Further testing and simulation of hay bale loading on semi ... · simulation of hay bale loading on semi-trailers A report for the Rural Industries Research and Development Corporation

Further testing and simulation of hay bale

loading on semi-trailers

A report for the Rural Industries Research and Development Corporation

by Robert Di Cristoforo

Dr Peter F Sweatman Roaduser Systems Pty Ltd

July 2004

RIRDC Publication No 04/124 RIRDC Project No ROA-2A

© 2004 Rural Industries Research and Development Corporation. All rights reserved. ISBN 1 74151 032 5 ISSN 1440-6845 Further testing and simulation of hay bale loading on semi-trailers Publication No. 04/124 Project No. ROA-2A The views expressed and the conclusions reached in this publication are those of the author and not necessarily those of persons consulted. RIRDC shall not be responsible in any way whatsoever to any person who relies in whole or in part on the contents of this report. This publication is copyright. However, RIRDC encourages wide dissemination of its research, providing the Corporation is clearly acknowledged. For any other enquiries concerning reproduction, contact the Publications Manager on phone 02 6272 3186. Researcher Contact Details Dr Peter F Sweatman 76-80 Vella Drive Sunshine Victoria 3088 Phone: (03) 9334 7888 Fax: (03) 9334 7877 Email: [email protected] In submitting this report, the researcher has agreed to RIRDC publishing this material in its edited form. RIRDC Contact Details Rural Industries Research and Development Corporation Level 1, AMA House 42 Macquarie Street BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: 02 6272 4539 Fax: 02 6272 5877 Email: [email protected] Website: http://www.rirdc.gov.au Published in July 2004 Printed on environmentally friendly paper by Union Offset Printing

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Foreword In recent years there has been a significant increase in the volume of hay traded in Australia, which has seen an increase in the public awareness of accidents involving hay truck rollovers or hay falling from trucks. As a consequence, enforcement officers have selectively focused load restraint and dimensional infringement notices on the hay transport sector, highlighting the inequity in the regulatory system that has different rules in each State. A significant study into the stability of hay trucks was completed for RIRDC in October 2003 (RIRDC publication 03/120). This report expands on the work carried out in the original study by incorporating physical testing of fore-aft load stability and some additional Performance-Based Standards assessment by computer simulation. This project was funded from industry voluntary R&D levies and RIRDC core funds provided by the Australian Government. This report is an addition to RIRDC’s diverse range of over 1000 research publications. It forms part of our Fodder Crops R&D program, which aims to facilitate the development of a sustainable and profitable Australian fodder industry. Most of our publications are available for viewing, downloading or purchasing online through our website:

downloads at www.rirdc.gov.au/reports/Index.htm

purchases at www.rirdc.gov.au/eshop

Simon Hearn Managing Director Rural Industries Research and Development Corporation

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http://www.rirdc.gov.au/reports/Index.htm

Acknowledgments Roaduser Systems Pty Ltd wish to acknowledge the efforts of Colin Peace of the Australian Fodder Industry Association (AFIA) in organising the resources required to complete this work. Special thanks are extended to the AFIA members (David Manifold, Graham Thompson, Jenharwill Baling, Alex Peacock, Logan Contracting and Gilmac Pty Ltd) who donated their time to source and deliver hay bales and to help with loading/unloading and load restraint during the test program.

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Contents Executive Summary ............................................................................................................................... vi

Background ........................................................................................................................................ vi Further testing and simulation........................................................................................................... vii Research conducted........................................................................................................................... vii Findings............................................................................................................................................. vii

Introduction ............................................................................................................................................. 1 Tilt testing ............................................................................................................................................... 3

Methodology ....................................................................................................................................... 3 Test equipment .................................................................................................................................... 5 Tests conducted ................................................................................................................................... 6 Test results........................................................................................................................................... 8 Discussion of results.......................................................................................................................... 12

Simulation modelling ............................................................................................................................ 13 Additional performance measures ..................................................................................................... 13 Restraint methods .............................................................................................................................. 14 Stacking arrangements ...................................................................................................................... 15 Performance results ........................................................................................................................... 16

Conclusion............................................................................................................................................. 19 Tilt testing ......................................................................................................................................... 19 Simulation modelling ........................................................................................................................ 19

References ............................................................................................................................................. 20

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Executive Summary Background In October 2003, Roaduser Systems completed a project for the Rural Industries Research and Development Corporation (RIRDC) [1]. The project focussed on the safety implications of possible changes to hay and straw loading regulations in terms of the NRTC/Austroads Performance-Based Standards for heavy vehicles (PBS) [2][3]. The study aimed to provide a sound technical basis to aid State jurisdictions in developing consistent hay bale loading rules which are more clearly related to safety objectives. There was a need to address the effects of load dimensions on both vehicle stability and road width requirements; these two vehicle performance measures are effectively controlled by PBS, which allows flexibility in vehicle regulation by exempting vehicles from prescriptive regulations without adversely affecting safety. The assessment covered the four common hay bale sizes (nominally expressed as 3’x3’x8’ rectangular, 4’x3’x8’ rectangular, 4’x4’x8’ rectangular and 5’x4’ round), along with the common stacking arrangements employed by industry, a variety of load restraint methods and a set of representative hay truck configurations, providing a total of 77 combinations. The assessment process [1] included two parts. Firstly, each load type was physically tested in a specially-designed rig to determine its lateral rigidity when properly restrained on a trailer deck. The load types included all bale sizes, stacking arrangements and load restraint methods for a total of 31 test set-ups. Lateral rigidity characteristics were recorded as force-displacement plots that were used in further analysis. Secondly, the stability and road width requirements were determined for each vehicle configuration and load type by computer simulation of vehicle dynamics. The lateral rigidity parameters obtained from the tests were incorporated into the models to pass the effect of load movement on to roll stability performance. These simulation models provided valuable information regarding the effect of load height and bale type on stability, with effects due to load restraint methods also observed. The physical tests revealed enormous variations in lateral rigidity between the different types of bales, with round bales offering the least rigidity. The 4’x4’x8’ rectangular bales were by far the best performers, with more than twice the rigidity of round bales at 4.6m high. The computer simulation models predicted considerable variation in rollover stability. The biggest contributing factor was bale type, followed by stacking arrangement, vehicle configuration and finally load restraint method. The stability assessment showed that practically all fully-laden hay truck configurations would comply with the stringent PBS stability standard, including loads that are not allowed under current regulations. The road width assessment showed that all vehicles were able to satisfy the PBS requirements at widths of up to 3m or more. The outcomes of the study showed that hay/straw industry vehicle loads are safe when properly restrained, and practices are currently unduly restricted by inconsistent loading rules. It was recommended that hay loading rules could be made uniform by applying a general hay loading rule across all States allowing the operation of complying hay trucks to a maximum overall height of 4.6 m and a maximum overall width of 3.0 m, provided axle mass limits were not exceeded. However, the poorer stability performance of tandem axle trailers in comparison with their triaxle counterparts suggested that hay trucks incorporating tandem axle trailers should be limited to an overall height of 4.3 m. Regarding load restraint, it was found that there are small but worthwhile benefits to be achieved by using more effective load restraint methods such as double-strapping or “double-dogging” of single straps (one load binder on each side of the load for a single strap).

