Certification for ROPS under OSHA 1928.53

[wfo74]

Full certification is here:

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=13077

I am not understanding some of this cert.
This is real world, I have applied loads and gathered results as below. This is for a 1500lb UTV.
First question regarding applied force. I have an applied force of 705 lbs to the rear of the cage. And a deflection of 1 inch of the structure under that load. That is 705 inch pounds? Right?
If the structure were so stiff that it did not move at all under this force, I would have zero inch pounds? Or if it moved .5 inches, I would have 352.5 inch pounds?
If it moved 12 inches, then I would have 705 foot pounds?
Even though the applied force is the same?
I need to understand this, as it is important as regards some further calculations.
Thanks,
Jon

 

[dhengr]

Your 705 inch pounds is a form of energy absorbed. That would be 58.75 foot pounds. The trick is that you want your ROPS to absorb some amount of energy during an occurrence without excessive deflection and without structural failure or excessive material yielding. Prior to yielding the ROPS structure acts much like a spring and just stores the energy it is absorbing and releases it when the loading is removed. Beyond yielding the structure has absorbed part of the energy by yielding of the material; plastification or buckling do a good job of this. There must be some limit on deflection too, so that you don’t crush the driver. You end up playing allowable deflection against strength/stiffness to absorb some specified amount of energy. A stiffer structure will take more load to deflect 1" (or any amount) thus it can absorb more energy. But, your statement “If the structure were so stiff that it did not move at all under this force, I would have zero inch pounds?” is really not correct. There is really not such thing as zero deflection under load, since .01" delta times 70,500 lbs. leads to the same energy.

 

[wfo74]

Yes, the structure will move under the 705 lbs, indeed it moved almost exactly an inch (this is real world, not some hypothetical situation).
What I am trying to get my head around is the unit of measure. Ft-Lbs. 58.75 in this instance.
If the same force (705 lbs) is applied, and the structure moves two inches, the Ft-Lbs doubles to 117.5
So a structure that deflects more, is seen to absorb more energy. Which sounds like a good thing, but is indeed a weaker structure.
If you have time, please read the cert to understand why I am pulling my hair. Particularly the calculation of FER(ir) which is Eu/Eir. If I can get that FER(ir) to 1.15, I have passed. But the numbers are working against me.
Tell you what, I am inserting the cert below.
Anyone have the time to look this over, will see why I am running in circles chasing this cert. Or am I missing a big piece of the puzzle?

1928.53(a)
Purpose. The purpose of this section is to establish the test and performance requirements for a protective enclosure designed for wheel-type agricultural tractors to minimize the frequency and severity of operator injury resulting from accidental upset. General requirements for the protection of operators are specified in 29 CFR 1928.51.
1928.53(b)
Types of tests. All protective enclosures for wheel-type agricultural tractors shall be of a model that has been tested as follows:
1928.53(b)(1)
Laboratory test. A laboratory energy-absorption test, either static or dynamic, under repeatable and controlled loading, to permit analysis of the protective enclosure for compliance with the performance requirements of this standard; and
1928.53(b)(2)
Field-upset test. A field-upset test under controlled conditions, both to the side and rear, to verify the effectiveness of the protective system under actual dynamic conditions. This test may be omitted when:
1928.53(b)(2)(i)
The analysis of the protective-frame static-energy absorption test results indicates that both FERis and FERir (as defined in paragraph (d)(2)(ii) of this section) exceed 1.15; or1928.53(b)(2)(ii)
The analysis of the protective-frame dynamic-energy absorption test results indicates that the frame can withstand an impact of 15 percent greater than the impact it is required to withstand for the tractor weight as shown in Figure C-7.
1928.53(c)
Descriptions. A protective enclosure is a structure comprising a frame and/or enclosure mounted to the tractor. A typical enclosure is shown in Figure C-12.
1928.53(d)
Test procedures.
1928.53(d)(1)
General.
1928.53(d)(1)(i)
The tractor weight used shall be that of the heaviest tractor model on which the protective enclosure is to be used.
1928.53(d)(1)(ii)
Each test required under this section shall be performed on a protective enclosure with new structural members. Mounting connections of the same design shall be used during each test.
1928.53(d)(1)(iii)
Instantaneous deflection shall be measured and recorded for each segment of the test; see paragraph (e)(1)(i) of this section for permissible deflections.
1928.53(d)(1)(iv)
The seat-reference point ("SRP") in Figure C-14 is that point where the vertical line that is tangent to the most forward point at the longitudinal seat centerline of the seat back, and the horizontal line that is tangent to the highest point of the seat cushion, intersect in the longitudinal seat section. The seat-reference point shall be determined with the seat unloaded and adjusted to the highest and most rearward position provided for seated operations of the tractor.
1928.53(d)(1)(v)
When the centerline of the seat is off the longitudinal center, the protective-enclosure loading shall be on the side with least space between the centerline of the seat and the protective enclosure.
1928.53(d)(1)(vi)
Low-temperature characteristics of the protective enclosure or its material shall be demonstrated as specified in paragraph (e)(1)(ii) of this section.
1928.53(d)(1)(vii)
Rear input energy tests (static, dynamic, or field-upset) need not be performed on enclosures mounted to tractors having four driven wheels and more than one-half their unballasted weight on the front wheels.
1928.53(d)(1)(viii)
Accuracy table:

