ASCE Los Angeles Section

“Intersection of North Main St and Albion St
Los Angeles, CA “

The North Main Street Bridge over Los Angeles River project is a $10 million bridge retrofit project that was completed in September, 2016 and is another major milestone for our City and our commitment to making Los Angeles a safer place to live. Per the latest California Department of Transportation (Caltrans) standards, the original North Main Street Bridge was determined to be a Category 1 bridge, which is one that could collapse in a seismic event and potentially threaten public safety. To meet the current seismic requirements, this retrofit project included replacing portions of the deck, retrofitting the arch ribs with a concrete jacket, and providing transverse in-fill walls between the spandrel walls that support the bridge deck. Furthermore, to maintain the historical finish as in the original design, the bridge rails and lamp posts were restored to the original 1910 design

Originally built by the Bureau of Engineering in 1910, the Bridge was documented by the Library of Congress Historic American Building Survey/Historic American Engineering Record in recognition of its historic status. The old Bridge was designated as a Category 1 bridge mandating that the bridge be retrofitted to meet the latest seismic requirements by replacing portions of the deck, retrofitting the arch ribs with concrete jackets, and providing transverse in-fill walls between the spandrel walls that support the bridge deck. As a historic bridge, elements of the original 1910 design were restored, including the bridge railings and lamp posts.

“Major challenges, such as interfering utilities and adjacent railroads, threatened to terminate the project’s construction.
During construction, the contractor uncovered DWP facilities embedded in the bridge deck that were not shown on the project’s utility plans. The only note on the plan relevant to these utilities was that “All utilities crossing the bridge structure shall remain in service and be protected in place.” This activity was on the critical path and all work had temporarily been suspended.
These DWP facilities included a cluster of twelve (12) - 4” conduits at the south side of the bridge and a cluster of six (6) - 5” & three (3) - 2½” conduits on the north side. All of these ducts were encased in concrete, but there was neither any indication of these concrete enclosures, nor the exact locations or dimensions on the utility plans. Furthermore, no potholing was performed during the design.
At the south of the bridge, there was additional duct bank consisting of seven (7) - 4” conduits that were also not shown on the utility plans. These duct banks were approximately 10 feet wide and directly on top of the arch rib crown at the mid-span. Further challenges were presented as these duct banks interfered with the highway arch rib to be retrofitted in Stage 3 of construction and also interfered with approximately 2’-6” of the railway arch rib to be retrofitted in Stage 1.
On the north side of the bridge, the duct bank interfered with approximately 6” of the highway arch ribs, which were to be retrofitted in Stage 2 of the construction. This conflict was limited to a length of approximately 25 feet at the arch crown at the mid-span of each of the 3 bridge spans.
Through a good partnership between the construction management team, it took 3 months to relocate 7 cables from the most southerly duct bank into an adjacent duct bank with empty conduits. The arch retrofit plans were modified to accommodate the changes.
Beyond the utility conflicts, the Bridge project was also located between two live railroad tracks with moving trains in both directions with the following safety issues:
1. Traffic queues at Main Street Bridge have the potential to obstruct the tracks at certain times.
2. Traffic backs up on the bridge and obstructs live railroad tracks when one set of the gates is down.
Traffic plans were modified to implement extra signs and employ flaggers at the railroad crossing to mitigate these issues and control traffic movements during construction.
The coordinated and cooperative efforts of the construction management team allowed this project to continue towards completion successfully. “

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Seismic Retrofit of North Main Street Bridge over Los Angeles River as mandated by Caltrans standards

“The seismic retrofit of North Main Street Bridge over the Los Angeles River represents an almost $10 million investment in the community, and is another major milestone for our city and our commitment to making the City of Los Angeles a safer place.
The North Main Street Bridge was designated as a Category 1 bridge by Caltrans, and as such, was mandated by the State of California to be retrofitted to meet current Caltrans seismic standards. The seismic retrofit work included replacing portions of the deck, retrofitting the arch ribs with a concrete jacket, and providing transverse in-fill walls between the spandrel walls that support the bridge deck.
As a historic bridge, elements of the original 1910 design were restored, including the bridge railings and lamp posts.
Major challenges, such as interfering utilities and adjacent railroads, threatened to terminate the project’s construction.
The coordinated and cooperative efforts of the construction management team allowed this project to continue towards completion successfully. “