SP-4a: Development and Validation Testing to Evaluate Seating System Crashworthiness

Task leader: Gina E. Bertocci, PhD, PE

Co-investigators: Larry Schneider, PhD, Miriam Manary, MSE, Dong Ran Ha, MS (graduate student)

Other participants: James Swinehart (Metalcraft Industries, seating system manufacturer), Tom Novotny (AES, seating system manufacturer), National (ANSI /RESNA) and International (ISO) Standards Committees (including consumers, clinicians, researchers and manufacturers)

Duration/Staging of task: This 24 month research task will be conducted in months 1-24 of the 60 month RERC cycle

Design of research activities

Literature review

While performance of all wheelchair components is key to occupant crash protection, seat design and integrity are of particular concern since vehicle seat characteristics and failure have been linked directly to injury risk in motor vehicle crashes (Warner, 1991; Viano, 1992; Strother, 1987; Saczalski, 1993; NHTSA, 1997; Blaisdell, 1993; Adomeit, 1979; Aibe, 1982). Frontal impact sled tests (20g/48kph) of commercial wheelchairs have shown seating system failures to be relatively common (see figure below) (ANSI/RESNA, 1996). Seat attachment hardware, seat support surfaces and seat backs (on rebound) are among the most common components to fail under frontal impact conditions (Schneider, 2001). Such failures can greatly increase the risk of injury and particularly the risk of submarining.

Crash Level Seat Loading

Prior to developing test methods to evaluate the crashworthiness of wheelchair seating systems it is necessary to quantify seating loads during a crash. Previous studies which have attempted to elucidate wheelchair seat loading under crash conditions have consisted of both computer simulation studies and limited sled testing. Computer simulation studies have shown that frontal impact seat forces are dependent upon crash pulse, rear securement point location, seat characteristics and restraint configuration (Kang, 1998; Gu, 1996; Bertocci, 1996; Bertocci, 2000). A limited series of frontal impact sled tests conducted by Gu and Roy with disc-type load cells incorporated into the ISO surrogate wheelchair and using a Hybrid III, 50th percentile male test dummy measured seat loads (Gu, 1996). Shaw also estimated seat loading in frontal impact sled testing using pressure-sensitive film placed on the seat and load cells located beneath the front wheels of commercial manual wheelchairs with various types of seating systems (i.e. sling, rigid foam mounted on plywood) (ANSI/RESNA, 1996). Recent frontal impact testing conducted by Bertocci and Manary using the SAE surrogate wheelchair evaluated seat loads using disc-type load cells incorporated into the wheelchair seat and also evaluated the effects of rear securement point location (see figure below) (Bertocci, 2001b). This recent series of sled tests provided validation of seat loads measured through a previously conducted computer simulation study (Bertocci, 1996).

Development & Application of a Static Test Method for Seating Systems

To provide the means for seating system testing independent of specific wheelchairs, the University of Pittsburgh has developed a static test method to evaluate seating system components (Ha, 2001b). Relying upon computer simulation studies and sled testing described above, test criteria for seat and back loading were established. Test loading criteria was based upon a wheelchair secured using 4-point tiedowns and a wheelchair-seated 50th percentile male test dummy subjected to a 20g/30mph frontal impact. Seat back loading criteria was based upon either the rebound phase of a 20g/30mph frontal impact or a 20g rear impact, depending upon which was greater. For the purposes of our proposed test protocol, a successful test, or "pass", required that the seating component under evaluation be capable of withstanding the test load. Failure was defined as component fracture or excessive deformation leading to an unstable support surface.

The design of the test setup was intended to isolate the performance of the tested seat component specimen from all other seating and wheelchair components. Accordingly, seat components (e.g., seat and back support surfaces, attachment hardware) were attached to a specially designed rigid test fixture that was mounted to a tension/compression loading device. The test fixture consisted of two solid rods spaced seating width apart simulating a wheelchair seat frame (see figure below). The test frame eliminated deformation that may be associated with the wheelchair frame so as to focus on seat component performance alone. A vertical downward load was then applied, transmitted to the test seat using the lower portion of the ISO 7176 anthropometric test device (ATD), which represents the buttocks and thigh of a 50th percentile male. When testing a seat back, the upper portion of the ISO 7176 ATD representing the torso was used to apply the load. Seat and back attachment hardware were tested using a rigid surrogate seat or back surface, to isolate attachment hardware performance.