Measurements Accuracy
Deflection of the enclosure, in. (mm) ±5 percent of the deflection measured.
Vertical weight, pounds (kg) ±5 percent of the weight measured.
Force applied to the enclosure, pounds force (newtons). ±5 percent of the force measured.
Dimensions of the critical zone, in. (mm). ±0.5 in. (12.5 mm).

1928.53(d)(1)(ix)
When movable or normally removable portions of the enclosure add to structural strength, they shall be placed in configurations that contribute least to structural strength during the test.
1928.53(d)(2)
Static test procedure.
1928.53(d)(2)(i)
The following test conditions shall be met:
1928.53(d)(2)(i)(A)
The laboratory mounting base shall be the tractor chassis for which the protective enclosure is designed, or its equivalent; and
1928.53(d)(2)(i)(B)
The protective enclosure shall be instrumented with the necessary equipment to obtain the required load-deflection data at the locations and directions specified in Figures C-13 and C-14.
1928.53(d)(2)(ii)
The following definitions shall apply:

W = Tractor weight (see 29 CFR 1928.51(a)) in lb (W' in kg);
Eis = Energy input to be absorbed during side loading in ft-lb (E'is in J [joules]);
Eis = 723 + 0.4 W (E'is = 100 + 0.12 W');
Eir = Energy input to be absorbed during rear loading in ft-lb (E'ir in J);
Eir = 0.47 W (E'ir = 0.14 W');
L = Static load, lbf [pounds force], (N) [newtons];
D = Deflection under L, in. (mm);
L-D = Static load-deflection diagram;
Lmax = Maximum observed static load;
Load Limit = Point on a continuous L-D curve where the observed static load is 0.8 Lmax on the down slope of the curve (see Figure C-5);
Eu = Strain energy absorbed by by the protective enclosure in ft-lbs (J); area under the L-D curve;
FER = Factor of energy ratio;
FERis = Eu/Eis; and
FERir = Eu/Eir.1928.53(d)(2)(iii)
The test procedures shall be as follows:
1928.53(d)(2)(iii)(A)
When the protective-frame structures are not an integral part of the enclosure, the direction and point of load application for both side and rear shall be the same as specified in 29 CFR 1928.52(d)(2);
1928.53(d)(2)(iii)(B)
When the protective-frame structures are an integral part of the enclosure, apply the rear load according to Figure C-14, and record L and D simultaneously. Rear-load application shall be distributed uniformly on the frame structure over an area perpendicular to the load application, no greater than 160 sq. in. (1,032 sq. cm) in size, with the largest dimension no greater than 27 in. (686 mm). The load shall be applied to the upper extremity of the structure at the point that is midway between the centerline of the protective enclosure and the inside of the protective structure. When no structural cross member exists at the rear of the enclosure, a substitute test beam that does not add strength to the structure may be used to complete this test procedure. The test shall be stopped when:
1928.53(d)(2)(iii)(B)(1)
The strain energy absorbed by the structure is equal to or greater than the required input energy Eir; or
1928.53(d)(2)(iii)(B)(2)
Deflection of the structure exceeds the allowable deflection (see paragraph (e)(1)(i) of this section); or
1928.53(d)(2)(iii)(B)(3)
The structure load limit occurs before the allowable deflection is reached in rear load (see Figure C-5);
1928.53(d)(2)(iii)(C)
Using data obtained in paragraph (d)(2)(iii)(B) of this section, construct the L-D diagram for rear loads as shown in Figure C-5;
1928.53(d)(2)(iii)(D)
Calculate Eir;
1928.53(d)(2)(iii)(E)
Calculate FERir;
1928.53(d)(2)(iii)(F)