vi

Further testing and simulation After detailed consideration of the original research by industry, it became clear that some further work was required to supplement the original research by Roaduser Systems. Firstly, seeing that the previous work did not investigate load restraint in the fore-aft direction, some testing of fore-aft load restraint was conducted in accordance with the draft Load Restraint Guide [4]. Secondly, in addition to the two PBS measures addressed by the previous RIRDC report [1], it was requested that three more PBS measures are included in the simulation task. These are Tracking Ability on a Straight Path (which addresses the lane width requirement of a heavy vehicle as it relates to vehicle dynamics, road crossfall and road roughness), High-Speed Transient Offtracking (which addresses the additional road width required by a combination vehicle undertaking a rapid avoidance manoeuvre) and Frontal Swing (Part B) (which addresses the additional road width required by the front corner of a trailer outside the envelope of the prime mover during a low-speed turn). These measures are described in Appendix A and Appendix B.

Research conducted The fore-aft load restraint investigation was conducted by tilt testing as described in the Load Restrain Guide. A tilt test requires a sample of the load to be properly restrained on a tilting deck (as it would be restrained for road travel) and tilted to a pre-determined tilt angle. Provided the pre-determined tilt angle is reached without failure or gross deformation of the load, the restraint is considered to be sufficient. The additional PBS vehicle simulations were undertaken by exercising the existing hay truck simulation models in some additional manoeuvres.

Findings The tilt testing program demonstrated that compliance with the requirements of the Load Restraint Guide [4] is possible for all four of the tested bale types when stacked to 4.6 metres high on a drop deck trailer. This includes 4’x4’x8’ rectangular bales at 2.7 metres wide and 5’x4’ round bales at 3 metres wide. In all cases, the level of load restraint was gradually reduced with each successive test. It was found that, for each bale type, compliance was demonstrated with a reduced level of restraint. Each bale type was tested with continually decreasing restraint until instability caused the test to be stopped. It was found that the use of a diagonal bracing strap provided an enormous improvement to load stability. It is strongly recommended that diagonal bracing is considered for at least the front and rear groups of bales on a trailer, with the bracing pulling towards the centre of the trailer. A reduced level of restraint is appropriate for centrally-mounted bales, provided the restraint of the end groups of bales is sufficient to withstand any possible load transfer from the centre bales. Alternatively, diagonally bracing all groups of bales is acceptable The simulation modelling demonstrated that all of the rectangular bale types could be considered to be acceptable on PBS grounds, while round bales stacked to 3 metres wide are too wide to satisfy PBS TASP. Round bales could be justified by stacking “on rounds” with the flat sides facing out. This would produce an overall width of 2.5 metres, but would degrade productivity and load stability considerably. The study of the lateral behaviour of this configuration (K) in [1] highlighted this configuration as a poor-performer.

vii

Introduction In October 2003, Roaduser Systems completed a project for the Rural Industries Research and Development Corporation (RIRDC) [1]. The project focussed on the safety implications of possible changes to hay and straw loading regulations in terms of the NRTC/Austroads Performance-Based Standards for heavy vehicles (PBS) [2][3]. The study aimed to provide a sound technical basis to aid State jurisdictions in developing consistent hay bale loading rules which are more clearly related to safety objectives. There was a need to address the effects of load dimensions on both vehicle stability and road width requirements; these two vehicle performance measures are effectively controlled by PBS, which allows flexibility in vehicle regulation by exempting vehicles from prescriptive regulations without adversely affecting safety. The assessment covered the four common hay bale sizes (nominally expressed as 3’x3’x8’ rectangular, 4’x3’x8’ rectangular, 4’x4’x8’ rectangular and 5’x4’ round), along with the common stacking arrangements employed by industry, a variety of load restraint methods and a set of representative hay truck configurations, providing a total of 77 combinations. The assessment process [1] included two parts. Firstly, each load type was physically tested in a specially-designed rig to determine its lateral rigidity when properly restrained on a trailer deck. The load types included all bale sizes, stacking arrangements and load restraint methods for a total of 31 test set-ups. Lateral rigidity characteristics were recorded as force-displacement plots that were used in further analysis. Secondly, the stability and road width requirements were determined for each vehicle configuration and load type by computer simulation of vehicle dynamics. The lateral rigidity parameters obtained from the tests were incorporated into the models to pass the effect of load movement on to roll stability performance. These simulation models provided valuable information regarding the effect of load height and bale type on stability, with effects due to load restraint methods also observed. The physical tests revealed enormous variations in lateral rigidity between the different types of bales, with round bales offering the least rigidity. The 4’x4’x8’ rectangular bales were by far the best performers, with more than twice the rigidity of round bales at 4.6m high. The computer simulation models predicted considerable variation in rollover stability. The biggest contributing factor was bale type, followed by stacking arrangement, vehicle configuration and finally load restraint method. The stability assessment showed that practically all fully-laden hay truck configurations would comply with the stringent PBS stability standard, including loads that are not allowed under current regulations. The road width assessment showed that all vehicles were able to satisfy the PBS requirements at widths of up to 3m or more. The outcomes of the study showed that hay/straw industry vehicle loads are safe when properly restrained, and practices are currently unduly restricted by inconsistent loading rules. It was recommended that hay loading rules could be made uniform by applying a general hay loading rule across all States allowing the operation of complying hay trucks to a maximum overall height of 4.6 m and a maximum overall width of 3.0 m, provided axle mass limits were not exceeded. However, the poorer stability performance of tandem axle trailers in comparison with their triaxle counterparts suggested that hay trucks incorporating tandem axle trailers should be limited to an overall height of 4.3 m. Regarding load restraint, it was found that there are small but worthwhile benefits to be achieved by using more effective load restraint methods such as double-strapping or “double-dogging” of single straps (one load binder on each side of the load for a single strap). After detailed consideration of the original research by industry, it became clear that some further work was required to supplement the original research by Roaduser Systems. Firstly, seeing that the previous work did not investigate load restraint in the fore-aft direction, some testing of fore-aft load restraint was conducted in accordance with the draft Load Restraint Guide [4]. Secondly, in addition to the two PBS