To date, we have conducted nearly 80 static tests of 40 unique commercial wheelchair seating components using our developed test protocol. In general, many of the products failed to withstand test criteria, failing often at loads which are 50% or less than that expected in a frontal crash. Failure modes were, in many cases, similar to those seen in impact testing.

In one series of tests, the crashworthiness of five combination wheelchair back support surfaces and attachment hardware was evaluated using our static test procedure (Ha, 2000). Crashworthiness was tested by applying a simulated rearward load to each seat back system. None of the five tested wheelchair back supports withstood the simulated rearward-directed crash load of 2400 lb. All failures were associated with attachment hardware.

In another study by Bertocci et al., the crashworthiness of commercially available seat attachment hardware was evaluated using our low cost static test procedure intended to replicate seat loading conditions associated with a 20g/30mph frontal impact (Bertocci, 2000). Eleven unique sets of drop hook type hardware were tested and none of the hardware sets met the crashworthiness test criterion. All hardware failed at less than 50% of the load that seating hardware may be exposed to in frontal impact. The primary failure mode was excessive deformation, leading to an unstable surrogate seat support surface (see figure below). These results suggest that commercially available seating drop hooks may be unable to withstand.

Post-Test Drop Hook Test Specimen Failures (Bertocci, 2000) loading associated with a frontal crash and should not be recommended for use with transport wheelchairs. Bertocci et al. also evaluated the performance of various types of commercially available drop seats against the loading test criteria (Bertocci, 2001c). Five different types of drop seats (two specimens each) constructed of various materials (i.e., plastics, plywood, metal) were evaluated. Two types of drop seats (three of the total 10 specimens) met the 3750 lb frontal impact test criteria (see below). While additional validation of the test protocol is necessary, this study also suggests that some drop seat designs may not be capable of withstanding crash level loads.

Another study evaluating the crashworthiness of 2 specimens each of 3 unique sling seats and 3 unique sling backs using our static testing protocol was also conducted (Ha, 2001a). Two of six sling seats failed to pass the test and two of six sling backs failed to meet the test criterion. In general, sling-type support surfaces tended to have improved crash performance as compared to other types of seating surfaces.

In summary, our static testing protocol has provided a method for screening the crashworthiness of wheelchair seating components. Accordingly, this test method has been incorporated as an informative annex of the draft standard, ISO 16840-4 Seating Devices for Use in Motor Vehicles, to aid manufacturers in the design of transport-safe wheelchair seating. However, further validation of this test method to determine its dynamic similarity with sled impact testing is needed.

Recently the ISO and ANSI/RESNA wheelchair transportation standards committees have agreed that a dynamic test method to evaluate seating systems independent of a specific wheelchair frame is necessary. Such a test would promote safety across a broader range of available commercial seating systems. Accordingly, the University of Pittsburgh and University of Michigan have joined efforts towards developing a reusable surrogate wheelchair base that could be used to dynamically test seating systems. Commercial seating systems would be mounted to the surrogate wheelchair base (shown below) for sled impact testing. This reusable base has been designed to represent an average power wheelchair in terms of inertial characteristics (Bertocci, 1997). To-date, two pilot tests have been conducted verifying the strength and reusability of the surrogate base. Additional efforts are needed to verify that the surrogate base provides a crash response similar to that of commercial wheelchairs.

Research objectives

Objective 1: Further development and refinement of surrogate wheelchair base (SWCB). The surrogate wheelchair base described here is a first prototype. Additional confirmation and validation efforts are necessary.

