Floor expansion joints
must be engineered to withstand the specific movements and stresses they
will encounter. In healthcare floors, any failure can be unsightly, noisy,
dangerous for people and harmful to expensive mobile medical equipment. The
number one cause of damage to interior floor expansion joints and
surrounding floor materials is point loads of equipment fitted with hard,
Yet despite the
destructive impact of high point loads on healthcare floor joints, this
factor is frequently ignored. Many expansion joint manufacturers fail to
rate the point load resistance level for their products under various wheel
types, making it difficult for architects, engineers, contractors and
building owners to make informed decisions.
Point load resistance is one of three
criteria for selecting a suitably engineered floor expansion joint. Whether
in new construction or retrofitting failed existing joints, the questions
that should drive product selection include:
1) Movement: Can this model handle the expected thermal and other
movements of the building?
2) Joint-Gap Size: Does this model have the correct dimensions to
straddle the designed joint-gap?
3) Point Load: Can this model handle the wheel and axle loads from
the expected traffic?
Hard, plastic tires–the
type most prevalent in hospitals–place the greatest stress on expansion
joints. In a survey of the web sites of seven floor expansion joint
manufacturers, only one, www.emseal.com, provided comprehensive loading
data, by wheel type, for joint systems offered as “heavy duty” or “high
point-load.” Four of the Web sites made no mention at all of wheel loading
capabilities. Two others made a cursory mention of total loads possible for
just one of each of the many models offered as “heavy duty” but with no
correlation to wheel type.
MIGUTRANS series of expansion joints on www.emseal.com are offered
specifically for the ability to handle point loads. The
FS 110 model, for example, shows a load capacity, for equipment with
solid, hard-plastic tires, of 365 lbs/inch width of tire (6.5 kg/mm, 63.7
N/mm). To calculate the total load capacity of the joint, this value is
simply multiplied by the total width of all tires on an axle.
In comparison, pneumatic
tires place significantly less stress on expansion joints. This same FS 110
model is rated to withstand a 22,500 lb (10,200 kg, 100 kN) load per axle of
a forklift, maintenance or other vehicle with pneumatic tires.
Higher Point Load Stress
In hospitals, floor expansion joints often
deteriorate faster than expected. This phenomenon is caused not only by the
failure to engineer for sufficient point load capacity, but also by the fact
that hospital operations have been changing in ways that significantly
increase point load stresses.
One such trend is
“patient-centered design” that has taken root during the past decade. The
goal of patient-centered hospital care is decentralization, which brings
services to the patient, rather than transporting the patient to centralized
locations for imaging, dialysis and other medical procedures.
movement of patients, along with the unnecessary staffing, waiting,
reporting and errors this movement entails. Patients remain in the relative
comfort of their rooms, where they benefit from familiar surroundings. They
are more comfortable, hospital operations are more efficient, and the spread
of infectious disease is reduced.
decentralization means more movement of equipment, as diagnostic and
treatment apparatus is transported to patient rooms. This adds expensive
and sensitive equipment to the already busy flow of cleaning, maintenance
and food service equipment traffic at hospitals.
Much of this
equipment is conveyed by small-diameter, hard wheels, which can and do cause
damage to floor expansion joints and surrounding flooring materials that are
not engineered to handle the high associated point loads. Equally as
important to the damage of the expansion joints is the potential damage to
the equipment itself.
motion of high-point-load, small wheeled traffic can quickly cup
under-designed coverplate systems as well as caused damage to
(click on image for larger view)
increasing point loads at hospitals is the need to accommodate an increasing
number of overweight patients as obesity among U.S. adults has increased
more than 60% during the past 20 years.
article “Designing for the Obese,” Dave Barista, assistant
managing editor of Building Design and Construction magazine, reports
the findings of interviews with leading healthcare design experts. Numerous
design considerations were advocated, including “everything from
wider doorways and heavy-duty beds to patient lifts.” The article also
mentions that “bariatric beds should be rated for at least 600 pounds.”
in this article is the impact of these design considerations on floor
expansion joint selection. Oversized wheelchairs, beds and gurneys are
increasingly common in hospitals. Bariatric beds can weigh up to 800 lbs
empty and, depending on the model, are rated to carry patients weighing up
to 1000 lbs.
load, for example, of bed and patient of 1,610 pounds, spread over four,
1-¼” (30mm) wide, hard rubber wheels, would result in a load per wheel of
402 lbs or 321 lbs per inch of wheel width.
402 lbs/wheel 402lbs/wheel = 321 lbs per inch of wheel
4 wheels 1 ¼” wheel width
joint system intended to handle this load must be selected for its ability
to handle this load without deflection. Compare, for example, the load
capacity of 365 lbs per inch of wheel width of the
FS 110 system.
select the expansion joint system based on this comparison could result in
the specification of an inappropriate expansion joint product.
Types of Floor Expansion Joints
The design of floor expansion joints presents
an engineering challenge. They must be able to handle transverse horizontal
opening and closing movement, longitudinal differential or shear movement,
as well as vertical differential shear movement. These requirements are
similar to the movement demands of wall, ceiling and roof expansion joints.
