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DEVELOPMENT AND VALIDATION OF A COMPUTER
PROGRAM TO DESIGN AND CALCULATE ROPS. J. Mangado, I. Arana*, C. Jarén, P. Arnal, S. Arazuri, J.L. Ponce de León
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The information contained in this article was presented in part at the OECD Annual Tractor Meeting. París 22-25 February 2005. The authors are: Jesús. Mangado, Graduate Student, Ignacio. Arana, Carmen Jarén, Pedro Arnal and Silvia Arazuri University Teachers of Mechanical Engineering at the Public University of Navarre (Spain) and José L. Ponce de León, Director of the Mechanisation Agricultural Station (Madrid). Corresponding author: Ignacio Arana Dpt. of Rural Engineering and Projects. Public University of Navarre. Campus Arrosadía. 31006 Navarra.
[email protected].
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mandatory for all new tractors to be equipped with a roll over protective structure (ROPS). A similar
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situation is found in the European Union, but the situation is worse in the USA and in developing countries.
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Directive 2003/37/EEC establishes that tractors over 800 kg weight can be homologated by using the OECD
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standard code for the official testing of protective structures on agricultural and forestry tractors (Static
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test), called CODE 4. A ROPS attachable to the rear axle of different tractor models has been designed and
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a computer program for the calculation of the ROPS has been developed. The program, named
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“ESTREMA”, is available at the website: www.cfnavarra.es/insl. Using this program it has been possible to
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design a ROPS for the Massey Ferguson model 178 tractor, one of the most frequent tractor models without
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a ROPS. Once the tractor was equipped with the designed ROPS, it was tested at the Spanish Authorized
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Station for testing ROPS, and passed homologation test (OECD Code 4), being the main results a maximum
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distortion of 21.3cm when the absorbed energy was 5437 N and a maximum force applied of 34 kN, during
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loading from the side test. Then, the ROPS was improved, redesigned and mounted again on the tractor, and
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the tractor was tested in a real overturn and no part of the structure infringed upon the clearance zone
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during the test. In conclusion, the “ESTREMA” program worked correctly and the designed structures were
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able to overcome the authorized test and to provide adequate protection to the operator during a real
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overturn.
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ABSTRACT. In Spain there are more than 250,000 tractors built before 1980, when it became
Keywords: ROPS, safety, frame, clearance zone, static test, real overturn, protective structure, cab.
INTRODUCTION In Spain, more than ten accidents involving agricultural machines occur daily, and at least,
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five of them result in grave consequences (Barco, 1999). Accidents that lead to a roll over are
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often fatal for the worker driving the tractor. Accidents caused by roll over represents one third of
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all deadly accidents in the agricultural sector, 90% of them refer to lateral roll over, and only 10%
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of them to roll longitudinally. A study carried out by the National Institute for Safety and Hygiene
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at Work reviewed 175 cases of tractor roll overs and provided the following statistics: 60% resulted
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in minor injuries, 19% of resulted in severe injuries and 21% resulted in fatalities. In Italy, during
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1995-1996, there were more than 6000 accidents related to the use of self- propelled machines of
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which about 1% of these were fatal (INAIL, 2000) of which tractor roll-overs were the principal
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cause (Casini-Ropa, 1980). In the USA, agriculture has the highest rate of occupational fatalities of
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any industry at 24.11 deaths per 100,000 workers per year and in the state of Kentucky, where
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fewer than 30% of working farm tractors are equipped with roll-over protective structures (ROPS)
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(Browning et al., 1998; Cole et al., 1998), this rate is even higher (Cole et al., 2000). The majority
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of the deadly accidents referred to tractors without a protective structure and not to tractors with
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protective structures (Arana et al., 2002). A ROPS in combination with a seatbelt can prevent
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nearly all tractor overturn related fatalities and serious injures (MMWR, 1993).
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Pana-Cryan and Myers (2000) compared three strategies to prevent injuries incurred as a
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result of tractor overturns. These strategies were “do nothing”, “install ROPS on tractor that lack a
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ROPS”, and “replace tractor”. They cobcluded that the preferred strategy in terms of cost-
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effectiveness is to “install ROPS” on tractors lacking them for which ROPS are available.
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The loss of stability is not only due to the slope of the ground, but to a multiplicity of causes.
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More than half of the lateral turnovers are caused by tractors slipping into ditches or bumping
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against obstacles (Chisholm, 1972). To limit the risk of overturn, active devices such as mobile
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ballast or inclinometer devices never left the experimentation circle (Fabri and Ward, 2002).