1

measures addressed by the previous RIRDC report [1], it was requested that three more PBS measures are included in the simulation task. These are Tracking Ability on a Straight Path (which addresses the lane width requirement of a heavy vehicle as it relates to vehicle dynamics, road crossfall and road roughness), High-Speed Transient Offtracking (which addresses the additional road width required by a combination vehicle undertaking a rapid avoidance manoeuvre) and Frontal Swing (Part B) (which addresses the additional road width required by the front corner of a trailer outside the envelope of the prime mover during a low-speed turn). These measures are described in Appendix A and Appendix B.

2

Tilt testing Methodology The Load Restraint Guide [4] defines a set of body forces to which a load restraint system needs to be designed. Figure 1 shows the load system, with components in the lateral, longitudinal and vertical directions.

Figure 1 Design body forces for a load restraint system Given that the lateral load restraint requirement has been extensively investigated [1], and assuming that the lashings are rated for carrying the additional tension brought about by the prescribed upward vertical load, the load restraint system needs to be assessed for longitudinal body forces of 0.8 g in the forward direction and 0.5 g in the aft direction. In a physical test, body forces may be applied to the restrained payload by tilting the load platform to a prescribed angle. As the tilt angle increases, so does the lateral or longitudinal body force. The body force is derived from the sine of the tilt angle, as shown in Figure 2.

Figure 2 Body forces acting on a tilt test specimen Therefore, to apply a body force of 0.5 g, the load platform needs to be tilted to an angle of 30°. It should be noted that tilting the load is an approximation of the real situation of a horizontal deck experiencing a gravitational load and an additional lateral or longitudinal load. Figure 3 shows that a 30° tilt results in an accurate representation of the 0.5 g lateral or longitudinal body force with a significantly reduced vertical force. The implication is that the available friction force between the payload and the deck is reduced in the tilt test in comparison with the real situation. Therefore the tilt test is highly conservative, as the restraints are expected to do more work in keeping the load in place.

3

Figure 3 Greater friction in real situation In evaluating the performance of a load restraint system for a 0.5 g load in the aft direction, the tilt deck simply needs to be tilted to an angle of 30°. In evaluating a load restraint system for a 0.8 g load in the forward direction, the Load Restraint Guide specifies two tilt angles, dependent upon the loading setup:

• If the load will be supported by a headboard, tilt to 30°;

• If the load will not be supported by a headboard, tilt to 53°.

Seeing that hay trailers are fitted with headboards, both the “0.8 g forward” and “0.5 g aft” tests need to achieve a tilt angle of 30°. Both tests should be done without any form of headboard restraint (ie. friction is the only source of restraint).

4

Test equipment Figure 4 shows the test equipment as it was set up in Roaduser’s workshop. The rig included the following items:

• Tilting load platform with rope rails for load binder and hand ratchet attachment;

• Accelerometer calibrated to electronically record the tilt angle;

• Potentiometer calibrated to electronically record the movement of the top of the load;

• Digital inclinometer as an additional tilt angle reading for the test operator;

• Data acquisition system for recording the accelerometer and potentiometer readings for each test; and

• Tele-handler for loading/unloading hay and tilting the load platform.

Potentiometer

Data acquisition

Accelerometer

Tele-handler

Inclinometer

Figure 4 Tilt testing equipment

5

Tests conducted Tilt tests were performed on the following loads (with reference to Figure 5), which result in an overall vehicle height of 4.6 m when loaded on a drop deck trailer:

(a) 3’x3’x8’ rectangular bales stacked four high;

(b) 4’x3’x8’ rectangular bales stacked four high;

(c) 4’x4’x8’ rectangular bales stacked three high; and

(d) 5’x4’ round bales stacked three high.

(a) (b) (c) (d)

Figure 5 Test loads Friction tests were performed to determine the friction coefficients for bales on steel checker-plate using a load cell to drag a bale and record drag force (Figure 6). The friction coefficients were found to be 0.71 (static) and 0.65 (dynamic).

Load cell

Figure 6 Friction test

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Each bale type was weighed prior to being tested, with results shown in Table 1. The round bales were found to be extremely heavy by industry standards. The 4’x4’x8’ bales were also found to be considerably above their typical mass.

Table 1 Bale weights

Bale type Industry-typical mass[kg]

Mass of specimen [kg]

Difference [%]

3’x3’x8’ rectangular 285 300 +5.3

4’x3’x8’ rectangular 550 540 -1.8

4’x4’x8’ rectangular 660 770 +16.7

5’x4’ round 330 500 +51.5

A range of tie-down methods was evaluated, including:

• single straps;

• double straps;

• belly straps; and

• diagonal straps.

The load platform was tilted until an angle of 30° was achieved, or until the bales began to lose stability or slide. Testing was generally done with the most highly restrained load first, with the amount of restraint being gradually decreased after each test.

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Test results Table 2 lists the observations of each test conducted.

Table 2 Test record

ID Tie-down method Maxtilt

Notes

3’x3’x8’ rectangular, four high

(a) Double straps, belly strap 30° OK.

(b) Double straps 30° OK. Load slipped on deck

(c) Single strap 15° Test stopped due to instability of load

4’x3’x8’ rectangular, four high

(a) Double straps, belly strap 30° OK. Very good test

(b) Double straps 30° OK. Very good test

(c) Single strap 25° Test stopped due to instability of load

4’x4’x8’ rectangular, three high

(a) Double straps, belly strap, diagonal bracing strap

30° OK. Very good test

(b) Double straps, diagonal bracing strap


(c) Single rear strap, diagonal bracing strap


(d) Double straps 22° Test stopped due to sliding of load

5’x4’ round, three high

(a) Single strap, belly strap, diagonal bracing strap


(b) Single strap, diagonal bracing strap


(c) Single strap, belly strap 15° Test stopped due to instability of load

8

The data acquisition system logged the movement of the top of each load as a function of longitudinal acceleration. Figure 7 shows some sample data, where horizontal displacement of the top of the load is plotted against longitudinal acceleration.