  • 1a: First, we will assure that SWCB is able to accommodate a wide range of commercial wheelchair seating system components. Various types of adult seat support surfaces and attachment hardware will be obtained and evaluated for compatibility with the SWCB. Currently the SWCB is able to accommodate only adult (18" x18") sized seating systems. To allow for accommodation of various sized seating systems, as well as pediatric seating systems, adapters will be designed and fabricated for mounting to the SWCB. These adapters will allow for accommodation of seating systems ranging from (18" x 18") to (12" x 12").
  • 1b: To allow for individual component testing (e.g., seat back, attachment hardware), we will develop surrogate seat and back surfaces, and surrogate attachment hardware that can be used for testing with the SWCB. This approach is similar to that which we used in our static testing of seating components. For example, when it is desired to test seating attachment hardware, surrogate seat and back surfaces would be utilized as the support surfaces so that testing will isolate the performance of the attachment hardware alone. Conversely, to test support surface performance, surrogate attachment hardware will be utilized.

Objective 2: Validation of surrogate wheelchair base dynamic crash response. As a part of this objective we will verify that the crash response of the SWCB is similar to that of commercial wheelchairs.

  • 2a: To accomplish this goal we will conduct a series of 20g/30mph frontal impact sled tests using a 50th percentile, Hybrid II anthropomorphic test dummy. Since rear securement point location has previously been shown to affect seat loading on impact (Bertocci, 2000), these tests will evaluate SWCB and ATD response associated with two unique rear securement point locations. Two series of 6 tests will be conducted. Each series of tests will be conducted using an identical seat and back. Each series of tests will consist of the following: three tests conducted using the lower SWCB securement points (vertically aligned with the SWCB center of gravity) and using the same test configuration, three additional tests conducted using the upper securement points (vertically aligned with the seat-to-back intersection). The crash response obtained from these tests will be compared to previously conducted sled tests of commercial wheelchairs with the same seats and backs. Tests previously conducted at the UMTRI will be used for comparison purposes. The following measures will be used as a means of comparison: wheelchair P-point excursion, ATD head forward and rear excursion, ATD knee excursion, rear tiedown loads, and occupant restraint loads.
  • 2b: To further investigate the design and crash response of the SWCB we will develop a computer simulation model. Dynaman software will be utilized to build the model. Sled impact testing conducted as a part of this task will be used to validate the simulation model. This model will be used to conduct parametric analyses of the following variables: wheelchair seat back frame stiffness, wheelchair seat frame stiffness and securement point location. Our analyses will aid in determining the effect that each design variable has on SWCB and ATD crash response. We will also investigate seat-loading characteristics of the various scenarios.
  • The findings of 2a and 2b will be used to adjust the SWCB design as needed to achieve dynamic similarity with commercial wheelchairs.

Objective 3: Comparison of static and dynamic test method results. Since dynamic testing can be more costly than static testing for seating manufacturers it is useful to determine if there is similarity between static and dynamic testing results. This objective will be accomplish by conducting frontal impact sled testing using the SWCB with seating systems that have been previously static tested by the University of Pittsburgh. We will conduct two sled tests each of the following seating components that have been previously static tested: i) drop hooks with rigid surrogate seat and back surfaces, ii) rigid plywood with molded foam seat and back, iii) contoured seat and back with manufacture provided attachment hardware, and iv) sling seat and back. In the case of failure, we will compare failure modes resulting from static and dynamic test methods.

Objective 4: Transfer of Recommendations and Findings to Standards Development Efforts

Anticipated outcomes

We expect that this task will result in test methods that can be used to evaluate the crash-worthiness of seating systems independent of a specific wheelchair frame. Such a method will benefit manufacturers of seating systems, eliminating the need to test all possible combinations of seating systems and wheelchair frames. The results of this task will likely provide rehabilitation technology suppliers and consumers a wider choice of transport-safe seating products. Since national and international standards groups have identified “after-market wheelchair seating systems” as a priority, the findings of this task will directly support the efforts of both the ISO and ANSI/RESNA Standards Committees. Transfer and implementation through standards provides an effective pathway for the results of this task to become integrated into industry practice and to be disseminated to manufacturers and suppliers. Additionally, one graduate student, Dong Ran Ha, MS, will be trained as a part of this task.

