TECHNICAL MEMORANDUM TEXAS TRANSPORTATION INSTITUTE TEXAS A&M RESEARCH FOUNDATION

Transcription

1 TECHNICAL MEMORANDUM TEXAS TRANSPORTATION INSTITUTE TEXAS A&M RESEARCH FOUNDATION A FEASIBILITY STUDY OF USING CORRUGATED STEEL PIPES IN MODULAR CRASH CUSHIONS A Tentative Progress Memo on Contract No. CPR l U. S. Department of Transportation Federal Highway Administration by Monroe C. White Engineering Research Associate Gordon G. Hayes Physics esearch Associate and T. J. Hirsch Research Engineer The tests reported herein were conducted under the Office of Research and Development, Structures and Applied Mechanics Division's Research Program on Structural Systems in Support of Highway Safety (4S Program). The opinions, findings, and conclusions expressed in this report are those of the authors and not necessarily those of the Federal High.18y Administration. August, 1971

2 Introduction Following the successful implementation of the 55 gallon steel drum modular crash cushion, a study of the feasibility of using other energy a b sor b d 1... d 1,2* ng mo u es was ntate One possible energy absorbing module is corrugated steel pipe. Corrugated steel pipe with diameters of 12, 15, 18, 21, 24, 30, and 36 inches, of 16, 14, and 12 gage steel with a specimen length of 25.5 inches, were statically crush tested and found to have reasonable static force and crush energy values for use in a modular crash cushion 3 (see Table 1 for summary of static crush force and energy for corrugated steel pipes used in the three tests reported herein). This multitude of available diameters and thicknesses of corrugated steel pipes encompasses a wide range of static force and crush energy characteristics, thus indicating the use of what is called the po1ymodu1ar design method. This design method is based on a row-by-row analysis of the force and energy relationships between the vehicle and modular crash cushion, whereas' the other simpler design method, called monomodular, involves using en:ergy absorbing modules of the same strength and designing the whole cushion from two vehicle parameters, ve 1 octy an d' weg h t. 2,4 Test Descriptions and Objectives Three experimental crash tests were conducted, two head-on tests and one side-angle test. The first test, CSP-l, was conducted to *Numbered superscripts correspond to like numbers in reference. 2

3 determine and to reveal the overall dynamic interaction of the vehicle and cushion during impact. The cushion consisted of fifteen rows of fifteen inch diameter pipes arranged four abreast. The first nine rows were of 16 gage metal and the last six rows were of 14 gage metal as shown in Figure 1. The second and third tests, esp-2 and esp-3, respectively, were conducted on a crash cushion designed for a 2000 lb. to 5000 lb. vehicle weight range and installed in a simulated median in front of simulated bridge piers. The sides of the bridge piers were protected by a modified concrete median barrier. The cushion installation, shown in Figure 2, consisted of one row of two and three rows of three 24 inch diameter 16 gage pipes, five rows of three 24 inch diameter 14 gage pipes, three rows of four 18 inch diameter 16 gage pipes, and five rows of four 18 inch diameter 14 gage pipes. The pipes in the last row and the offset pipes each contained an inner pipe which increased the module stiffness and was intended to protect against angle impacts near the last row and at the transition to the concrete median barrier. The objective of the angle test, esp-2, was to evaluate the redirection capability of the flexbeam panels installed along the side of the crash cushion. The objective of the head-on test, CSP-3, was to determine if the addition of the flexbeam on the nose and the more numerous and stronger support posts would eliminate the ramping tendency observed in esp-i. 3

4 15" OIA. CSP 9 ROWS-16 GAGE FSTAT =4(5780) = Ibs 15" OIA. CSP 6 ROWS-i4 GA F STAT = 4 (7200) = Ibs - 1.==-a== =- =- == 3---1/2" DIA. BOLTS AT I!t2"X I "X 1/8" ANGLE SUPPORT POST EACH CONTACT POINT 2'-10" 20' - 0" 2'-0", -CD "RIGID BACKUP WALL r 2-314" OIA. STEEL WIRE ROPES PER SIDE 10 C\J = rtf CO >-----C FIGURE I. b-r::c >-r-r--( -====== po =."...."... N : == l- N :::,... -,!'J II 11 ]I - CORRUGATED STEEL PIPE CRASH CUSHION USED FOR 505 esp-i - f() en TEST