0

50

100

150

200

250

0 0.1 0.2 0.3 0.4 0.5 0.6

Longitudinal acceleration [g]

Disp

lace

men

t [m

m]

Residual displacement (settling)

Lowering phase

Lifting phase

Figure 7 Sample of logged data Starting at the bottom left corner, it can be seen that as the longitudinal acceleration increases, the displacement increases. The rate of displacement also increases at higher acceleration levels (ie. at higher tilt angles). At 0.5 g (ie. 30°), the deck is brought back to level. The displacement does not return back to zero, due to some residual movement in the bales. The residual displacement tended to be greatest after the first tilt for each load, due to settling of the bales. After that, each test only showed a small amount of residual displacement. Therefore, the maximum displacement obtained for the first test in each series is considered to be unrealistic, as it does not account for settling of the bales during transport. Figure 8 to Figure 11 show plots of displacement versus longitudinal acceleration for each of the tests listed in Table 2.

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3'x3'x8' bales stacked four high

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6

Longitudinal Acceleration (g)

Dis

plac

emen

t (m

m)

(a)(b)(c)

Figure 8 3’x3’x8’ bale results

4'x3'x8' bales stacked four high

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6


Dis

plac

emen

t (m

m)

(a)(b)(c)

Instability

Slip Instability


10

4'x4'x8' bales stacked three high

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6


Dis

plac

emen

t (m

m)

(a)(b)(c)(d)

Sliding


5'x4' round bales stacked three high

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6


Dis

plac

emen

t (m

m)

(a)(b)(c)

Instability

Figure 11 5’x4’ round bale results

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Discussion of results The tilt tests proved that all four bale types satisfy fore and aft load restraint requirements when stacked to 4.6 m high on a drop deck trailer. In all cases compliance was demonstrated with a reduced level of restraint. This is particularly encouraging because the tests were carried out under conservative conditions, such as bales being heavier than typical industry weights and the tilt deck having a low-friction surface. As described in “Methodology”, the act of tilting a load reduces the available friction considerably. Figure 8 shows that the performance of the load of 3’x3’x8’ bales was clearly reduced each time the level of restraint was reduced. This is in agreement with the general test observations in Table 2. Although the first two tests demonstrated compliance, the amount of displacement recorded for the 3’x3’x8’ bales is considered to be quite high. Figure 9 shows that the 4’x3’x8’ bales performed exceptionally well in all tests, with the final test bringing the load close to instability. Displacement was small in all tests, with compliance demonstrated in the first two tests. Figure 10 shows that performance of the 4’x4’x8’ bales was almost identical in the first three tests, apart from the settling of the load seen during the lifting phase of the first test (the lowering phase was almost identical in the first three tests). The final test, which had the least amount of load restraint, was observed to be sliding at around 0.4 g. Compliance was easily demonstrated in the first three tests, where a diagonal bracing strap was in place. Figure 11 shows that performance of the 5’x4’ round bales was severely reduced by the removal of the diagonal bracing strap. Compliance was demonstrated in both cases using the diagonal bracing strap. It is concluded that the restraint methods demonstrating compliance in these tilt tests are suitable for the transport of bales to 4.6 m high on drop deck trailers. Diagonal bracing straps in particular proved to be very effective. It is strongly recommended that diagonal bracing is considered for at least the front and rear groups of bales on a trailer. Unlike the lateral stability tests, the movement of the load in the fore-aft direction is less important, provided the load remains stable, because load movement up to 300 mm does not significantly affect braking performance. The braking performance of a vehicle would only be significantly affected if the axle load distribution was significantly affected. Load movement up to 300 mm (150 mm at the centre-of-gravity) represents a centre-of-gravity shift of approximately 1.5% of the trailer wheelbase, meaning that the effect on load distribution is very small. In the case of lateral load shift, a generally-accepted lateral movement of 100 mm (50 mm at the centre-of-gravity) represents a centre-of-gravity shift of approximately 3% of the axle track width. Therefore the fore-aft movement of a load is not considered to be a significant factor in the stability equation.

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Simulation modelling Additional performance measures The computer simulation models used in the previous study [1] were exercised in a further set of manoeuvres to evaluate their performance in some additional PBS measures. Previously evaluated PBS measures include:

• Static Rollover Threshold (the ultimate lateral g-forces that can be supported by the vehicle and its load; and

• Low-speed offtracking (the amount of road space required to undertake a tight, low-speed turn).

Additional measures evaluated in the study include:

• Tracking Ability on a Straight Path (a measure of the high-speed swept width of a vehicle, evaluated in a simulation of straight line travel on a road with prescribed cross-fall and roughness);

• High-Speed Transient Offtracking (a measure of the additional road width required when performing a prescribed evasive manoeuvre); and

• Frontal Swing (Part B) (a measure of trailer frontal outswing that is evaluated from the existing low-speed turn simulations).

Figure 12 Front Swing (Part B)

These measures are described in more detail in Appendix A and Appendix B. Tracking Ability on a Straight Path is a standard that has been revised by the National Transport Commission since the original simulation work was conducted in June 2003. The required performance levels have been made more stringent, which means that the standard is now difficult for wide loads to satisfy. This standard is evaluated for all vehicles, taking into account the lateral movement of hay adding to the overall swept width.

Path of front corner of trailer/load

Path of front corner of prime mover

Trailer/load protrudes beyond path of prime mover Frontal Swing

(Part B)

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High-Speed Transient Offtracking was originally not evaluated because it is not affected by load width. However, it has been suggested that the relationship between HSTO and road width needs to be determined. Frontal Swing of the first trailer in a semi-trailer or B-double combination is normally not a safety issue. However, when a trailer is carrying a wide load of hay, the outswing of the front corner of the trailer during a low-speed turn will be more pronounced with respect to the outswing of the front corner of the prime mover. The Frontal Swing (Part B) measure provides a means of evaluating vehicles in this regard.

Restraint methods Performance results for TASP and HSTO have been evaluated for the various restraint methods. Restraint method is indicated in the results tables using the following number system: Restraint 1 Single strap

A single strap hooked on to the rope rail on one side of the deck, passed over the load and tightened on the other side by a rope rail winch. This is considered to be the minimum practical amount of restraint. In all cases the load was applied on the side of the stack opposite the rope rail winch (ie. “lifting” the side with the least strap tension), so that a worst case was assessed.

