PROBLEM STATEMENT

Buried (in backslope) terminal designs for beam guardrail were developed under NCHRP Report 350 criteria for 27-inch (27 ¾-inch) high guardrail systems.  Some states have modified this design so that it could be used with 31-inch high guardrail systems.  Other agencies are hesitant to use this design for 31-inch high guardrail until it has been crash tested or deemed acceptable for use by FHWA.

BACKGROUND

A W-beam guardrail can be terminated by burying the end of the rail element into a soil berm.  This type of guardrail termination installation is referred to as a “buried-in-backslope end treatment”.  Buried in backslope terminal designs for beam guardrail were developed under NCHRP Report 350 criteria for 27-inch (760-mm) high guardrail systems (Ross et al., 1993).  

With the satisfactory performance of the modified G4(1S) W-beam guardrail system with timber blockouts, FHWA decided to evaluate two terminal designs of the W-beam, steel-post guardrail system with similar modification (i.e., timber blockouts).  Texas Transportation Institute (TTI) conducted the study with the scope of assessing the G4 guardrail system with timber blockouts as incorporated in two buried-in-backslope end treatments for W-beam guardrails (Arnold et al., 1999).  Tests were conducted in accordance with NCHRP Report 350, and involved a 2000P vehicle impacting the treatment conditions at nominal speed and angles of 62 mph (100 km/h) and 20 degrees, respectively.  The buried-in-backslope end treatment for the W-beam guardrail was tested under two configurations: one with a ditch and the other with a drop inlet.  The top of the rail was 27 inches (706 mm) measured from the shoulder grade  and the guardrail end was anchored to a concrete block buried in the backslope.     

For the ditch configuration, the earth was graded away from the shoulder at a 1V:10H slope for 5.9 ft (1800 mm), followed by a 2.95 ft (900-mm) wide ditch, then by a 1V:2H backslope.  For the drop inlet configuration, the earth was graded away from the shoulder at a 1V:10H slope for 8.85 ft (2700 mm), followed by a 1V:2H backslope.  Both installations met evaluation criteria set forth for NCHRP Report 350 test designation 3-35. there was minimal deformation and no intrusion into the occupant compartment.  The occupant risk factors were all well within the recommended limits.  

The buried terminal design was also successfully tested on installations with a 1V:6H V-ditch and with a 1V:4H foreslope, both according to NCHRP Report 350 test designation 3-35 (Buth et al., 2000).  These tests were intended primarily to evaluate the ability of the device to contain and redirect a 2000-kg pickup truck (structural adequacy criteria).  The tests performed were NCHRP Report 350 test designation 3-35, with a 2000P vehicle impacting the beginning of the length of need of the terminal at a nominal speed and impact angle of 62 mph (100 km/h) and 20 degrees, respectively.

 The buried-in-backslope terminal with a 1V:6H ditch contained and redirected the vehicle.  Maximum deformation of the occupant compartment was 1.77 inches (45 mm) and was judged to not cause serious injury.  The terminal performed acceptably for NCHRP Report 350 test designation 3-35.  The buried-in-backslope terminal with a 1V:4H slope contained and redirected the vehicle.  Maximum deformation of the occupant compartment was 4.9 inches (125 mm) and was judged to not cause serious injury.  The terminal performed acceptably for NCHRP Report 350 test designation 3-35.  

The satisfactory performance of the buried-in-backslope guardrail tests in different ditch configurations culminated with an FHWA letter of acceptance # CC 53A (Acceptance Letter, 2001).  

During the last years, the existing standard guardrail heights were increased to 31 inches.  In addition, an update to NCHRP Report 350 was developed under NCHRP Project 22-14(02), “Improvement of Procedures for the Safety-Performance Evaluation of Roadside Features” (AASHTO, 2009).  AASHTO published this document, the Manual for Assessing Safety Hardware (MASH), which contains revised criteria for safety-performance evaluation of virtually all roadside safety features.  For example, MASH recommends testing with heavier light truck vehicles to better represent the current fleet of vehicles in the pickup/van/sport-utility vehicle class.  The large design test vehicle was changed from a ¾ ton pickup to a ½ ton, four-door pickup.  Also, certain nominal conditions for certain type of tests have changed.  For example, MASH test designation 3-35 requires an impact nominal angle of 25 degrees, instead of the 20-degree angle required by NCHRP Report 350 test 3-35.  

