MASH TL-3 Evaluation of Transition to Hawaii Modified Delaware Retrofit Thrie-beam Bridge Rail

Report Number(s): TRP-03-449-22

Description: The test installation had a total length of 177 ft – 6 in. and consisted of a 100-ft long section of the Hawaii Modified Delaware Thrie-Beam Bridge Rail, the preliminary design of the HDOT thrie-beam AGT, MGS rail, and anchorage system at the upstream end, and a thrie-beam anchorage system at the downstream end of the bridge rail. Note that the drawing set includes details for the entire system, including the bridge rail, AGT, W-beam rail installation, and anchorage systems. However, only the AGT details are described below and in Appendix B. The preliminary design of HDOT’s thrie-beam AGT consisted of a 12-ft 6-in. long, 12- gauge nested thrie-beam rail and 6-ft 3-in. of single ply 12-ga. thrie beam rail supported by W6x15 and W6x9 steel posts at various spacings. Posts in the nested thrie-beam section of AGT consisted of three 6-ft 6-in. long W6x15 steel sections with 37½-in. spacing and four 6-ft long W6x9 steel sections with 18¾-in. spacing. The remaining posts were 6-ft long W6x9 steel sections. The upstream end of the AGT incorporated the previously MASH-tested MGS upstream stiffness transition to connect the AGT to the adjacent MGS [5]. Approximately 50 ft of the MGS extended from the upstream end of the AGT and was anchored using an MGS trailing end anchor system. The guardrail anchorage system consisted of timber posts, foundation tubes, anchor cables, bearing plates, rail brackets, and channel struts, which closely resembled the hardware used in the Modified Breakaway Cable Terminal (BCT) system. The guardrail anchorage system has been MASH TL3 crash tested as a downstream trailing end terminal [6-9]. Blockouts within the AGT consisted of rectangular HSS steel tubes. Blockouts on the W6x15 posts were 6 in. wide, while 4-in. wide blockouts were used with W6x8.5/W6x9 posts. This MGS upstream stiffness transition was designed to transition from the 31-in. tall Midwest Guardrail System (MGS) to the stiffened thriebeam regions of the AGT using an asymmetrical W-to-thrie transition rail segment and standard 6-ft long W6x8.5 or W6x9 guardrail posts. The MGS upstream stiffness transition was already successfully evaluated, and crash tested to MASH TL-3 [5].   Design Modification Round 2: As previously described, test no. HMDT-3 did not pass the MASH 2016 safety performance criteria for test designation no. 3-20 due to the excessive side front panel deformation and vehicle component penetration of the occupant compartment. During the test, the bottom rail corrugation of the nested thrie beam AGT rails were flattened and formed a sharp kink adjacent to the first bridge rail post (i.e., post no. 20), as shown previously in Figures 137 through 139. These localized rail deformations resulted in the front wheel snagging on the bridge rail post and being pushed toward the occupant compartment. Thus, the AGT rail segments adjacent to the bridge rail post needed to be reinforced against localized deformations (flattening and kinking) to mitigate wheel snag and the corresponding occupant compartment deformation. To increase the stiffness of the thrie-beam rail, a 43¼-in. long x 16-in. wide x ⅜-in. thick ASTM A36 steel plate was added to the back side of the nested thrie-beam rail between the last transition post and the first bridge rail post. This back-up plate extended from the upstream edge of the transition post (post no. 19) to ¼ in. short of the downstream edge of the bridge rail post’s flange. This ¼-in. longitudinal offset from the edge of the post was designed to avoid vehicle snag on that edge during reverse-direction impacts. The plate was attached to the front flange of the bridge rail post using two ⅝-in. diameter by 10-in. long guardrail bolts with heavy hex nuts and plain washers through the existing holes. Note, this attachment used the existing holes in the post and the same attachment bolt as the adjacent transition post. Similarly, the plate was attached to the downstream side of the steel blockout and transition post using the existing attachment bolt. The plate was also connected to the nested thrie-beam rails using two splice bolts (i.e., ⅝-in. diameter by 2-in. long guardrail bolts with heavy hex nuts and plain washers) at the existing slots in the rail section at mid-span. The finalized AGT design is detailed in Figures 146 through 181. Photographs of the test installation are shown in Figures 182 and 183. Material specifications, mill certifications, and certificates of conformity for the system materials are shown in Appendix J.

Test Level: 3

System Type: Guardrail to Bridge Rail

MASH Test Number: 3-21, 3-20

Proprietary/Non-proprietary: Proprietary

Pass/Fail: Pass

Evaluation: Full-Scale Crash Testing

Sponsor: Hawaii Department of Transportation