Restraint 2 Single strap “double-dogged”

Same as Restraint 1 but with a hand ratchet inserted on the side opposite the rope rail winch and tightened after the rope rail winch was tightened. This method ensured high tension on both sides of the load, while Restraint 1 could only guarantee high tension on the winch side due to friction effects from the strap rubbing against the load. This could also have been achieved with two hand ratchets and a plain strap, rather than a rope rail winch and one hand ratchet.

Restraint 3 Double straps

Same as Restraint 1 but with two straps per block of bales. This method was not employed for round bales.

Restraint 4 Belly strap

Same as Restraint 3 but with an additional “belly” strap that passed over the lower half of the load. The belly strap needed to be fitted during the loading of the hay, before the upper bales were loaded. This method was only employed on the higher drop deck loads.

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Stacking arrangements Figure 13 shows the various stacking arrangements assessed in [1] and revisited in this study. The letter codes relate to the performance results listed afterwards.

3’x3’x8’ 4’x3’x8’ 4’x4’x8’ 5’x4’

Figure 13 Stacking arrangements

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Performance results Performance results for the three additional measures are shown in Table 3, Table 4 and Table 5. Table 3 shows that the lane width requirement given by TASP is satisfied in all cases except for round bales at 3 metres wide (H/J). Load restraint method has virtually no effect.

Table 3 Tracking Ability on a Straight Path

B-double 24’ flat top + 45’ drop deck

Prime mover / semi-trailer 48’ drop deck


Prime mover / semi-trailer 45’ flat top


PBS Limit: 3.0 m 2.9 m 2.9 m 2.9 m 2.9 m

A/B

1 – 2.78 m 2 – 2.77 m 3 – 2.78 m 4 – 2.78 m

1 – 2.76 m 2 – 2.76 m 3 – 2.77 m 4 – 2.77 m

1 – 2.76 m 2 – 2.75 m 3 – 2.76 m 4 – 2.76 m

N/A N/A

C/E

1 – 2.73 m 2 – 2.73 m 3 – 2.73 m 4 – 2.73 m

1 – 2.72 m 2 – 2.71 m 3 – 2.72 m 4 – 2.72 m

1 – 2.71 m 2 – 2.71 m 3 – 2.71 m 4 – 2.71 m

N/A N/A

F/G

1 – 2.89 m 2 – 2.89 m 3 – 2.89 m 4 – 2.89 m

1 – 2.89 m 2 – 2.88 m 3 – 2.88 m 4 – 2.88 m

1 – 2.88 m 2 – 2.77 m 3 – 2.77 m 4 – 2.77 m

N/A N/A

H/J 1 – 3.18 m 2 – 3.18 m 4 – 3.18 m

1 – 3.20 m 2 – 3.20 m 4 – 3.20 m

1 – 3.16 m 2 – 3.15 m 4 – 3.16 m

N/A N/A

A N/A N/A N/A 1 – 2.73 m 2 – 2.72 m 3 – 2.72 m

1 – 2.76 m 2 – 2.76 m 3 – 2.76 m

C N/A N/A N/A 1 – 2.68 m 2 – 2.67 m 3 – 2.68 m

1 – 2.71 m 2 – 2.71 m 3 – 2.71 m

D N/A N/A N/A 1 – 2.70 m 2 – 2.70 m 3 – 2.71 m

1 – 2.74 m 2 – 2.74 m 3 – 2.74 m

F N/A N/A N/A 1 – 2.83 m 2 – 2.83 m 3 – 2.82 m

1 – 2.87 m 2 – 2.87 m 3 – 2.87 m

H N/A N/A N/A 1 – 3.14 m 2 – 3.14 m

1 – 3.16 m 2 – 3.16 m

K N/A N/A N/A 1 – 2.61 m 2 – 2.61 m

1 – 2.63 m 2 – 2.63 m

16

Table 4 shows that all vehicles easily satisfy HSTO requirements, with excellent performance across the board.

Table 4 High-Speed Transient Offtracking






PBS Limit: 0.8 m 0.6 m 0.6 m 0.6 m 0.6 m

A/B

1 – 0.21 m 2 – 0.21 m 3 – 0.21 m 4 – 0.20 m

1 – 0.19 m 2 – 0.18 m 3 – 0.18 m 4 – 0.18 m

1 – 0.17 m 2 – 0.16 m 3 – 0.17 m 4 – 0.17 m

N/A N/A

C/E

1 – 0.23 m 2 – 0.22 m 3 – 0.23 m 4 – 0.23 m

1 – 0.22 m 2 – 0.21 m 3 – 0.21 m 4 – 0.21 m

1 – 0.20 m 2 – 0.19 m 3 – 0.19 m 4 – 0.19 m

N/A N/A

F/G

1 – 0.25 m 2 – 0.25 m 3 – 0.24 m 4 – 0.24 m

1 – 0.25 m 2 – 0.25 m 3 – 0.24 m 4 – 0.24 m

1 – 0.23 m 2 – 0.22 m 3 – 0.22 m 4 – 0.22 m

N/A N/A

H/J 1 – 0.17 m 2 – 0.14 m 4 – 0.15 m

1 – 0.16 m 2 – 0.14 m 4 – 0.14 m

1 – 0.14 m 2 – 0.12 m 4 – 0.12 m

N/A N/A

A N/A N/A N/A 1 – 0.13 m 2 – 0.12 m 3 – 0.12 m

1 – 0.25 m 2 – 0.24 m 3 – 0.24 m

C N/A N/A N/A 1 – 0.14 m 2 – 0.13 m 3 – 0.13 m

1 – 0.27 m 2 – 0.26 m 3 – 0.28 m

D N/A N/A N/A 1 – 0.20 m 2 – 0.20 m 3 – 0.20 m

1 – 0.35 m 2 – 0.35 m 3 – 0.35 m

F N/A N/A N/A 1 – 0.14 m 2 – 0.14 m 3 – 0.13 m

1 – 0.26 m 2 – 0.26 m 3 – 0.26 m

H N/A N/A N/A 1 – 0.09 m 2 – 0.08 m

1 – 0.19 m 2 – 0.19 m

K N/A N/A N/A 1 – 0.09 m 2 – 0.09 m

1 – 0.18 m 2 – 0.17 m

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Table 5 shows that round bales at 3 metres wide (H/J) clearly do not meet the PBS requirement for Frontal Swing (Part B). Square bales satisfy the requirement, with loads of 2.7 metres wide (F/G) demonstrating borderline performance.

