How did Langan’s expertise assist with the design of Zuckerberg San Francisco General Hospital and Trauma Center’s base-isolated foundation?

The Zuckerberg San Francisco General Hospital and Trauma Center (ZSFG) is the first hospital in San Francisco to be built with a base-isolated foundation — the latest technology for protecting buildings during seismic activity. ZSFG is the only Level One trauma center in San Francisco, so maintaining operations during a natural disaster is critical.

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Zuckerberg San Francisco General Hospital & Trauma Center
(photo credit: Agnieszka Jakubowicz)

By incorporating a base isolation system at the foundation level, the building can move freely up to 33 inches during the Maximum Considered Earthquake (MCE). This free movement reduces the seismically-induced forces in the structure, resulting in an enhanced seismic performance and lowering the cost of the structure.

To accommodate the movements, Langan recommended a void space (commonly referred to as a moat) be constructed between the structure’s basement wall and the adjacent permanent perimeter retaining wall (moat wall).  The moat wall is a permanently tied-back retaining wall ranging from 25 to 41 feet in height.

As the seismic engineers on this project, Langan also developed earthquake ground motions and estimated ground deformations during and following the MCE shaking for use in the structural evaluations and design of the base isolation system and the superstructure.

In addition, we performed nonlinear time series Soil-Structure Interaction (SSI) analyses to estimate seismic forces and displacements of the moat wall as a result of shaking during an MCE event. We used the results to evaluate the potential of out-of-phase motion between the moat and basement walls during the MCE event.

It was very rewarding to be part of this project team and assist with the design and evaluation of the base-isolated foundation, the most earthquake-resistant design known today.

Answer provided by Haze M. Rodgers, PE, GE, Senior Project Engineer 
Haze has nearly 15 years of experience providing geotechnical consulting services, including subsurface exploration, laboratory testing, and construction observation. During design, he provides soil structure interaction evaluations (static and dynamic), ground improvement evaluations, slope stability, and foundation designs. His projects include commercial and residential structures, deep excavations, infrastructure (roadways and utilities), marine and waterfront developments (piers, wharves, and harbors), seismic strengthening, and landslide stabilizations

Q&A: What are the unique engineering challenges for San Francisco’s burgeoning downtown area?

706 Mission, San Francisco, CA

706 Mission, San Francisco, CA

Background Information

Langan Treadwell Rollo is performing engineering services for several new high-rise residential developments in downtown San Francisco: 706 Mission Street, Transbay Blocks 6/7 and Block 8, 201 Folsom Street, and 41 Tehama Street, among others. These projects address both the city’s lack of land space (only 7 miles wide by 7 miles long) and desire for smaller units (an estimated 38% of residents are single occupants). According to the San Francisco Planning Department’s 2014 Housing Inventory Report, the production of new housing has increased by 50% from 2013.

What makes all this interesting — and challenging — to an environmental scientist is these projects focus on sky-high vertical growth built on land that our ancestors extended horizontally.

Solutions to Challenges
As a result of the 1906 earthquake and subsequent fire and the preceding Gold Rush era, many of the new downtown developments exist on, or are close to, infill. Rubble, wreckage, old wharves and piers, and abandoned ships can be within these infills.

Boat

Remnants of an old ship found during an excavation in downtown San Francisco.

Given the nature of infill, we recognize that contamination and historical concerns will likely result in additional costs for soil handling and disposal. San Francisco’s infill is the reason why the city created the Maher Ordinance (Article 22A of the San Francisco Health Code), regulated by the city’s Department of Public Health (SFDPH). This city code mandates stricter protocols, including site history, soil sampling, and site mitigation, which SFDPH oversees and approves.

Another challenge we face when excavating is the discovery of potential artifacts. These areas within the excavation are then left undisturbed so archaeologists can investigate. While this process can delay a project, it can be quite interesting. During recent excavations, we encountered remnants of an old ship as well as a lighter boat that originated from New England. Our construction crews have discovered items of interest that were as deep as 60 feet below ground so they likely existed several thousand years ago. Some of these artifacts are now displayed in museums. This is why I like the more complex projects: the more challenges we face, the more fascinating these projects become.

Answer provided by Peter J. Cusack
Peter Cusack is an environmental scientist who has worked on San Francisco and other Bay Area projects for the last 26 years. He manages and implements hazardous waste characterization and remediation projects. His experience includes pre-acquisition site assessments, site investigations, underground storage tanks removal, Phase II investigations, soil and groundwater sampling and remediation, development of soil management plans, aquifer pumping tests, contractor oversight, and field inspection for numerous construction projects. His work is often done in coordination with our geotechnical practice. He has extensive experience in site investigations and regulatory agency interaction prior to new construction/development.

Q&A: What were the challenges of the Crescent City Harbor Rehabilitation Project?

Crescent City Inner Harbor

Floating docks and piles were replaced with stronger concrete versions.

A little background information

Four years ago the Crescent City Harbor, named for the crescent shaped beach south of the city, was destroyed by devastating tsunami waves generated from an 8.9 magnitude earthquake in Japan. Langan provided geotechnical engineering services during design, contractor selection, and construction for the rehabilitation of the harbor. The harbor previously consisted of floating docks, which served as slips for commercial and recreational boats, supported by concrete piles with relatively little embedment into the weak bedrock. Most of the concrete piles were sheared off by the forces generated by the tsunami waves. The project included replacing the old piles with piles designed to resist future tsunamis, stabilization of the harbor slopes, and other onshore improvements.

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New foundations were constructed for the three gangway landings.

Challenges

Langan was a critical part of the project team, working closely with Ben C. Gerwick and Strover Engineering, from 2011 to 2014.  The challenges of this project included designing the facility to resist future tsunamis, shallow highly-fractured bedrock, and high seismicity and potential for strong ground shaking.

Langan’s geotechnical engineering services included developing lateral pile response analyses (L-Pile) to aid in the design of the floating boat docks, providing recommendations and design criteria for the foundations of the gangway landings, and reviewing contractor value engineering, testing, and installation logs. The lateral capacity of the piles included kinematic forces due to a design level tsunami.  In addition to foundation design, we also evaluated the stability of harbor slopes for both static and seismic conditions, and provided recommendations for increasing their stability. We used historical design documents and boring longs, as well as the result of our exploration on land and water.

Crescent City Inner Harbor

A barge-mounted drill rig was used to advance the borings over water.


Today, Crescent City Harbor is completely restored and fully operational. Overall, Langan’s engineering design services were a critical part of assisting the Harbor District in achieving their goal to recreate the harbor better than it was, with the ability to withstand future natural disasters.

 

Answer provided by Haze Rodgers, PE, GE
Haze has over twelve years of professional experience managing, developing, and performing geotechnical studies including explorations, analyses, and construction observation services for various projects throughout California, specializing in offshore design.

Dr. Ramin Golesorkhi Discusses the ASCE 7-10 Ground Motion Provisions with Top New York Structural Engineers

On November 18, 2011 Dr. Ramin Golesorkhi addressed the new ground motion provisions of ASCE 7-10 in a presentation at Langan’s NY Learning Center. This presentation was a part of a Langan’s Technical Center of Excellence series of presentations. The new ASCE 7-10 provisions present a significant change from previous codes. 

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