When the protective-frame structures are an integral part of the enclosure, apply the side load according to Figure C-13, and record L and D simultaneously. Static side-load application shall be distributed uniformly on the frame over an area perpendicular to the direction of load application, and no greater than 160 sq. in. (1,032 sq. cm) in size, with the largest dimension no greater than 27 in. (686 mm). Side-load application shall be at a 90º angle to the centerline of the vehicle. The center of the side-load application shall be located between point k, 24 in. (610 mm) forward of the seat-reference point, and point l, 12 in. (305 mm) rearward of the seat-reference point, to best use the structural strength (see Figure C-13). This side load shall be applied to the longitudinal side farthest from the point of rear-load application. The test shall be stopped when:
1928.53(d)(2)(iii)(F)(1)
The strain energy absorbed by the structure is equal to or greater than the required input energy Eis; or
1928.53(d)(2)(iii)(F)(2)
Deflection of the structure exceeds the allowable deflection (see paragraph (e)(1)(i) of this section); or
1928.53(d)(2)(iii)(F)(3)
The structure load limit occurs before the allowable deflection is reached in side load (see Figure C-5).
1928.53(d)(2)(iii)(G)
Using data obtained in paragraph (d)(2)(iii)(F) of this section, construct the L-D diagram for the side load as shown in Figure C-5;
1928.53(d)(2)(iii)(H)
Calculate FERis;
1928.53(d)(2)(iii)(I)
Calculate FERir.
1928.53(d)(3)
Dynamic test procedure.
1928.53(d)(3)(i)
The following test conditions shall be met:
1928.53(d)(3)(i)(A)
The protective enclosure and tractor shall be tested at the weight defined by 29 CFR 1928.51(a);
1928.53(d)(3)(i)(B)
The dynamic loading shall be accomplished by using a 4,410-lb (2,000-kg) weight acting as a pendulum. The impact face of the weight shall be 27 ± 1 in. by 27 ± 1 in. (686 ± 25 mm by 686 ± 25 mm), and shall be constructed so that its center of gravity is within 1.0 in. (25.4 mm) of its geometric center. The weight shall be suspended from a pivot point 18 to 22 ft (5.5 to 6.7 m) above the point of impact on the enclosure, and shall be conveniently and safely adjustable for height (see Figure C-6);
1928.53(d)(3)(i)(C)
For each phase of testing, the tractor shall be restrained from moving when the dynamic load is applied. The restraining members shall have strength no less than, and elasticity no greater than, that of 0.50-in. (12.7-mm) steel cable. Points of attachment for the restraining members shall be located an appropriate distance behind the rear axle and in front of the front axle to provide a 15º to 30º angle between the restraining cable and the horizontal. For impact from the rear, the restraining cables shall be located in the plane in which the center of gravity of the pendulum will swing, or alternatively, two sets of symmetrically located cables may be used at lateral locations on the tractor. For the impact from the side, restraining cables shall be used as shown in Figures C-15 and C-16;
1928.53(d)(3)(i)(D)
The front and rear wheel-tread settings, when adjustable, shall be at the position nearest to halfway between the minimum and maximum settings obtainable on the vehicle. When only two settings are obtainable, the minimum setting shall be used. The tires shall have no liquid ballast, and shall be inflated to the maximum operating pressure recommended by the manufacturer. With specified tire inflation, the restraining cable shall be tightened to provide tire deflection of 6 to 8 percent of nominal tire section width. After the vehicle is retrained properly, a wooden beam no smaller than 6-in. x 6-in. (150-mm x 150-mm) cross-section shall be driven tightly against the appropriate wheels and clamped. For the test to the side, an additional wooden beam shall be placed as a prop against the wheel nearest the operator's station, and shall be secured to the base so that it is held tightly against the wheel rim during impact. The length of this beam shall be chosen so that it is at an angle of 25º to 40º to the horizontal when it is positioned against the wheel rim. It shall have a length 20 to 25 times its depth, and a width two to three times its depth (see Figures C-15 and C-16);
1928.53(d)(3)(i)(E)
