We are employing PennDOT’s PA steel-on-concrete MASH TL-5 barrier on our upcoming Mississippi River bridge replacement project at Lansing. We’ve previously discussed the superstructure setback distance, bicyclist pass-through protection elements, and 2” overall height increase for overlay associated with the barrier’s design. (BTW for your records, we ultimately decided to accommodate the full as-tested working width in our superstructure setback location).
We are now faced with some minor detail issues associated with attachment of guide rail to the PennDOT standard end section of this rail system. The 2 inch overall height increase creates a non-standard condition when compared to the PennDOT standard drawings, and the overall height of guide rail that PennDOT uses is also slightly less (-3/8”) than Wisconsin’s standard 2’-8 guide rail. Please review the attached markups of the PennDOT standard drawings for our proposal (“PennDOT PA Stds MODIFIED.pdf”). Essentially, we’d like to accommodate the 2 inch overall barrier height increase at the AGT by employing the symmetrical thrie beam guide rail transition configuration detailed in TRP-03-387-19, 34-IN. Tall Thrie Beam Transition to Concrete Buttress. Other minor detail adjustments are required in the steel connection plates at the AGT to PennDOT PA end section because of the overall 2 inch height raise, the minor 3/8” discrepancy between PennDOT standards, and the setup shown in TRP-03-387-19. Our posted speed for the affected segment will be 40 MPH (see “Lansing bridge with speeds.pdf”). Also attached are some illustrative 3D views of the proposal.
I believe you’ve already had some correspondence with Erik at Wisconsin DOT regarding the position of the first guide rail mounting post relative to the end of concrete parapet, which does not match the standard dimension in this scenario. Apparently this did not raise any concerns for you about AGT performance. Please reiterate that opinion as part of this review. Also, the AGT shoe in this configuration requires 4 additional bolt holes to accommodate the PennDOT connection detail. Please assess this configuration for us, since both WI and IA typically use a standard 5-hole shoe.
We are also interested in your opinion of the PennDOT standard terminal configuration of the steel tube traffic rails. If you identify any potential concerns with the details for our conditions, please let us know if you have any recommendations for improving the details.
As always, thank you very much for your time and expertise in reviewing these items.
We reviewed the proposed modification of the PennDOT system and believe that it looks acceptable for the most part. We do have a few comments.
Let me know if you have comments or questions.
Thanks for the thorough feedback.
A couple of questions come out of a closer look at applying your recommendations. These are illustrated in the attachment.
Q1. Does extending the PennDOT PA standard ½” thick mounting plate slightly (0.5 inches) downstream in order to get the tapered edge out from behind the AGT shoe create any concerns?
Q2. The 2:1 steel top tube gets excessively long if the end is to be held entirely below the top of thrie beam. While I don’t think this presents any constructability or fit-up concerns, it’s very unusual to have the steel portion of a combination barrier extend beyond the concrete parapet. Even if we were to move the bend point of the tube closer to the post, I don’t think we can gain the roughly 4.5 inches necessary to keep the end of the steel coincident with the end of the concrete. Any thoughts or suggestions? Must the entire top tube terminus be kept below the top of thrie beam?
In response to your questions: