Concrete Products

MAR 2016

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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www.concreteproducts.com March 2016 • 55 TECHNICAL TALK 2016 TRB MEETING Also, as most highway pavement work zones are restricted in lateral width, it's desirable to minimize the deflection of tempo- rary barriers to minimize required buffer distance, and optimize the space and number of lanes available for traffic. Normally, Jersey or the refined F-shape barriers utilize tie-down systems, which anchor barriers to the roadway surface, Bielenberg, Schmidt, Faller, Reid and Emerson observe. But these require alteration of the road or bridge surface, and also pose the risk of damaging the pavement during a severe impact event. In response, the Wisconsin DOT looked for a retrofit method for limiting barrier deflection without the need for additional tie-down anchors. WisDOT also desired the safety performance of the new low-deflection TCB system meet the Test Level 3 (TL-3) safety require- ments published in AASHTO's Manual for Assessing Safety Hardware (MASH). The research effort developed a stiffening mechanism to reduce the deflection of temporary concrete barriers without requir- ing anchorage of the barrier segments to the road surface, and was developed for use with the Midwest Pooled Fund States 12.5-ft long, F-shape, precast TCB. This new, low-deflection system is designed to be retrofitted to an existing F-shape TCB and not require anchoring to the roadway surface. "After considering several alternatives, the researchers selected a low-deflection TCB design focused on a steel cap plate bolted across the TCB joint and continuous steel tubes running along the sides of the barrier segments," write Bielenberg, Schmidt, Faller, Reid and Emerson. "It was anticipated that combination of the steel cap and the tubes would be effective at limiting barrier deflection through composite action, and the continuous tubes would provide for increased vehicle stability by presenting a more vertical impact face." Ultimately, the barrier system test installation was composed of 16 12.5-ft.-long F-shaped TCB installed with the back of the barrier segments offset 24 inches from a simulated bridge deck edge. This ini- tial barrier system consisted of a cap plate bolted across the TCB joint and continuous tubes running along the sides of the barriers that would limit unit deflection and provide for increased vehicle stability by providing a more vertical face during vehicle impact. An initial full-scale crash test was conducted on this low-deflec- tion TCB design. The impacting vehicle was safely and smoothly redi- rected in the test and all of the barrier segments were safely retained on the edge of the bridge deck with a peak dynamic lateral deflec- tion of 43 inches. Via simulation tests, additional attachment points between the tubes and the TCB were developed to further stiffen the barrier system. Another full-scale crash then was conducted on this revised, low-deflection TCB design. The impacting vehicle was safely and smoothly redirected in the test, and all of the barrier segments were safely retained on the edge of the bridge deck, with a peak dynamic lateral deflection of the barrier system at 40.7 inches. The latter test suggested that the low-deflection TCB design was limited by the TCB segment capacity, and that further redesign of the retrofit deflection reducing system would have negligible benefit without additional deflection limiting mechanisms or barrier rein- forcement changes. "[T]here may be a desire to adapt the low-deflection TCB system developed in this research to other TCB designs," Bielenberg, Schmidt, Faller, Reid and Emerson say. "It is believed that this design could be adapted to other systems with some additional considerations with respect to barrier segment capacity, joint design, barrier geometry and other factors." Continued on page 56 Stephens manufactures dry bulk pneumatic trailers, crude oil trailers, gasoline trailers and vacuum trailers. Stephens sells parts and performs minor and major repair work. Contact us at 800-353-1033 or at sales@stephenstankproducts.com. STEPHENS

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