Means shall be provided for indicating the maximum instantaneous deflection along the line of impact. A simple friction device is illustrated in Figure C-4;
1928.53(d)(3)(i)(F)
No repairs or adjustments shall be made during the test; and
1928.53(d)(3)(i)(G)
When any cables, props, or blocking shift or break during the test, the test shall be repeated.
1928.53(d)(3)(ii)
H = Vertical height of the center of gravity of a 4,410-lb (2,000-kg) weight in in. (H' in mm). The weight shall be pulled back so that the height of its center of gravity above the point of impact is: H = 4.92 + 0.00190 W (H' = 125 + 0.170 W') (see Figure C-7).
1928.53(d)(3)(iii)
The test procedures shall be as follows:
1928.53(d)(3)(iii)(A)
The enclosure structure shall be evaluated by imposing dynamic loading from the rear, followed by a load to the side on the same enclosure structure. The pendulum swinging from the height determined by paragraph (d)(3)(ii) of this section shall be used to impose the dynamic load. The position of the pendulum shall be so selected that the initial point of impact on the protective structure is in line with the arc of travel of the center of gravity of the pendulum. When a quick-release mechanism is used, it shall not influence the attitude of the block;
1928.53(d)(3)(iii)(B)
Impact at rear. The tractor shall be restrained properly according to paragraphs (d)(3)(i)(C) and (d)(3)(i)(D) of this section. The tractor shall be positioned with respect to the pivot point of the pendulum so that the pendulum is 20º from the vertical prior to impact as shown in Figure C-15. The impact shall be applied to the upper extremity of the enclosure structure at the point that is midway between the centerline of the enclosure structure and the inside of the protective structure. When no structural cross member exists at the rear of the enclosure structure, a substitute test beam that does not add to the strength of the structure may be used to complete the test procedure; and
1928.53(d)(3)(iii)(C)
Impact at side. The blocking and restraining shall conform to paragraphs (d)(3)(i)(C) and (d)(3)(i)(D) of this section. The center point of impact shall be at the upper extremity of the enclosure at a 90º angle to the centerline of the vehicle, and located between a point k, 24 in. (610 mm) forward of the seat-reference point, and a point l, 12 in. (305 mm) rearward of the seat-reference point, to best use the structural strength (see Figure C-13). The side impact shall be applied to the longitudinal side farthest from the point of rear impact.
1928.53(d)(4)
Field-upset test procedure.
1928.53(d)(4)(i)
The following test conditions shall be met:
1928.53(d)(4)(i)(A)
The tractor shall be tested at the weight defined in 29 CFR 1928.51(a);
1928.53(d)(4)(i)(B)
The following provisions address soil bank test conditions.
1928.53(d)(4)(i)(B)(1)
The test shall be conducted on a dry, firm soil bank. The soil in the impact area shall have an average cone index in the 0-in. to 6-in. (0-mm to 152-mm) layer of not less than 150. Cone index shall be determined according to American Society of Agricultural Engineers ("ASAE") recommendation ASAE R313.1-1971 ("Soil cone penetrometer"), as reconfirmed in 1975, which is incorporated by reference. The incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. The path of vehicle travel shall be 12º ± 2º to the top edge of the bank.
1928.53(d)(4)(i)(B)(2)
ASAE recommendation R313.1-1971, as reconfirmed in 1975, appears in the 1977 Agricultural Engineers Yearbook, or it may be examined at: Any OSHA Regional Office; the OSHA Docket Office, U.S. Department of Labor, 200 Constitution Avenue, NW., Room N-2625, Washington, DC 20210 (telephone: (202) 693-2350 (TTY number: (877) 889-5627)); or the National Archives and Records Administration ("NARA"). (For information on the availability of this material at NARA, telephone (202) 741-6030 or access the NARA Web site at

