Safety Analysis of the Five – Point Harness - Weebly

ENSC 490 - Introduction to Biomechanics

- Project Report -

Safety Analysis of the Five – Point Harness

Student name & number: Miguel Cruz - 301074030

Student name & number: Luke Gall – 301089500

Student name & number: George Ioannou -301092041

Student name &number: Vassili Nossov - 985765099

Report due date: July 31, 2013


Miguel Cruz, George Ioannou, Luke Gall, Vassili Nossov Page 2

Abstract

The following report investigates the effects of a 5-point harness on the cervical spine,

mainly C1 and C2 vertebrae. Using Madymo and a class distributed model of a dummy in a car

seat we create a 5-point harness system and perform frontal collision testing at 30km/h and

50km/h. Using the results we analyze the torque, displacement, acceleration and velocity of the

head and neck to determine if the 5-point harness is more beneficial or detrimental to a typical 3-

point harness. We validate our results with previously conducted research and present future

recommendations for similar testing.



Contents Abstract ....................................................................................................................................... 2

Introduction ................................................................................................................................. 4

Background ................................................................................................................................. 4

Method ........................................................................................................................................ 5

Experimental Results and Comparison ....................................................................................... 7

Result Validation ......................................................................................................................... 9

Conclusion ................................................................................................................................. 11

References ................................................................................................................................. 12



Introduction A 5-point harness is one of the most common seatbelts used in the racing industry

and is preferred for its high safety ratings. It consists of 5 straps, 2 located at the shoulders, 2 at

the hips and one at the crotch all coming together at a buckle release mechanism (see figure 1).

Although this ensures the upper body of the driver is tightly secured at all times, the downfall of

this design is the lack of security of the drivers head. In our

project we will be focusing on analyzing the accelerations

and forces that the human body experiences upon sudden

braking with the 5-point harness as the safety mechanism.

Using Madymo we will create the 5-point harness

over a dummy which is situated inside the default car

scenario. The simulation will consist of frontal collisions at

both 30 km/hr and 50 km/hr. The data will be compared

between the two different speeds as well as the difference

between the 5 – point harness and a regular seat belt at these

speeds.

With data to show the benefits/drawbacks of the 5-

point harness we will make several suggestions on how it is

possible to improve on any drawbacks we find. Emphasis

will be placed on the G-forces that the cervical spine experiences

as it is the only part of the body that is not held securely by the harness. Our aim is to ensure that

the sudden stopping motion will not cause permanent damage to the cervical spine.

Background In 2001, the death of the iconic NASCAR racer Dale Earnhardt proved to be the catalyst that will

push the motorsport industry to make major overhauls in the safety of its drivers, especially in

harnesses. Dale Earnhardt suffered from Basilar Skull fracture due to having his neck exposed to

fatally high loads during the crash. Earnhardt suffered the full whiplash motion of the crash due

to stock racing cars having a lack of head restraints as well as having a less than optimal harness

restraint. The motion was such that Earnhardt’s head was oscillating back and forth without

hitting the steering wheel which would have absorbed the impact and undoubtedly saved his life.

The aftermath of Earnhardt’s death called for more transparency within the motorsport industry

with special considerations to safety. Several actions have since been taken to protect drivers,

such as improvements on the five-point harnesses and the design of the six-point harness.

Furthermore, the use of the HANS device was deemed to be mandatory in order to reduce the

whiplash motion of the head.

The MADYMO simulation makes several assumptions on the experiment parameters. The first

assumption is that the person has a height of two metres. The second assumption is that the

Figure 1: 5-point Harness



person has a weight of 100 kilograms. The third assumption is that the forces in the neck are

simply the joint forces. Furthermore, the time period of interest is between 110 milliseconds and

145 milliseconds. The calculations will refer to the 130 millisecond time frame when the peak

torque and forces in the neck occur. Therefore the acceleration used for the calculations is 120

m/s2 which occurs at 130 milliseconds as presented in Figure 7. The purpose of the calculations

is to verify the accuracy of the MADYMO simulation.

Method The approach to this project was to minimize the setup time and maximize the time spent on

running simulations and acquiring test results. With this in mind we concluded that the simplest

approach was to modify the 3-point seatbelt model that was used in lab 4 and optimize the

parameters for our project. Our first step was to relocate and reshape the buckle to mimic a real

5-point harness. The buckle was relocated from the right side of the dummy to just above its

pelvis which is where the 5 straps of the belt meet. Reshaping of the buckle was also required as

the lab 4 model was a rectangle and the 5-point harness utilizes a circular buckle with roughly

½” thickness. Following this we recreated the 2 belt straps that already existed using new bodies,

points and joints and placed them on the right side of the dummy (looking from behind the

dummy). Additionally we moved the 2 shoulder straps more proximally to the centre of the

dummy. Shoulder straps on the 5-point harness are intended to pass over the clavicle and rib

cage and converge at the buckle located slightly above the pelvis. The final modification came

with the creation of the 5th

belt strap that passes over the pelvis. A similar procedure was used

where a new body, point and joint was created and the belt was fitted optimally around the

surfaces of the dummy.

