FUNCTIONAL LIMITS OF THE W-BEAM SAFETY BARRIER TMALL 0143 Presentation engelsk v 1.0 Göran Fredriksson, Swedish Safety Barrier Association Hans G Holmén, Swedish Transport Administration
Grundpaket Drift Basic maintenance contracts on the Road 115 maintenance areas App. 60 to 170 metric miles /area Contract period 4 years with an option to an additional 1 or 2 years Main contractors are Svevia NCC Skanska PEAB 2
Preconditions Different road classes (class 1-5) governing Inspection intervals (detect shortcomings) Requirements (how to regain functionality) Action times (when to do it) Control STA performe random sample checks Third party follow up Fines and deductions According to specification 3
Road side safety and ageing safety barriers.. The aim - questions to be answered: Height limits, especially low position How much can the barrier lean outwards (inclination)? Low and leaning, where is the limit now? Will a higher than standard barrier improve functionality? If a SUV can be contained, will a sportscar get stuck? How is functionality affected in poor (loose) soil conditions? What happens if a post is cut off? What if there is a tear in the W-beam?..a project was formed. 4
Project members Steering Committee and project founding Project management Swedish Safety Barrier Association Crash testing The Swedish National Road and Transport Research Institute Computer simulations DYNAmore Nordic AB 5
Methodology Design of Experiments Duplicate original TB 32 test (1500 kg car, 110 km/h, 20 impact angle) on Swedish standard EU4 W-beam safety barrier. Exclude measurements for ASI and Working width Simulate to find probable limits and decide on initial test positions Decide on PASS or FAIL criteria Outcome of physical test determines next step Post distance 4 m Barrier length 76 m between sloped anchored terminals Sigma shaped post, 4 mm thick steel W-beam, 3 mm thick. 6
Variations in barrier position Low Low and/or inclined 7 Nominel height, 550 mm = approx. 700 mm to top Lowering Effective height, Eh Inclination, angle in
Results from simulations 8
Result low position. Functional limit 450 mm. 400 mm to centerline 450 mm to centerline FAIL! PASS! 9
Result inclined position. Functional limit approx. 30.8, Eh 500 mm. PASS! 10
Result low and inclined position. Functional limit, but still not acceptable: inclination approx. 9, post protrusion -50 mm, Eh approx. 503 mm. Position at fourth attempt First attempt, Inclination 30.8, Post protrusion 60 mm 11
PASS, but not acceptable! Test vehicle after the 8th and final attempt... Rolls over 3 times after impact. 12
Result SUV, Volvo XC 90, TB32 -collision with Swedish standard W-beam barrier, 550 mm high Car with family of 2 adults and 3 children, Weight 2 322 kg, speed 104.6 km/h FAIL! 13
Result SUV, Volvo XC 90, TB32 -collision with Swedish standard W-beam barrier, 650 mm high. Raised 100 mm.. PASS! 14
Result Mazda MX5 Miata, TB32 -collision with Swedish standard W-beam barrier, 650 mm high. Raised 100 mm.. Weight 1124 kg PASS! 15
Result poor ground conditions. Test site soil replaced by non compacted gravel. 4-8 mm sieving. Barrier retains vehicle but posts are pulled out and thrown. PASS, but not acceptable. Posts with original length, 1 950 mm. Approx 1 350 mm in the ground. Posts with new design, shortened to 1 650 mm. Approx. 1 050 mm in ground 4 posts are pulled out. 16
Result Cut off post at ground level. W-beam barrier at nominal height. PASS, but not acceptable. Post is thrown like a projectile! 17
Result W-beam with a 155 mm long cut. Barrier at nominal height. PASS but not a guarantee Cut is positioned 5.65 m after initial impact point. Worst case acc. to simulations Before impact After impact, lenght of tear increases to 205 mm 18
Conclusions (barrier type and test conditions as presented): Functional limit of a low, but still vertical, barrier around 450 mm A barrier with a moderate inclination functions IF there is full post protrusion. A low barrier with an inclination is a devastating combination that ceases to function already when there are small deviations from its nominal position. A barrier height of 650 mm to W-beam centerline* (approx. 800 mm to top) would provide better function for a wider scope of car types. * Similar conclusion has been drawn from research in the US by Midwest Roadside Safety Facility 19
Conclusions, continued.. Properly anchored, vertical and at nominal heigth the W- beam barrier is rather forgiving to deviations in soil and mechanical damages. Cut off posts present a danger to other road users as they tend to be thrown about at impact. Shortened posts have a similar behaviour. Impacts at more narrow angles than 20 will improve the chances of any type of vehicle being contained by the safety barrier (law of physics and simulation studies). 20
We hope that these findings will come to good use in the efforts to increase and maintain Traffic Safety. Thank you for listening! Göran Fredriksson Hans Holmén 21