Considering these vehicle and nominal impact modifications, it is advisable that the buried-in-backslope terminal design for a 27-inch high guardrail is revised to satisfy the new MASH criteria for a 31-inch high guardrail.

OBJECTIVE

The objectives of this study are to identify design modifications necessary to adapt a buried terminal design for 27-inch (27¾-inch) guardrail for use with a 31-inch guardrail system and to determine the terminal crashworthiness according to MASH criteria.  This project is expected to culminate with a request for an FHWA acceptance letter for this design.

BENEFITS

A successful outcome will increase the application of this countermeasure through a higher confidence level in the acceptability of this design.  It will offer a means to shield guardrail ends from direct hits, reducing potential for penetration behind the end terminal and/or for the guardrail to penetrate the vehicle.

PRODUCTS

TTI will provide a detailed design of a buried terminal anchorage of 31-inch guardrail systems.  TTI will generate standard sheets including design details and drawings based on the study results of the proposed device.

IMPLEMENTATION

Details and drawings will be used to develop standard sheets.  The results of the simulations will help determine if any crash test(s) will be required to validate the proposed design’s MASH crashworthiness. If the researchers and the WSDOT agree that no crash test(s) is/are required as further validation of crashworthiness, proper documentation and drawings will be developed with the intent of requesting an acceptance letter from FHWA. 

WORK PLAN

Task 1 — Conduct literature review on existing buried terminal anchorage of 27-inch guardrail system designs

The researchers will perform a literature review of current designs for buried terminal anchorage of 27-inch (27¾-inch) guardrail systems.

Task 2 — Perform strength analysis of selected design(s)

The researchers will explore current buried terminal designs and evaluate their compatibility with a 31-inch high guardrail system.  Detail design for the anchor will be investigated, if necessary.  1V:4H and 1V:6H slope installations will be evaluated.  The researchers will perform engineering strength analysis on the selected design(s) according to AASHTO LRFD.  This analysis will evaluate the design(s) ability to anchor the guardrail system in a MASH impact condition (AASHTO, 2009).

Task 3 — Perform finite element analysis for buried terminal crashworthiness

The researchers will investigate and determine the crashworthiness of terminal design selected.  The investigation will be conducted by simulating the impact conditions recommended by the Manual for Assessing Safety Hardware (MASH) 2009 for terminals.  LS-DYNA program will be used for the non linear finite element analyses.  A total of four impact conditions will be considered for finite element simulations during this evaluation:

◊ Test 3-34.                 It involves a 2425-lb passenger car (designation 1100C) impacting the test article at 15 degrees and 62 mph.  By considering this impact condition, the researchers would like to evaluate the impact performance of terminals at the critical impact point (CIP) where the behavior of these devices changes from gating or capturing to redirection.  CIP locations will be determined through a series of finite element simulations.  1V:4H and 1V:6H slope installations will be evaluated to determine worst case for impact performance.  The selected worst case slope condition will be used for all finite element simulations.  Vehicle trajectory and occupant risk are the primary concerns for this test configuration. 

◊ Test 3-35.                 It involves a 5000-lb pickup truck (designation 2270P) impacting the test article at 25 degrees and 62 mph.  By considering this impact condition, the researchers would like to examine the capacity of a terminal for containing and redirecting heavy passenger vehicles.  For this configuration, a 2270P vehicle is directed into the system at the beginning of the length of need at an impact angle of 25 degrees.

◊ Test 3-37.                 It involves a 5000-lb pickup truck (designation 2270P) impacting the test article at 25 degrees and 62 mph.  By considering this impact condition, the researchers would like to examine the behavior of terminals during reverse direction impacts for a 2270P vehicle.

