THE STRESS OF LASHING POINTS IN FULL- LOADED 3,5-TONNE VAN DURING EMERGENCY BRAKING Ján ZÁMEČNÍK, Juraj JAGELČÁK 1 Introduction and description of the tests During the emergency the forces occuring on the vehicle and therefore on loaded cargo and lashing points used for its fixation markedly increase. The acceleration occures mainly in the ride direction. For determination of influence of these forces on the stress of lashing points in full-loaded van, there were realized the tests on 21 st October 214 at Rosina airport (fig. 1). There was used a van type L3H3, parametres of which are stated in the table 1. The certificated strenght of van`s lashing points is 5 dan. Parameter Vehicle lenght Vehicle width Vehicle height Service weight Tab. 1 Parametres of vehicle, on which were the tests realized Maximum total weight in road traffic Real weight during the tests Weight of secured cargo Front axle load Rear axle load Vehicle floor Tyres on vehicle Hodnota 6 35 mm 2 59 mm 2 786 mm 2 178 kg 3 5 kg 3 5 kg 1 3 kg 1 85 kg 1 65 kg plastic Michelin Agilis 235/65R16C The vehicle was loaded by 12 drums laden with rubble, each weighting cca 1 kgs. The drums were on two pallets, 6 drums on each of them. In the first tests series the pallets with drums were purposely seated on slippy surface created from 2 plywoods laid the slippy side to each another. Dynamic friction coefficient of this surface is,28. The second test series were done with the pallets on rubber anti-skid pads. However, the plastic floor of tested vehicle does not allow so good anti-skid -136-
characteristics of these pads like when they are used on some other surfaces and we measured dynamic friction coefficient,36 between it and anti-skid pads. In each of the test series were realized tests from various initial speed including tests on rearward driving vehicle. There were realized total 39 tests, therefrom the tests no. 1 to 2 in the first series and no. 21 39 in the second series. The tests were done on dry asphalt surface with light degression about,7 %. The temperature was from 16 C at the beginning to 12 C at the end of testing with air humidity from 55 % with the higher temperature to 75 % after its descent. Fig. 1 Place, where were realized the tests Source: http://www.freemap.sk/ The cargo was secured by front lashing by two lashing straps, in addition six drums on each of pallets were lashed together with lashing strap. For lashing stabilization there was either on front and rear side of cargo added a pallet. The lashing straps were fastened through these pallets with using of metal corner plates. The forces in lashing points were measured in 4 places (fig. 2). Force F1 was measured in the front on the left, F2 in the front on the right, F3 in the rear on the left and F4 in the rear on the right. The forces were recorded with frequency 5 Hz, only during tests no. 32 to 39 were recorded with frequency 1 Hz. In addition there was used equipment VDSU of Žilinská univerzita in Žilina, which provided data from GPS, data about accelerations in axes x, y and z and data about pitch, roll and yaw from two measuring probes. One of them was placed on the vehicle`s bodyshell, another of them on the cargo. There was used also equipment XL-meter of Žilinská univerzita in Žilina, which provided data about time, distance, initial -137-
speed of and the mean fully developed deceleration (MFDD). Data from both equipment were provided with frequency 2 Hz. Fig. 2 The way of cargo securing of 12 drums on 2 pallets by front lashing with two lashing straps (on the left figure red) and tying 6 drums together on each of pallets (on the left figure green) 2 Measurements of lashing points stress during the the vehicle driving in front direction These measurements were done with from various initial speed in ranges 15 2 km/h, 35 4 km/h, 55 6 km/h, 65 7 km/h and 8 9 km/h. In each of them there were realized 3, resp. 4 tests in first series (when the cargo was on slippy surface) and next 3, resp. 4 tests in second series (with cargo on anti-skid pads). According to norms EN 12195-1:21 and EN 12642 should the maximum value of deceleration occuring on cargo during 8 ms reach at least,8 g. In our measurements was this value from,74 g to 1,4 g, whereas the average maximum value was 1,4 g in measure series on slippy surface and 1,14 g in measures on antskid tapes. In most cases were measured the values near these average values. The mean fully developed deceleration (MFDD) reached in average,79 g when the cargo was laid on plywoods and,88 g in case of using anti-skid pads. When the front-driving vehicle brakes, the cargo tends to move forward, which causes in front lashing used in our tests increasing of forces in rear lashing points. So, the biggest values reached the forces F3 and F4. The forces in rear lashing points markedly increased during the whilst forces in opposite lashing points on the -138-
