Jan 2018

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Isolation Bearings Key to Sixth Street Viaduct Safety

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The Sixth Street Viaduct is in a high seismic zone, which means that there is a high risk of an earthquake happening during its 100 year lifespan. To ensure the safety of the viaduct and everyone who uses it, the Sixth Street Viaduct team is taking extra precautions to make sure the bridge exceeds the latest seismic safety codes. One of the safety measures we are using is the inclusion of sliding seismic isolation bearings being placed at mid-height in the columns.

The isolation bearings, which are currently being installed at the viaduct,  allow lateral movement of up to 30 inches in the case of an earthquake. They were designed by Earthquake Protection Systems, a company that specializes in this kind of construction. The bearings are made of steel and will isolate the bridge above them from the shaking of an earthquake; the movement of the ground will not be able to move past the isolation system.

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The bearing consists of an inner sliding core (in grey on the diagram shown on the left) that sits on and under a set of spherical concave surfaces (in black, labeled "Slider Concave," in the diagram). This first set of concave surfaces also functions as a slider, and sits on and under a larger set of concave surfaces (in blue, labeled "Main Concave," in the diagram). The bottom of the largest set of concave surfaces is connected to the base of the structure and the top concave surface is connected to the structure above it. The sliders are designed to activate once a certain force is exerted on them. When this happens, the inner-most sliding core will break free and move up the concave surface, which may also break free and slide up the larger concave surface once a different friction level has been achieved.

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Once the shaking stops, the sliding aspects of the system will slide back down to the deepest point in the concave surfaces, which functions as a self-centering mechanism. All of the movement that is allowed by these sliders will keep the viaduct safe from earthquakes by allowing the earthquake’s force to dissipate in the isolation bearings rather than destroying the entire structure.

The bearings being used for the Sixth Street Viaduct vary in size, with the majority of them being six and a half feet in diameter. On the bridge alone, there will be 26 isolation bearings, and even more will be used in the ramps. These specific bearings were chosen for the Sixth Street Viaduct Replacement Project because they allow for the bridge to retain its architectural features while also providing exceptional protection from seismic events.

 Sixth Street Viaduct Construction Update

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Construction is moving forward every day. Check out the diagram above to see what is going on on-site.

Currently, retaining walls at the west abutment are under construction. Falsework installation and Y-bent construction is also taking place near Clarence Street, Anderson Street, and Mission Road. Cast-In-Drilled-Hole foundation installation is taking place near Santa Fe Avenue, and there is on-going storm drain installation on Mateo Street.

 About the Project

 Stay Involved!

The Sixth Street Viaduct Replacement Project is a new, 3,500-foot long viaduct connecting Boyle Heights and the Arts District across the Los Angeles River. The original viaduct was built in 1932, but had significantly deteriorated due to "concrete cancer"; it was demolished in 2016. The new viaduct will have ten pairs of lit arches, bike lanes and wider sidewalks, along with stairway access and bike ramps connecting to 12 acres of recreational and open space under the bridge. The $482 million dollar project is the largest bridge project in the history of the city. The bridge is funded primarily through the Federal Highway Administration, with additional City support. The viaduct is expected to be completed by the end of 2020.

To stay involved, sign up for email or text updates at: 
www.sixthstreetviaduct.org/join_our_mailing_list

 Follow us on Facebook (@sixtstreetbridge), Twitter (@6thstviaduct) and Instagram (@6thstviaduct)
And check out our website at www.sixthstreetviaduct.org

The Bureau of Engineering is the City's lead agency for the planning, design and construction management of the City's public buildings and its public infrastructure. Engineering is also responsible for managing permitting for all construction that takes place in the public right-of-way, as well as managing the City's state-of-the-art online mapping system, NavigateLA. Engineering is committed to designing and building environmentally-sustainable projects that include extensive community input. Engineering projects and services support the City's goals of creating a prosperous, livable and safe city for all residents and businesses.


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