◊ Test 3-37 (mod).    In addition to the three configurations above, the researchers suggest simulation of Test 3-37 with use of a 1100C vehicle (Test 3-37 modified). It involves a 2425-lb passenger car (designation 1100C) impacting the test article at 15 degrees and 62 mph.  By considering this impact condition, the researchers would like to examine the behavior of terminals during reverse direction impacts for a 1100C vehicle, to evaluate the potential of under riding and snagging of a small passenger car in this condition.

Task 4 — Evaluation and Reporting

The researchers will generate a final report documenting the findings from the study approach, findings and recommendations.  In addition, the report will include drawings and details that may be used in the development of a request for a FHWA letter of acceptance. 

____________________

AASHTO (2009). Manual for Assessing Safety Hardware. American Association of State Highway and Transportation Officials. Washington, D.C. 

Acceptance Letter: Buried-in-backslope Guardrail. Anchor on 1V:4H Foreslope, http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/barriers/pdf/cc_53a.pdf, Accessed in 2011. [FHWA Approval Letter No. CC53A]. 

Arnold, G.A., Buth, C.E., and Menges, W.L., S.K. (1999). Testing and Evaluation of W-Beam Guardrails Buried-in-Backslope. FHWA-RD-99-055.  

Buth, C.E., Menges, W.L., and Schoeneman, S.K. (2000). NCHRP Report 350 Assessment of Existing Roadside Safety Hardware. FHWA-RD-01-042.  

Ross, H. E., Sicking D. L., et al. (1993). Recommended Procedures for the Safety Performance Evaluation of Highway Features. NCHRP Report 350. Washington D.C.

Problem Statement

A general problem occurs at many bridge locations along highways where the required length of need for bridge approach rails cannot be met within the existing right-of-way (ROW) limits.  These conflicts occur when existing driveways, roads, or other objects are within the ROW.  It is not unusual to have less than 15 feet length between the end of the bridge and conflict.  Solutions to this problem have included using short radius guardrail, a shortened guardrail section, or a crash attenuator.  Typically, these solutions are not practical for the site location or are not cost effective.  This project is intended to develop a best practices guideline for solutions implemented at these locations.  The scope of this study will include a literature review and survey of state’s departments of transportation (DOT) to develop a best practices guideline.

Background

Typically, a rigid longitudinal barrier is used to contain errant traffic at a highway bridge location.  These rigid longitudinal barriers present an obstacle at their terminations for oncoming traffic.  There are several methods designers use to alleviate these obstacles.  Often a guardrail terminal system is used as an approach rail to the bridge location; however, a general problem occurs at many bridge locations along highways where the required length-of-need for the bridge approach rail cannot be met.  Alternate solutions to these obstacles include using short radius guardrail, a shortened guardrail section, or a crash attenuator.  Historically, short radius guardrail have been used at most locations as crash attenuators are not feasible or economical.  Several studies and tests have been conducted by Southwest Research Institute (SwRI), Midwest Roadside Safety Facility (MwRSF), and Texas Transportation Institute (TTI) on various short radius guardrail systems (1).  These were evaluated under multiple performance criteria including AASHTO’s 1989 Guide Specification for Bridge Railings, NCHRP Report 230, and NCHRP Report 350 (2, 3, 4).  Currently, these systems are limited to test level 2 (TL-2) under NCHRP Report 350 performance criteria (1).

Objective

The purpose of the study is to develop a guide document that identifies the best practices used to alleviate problems where length-of-need requirements for bridge approach rails cannot be met.  The guide document will be developed through a literature review and survey of state DOTs.

Benefits

The guideline document produced will provide state DOTs with a reference for how others handle installations where the required length-of-need cannot be met for bridge approach rails.  Aside from providing DOTs with a detailed list, this document will increase the knowledge base for such installations.