http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.)

Copies may be purchased from the American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, MI 49085.
1928.53(d)(4)(i)(C)
An 18-in. (457 mm) high ramp (see Figure C-10) shall be used to assist in upsetting the vehicle to the side; and
1928.53(d)(4)(i)(D)
The front and rear wheel-tread settings, when adjustable, shall be at the position nearest to halfway between the minimum and maximum settings obtainable on the vehicle. When only two settings are obtainable, the minimum setting shall be used.
1928.53(d)(4)(ii)
Field upsets shall be induced to the rear and side.
1928.53(d)(4)(ii)(A)
Rear upset shall be induced by engine power, with the tractor operating in gear to obtain 3 to 5 mph (4.8 to 8.0 kph) at maximum governed engine rpm by driving forward directly up a minimum slope of 60º ± 5º as shown in Figure C-11, or by an alternate equivalent means. The engine clutch may be used to aid in inducing the upset; and
1928.53(d)(4)(ii)(B)
To induce side upset, the tractor shall be driven under its own power along the specified path of travel at a minimum speed of 10 mph (16 kph), or at maximum vehicle speed when under 10 mph (16 kph), and over the ramp as described in paragraph (d)(4)(i)(C) of this section.
1928.53(e)
Performance requirements.
1928.53(e)(1)
General requirements.
1928.53(e)(1)(i)
The protective enclosure structural members or other parts in the operator area may be deformed in these tests, but shall not shatter or leave sharp edges exposed to the operator. They shall not encroach on a transverse plane passing through points d and f within the projected area defined by dimensions d, e, and g, or on the dimensions shown in Figures C-13 and C-14, as follows:

d = 2 in. (51 mm) inside of the protective structure to the vertical centerline of the seat;
e = 30 in. (762 mm) at the longitudinal centerline;
f = Not greater than 4 in. (102 mm) measured forward of the seat-reference point ("SRP") at the longitudinal centerline as shown in Figure C-14;
g = 24 in. (610 mm) minimum;
h = 17.5 in. (445 mm) minimum; and
j = 2.0 in. (51 mm) measured from the outer periphery of the steering wheel.
1928.53(e)(1)(ii)
The protective structure and connecting fasteners must pass the static or dynamic tests described in paragraphs (d)(2), (d)(3), or (d)(4) of this section at a metal temperature of 0 ºF (-8 ºC) or below, or exhibit Charpy V-notch impact strengths as follows:

10-mm x 10-mm (0.394-in. x 0.394-in.) specimen: 8.0 ft-lb (10.8 J) at -20 ºF (-30 ºC);
10-mm x 7.5-mm (0.394-in. x 0.296-in.) specimen: 7.0 ft-lb (9.5 J) at -20 ºF (-30 ºC);
10-mm x 5-mm (0.394-in. x 0.197-in.) specimen: 5.5 ft-lb (7.5 J) at -20 ºF (-30 ºC); or
10-mm x 2.5-mm (0.394-in. x 0.098-in.) specimen: 4.0 ft-lb (5.5 J) at -20 ºF (-30 ºC).

