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Minnesota DOT T-1 Railing

Question
State	MN
Description Text	For your info I've attached a copy of our proposed railing standard that we discussed on the phone (with the slotted holes in the base plate). The areas in green indicate the proposed changes.

System Performance Evaluation

System Types
Bridge Rails

Applications

System Features

Date January 5, 2010
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Attachment T-1.pdf

Response
Response (active)	The crash tested, combination tube bridge rail with concrete parapet and brush curb utilized a ¾-in. thick post base plate for anchoring the tubular post and rail system. The base plate was anchored to the concrete parapet with four 7/8-in. diameter, A193 B7 threaded rods which were provided as an equivalent option to the ASTM A325 anchor bolts (or SAE Grade 5 threaded rods). One inch diameter holes were used in the anchor plates. Recently, the MnDOT inquired about replacing the existing 1-in. diameter holes with 2" long by 1-3/16" slotted openings in the longitudinal rail direction. This modification was desired in order to allow for improved constructability and attachment of the upper steel railing system to the parapet after the anchor bolts have been installed. Based on the safety performance observed for the bridge railing using the TL-4 guidelines found in NCHRP Report No. 350, it would seem reasonable to modify the holes in the anchor plate to use a 2" by 1-3/16" slotted holes. However, it would be recommended that ¼-in. or 5/16-in. thick plate washers made from a structural grade material be used with the 7-8-in. diameter, high-strength anchor rods in combination with the slotted holes. When increasing the hole size, it is also recommended that consideration be given to providing the appropriate end/edge distances

Response

Response
(active)

The crash tested, combination tube bridge rail with concrete parapet and brush curb utilized a ¾-in. thick post base plate for anchoring the tubular post and rail system. The base plate was anchored to the concrete parapet with four 7/8-in. diameter, A193 B7 threaded rods which were provided as an equivalent option to the ASTM A325 anchor bolts (or SAE Grade 5 threaded rods). One inch diameter holes were used in the anchor plates.

Recently, the MnDOT inquired about replacing the existing 1-in. diameter holes with 2" long by 1-3/16" slotted openings in the longitudinal rail direction. This modification was desired in order to allow for improved constructability and attachment of the upper steel railing system to the parapet after the anchor bolts have been installed.

Based on the safety performance observed for the bridge railing using the TL-4 guidelines found in NCHRP Report No. 350, it would seem reasonable to modify the holes in the anchor plate to use a 2" by 1-3/16" slotted holes. However, it would be recommended that ¼-in. or 5/16-in. thick plate washers made from a structural grade material be used with the 7-8-in. diameter, high-strength anchor rods in combination with the slotted holes. When increasing the hole size, it is also recommended that consideration be given to providing the appropriate end/edge distances

Date January 8, 2010
Previous Views (47) Favorites (0)