Our final step was to create all the necessary groups and contacts between the dummy and the

new belt straps to ensure that the belt was limiting the motion of the dummy and not passing

through it. Upon completion a final belt fitting was performed to optimize the surfaces that the

belt interacted with and to ensure they all met at the centre of

the buckle. As mentioned in the introduction tests were

performed at 30km/h and 50km/h with our main focus centered

on the forces on the head and neck while also looking at the

displacement of the head and neck and comparing this with the

results we attained in lab 4 using the 3-point harness. In Figure

3 you can see the final Madymo representation of our 5-point

harness. The belts are located optimally for our tests and the

retractor has been removed mimicking a true harness that keeps

the driver constrained to the seat at all times, not only when a

collision is detected.

In Figure 2 you can see a 5-point harness installed in a race

car. Notice that it is relatively similar to the model in Madymo. Figure 2: 5-point harness in a race car



Figure 3: Snapshot of 5-point harness



Experimental Results and Comparison Shown below in Figure 4 is a snapshot comparison of a 3-point harness to a 5-point harness.

This snapshot was taken at the same time for both simulations for an impact at 30 km/h. It is

clear that the 5-point harness does its job at restraining the body of the driver. With a 3-point

harness, the head of the driver impacts on the steering wheel even at this low speed. The 5-point

harness protects the driver from cranial injury, but this is done at the cost of increased stress on

the neck which could potentially cause more harm.

Figure 4: Comparison of 3-point and 5-point impact

Looking at the position of the driver’s head for the two tests in Figure 4 we confirm that the

motion is more restricted when using a 5-point harness, reducing the risk of collision with the

steering wheel or the cab of the vehicle. This can be seen in Figure 5 where the position of the

head is compared for the two scenarios.



Figure 5: Head position comparison

The damage to the driver becomes more apparent when the moment applied to the base of the

skull is considered. The graph in Figure 6 shows a comparison of the moments applied on the

C1 vertebrae when using the two restraint systems (3-point in blue and 5-point in green). Due to

the restraint of the body by the 5-point harness, the neck experiences a smoother load with only

one peak unlike the 3-point harness, but this peak is greater in magnitude as expected.

Figure 6: Neck moment comparison



The second criteria checked was the force applied to the head. One of the main benefits of the 5-

point harness is that it prevents the driver from hitting objects in the cab. To compare the net

force exerted on the skull of the driver, the acceleration was measured. The results in Figure 7

(3-point in orange, 5-point in blue), show that the acceleration of the skull is actually greater

when using the 5-point harness. This does not contradict the design purpose of the restraint, but

points out that its presence causes other sources to exert greater stress than the impacts that it

prevents.

Figure 7: Head acceleration comparison

Result Validation

To validate our model and the results from it, the 5-point harness results were compared with

that of literature. In ‘An investigation into neck injuries in simulated frontal impacts’ by Naif Al-

Shammari and Clive Neal-Sturgess it can be seen that the acceleration of the head in Figure 8

matches our results very closely. Both values can be seen to peak at ~300m/s2 for the 30km/h

case at C1. The difference in magnitude of the acceleration reported is due to their test being a

15g impact compared to our 7g impact. If scaled, the magnitude of our results closely matches

theirs.



Figure 8: Head acceleration from Al-Shammari

Al-Shammari also reported on the moment that the vertebrae of the cervical spine experience for

a series of impacts shown in Figure 9. Our reported moments for C1 are ~40Nm where their

tabulated value can be seen at roughly 100Nm. Our results are similar but not identical which is

expected due to our different impact force and simulation parameters.

Figure 9 Cervical bending moment from Al-Shammari



Conclusion Firstly it must be noted that the analysis conducted was not optimal for a 5-point harness. In a

real life scenario the driver is placed in a race seat that eliminates and movement of the body

laterally and the 5-point harness limits movement of the body anteriorly. With our results we can

conclude that the belt was not optimized to limit the motion of the dummy. Although the motion

was greatly reduced in comparison to the 3-point harness it still allowed the dummy to displace

to a point where the head made contact with the steering wheel at 50km/h. Secondly, in a race

car the steering wheel is placed in a location where the head of the driver cannot impact it at any

point during a collision.

In regards to our results we find that the 5-point harness aids in restraining the body and

preventing the head with making impact with the steering wheel but because of this it sharply

increases the forces experienced by the cervical spine. The current solution to this issue is a neck

brace that is worn by professional race car drivers. This neck brace limits the movement of the

neck and in a collision the neck will not displace more than several millimeters in any direction.

In future testing it would be ideal to implement a similar neck brake and also add the helmet as

an additional protective measure. The helmet will add weight to the system but the brace should

counteract this by limiting the displacement as mentioned earlier.



References

I. Al-Shammari, Naif & Neal-Strugess, Clive (April 27th

, 2012): “An investigation into neck

injuries in simulated frontal impacts”

II. Ed Hinton, ESPN.com (February 7th

, 2001): “Earnhardt’s death a watershed moment”

III. T.J Gibson, K. Thai, Australian Transport Safety Bureau (June, 2007): “Helmet

protection against Basilar Skull Fracture”





Description of tasks

Miguel Cruz: Madymo simulations, hand calculations, background research, report writing

George Ioannou: Madymo simulations, methodology development, report writing

Vassili Nossov: Madymo simulations, validation research, report writing

Luke Gall: Madymo simulations, theory development, report writing

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