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ROPS, acronym of roll-over protective structure, are sturdy frames attached to tractors or
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built into tractor cabs, to limit the risk for the driver in case of overturn. They consist of fixed or
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partially tiltable structures, with defined clearance zones around the driver’s seat, thereby offering
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the driver protection in the event of an overturn (both lateral and longitudinal) (Febo and Pessina,
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1989; Ayers et al., 1994). These protective structures are usually built with tubular elements, with a
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square or circular cross section, and attached to the tractor by means of threaded fasteners.
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In June 1979 the Directive 79/622/EEC established the static tests for the homologation of
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tractors with protective structures. In 1979, it became mandatory in Spain for all tractors to
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have a safety cab or frame (BOE 11-8-1979). However, both in Spain and other countries
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there is still a large number of tractors without an adequate structure to protect the driver in
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case of overturn or roll over (Arana et al., 2002). After the publication of the 95/63/EEC it
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is obligatory for all tractors to have a device for driver’s protection. On July 18th 1997 a
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royal Spanish decree was signed to require all tractors to have a safety cab installed and it
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was officially approved on December 5th 2002.
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Given the age of these non-ROPS equipped tractors, they are more prone to have accidents
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due to general wear and tear, they are lighter and less stable, and oftentimes they are used with
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newer implements that are too big for the tractor. Some of these tractors have conventional cabs
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which, in spite of protecting the driver from inclement weather, and improving the comfort level,
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cannot be considered as protection against roll over. Sometimes it they can even trap the operator
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in a manner that could worsen the consequences of an accident when it happens. This situation
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forces one to design a protective structure compatible, economical and easy to build. This structure
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should be adaptable in any tractor model built without a commercial roll over protective structure.
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Tractors with at least two axles for pneumatic tired wheels or having tracks instead of wheels
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and with an unballasted tractor mass not less than 800 kg may be homologated by CODE 4. This
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test code is the Organisation for Economical Co-operation and Development (OECD) standard
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code for the official static test of protective structures on agricultural and forestry tractors. The
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minimum track width of the rear-wheels should generally be greater than 1150 mm. CODE 4,
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modified on March 2005, determines the energy and forces that a ROPS must withstand in order to
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be approved. The ROPS must be tested by a sequence of four static tests and must reach a
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predefined level of absorbed energy. The sequence consists on a longitudinal loading test, a first
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crushing test, a loading from the side test and a second crushing test and, during the loading, no
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parts may intrude into the driver’s clearance zone (fig. 1), which is the area occupied by the
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driver during the roll-over, when he stays in his seat holding on the steering wheel.
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Figure 1. Clearance zone.
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In Spain ten tractors per year were tested at the Mechanization Agricultural Station (M.A.S.)
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during the last years and 10% of the tests resulted in failure and at the Testing Station of Bologna
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University (Italy) 100 new structures were tested from 1994 to 1998 resulting a third of the test in
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failure (Fabri, 1999).
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The objectives of our research were:
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To identify the most frequent tractor trademarks and models without ROPS in Navarre (Spain).
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To design a ROPS in order to absorb the calculated energy required in CODE-4 tests and to
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achieve the zone of clearance not impinging upon during the test. •
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To develop a calculation program for the design of ROPS that meets the performance requirements of OECD CODE 4.
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To validate the calculation program for ROPS.
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To test the built ROPS in Authorised Testing Stations according to OECD CODE 4.
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To improve ROPS after the results of the previous homologation tests.
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DESIGNING THE ROPS FOR TRACTORS
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To test the improved ROPS in real tractor overturns.
Tractors designed before 1980 were studied using the database of the Government of Navarre.
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The following information was collected: trade mark, model, age, power, dimensions, weight and
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zones in which are registered. This information belongs to the Registry of the Livestock Food and
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Agricultural Department.
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To design the protective structure the following criteria were considered:
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The only resistant point common to most of tractors, the rear axle housing, determined the
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structure design for the ROPS. In the initial structure design, the structure was attached to the rear
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axle housing, open in a “V” shape, and made a parallelogram that wrapped around the driver’s
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safety zone (fig. 2).
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Figure 2. Tractor having roll-over protective structure attached to the rear axle housing.
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The protective structure has to absorb the energy, as specified by CODE 4 without infringing
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upon the driver’s clearance zone during any part of the longitudinal loading test and the loading
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from the side test.