References

Adomeit, D., Seat Design - A Significant Factor For Safety Belt Effectiveness. SAE Paper No. 791004, 1979.

Aibe, T., Watanabe, K., Okamoto, T. and Nakamori, T., Influence of Occupant Seating Posture and Size on Head and Chest Injuries in Frontal Collision. SAE Paper No. 826032, 1982.

American National Standards Institute (ANSI)/Rehabilitation Engineering Society of North America (RESNA), Seating Insert Eval Sled Tests, Greg Shaw - University of Virginia Auto Safety Lab, 1996.

ANSI/RESNA, ANSI/RESNA WC19: Wheelchairs Used as Seats in Motor Vehicles. American National Standards

Institute (ANSI)/Rehabilitation Engineering Society of North America (RESNA). 2000.

ATBCB, Americans with Disabilities Act (ADA) Accessibility Guidelines for Transportation Vehicles. 1991.

Bertocci, G.E., Digges, K. and Hobson, D., Development of Transportable Wheelchair Design Criteria using Computer Crash Simulation. IEEE Transactions of Rehabilitation Engineering, 1996. 4(3): p. 171-181.

Bertocci, G., Karg, P., Hobson, D., Wheeled Mobility Device Database for Transportation Safety Research and Standards. Assistive Technology, 1997. 9.2: p.102-115.

Bertocci, G., Szobota, S., Ha, D. and Roosmalen, L., Development of Frontal Impact Crashworthy Wheelchair Seating Design Criteria Using Computer Simulation. Journal of Rehab Research and Development, 2000. 37(5): p. 565-572.

Bertocci, G., Ha, D., Deemer, E. and Karg, P., Evaluation of Wheelchair Seating System Crashworthiness: Drop Hook Type Seat Attachment Hardware. Archives of Physical Medicine and Rehabilitation, 2001a. 82(April): p.534-540.

Bertocci, G., Manary, M. and Ha, D., Wheelchairs as Seats in Motor Vehicles: Frontal Impact Seat Loading. submitted to Medical Engr & Physics, 2001b.

Bertocci, G., Ha, D., van Roosmalen, L., Karg, P. and Deemer, E., Evaluation of Wheelchair Drop Seat Crashworthiness. To appear in Medical Engineering & Physics, 2001c.

Blaisdell, D.M., Levitt, A.E. and Varat, M.S., Automotive Seat Design Concepts for Occupant Protection. Society of Automotive Engineers, 1993. SAE 930340: p. 109-119.

Bunai, Y., Nagai, A., Nakamura, I., Ohya, I., Blunt Pancreatic Trauma by a Wheelchair User Restraint System During a Traffic Accident, J Forensic Sci 2001. 46(4): p. 965-968.

Dept of Transportation, FMVSS Seating Systems 571.207. Washington, D.C.: Department of Transportation (DOT). 1993.

Gu, J. and Roy, P. Optimization of the Wheelchair Tiedown and Occupant Restraint System. in 15th International Technical Conference on Enhanced Safety of Vehicles. 1996. Melbourne, Australia.

Ha, D., Bertocci, G., Deemer, E., Roosmalen, L. and Karg, P., Evaluation of Wheelchair Seating System Crashworthiness: Combination Wheelchair Seat Back Surfaces and Attachment Hardware. Journal of Rehabilitation Research and Development, 2000. 37 (5)(Sept/Oct): p. 555-563.

Ha, D., Bertocci, G., Karg, P., Evaluation of Wheelchair Sling Seat and Sling Back Crashworthiness. Submitted to the Journal of Rehabilitation Research and Development, 2001a.

Ha, D., Bertocci, G., van Roosmalen, L., Karg, P., Development of a Static Test Method to Evaluate Crashworthiness of Wheelchair Seating Systems Used as Motor Vehicle Seats. Proceedings of RESNA 2001 Annual Conference; Reno, Nevada, June 2001b.

Kang, W. and Pilkey, W., Crash Simulations of Wheelchair Occupant Systems in Transport. Journal of Rehabilitation Research and Development, 1998. 35(1): p. 73-84.

