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Last summer (16/7/2005) I posted a query about the validity of inverse methods for recovering GRF compared to direct force measurements. Belatedly I have gathered the responses as below.
Many thanks to everyone who responded.
I aim (funding permitting) to try this out via a combination of 3D treadmill and imaging system to assemble a structure-friendly 3D GRF database that reflects the influence on gait of moving contact surfaces and fellow pedestrians. If anyone is interested in this area (i.e. from the point of view of human effects on structures and vice versa) please contact me as our research team, being civil engineers, could certainly benefit from a bit of collaboration.
James.brownjohn@sheffield.ac.uk
ORIGINAL POST:
As a structural engineer, I have interests in determining directly or indirectly the 3D contact forces between a pedestrian and a structure (e.g. bridge or floor).
Ultimately it would be great to be able to measure these forces for a structure that moves significantly.
This is (still) an interesting topic in structural engineering and leads into identification of physical explanations for observed phenomena.
Without having something like a 3D tekscan or array of force plates covering the entire walking area it would seem impossible to measure directly and I’m not sure if Vicon can be used well in extended open areas. So for now getting reliable continuous footfall force data probably needs to be constrained to the lab.
Treadmills (e.g. ADAL 3D) appeal for a number of reasons, but naturally there is a question about the validity due to the artificial condition of not actually moving forwards and maintaining a constant speed.
Alternatives could be Vicon system (which I guess requires knowledge of body mass distribution) and insole or other footwear (but I want forces in a constant Cartesian axis system).
Can anyone point me to research that compares force identification methods or can anyone offer their €0.02 worth?
James MW Brownjohn
Professor of Structural Dynamics
Vibration Engineering Section
Department of Civil and Structural Engineering
University of Sheffield
Mappin Street
SHEFFIELD S1 3JD
james.brownjohn@sheffield.ac.uk
RESPONSE 1:
Dear Prof James Brownjohn,
An alterative treadmill to consider would be the 'Woodway' non motorised treadmill in combination with a 'Fitness Technology' system which has this integrated with a 4 load cell force plate - this is an Australian company developed with Prof Robert Newton. The software and system allows for continuous footfall movement contact forces in the X, Y and Z planes. Sorry I don't have any of the company links to assist you with.
Regards
Dale Chapman
PhD candidate
School of Exercise, Biomedical and Health Sciences Edith Cowan University Perth, Australia
INDIRECT RESPONSE 2:
Dear Professor Brownjohn,
There is currently research going on at our biomedical signals and systems group, at the university of Twente, Enschede, The Netherlands. I am not part of this research, and two of the researchers are on holiday, but if you are interested, I have forwarded some conference abstracts that they have written regarding this, also a paper is due to appear in IEEE transactions on neural rehabilitation, leading author Veltink, P.H. I checked and it is not yet on the IEEE website.
However, if the conference abstracts are of any use to, perhaps you can take up contact with Professor Peter Veltink or one of the other researchers on the list.
(Veltink and Liedtke are on holiday, however Droog is still here if you have any inquiries.)
Kind Regards,
Colleen Monaghan
RESPONSE 3:
Professor Brownjohn,
I run the gait analysis laboratory (6 camera Vicon + single Kistler forceplatform + Fscan in-shoe insoles) at Northern General. If you are interested I could give you a tour of the lab and discuss these issues with you. As part of a current grant application we are hoping to buy or develop a treadmill-based force-platform system.
_______________
Ben Heller PhD, SRCS
Research Fellow
Sports Engineering Research Group
Department of Mechanical Engineering
University of Sheffield
Mappin St
Sheffield
S1 3JD
UK
RESPONSE 3:
Forner-Cordero, Koopman, & van der Helm recently used insole pressure measurement as a surrogate for force plate ground reaction forces (see attachment). However, if you're just interested in the effects on a structure of a generalized person, this level of detail would probably be more than you need. Using direct measurements to set up a valid simulation would be much easier and probably more useful. You could just characterize the forces from the steps of a person in a laboratory setting with as little as a single force plate, then apply those forces to foot contact locations in the building of interest. Someone might even be willing to send you this data. It would take some work, but you could even apply a "crowd" of simulated steps to a building at once, scaling the force magnitudes to account for different sizes of people and scaling the foot spacing and speed to account for different gait velocities.
Brian Schulz, Ph.D.
Program Specialist
VISN 8 Patient Safety Research Center (118M) James A. Haley Veterans' Hospital
11605 North Nebraska Ave.
Tampa, FL 33612-5738
Phone: (813) 558-3944
Fax: (813) 558-3990
RESPONSE 4:
Hi James,
I believe a relatively easy and cheap alternative to what you describe would be to use a three-dimensional accelerometer on the distal tibia. These are typically used to measure the 3D forces entering the human body when wearing a variety of footwear. I am aware that in years past people were typically tethered to the device, but they may offer telemetered options. Also, it should be relatively easy to either the power supply (9V battery), amp, and transmitter in a small pouch. On the other hand, you could build a data logger and download it later.
With regards to its location in the Cartesian system, you could either place a marker over the device to know its position or have it a known distance from a marker at the knee (or something).
Just a thought...
Andrew
Andrew Mahar
Director
Orthopaedic Biomechanics Research Center
Children's Hospital - San Diego
MC5054
3020 Children's Way
San Diego, CA 92123
Phone: 858-576-1700 x3181
Lab: 858-966-4975
Fax: 858-966-8187
amahar@chsd.org
RESPONSE 5:
Dear Dr. Brownjohn,
perhaps the best solution is the use of a portable biomechanics platforms:
http://www.amtiweb.com/bio/force_platforms.htm
Best regards,
Wagner de Godoy
Brazil
Many thanks to everyone who responded.
