Modular Composite Wheel Chair Ramp
Modular Composite Wheel Chair Ramp
Designers: Genevieve Martin, Donald Pritchett, Jessica Robertson, Regina Scarber
Client Coordinator: Alan Eberhardt, Department of Biomedical Engineering
This problem arose from a request for a non- or semi-permanent wheelchair ramp for residences with stairs leading up to the entryway. Careful consideration was given to the potential clientele and observation of subdivisions in the surrounding Birmingham area. From this, it was concluded that the ramp to be constructed would not be custom designed for one specific home, but it would be sufficiently flexible in design to accommodate nearly all dwellings that currently use stairs to gain entry.
The design constraints established that the ramp must comply with the American Disabilities Act (ADA). ADA compliant ramps cannot have slopes exceeding a ratio of 1:12. The maximum rise for any ramp run is 30 inches. The ramp landing has to be at least 60 inches long and at least as wide as the ramp run. Both ramp runs and landings must have handrails, which must extend 34-38 inches high. They must be easy to grab and remain rigid in their fittings. Handrail edges must be rounded; if they are circular, the outer diameter must be between 1.25-2 inches. They must extend horizontally above landing a minimum of 12 inches. Curbs are required on the ramp and landing and necessitate a minimum 2 inches in height. The width between handrails must be at least 36 inches wide. It must have edge protection, by means of either extended floor or curb/barrier protection. Other factors and project limitations included sensitivity to ultraviolet light, water absorption, corrosion, and support the live load of a person whose weight is in the 99th percentile who is in a motorized wheelchair. Modularity was also required, such that the ramp should be easily maneuvered by two average adults.
The prototype system was comprised of two pieces, one sloping and one landing platform made from a sandwich composite which would minimize weight. The legs of the structure contained a mechanism for height and slope adjustments to provide maximum flexibility. The rails were prefabricated and held in place by custom made aluminum brackets.
The ramp deck was built of carbon fiber, a polypropylene honeycomb core, 1 inch square steel tubing, and 0.75 inch square steel bar, epoxy resin and polyurethane stiffeners coated with fiberglass. The ramp and landing were constructed by hand lay-up. The steel bar was cut to length and ground to form a tight fit in the ends of the steel tube and driven into place. The tubing was then welded to form the outside dimensions of the ramp deck. The railing was made from 6061 aluminum and connected with couplings fitted with set screws. Post testing was done, which included testing the deflection of the deck and strength of the legs and bolts.
The result was a composite ramp system (Figure 26) that was modular, but somewhat heavier and more expensive then desired. The manufactured platform pieces were too large for easy assembling. The ramp landing was not as strong as desired, but corrections in manufacturing errors promise to increase stiffness in future designs. For future work on this project, stainless steel tubes will be replaced with fasteners. Vacuum Assisted Resin Transfer Molding (VARTM) will be used instead of hand lay-up. Materials will be ordered much earlier to extend the period needed for revisions.
Figure 26. Composite modular ramp system