5 I 24" OIA. 4 ROWS-I6GAGE 24" OIA. 5 ROWS-14 GAGE F STAT = 2(3441) F STAT = 3(3441) = 6882 Ibs = Ibs FSTAT = 3(4270) = Ibs IS" DIA.3ROWS 16 GAGE 18" DIA. 5 ROWS-14 GAGE F STAT =4(4789) F STAT = 4(6722) = Ibs = Ibs I " 3'-1 i'2 30'-10" I hh WIDE, GAGE MOUNTING STRIP BENT TO FIT VALLEY OF CSP a PANEL. 3'" 1/2" DIA. BOLTS SECURE EACH STRIP TO PANEL a PIPE FLEXBEAM PANEL DETAIL -Ī N OVERLAPPING FUfXBEAM ;; NELS - 3'-1 :12" LONG FLEXBEAM END " SECTION (FLARED) /2-3/4 DIA. STEEL WIRE r 3,v 1/2" OIA. BOLTS SECURE ROPES PER SIDE CSP AT EACH CONTACT PT. r- 6 IL -0 l - ""'11 t-., I- ll b -; 10 - I.5L _'tl - Jl J1 II Jl Ill" -_. --- AGURE 2. CORRUGATED STEEL PI PE CRASH CUSHION USED FOR TESTS 505CSP-283

6 TABLE 1. SUMMARY OF STATIC CRUSH TEST RESLTS FOR CORRUGATED STEEL PIPES 25.5 IN. LONG Nominal Wall Module Crush Crush* Average* Inside Thickness Weight Distance Energy Force Diameter (in. ) (ga. ) (lb. ) (in. ) (ft.-lb. ) (lb. ) , , , , , ,470 5,780 7,200 4,790 6,720 3,440 4,270 *Values are rounded off to nearest ten pounds. Note: Data taken from curves on Figures All, A12, and A13 in the Appendix. 6

7 Experimentation Test Instrumentation Photographic instrumentation. Data from high-speed films were used to determine vehicle time-displacement. Vehicle speeds and average decelerations were computed from this data. For an angle test, such as esp-2, the high-speed film was used to estimate the time when the vehicle was parallel to the barrier and when it had completely lost contact with the barrier. Each high-speed film had a timing mark placed on it at specific time intervals, usually 1 mark every 0.01 seconds. Thus, elapsed time could be determined. A stadia board placed on the side of the vehicle was used to relate actual distances with apparent distances on the film, so that vehicle displacement along its path could also be determined. In test esp-i, three high-speed cameras were used. Two cameras, both running at 250 frames per second, were located perpendicular to the vehicle's path (also perpendicular to the barrier as this was a head-on crash). The third camera, running at 400 frames per second, was placed overhead. Four cameras, all running at 400 frames per second, were used to photograph test esp-2. One was perpendicular to the vehicle's path, another parallel to the barrier, a third perpendicular to the barrier, and the last, overhead. 7

8 Three high-speed cameras, all running at 400 frames per second, were used in test CSP-3. Two cameras were perpendicular to the vehicle's path (also perpendicular to the barrier). The third was placed on the other side of the barrier at an angle of with respect to the vehicle's path. Electromechanical instrumentation. Accelerometers placed in the test cars provided a trace of longitudinal and transverse acceleration (g's) versus time for the car axes. In test CSP-2, both longitudinal and transverse accelerometers were used, but in the two head-on tests, CSP-l and CSP-3, only the longitudinal accelerometers were used. The right longitudinal and right transverse accelerometers were mounted on short flanges which were welded to the right longitudinal frame member just behind the front seat. Similarly, the left longitudinal and left transverse accelerometers are mounted on the left longitudinal frame member. The data recorded from these accelerometers were run through an 80 Hz low pass filter to reduce the "ringing" effect. An Impact-Q-Graph, an alternative source of acceleration data, was mounted in the trunk of each test vehicle. In all tests a 160 lb. anthropometric dummy was placed in the driver's seat and secured with a lap belt. A force versus time trace was obtained from a load cell attached to the lap belt. The actual signals produced by all of the electromechanical instruments were transmitted from the car by telemetry and recorded on magnetic tape. 8

9 Test Results Summary of results. Summaries of the analyses of film data and accelerometer data for the three tests are presented in Tables 2 and 3, respectively. The accelerometer traces and seat belt force traces are presented in Figure A1 through A10 in the appendix. The film data are presented in Tables Al, A2, and A3, also in the appendix. Test esp-1. The 1964 Dodge weighing bs. impacted the barrier head-on at a speed of 58.4 mph. After seven rows of pipes had crushed, the front portion of the barrier pivoted upward at the 8th and 9th rows of pipes. The vehicle ramped upward and became airborne. The first five rows of pipes became detached in a group and rotated through in the air before coming to rest on top of the rear portion of the barrier near the backup wall (see Figure 3). Little vehicle damage resulted (0.5 ft) despite a high peak deceleration of 24 g's noted from the accelerometers. The average deceleration from the accelerometers, however, was only 5.6 g's over seconds impact duration. Figure 4 shows sequential photos of the test. The support posts, instead of sliding as intended, buckled from the high frictional force which apparently resulted from the normal force exerted by the initial tension in the cables. Since the vehicle ramped and became airborne, the dynamic-tostatic force (and energy) ratio can not be accurately determined. 9

