Caltrans is retrofitting four bridges in California to improve seismic resilience, with Powell Constructors on the job. The $30 million project includes reinforcing bridge columns and adding safety features to protect against earthquakes, aiming for completion by fall 2026.
Caltrans photo
The Echo Summit Bridge reworking in 2022 provides guidance for ongoing bridge seismic retrofitting.
Earthquakes are a concern in parts of California, and to ensure its infrastructure can withstand major seismic activity, the California Department of Transportation (Caltrans) designs roads and bridges to protect its network.
Yet over the past few decades, the Los Angeles County area has experienced several earthquakes in which older infrastructure was damaged.
So, in late 2024, Caltrans announced a $30 million seismic retrofitting project to improve four bridges along State Route 91, Interstate 110 and Interstate 710. Powell Constructors started work on Dec. 9, 2024, with the entire project anticipated to be completed by fall 2026.
"The project addresses potential seismic vulnerabilities and modernizes safety and electrical equipment at four bridges located in the cities of Compton and Long Beach, and the San Pedro community in the city of Los Angeles," said Nathan Bass, Caltrans public information officer.
"These enhancements will preserve the structural integrity of the bridges and increase commuter safety. This project was initiated in 2015. Construction follows a years-long developmental process, during which the project was designed, and Caltrans sought necessary permits from the numerous jurisdictional agencies with authority in the project area. Those include the U.S. Army Corps of Engineers, California Department of Fish and Wildlife and city of Long Beach, among others."
Seismic retrofitting is an ongoing program for Caltrans.
For example, the Echo Summit Bridge replacement near Lake Tahoe was completed in 2022.
The project "incorporated precast, prestressed girders, concrete overlays, precast column, and precast abutments," according to Caltrans. "Seven 96-foot girders were connected with ultra-high performance concrete to enhance the durability of the structure. The new bridge replaced a 24-foot road width with a 30.75-foot road width to provide for safer 12-foot lanes and increased shoulder widths."
The four bridges in this group present their own challenges.
Built in 1935, the Gaffey Street Bridge in San Pedro is a reinforced-concrete, T-beam structure with three spans of 68 ft. each. The I-710 Harbor Scenic Drive and two SR 91 Compton Creek bridges were built in 1970 and 1974, respectively.
"These bridges were built before Caltrans' post-1990 seismic design criteria were established, meaning certain components of the bridges could be more vulnerable to seismic activity than those of a bridge built today," Bass said. "As such, this project aims to retrofit the bridge facilities identified in this project with new features to protect them from seismic damage.
"Bridge columns, which reliably support the weight of the bridges, will be reinforced to prevent their lateral movement during a seismic event. Caltrans will utilize steel casings to reinforce the I-710 and SR 91 bridge structures, while a unique fiber-reinforced polymer system will be used to reinforce the Gaffey Street Bridge and preserve its aesthetic features.
"Both the steel and polymer reinforcement techniques involve jacketing the perimeter of bridge columns with strong materials to increase their seismic resiliency by restricting movement from side to side. Bridges constructed today would include this column reinforcement internally," he added.
"Pipe seat extenders will be installed beneath the bridge deck of the Compton Creek Bridge (SR 91) to ensure that the deck remains securely seated during an earthquake. Additionally, concrete catcher blocks will be installed on the Gaffey Street Bridge to catch the bridge deck in the event of structural failure, preventing it from dropping due to seismic activity. Both these mechanisms will enhance the safety of the bridges as they may move or expand during seismic activity, serving to prevent their collapse."
Caltrans' Office of Structures, Maintenance and Investigations conducts biennial inspections of every bridge statewide, including locally owned bridges; it has invested $12.2 billion in retrofitting or replacing 2,279 of the 13,214 bridges on the state highway system, using updated seismic design standards.
Additionally, local agencies have invested more than $1.4 billion toward retrofitting or replacing 1,204 of the 13,400 locally owned bridges.
"Engineering Analysis & Research (OEEAR) provides cost effective, timely and efficient delivery of structure-related earthquake engineering and seismic hazard services to Caltrans Division of Engineering Services and other clients," Bass said.
With a wide-ranging authority, OEEAR can propose bridge seismic policy; create and maintain bridge seismic guidance, tools and procedures; perform seismic and structural analysis; support bridge analysis and design software; manage Caltrans' seismic research program; support Caltrans Structure Design and Consultants in project delivery; serve as a custodian for the State Seismic Fault map; provide services for the estimate of site hazards including fault rupture; support bridge seismic retrofit strategies and provide seismic standard details; and provide expertise in seismic instrumentation soil structure interaction and post-earthquake investigation.
The project supports Caltrans' statewide effort to repair 500 bridges by 2028, as directed by 2017's Senate Bill 1.
Seismic retrofitting activities will include reinforcing 36 potentially vulnerable columns, replacing more than 5,000 ft. of bridge railing with standardized concrete barriers' upgrading crash cushion devices and adding new electrical systems at the bridges.
The Harbor Scenic Drive Bridge on I-710 (Long Beach) is the first structure to undergo a renovation, with work to be completed in July, having started on Dec. 18, 2024
The Compton Creek Bridge is the second crossing to be dealt with and is expected to be upgraded by February 2026.
Operations for the Gaffey Street Bridge on I-110 in San Pedro began last January. The goal is to complete this element in June 2026.
The Compton Creek Off-Ramp Bridge will be tackled starting in May, with a February 2026 delivery date.
The project was designed by District 7's Division of Design, which collaborated closely with designers at Caltrans' headquarters, as well as private firms including TranSystems, WSP, AECOM and ADKO Engineering Inc.
The project presented several engineering and procedural challenges, Bass said.
"The SR 91 bridge facilities also cross over a waterway, railroad and privately owned business, necessitating additional mitigation measures," said Bass. "During construction on those facilities, Compton Creek, a tributary of the Los Angeles River, will be diverted to one side or the other to allow for safe and efficient seismic retrofitting activities. All the bridges in this project are structurally sound but have been identified for seismic retrofitting based on their non-conformance with Caltrans' current seismic design criteria. The performance of retrofitted bridges in recent earthquakes demonstrates an increase in their seismic resilience."
Instead of steel, a fiber-reinforced polymer system will be used to seismically retrofit the columns on the Gaffey Street Bridge, he added. Similar to fiberglass in composition, the polymer system will be wrapped tightly around the bridge columns, enhancing their structural integrity, restricting their lateral movement and preserving the aesthetic features on the historic bridge.
Bass noted that Caltrans will pause construction on the Gaffey Street Bridge one Saturday per month to allow for area community meetings. CEG
Irwin Rapoport
A journalist who started his career at a weekly community newspaper, Irwin Rapoport has written about construction and architecture for more than 15 years, as well as a variety of other subjects, such as recycling, environmental issues, business supply chains, property development, pulp and paper, agriculture, solar power and energy, and education. Getting the story right and illustrating the hard work and professionalism that goes into completing road, bridge, and building projects is important to him. A key element of his construction articles is to provide readers with an opportunity to see how general contractors and departments of transportation complete their projects and address challenges so that lessons learned can be shared with a wider audience.
Rapoport has a BA in History and a Minor in Political Science from Concordia University. His hobbies include hiking, birding, cycling, reading, going to concerts and plays, hanging out with friends and family, and architecture. He is keen to one day write an MA thesis on military and economic planning by the Great Powers prior to the start of the First World War.
Read more from Irwin Rapoport here.
Today's top stories