front side decreased almost to zero. The period, during which lasted this stress of rear lashing points, was about,2,35 s shorter than time. The difference between time and duration of maximal forces in lashing points is the time of force inclination. After the finished the lashed cargo tended to move backwards which caused releasing the forces F3 and F4 in rear lashing points and growing the forces F1 and F2 in front lashing points. These forces occured during about,5 s, the peak values of them about,25 s. Fig. 3 Run of the forces during test no. 1 with slippy plywood surface under cargo (up) and run of accelerations in axes x and z during this test (down) Acceleration [m/ ] 15 1 5-5,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6-1 -15 Time [s] acc x acc z -139-
Fig. 4 Run of the forces during test no. 36 with anti-skid pads under cargo (up) and run of accelerations in axes x and z during this test (down) Force 8 7 6 5 4 3 2 1 1 2 3 4 5 6 Time [s] F1 F2 F3 F4 Acceleration [m/ ] 15 1 5,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5 6-5 -1-15 Time [s] acc x acc z The main differences in run of forces during between measurements with plywoods and anti-skid pads were: -14- in most cases with using slippy plywoods arised short-term, but relatively high peak forces at the beginning of their occuring. These peak forces lasted about,2 s (pic. 3) and in most cases of from 5 (or more) km/h reached more than 7 dan. The highest reached peak force F3 was 783 dan and F4 789 dan, both during test no. 15 from initial speed 86,9 km/h. These peak forces decreased in tests with using anti-skid pads; in consequence of sliding the plywoods one on another arose the cargo movement sideward, which caused the differences between F3 and F4 in some cases; after the vehicle stopped, there arose stronger reaction on the opposite side where grew the forces F1 and F2. This reactions were much stronger when the slippy plywood surface was used under cargo.
An example of typical run of forces in lashing points during the test when there are slippy plywoods under cargo is on the figure 3. On the figure 4 is an example of run of forces in lashing points in case that anti-skid pads were used. These differences are also visible in table 2, where there are stated average and maximum forces reached during the tests, averaged from all the tests with slippy surface, resp. all the tests with using anti-skid pads. Tab. 2 Differences in forces reached in lashing points between using slippy plywood surface and anti-skid pads Maximum forces reached in lashing points during front tests F1 F2 F3 F4 Slippy surface - plywoods 175 212 69 614 Anti-skid pads 85 14 543 547 Average forces reached in lashing points during front tests (excepting force inclination) Slippy surface - plywoods 3 7 54 58 Anti-skid pads 4 5 49 493 When the anti-skid pads were used, the stress in front lashing points by forces F1 and F2 decreased by more than 5 %, peaks of forces F3 and F4 decreased by 12 %. Increasing of friction although had not substantial effect on average forces straining on lashing points during whole. The results of tests from particular initial speed ranges are stated in tables 3 and 4. There are stated average values from tests belonging to particular ranges of initial speed. Maximum force was reached in rear lashing points (F3 and F4) mostly at the beginning of, in front lashing points (F1 and F2) after the vehicle stopped. Data about average force in lashing points during do not contain forces recorded during force inclination and forces generated after vehicle stopped. Short-term occuring peak forces are included in these data (fig. 3). The forces reached in tests from initial speed upon 5 km/h on slippy plywoods did not increased with further increasing of speed. When the anti-skid pads were used, the forces grew with speed increasing to 65 km/h. With increasing speed increased time and therefore also duration of high forces straining the lashing points. Duration of high forces was always shorter by about,3 s than duration of. When there were used plywoods with low friction coefficient, the cargo subsequently moved sideward, which caused the differences between F3 and F4. -141-