10 Table 2. DATA FROM FILM ANALYSIS Test Factor CSP-l CSP-2 CSP-3 Vehicle weight, lb Impact angle, deg Initial speed, ft/sec. (V. ) mph Final speed, ft/sec. (V f) 0 0 Total stopping distance, ft (S) Total stopping time, sec Average longitudinal deceleration, gls (G) 4.0** 4.8** Speed after contact*, ft/sec. (V f ) 57.1* * mph 39.0* * Time in contact, sec ,093 Distance in contact, ft. (S) Average longitudinal deceleration, gls. (G) 10.2** 2.2** 9.3** Exit angle, degrees 7.7 * In Tests CSP-l and CSP-3 the vehicle "ramped" shortly after impact. Data immediately below asterisk applies only during contact before ramping. ** V. 2 _ V 2 longitudinal acceleration parallel to vehicle 1. f G 2gS path or parallel to side of barrier for redirection tests 10

11 Table 3. DATA FROM ACCELEROMETERS Factor Vehicle weight, lb. Impact angle, deg. Test CSP-l CSP-2 CSP o 20 0 Maximum deceleration a, g's. Longitudinal b Transverse Average deceleration a Longitudinal Total event, g's. Time interval, sec. Before ramping, g's. Time interval, sec. b Transverse, g's. Time interval, sec a Values given are averages of right and left accelerometer outputs. b Transverse to vehicle longitudinal axis. 11

12 Test CSP-2. A 3810 lb. Plymouth sedan traveling 59.8 mph impacted the barrier at an angle of 20 0 with respect to the barrier centerline. Dynamic lateral deformation of the barrier started at impact, reaching a maximum of 1.0 ft. in sec. as determined from the overhead camera film. The residual lateral deformation of the barrier was 0.4 ft. Damage to the left front quarter of the vehicle was considerable (see Figure 5), with a deformation on the left fender of 1.8 ft. and a deformation of the left side of the bumper of 1.4 ft. Damage to the barrier was much less severe (see Figure 6), consisting of scrapes along the guardrail and pipes and also some crushing of the lower portions of the outside row of pipes. With only minor repair, the barrier was used again for test CSP-3. The vehicle redirected smoothly, with an average longitudinal deceleration, determined from the accelerometer traces, of 1.5 gls over sec. The maximum longitudinal deceleration was 6.3 gls (accelerometer). Average transverse deceleration, also determined from accelerometer traces, was 3.4 gls over sec., with a maximum of l2.0 gls. The average longitudinal deceleration, as determined from film, was 2.2 gls over sec. The exit angle was and the velocity after contact was terminated was 44.9 mph. Sequential photographs from two different views of the crash may be seen in Figures 7 and 8. Test CSP-J. Text CSP-3 was a head-on test of the corrugated steel pipe crash cushion. In this test, the barrier was impacted by a 1963 Plymouth sedan weighing 3880 lbs. and traveling 62.3 mph. 12

13 Figure 9 shows the vehicle before and after and Figure 10 shows the cushion before and after the collision. The barrier-vehicle interaction was similar to that of test esp-l, the first head-on test of this series. As in esp-l, the first rows of the barrier (rows 1-6) were crushed and bent downward, then pivoted upward from a point between the 6th and 7th rows. The front of the vehicle was lifted upward by one of the flexbeam panels which dug into the ground, pushing against the first rows of the barrier (see Figure 11). The vehicle continued to ramp upward, pushing the first four rows of pipes, which had become detached, over the right side of the barrier. The front wheels of the vehicle recontacted the remaining portion of the barrier, then the car started to slide down backwards, with the head end of the vehicle sliding along the support cables. Figure 12 shows the vehicle at rest, suspended by the barrier and support cables. The peak deceleration taken from the accelerometer traces was 19.5 g's. The average longitudinal deceleration, also from accelerometer data, was 4.3 g's over sec. (total event) and 5.0 g's over sec. (before ramping). Since the vehicle again ramped and became airborne, the dynamicto-static force (and energy) ratio canot be determined. 13

14 FIGURE 3. Vehicle and cushion before and after the collision, Test esp-i. 14

15 t sec. t = sec..n.. t = sec. t sec. t sec. t sec. t sec. t sec. t = sec. t sec. FIGURE 4. Sequence Photos of Test esp-i. 15

16 FIGURE 5. Vehicle before and after the collision, Test CSP-2. 16

17 = before before after after FIGURE 6. Two views of cushion before and after the collision, Test CSP-2.

