Link to: Phase I
|TTI Research Supervisor:
William F. Williams, P.E.
Texas Transportation Institute
Texas A&M University System
College Station, Texas 77843-3135
|Pooled Fund Technical Representative:
Rod Erickson P.E.
Washington State Department of Transportation
310 Maple Park Avenue
P.O. Box 47329
Olympia, Washington 98504-7329
Adequate storm water drainage is necessary for safety on vehicular bridges and roadways. Washington State Department of Transportation (WSDOT) has developed a single slope concrete barrier that provides drainage to scupper openings located through the base of each barrier segment. This barrier is planned for use on high-speed roadways where drainage of the pavement surface is needed. The purpose of this project was to review the proposed barrier geometry and perform engineering analyses to size reinforcing steel and placement to resist Test Level 3 (TL-3) impact with respect to American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) crash specifications for TL-3 impact conditions.
The Washington Pin and Loop Barrier system tested for this project consisted of precast concrete barrier segments that were 12 ft-6 inches in length and 34 inches in height. The barrier segment was 8 inches wide at the top and 21 inches wide at the base with a uniform single slope surface on each side face of the barrier. A 4-inch high by 15‑inch wide “V” shaped cutout was centered in the base of the barrier and continuous along the entire length of the barrier segment. In addition to this longitudinal drainage slot, a drainage scupper opening was located at the center of the barrier segment. The drainage scupper opening was 9-inch high by 28 inches in width. This drainage scupper opening would permit drainage from the roadway through the barrier segment or along the barrier through the “V” shape drainage slot located in the base of the barrier. Three ¾-inch diameter steel loops were constructed on the ends of the barrier segments. These loops overlay three loops on the end of the adjacent barrier segment. The segments were connected together by inserting a 1¼-inch diameter steel rods. The ¾-inch steel loops were fabricated using A36 material. The 1¼-inch diameter steel rods were fabricated from ASTM F1554 grade 105 material and were 31 inches in length.
Vertical reinforcement (stirrups) in each barrier segment consisted of #4 rebar stirrups spaced as close as 4 inches on the ends to 11½ inches toward the center of the barrier segment . The stirrups were spaced on 7-inch centers (3 spaces) immediately above the drainage scupper located in the center of the segment. Longitudinal reinforcement in the barrier segment consisted of twelve #5 bars. The bars located in the bottom of the barrier segment were bent to accommodate the drainage scupper opening located in the center of the barrier segment.
The test installation consisted of 16 barrier segments connected together using the 1¼-inch diameter ASTM F1554 grade 105 rods. The total length of the test installation was approximately 200 ft. The minimum compressive strength of the concrete used to construct the units was specified to be 4000 psi. All reinforcing steel used to construct the barrier units was specified to be grade 60 material.
Figure 1. WSDOT Pin and Loop Barrier System.
MASH test 3-11 involves a 2270P vehicle weighing 5000 lb ±100 lb impacting the WSDOT pin and loop barrier with drainage slots at an impact speed of 62.2 mi/h ±2.5 mi/h and an angle of 25 degrees ±1.5 degrees. The target impact point was 4.3 ft upstream of the joint between segments 6 and 7.
The WSDOT pin and loop barrier with drainage slots contained and redirected the 2270P vehicle. Maximum deflection of the barrier during the test was 5.4 ft. No detached elements, fragments or other debris were present to penetrate the occupant compartment, show potential for penetrating the occupant compartment, or to present undue hazard to others in the area. Maximum occupant compartment deformation was 1.0 inch in the rear passenger area near the hip level. After loss of contact with the barrier, the 2270P vehicle rolled counterclockwise 121 degrees and came to rest on its left side. Occupant risk factors were within the limits specified in MASH. The 2270P vehicle exited within the exit box.
According to criteria for MASH test 3-11, the WSDOT pin and loop barrier with drainage slots did not perform acceptably due to rollover of the test vehicle.
Figure 2. WSDOT Pin and Loop Barrier and Test Vehicle
after MASH Test 3-11.