Evaluation of the Midwest Guardrail System stiffness transition with curb

Faller

et al. 2022

Self Cite

A Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL-3) approach guardrail transition (AGT) was designed to connect the Midwest Guardrail System to a MASH TL-4 steel tube bridge rail, designated Steel Railing, Type IL-OH. The AGT connection consisted of a 34 in. tall thrie-beam AGT, HSS8 × 6 × ¼ transition tube rails that aligned with the lower and middle bridge rail tubes, and new connection hardware designed to prevent vehicle snag during impacts. The new AGT connection was evaluated using a combination of LS-DYNA finite element analysis software and full-scale crash testing in accordance with MASH TL-3 impact criteria. The critical impact points were selected using LS-DYNA for MASH test nos. 3-20 and 3-21. In test SBRTR-1, a 2,404 lb small car struck the AGT at a speed of 64.6 mph, an angle of 25.2°, and at a location 21.3 in. upstream from the last transition post. In test SBRTR-2, a 5,007 lb quad cab pickup truck struck the AGT at a speed of 62.7 mph, an angle of 24.9°, and at a location 15.9 in. upstream from the last transition post. The small car and pickup truck were both contained and redirected and the tests resulted in a successful evaluation according to MASH TL-3 safety performance criteria. Implementation guidance for the new AGT in various configurations is provided.

Section: Conclusion and Recommendationsmentioning

confidence: 99%

Development of a Test Level 3 Approach Guardrail Transition to Steel Tube Bridge Rail

Rasmussen¹,

Faller

et al. 2022

Self Cite

“…deep blockouts. Full-scale testing of MGS stiffness transition did result in moderate vehicle snag on the guardrail posts when impacted with the small car (18,19,29,30). There are concerns that reducing the blockout depth in the MGS stiffness transition may result in increased vehicle snag.…”

Section: Conclusion and Implementation Guidancementioning

confidence: 99%

“…As such, the addition of a curb below the 34-in tall AGT should also be considered a crashworthy configuration. However, if the curb extends into the region of the upstream stiffness transition, 12.5-ft of nested W-beam rail must be placed upstream of the W-to-thrie transition segment to prevent rail rupture ( 29 , 30 ).…”

Section: Conclusion and Implementation Guidancementioning

confidence: 99%

Development of a 34-in. Tall Thrie-Beam Guardrail Transition to Accommodate Future Roadway Overlays

Faller²,

Schmidt

et al. 2019

Self Cite

Roadway resurfacing and overlay projects effectively reduce the height of roadside barriers placed adjacent to the roadway, which can negatively affect their crashworthiness. More recently, bridge rails and concrete barriers have been installed with slightly increased heights to account for future overlays. However, adjacent guardrails and approach transitions have not yet been modified to account for overlays. The objective of this project was to develop an increased-height approach guardrail transition (AGT) to be crashworthy both before and after roadway overlays of up to 3 in. The 34-in. tall, thrie-beam transition detailed here was designed such that the system would be at its nominal 31-in. height following a 3-in. roadway overlay. Additionally, the upstream end of the AGT incorporated a symmetric W-to-thrie transition segment that would be replaced by an asymmetric transition segment after an overlay to keep the W-beam guardrail upstream from the transition at its nominal 31-in. height. The 34-in. tall AGT was connected to a modified version of the standardized buttress to mitigate the risk of vehicle snag below the rail. The barrier system was evaluated through two full-scale crash tests in accordance with Test Level 3 (TL-3) of AASHTO’s Manual for Assessing Safety Hardware (MASH) and satisfied all safety performance criteria. Thus, the 34-in. tall AGT with modified transition buttress was determined to be crashworthy to MASH TL-3 standards. Finally, implementation guidance was provided for the 34-in. tall AGT and its crashworthy variations.

“…For installations transitioning from MGS to the standardized buttress, it is recommended to utilize the MGS stiffness transition on the upstream end of the AGT, as was done here with the Iowa AGT. Details on how to incorporate the MGS stiffness transition into a Thrie beam AGT can be found in previous reports and papers ( 8 , 9 , 23 , 24 , 27 ).…”

Section: Conclusion Recommendations and Implementation Guidancementioning

confidence: 99%

“…Changing only a single component or feature of an AGT can significantly alter its safety performance. For example, the addition/removal of a curb, altering the geometry of the rigid parapet, or altering the embedment length of the transition posts, can be the difference between a failure and a successfully crash tested AGT ( 3 – 11 ). Owing to the sensitivity of stiffness transitions, AGT components and features (e.g., curb usage and rigid barrier geometry) are not interchangeable between systems.…”

mentioning

confidence: 99%

Development of a Standardized Buttress for Approach Guardrail Transitions

Schmidt

Faller

2018

Self Cite

Approach guardrail transitions (AGTs) incorporate increased post and rail sizes, reduced post spacings, and specialized buttress end geometries to smoothly transition from deformable W-beam guardrail to rigid barriers. This transition in barrier stiffness makes AGTs sensitive systems that require specific combinations of these components to function properly. Changing components, or even the removal of a curb below the rail, can negatively affect the safety performance of an otherwise crashworthy system. However, recent full-scale crash testing has indicated that a properly designed buttress at the downstream end of an AGT may be utilized with multiple AGT systems. Thus, the objective of this project was to develop a standardized buttress to reduce vehicle snag and be compatible with a wide variety of previously developed Thrie beam AGT systems, either with or without a curb. The standardized buttress was designed with a dual taper on its front upstream edge. A longer lower taper was designed to mitigate tire snag below the rail, while a shorter upper taper was designed to prevent vehicle snag and limit the unsupported span length of the rail. This buttress design was evaluated in combination with a critically weak AGT without a curb, which represented the worst-case scenario. The standardized buttress was successfully crash tested to MASH TL-3. Guidance was provided for both the attachment of the buttress to various Thrie beam AGTs as well as how to transition the shape of the buttress to adjacent bridge rails or rigid parapets downstream of the AGT.