The existing mat is supported by 950 14-in.-square precast concrete piles. And it assessed the existing piles, mat and superstructure under the existing-buildings code.
#Millennium tower tilts quarter four days code
The team also considered whether the design of the new piles and mat extension meets the seismic code requirements for new buildings. In addition, the team studied structural models and criteria to assess the safety of the superstructure and foundations under MCE ground motions and gravity loads.
They also went over the geotechnical data and models to estimate resistance of the foundation elements to MCE ground motions and settlement under gravity loads. Reviewers studied the retrofit design criteria, including performance objectives, site-specific spectra for the maximum considered earthquake hazard and MCE ground motion histories. The primary intent is to arrest settlement, but the 52 piles also will improve seismic performance, he adds. “The building code has provisions to allow VSUs without having to bring the building into conformance with the current code,” he says.
#Millennium tower tilts quarter four days upgrade
SGH’s Hamburger says his team selected the voluntary seismic upgrade route because it offered the easiest path through the permitting process. The structural upgrade is designed to meet the requirements of the voluntary seismic improvements section of the San Francisco Existing Building Code. This included a more extensive set of calculations by the design team’s geotechnical engineers, John A. The review took 11 months, which was longer than anticipated, in part because the team asked the fix engineers to demonstrate through calculations that “they had thought of all design details,” says Deierlein. In addition to Deierlein, the team consists of structural engineer Marko Schotanus, geotechnical engineer Craig Shields and geotechnical-seismic hazards consultant Shahriar Vahdani. Due to characteristics of the Old Bay clay, which underlies the building foundation, the maximum stress developed within the existing mat and its extension due to uplift forces imposed by the new piles could occur over several months, if not years, after jacking of the new piles has been completed,” said the review-team letter. “Given the inherent uncertainties in the foundation settlement and response, we recommend that the building performance be monitored during and upon completion of the proposed construction. One review team recommendation calls for monitoring the tower during construction and for a decade after. And the public health department is reviewing the project for conformance with applicable city regulations related to soil and groundwater contamination. The municipal transportation agency is reviewing the construction logistics plan. The public works department is reviewing all permanent and construction-related occupancy of the public right of way. The project team also must obtain permits from the public utilities commission, which will test samples of any groundwater removed from the site. is conducting an environmental review under the California Environmental Quality Act. The pending permit reviews are expected to take about one month. Retrofit permit applications dated last Dec.
“We anticipate that even if the upgrade is not done, the rate of settlement will continue to reduce and eventually stop,” he says.
Hamburger, a senior principal of Simpson Gumpertz & Heger Inc. per year and there has been a negligible increase in tilt, says Ronald O. Over the past 18 months, the building has been settling at a rate of about 1⁄4 in. to the northwest, where the greatest amount of differential settlement has occurred. “We can now put this legal chapter behind us and concentrate our efforts on the upgrade that will restore our building’s reputation.”Ĭurrently, the top of the tower is tilting about 15.5 in. “This agreement represents a critical turning point for our building and for homeowners, who have patiently waited for a resolution that would put us on a positive track forward,” said Howard Dickstein, MTA president, in a statement. The settlement will provide funds for the retrofit, according to an MTA statement.
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