|Logged in as: Public User|
Are you aware of any states using your pin and loop in a median application using steel pins driven
through the asphalt pavement to minimize deflection? We were wondering if we
would need to use 3 steel pins on both sides of each unit (6 per unit)
throughout the installation where we needed to reduce deflection, or if the
pins could be alternated from side to side (3 per unit - 2 on one side and 1 on
other) throughout the installation.
|Date||December 18, 2013|
Currently, we do not recommend pinning or anchoring both side of the TCB in a tie-down application. Anchoring the barrier on the both sides creates a pivot point on the non-impacted side of the barrier that promotes barrier rotation and tipping and thus promotes vehicle instability. We cannot eliminate this concern without further analysis and/or testing, so we would recommend against it.
MwRSF previously developed and full-scale vehicle crash tested a tie-down system for use on concrete bridge decks and with the redesigned F-shape temporary concrete barriers, as shown in Figure 1. The tie-down system consisted of three 1â…›-in. diameter Grade 2 (ASTM A307) threaded dowel connections embedded approximately 12 in. into the concrete on the traffic side of each of the redesigned F-shape temporary concrete barriers. The barriers were placed 1 in. away from the edge of the concrete bridge deck. During full-scale crash testing with a ¾-ton pickup truck, the barrier safely redirected the pickup truck with minimal barrier deflections. The barrier system and was determined to be acceptable according to the TL-3 safety performance criteria presented in NCHRP Report No. 350.
A second a tie-down system for asphalt road surfaces was also developed at MwRSF that utilized three 1.5-in. diameter x 38.5-in. long ASTM A36 steel pins with 3.0-in. x 3.0-in. x 0.5-in. ASTM A36 steel caps installed in holes on the front face of each barrier segment, as shown in Figure 2. The tie-down design was then installed in combination with sixteen F-shape barriers on a 2-in. thick asphalt pad and crash tested according to NCHRP Report No. 350 test designation no. 3-11. The results showed that the vehicle was safely contained and redirected, and the test was judged acceptable according to the NCHRP Report No. 350 criteria. Barrier deflections for the system were reduced, and all of the barriers in the system were safely restrained on the asphalt road surface.
Both the bolted and asphalt pin tie-down options work by passing the anchors through holes in the toe of the traffic-side face of the PCB. Application of these options to two-way traffic installations has not been recommended in the past due to the need to place anchors on both sides of the barrier system. There are concerns that anchors on the backside of the barrier can create a rotation point when impacted and that may cause increased vertical barrier rotation and potential vehicle instability. CALTRANS testing conducted on the K-Rail PCB with anchorage on both sides of the barrier indicated that pins on the backside of the barrier system can safely redirect impacting vehicles, but also confirmed that vehicle instability was a problem. MwRSF conducted testing of a median approach transition between free-standing PCB segments and permanent concrete barrier with anchors on both sides of the PCB barrier segments to TL-3 of MASH using two crash tests. Both tests were successful, but the use of anchors on both sides of the barrier did seem to increase instability, especially the testing on the upstream end of the transition. However, it was difficult to determine from the approach transition tests how much of the vehicle instability was due to the transition in stiffness versus the increased rotation of the barriers with anchors on the back side. In addition, the impact occurred in a region where the anchor spacing was varied. Thus, there is potential for the F-shape PCB to perform safely when anchored on both sides for median applications. Finally, it is believed that if the asphalt pin tie-down system were demonstrated to perform safely with anchors on both sides of the barrier, then the bolted tie-down system would perform equally as well due to its increased rotational restraint.
There has been interest in the past from various state DOT’s to evaluate the use of pins on both sides, but no formal project has ever resulted.
Let me know if you have further questions.
|Date||December 18, 2013|
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
The information contained on the Midwest Roadside Safety Facility (MwRSF) website is subject to change without prior notice. The University of Nebraska and the MwRSF is not responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the use or misuse of or reliance upon any such content, goods, or services available on this site.