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, small-diameter wheels.
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.
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)
Another trend 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.
In his 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.”
Not included 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.
A combined 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
The expansion 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.
Failure to select the expansion joint system based on this comparison could result in the specification of an inappropriate expansion joint product.
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 failures.
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.
Photograph 1: MIGUTRANS joint systems ensure smooth, quiet rolling surfaces while withstanding point loads.
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.
Another simple 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.
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.
Expansion joints and
sealants by EMSEAL
Last Modified: March 11, 2014