Leary, A., Bertocci, G., Injury Risk Analysis of Wheelchair User in a Frontal Impact Motor Vehicle Crash. Proceedings of RESNA 2001 Annual Conference; Reno, Nevada, June 2001.

NHTSA, Preliminary Assessment of NASS CDS Data Related to Rearward Seat Collapse and Occupant Injury. Washington, DC: NHTSA. 1997.

Saczalski, K.J., Syson, S.R., Hille, R.A. and Pozzi, M.C. Field accident evaluations and experimental study of seat back performance relative to rear-impact occupant protection. in Society of Automotive Engineers. 1993: SAE.

Schneider, L. and Manary, M., UMTRI Wheelchair and WTORS Sled Impact Test Status Report, Feb 7, 2001.

Strother, C. and James, M., Evaluation of seat back strength and seat belt effectiveness in rear impact. SAE. 1987.

Viano, D., Influence of Seat Back Angle on Occupant Dynamics in Simulated Rear-End Impacts. SAE Paper No. 922521, 1992.

Warner, C., Stother, C., James, M. and Decker, R., Occupant Protection in Rear End Collisions: The Role of Seat Back Deformation in Injury Reduction. 1991: p. 2028-38.

Whitehouse.gov, Fullfilling America's Promise to Americans with Disabilities: New Freedom Initiative; http://www.whitehouse.gov/news/freedominitiative/, Feb 6, 2001.


Progress Report June 1, 2003

Output targets

  • Utilizing computer simulation, investigate the effects of wheelchair characteristics on wheelchair seat loading to aid in the development of the surrogate wheelchair base. Present and publish (peer-reviewed) the findings of this investigation.
  • Develop a surrogate wheelchair base (SWCB) prototype capable of evaluating frontal crashworthiness of wheelchair seating systems.
  • Develop and validate a computer simulation model of the developed SWCB. Present and publish (peer-reviewed) the development and validation of this model.
  • Working with standards groups, develop an international and national standard to evaluate the crashworthiness of wheelchair seating systems independent of a specific wheelchair frame. This standard will depend upon testing using the SWCB developed in this project.

Progress toward planned outputs

  • Ha D, Bertocci G, An Investigation of Manual Wheelchair Seat Pan and Seat Back Loading Associated with Various Wheelchair Design Parameters Using Computer Simulation, to appear in RESNA 2003 Conference Proceedings, June, 2003. This abstract will be expanded into a full peer-reviewed manuscript.
  • Manary M, Woodruff L, Bertocci G, Schneider L, Patterns of Wheelchair Response And Seating-System Failures In Frontal-Impact Sled Tests, to appear in RESNA 2003 Conference Proceedings, June, 2003. This abstract will be expanded into a full peer-reviewed manuscript.
  • A 2nd surrogate wheelchair base prototype that incorporates key wheelchair characteristics has been developed and preliminary validation testing has been completed.
  • 2nd and 3rd ISO Committee Draft Standard – 16840-4 Wheelchairs Seating Systems Used in Motor Vehicles. The 2nd CD was completed and international voting comments were incorporated into the development of a 3rd CD. The 3rd CD international voting process is currently underway. The 3rd CD reflects the use of the SWCB prototype developed in this project to evaluate seating systems.

Problems encountered

To-date no problems have been encountered that have greatly impeded the work progress or altered the originally proposed schedule. However, a change to the original plans regarding the SWCB has occurred. Original plans were to modify the 1st prototype to accommodate varied seat widths. Upon gathering input from the ISO standards group, it was decided that a 2nd prototype having a structure different from the 1st prototype was necessary. This 2nd prototype was developed at UMTRI with only slight impact to the originally proposed project schedule. This change has resulted in a 2-3 month delay which will not impact the final completion date of the project.