Table 5 Frontal Swing (Part B)






PBS Limit: 0.4 m 0.4 m 0.4 m 0.4 m 0.4 m

A/B 0.35 m 0.37 m 0.37 m N/A N/A

C/E 0.32 m 0.34 m 0.34 m N/A N/A

F/G 0.38 m 0.42 m 0.41 m N/A N/A

H/J 0.54 m 0.55 m 0.56 m N/A N/A

A N/A N/A N/A 0.37 m 0.21 m

C N/A N/A N/A 0.33 m 0.19 m

D N/A N/A N/A 0.41 m 0.27 m

F N/A N/A N/A 0.40 m 0.27 m

H N/A N/A N/A 0.54 m 0.42 m

K N/A N/A N/A 0.31 m 0.16 m

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Conclusion Tilt testing The tilt testing program demonstrated that compliance with the requirements of the Load Restraint Guide [4] is possible for all four of the tested bale types when stacked to 4.6 metres high on a drop deck trailer. This includes 4’x4’x8’ rectangular bales at 2.7 metres wide and 5’x4’ round bales at 3 metres wide. In all cases, the level of load restraint was gradually reduced with each successive test. It was found that, for each bale type, compliance was demonstrated with a reduced level of restraint. Each bale type was tested with continually decreasing restraint until instability caused the test to be stopped. Of particular importance was the finding that all loads could satisfy load restraint guide requirements for rearward body load (0.5 g) without the use of rear gates. This is a major finding that implies enormous benefits for the hay and straw cartage industries. Also of significance is the fact that all of the 4’x4’x8’ bale tests were carried out with bales weighed to be almost 17% heavier than typical. This implies that actual performance on-the-road is likely to be much improved above that demonstrated in these tests. It was found that the use of a diagonal bracing strap provided an enormous improvement to load stability. It is strongly recommended that diagonal bracing is considered for at least the front and rear groups of bales on a trailer, with the bracing pulling towards the centre of the trailer. A reduced level of restraint is appropriate for centrally-mounted bales, provided the restraint of the end groups of bales is sufficient to withstand any possible load transfer from the centre bales. Alternatively, diagonally bracing all groups of bales is acceptable. Figure 14 demonstrates examples of these recommendations.

Figure 14 Diagonal bracing recommendations

Simulation modelling The simulation modelling demonstrated that all of the rectangular bale types could be considered to be acceptable on PBS grounds, while round bales stacked to 3 metres wide are too wide to satisfy PBS TASP. Round bales could be justified by stacking “on rounds” with the flat sides facing out. This would produce an overall width of 2.5 metres, but would degrade productivity and load stability considerably. The study of the lateral behaviour of this configuration (K) in [1] highlighted this configuration as a poor-performer.

19

References [1] Di Cristoforo, R. & Sweatman, P.F., Testing and simulation of hay bale loading on semi-trailers,

Rural Industries Research and Development Corporation, Publication No. 03/120, October 2003.

[2] National Road Transport Commission, PBS Safety Standards for Heavy Vehicles, January 2003.

[3] National Road Transport Commission, PBS Infrastructure Protection Standards for Heavy Vehicles, January 2003.

[4] National Road Transport Commission & Roads and Traffic Authority New South Wales, Load restraint guide: Guidelines and performance standards for the safe carriage of loads on road vehicles, Draft version 2.5, January 2002.

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Appendix A Performance-Based Standards (PBS) This appendix lists the performance standards that vehicles need to comply with under the proposed PBS system. Each standard addresses some aspect of vehicle performance in terms of safety (of vehicle drivers, other road users and pedestrians) or protection of infrastructure (pavements and bridges). For each standard, a performance measure is used to evaluate a vehicle’s performance in that standard by providing a numerical value that can be attributed to the level of performance exhibited by the vehicle. This performance is compared against the required performance level to ascertain whether the vehicle meets (or fails to meet) the standard. Table 6 lists each standard along with its associated measures. For each measure, the required performance level is shown. In most cases the required performance level is dependent upon the road network on which the vehicle will be operating.

Table 6 PBS standards, measures and levels [2], [3]

Performance level by road classification Performance standard

Performance measure

Level 1 Level 2 Level 3 Level 4

Longitudinal performance (low speed)

Startability Ability to commence forward motion on specified grade.

15% 12% 10% 5%

Low speed environment: Ability to maintain forward motion on specified grade.

20% 15% 12% 8% Gradeability

High speed environment: Minimum speed on 1% grade.

80 km/h 70 km/h 70 km/h 60 km/h

Acceleration capability Ability to accelerate either from rest or to increase speed (no grade).

As shown in Fig. 2(a) of [2].

Longitudinal performance (high speed)

Overtaking Provision Time taken for a passenger car to safely overtake the subject PBS vehicle to be no greater than can be accommodated by overtaking opportunities provided by the road at the specified traffic flow level of service (LoS)

LoS C LoS C LoS B LoS B

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Performance measure


Tracking ability on a Straight Path

The total swept width while travelling on a straight path, including the influence of variations due to road crossfall, road surface unevenness and driver steering activity.

2.9 m 3.0 m 3.1 m 3.3 m

Directional Performance (low speed)

Low speed swept path Maximum width of swept path in a 90° low speed turn.

7.4 m 8.7 m 10.1m 13.7m

Frontal Swing The maximum lateral displacement between the path of the front outside corner of the vehicle (or vehicle unit) and (a) the outer edge of the front-outside wheel of the hauling unit; or (b) the outside part of a semi-trailer or trailer during a small-radius turn manoeuvre at low speed.

0.70 m maximum for part (a) 0.40 m maximum for part (b)

Trailer value not to exceed prime mover value by more than 0.20 m.

Tail Swing The maximum lateral distance that the outer rearmost point on a vehicle moves outwards, perpendicular to its initial and final orientation, when the vehicle commences and completes a small-radius turn at low speed.

0.30 m 0.35 m 0.35 m 0.50 m

Steer Tyre Friction Demand

The maximum friction level demanded of the steer tyres of the hauling unit in a tight-radius turn at low speed.