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Oversize is as detrimental as undersize, because it can increase the forces and stress in the element connections (Arana et al., 2004).
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Protective structure 3D design, constructive planes and finite elements simulation of strains and deformations were obtained using the CADAM Catia V.5R7 program.
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A protective tubular structure attachable to the rear axle of any tractor was designed and built
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in steel with a strength of 420 MPa (A-42b). The hollow steel section can be square or circular.
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This structure was attached to the rear axle and to the fenders if they are well-preserved.
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In order to make the protective structure more rigid and to reduce the value of the maximum
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moments, it was possible to include in the structure a horizontal beam to join the two beams in “V”
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at a chosen height.
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The program calculated the minimum steel section of the structure tube to absorb the roll-over
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energy, determined by CODE 4, which is a function of the tractor mass, without infringing upon
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the clearance zone, as defined also by CODE 4. A permitted maximum deformation for each static
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test was determined to avoid the structure to infringing on the clearance zone. From the value of the
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permitted maximum deformation and from the experimental force-deformation curve, the
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maximum force and development of the moments on the respected frame were calculated as
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statically indeterminate systems. A totally plastic deformation of a flexor section of ideal plasticity
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was considered. A small reinforcement of the structure on the lower part was also allowed in the
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calculation due to the fender. In the screws and flanges calculation an admissible resistance from
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the 60% of the fluency limit was employed to increase the safety factor.
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The designed ROPS was calculated to be mounted on a Massey Ferguson 178 model tractor,
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one of the most frequently used in Navarre (Spain), without a protective structure. The tractor
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weight is 3000 kg, including cab and driver, has an unballasted mass of 2700 kg and a track of 2.23
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m.
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TESTING THE DESIGNED ROPS MOUNTED ON A MASSEY FERGUSON 178
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Following the design, manufacture and mounting of the ROPS on a Massey Ferguson 178, the
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tractor was moved to the Mechanization Agricultural Station (M.A.S., Madrid) in order to perform
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the tests needed to homologate ROPS for tractors. The tractor were prepared and tested according
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to OECD code.
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LONGITUDINAL LOADING TEST The tractor structure was pushed by a hydraulic cylinder in its rear part and in one of its sides, as shown in figure 3.
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Figure 3. Longitudinal Loading test carried out in EMA on Massey Ferguson 178 tractor, equipped with the
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The longitudinal loading was stopped when the energy absorbed by the protective structure
designed ROPS.
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was equal to or greater than the required energy input established by CODE 4, as given by the
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equation 1:
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EIL1 = 1.4 M = 4200 J
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where
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EILI = required absorbed energy (J)
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M = tractor mass (kg)
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(1)
FIRST CRUSHING TEST The first crushing test was performed on the rear of the ROPS , as was the longitudinal loading test (fig. 4).
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Figure 4. First crushing test carried out in EMA on Massey Ferguson 178 tractor, equipped with the designed ROPS.
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The crushing force established by CODE 4 is given by equation 2:
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F = 20 M = 60,000 N
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where
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F = applied force (N)
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M = tractor mass (kg)
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This force was maintained for five seconds after cessation of any visually detectable
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movement of the protective structure.
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LOADING FROM THE SIDE TEST
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(2)
For the side test, the hydraulic piston pushed the structure from its lateral part in the structure’s highest front part, as shown in figure 5.
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Figure 5. Loading from the side test carried out in EMA on Massey Ferguson 178 tractor, equipped with the
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The side loading was stopped when the energy absorbed by the protective structure was equal
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designed ROPS.
to or greater than the required energy established by CODE 4, as given by equation 3:
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EIS (Joules) = 1.75 M (kg) = 5250 J
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where
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EIS = required absorbed energy (J)
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M = tractor mass (kg)
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The energy was superior to the one applied in the first test.
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(3)
SECOND CRUSHING TEST The final test consists of a crush test equivalent to the first crush test, but over the front part of
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the protective structure. It also rose above 60 kN. In the visual inspection there was no reportable
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distortion.
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ACCEPTANCE CONDITIONS
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To be accepted, the ROPS must fulfill the following conditions during and after completion of
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the tests: no part will either enter the clearance zone or strike the seat during the tests. Furthermore,
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the clearance zone, defined and located by CODE 4, will not be outside the protection of the ROPS.
