TL-2 height to remain in place with steel blockouts?
Guardrails
A strongpost guardrail with steel blockouts is considered a Report 350 TL-2 application. There was successful crash testing for a TL-2 MASH guardrail with wood blockouts at 24″ and 25″. We are trying to determine an acceptable height to remain in place for a TL-2 application with steel blockouts on a 3R type project. Is there any past testing or guidance that is available for consideration?
Nauman Sheikh ( [email protected]) Texas A&M Transportation Institute
TTI’s MASH TL-2 testing was performed with 24-inch and 25-inch guardrail heights. The W-beam guardrail system used 6”x8” wood blockouts. Both these tests passed the MASH TL-2 criteria. A closed section steel blockout (HSS) used instead of the wood blockout is also expected to pass MASH TL-2. However, a steel blockout comprised of W6x8.5 or other similar I-beam section cannot be considered to work acceptably without additional testing. Past TL-3 test of the W-beam guardrail with such a blockout under NCHRP Report 350 did not pass. The design was changed to include the timber blockouts and it passed the NCHRP Report 350 testing criteria. Even though the question at hand is related to TL-2, which has much lower impact speed, past testing shows that W6x8.5 or similar blockouts present a more stringent design condition compared to the wood blockouts. Thus, additional testing should be performed prior to using the W6x8.5 or similar blockouts with the W-beam guardrail with reduced height.