Not more than 80% of the maximum available for all road types.

Directional performance (high speed)

Static Rollover Threshold

The steady-state level of lateral acceleration that a vehicle can sustain during turning without rolling over.

Road tankers hauling dangerous goods, and buses – 0.40g for all road types.

All other vehicles – 0.35g for all road types.

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Performance measure


Rearward Amplification

Degree to which the trailing unit(s) amplify or exaggerate lateral motions of the hauling unit.

No greater than 5.7 times the static rollover threshold of the rearmost roll–coupled unit.

High Speed Transient Offtracking

The lateral distance that the last axle on the rear trailer tracks outside the path of the steer axle in a sudden evasive manoeuvre.

0.6 m 0.8 m 1.0 m 1.2 m

Yaw Damping Coefficient

The rate at which ‘sway’ or yaw oscillations of the rearmost trailer decay after a short duration steer input at the hauling unit.

Not less than 0.15 at the certified maximum speed for all road types.

Directional Stability Under Braking

The ability to maintain stability under braking.

(a) A vehicle must not exhibit any wheel lock when it is braked at a deceleration rate of 0.45 g from an initial speed of 60 km/h on a high friction pavement in both the laden and unladen states (momentary wheel lock associated with ABS brake modulation is acceptable).

(b) A vehicle must meet the stopping distance performance levels in the relevant versions of ADRs 35 and 38 (as applicable).

(c) Auxiliary brakes (if fitted) must not apply automatically if the computed friction utilisation at any wheel can exceed 0.1 when the vehicle is braked from a road speed corresponding to three quarters (3/4) governed engine speed (unless the motive vehicle has an acceptable ABS).

Infrastructure (pavements)

Pavement Vertical Loading

The degree to which vertical forces are applied to the pavement.

(a) The Average Road Wear per Axle Group (SARs/AG) shall not exceed the level calculated for a vehicle with the same number of rigid parts and the same number of axles on each rigid part as is permitted by prescriptive (or equivalent) regulations.

(b) All axles on each rigid part of a vehicle (apart from the steering axles of a motor vehicle) must be joined by a load sharing suspension system (for the purposes of this standard, the drawbar of a dog trailer is considered a separate rigid part).

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Performance measure


Pavement Horizontal Loading

The degree to which horizontal forces are applied to the pavement.

(a) Steerable axles

(i) at least one axle of any two axles joined by a load sharing suspension system and greater than 2.0 metres apart must be steerable.

(ii) with all other groups of axles joined by a load sharing suspension system with a spread of greater than 3.05 metres, all axles beyond the 3.05 metre spread must be steerable.

(b) Driving axles

(i) the maximum gross mass of a vehicle with either one or two driving axles are detailed.

(ii) all driving axles must distribute tractive forces equally between the axles within ± 10% of the proportion of the tractive force delivered by the driving axle.

Bridge Loading Maximum effect relative to reference vehicle

Bending moments and shear forces not to exceed those of the reference ABAG vehicles.

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Appendix B Evaluation of performance measures This appendix describes the methods used to evaluate the various PBS performance measures for a vehicle.

B.1 Longitudinal performance (low speed)

B.1.1 Startability Startability is defined as the maximum uphill gradient, expressed as a percentage, on which a vehicle is capable of starting forward movement from rest. Startability is calculated using the following basic formula:

GCMMRTeη064.0

(%)tyStartabili =

where: M = number of tyre revolutions per kilometre (m-1) R = overall gear reduction between the engine and drive wheels (-) Te = clutch engagement torque (Nm) η = combined efficiency of transmission and final drive (-) GCM = gross combination mass (or gross vehicle mass) (kg)

B.1.2 Gradeability Gradeability is defined as the maximum uphill gradient, expressed as a percentage, on which a vehicle can climb at a specified constant speed. Gradeability is applicable to all heavy vehicle operations – in urban, rural/regional and remote areas – and to all classes of heavy vehicles. In addition to safety considerations and concerns, gradeability also influences vehicle productivity, route selection and access. In addition to being capable of starting from rest on the steepest grade encountered on the route, heavy vehicles when fully laden should be able to maintain a reasonable speed on gradients. This is desirable in order to minimise traffic congestion or delays to other vehicles travelling in the same direction. A vehicle’s gradeability is dependent on the specifications of its driveline (engine torque and gear ratios), tyre rolling resistance, aerodynamic drag, and gross combination mass. Figure 15 shows the major forces acting on a vehicle that is travelling up a grade.

Figure 15 Forces acting on a vehicle driving up a grade

25

Gradeability is determined using Roaduser’s longitudinal performance simulation model which includes: • Driveline characteristics

• Tyre rolling resistance

• Aerodynamic drag

• Road grade

• Vehicle rotation inertia (tyres, rims and driveline)

B.1.3 Acceleration capability Acceleration capability is determined using Roaduser’s RATED longitudinal performance models. To determine a vehicle’s acceleration performance, the distance-time performance is compared with the baseline distance-time curves which depend upon the road environment in which the vehicle is operating.

B.2 Longitudinal performance (high speed)

B.2.1 Overtaking provision As described in Appendix A of [2][2].

B.2.2 Tracking ability on a straight path When a combination vehicle is travelling at highway speed, the rear unit of the combination tends to exhibit more lateral movement than the hauling unit. This may be caused by external disturbances such as road roughness, changes in crossfall, wind effects, etc. The total excursion of the rear unit is sometimes called the swept width of the vehicle. Swept width is evaluated by measuring the rear trailer’s lateral motion in relation to the front of the vehicle when travelling at 90 km/h on an “isotropic” road surface with IRI roughness of approximately 4.0 m/km and average crossfall of 4%. The isotropic road surface is a mathematically-generated 3D surface with randomly generated roughness. From this manoeuvre it is possible to determine the 95th percentile value of the rear trailer’s lateral motion relative to the path taken by the vehicle. The 95th percentile lateral motion, when added to the vehicle’s width, indicates the amount of road space that is required to accommodate the vehicle while travelling in a straight line.

Figure 16 Tracking ability on a straight path

26

B.3 Directional performance (low speed)

B.3.1 Low speed swept path Low speed swept path performance is assessed by measuring the total swept width when performing an 11.25 metre radius 90° turn at a speed not exceeding 5 km/h. The radius of the turn is measured to the centre of the steering axle. Low speed swept path is calculated as shown in Figure 17, and indicates the lateral road space requirement when turning.