Key preliminary findings to date

  • An investigation of wheelchair crash response and seat failure modes associated with previously conducted frontal impact sled tests was conducted and was used in the development of the SWCB prototype. The following trends were identified in a sample that represents most ANSI WC19 wheelchairs: 1) Seating failures are relatively rare and usually result from attachment hardware failures. 2) Much of the attachment hardware that fails is not positively locked to the frame, suggesting that simple design changes could improve seat system crashworthiness. 3) Manual WCs experience little rotation in a crash but account for the majority of WC seat pan failures, suggesting that shear loading is the worst-case scenario.
  • An investigation of wheelchair characteristics on seat loading using computer crash simulation was used to aid in the design of a 2nd SWCB prototype. This investigation showed that seat back loading can be affected by wheelchair characteristics such as seat back angle, rear securement location and seat-to-back intersection. Seat pan loading was found to be less sensitive to these same wheelchair design parameters.
  • Development of a second surrogate wheelchair base prototype which incorporates key characteristics of commercial wheelchairs (e.g. seat-to-back deflection, frame/caster deformation). Preliminary validation testing of this prototype was recently completed. Preliminary testing suggests that the SWCB will provide an appropriate means for evaluating the crashworthiness of wheelchair seating systems.
  • Development of 2nd and 3rd International Standards Organization (ISO) Committee Draft (CD) Standard documents (ISO 16840-4 Wheelchair Seating Systems for Motor Vehicles). The 3rd CD is currently undergoing international voting. This Standard incorporates testing of seating systems using the newly developed SWCB prototype.

Progress Report May 1, 2004

Output targets

  • Utilizing computer simulation, investigate the effects of wheelchair characteristics on wheelchair seat loading to aid in the development of the surrogate wheelchair base. Present and publish (peer-reviewed) the findings of this investigation.
  • Develop a surrogate wheelchair base (SWCB) prototype capable of evaluating frontal crashworthiness of wheelchair seating systems.
  • Develop and validate a computer simulation model of the developed SWCB. Present and publish (peer-reviewed) the development and validation of this model.
  • Working with standards groups, develop an international and national standard to evaluate the crashworthiness of wheelchair seating systems independent of a specific wheelchair frame. This standard will depend upon testing using the SWCB developed in this project.

Progress toward planned outputs

  • Ha D, Bertocci G, An Investigation of Manual Wheelchair Seat Pan and Seat Back Loading Associated with Various Wheelchair Design Parameters Using Computer Simulation, RESNA 2003 Conference Proceedings, June, 2003. This abstract will be expanded into a full peer-reviewed manuscript.
  • Manary M, Woodruff L, Bertocci G, Schneider L, Patterns of Wheelchair Response And Seating-System Failures In Frontal-Impact Sled Tests, RESNA 2003 Conference Proceedings, June, 2003. This abstract will be expanded into a full peer-reviewed manuscript.
  • 2nd surrogate wheelchair base prototype that incorporates key wheelchair characteristics has been developed and validation testing is underway. The SWCB includes design features that permit testing and evaluation of a wide range of commercial seating systems. The SWCB is equipped with an interchangeable cross brace frame, interchangeable seat rails, deformable seat back elements, deformable caster elements and multiple rear securement points. Validation testing will compare performance of the SWCB to commercial wheelchairs, with a particular focus on seating system performance.
  • ISO – 16840-4 Wheelchairs Seating Systems Used in Motor Vehicles DIS. The Draft International Standard was completed and is currently undergoing international voting. Voting comments are expected for the Nov, 2004 ISO meeting. At this meeting, comments will be reviewed and the standard will be modified for preparation as a Final Draft International Standard (FDIS). This standard relies upon test methods using the surrogate wheelchair base to evaluate seating systems independent of a specific wheelchair frame.
  • A parallel ANSI standard, WC 20 Wheelchair Seating Devices for Use in Motor Vehicles has been compiled and is undergoing preparations for voting. A draft version of the standard was reviewed by the SOWHAT Committee and modified at the June, 2004 ANSI meeting. The WC20 version of the standard is harmonized with ISO 16840-4 to the extent possible.

