U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Ave. S.E.
Washington, D.C. 20590
May 17, 2011
In Reply Refer To:
HSST/B-221
Mr. Robert Bielenberg
Midwest Roadside Safety Facility
527 Nebraska Hall
P. O. Box 880529
Lincoln, NE 68588-0529
Dear Mr. Bielenberg:
This letter is in response to your request for Federal Highway Administration’s (FHWA) acceptance of a roadside safety system for use on the National Highway System (NHS).
Name of system: TL-3 Upstream Anchorage for F-shape Temporary Concrete Barrier Type of system: Portable Longitudinal concrete Barrier End Anchorage Test Level: AASHTO Manual for Assessing Safety Hardware TL-3 Testing conducted by: Midwest Roadside Safety Facility Date of request: December 20, 2010 Date initially acknowledged: December 22, 2010 Task Force 13 Designator: SWC17
You requested that we find this system acceptable for use on the NHS under the provisions of the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH).
Requirements
Roadside safety devices should meet the guidelines contained in the MASH.
Decision
The following devices are found acceptable, with details provided below:
Description
The as tested barrier consisted of 156.5 feet (47.7 meter) long test installation consisting of the following two major components:
The concrete barrier utilized Iowa’s Concrete Barrier Mix, which was configured with a minimum 28 day concrete compressive strength of 5,000 psi (34.5 MPa). A minimum concrete cover varied at different rebar positions within the barrier. A minimum concrete cover of 2 inches (51 millimeters) was used along the top of the vertical stirrup rebar and at the bottom of the longitudinal rebar. Minimum concrete cover of 1-3/4 inches (44 millimeters) and 1 inch (25 millimeters) were used along the sides of the vertical stirrup rebar and at the rebar around the anchor bolt block, respectively. All steel reinforcement in the barrier conformed to ASTM A615 Grade 60 rebar, except for the loop bars which were ASTM A706 Grade 60 rebar. Barrier reinforcement consisted of three Number 5 and two Number 4 longitudinal bars, twelve Number 4 bars for the vertical stirrups, and six Number 6 bars for the anchor bolt block reinforcement loops. Each of the 5 longitudinal rebars was 12 feet 2 inches (3.71 meters) long. The vertical spacing of the lower, middle, and upper longitudinal bars were 6-1/2 inches (165 millimeters), 14-1/2 inches (368 millimeters), and 29-1/8 inches (780 millimeters) from the ground to their centers, respectively. The vertical stirrups were 72 inches (1,829 millimeters) long and were bent into the shape of the barrier and the spacing is varied longitudinally. The reinforcing steel loops used around the tie-down anchor holes in the barrier were 35 inches (889 millimeters) long, were bent into a U-shape, and were used to reinforce the anchor bolt area.
The barriers used a pin and loop type connection comprised of two sets of three rebar loops on each barrier interconnection. Each loop assembly was configured with three ASTM A706 Grade sixty Number 6 bars that were bent into a loop shape. The vertical pin used in the connection consisted of a 1-1/4 inches (32 millimeter) diameter x 28 inches (711 millimeter) long round bar comprised of ASTM A36 steel. The pin was held in place using one 2-1/2 inches wide x 4 inches long x 1/2 inch thick (64 millimeters x 102 millimeters x 13 millimeters) ASTM A36 steel plate with a 1-3/8 inches (35 millimeters) diameter hole centered on it. The plate was welded 2-1/2 inches (64 millimeters) below the top of the pin. A gap of 3-5/8 inches (92 millimeters) between the ends of two consecutive barriers was formed from the result of pulling the connection taut.
The upstream-most barrier segment was installed with 36 inches of the downstream end placed on the concrete surface and the remainder of the barrier segment resting on soil. This end barrier was anchored by two cable assemblies that connected the end connector pin to two driven, steel pile, anchor posts. Each of the two anchor posts was a 8 feet (2,438 millimeters) long, W6 x 25 (W152 x 37.2) steel section with a 24 inches x 24 inches x 1/2 inch thick (610 millimeters x 610 millimeters x 13 millimeters) soil plate welded to the front flange and a 1/2 inch (13 millimeters) thick plate welded to the top of the post. The anchor posts were placed in soil with an embedment depth of 8 feet (2,438 millimeters). One post was located along the longitudinal axis of the system, 45-3/8 inches (1,153 millimeters) upstream of the edge of the first barrier. The second post was located 29-3/8 inches (746 millimeters) upstream of the first barrier and offset 11-1/2 inches (292 millimeters) laterally from the traffic side face of the barrier.
The soil pit underneath the asphalt surface was comprised of a crushed limestone aggregate soil satisfying the standard soil requirements of MASH. Cable brackets were bolted to the top of the anchor posts.