Low speed swept path

Figure 17 Low speed swept path manoeuvre

B.3.2 Frontal swing The maximum lateral displacement between the path of the front outside corner of the vehicle (or vehicle unit) and the outer front edge of the front outside steered wheel of the hauling unit during a small radius turn at low speed. This measure is evaluated for Part (a) as shown in Figure 18 while undertaking the low speed offtracking manoeuvre shown in Figure 17.

Figure 18 Frontal swing

27

Part (b) of the Frontal Swing measure is determined by measuring the maximum distance that the front corner of any trailing unit protrudes past the path taken by the front corner of the hauling unit.

B.3.3 Tail swing The maximum lateral distance that the outer rearmost point on a vehicle moves outwards, perpendicular to its initial or final orientation, when the vehicle commences a small radius turn at low speed. This measure is evaluated as shown in Figure 19 while undertaking the low speed offtracking manoeuvre shown in Figure 17.

Figure 19 Tail swing

B.3.4 Steer tyre friction demand In low speed turns, such as at intersections, the tyres on certain axles may be required to generate sufficiently high lateral forces that loss of adhesion could occur on slippery surfaces. The friction demand of the steer axle tyres is considered to be the most critical parameter under low speed conditions. If saturation occurs, the vehicle may plough straight ahead and fail to negotiate the turn. This is particularly important on low friction surfaces. This measure is calculated by the following expression:

100(%)DemandFriction ×=PEAK

Z

YF

F

µ

where: FY = lateral tyre force (cornering force) (N) FZ = vertical tyre force (N) µPEAK = peak tyre/road friction coefficient This measure is evaluated in the low speed offtracking manoeuvre shown in Figure 17.

B.4 Directional performance (high speed)

B.4.1 Static rollover threshold Static rollover threshold is the amount of the lateral acceleration required to produce total rollover of a vehicle or roll-coupled unit, and is given as a proportion of gravitational acceleration (g).

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Total rollover occurs when all the wheels on one side of the vehicle (or roll-coupled unit) lift off the road surface. This situation is illustrated in Figure 20. Rollover occurs when the lateral acceleration equals or exceeds the vehicle's rollover limit (which may be assisted by roadway crossfall or camber). Lateral acceleration on a curve is highly sensitive to speed, and the speed required to produce rollover reduces as the curve radius reduces.

Figure 20 Lateral acceleration while turning, showing wheel lift-off Static Rollover Threshold is calculated by simulating the vehicle negotiating a 100m radius turn at gradually increasing speed until rollover occurs. The SRT for each roll-coupled unit is determined by recording the maximum trailer lateral acceleration obtained during the manoeuvre. For vehicles featuring more than one trailer in a roll-coupled unit, the maximum value is recorded.

B.4.2 Rearward amplification When multi-articulated vehicles undergo rapid steering, the steering effect at the rear trailer is magnified, and this results in increased side force, or lateral acceleration, acting on the rear trailer. This in turn increases the likelihood of the rear trailer rolling over under some circumstances. Rearward amplification is defined as the ratio of the lateral acceleration at the COG of the rearmost unit to that at the steer axle in a dynamic manoeuvre of a particular frequency. Steering from side to side produces more lateral movement at the rear unit than at the hauling unit, as illustrated in Figure 21. Rearward amplification expresses the tendency of the vehicle combination to develop higher lateral accelerations in the rear unit when undergoing avoidance manoeuvres. It is therefore an important consideration, in addition to roll stability of the rear unit, in evaluating total dynamic stability.

steer ingw heel angle

vs. t ime

lateral accelerationat tractor COG

vs. t ime

lateral accelerationat rear trai ler COG

vs. time

aA

RA = A / a

Figure 21 Rearward amplification of lateral acceleration

29

For combinations having two or more roll-coupled trailers in the rearmost roll-coupled unit, an instantaneous averaging process is used to determine the equivalent overall lateral acceleration on the roll-coupled unit for determining rearward amplification. Rearward amplification is computed in the standard SAE J2179 lane change manoeuvre.

B.4.3 High speed transient offtracking High speed transient offtracking is a measure of the lateral excursion of the rear of the vehicle with reference to the path taken by the front of the vehicle during a dynamic manoeuvre. This expresses the amount of additional road space used by the vehicle combination in an avoidance manoeuvre. This measure is computed in the standard SAE J2179 lane change manoeuvre.

B.4.4 Yaw damping coefficient Yaw damping is defined as the rate at which ‘sway’ or yaw oscillations of the rearmost trailer decay after a short duration steer input at the hauling unit. To evaluate this measure a vehicle is simulated at a speed of 90 km/h in a straight line and then a pulse of steering input is applied. This pulse is a half sine wave that produces a peak angle at the steering road wheel of 3.2° over a time interval of 0.1 seconds. The resultant vehicle body motions are then measured to estimate the yaw damping response, which is given by the following expression:

22)2(YDC

δπ

δ

+=

In this expression, δ is the standard logarithmic decrement given by:

⎟⎟⎠

⎞⎜⎜⎝

⎛=

2

1lnAA

δ

where: A1 = amplitude of the first peak in the response A2 = amplitude of the second peak in the response

30

B.5 Infrastructure

B.5.1 Pavement vertical loading As a vehicle travels over the road an amount of road wear occurs which is dependent upon the mass of the vehicle and the number of axles on the vehicle. Each axle group can be seen as producing the same amount of damage as a certain number of standard axle repetitions, or SARs. The SAR value for a single group is computed using a twelfth power law according to the following formula:

12

LoadAxleStandardLoadGroupSAR ⎟⎟

⎠

⎞⎜⎜⎝

⎛=

The standard axle load varies according to the number of axles and or tyres per axle in a group. Table 7 shows applicable standard axle loads for various axle groups.

Table 7 Standard axle loads

Axle group Standard axle load (t)

Single axle / single tyres 5.40

Single axle / dual tyres 8.20

Tandem axle / single tyres 9.18

Tandem axle / dual tyres 13.80

Triaxle / dual tyres 18.50

Quad axle / dual tyres 22.50

The SARs/AG measure is computed as the summation of SARs for the total vehicle divided by the number of axle groups.

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Further testing and simulation of hay bale loading on semi ... · simulation of hay bale loading on semi-trailers A report for the Rural Industries Research and Development Corporation