Key preliminary findings to date

  • An investigation of wheelchair crash response and seat failure modes associated with previously conducted frontal impact sled tests was conducted and was used in the development of the SWCB prototype. The following trends were identified in a sample that represents most ANSI WC19 wheelchairs:
  1. Seating failures are relatively rare and usually result from attachment hardware failures.
  2. Much of the attachment hardware that fails is not positively locked to the frame, suggesting that simple design changes could improve seat system crashworthiness.
  3. Manual WCs experience little rotation in a crash but account for the majority of WC seat pan failures, suggesting that shear loading is the worst-case scenario.
  • An investigation of wheelchair characteristics on seat loading using computer crash simulation was used to aid in the design of a 2nd SWCB prototype. This investigation showed that seat back loading can be affected by wheelchair characteristics such as seat back angle, rear securement location and seat-to-back intersection. Seat pan loading was found to be less sensitive to these same wheelchair design parameters.
  • Development of a second surrogate wheelchair base prototype which incorporates key characteristics of commercial wheelchairs (e.g. seat-to-back deflection, frame/caster deformation). Preliminary validation testing of this prototype was recently completed. Preliminary testing suggests that the SWCB will provide an appropriate means for evaluating the seating systems.

Progress Report May 1, 2005

An investigation of wheelchair crash response and seat failure modes associated with previously conducted frontal impact sled tests was conducted and was used in the development of the SWCB prototype. The following trends were identified in a sample that represents most ANSI WC19 wheelchairs: 1) Seating failures are relatively rare and usually result from attachment hardware failures. 2) Much of the attachment hardware that fails is not positively locked to the frame, suggesting that simple design changes could improve seat system crashworthiness. 3) Manual WCs experience little rotation in a crash but account for the majority of WC seat pan failures, suggesting that shear loading is the worst-case scenario.

  • An investigation of wheelchair characteristics on seat loading using computer crash simulation was used to aid in the design of a 2nd SWCB prototype. This investigation showed that seat back loading can be affected by wheelchair characteristics such as seat back angle, rear securement location and seat-to-back intersection. Seat pan loading was found to be less sensitive to these same wheelchair design parameters.
  • Development of a second surrogate wheelchair base prototype which incorporates key characteristics of commercial wheelchairs (e.g. seat-to-back deflection, frame/caster deformation). Preliminary validation testing of this prototype was recently completed. Preliminary testing suggests that the SWCB will provide an appropriate means for evaluating the seating systems.

5 year report June 1, 2006

 Output targets

  • Utilizing computer simulation, investigate the effects of wheelchair characteristics on wheelchair seat loading to aid in the development of the surrogate wheelchair base. Present and publish (peer-reviewed) the findings of this investigation.
  • Develop a surrogate wheelchair base (SWCB) prototype capable of evaluating frontal crashworthiness of wheelchair seating systems.
  • Develop and validate a computer simulation model of the developed SWCB. Present and publish (peer-reviewed) the development and validation of this model.
  • Working with standards groups, develop an international and national standard to evaluate the crashworthiness of wheelchair seating systems independent of a specific wheelchair frame. This standard will depend upon testing using the SWCB to be developed in this project.

 