Tab. 3 Influence of front from particular initial speed on forces reached in lashing points during tests with slippy surface (plywoods) under cargo Initial speed [km/h] Braking tests Braking time [s] MFDD [g] Maximum deceleration in axis x [g] Maximum force reached in lashing points Average force straining the lashing points during Duration of straining force during [s] 15-2 1,3 1,89 -,68 -,88 74 176 347 431 5 25 323 397,6 35-4 4,5,6 1,43 -,8 -,92 175 234 56 58 3 3 471 468 1,11 55-6 7,8,9 1,99 -,83-1,9 213 235 716 715 2 1 591 577 1,71 65-7 1,11,12 2,53 -,84-1,12 179 164 774 713 1 572 532 2,14 8-9 13,14,15,16 2,92 -,87-1,18 225 25 73 712 2 3 577 584 2,63 Tab. 4 Influence of front from particular initial speed on forces reached in lashing points during tests with anti-skid pads under cargo Initial speed [km/h] Braking tests Braking time [s] MFDD [g] Maximum deceleration in axis x [g] Maximum force reached in lashing points Average force straining the lashing points during Duration of straining force during [s] 15-2 21,22,23,81 -,84-1,5 54 93 43 418 7 13 375 394,47 35-4 24,25,26 1,48 -,86-1,12 99 128 48 485 4 5 448 455 1,17 55-6 27,28,29 1,92 -,88-1,15 97 111 546 537 4 3 51 495 1,62 65-7 3,31,32 2,39 -,87-1,27 83 97 626 633 3 1 55 547 2,11 8-9 33,34,35,36 2,83 -,92-1,12 93 96 638 641 3 2 559 556 2,54 In the following table 5 are stated the standard deviations of measured values of forces in lashing points for particular initial speed ranges. There are also stated standard deviations of durations and force durations for particular ranges. The standard deviations of occuring forces F3, F4 are less for cases when anti-skid pads were used and was realised from higher initial speed. It is caused mainly due to decreasing of peak forces. 1 test no. 2 was not taken into consideration because of low value of MFDD -142-
Initial speed [km/h] Standard deviaton of average forces straining the lashing points during the when plywood surface was used Tab. 5 Standard deviations of selected average values Standard deviaton of average forces straining the lashing points during the when antiskid pads were used Standard deviation of time in tests when plywood surface was used [s] Standard deviation of straining forces duration during in tests when plywood surface was used [s] Standard deviation of time in tests when anti-skid pads were used [s] Standard deviation of straining forces duration during in tests when anti-skid pads were used [s] 15-2 2 4 11 14 2 2 12 11,6,2,2,5 35-4 1 2 9 1 2 2 12 11,7,8,1,1 55-6 1 1 25 27 2 2 12 12,4,4,12,12 65-7 1 1 35 31 1 1 17 19,17,3,6,6 8-9 1 1 31 3 1 1 13 14,8,11,6,5 Results from measurements show that there exists a dependence between the mean fully developed deceleration (MFDD) and the forces occuring in the lashing points stressed during the (in out case it means forces stressing the rear lashing points). For pusposes of evaluating this dependence we considered with sum of forces in both lashing points on the stressed side, that means with sum F3 + F4. Forces in these lashing points grow relatively proporcionally with growing MFDD. Dependence between MFDD and forces occuring during the is shown on graphs in figure 5. The graph in the figure 6 shows forces measured in lashing points at the beginning and at the end of each test no. 1 to 16 (when the cargo was placed on plywoods). After the test no. 11 were the lashings tightened. There is visible that forces in lashings rapidly decreased right after first emergency s. After 1 s were the forces only about 2 dan in each lashing point. -143-
Fig. 5 Dependence between MFDD and average forces occuring in lashings during the, when the cargo was placed on slippy plywood surface (up) and on antiskid pads (down) MFDD [g] 1,95,9,85,8,75,7,65,6,55,5 y =,4x +,344 R² =,8774 2 4 6 8 1 12 14 Average forces reached in lashing points F3 + F4 during the MFDD [g] 1,95,9,85,8,75,7,65,6,55,5 y =,1x +,7317 R² =,385 2 4 6 8 1 12 14 Average forces reached in lashing points F3 + F4 during the In the figures 7 and 8 are the graphs showing maximum forces reached in lashing points (F3 and F4 during, F1 and F2 in reaction immediately after vehicle stopped), resp. average forces occuring in lashing points during (for all 4 lashing points) from particular tests with cargo placed on plywoods (fig. 7) and on anti-skid pads (fig. 8). There are visible either differences between forces generated in front lashing points (F1 and F2) and also decreasing of differences -144-
