., stretching over 2,500 miles from the coast of North Carolina to California. The section of highway through Buncombe County, North Carolina, completed in 1968 as part of the Interstate Highway System, connects travelers and tourists to the Blue Ridge Mountains and historic Asheville, home to the 8,000-acre Biltmore Estate and Biltmore Forest. The bucolic terrain features a gateway to the Great Smoky Mountains, Blue Ridge Parkway, and Mount Mitchell, the highest peak east of the Mississippi River.

The now 50+-year-old I-40 mainline bridges over Biltmore Forest roads are iconic, having been designed with natural granite veneers installed on the bridge substructure and superstructure elements. The granite blocks are 6 feet thick, with varying area dimensions, and weigh up to 350 pounds each. The bridges have arched piers supporting reinforced concrete bridge decks on steel I-beams. However, the mountain’s beauty brings with it challenges for transportation asset managers and the construction industry. The region’s climate typically produces freezing road conditions for up to five months of the year, which require frequent de-icing with salt-based chemicals to keep roads safe for travel. These 1960s-era bridges are on the receiving end of a brutal combination of heavy truck traffic and concentrated applications of corrosion-inducing chlorides.

Our team worked with the North Carolina Department of Transportation (NCDOT) on the preservation design of 48 bridges as part of the NCDOT Interstate Maintenance and Preservation Program. For the 12 I-40 bridges through Biltmore Forest in Buncombe County, NCDOT contracted with our firm to provide bridge rehabilitation plans for six of the I-40 mainline bridges and the historic restoration of four bridges. Bridge preservation plans were also carried out for the six mainline bridges west of Biltmore Forest. Additionally, the project scope involved bridge deck evaluations to determine chloride profiles and extensive field assessments to identify repair requirements and quantities.

NCDOT requested a design scope to extend the service life of the Biltmore bridges for an additional 40 years, while the remaining six bridges west of Biltmore were scoped for 15-year service life improvements. The project included:

Hydro-demolition of bridge decks and overlays using high-early-strength, latex-modified concrete.
Repairing steel beams.
Installing low-profile bearings.
Removing coatings with lead abatement.
Repainting steel superstructure.
Repairing substructure with shotcrete.
Removing, storing, cleaning, and re-installing natural granite stone veneer.

The project required diligent coordination with NCDOT and the Biltmore Estate’s owners, alongside strict adherence to state historic standards and guidelines. The team navigated the complexities of repairing the bridge’s unique granite veneer façade, balancing the challenges of interstate highway construction on I-40 with the need to minimize disruptions for those visiting the Biltmore Estate.

Substructure repairs required the complete removal, cleaning, and storage of the granite facades to allow inspection and repair of the reinforced concrete beneath. The position of the granite blocks was recorded, and each block was marked with its respective position for proper re-installation to match the original construction.

The rehabilitation of the historic I-40 bridges over Biltmore Forest Roads exemplifies a meticulous blend of engineering precision and historic preservation. Tasked with extending the service life of these engineering and architectural landmarks, the project team successfully addressed structural and safety improvements while diligently preserving the bridges’ aesthetic and historical integrity. Strong collaboration among our team, NCDOT, Biltmore representatives, preservation experts, and other stakeholders ensured that the bridge restorations met rigorous standards while accommodating the region’s heavy traffic and environmental challenges. The project ultimately preserved key pieces of the region’s history and heritage while enhancing the functionality and safety of a critical transportation corridor, serving as a model for historic infrastructure preservation.