Transition Design for Temporary Concrete Barrier (405160-26)

Transition Design for Anchored to Free-Standing Temporary Concrete Barrier

Problem Statement

TTI recently develop a pinned down F-shape temporary concrete barrier system that provides limited lateral deflection (less than 6 inches) and can be used for bridge or roadway applications. The design was developed for use on concrete pavements or bridge decks as thin as seven inches. If this application is used on a roadway and bridge project, it is possible that a non-anchored free-standing barrier section may be used with the anchored section. A transition detail from the anchored to free-standing barrier is needed to prevent increased occupant risk or vehicle instability due to abrupt changes in barrier’s lateral stiffness.

Background

In 2008, TTI developed a restrained F-shaped temporary concrete barrier design that was easy to install and minimized damage to the bridge deck or concrete pavements (1). This restraint mechanism was developed for use on concrete bridge decks and pavements. It used 1.5-inch diameter steel pins that were dropped into inclined holes cast in the toe of the barrier segments. The pins passed through the holes in the barrier and continued short distance into the underlying concrete pavement, thus locking the barrier in place. The pinned-down barrier successfully passed the National Cooperative Highway Research Program (NCHRP) Report 350 Test Level 3 requirements. The maximum permanent and dynamic barrier deflections were 5.76 inches and 11.52 inches, respectively. There was no significant damage to the underlying concrete pavement. The design has now been adopted by some of the participating pooled-fund states and there is a desire to develop a transition for using the pinned down barrier with the free-standing barrier.

In 2003, Midwest Roadside Safety Facility (MwRSF) developed a concrete bridge deck tie-down system for 12.5 ft long, F-shaped Kansas temporary barriers (2). Three anchor bolts were passed through the holes in the barrier and fastened to the bridge deck on the traffic side of the barrier. The maximum static and dynamic deflections were 3.5 in. and 11.3 in., respectively. Later on in 2005, MwRSF developed an NCHRP Report 350 compliant tie down design for 12.5-ft long temporary concrete barriers with pin-and-loop type connection for use on asphalt pavements that are at least two inches thick (3). The barrier was installed at a 6-inch lateral offset from the edge of a ditch. This tie-down system used three 1.5-inch diameter steel pins that were driven down vertically through holes cast in each barrier segment. The pins were 3-ft long and pinned the barrier to the underlying asphalt ground. The maximum static and dynamic deflections in the test were 11.1 inches and 21.8 inches, respectively.

In this same study, MwRSF also developed a transition from the free-standing 12.5-ft long temporary concrete barrier to the anchored temporary concrete barrier design developed earlier in 2003. The transition section comprised of four 12.5-ft long barrier segments in which steel pins were driven in through the holes in the barrier. The number of pins in the transition barrier segments was gradually reduced to transition from the anchored to the free standing barrier. Barrier segment in the transition section of this design were placed on a 2-inch thick asphalt layer. The barrier was installed at a 6-inch lateral offset from the edge of a ditch. The maximum static and dynamic deflections in the test were 5.25 inches and 18.39 inches, respectively.

In 1999, California Department of Transportation (Caltrans) developed a pinning/staking configuration for its 20-ft long, NJ profile concrete barriers connected with a pin-and-loop type connection (4). The configuration met NCHRP Report 350 evaluation criteria and consisted of four 1-inch diameter pins that were driven 16.5 inches vertically into the underlying asphalt pavement. Each barrier segment was pinned at its four corners. The barrier was tested in a median configuration and there was no ditch or slope behind the barrier. The maximum static and dynamic deflections of the system were 2.75 inches and 10 inches, respectively.

Objective

The objective of this research is to develop a transition design that can be used to transition from the pinned-down F-shape barrier placed on concrete to free-standing F-shape barrier placed on pavement (concrete or asphalt). If it is determined during initial evaluation that a single transition design cannot be achieved for the free-standing barrier placed on both, concrete and asphalt, the transition will be developed for use with the free-standing barrier on concrete pavement only. The transition is to be developed for MASH test level 3 criteria, using the existing pinned F-shape temporary concrete barrier design to the extent possible.

Benefits

A successful transition detail can be applied in situations when the pinned-down barrier on concrete transitions to free-standing barrier. The design will result in successful redirection of impacting vehicles in the transition zone as per the MASH test level 3 requirements.