What makes the design of floor systems so challenging is that they must
perform these movement functions while also providing a strong “bridge” that
can bear point loads and provide a smooth, quiet transition for wheeled
traffic, as well as a slip-free surface for pedestrians.
Manufacturers of floor
expansion joints have used a variety of approaches, with varying degrees of
success. The available products fall into three design categories:
Rubber and Rail
The most common and least expensive system comprises two extruded-metal
(usually aluminum) angles, between which an elastomeric filler is inserted
or adhered. To enable expansive and compressive movement, the insert needs
to be a soft, elastic material and/or shaped into a bellows form. However,
soft materials and bellows shapes are incapable of resisting even relatively
small point loads. Because the rubber material is soft, wheels sink in and
bang against the metal angle on the far side of the joint. This results in a
nasty jolt to patients and medical equipment, causes damage to the adjacent
flooring, and results in early failure of the expansion joint itself.
Figure 1: Rubber inserts cannot
support point loads resulting in jarred patients and equipment and failed
joints, and flooring.
Cover Plate Systems
To provide better point load resistance, a second product category
employs a metal plate. The plate can be anchored on one side [See Figure
2], can float between clamping plates [See Figure 3], or can be
held in the middle with a centering bar. These systems provide a stronger
bridge than rubber and rail systems, and they are capable of handling small
to moderate point loads, although manufacturers regularly fail to provide
point load ratings from which to match models to expected traffic loads.
Most of these systems are especially poor at handling floor height
differences or vertical differential movement which causes the cover plate
to float unsupported at various locations. This phenomenon makes cover
plates noisy, and when deformed by the torque of differential vertical
movement, can result in a tripping hazard. Additionally, the gaps under the
cover plates create cleaning problems, as moisture and dirt collects in the
recesses–an unacceptable hygiene problem in a healthcare setting. Finally,
because there is a transition on each side of the cover plate, wheels bump
twice during transition over the joint.
Figure 2: Side-anchored coverplates buckle
and transfer live-load deflection into anchors causing concrete and flooring
Figure 3: Clamped coverplates created four
plane changing bump points. Expansion anchors close to the joint edge
cause a "fault line" where spalling will occur.
A purpose-designed alternative interlocks two extruded metal
components in a design that accommodates horizontal opening and closing, as
well as differential lateral and vertical movements, while providing high
point load resistance [See Figure 4]. This solid-interlocking system
was specifically designed to withstand the pounding from small-diameter,
hard wheel traffic, while respecting aesthetic integration with adjacent
flooring materials [See Photograph 1]. The design provides a smooth,
quiet rolling surface. Integrated gaskets that seal out dust and dirt are
also thoughtfully engineered features for hospital environments.
Figure 4: Purpose-designed
interlocking system --MIGUTRANS from EMSEAL--ensures smooth passage,
positive anchoring and the ability to handle point loads.
MIGUTRANS joint systems
ensure smooth, quiet rolling surfaces while withstanding point loads.
Anchoring Systems and Epoxy Leveling Beds
Another important consideration when
evaluating floor expansion joint systems is the anchoring method.
Mechanical masonry screws or “expansion anchors” supplied by most expansion
joint manufacturers hold themselves into drilled holes by means of an
outward pressure against the substrate. This creates a fault line close to
the edge of the floor substrate, leading to fractures in the concrete edge.
Spalling at the joint edge leaves the mounting flanges of the expansion
joint system unsupported and liable to downward deflection under loads from
Better suited for
expansion joint applications is the use of chemical anchors. Chemical
anchors use a hard-setting epoxy adhesive to lock a threaded rod into a hole
drilled in the concrete floor. This method ensures the necessary hold-down
force without causing stress to the concrete.
installation practice that can substantially prolong the useful life of any
expansion joint system, but particularly those in high point load
environments, is the application beneath the mounting flanges of an epoxy
setting bed. This ¼” (6mm) layer of epoxy mortar eliminates any unevenness
in the substrate, which ensures that the mounting flanges are fully
supported throughout their lengths. An epoxy bed also acts as a dielectric
insulator between the concrete and the metal flange to prevent corrosion.
Costs of Failure
When point loads cause the failure of floor
expansion joints, healthcare facilities incur significant costs. The uneven surfaces
harm expensive mobile medical equipment and constitute a risk for personal
discomfort and even
injury. In addition to the labor and material costs involved in replacement
of floor expansion joints, the real cost to hospitals lies in the disruption
involved in closing off entire sections of the facility during the
The initial purchase
costs of high-quality floor expansion joints are more than for inexpensive
rubber and rail or coverplate systems. However, this incremental cost is
small compared to the long-term economic benefits of durable and
trouble-free floor expansion joints that withstand the point load of
expected healthcare traffic conditions.
“It is unwise to pay too much, but it’s worse
to pay too little. When you pay too much you lose a little money—that is
all. When you pay too little you sometimes lose everything, because the
thing you bought was incapable of doing the things it was bought to do. The
common law of business balance prohibits paying a little and getting a lot.
It can’t be done. If you deal with the lowest bidder, it is well to add
something for the risk you run, and if you do that you will have enough to
pay for something better.”
-- John Ruskin.