18 t = sec. t = sec. t = sec. t sec. t = sec. t sec. FIGURE 7. Overhead sequential photos of Test CSP-2. 18

19 t = sec. t sec. t sec. t = sec. t = sec. t sec. FIGURE 8. End view sequential photos of Test esp-2. 19

20 ... \1 A I FIGURE 9. Vehicle before and after the collision, Test CSP-3. 20

21 FIGURE 10. Cushion before and after the collision, Test CSP-3. 21

22 vr::l.. rl t = sec. t = sec. t sec. t = ;...;:::::::\/...,. \ :::::. "., : : : :. 1, ,,, t = sec. t sec. t sec. t sec. FIGURE 11. Sequential photos of Test CSP-3. 22

23 FIGURE 12. Vehicle and cushion after the collision, Test CSP-3. 23

24 Conclusions and Recommendations The corrugated steel pipe crash cushion did not perform as intended during the two head-on tests. From the high speed films of CSP-l it was surmised that the pipe support legs were insjfficiently strong, particularly at the point where the cables angle downward from the horizontal. Also, it is believed that the strength distribution of the pipe contributed to the ramping, i. e., the pipe is weaker at top and bottom and stronger in the midsection, thus tending to deform first at one of the weaker points and allowing the vehicle to ramp. The addition of more and stronger legs, and the flexbeam on the nose and side of the cushion did not prevent ramping in test CSP-3, in fact one of the flexbeam panels aided ramping by digging in the ground and "vaulting" the vehicle upward. It appears that the strength distribution of the pipe along with the frictional forces on the support legs and the length-to-height ratio of the cushion work in combination during impact to cause a vertical force to be applied to the vehicle, causing it to ramp. Three changes are suggested below as possible remedies to the ramping problem. They are: 1. Increase the length of the module such that the top and bottom of the pipe will not be in contact with the distributed force from the nose of the impacting vehicle, i. e., the vehicle will feel the more uniform strength distribution of only the midsection of the pipe. will also decrease the length-to-height ratio. An This 24

25 alternate to increasing the module length would be to raise the bottom of the cushion to approximately 15 inches above grade. 2. Add dish shaped skid plates to the support posts to decrease frictional forces on the bottom of the cushion, particularly at the post where the cables angle downward. 3. Decrease the initial tension in the cables from the present 4000 to 5000 lbs. down to 500 to 1000 lbs. This will also help to decrease the frictional forces on the bottom of the cushion and perhaps allow the support post to remain upright and also keep the flexbeam panels from digging into the ground. It is recommended that the above suggestions be investigated before deletion of or implementation of the corrugated steel pipe crash cushion as a viable vehicle impact attenuator. A reliable experimental value for the dynamic-to-static force (and energy absorption) ratio still remains to be found from further tests where the vehicle does not ramp on head-on impact. The corrugated steel pipe crash cushion with flexbeam side panels indicated excellent side-deflection behavior in test esp-2. In summation, the corrugated steel pipe crash cushion performs well under side impact but needs further investigation to correct the ramping problem during head-on impact. 25

26 References 1. White, M. C., Ivey, D. L., and Hirsch, T. J., "In-Service Experience on Installations of Texas Nodular Crash Cushions," Research Report 146-2, Texas Transportation Institute, Texas A&M University, College Station, Texas, December, lfuite, 11. C., and Hirsch, T. J., "Highway Crash Cushions," a Special Report for the Federal High,1ay Administration, Department of Transportation, Texas Transportation Institute, Texas A&M University, College Station, Texas, (pending publication). 3. White, M. C., "The Modular Crash Cushion: Design Data from Static Crush Tests of Steel Drums and of Corrugated Steel Pipes," Technical Memorandum , Texas Transportation Institute, Texas A&M University, College Station, Texas, April, White, M. C., "The Polymodular Design Method for Designing Modular Crash Cushions," a Report for United States Steel Metal Products Division, United States Steel Corporation, Pittsburgh, Pennsylvania, (pending publication). 26

27 Appendix 27

28 +10 _Impact Right Frame Member r-- (fj - b!) c 0." o.w <1l -10,... QJ.--! QJ U (J <:: n /I I\ LJv \J\ rvv (\J ;0 V o !' Time (msec) FIGURE AI. LONGITUDINAL ACCELEROMETER DATA, TEST CSP-l (80 HZ LOW-PASS FILTER) 28