Products

TTI will provide composite video and photographic documentation of the crash test and a final report suitable for submittal to Federal Highway Administration (FHWA) documenting the research and/or testing performed. Discussion needed to request FHWA’s acceptance of the concrete barrier system for use on the National Highway System will be provided.

TTI will further provide drawings of the concrete barrier system and of each of the components of the system in the format required for inclusion in hardware standards documents of the AASHTO-ATRBA-AGC Task Force 13.

Implementation

As stated above, TTI will provide all the supporting information and written discussion for submitting a request to FHWA for acceptance of the concrete barrier system for use on the National Highway System.

The research will provide information and documentation on testing of the concrete barrier system so that design and operational standards can be further reviewed and evaluated. Detailed engineering drawings that will facilitate development of standards sheets and specifications will be provided to each participating state.

Drawings provided for Task Force 13 documents will further support implementation of the research.

Work Plan

The researchers will develop transition details using the existing F-shape pinned-down barrier design to the extent possible. The transition will be connected to the pinned-down temporary concrete barrier installed on concrete pavement on one side. The other side of the transition will connect to the free-standing concrete barrier placed on concrete or asphalt. The overall design approach of the researchers will be to install inclined pins into the holes cast into the barrier’s toe and drive them into the underlying surface to attain sufficient lateral restraint. The number of pins installed in the barrier segments will be gradually reduced from the pinned-down barrier side to the free-standing barrier side, thus allowing a smoother transition between the two barriers.

Along with this research Task Order, the pooled-fund states have agreed to fund another research Task Order (2010 TTI/21) that has the objective of extending the pinned-down anchored barrier design for use on soil or asphalt. Due to the similarities and overlap of some of the tasks needed to complete both of these Task Orders, the researchers have prepared this proposal assuming that both Task Orders will be executed in parallel. Thus cost of some of the needed tasks (Task 1 and Task 2 below) that will be performed under the other Task Order (2010 TTI/21) have not been included in this proposal. If the pooled-fund states decide not to proceed with the Task Order 2010 TTI/21, additional financial resources will need to be allocated to this project for completing Tasks 1 and 2. For the sake of completeness, all tasks needed for this research (whether budgeted herein or in the other Task Order) have been described in the work plan below.

Task 1: Pendulum Testing for Pin Pullout Response

This task has been budgeted under the separate parallel Task Order (2010 TTI/21) (Development of Pinned-Down Barrier for use on Soil or Asphalt).

In this task, the researchers will conduct a series of pull-tests to determine the response of the inclined steel pins embedded in soil. The pins will be embedded to different depths and will be pulled by applying a lateral dynamic load using a drop pendulum. A load cell will be used to determine the lateral load applied on the pins. The lateral movement of the pins will also be measured. A total of three tests will be performed.

Task 2: Simulation Analysis for Calibrating Soil Response

This task has been budgeted under the separate parallel Task Order (2010 TTI/21) (Development of Pinned-Down Barrier for use on Soil or Asphalt).

In this task, the researchers will develop finite element models of the pendulum tests conducted in Task 1. By simulating the pull tests with pins at various embedment depths, the researchers will calibrate properties of the soil material model and ensure that the soil-pin interaction is adequately captured by the model. LS-DYNA finite element analysis package will be used for performing all simulations in this research.

Task 3: Design and Analysis of Transition Barrier System

In this task, the researchers will make a determination if a single transition design can be achieved for transitioning from the anchored barrier to free standing barrier placed on concrete and asphalt/soil. The researchers will perform drop-pin pullout simulations to determine the force required to plastically deform the drop-pins installed in concrete pavement (similar to Task 2). A comparison of the lateral force will be made with the force levels observed in pull tests of pins embedded in soil (as determined in Task 1). If the force required to the bend the drop-pins in concrete is comparable to the force required to bend the drop-pins embedded in soil, it would imply that a transition design that works on soil will also work on concrete and asphalt. Thus the researchers will develop the transition design for placement on soil. However, if the drop-pins embedded in soil are not able to achieve the same lateral restraint for a reasonable pin embedment, it would imply that a barrier segment placed on soil will need more than two pins to achieve the same level of lateral restraint as a barrier segment pinned on concrete. Thus a transition design that performs successfully on soil may be too stiff when installed on concrete, and therefore a different design would be needed for use on concrete. In this scenario, the researchers will develop the transition design for use on concrete pavement only.