Specimens shall be longitudinal and taken from flat stock, tubular, or structural sections before forming or welding for use in the protective enclosure. Specimens from tubular or structural sections shall be taken from the middle of the side of greatest dimension, not to include welds.
1928.53(e)(1)(iii)
The following provisions address glazing requirements.
1928.53(e)(1)(iii)(A)
Glazing shall conform to the requirements contained in Society of Automotive Engineers ("SAE") standard J674-1963 ("Safety glazing materials"), which is incorporated by reference. The incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51.
1928.53(e)(1)(iii)(B)
SAE standard J674-1963 appears in the 1965 SAE Handbook, or it may be examined at: any OSHA Regional Office; the OSHA Docket Office, U.S. Department of Labor, 200 Constitution Avenue, NW., Room N-2625, Washington, DC 20210 (telephone: (202) 693-2350 (TTY number: (877) 889-5627)); or the National Archives and Records Administration ("NARA"). (For information on the availability of this material at NARA, telephone (202) 741-6030 or access the NARA Web site at

http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.)

Copies may be purchased from the Society of Automotive Engineers, 400 Commonwealth Drive, Warrendale, Pennsylvania 15096-0001.
1928.53(e)(1)(iv)
Two or more operator exits shall be provided and positioned to avoid the possibility of both being blocked by the same accident.
1928.53(e)(2)
Static test-performance requirements. In addition to meeting the requirements of paragraph (e)(1) of this section for both side and rear loads, FERis and FERir shall be greater than 1.0.
1928.53(e)(3)
Dynamic test-performance requirements. The structural requirements shall be met when the dimensions in paragraph (e)(1) of this section are used in both side and rear loads.
1928.53(e)(4)
Field-upset test performance requirements. The requirements of paragraph (e)(1) of this section shall be met for both side and rear upsets.

[61 FR 9227, March 7, 1996; 70 FR 77006, Dec. 29, 2005; 71 FR 41146, July 20, 2006]

 

[dhengr]

Wfo74:
That OSHA stuff is some really unpleasant reading, when each section refers you to seven other sections and figures which are all equally incomprehensible from any engineering standpoint. So, with a very quick look at some of the verbiage and figures, I’ll try to push you in the right direction of thinking, again. Look at figs. C-1, 2 & 3, and fig. C-5. OSHA sets some ROPS deformation limits, about the drivers position in the seat. And, these deformations are based on a loading (your 705lbs.) which is a function of the weight of the ATV. It seems to me that if you can stay within these deformation limits when you statically apply a load of (1.15+)(705lbs.), you are meeting the requirements. Look at the load/deformation curve C-5, you should plot this curve during your testing. Lmax. represents the load at which you particular structural element starts to yield (plastification, at the max. stress location). With very small load increase, you will get significant deflection increase; and then the load will actually fall off at some point, while deflection increases. That is exactly the trace of the curve they show.

Given your structural element design, if you reach the required loading without exceeding the deformation limits (envelope), you have passed the test; and the area under the load/deformation curve is a good representation of the energy that your structure can absorb, under those loading conditions. But, your design trick is that you must do this without your structural elements yielding very much or things start to go south very quickly on the l/d curve, a certain failure.

So, your statement.... “If the same force (705 lbs) is applied, and the structure moves two inches, the Ft-Lbs doubles to 117.5. So a structure that deflects more, is seen to absorb more energy. Which sounds like a good thing, but is indeed a weaker structure.” is basically correct; the load/delta point is moving up or to the right on the curve. But, given that 705lbs. produced 1" delta on your structure, the 2" delta only occurred because the second structure was half as stiff as the first. Thus, the second structure is working at a much higher stress under the 705lb. loading, and is closer to its load limit on the curve. The weaker second structure gives you a lower curve, and likely a shortened delta axis also, before yielding, and thus less area under the curve. A lesser total ability to absorb energy, and therefore a failed test. Remember, you have to balance strength, so as not to yield, against deflection limits; and given your machine dimensions and weight, the only way you can practically do that is by adjusting the strength/stiffness of the vertical members on your ROPS.