The cable brackets were assembled using multiple 1/2 inch (13 millimeters) thick A36 steel plates welded together. The cable assemblies were comprised of a 3/4 inch (19 millimeters) diameter, 7 x 19 wire rope, BCT cable end fitting, a Crosby heavy-duty HT thimble, and a 115-HT mechanical splice. It should be noted that the wire ropes were ordered as 6 x 19 IWRC IPS wire ropes in order to be consistent with the wire rope specifications for W-beam guardrail cable anchorages. However, the manufacturer substituted the 7 x 19 wire rope as an equivalent to the 6 x 19 IWRC IPS. The substitution was not determined until the wire ropes were disassembled after the full-scale crash test. One 54-3/4 inches (1,391 millimeters) long cable assembly was aligned with the longitudinal axis of the barrier system. This cable assembly was attached with one end fixed between the lower barrier loops on an additional connection pin on the upstream end of the barrier and the other end attached to the anchor post. The end connector pin utilized a second 2-1/2 inches wide x 4 inches long x 1/2 inch thick (64 millimeters x 102 millimeters x 13 millimeters) ASTM A36 steel plate and a ½ inch diameter x 10 inches long (13 millimeters diameter x 254 millimeters long) Grade 8 hex bolt and nut at the bottom of the pin to prevent the pin from pulling out of the barrier loops when the anchorage was loaded.
The second cable assembly measured 48 3/8 inches (1,229 millimeters) long, and it was attached from just below the top barrier loop on the connector pin on the end of the barrier to the offset anchor post. A pin sleeve, made from 1-1/2 inches (38 millimeters) Schedule 40 pipe, was used to keep the anchor cables in the correct vertical positions. The use of the pin sleeve also allowed the cable anchorages to be attached at the same vertical position on the end pin regardless of which end of the F-shape barrier was used. Thus, if the barrier ends were reversed, the offset cable would attach to the connection pin between the top two barrier loops, and the in-line cable would attach to the connection pin between the pin sleeve and lower barrier loop.
However the as-built physically crash tested system details as described herein slightly vary from the following Test House recommended variances.
Crash Testing
The barrier was crash tested at the test facilities at the Midwest Roadside Safety Facility. Terminals and crash cushions, such as temporary concrete barrier terminations, must satisfy impact safety standards provided in the MASH, in order to be accepted by the FHWA for use on the NHS for new construction projects or as a replacement for existing designs not meeting current safety standards. According to Test Level 3 of MASH, non-gating terminals and crash cushions must be subjected to the following 9 full-scale vehicle crash tests:
The temporary concrete barrier termination and anchorage system, as described herein was designed with the intention of either placing an approved impact attenuator, such as sand barrels, in front of the anchorage posts or placing the anchorage system outside of the clear zone. However, most of the crash tests for terminals and crash cushions that are required in the MASH test matrix do not need to be conducted because they have been previously addressed in the prior successful compliance testing programs. Placement of the termination and anchorage system outside of the clear zone would also negate the need for the majority of the required terminal and crash cushion tests. Tests 3-30 through 3-33 and 3-38 are used to evaluate vehicle stability and containment issues related to impacts at the head of a crash cushion. Tests 3-34 and 3-36 evaluate the front end of crash cushions for either their behavior when impacted at a critical impact point or for transitioning to rigid barriers, respectively. Thus, both tests are not intended to evaluate the safety performance of the concrete barrier or termination anchor system.
Therefore, Test 3-35 is only crash test recommended for this test with further recommendation to waive the remaining tests.
Findings
The analysis of the test results showed that the temporary concrete barrier termination and anchorage system adequately contained and redirected the vehicle. There were no detached elements or fragments which neither showed potential for penetrating the occupant compartment nor presented undue hazard to other traffic. The deformation of, or intrusion into, the occupant compartment was minimal and did not pose a threat to cause serious injury. The test vehicle did not penetrate nor ride over the barrier and remained upright during and after the collision. Vehicle roll, pitch, and yaw angular displacements were within tolerable limits of the MASH. The occupant impact velocities and ridedown accelerations were within the recommended limits for the impacting vehicle. There was no significant deformation of the roof, windshield or occupant compartment. After impact, the vehicle exited the barrier at an angle of 15.9 degrees and did not intrude into adjacent traffic lanes.
The system described in the request above and detailed in the enclosed drawings is acceptable for use on the NHS under the range of conditions tested, when such use is acceptable to a highway agency.
Crash Test Summary details of this system are provided as enclosures to this correspondence.
Please note the following standard provisions that apply to FHWA letters of acceptance:
Sincerely yours, /* Signature of Michael S. Griffith */ Michael S. Griffith |
Enclosures