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For this purpose, it will be considered “outside the protection of the structure” if any part comes in
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contact with flat ground when the tractor overturns towards the direction from which the test load is
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applied. To estimate this, the tires and track width settings must be the smallest standard fitting
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specified by the manufacturer. At the point where the required energy absorption is met in the
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horizontal loading tests, the force shall exceed 0.8 Fmax.
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RESULTS AND DISCUSSION
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THE TRACTOR FOR INSTALLING A ROPS
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Data from the Government of Navarre’s database allowed us to know that there were 3576
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tractors, built before 1980, working in Navarre. There were 61 different trademarks and the Ebro
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Super 55 was the tractor model, without a protective structure, most used in Navarre (Spain).
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Massey Ferguson model 178 was another of the most frequent tractors without a ROPS.
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THE ROLL-OVER PROTECTIVE STRUCTURE
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A protective structure, as shown in figure 2, was designed and built according to the
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objectives of this research. It is a tubular structure attachable to rear axle of any tractor, built in
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steel of 4200 kg/cm2 of yield stress (A-42b). The hollow steel section is square and the structure is
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set to the rear axle and to fender.
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The protective structure was formed by the following elements:
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Two upright beams attached to the rear axle (trumpet) by means of two steel plates joined by
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anchorage bolts.
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Two transversal beams (front and rear).
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Two upright beams in the upper part of the structure, joining the transversal beams.
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Two horizontal beams in the lower part of the structure, at a chosen height, joining the parts of
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the arches in “V”, that reach the attachment point on the rear axle, in order to make the
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protective structure more rigid and to reduce the value of the maximum moments.
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Steel angled braces used for attaching parts of the structure to the fender. The ROPS attachment to the rear axle was made in the following way: the ROPS was welded
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to a steel plate, which was attached by screws to another similar plate below the rear axle (fig 1).
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The attachment screws were placed along the vertical grooves of the rear axle, except where the
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rear axle lacked grooves. The relative position between the screws and the attaching point of the
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ROPS to rear axle and the distance between the screws and this point determine the calculation of
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the necessary section in the screws.
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CALCULATION PROGRAM “ ESTREMA”.
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Once the basic design was established, a method to calculate the roll over protection structure
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was developed for general wheeled tractors over 800 kg. These tractors are required to meet the
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requirements of the European Directive 79/622/EEC.
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The structure calculation method was based on:
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The OECD standard code of static test (CODE 4).
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The structure design.
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The tractor measurements and mass.
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The method calculates the structure to theoretically endure the homologation tests to get the
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approval of the new roll over protective structures. Those tests have to follow the OECD test code (CODE 4) which determines the forces and
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energies that a ROPS has to withstand in order to be approved. To develop the calculation method
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already described, an Excel program was made and named “ESTREMA”, the Spanish acronym of
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safety structure for mechanical agricultural tractor equipment.
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The program needs certain data to calculate the structure requirements, mainly: tractor mass,
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vertical and horizontal distance from seat reference point to rear axle, rear axle section, horizontal
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distance between the interior points of the ROPS to screws attaching to the rear axle, fender height,
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distance between fenders and number and quality of the screws. It requests data through different
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simple forms illustrated and wholly explained, including explanatory drawings. Moreover, it
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specifies the units that should be employed and limits the data entry to a range of logical values.
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Error messages are shown if inadmissible data are introduced, resulting in easy management and
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avoiding the execution of the calculation in case of illogical data or gaps in the forms.
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As the relative position between screws and ROPS attached to the rear axle and the distance
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between screws and this point determine the calculation of the needed section in the screws, it is
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necessary to select one of the following options: “screws at both sides of the ROPS union to the
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rear axle”, or “screws at the outer side of the ROPS”.
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Using this data, the program calculates the energy absorbed in the test, the lengths of the
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beams of the structure and the moments produced in the test. In addition, it searches in the
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normalized steel section tables, the minimum steel section of a hollow square that, theoretically,
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will resist the test. The program also calculates the measurements – section – of the anchorage
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screws attaching the structure to the rear axle, the construction details, and checks if the resulting
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section will resist the CODE 4 crushing tests. This program is available for free at the following
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website: www.cfnavarra.es/insl.
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The calculation of the structure anchorage on the tractor rear axle is as important as the
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structure calculation, because if the anchorage collapses the structure will infringe upon the
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clearance zone. In the crushing test, the theoretical moment in the attaching point of the rear axle
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and the structure is usually high. That is why a horizontal beam was included in the protective
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structure to make rigid the lower part. The program calculates the minimum height of this rigid
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steel beam.