Products

TTI will provide a detailed report that identifies the best practices used to alleviate problems where the length-of-need requirements for bridge approach rails cannot be met

Implementation

The guideline for best practice methods for solving problems where the length-of-need requirements for bridge approach rails cannot be met will be available for DOTs to use for these situations.

Work Plan

Task 1 — Literature Review

The researchers will conduct a literature review and survey to document the best current practices for solving problems where the length-of-need requirements for bridge approach rails cannot be met.

Task 2 — Evaluation and Reporting

The researchers will generate a final report documenting the findings from the literature review and survey conducted in task 1.
 

____________________
(1) Abu-Odeh A.Y., Kim K.-M., Alberson D.C., Evaluation of Existing T-Intersection Guardrail Systems for Equivalency with NCHRP Report 350 TL-2 Test Conditions, Texas Transportation Institute, Test Report No. 405160-10, College Station, Texas, August 2010.  
(2) AASHTO, 1989 Guide Specification for Bridge Railings, American Association of State Highway and Transportation Officials, Washington D.C., 1989.
(3) Michie J.D., Recommended Procedures for the Safety Performance Evaluation of Highway Appurtenances, NCHRP Report 230, Transportation Research Board, Washington D.C., March 1981.
(4) Ross H. E., Sicking D. L., et al., Recommended Procedures for the Safety Performance Evaluation of Highway Features, NCHRP Report 350, Washington D.C., 1993.

Problem Statement

Texas Transportation Institute (TTI) has completed the development of a pinned F-shape temporary concrete barrier system that can be used for bridge or roadway applications and provides limited deflection.   If this application is used on a road or bridge project, it is possible that during construction, these barriers may need to be repositioned to accommodate traffic and construction phasing.  However, with pinning holes on only one side of the barrier segments, the segments would need to be moved as well as rotated to re-secure them properly.  This poses an inconvenience for the contractor and lengthens the amount of time needed to reposition the barriers.

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 (Sheikh 2008). 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 a short distance into the underlying concrete pavement, thus locking the barrier in place. The pinned-down barrier successfully passed the National Cooperative 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 rigid concrete barrier.

Objective

To analyze the existing F-shape temporary concrete barrier detail and determine if additional pinning holes can be added alongside the opposite face of the barrier.  These holes should be slightly offset from the existing ones to avoid interference with rebar and the pinning holes.

Benefits

A successful barrier detail with pinning holes along both faces of the barrier would allow the contractor to reposition the barriers more easily and in a shorter amount of time.

Products

TTI will 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.

A copy of all deliverables will be provided for each participating member state. 

Implementation

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 work plan for this research will be comprised of the following task.

Task 1: Barrier Design

In this task, the researchers will modify the pinning hole details of the existing anchored barrier design.  The modified design will incorporate diagonal holes on both sides of the barrier to allow pinning from either side.  The modified design is expected to result in minimal changes to the existing anchoring mechanism using the drop pins.  Thus, a detailed finite element analysis or full-scale crash testing will not be needed to reevaluate the barrier performance due to the new design modifications.

____________________
(Sheikh 2008) 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.

Problem Statement

Texas Transportation Institute (TTI) has completed the development of a pinned F-shape temporary concrete barrier system that provides limited deflection and can be used for bridge or roadway applications.   If this application is used on a road and bridge project, it is possible that a non-anchored barrier section may be used with the anchored section.   An on-going TTI project is developing a transition from anchored to free-standing barrier.  This transition is being developed for placement on concrete pavement or bridge deck, but not for asphalt. There are several situations where the transition needs to be placed on asphalt. One possibility is to perform peak lateral or pullout tests on an equivalent asphalt thickness to the concrete pinning. This can possibly enable using the transition design developed for placement on concrete to be used on asphalt.

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 (Sheikh 2008). 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 a short distance into the underlying concrete pavement, thus locking the barrier in place. The pinned-down barrier successfully passed the National Cooperative 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 rigid concrete barrier.

