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How To Select: Manual Wheelchairs
How Long Will My Wheelchair Last?
The lifespan of a manual wheelchair depends on the chair material as well as how you use and abuse your chair.
by Andy Rentschler and Rory Cooper

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There are many different makes and models of manual wheelchairs available. Just like a car or bicycle, some are made with better parts than others. Therefore, some will last longer than others. Even so, it is sometimes difficult for you to determine exactly how long a wheelchair will last.

The good news is that there are ways to help you determine the life of your manual wheelchair based on individual use. And, while there are many components on a manual wheelchair that can fail or might need to be replaced, some of them can be repaired by you without much difficulty.

There are three common frame failure points on a manual wheelchair.

  1. the cross-brace,
  2. the caster connections and
  3. the seat/backrest interface.

A good maintenance plan for your chair will help you to spot any of these problems early on.

  1. The Cross-Brace. If you own a folding wheelchair, then the cross-brace beneath the wheelchair is a prime site for failure. Many wheelchairs have two circular or square cross-braces that are connected by a bolt. Fatigue cracks can form near that bolt's hole on either cross-brace and ultimately cause the brace to fail. Cracks can also start at the welds that connect the cross-braces to the horizontal seat tubes. This renders the wheelchair inoperable and the entire cross-brace must then be replaced. Depending on the chair, you can purchase a new cross-brace and replace it yourself.
  2. The Caster Connections. Another common failure point is where the casters connect to the frame at the front of the wheelchair. Casters are connected to the frame either by bolts or welds. Again, the bolt holes are areas of high stress concentrations and can often crack. Generated by everyday use, the forces or pressure on the casters are transmitted directly to the connecting bolts. This places a high amount of stress on the frame, which is already weakened by the bolt hole. Welds are also commonly used to attach the caster to the frame. Failures at or around the welds are common. A failure of this type renders the wheelchair useless and a new frame must be purchased.
  3. The seat/backrest interface. The tubing that forms the area that holds the wheelchair seat connects to the tubing that forms the backrest. This is most often accomplished through welding or brazing. Brazing means a filler material was used to join two base materials. The filler material is different than the base materials. It has a lower melting point. Unlike normal welding, the base material does not reach its melting point during the process. This prevents changes in the properties of the base materials due to heating. During propulsion, the cyclic or repetitive force exerted on the backrest is transmitted to this joint. When you propel your chair, you rock back and forth against the backrest. This force is exerted on the backrest during every propulsion stroke. Because of this, high stress concentrations can develop at the weld and lead to failure. Once again, the wheelchair becomes inoperable and a new frame is required.

Cross-braces are connected by a bolt. Fatigue cracks can form near that bolt's hole on either cross-brace and ultimately cause the brace to fail

Most frame failures occur at the areas mentioned above. However, frame failures can also occur at other locations. Any part of the frame which has a bolt hole or a weld joining two pieces is susceptible to failure. It is often a good idea for you to inspect your wheelchmair at these areas and look for nicks or small cracks. Catastrophic frame failures often take time to develop and start commonly as small nicks or cracks and then propagate until the entire component fails.

How long will your wheelchair last before you need to replace it? The answer depends on many factors. If you are a typical wheelchair rider and don't constantly bang your chair around on rough roads or down steps, your chair will probably last as long as five years. Factors to consider are wheelchair materials, wheelchair components and your lifestyle.

Material: One of the most significant factors in determining the lifespan of a wheelchair is the material that the wheelchair is made of. Today, there are many different types of materials available. Steel and aluminum are two of the most common types. If a wheelchair is made out of high-quality steel, then its frame should be very rugged. However, steel tends to be heavy. Many of the lower priced wheelchairs are often made of low-grade steel. This includes depot and lightweight wheelchair models found in many nursing homes and hospitals.

Aluminum is much lighter than steel and can reduce the overall weight of the wheelchair. However, it is also weaker than most steels. Titanium is beginning to be used more often. It has the strength of steel but is also very light. The only drawback is that it is expensive and can drive up the cost of a manual wheelchair. Composites are also starting to be developed for use with wheelchairs. Carbon fiber composites can produce high strength with very little weight. Once they are further developed and tested, the use of composites should reduce the weight of wheelchairs considerably.

It is becoming more common for manufacturers to use a combination of different materials in order to create the strongest and lightest wheelchair. It is important for you to know what type of material your wheelchair is made of.


Cracks can start at the welds that connect the cross-braces to the horizontal seat tubes

Components: Accessories and components can also have a significant effect on the life of a wheelchair. For instance, there are different types of wheels available. You can choose from pneumatic, solid or foam tires for your casters and propelling wheels. Solid tires provide less cushion and thus produce higher forces on the wheelchair than the other types. Pneumatic tires often provide the most comfortable and shock absorbent ride. However, if the tire pressure is not maintained, then this can lead to higher forces and difficulty with propulsion.

Many wheelchairs now also incorporate suspension systems. This can greatly reduce the forces experienced by the wheelchair frame. Rear suspension units are becoming more common, and now companies have also started to develop casters that incorporate shock absorption.

Lifestyle: The life of your manual wheelchair also depends heavily on your lifestyle. If you are very active and spend time outdoors, you usually will put higher stresses on your wheelchair than someone who stays indoors. Going over curbs and other obstacles can produce very high stresses. Wheelchairs that are dropped or banged while getting into and out of cars can also develop failures more quickly. It is important for active users to maintain their wheelchairs on a regular basis.

Wheelchair standards have been developed in order to provide a basis of comparison for different types of wheelchairs. A manual wheelchair that passes the ANSI/RESNA standards is predicted to last three to five years before it fails. However, meeting these standards is not mandatory for manual wheelchairs, and their manufacturers rarely provide information on fatigue testing of their products to consumers.

Although it is difficult to accurately predict the life of a manual wheelchair based on individual use, there are many factors that can be analyzed to help you determine this life. The type of wheelchair, the frame material, the components, and your own activity level can all be used as a gauge to help determine whether or not, and when, your wheelchair will be susceptible to failure.



manualfatigureauthors

Andy Rentschler , B.S., is a bioengineer specializing in rehabilitation engineering at the Center of Excellence in Wheelchairs & Related Technologies/Human Engineering Research Laboratories, VAMC, Pittsburgh, PA. In addition, he is a Ph.D. candidate in the bioengineering department at the University of Pittsburgh.



Rory A.

Rory A. Cooper, Ph.D., is chairman and a professor of the Department of Rehabilitation Science and Technology at the University of Pittsburgh. He is also the director of the Center of Excellence in Wheelchairs & Related Technologies/Human Engineering Research Laboratories, VAMC, Pittsburgh, PA. A former Paralympic wheelchair racer, he is active in designing and studying wheelchairs. School of Health and Rehabilitation Sciences, Rehabilitation Engineering Research Center on Wheeled Mobility , Center for Injury Research & Control .

WaRT/HERL, VA Pittsburgh Health Care System, 7180 Highland Drive, 151R-1, Bldg.4 Rm 058e, Pittsburgh, PA 15206.



January 02, 2000

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