29 +10 Impact Left Frame Member,-.,. UJ o -tl()..., s:: (\ 0 'N -10 C'd Q) r-1 Q) (J (J <t:,.. - I\I'-J"'\. rj ra W'JVV V -20 " -30 o Time (msec) 500 FIGURE A2. LONGITUDINAL ACCELEROMETER DATA TEST CSP-1 (80 HZ LOW-PASS FILTER) 29

30 1000.-Impact r i '-" QJ w 0 o o Time (msec) FIGURE A3. LAP BELT DATA, TEST CSP-l (80 HZ LOW-PASS FILTER)

31 CIJ - bo '-' +10 Impact Left Frame Member 0 OM.w co H (])..-t (]) () () <t; w CIJ - tlc Impact Right Frame Member ::: 0 OM.w co H Q)..-t Q) c.; c.; <t; Time (msec) FIGURE A4 LONGITUDINAL ACCELEROMETER DATA, TEST CSP-2 (80 HZ LOW-PASS FILTER)

32 +10 Impact Right Frame Hember ---- UJ 0-00 '-' W N p 0 OM C1l 1-1 til rl Q) tj tj < o Time (msec) FIGURE AS. TRANSVERSE ACCELEROMETER DATA, TEST CSP-2 (80 HZ LOhT-PASS FILTER)

33 +10 --Impact Left Frame Member,.-... CIJ 0 - OIJ '-' W W P 0 01"1 +J til H Q) r-i Q) u -10 u <t: -20 o Time (msec) FIGURE A6. TRANSVERSE ACCELEROMETER DATA, TEST CSP-2 (80 HZ LOW-PASS FILTER)

34 +500 Impact '""'.0 r-i '-" Cl) 0 () I-< 0 I'< w -500 o Time (msec) FIGURE A7. LAP BELT DATA, TEST CSP-2 (80 HZ LOW-PASS FILTER)

35 +10 Impact Left Frame Member "" '",-... UJ - 00 '-' a or-f.,;,... co OJ rl OJ (j (j -< o Time (msec) FIGURE A8. LONGITUDINAL ACCELEROMETER DATA, TEST CSP-3 (80 HZ LOW-PASS FILTER)

36 +10 -Impact Right Frame Member W '""' Ul - bo '-" s:: 0 om m l-< 0 (j\ Q)..-i Q) -10 () () -20 o Time (msec) FIGURE A9. LONGITUDINAL ACCELEROMETER DATA, TEST CSP-3 (80 HZ LOH-PASS FILTER)

37 L L _L L _ p r_ _, _, _ _r----_, w M '-' u o o Time (msec) FIGURE A10. LAP BELT DATA, TEST CSP-3 (80 HZ LOW-PASS FILTER)

38 " DlA, 16 15"D, 14 21"OIA, p :i: -Q «o -' , 'I r J j 8" OIA, 2T'DIA, 30''!'A. 36" DlA, J J! ) J V V ) II ) 7 r a --./ J v l/ -... V ""!".. r--e & o CRUSH DISTANCE (in) FIGURE All, LOADvs. CRUSH DISTANCE 16go. CORRUGATED STEEL PIPE OF VARIOUS DlAt. TERS a 25.5" Ig. 38

39 20 r----, _._-- " 1801A DlA "0IA o CRUSH DISTANCE (in.) FIGURE A12. LOAD vs. CRUSH DISTANCE FOR 14ga. CORRUGATED STEEL PIPE OF VARIOUS DIAMETERS 8c Ig. 39

40 a «o -' 8 -en 0- :; r I If r' -..- / I "' II I I j T2411 DIA. / J/ 1// V hj If II 36 DIA., j 30't V o CRUSH DISTANCE (in.) FIGURE A13. LOAD VS. CRUSH DISTANCE FOR 12go. CORRUGATED STEEL PIPE OF VARIOUS DIAMETERS a 25.5" Ig. 40

41 TABLE AI. TEST 505 CSP-1 HIGH-SPEED FILM DATA Time (milliseconds) Displacement (feet) Impact VEHICLE "RAMPS" MAXIMUM FORWARD TRAVEL 41

42 TABLE A2. TEST 505 CSP-2 HIGH-SPEED FILM DATA Time Displacement Time Displacement (milliseconds) (feet) (milliseconds) (feet) (continued) Impact

43 TABLE A3. TEST 505 CSP-3 HIGH-SPEED FILM DATA Time (millis econds) Displacement (feet) Impact 0 8 O VEHICLE "RAMPS" MAXIMUM FORWARD TRAVEL 43

44