TTI researchers are currently developing a transition design to transition from the anchored barrier on concrete to the free standing F-shaped barrier.   The researchers have also just recently developed an anchoring design for the temporary concrete barrier pinned to asphalt.  Based on the results of some preliminary surrogate testing during the course of these two projects, the researchers determined that a single transition design that could be placed on both asphalt and concrete is not straightforward.  This is because the barrier segments over the transition region are also pinned to the underlying surface, even though the pinning scheme is selected such that the lateral resistance of the pinned segments in the transition region varies gradually to allow smooth vehicle transition. The lateral resistance response of the pin may vary depending on whether the underlying surface is concrete or asphalt.  Thus, in the ongoing transition design project, the researchers are focusing on developing the transition design for placement on concrete.  However, there are many field applications where the transition segments will need to be placed on asphalt.  To achieve installation of the transition on asphalt, in this proposed research, the researchers will be investigating the possibility of using the same transition design for placement on both concrete and asphalt.

Objective

Perform quasi-static and dynamic drop-pendulum load tests to evaluate if equivalency in lateral resistance and deflection can be achieved between an anchoring pin installed in asphalt and concrete.  If an equivalency can be achieved, develop details of the transition from free-standing to pinned down barrier for placement on asphalt using the results of the ongoing research to develop the transition for placement on concrete.

Benefits

A successful design will allow placement of the transition segments on asphalt, which will provide greater flexibility in the use of the pinned down barrier transition.

Products

TTI will provide video and photographic documentation of the quasi-static and dynamic pendulum tests, 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.

A copy of all deliverables will be provided for each participating member state.

Implementation

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

The research will provide information and documentation on testing performed during this research so that design and operational standards can be further reviewed and evaluated. Drawings provided for Task Force 13 documents will further support implementation of the research.

Work Plan

The work plan for this research will be comprised of the following two tasks.

 Task 1: Quasi-Static Push Tests

In this task, the researchers will perform a static push test with the 1.5-inch diameter anchoring pin installed in concrete, similar to the way it is installed in a temporary concrete barrier pinned to concrete pavement.  A quasi-static load will be applied to deflect the pin in the concrete hole.  The deflection and load data will be recorded in the test. 

After determining the response of a single pin installed in concrete, the researchers will perform quasi-static push tests with 1.5-inch diameter pins installed in road base with overlying asphalt pad of various thicknesses.  The force required to deflect and bend the pins in each of the asphalt pad thickness will be recorded, in addition to the deflection of the pin. The researchers will compare the load and deflection for each of the pins installed in asphalt to the pin installed in concrete.  The data will be analyzed to determine if the response of a pin installed in certain thickness of asphalt relates closely to the response of the pin installed in concrete.

A total of five quasi-static tests will be performed under this task.  Of these, one will be with pin installed in concrete, and four with pins installed in asphalt pads of 4, 6, 8 and 10-inch thicknesses.

Task 2: Pendulum Testing and Final Report

The researchers will perform task 2 if equivalency between the anchoring pin installed in concrete and some thickness of asphalt pavement can be achieved in the quasi-static testing of Task 1.  In addition to evaluating the quasi-static response of the pins, it is also important to evaluate the dynamic response.  In this task, the researchers will perform two dynamic pull tests.  The first test will be performed by dynamically loading the anchoring pin installed in concrete pavement.  The load will be applied by pulling the pin using a cable attached to the back side of a dropping pendulum with a calculated speed at its mean position.  The load will be measured as a function of time using a load cell.  Similarly, the corresponding deflection of the pin will also be recorded as a function of time using the analysis of high-speed test videos.  

Once the dynamic response of the pin installed in concrete has been evaluated, the researchers will perform a second test with the pin installed in asphalt. The thickness of the asphalt pad will be determined from the comparison of the quasi-static response in Task 1.  Load and deflection will be measured as a function of time in this case as well. 

A comparison of the static and dynamic load and deflection response of the anchoring pin installed in concrete and asphalt will be performed to determine if an equivalency can be achieved.  If this is possible, the researchers will develop details of the transition for placement on asphalt using the same design as the transition for placement on concrete.