between maximum and average forces F3 and F4 during the in case of using anti-skid pads. Fig. 6 Forces in the lashing points at the beginning and at the end of each test with the cargo placed on plywoods Force 25 2 15 1 5 F1 before F1 after F2 before F2 after F3 before F3 after F4 before F4 after Fig. 7 Forces reached during particular tests no. 1 to 16 with plywoods under the cargo Force 8 7 6 5 4 3 2 1 Maximum forces reached during the (F3, F4), resp. immediately after the vehicle stopped (F1, F2) Average forces occuring in lashing points during the -145-
Fig. 8 Forces reached during particular tests no. 21 to 36 with anti-skid pads under the cargo Force 8 7 6 5 4 3 2 1 Maximum forces reached during the (F3, F4), resp. immediately after the vehicle stopped (F1, F2) Average forces occuring in lashing points during the Fig. 9 The plywoods used under the cargo in tests no 1 to 16 moved one on another which caused that cargo moved sideward and the forces on the left and on the right were inequal 3 Measurements of lashing points stress during the the vehicle driving in rear direction Braking tests in rear driving van were realized from initial speed 15 2 km/h. There were realized 4 tests when the cargo was placed on plywoods laid the slippy side on each another and 3 tests when the cargo was placed on anti-skid pads. According to norms EN 12195-1:21 and EN 12642 the maximum value of deceleration occuring on the cargo during 8 ms should reach at least,5 g for these tests. In our case these values moved from,68 to,77 g. The average value of MFDD -146-
was,53 g in tests with plywoods and,58 g in tests with anti-skid pads. During the rear driving van the cargo tended to move rearwards, what in the front lashing used in our testing strained mainly the front lashing points. So the forces F1 and F2 grew and lashings in rear part of cargo space became loose. In table 6 is stated the comparison of averaged values from particular tests between tests with plywoods and with anti-skid pads. Standard deviations of values from these tests are stated in table 7. When the anti-skid pads were used, the forces occuring on lashing points decreased although increasing of MFDD. Maximum forces reached during the in front lashing points (F1 and F2) were reduced by 41 %, the same decreasing of forces was found out in rear lashing points in reaction after vehicle stopped. The average force occuring in front lashing points (F1, F2) during decreased by 38 % when the anti-skid pads were used. Also the lashing straps in the rear part of cargo area became not completely loose as that was usual when the plywoods were used. Tab. 6 Comparison of forces measured in lashing points in rear tests between the plywoods and anti-skid surface was used under the cargo Surface used under the secured cargo Slippy plywoods Anti-skid pads Braking tests 17, 18, 19, 2 37, 38, 39 Braking time [s] MFDD [g] Maximum deceleration in axis x [g] Maximum force reached in lashing points Average force straining the lashing points during Duration of straining force during [s] 1,7 -,53 -,72 429 451 175 128 392 47,75,86 -,58 -,76 257 269 73 16 242 252 33 54,63 Initial speed [km/h] Tab. 7 Standard deviations of selected average values from rear tests Standard deviaton of average forces straining the lashing points during the when plywood surface was used Standard deviaton of average forces straining the lashing points during the when anti-skid pads were used Standard deviation of time in tests when plywood surface was used [s] Standard deviation of straining forces duration during in tests when plywood surface was used [s] Standard deviation of time in tests when anti-skid pads were used [s] Standard deviation of straining forces duration during in tests when anti-skid pads were used [s] 15-2 14 15 1 8 1 4 5,12,24,4,1-147-
In the tests of rear driving vehicle there were big differences between using the plywoods and the anti-skid pads under secured cargo not only in intensity, but also in run of forces during the and after the vehicle stopped. Typical run of forces in tests with using plywoods was similar as in front s, only the direction of forces was opposite, so the front lashing points were mainly strained (fig. 1). When the anti-skid pads were used, the run of forces changed as illustrates figure 11. There were not generated so high forces in the front lashing points and as opposite, in the rear lashing points remained some force so they were not completely loose. The results of particular rear driving vehicle tests are shown at the graph in figure 12. There is visible decreasing of either peak forces and average forces in front lashing points. The straps became not completely loose in rear lashing points as consequence of less cargo movement during the. Fig. 1 Run of the forces during rear test no. 2 with slippy plywood surface under cargo (up) and run of accelerations in axes x and z during this test (down) Force 5 45 4 35 3 25 2 15 1 5 1 2 3 Time [s] F1 F2 F3 F4 Acceleration [m/ ] 15 1 5-5,5 1 1,5 2 2,5 3-1 Time [s] acc x acc z -148-