 Progress toward planned outputs

  •  Ha D, Bertocci G, An Investigation of Manual Wheelchair Seat Pan and Seat Back Loading Associated with Various Wheelchair Design Parameters Using Computer Simulation,  RESNA 2003 Conference Proceedings, June, 2003.
  • Manary M, Woodruff L, Bertocci G, Schneider L, Patterns of Wheelchair Response And Seating-System Failures In Frontal-Impact Sled Tests, RESNA 2003 Conference Proceedings, June, 2003.
  • Bertocci GE, Souza A, Szobota S, The Effects of Wheelchair Seating Stiffness and Energy Absorption on Occupant Frontal Impact Kinematics and Submarining Risk using Computer Simulation. Journal of Rehab Research and Development, Vol 40, No 2, March/April, 2003.
  • Manary M, Woodruff L, Bertocci G, Schneider L, Patterns of Seating Systems Failures and Kinematics in Frontal Crash Tests of Commercial Wheelchairs, submitted to Assistive Technology, Feb, 2005.
  • Ritchie N, Manary M, Bertocci G, Schneider L, Validation of a Surrogate Wheelchair Base for Evaluation of Wheelchair Seating System Crashworthiness, RESNA 2006 Conference Proceedings, Atlanta GA, June 2006.
  • A surrogate wheelchair base that incorporates key wheelchair characteristics has been developed and validated. The SWCB includes design features that permit testing and evaluation of a wide range of commercial seating systems independent of specific wheelchair frames. The SWCB is equipped with an interchangeable cross brace frame, interchangeable seat rails, deformable seat back elements, deformable caster elements and multiple rear securement points. Validation testing compared performance of the SWCB to commercial wheelchairs, with a particular focus on seating system performance. Validation testing demonstrated that the SWCB introduces seating system loading patterns which are similar to or more severe than those of a commercial wheelchair frame.
  • ISO – 16840-4 DIS Wheelchairs Seating Systems Used in Motor Vehicles. This second version of a Draft International Standard was completed and is currently undergoing preparation for international voting. Once comments are received, the standard will be modified for preparation as a Final Draft International Standard (FDIS). This standard relies upon test methods using the surrogate wheelchair base to evaluate seating systems independent of a specific wheelchair frame.
  • A parallel ANSI standard, WC 20 Wheelchair Seating Devices for Use in Motor Vehicles has been developed and is currently out for voting. The WC20 version of the standard is harmonized with ISO 16840-4.

 

 Key findings to-date

  • An investigation of wheelchair crash response and seat failure modes associated with previously conducted frontal impact sled tests was conducted and was used in the development of the SWCB prototype. The following trends were identified in a sample that represents most ANSI WC19 wheelchairs: 1) Seating failures are relatively rare and usually result from attachment hardware failures. 2) Much of the attachment hardware that fails is not positively locked to the frame, suggesting that simple design changes could improve seat system crashworthiness. 3) Manual WCs experience little rotation in a crash but account for the majority of WC seat pan failures, suggesting that shear loading is the worst-case scenario. These findings were compiled into a peer review journal submission (Manary M, Woodruff L, Bertocci G, Schneider L, Patterns of Seating Systems Failures and Kinematics in Frontal Crash Tests of Commercial Wheelchairs, submitted to Assistive Technology, Feb, 2005) that will aid manufacturers in the development of crashworthy seating systems.
  • An investigation of the effect of wheelchair characteristics on seat loading using computer crash simulation was conducted. This investigation showed that seat back loading can be affected by wheelchair characteristics such as seat back angle, rear securement location and seat-to-back intersection. Seat pan loading was found to be less sensitive to these same wheelchair design parameters. These findings were compiled in a peer-reviewed journal paper (Bertocci GE, Souza A, Szobota S, The Effects of Wheelchair Seating Stiffness and Energy Absorption on Occupant Frontal Impact Kinematics and Submarining Risk using Computer Simulation. Journal of Rehab Research and Development, Vol 40, No 2, March/April, 2003) which will aid manufacturers in the development of crashworthy seating systems.

 

Future plans through end of grant cycle

  • Completion of ISO 16840-4 and ANSI WC20 standards process to provide  finalized voluntary industry standards.
  • Begin to evaluate commercial seating systems against ANSI WC20 and ISO 16840-4.

 

Summary

This project has achieved the originally proposed objectives described above. Over the past 4 years, SP4a investigators have submitted 3 conference abstracts and 2 peer-reviewed journal papers describing the findings of this project. These publications are expected to aid manufacturers in the design and development of crashworthy seating systems. Moreover, national and international industry standards have been developed as a part of this project that will allow manufacturers to evaluate the performance of their seating systems under frontal impact conditions. These standards define test methods that will now allow seating systems to be evaluated independent of a specific wheelchair frame. (Previously existing standards required that a complete wheelchair – frame and seating system – be tested together as one unit. This testing scheme did not address service delivery needs of providing a seating system from one manufacturer and wheelchair frame from another manufacturer.) Ultimately this will lead to an increase in availability of crash-safe seating systems, improving safety for those using their wheelchair as a motor vehicle seat.

Last updated: August 30, 2006

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