The researchers will develop a design concept of the transition barrier that includes varying the number of the inclined anchoring pins along the length of the transition. This will allow gradual variation in the lateral restraint of the barrier as it transitions from the nearly rigid pinned-down barrier to the more flexible free-standing barrier.

The researchers will develop a full-scale model of the transition barrier installation. The model will include the pinned-down anchored barrier system at one end of the transition, and the free-standing barrier on the other end. Different combinations of pin numbers and locations in the transition section will be evaluated by performing full-scale vehicle impact simulations. These simulations will be performed with MASH test level 3 conditions (i.e. 2270-kg pickup vehicle, impacting at 100 km/h and 25-degrees). The results of the simulation analysis will be used to arrive at the final transition design for crash testing.

For transitions between rigid and free-standing barrier, there are generally two locations of significant change in lateral resistance of the barrier. One is where the vehicle impacts from the rigid barrier, going towards the free-standing barrier. The other is where the vehicle impacts from the free-standing barrier, going towards the rigid barrier. Crash testing is generally required to demonstrate adequate performance of the transition at both of these locations. However, it can be argued that the anchored barrier on concrete is not a completely rigid system and has shown some flexibility in previous testing. This flexibility reduces the abrupt change in lateral resistance of the barrier in the transition region. Thus the test in which the vehicle transitions from the semi-rigid anchored barrier to the free-standing barrier is not critical. In the past, researchers (3) have developed a transition design which was accepted by FHWA based on a single test (vehicle transitioning from free-standing to semi-rigid anchored barrier). Due to the similarities of the overall transition design methodology, it is expected that only one test will be ultimately required for the new transition design. The researchers will however perform full-scale impact simulations for both transition locations to demonstrate that the transition from the semi-rigid anchored barrier to free-standing barrier is not critical, and only one test is needed. This proposal therefore budgets only one crash test, where vehicle transitions from free-standing to semi-rigid anchored barrier. It should be noted that if the simulation results indicate that transitioning from anchored to free-standing barrier is also critical, a crash test may need to be performed under a separate project.

Task 4: Full-Scale Crash Testing and Final Report

Once the transition design has been has been finalized in Task 3, the researchers will perform test 3-11 of MASH (2270-kg vehicle, 100 km/hr, 25 deg). The test will be performed to verify simulation results. It is argued that the test with smaller 1100-kg is not needed. Due to higher impact energy, the test with the 2270 kg pickup truck will result in greater lateral deflection and help evaluate connection strength and the tendency of the barriers to rotate. An impact resulting from the lighter 1100-kg passenger car under same impact speed and angle will not result in any increase in lateral deflection of the barrier nor will it impart a higher force on the barrier to evaluate connection strength and barrier rotation. Thus the test will be conducted with the 2270-kg pickup only.

Waskey Bridge, which is a concrete barrier manufacturer in Louisiana, has agreed to donate 12.5-ft long concrete barrier segments for this research. TTI will arrange for shipping the barriers from the manufacturer to its testing facility under this contract. In the event that Waskey Bridge is unable to donate the barriers, additional funds will be needed to construct the barriers for testing.

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[1] Sheikh, N.M., Bligh, R.P., and Menges, W.L. (2008). “Crash Testing and Evaluation of the 12 ft Pinned F-shape Temporary Barrier.” Texas Transportation Institute, College Station, Texas.
[2] Polivka, K.A., Faller, R.K., Rohde, J.R., Holloway, J.C., Bielenberg, B.W., and Sicking, D.L. (2003). “Development and Evaluation of a Tie-Down System for the Redesigned F-Shape Concrete Temporary Barrier.” Midwest Roadside Safety Facility, Nebraska.
[3] Bielenberg, B.W., Reid, J.D., Faller, R.K., Rohde, J.R., and Sicking, D.L. (2006). “Tie-downs and Transitions for Temporary Concrete Barriers.” Transportation Research Record, TRR 1984.
[4] Jewel, J., Weldon, G., and Peter, R. (1999). “Compliance Crash Testing of K-Rail Used in Semi-Permanent Installations.” Report No. 59-680838, Division of Materials Engineering and Testing Services, CALTRANS, Sacramento, CA.