As part of this task, the researchers will also prepare a final report documenting the research performed. 

____________________
(Sheikh 2008) 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.

Problem Statement

When widening of an existing divided highway with depressed median is proposed, adding inside lanes by using the depressed median opening is the preferred method since no addition right of way (ROW) is required.  Extending the pavement at superelevations, however, requires the use of a retaining wall along with the concrete median barrier due to the grade separation that occurrs.  Previous research project “Split Single Slope Meidan Wall for Grade Separations” (2011-TN/28) (405160-33) explored the use of a single slope median wall to provide a test level 3 median barrier on split level highways.  This project is intended to be a second phase of the TN/28 study.  The scope of this study will include analysis of the structure and stability of the barrier, as well as finite element modeling to determine its crashworthiness at test level 4 (10000S vehicle).

Background

Median barriers are typically installed to prevent errant vehicles from crossing a divided area between travelways so as to prevent collision with oncoming traffic (AASHTO 2004).  The application of median barriers depends on multiple factors, including median width, traffic volume, adverse geometrics (split elevations), and severity of consequences due to vehicular penetration into opposing traffice lanes (AASHTO 2002; AASHTO 2004).  Special considerations are taken when the travelways are at different elevations (AASHTO 2002; AASHTO 2004).

The correct median barrier must be selected such that the maximum dynamic deflection that occurs is less than one-half of the median width (AASHTO 2002).  The barrier should prevent the errant vehicle from penetrating into oncoming traffic lanes and redirect the vehicle to the correct direction of travel (AASHTO 2004).

Median barrier can be categorized as flexible, semi-rigid, and rigid (AASHTO 2002).  Examples of typical median barriers include weak post W-beam, three strand cable, box beam median barrier, blocked out W-beam strong post, blocked out thrie beam strong post, modified thrie beam median barrier, and concrete barrier (AAHSTO 2002).

The use of W-beam, box beam, and cable systems are limited to flat medians and are typically not used when a split elevation between traffic ways greater than 3:1 occur (AASHTO 2004).  In the case of split elevation highways with little to no median width, such as when inside lanes are added by using the depressed median, dynamic deflection is restricted.  In this situation, use of rigid barriers are most appropriate.

Concrete median barriers are the most common types of rigid barriers and include the New Jersey, F-shape, single slope barrier and vertical walls (AASHTO 2002).  These systems present low life cycle due to their effective performance  and maintenance-free life.  For the research conducted herein, the single slope barrier will be considered exclusively. 

A single slope barrier can have either a 9.1 or 10.8 degree of slope and may be used as either a temporary or permanent longitudinal barrier (Beason et al., 1989).  Each has been successfully tested according to criteria presented in NCHRP Report 350 (Ross et al., 1993; AASHTO 2002).  The primary advantage of the single slope barrier is that the pavement adjacent to the sloped face may be overlaid multiple times without degrading the performance of the barrier (Beason et al., 1989).  These barriers are typically 42 inches tall, but may be found as short as 30 inches (AASHTO 2002).

Reasearchers at Texas Transportation Institute (TTI) used computer simulations to evaluate the stability and crashworthiness of a single slope median wall to provide a test level 3 median barrier on split level highways.  This study was accomplished under a pooled fund research project “Split Single Slope Meidan Wall for Grade Separations” (2011-TN/28) (405160-33) (Silestri et al., draft report not yet published 2012).

Objective

The purpose of the study is to explore the use of a sloped median barrier on split level highways.  Objectives of the study will include analysis of the structure and stability of the barrier, as well as finite element modeling to determine its crashworthiness at test level 4 (10000S vehicle).

Benefits

The use of a sloped median barrier provides design and construction flexibility as shoulder elevations vary along the road.  This type of design and construction provides an economical way to construct a median barrier on split elevation highways.

Products

TTI will provide a detailed design of the sloped median barrier for use as a median wall.  TTI will generate standard sheets including design details and drawings based on the study results of the proposed device.