Fig. 11 Run of the forces during rear test no. 39 with slippy anti-skid pads under cargo (up) and run of accelerations in axes x and z during this test (down) Force 35 3 25 2 15 1 5,5 1 1,5 2 2,5 3 Time [s] F1 F2 F3 F4 Acceleration [m/ ] 15 1 5,25,5,75 1 1,25 1,5 1,75 2 2,25 2,5 2,75 3-5 -1 Time [s] acc x acc z -149-
Fig. 12 Forces reached during particular tests no. 17 to 2 with plywoods under the cargo (on the left) and during particular tests no. 37 to 39 with antiskid pads under the cargo (on the right) Force 5 45 4 35 3 25 2 15 1 5 Maximum forces reached in lashing points during the (F1, F2), resp. immediately after the vehicle stopped (F3, F4) Average forces occuring in lashing points during the Force 5 45 4 35 3 25 2 15 1 5 Maximum forces reached Average forces in lashing points during occuring in lashing the (F1, F2), resp. points during the immediately after the vehicle stopped (F3, F4) 4 Conclusions The tests confirmed, that during the emergency there are generated high forces in lashing points. When the van is full-loaded (we used a cargo weighting 1 3 kg) and the front lashing is used, these forces reach more than 5 dan, especially in cases of from higher initial speed. Already during from low initial speed about 15 2 km/h there are generated forces about 4 dan. Duration of these forces is directly proportional with duration of (it is lower only by time of forces inclination) and their intensity grow with growing mean fully developed deceleration of vehicle. If the cargo is placed on surface with low friction coefficient, there is temporarily (for about,2 s) generated high growth of forces in strained lashing points to 7 8 dan, what means high overrun of strenght of lashing points having strenght 5 dan. The cargo secured by front lashing tends on the surface with lower friction coefficient to stronger movement in the direction of previous driving and after stopping of vehicle to movement back, which cause higher stress in opposite lashing points. However, forces in these points have not such intensity like forces occuring in the driving direction and they occure for a shorter time. When there is used a surface -15-
with higher friction coefficient under the cargo, these forces are decreased, in our measurements they decreased by about 5 %. References [1] STN EN 12195-1:21. Load restraining on road vehicles.safety.part 1:Calculation of securing forces. 211. [2] EN 12642:26 L & XL: Securing of cargo on road vehicles - Body structure of commercial vehicles - Minimum requirements. 26. [3] STOPKA, O., KAMPF, R., KOLÁŘ, J., KUBASÁKOVÁ, I., SAVAGE, CH. Draft guidelines for the allocation of public logistics centres of international importance, (214), Communications, Vol. 16 (2), pp. 14 19, ISSN: 1335-425. Resume This paper deals with characteristics of forces generated in lashing points of fullloaded van during the emergency from various initial speed and the emergency of rearwards driving van. There are described maximum forces, average forces and run of forces in particular lashing points during when cargo was secured by front lashing. For finding out these data, the tests of full-loaded van were done with using the measure equipment from Centre of excellence for systems and services of intelligent transport, ITMS 26221228. The paper deals also with the differences of generated forces between two various surfaces used under the secured cargo with lower and higher friction coefficient. This contribution/publication is the result of the project implementation: Centre of excellence for systems and services of intelligent transport, ITMS 26221228 supported by the Research & Development Operational Programme funded by the ERDF. "Podporujeme výskumné aktivity na Slovensku/Projekt je spolufinancovaný zo zdrojov EÚ" Keywords Front lashing, forces, lashing points, friction, -151-
doc. Ing. Juraj Jagelčák, Ph.D. Univerzity of Žilina in Žilina Faculty of Operation and Economics of Transport and Communications Department of Road and Urban Transport e-mail: juraj.jagelcak@fpedas.uniza.sk Ing. Ján Zámečník Univerzity of Žilina in Žilina Faculty of Operation and Economics of Transport and Communications Department of Road and Urban Transport e-mail: jan.zamecnik@fpedas.uniza.sk -152-