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The ESTREMA program is applicable to agricultural tractors with, at least, two axles for
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pneumatic tire wheels or with tracks instead of wheels, having an unballasted mass not less than
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800 kg and a minimum track width of the rear-wheels generally greater than 1150 m.
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The program shows the calculated structure in a form displaying the section (square or
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circular) of the steel profile needed, the measurements of the structure and the anchorage (steel
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plates and screws), different views of the structure, braces and joining points and several
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specifications to build it.
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This program requires relatively little operator training.
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The software calculates the necessary sections of the ROPS′ beams. In a first step, it
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calculates the maximum admissible deflections of the ROPS during each test that ensures that the
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deformation produced will not be so high that the structure imfringes upon the clearance
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zone.These deflections depend on the location of the SRP and the shape and meassurements of
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the ROPS. In a second step, it calculates the maximun strenghts produced during the tests that
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depend on the maximun admissible deflections, the absorbed energy required by Code 4, and
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fluency. In a third step, it calculates the maximum moments in the critic sections of the ROPS,
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during each test, and the necessary section modulus of the steel section of the ROPS′ beams
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Then, the software chooses the steel section with a section modulus inmediately higher
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than the calculated. Finally, it calculates the attachment moments during each test and
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chooses the necessary quality and section of the screws that attach the ROPS to the tractor
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CALCULATING ROPS FOR A MASSEY FERGUSON 178 TRACTOR USING “ESTREMA”
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PROGRAM
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To calculate the protective structure for a Massey Ferguson model 178 tractor, one of the
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most used tractors without a protective structure in Navarre, the “ESTREMA” program requested
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the characteristics of this tractor model as listed in table 1. After introducing those data on the
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corresponding forms, the program calculated the structure and the results showed that the needed
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hollow steel profile was 0.050 m width and 0.004 m thick and the appropriate screws were M-14.
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Table 1. Massey Fergusson 178 characteristics requested by “ESTREMA” program Characteristic Mass, including cab and driver Distance from seat rear plane to rear axle vertical plane Seat reference point height Distance between fenders Fender height Rear axle section Distance from structure axle to screws Transversal distance between screw axles Longitudinal distance between screw axles Screw quality Number of screws at any side of the steel plate
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Measurement 3,000 kg 0.130 m 0.570 m 0.900 m 0.900 m 0.170 m 0.070 m 0.180 m 0.175 m 10 K (10.9) 2
The program displayed a final report, listed in table 2 referred to figure 6. Table 2. ROPS calculation report Characteristic
Data
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Operator’s name Tractor model Minimum hollow square section needed Other possible option that do not oversize too much Mass (kg) SRP height (m) Rear axle section (diameter m) Horizontal distance between rear axle and SRP (m) SRP in front of rear axle SRP behind rear axle Fender height (m) Distance between fender (m) Distances in the attachment zone (m) Between screws in the rear axle direction Between structure and near screw in the rear axle direction Between screws in the advance direction Screw couple number per attachment Screw quality Screw section (diameter m) STRUCTURE MEASUREMENTS (fig.6) The ROPS is attached to the fender by braces Total frame height (m) Bottom frame width (m) Top frame width (m) Minimum reinforced distance in the top of the ROPS (m) Minimum reinforced distance in the bottom of the ROPS (m) ROPS upper part height (m) ROPS lower part height (m) Frame length in the top (m) Minimum horizontal distance between lower point of the seat back and the back plane of the ROPS (m) Minimum vertical distance between horizontal beam that makes rigid the lower part of the ROPS and the rear axle top (m)
Mangado J 178 50 mm long 4 mm thick 55 mm long 4 mm thick 3,000 0.57 0.17 0.13 True False 0.87 0.87 0.06 0.012 0.017 2 10K (10.9) 0.014 True 1.69 0.87 1.12 0.15 0.15 0.90 0.79 1.10 0.50 0.60
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Figure 6. ROPS measurements calculated by program “ESTREMA”.
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The report included front, side and top views of the structure, structure measurements, details
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of the braces, the structure attachment to the tractor rear axle, the situation of the seat reference
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point with regard to the protective structure and the rear tractor axle. In addition, the program gave
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several indications as it follows:
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The ROPS has to be built with A-42 steel
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The ROPS has to be attached as such as the distance between back vertical plane of the ROPS
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and the lower point of the back seat was over 40 cm
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The ROPS has to comply with all specified distances
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The lower part of the ROPS has to be located beside fenders and as possible, between fender
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and wheel, looking for the maximum room between the ROPS and the driver’s seat.