I aim (funding permitting) to try this out via a combination of 3D treadmill and imaging system to assemble a structure-friendly 3D GRF database that reflects the influence on gait of moving contact surfaces and fellow pedestrians. If anyone is interested in this area (i.e. from the point of view of human effects on structures and vice versa) please contact me as our research team, being civil engineers, could certainly benefit from a bit of collaboration.
James.brownjohn@sheffield.ac.uk
ORIGINAL POST:
As a structural engineer, I have interests in determining directly or indirectly the 3D contact forces between a pedestrian and a structure (e.g. bridge or floor).
Ultimately it would be great to be able to measure these forces for a structure that moves significantly.
This is (still) an interesting topic in structural engineering and leads into identification of physical explanations for observed phenomena.
Without having something like a 3D tekscan or array of force plates covering the entire walking area it would seem impossible to measure directly and I’m not sure if Vicon can be used well in extended open areas. So for now getting reliable continuous footfall force data probably needs to be constrained to the lab.
Treadmills (e.g. ADAL 3D) appeal for a number of reasons, but naturally there is a question about the validity due to the artificial condition of not actually moving forwards and maintaining a constant speed.
Alternatives could be Vicon system (which I guess requires knowledge of body mass distribution) and insole or other footwear (but I want forces in a constant Cartesian axis system).
Can anyone point me to research that compares force identification methods or can anyone offer their €0.02 worth?
James MW Brownjohn
Professor of Structural Dynamics
Vibration Engineering Section
Department of Civil and Structural Engineering
University of Sheffield
Mappin Street
SHEFFIELD S1 3JD
james.brownjohn@sheffield.ac.uk
RESPONSE 1:
Dear Prof James Brownjohn,
An alterative treadmill to consider would be the 'Woodway' non motorised treadmill in combination with a 'Fitness Technology' system which has this integrated with a 4 load cell force plate - this is an Australian company developed with Prof Robert Newton. The software and system allows for continuous footfall movement contact forces in the X, Y and Z planes. Sorry I don't have any of the company links to assist you with.
Regards
Dale Chapman
PhD candidate
School of Exercise, Biomedical and Health Sciences Edith Cowan University Perth, Australia
INDIRECT RESPONSE 2:
Dear Professor Brownjohn,
There is currently research going on at our biomedical signals and systems group, at the university of Twente, Enschede, The Netherlands. I am not part of this research, and two of the researchers are on holiday, but if you are interested, I have forwarded some conference abstracts that they have written regarding this, also a paper is due to appear in IEEE transactions on neural rehabilitation, leading author Veltink, P.H. I checked and it is not yet on the IEEE website.
However, if the conference abstracts are of any use to, perhaps you can take up contact with Professor Peter Veltink or one of the other researchers on the list.
(Veltink and Liedtke are on holiday, however Droog is still here if you have any inquiries.)
Kind Regards,
Colleen Monaghan
RESPONSE 3:
Professor Brownjohn,
I run the gait analysis laboratory (6 camera Vicon + single Kistler forceplatform + Fscan in-shoe insoles) at Northern General. If you are interested I could give you a tour of the lab and discuss these issues with you. As part of a current grant application we are hoping to buy or develop a treadmill-based force-platform system.
_______________
Ben Heller PhD, SRCS
Research Fellow
Sports Engineering Research Group
Department of Mechanical Engineering
University of Sheffield
Mappin St
Sheffield
S1 3JD
UK
RESPONSE 3:
Forner-Cordero, Koopman, & van der Helm recently used insole pressure measurement as a surrogate for force plate ground reaction forces (see attachment). However, if you're just interested in the effects on a structure of a generalized person, this level of detail would probably be more than you need. Using direct measurements to set up a valid simulation would be much easier and probably more useful. You could just characterize the forces from the steps of a person in a laboratory setting with as little as a single force plate, then apply those forces to foot contact locations in the building of interest. Someone might even be willing to send you this data. It would take some work, but you could even apply a "crowd" of simulated steps to a building at once, scaling the force magnitudes to account for different sizes of people and scaling the foot spacing and speed to account for different gait velocities.
Brian Schulz, Ph.D.
Program Specialist
VISN 8 Patient Safety Research Center (118M) James A. Haley Veterans' Hospital
11605 North Nebraska Ave.
Tampa, FL 33612-5738
Phone: (813) 558-3944
Fax: (813) 558-3990
RESPONSE 4:
Hi James,
I believe a relatively easy and cheap alternative to what you describe would be to use a three-dimensional accelerometer on the distal tibia. These are typically used to measure the 3D forces entering the human body when wearing a variety of footwear. I am aware that in years past people were typically tethered to the device, but they may offer telemetered options. Also, it should be relatively easy to either the power supply (9V battery), amp, and transmitter in a small pouch. On the other hand, you could build a data logger and download it later.
With regards to its location in the Cartesian system, you could either place a marker over the device to know its position or have it a known distance from a marker at the knee (or something).
Just a thought...
Andrew
Andrew Mahar
Director
Orthopaedic Biomechanics Research Center
Children's Hospital - San Diego
MC5054
3020 Children's Way
San Diego, CA 92123
Phone: 858-576-1700 x3181
Lab: 858-966-4975
Fax: 858-966-8187
amahar@chsd.org
RESPONSE 5:
Dear Dr. Brownjohn,
perhaps the best solution is the use of a portable biomechanics platforms:
http://www.amtiweb.com/bio/force_platforms.htm
Best regards,
Wagner de Godoy
Brazil