Implementation

If acceptable test results are achieved, methods for the use of the sloped median barrier as a median wall will be provided.  Details and drawings will be used to develop standard sheets.  These standards will be provided in the Task Force 13 format for submittal to AASHTO to be included in the AASHTO/ARTBA/ABC Barrier Hardware Guide.

Work Plan

Task 1 — Wall stability and geotechnical analysis

 The researchers will investigate the strength of the system based on a geotechnical propective.  The loads imposed on the wall due to soil pressures and superimposed lane loading will be determined.  In addition, the soil slope stability will be analyzed.

The researchers will determine the wall’s structural strength to resist soil and any superimposed loads from traffic on the higher elevation.  In addition, the adequacy of the wall’s foundation will be analyzed.

In the case the wall cannot adequately retain the soil, a new design will be investigated and guidelines proposed for the implementation of the installation.

Task 2 — Perform finite element analysis for median crashworthiness

The researchers will investigate and determine the crashworthiness of the sloped median wall by performing finite element analysis for a proposed installation.  The crashworthiness of the median will be verified by simulating the impact conditions to the Manual for Assessing Safety Hardware (MASH) test 4-12 (AASHTO 2009).  Test 4-12 involves a 10,000-lb single-unit truck (designation 10000S) impacting the test article at 15 degrees and 56 mph.

Task 3 — Evaluation and Reporting

The researchers will generate a final report documenting the findings from the analysis and design details and drawings.  In addition, the report will include drawings and details that may be used in the development of standard sheets for AASHTO Task Force 13.

____________________

AASHTO (2002). Roadside Design Guide. American Association of State Highway and Transportation Officials. Washington, D.C.
AASHTO (2004). A Policy on Geometric Design of Highways and Streets. American Association of State Highway and Transportation Officials. Washington, D.C.
AASHTO (2009). Manual for Assessing Safety Hardware. American Association of State Highway and Transportation Officials. Washington, D.C.
Beason, W. L., J. Ross, H. E., et al. (1989). “Development of a Single-Slope Concrete Median Barrier.” Research Report 9429CDK. Texas Transportation Institute, College Station, TX.
Ross, H. E., D. L. Sicking, et al. (1993). “Recommended Procedures for the Safety Performance Evaluation of Highway Features.” NCHRP Report 350. Washington D.C.

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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 road and bridge project, it is possible that this barrier section may be used during phased construction with a permanent concrete barrier section or in a permanent application when transitioning to a fixed concrete median barrier.   A transition design from the anchored precast concrete barrier to a permanent concrete barrier is needed to allow smooth redirection of impacting vehicle in this area. 

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 (Sheikh 2008). 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 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 rigid concrete barrier.

Among other anchored concrete barrier designs, Midwest Roadside Safety Facility (MwRSF) has developed a design for the F shape temporary concrete barrier along with various transition details.  In 2003, MwRSF developed a concrete bridge deck tie-down system for 12.5 ft long, F-shaped Kansas temporary barriers (Polivka 2003). 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 (Bielenberg 2006). 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 the same study, MwRSF 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 segments 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.

And more recently in 2009, MwRSF developed a transition design for attaching free-standing F-shape barrier to the rigid concrete barrier (Wiebelhaus et al., 2009).  This design employs the anchored barrier section developed by MwRSF earlier in 2005 and an intermediate section to transition from the free-standing to the rigid barriers.  At one end the anchored barrier segments connect to the free-standing barrier, and at other end they connect to a rigid concrete barrier.  A 42-inch tall single slope barrier was used as the rigid barrier system.  The number of pins in the anchored barrier segments was varied to gradually increase the lateral restraint of the barrier over four 12.5-ft long segments.  The anchored barrier segments were place on a 3-inch thick asphalt pad.  To reduce snagging of the vehicle while transitioning from anchored barrier to the rigid barrier, a nested 12-guage thrie beam section was used.  The rail segment was attached to the traffic side face of the rigid and the anchored barrier segments.

