Home > Mills Building
684 Ellis Street
The Chew Bldg.
Cartwright Hotel
1904 Franklin St.
291 Geary St.
Mills Building

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Mills Building

Mills Building, San Francisco, CA
Contractor:  KONE, Inc.
Building alteration to provide a permanent and service removable barrier and catwalk to an existing mid-flight counter-weight hoistway access hall. 

RCB Elevator Consulting, LLC and its associate structural engineering firm performed all of the design and engineering required for the work.  This included performing all field surveys.

Project Description 

The Mills Building is an early downtown San Francisco landmark, one of the tallest buildings of its time.  The original elevator serving the structure were water hydraulics.  These were replaced with gearless elevators in the 1930s. 

Due to the original building design, this three car group had a separate hoistway for the counterweights.  There were access doors and walkways to access and service the counterweight hoistway at three levels.  Only one of these was properly constructed with a permanent metal walkway and screen protective barrier to the running counterweights.  The other two accesses were not properly constructed or protected as shown in the pictures below.  This presented a severe hazard for anyone accessing these spaces as the counterweights almost silently whizzed by at 500 fpm with nothing between you and the moving iron mass. 

To rectify the hazard, it was decided to permanently closed off one of these counterweight hoistway accesses and to make the remaining one safe and code compliant.  RCB Elevator Consulting, LLC designed a  new structural steel walkway and screen enclosure barrier as shown on the drawings below.  The design retained the existing steel beams and added additional steel as needed and included anchoring into concrete from a previous seismic upgrade.  Complete structural engineering was performed including seismic calculations.


The existing condition was a severe hazard due to the unstable and incomplete plank & plywood deck and the entire lack of barrier between the walkway and the passing counterweights. 

These pictures shows some of the existing steel remaining from the earlier water hydraulic elevator installation.  This steel was used and augmented with additional steel for support of the new steel deck walkway and barrier (see drawings).

You can see the ropes to the counterweight in the far hoistway.  Great care was taken during the survey by the author and his structural engineer to keep out of the running counterweights' paths!

Drawings & Engineering

Click on the drawing above to open the full drawing set in PDF format.  To see drawings in landscape view, click on your Adobe Reader's Rotate Counterclockwise image button.  Note drawings cannot be printed or altered.  All drawings and artwork are the property of RCB Elevator Consulting, LLC and may not be used, copied, or in anyway used without the owner's consent.  To return to this page, click the Back button on your browser.

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