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ARCH 2614/5614 Lecture notes

Jonathan Ochshorn

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Large-scale views of conveying systems (elevators, escalators) and stairs

Note that Conveying Systems (including elevators and escalators) is Division 14 of the Masterformat Facility Construction Subgroup (see week 1 Wednesday lecture). Stairs, on the other hand, are spread out under the various material divisions (concrete, wood, metal) or as finishes (for special tread and riser covers).

Elevators

1853 Otis Elevator "safety elevator"

1857 Otis elevator installed, 488 Broadway, NYC

elevator images
From left to right: (a) Elisha Otis at the Crystal Palace in New York, 1853; (b) Otis piston-type hydraulic elevator; and (c) steam-powered engine.

Technology keeps advancing: e.g., computer controlled optimal placement of cabs.

Typical capacity for passenger elevator = 2000 - 5000 lbs.

Two primary means of lifting the cabs (hoist mechanisms): traction and hydraulic.

Typical planning module in institutional/commercial settings can be taken as 10'x10' grid (including lobbies between banks of elevators).

typ. elevator plan

Hancock Building plan showing active and inactive elevators
Hancock Building plan showing active and inactive elevators

3-tier elevator system
Elevators in skyscrapers: with sky lobbies, express elevators, and "unused" shafts.

As buildings get taller, elevator companies are also competing on the basis of how fast they move, with some projected speeds as fast as 20 meters/second (4,000 feet per minute). See Elevators race to top as technology matches skyscraper growth from the Financial Times [Cornell students can sign up for free; then search for "elevators"].

Escalators

Most common angle is 30 degrees. Establish "working point" in plan and section and determine required dimensions based on floor-to-floor height.

escalator diagrams
Schematic section and plan of typical escalator

escalator diagrams
How escalators work: see it move at howstuffworks.com

escalator Hong Kong Shanghai Bank by Foster
Escalator at Foster's Hong Kong Shanghai Bank Headquarters Building

escalator at Pompidou Center by Piano and rogers
Piano and Rogers, Pompidou Center, Paris (photo by J. Ochshorn)

escalator diagrams
Piano and Rogers, Pompidou Center, Paris (photo by J. Ochshorn)

escalator diagrams
Piano and Rogers, Pompidou Center, Paris (photo by J. Ochshorn)

escalator calculations
Calculations: finding the overall plan dimension between structural supports for an escalator with a floor-to-floor height of 12'-10".

Typical egress stairs

Commonly steel or reinforced concrete (depending upon primary framing material of building structure).

stair details

stair details
Steel-pan stair under construction on College Avenue, Ithaca, NY; notice how steel beam is inserted into masonry wall (photo by Jonathan Ochshorn, April 2017)

Johnson stair at Lincoln Center
Philip Johnson, stair at Lincoln Center: handrails align precisely, with risers offset (photo by J. Ochshorn)

Stirling stair at Schwartz Center, Cornell
James Stirling, stair at Schwartz Center for the Performing Arts, Cornell: handrails align precisely, but only with some "fudging" (photo by J. Ochshorn)

stair at ILR building, Cornell
Stair at ILR building, Cornell: when risers align, handrails must do a dance in order to maintain continuity (photo by J. Ochshorn)

Stirling stair at Schwartz Center, Cornell
James Stirling, stair at Schwartz Center for the Performing Arts, Cornell; gate directs people exiting from above to get out at first-floor lobby rather than continuing into basement levels (photo by J. Ochshorn)

Meier stair at Weill Hall, Cornell  Renovated exit stair at E. Sibley Hall, Cornell
Richard Meier, stair at Weill Hall, Cornell (left) and renovated stair at E. Sibley Hall, Cornell (right); gates direct people exiting from above to get out at first-floor lobby rather than continuing into basement levels; and extra door allows egress from basement (photos by J. Ochshorn)

Stair tread and riser calculations
Calculations: find the minimum interior dimension of an egress stair shaft for a switch-back steel stair, hwere the floor-to-floor height is 12'-10" (154 in.). Note the number of treads between landings, and sketch a section through the stair showing the number of risers.

This example was rigged so that the number of risers (154 / 7 = 22) came out as an integer. What happens for the more typical condition? Here is a modification of the example shown above, with a floor-to-floor height of 12 ft. (144 inches) instead of 12'-10". In this case, the number of risers is 144 / 7 = 20.57. We use 21 risers so that the actual riser height becomes 144 / 21 = 6.857 in. We do not use 20 risers, since this would result in a riser height greater than 7 in., which is not permitted. This is one of the only instances where a strange number like 6.857 inches does not create any problems: stair fabricators can easily handle such things. The switchback stair could then be configured with 10 treads + 9 treads (since each run of the stair creates one more riser than the number of treads). The overall stair shaft dimension, governed by the 10 tread stair run, is therefore the same as before.

Handrails:

Continuous, and between 34"-38" higher than nosing.

Stair handrail heights
Stair handrail heights.

Guardrails (or just guards)

Typically, 42" high, required wherever there is a discontinuity in the "ground plane" of 30" or more. Must be configured so that a 4" sphere cannot pass through; horizontal bars were formerly prohibited in the IRC (International Residential Code), as they can be used as a "ladder," but current Codes permit such configurations.

Because handrail heights and guard rail heights do not generally coincide, the handrail must be separated from the guard rail, as in the typical stair shown at left below. However, for residential applications, guard rails need only be 36 inches high, so (with careful planning and attention to the geometry) it is possible to have a single hand-guard rail, as in the exterior stair shown at right below.
hand rails and guard rails in stairs
Typical commercial or institutional stair (left); residential stair with single hand-guard rail that also happens to be the structural truss holding up the whole thing (right)

inadequate guard rails in Sibley Dome, Cornell, Ithaca, NY
Inadequate (and dangerous) guard rails, Sibley Dome, Cornell (photo and Photoshopped toddler by Jonathan Ochshorn, Sept., 2017)

Difference between a handrail and guardrail? See YouTube video.