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Blockout Dimensions and Material

Question
State IN
Description Text

INDOT has had a Composite Blockout supplier contact us about blockouts for the MGS Approach Guardrail Transition.  They wanted to know if a composite blockout with dimensions 6 inch wide x 12 inch deep x 18 inch long can be used on a MGS Approach Guardrail Transition.  The crash tests TRP-03-210-10 and TRP 03-291-14 seem to give guidance for dimensions of 6 inch wide x 12 inch deep x 19 inch long.  Can there be any variance in the blockout dimensions and can a composite blockout  with a "long" dimension of 18 inches be used?  The reason they are asking is because they do not make blockouts 19 inches in length.  Thank you

Keywords
  • Approach Guardrail Transitions
Other Keywords none
Date May 21, 2018


Response
Response Multiple thrie-beam approach guardrail transitions have been designed and successfully tested with blockout heights measuring either 18" or 19".  MwRSF feels that both blockout sizes will perform in the same manner and allow the lower corrugation to fold back due to tire contact, which has been shown to aid vehicle stability during impact events.  Thus, either blockout height is acceptable for use within thrie beam approach guardrail transitions.

This conclusion was previously established during a project with FHWA Central Federal Lands in which MwRSF designed steel tube blockout equivalents as alternatives for the wood blockouts typically used in guardrail transitions.  The height of those steel tube blockouts was modeled after the 18" tall blockouts, but was recommended for use in guardrail transitions originally developed with either 18" or 19" blockout heights.
Date May 21, 2018


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