There are numerous instances in the elevator industry
when structural engineering may be called for. RCB
Elevator Consulting, LLC (RCB), in concert with our
subcontract California licensed structural engineer, provide elevator structural engineering
services nationwide.
8.7.1.5 Design. Design shall be
verified by a licensed professional engineer for welding,
repair, cutting, or splicing of members upon which the
support of the car, counterweight, escalator, or moving
walks, trusses, girders, and tracks depends.
This alteration code section is fairly broad in scope.
Any modifications to an elevator's machine beams or an
escalators truss would trigger this section.
8.7.2.9 Machinery and Sheave Beams, Supports, and
Foundations. Where new machinery and sheave
beams, supports, foundations, or supporting floors are
installed, relocated, or where alterations increase the
original building design reactions by more than 5%, they
shall conform to 2.9, and the adequacy of the affected
building structure to support the loads shall be verified
by a licensed professional engineer. (also see
8.7.3.9)
Note this section can be triggered in two different
ways: A change to the structure or an increase in
loading. Also note that engineering is required not
just for the elevator equipment but also for the "affected
building structure..." We have found cases where
the existing building structure supporting the machine
beams was deficient. Some authorities having
jurisdiction (AHJ) cite this section whenever a traction
drive machine is replaced and especially so when a winding
drum is converted to a traction elevator.
8.7.2.15.1 Alterations to Car Frames and
Platforms. (also see 8.7.3.14) This
section doesn't specifically require professional
engineering but, depending on the alteration, proper
engineering may be imperative. We have seen cases
where the client added extensions to existing car stiles,
to obtain a taller car, that didn't structurally work.
8.7.2.15.2 Increase or Decrease in Deadweight of
Car. (references 8.7.2.9) This is the
other "5% Rule." This section does require
professional engineering to re-certify the elevator and
the specific components affected. Often the
building owner would like to replace the car interior
finishes but the new design is limited by the 5% rule. By performing the
engineering, and any elevator upgrades the engineering
requires, the deadweight of the car can be increased
beyond 5% the meet the owner's needs.
8.7.2.16.1 Change in Type of Service.
(also see 8.7.3.17) The most common application of
this section is the conversation of a Freight elevator to
a Passenger elevator. Though technically
professional engineering isn't required by this section,
what is retained of the original elevator should be
properly certified for the new loads applied. Also,
often the original freight platform is replaced with a
smaller passenger platform. This requires new
passenger entrances to be set some distance inside the
hoistway to the proper clearance with the new platform.
New landing extensions are required between the original
entrances and the new entrances, which must be properly
engineered.
8.7.2.16.4 Increase in Rated Load.
(references 8.7.2.9)This section, similar to 8.7.2.15.2,
does require professional engineering to re-certify the
elevator and the specific components affected.
Something often misunderstood, the code prescribes the
minimum load rating based on the inside car area.
Cars of the same area can have a greater load rating if
desired - you can over-rate but you can't under-rate an
elevator's rated load (capacity). We've encountered
situations when the owner wanted an elevator with a higher
load rating than the minimum the code required.
8.7.2.17.1 Increase or Decrease in Travel.
On a traction elevator in particular, changing the travel
often means relocating the drive machine in an overhead
arrangement or the overhead sheaves in a basement
arrangement. This would likely trigger sections
8.7.1.5 and 8.7.2.9, which require professional
engineering.
8.7.2.17.2 Increase in Rated Speed. In
most cases increasing the rated speed of a traction
elevator requires replacing the drive machine. If
the new machine is heavier, the machine beams must be
re-certified. The new machine will likely require a
change in its connection to the machine beams, new
blocking beams, anchorage, etc., which should be
engineered. If sections 8.7.1.5 and 8.7.2.9 are
triggered, professional engineering would be required.
8.7.2.20 Ascending Car Overspeed and Unintended
Car Movement Protection. (references 2.19)
In an alteration, this section typically means installing
either a Hollister-Whitney Rope Gripper or a BODE Rope
Brake. California DOSH-ERT has indicated that
professional engineering is not required in all cases,
however, they may require it if the installation appears
not to be structurally sound. We've designed dozens
of rope brake installations and many require creative
solutions (see
Rope Grippers & Brakes).
8.7.2.21.1 Change in Rope. This section
relates to changing the "material, grade, number, or
diameter of ropes" while retaining the original
sheaves. It calls for certification of the rope
change by either "the original elevator manufacturer or
a licensed professional engineer..." We've never
encountered such a situation and would generally recommend
replacing the sheaves. We have engineered drive
machine replacements and retained the deflector sheaves,
but only when the same quantity, grade and diameter ropes
are used. A change from standard to high strength
ropes should be certified by the machine manufacturer.
8.7.2.24 Guide Rails, Supports, and Fastenings.
(also see 8.7.3.28) The code doesn't specifically
call for professional engineering when altering the guide
rails and supports. However, engineering should be
performed to correctly determine the maximum bracket
spans, the bracket design, fastenings, etc. This is
especially important in seismic zones where compliance
with section 8.4 is required. If the alteration
involves an elevator installed prior to the adoption of
the seismic codes, very often the existing guide rails and
brackets - especially for the counterweight - do not
comply with the current standards.
8.7.2.25.1 Alteration to Driving Machines and
Sheaves. This section includes the replacement
of traction drive machines. As stated above, the
section does not necessarily require professional
engineering but there are many reasons that the
installation should be properly engineered. However,
if sections 8.7.1.5 and 8.7.2.9 are triggered,
professional engineering is required.
8.7.2.25.2 Change in Location of Driving Machine.
Changing the drive machine location necessarily means
changing the machine's building support, whether it
includes new machine beams or structural slab in an
overhead installation or a new anchorage means in a
basement or offset installation. This would trigger
sections 8.7.1.5 and 8.7.2.9, which require professional
engineering.
The proper approach is to prepare the engineering prior
to performing the work. If the code or AHJ require it,
the engineering should be submitted for approval prior to
performing the work. When performing an inspection, an
AHJ inspector may request professional (structural)
engineering if something does not appear to them to be
structurally sound. We have seen this occur for items
as varied as the mounting of a new AC motor on a geared
machine to car frame stile extensions to access work
platforms.
Some alterations, in our belief, should not be attempted
without full engineering, including structural engineering.
These include winding drum elevator conversions to traction
(see
Winding Drum Elevators), freight to passenger elevator
conversions, seismic upgrade and certification, major car
frame modifications, some drive machine replacements where
the supports are to be modified, etc.
Sometimes structural engineering can be as simple as a
preparing a sketch of the equipment and a few sheets of
structural calculations. On a large alteration, such
the examples above, the project should include detailed shop
drawings as well as the structural engineering (see
Projects). These shop drawings can serve many
purposes including approval submittals for the client and
the AHJ, planning, coordination, fabrication, installation,
inspection and record sets.
Our elevator structural engineering service is especially
suited to the alteration (modernization) market in that we
perform our own field surveys as required for most existing
conditions. Most often when modifying existing
equipment there is no original engineering to draw from.
When shop drawings of the old equipment do exist, seldom are
they sufficiently detailed to show the information needed.
Having the client sketch the condition can often leave out
important information. So, especially on the more
complex issues, performing our own field survey assures the
most accurate and efficient outcome.
If you are an elevator contractor with a project in need
of professional structural engineering, please give us a
call.
Elevator
Structural Engineering