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ESTREMA program showed the following specifications related to the program application
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field and to the laws that apply to these tractors:
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The program calculates ROPS for tractors over 800 kg.
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The calculation does not apply to narrow tractors with a track width less than 1150 mm
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This program has been developed for tractors abiding by the 2003/37/EEC European directive,
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published on 26 May 2003 that obliges all tractors to bear a ROPS to protect tractor’s driver in
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case of overturn.
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Calculated ROPS has not been proved in real tests and they are not homologated.
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Because of the great variability of ancient tractor models, the calculated ROPS is attached to
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the only common resistant point, the rear axle housing. That is why the tractor rear axle has to
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be strong enough and in good condition.
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Drawings and schemes are only for explanation and are not drawn to scale.
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The calculations have been carried out using the real tractor data, measured as exactly as
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possible. The ROPS and the necessary attachments are a function of the tractor characteristics
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and of the ROPS design.
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TESTING THE DESIGNED ROPS MOUNTED ON MASSEY FERGUSON 178 TRACTOR A protective structure was built according to the indications of “ESTREMA” program and
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was mounted on a Massey Ferguson 178 and tested at the M.A.S. according to the static sequence
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test established by CODE 4. The results were the following:
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LONGITUDINAL LOADING TEST
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The structure distortion was 18.5 cm and the safety zone located at more than 50 cm was not
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reached. Once the energy limit was exceeded the pushing stopped and the elastic component of
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distortion, which corresponded to the hydraulic cylinder, appeared in parts of the structure that
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tended to move to its original position. The applied energy was 4200 J at a maximum velocity of 5
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mm/s.
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FIRST CRUSHING TEST
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The total and applied strengths for the cylinders in terms of the total time are recorded by the
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computer of the EMA and represented in figure 7. The mass time limit set by the code is reached
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when arriving at 61,000 N. In the crushing tests the structure is set up just by correcting a bit the
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movement from the previous test. The clearance zone was not infringed upon by the structure. First mash
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Force (kN)
60 50 40 30 20 10 0 4,3
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9,8 15,2 20,6 26 31,4 36,8 42,2 47,7 53,1 58,5 63,9 69,3 74,7 80,1 Time (s)
Figure 7. Strengths in the first crushing test.
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LOADING FROM THE SIDE TEST
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The distortion reached 21.3 cm with an applied energy of 5437 Joules at a maximum velocity
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of 5 mm/s. Although the distortion is greater, it still does not infringe upon the clearance area. The
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maximum force applied during the test (Fmax) was 34 kN, as shown in figure 8, and at the moment
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of stopping the test, when the required energy absorption was met, the applied force was 32 kN,
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that is higher than 0.8 Fmax. Therefore, the ROPS complied this acceptance condition recorded on
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CODE 4. 40 35
Force (kN)
30 25 20 15 10 5 0 0
20
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60
80
100
120
140
160
180
Deformation (mm)
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40
Figure 8. Curve (Force-Deformation) in the loading from the side test of CODE 4.
SECOND CRUSH The total and applied strengths for the cylinders in terms of total time are represented in figure 9. The mass time limit set by the code was reached and went up to 63 kN.
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Second Crush 70
Force (kN)
60 50 40 30 20 10 0 1
11
21
31
41
51
61
71
81
91
101
111
121
Time (s)
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Figure 9. . Strengths in the second crush.
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From the tests performed at the M.A.S. and following the testing of the designed protective
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structure it was possible to conclude that:
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The ROPS supported the authorized tests without ever compromising the clearance zone.
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•
Theoretically, in case of tractor rolling over, the structure should provide adequate safety for
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the driver. •
The “ESTREMA” program was able to calculate the minimum section of the ROPS beams and
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their measurements to ensure that the ROPS will support the homologation tests without failure
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on any of the acceptance conditions.
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•
360
361
It is possible to use “ESTREMA” program to design ROPS for new tractor models, which will not result in failure in the homologation tests.
IMPROVING THE STRUCTURE
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Although the designed and calculated structure was built and successfully tested, the results
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revealed the following aspects to improve:
364
•
The structure was too big, too tall.
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•
The curved parts on top of the structure increased construction costs and made it more difficult
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to build. •
The structure was old fashion.
