Development of a Tie-Down System for Temporary Concrete Barriers
Bob Bielenberg, Ronald Faller, John Reid, James Holloway, John Rohde, Dean Sicking
During construction of highways and bridges, it is common for temporary concrete barriers to be installed near the edge of a roadway or bridge deck during construction. Free-standing temporary barriers placed close to the bridge deck edge pose a major safety hazard to errant vehicles as there is a significant risk for the barrier segments to be propelled off of the bridge. Previous testing of temporary barriers have shown deflections of more than one meter. These large dynamic deflections, in combination with a narrow gap located behind the barriers, would prove sufficient to push the barriers as well as the impacting vehicle off of the bridge deck. In 1998, researchers at the Midwest Roadside Safety Facility (MwRSF) at the University of Nebraska-Lincoln (UNL) were approached to develop a tie-down system for this type of installation. This report details the development and testing of an NCHRP 350-compliant tie-down system for use with F-shape temporary concrete barriers. Development of the tie-down system began with the creation and evaluation of several design concepts. Following the researchers' evaluation of the design prototypes, the steel strap tie-down concept was selected for further study. This concept consisted of a steel strap that connected to the barrier joints and then bolted to the concrete bridge deck. The steel strap tie-down was analyzed and redesigned using LS-DYNA finite element computer simulation modeling. The strap tie-down is comprised of a 76-mm x 6.4-mm x 914-mm piece of ASTM A36 steel bent into a trapezoidal shape. Holes are punched in the plate to allow the connecting pin at the barrier joints to pass through the strap as well as allow the strap to be anchored to the bridge deck at each end. Anchoring of the strap to the bridge deck is done using two of 19-mm diameter drop-in anchors for each strap. The steel strap tie-down was bogie tested to evaluate its performance. One full-scale vehicle crash test, test no. ITD-1, was conducted according to Test Level 3 (TL-3) test no. 3-11 found in the NCHRP Report No. 350. The test consisted of a 2,012-kg pickup truck impacting the temporary barrier system at a speed of 97.6 km/h and at an angle of 24.3 deg. The impact occurred 1.2 meters upstream of the barrier joint. Results from the crash test showed that the system safely redirected the impacting pickup truck, and the test was judged to be successful according to the NCHRP Report No. 350 safety performance criteria. Based on the results of the NCHRP 350 compliance test, it is recommended that this design be approved for use on Federal-aid highways. Recommendations for proper application of the new design are also given.
Highway Safety, Temporary Barriers, Work Zones, Longitudinal Barriers, Concrete Barriers