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

 
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address:
2117 Bush St.
San Francisco, CA
94115-3103

phone:
415.819.5744

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415.354.3454

email:
rich AT blaska DOT com


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Cartwright Hotel

Cartwright Hotel, San Francisco, CA
Contractor:  Empire Elevator Co., Inc.
Major alteration of 1913 Otis basement winding drum, 10 story passenger elevator.  New Hollister Whitney #54 O.D. basement machine, counterweight, sling & platform, safeties, governors, seismic reinforced guiderails, GAL door equip, MCE controls, cab & fixtures. 

RCB Elevator Consulting, LLC and its associate structural engineering firm, Eddington Engineering, performed all of the elevator and building engineering required to make the conversion.  This included performing all field surveys.

Project Description

This project is a good example of a full conversion of an ancient basement winding drum system into a modern geared basement traction passenger elevator.  Typical with these jobs, the existing structure and costs preclude a complete tear-out of the existing system, enlarging the hoistway, building a new machine room, etc., which would be required to install a new, pre-engineered elevator system.  Instead, the order is to alter the existing system to bring it up to today's operational standards, the the extent that that is possible.

Without giving away all of my secrets, we were able to anchor the new basement machine into the existing building structure without demolition beyond the removal of the existing upper machine components.  Although we married the new machine to the old Otis machine cast steel base, that original base accounts for none of the upthrust loads.  All of those loads are transferred to the existing structure through a combination of new connection points.  

The new overhead sheaves required were connected and supported by a combination of the reuse of some of the original beams in their original locations, some original beams reused but relocated and some new steel.  A new overhead service deck was installed to enhance safety. 

This winding drum installation, like so many, used a second independent rope loop from the car to the counterweight, which never see the drive machine.  As such, the old sash-weight-type counterweight had independent upper and lower sections.  This arrangement allows the counterweight to be lighter, which along with other code considerations, makes them unsuitable for reuse. 

So a new counterweight was required and due to its greater weight, the stress to the existing 8 lb/ft guiderails far exceeded the 5% allowance.  As with most of these conversions, space constraints preclude the installation of heavier rails.  The existing guiderails were retained in their original locations along with their original, inadequate bracketing.  Additional steel and anchors were applied using creative engineering to reinforce the rail stacks to meet the new loads.

In fact, all of the structural elements of the converted systems were fully structurally calculated and designed not only to meet the standard A17.1 code requirement but to comply with the stress and deflection criteria of the seismic code (A17.1-1996, Part 24).

It is critical that a job such as this that be properly engineered.  We have seen cases where the materials and equipment are ordered and delivered to the job with negligible thought or planning with regard to how it will all go together.  The "plan" is for the mechanic to "engineer" the job "by the seat of his/her pants."  I've met and worked with many very good modernization mechanics.  But very, very few have the math and engineering skills to prepare the proper calculations to prove out support member sizes in compliance with the deflection criteria, bolting and welding strength sufficiency, etc.  For this reason, the code requires the review of a licensed engineer for altering members that support the elevator system.

Pictures  

A classic early 1900s Otis basement winding drum drive machine.  The new Hollister Whitney #54 O.D. Basement Set geared drive machine is located in its place via an adapter plate and with structural connections to the building independent of the old Otis base (see drawings below).

The old sheaves original three loop system whereby ropes travel from the machine drum to the car, the machine O.D. sheave to the first stage of the counterweight and a separate, independent loop between the car and the second stage of the counterweight.  These were replaced with new overhead sheave reusing many of the original beams, some relocated and some new steel.

This picture shows the original screen work platform which was replaced with steel deck.  It also shows the inadequate rail bracketing, which were reinforced to meet the new loading per seismic standards.

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.

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