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Considering those aspects the ROPS was redesigned, better adapting height to the security
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zone, as shown in figure 10. In addition, the moments generated to apply the energy of the test
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were reduced and, as a consequence, it was possible to build the new ROPS using smaller beam
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sections.
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Figure 10. Redesigned ROPS and clearance zone.
This first adjustment made the structure less expensive because of the reduction of metal profile and the smaller cross section required. A second adjustment eliminated the curves in the back part making the structure easy to build in any workshop. For the same reason, the calculation program was improved by including the option to
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calculate the lower part of the structure with a solid mass profile, since the ROPS was curved at the
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bottom following the curve of the fender. The option of placing a solid mass structure in the bottom
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had an added advantage: it required less space between the wheel attachment and the fender.
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Finally, the test done at the M.A.S revealed an excessive distance between the seat and the
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rear part of the structure. In this way, the structure wrapped better the security zone and improved
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the aesthetic appearance.
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Once the above mentioned aspects were corrected, a new ROPS for the same tractor was
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calculated by the “ESTREMA” program. This structure was manufactured at the “Verges”
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workshop (Lleida), and was mounted on a Massey Ferguson 178 tractor, between the wheel and the
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fender, just as indicated by the program, as shown in figure 11.
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Figure 11. Redesigned ROPS (calculated by program “ESTREMA” and built by Verges workshop) mounted on Massey Ferguson 178.
TESTING THE IMPROVED STRUCTURE The Massey Ferguson 178 with the new structure was exhibited in Lleida (Spain) during the Second National Congress on Prevention of Workplace Risks in the Agricultural sector. Moreover, a demonstration of a real turnover was performed with the tractor carrying the new
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ROPS. To induce a roll over, the tractor was placed on a platform that was turned over laterally
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from a height of 1.2 m and over a highly compacted floor, as shown in figure 12. This roll over was
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extremely hard and violent. However the security zone was not infringed upon, due to the security
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structure (see figure 13).
20
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Figure 12. Tractor Massey Ferguson 178 equipped with ROPS just before the overturn.
401 402
Figure 13. Tractor Massey Ferguson 178 equipped with ROPS just after the overturn.
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The absorbed energy was the difference between the potential energy before and after the roll
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over. The center of gravity height was measured just before and after the rollover, and the height
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difference was 1.65 m. The absorbed energy is given by equation 4:
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E = M g (∆h) = 45,322 J
(4)
21
407
where
408
E = absorbed energy (J)
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M = tractor mass without driver and with the new ROPS (2800 kg)
410
g = gravity acceleration (9.81 m s-2)
411
∆h = height difference of the center of gravity just before and after the roll over (m).
412
The energy was greater than that required by the homologation test although, in this case, the
413
energy was not only absorbed by the ROPS, but also by the tractor and floor.
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This test, different from the one performed at the M.A.S., did not allow us to make energy or
415
distortion graphs. However, it is a real test, and it is possible to affirm, with no doubt, that the
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structure resisted a real turnover without compromising the clearance zone reserved for the driver,
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as shown in figure 14.
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Figure 14. Tractor Massey Ferguson 178 equipped with ROPS after the overturn.
420
CONCLUSIONS
421
•
422
It is necessary and possible to design a protective structure attachable to different trademarks and models of older tractors.
22
423
•
A computer program (ESTREMA) has been developed to calculate the necessary steel section
424
of the protective structure and the necessary attachment screws for each tractor to overcome the
425
homologation tests defined by CODE 4.
426
•
The “ESTREMA” program is able to calculate the minimum section of the ROPS beams and
427
its measurements to ensure the ROPS success in the homologation tests without any failure on
428
the acceptance conditions.
429
•
The necessary hollow square section of the ROPS for the most frequent tractor model without a
430
protective structure in Navarre (Massey Ferguson 178) is 0.05 m width and 0.004 m thick, and
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the required screws are M-14.
432
•
433 434
any failure. •
435 436 437
The designed ROPS for Massey Ferguson 178 model overcame the homologation tests without
It is possible to improve the calculation program and the ROPS after the results of the homologation test.
•
The improved ROPS should guarantee the security of the driver, both in theory and in practice, in case of tractor overturn.
438
REFERENCES
439
Journal Article
440
Ayers, P., M. Dickson, and S. Warner. 1994. Model to evaluate exposure criteria during roll-
441
over protective structures (ROPS) Testing. Transactions of the ASAE 37(6): 1763-
442
1768.