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 (Jewel 1999).  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 and crash test a transition design that can be used to transition from the pinned-down F-shape temporary concrete barrier placed on concrete to a permanent concrete barrier. The transition is to be developed for American Association of State Highway and Transportation Officials Manual for Assessment of Safety Hardware (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 transitions to permanent concrete 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.

A copy of all deliverables will be provided for each participating member state.

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 work plan for this research will comprise of three tasks as described below. 

Task 1: Conceptual Design

In this task, the researchers will evaluate rigid concrete barrier systems used by the participating pooled fund states to select a system that is most critical for the transition design. The researchers will develop conceptual designs of the transition based on evaluation of existing transition systems. The conceptual design will take into consideration compatibility with research being performed under Task Order LA/26 (to develop transition design for connecting anchored barrier to free-standing barrier).  The transition concept selected will be presented to the Task Order Technical Representative for approval before further design and development. 

Task 2: Finite Element Analysis

In this task, the researchers will develop full-scale finite element system model of the transition concept selected in Task 1.  Once the system model has been developed, the researchers will perform vehicular impact simulations using MASH TL-3 impact conditions (i.e. 2270-kg pickup vehicle, impacting at 100 km/h and 25-degrees) to evaluate the design’s performance.

Most longitudinal barrier transitions have two points of transition of the barrier’s lateral stiffness.  In this design, there will be a transition point when the vehicle approaches from the rigid barrier to the pinned-down barrier, and another transition point when the vehicle approaches from the pinned-down barrier to 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 due to the limited deflection of the pinned-down barrier observed in previous testing, this transition design will not result in excessive change in lateral barrier stiffness.  Thus the performance differences between the two transition points will not be too significant.  The researchers will however perform impact simulations to determine the critical impact point (CIP) for both transition locations (from rigid to pinned-down barrier and from pinned-down to rigid barrier) and then evaluate the most critical case.  Also based on this expectation, the researchers have budgeted only one crash test at the CIP determined to be most critical from the simulation analysis. It should be noted that if simulation results indicate significant differences in performance between transitioning from rigid to pinned-down and pinned-down to rigid barrier, additional crash test may need to be performed under a separate contract to evaluate both transition points. 

Task 3: Full-Scale Crash Testing and Final Report

Once the transition design has been finalized in Task 2, the researchers will perform test 3-21 of MASH (2270-kg vehicle, 100 km/hr, 25 deg).  TTI will construct the rigid concrete barrier for the testing.  The current proposal and budget do not include cost of manufacturing or purchasing temporary pinned-down concrete barrier needed for the testing.  The researchers are currently working on two other Pooled-fund Task Orders that will use the same concrete barrier design.  The researchers are hopeful that sufficient length of barrier segments will be salvaged from these Task Orders for use in this study.  If however, the barrier segments are severely damaged in the previous studies and are no longer usable, it is expected that one of the Pooled Fund states will provide the barrier for testing.

The test will be performed to verify simulation results. TTI will provide the test facility, test vehicle, instrumentation of the vehicle, high-speed film, video, still photographs, and a final report suitable for submittal to Federal Highway Administration (FHWA). 

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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.] Wiebelhaus, M.J., Terpsma, R.J., Lechtenberg, K.A., Reid, J.D., Faller, R.K., Bielenberg, R.B., Rohde, J.R., and Sicking, D.L. (2009). “Development of Temporary Concrete Barrier to Permanent Concrete Median Barrier Approach Transition.” Draft Report to the Midwest State’s Regional Pooled Fund Program, Transportation Research Report No. TRP 03-208-09.
[5] 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.

Research also addresses the influence of highway features such as driveways, slopes, ditches, shoulders, medians, and curbs on single vehicle collisions. The problems identified with these structures and features are addressed through in-service performance evaluation studies, computer simulation, full-scale crash testing, clinical analyses of real-world crash data, and benefit cots analyses. The specific identification, selection and prioritization of research issues is made by the technical committee on an annual basis, unless emerging issues require committee decisions in the interim.