443
Browning, S. R., H. Truszczynska, D. Reed, and R. H. McKingt. 1998. Agricultural injuries among
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older Kentucky farmers: the Farm Family Health and Hazard Surveillance study. Am.
445
Journal of Industrial Medicine 33: 341-353.
446 447
Casini-Ropa, G. 1980. Il trattore agricolo: stato di sicurezza e sicurezza nell´ impiego. [The agricultural tractor: safety state and safety in the use]. Machine e Motori Agricoli 2 : 27-42.
23
448
Fabri, A., and S. Ward. 2002. Validation of a Finite Element Program for the Design of Roll-
449
over Protective Framed Structures (ROPS) for Agricultural Tractors. Biosystems
450
Engineering 81(3): 287-296.
451 452
Febo, P., and D. Pessina. 1989. Sicurezza ed ergonomia del tratore [Safety and comfort of the tractor]. Machine e Motori Agricoli 6/7: 27-60.
453
Pana-Cryan, R., and M. L.Myers. 2000. Prevention Effectiness of Rollover Protective
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Structures-Part III: Economic Analysis. Journal of Agricultural Safety and Health 6
455
(1): 57-70.
456
Bulletin or Report
457
Barco, E. 1999. Estudio de las necesidades de formación para la prevención de accidentes laborales
458
en el sector agrario. [Educational need study two prevent agricultural occupational
459
accidents]. COAG.
460
Chisholm, C. J. 1972. A survey of 114 tractor sideways overturning accidents in the UK, 1969 to
461
1971. Dep. Note DN/TE/238/1425, National Institute of Agricultural Engineering, Silsoe,
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UK.
463
Cole, H. P., S. Westneat, and S. Browning. 1998. Results of a preintervention survey of principal
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farm operator´s demographics, beliefs, and practices related to farm tractor ROPS, seatbelts
465
and estra riders. (Technical Report to CDC/NIOSH, May 29). P-36. Lexington, KY:
466
University of Kentucky, Southest Center for Agricultural Health and Safety.
467
INAIL, 2000. Banca Dati Pubblicaa INAIL- Infortuni indennizatti in agricultura a tutto il 31
468
Dicembre 1999 per anno, evento, conseguence, tipo de lavorazione e forma di
469
avvenimento. [Accidents indemnified in agriculture up to December 31 1999 for
470
year, event, consequences, type of working and type of event.* Monografie INAIL,
471
Roma.
472
MMWR. 1993. Public health focus: Effectiveness of roll-over protective structures for preventing
473
injuries associated with agricultural tractors. Morbidity and Mortality Weekly Report (3):
474
57-59.
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475
Published Paper and Conference Proceedings
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Arana, J. I., J. Mangado, A. Hualde, C. Jarén, C. Pérez de Larraya, S. Arazuri, and P. Arnal.
477
2004. Program “ESTREMA” for the calculation of a Roll-over Protective Structure
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for agricultural Tractors Before 1976. In Actas EuroAgEng’04, 02-P- 412-413 ISBN
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90/76019-258. Leuven.
480
Arana, J. I., J. Mangado, A. Hualde, C Jarén, C. Pérez de Larraya, S. Arazuri, and P. Arnal.
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2002. Tractors without protective structures in Navarre (Spain): actual situation and
482
problems. In Actas EuroAgEng’02: 02-P-059.Budapest.
483
Cole, H. P., R. H.McKnight, S. R. Browning, D. B. Reed, T. W. Struttman, L. R. Piercy, and S.
484
Westneat. 2000. Estimates of the probability of death during farm tractor overturns.
485
Proc.National Occupational Injury Reserch Synphosium, Pittsburg, PA, October 17.
486
Fabri, A. 1999. Il metodo degli elementi finiti nella progectazione delle structure di
487
protezione installati sulle traticci. [The finite element method in designing protective
488
structures mounted on agricultural tractors]. Proceedings of the Convegno nazionale
489
AIIA L´Innovacione tecnologica per l´agricoltura di precisione e la qualià
490
productiva, Grugliasco. Torino.
491
Online Source
492
Public University of Navarre (Spain). Department of Rural Engineering and Proyects.
493
Agricultural mechanization Laboratory. Computer program to calculate ROPS. Available
494
in http://www.unavarra.es/organiza/laboratoriotractor.htm.
495
Unpublished Material
496
OECD. 2005. Standard Codes for The Official Testinf of Protective Structures Mounted on
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Agricultural and Forestry Tractors. OECD, Paris.
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