Jennifer D. Schmidt

Evaluation of the Midwest Guardrail System Stiffness Transition with Curb

ABSTRACT A W-beam to thrie beam stiffness transition with a 102-mm (4-in.) tall concrete curb was developed to connect 787-mm (31-in.) tall W-beam guardrail, commonly known as the Midwest Guardrail System (MGS), to a previously developed thrie beam approach guardrail transition system. This upstream stiffness transition was configured with standard steel posts that are commonly used by several state departments of transportation. The toe of a 102-mm (4-in.) tall sloped concrete curb was placed flush with the backside face of the guardrail and extended the length of the transition region. Three full-scale crash tests were conducted according to the Test Level 3 (TL-3) safety standards provided in AASHTOs Manual for Assessing Safety Hardware (MASH). The first test, MASH Test No. 3-20, was deemed a failure due to guardrail rupture. The stiffness transition was modified to include an additional nested W-beam rail segment upstream from the W-beam to thrie beam transition element. MASH Test No. 3-20 was repeated on the modified system, and the 1100C small car was successfully contained and redirected. During MASH Test No. 3-21, a 2270P pickup truck was successfully contained and redirected. Following the crash testing program, the system was deemed acceptable according to the TL-3 safety performance criteria specified in MASH.

Safety Investigation and Guidance for Retrofitting Existing Approach Guardrail Transitions

Approach guardrail transition systems have been designed, tested, and evaluated according to various impact safety standards. Unfortunately, approach guardrail transitions that are installed in the field may deviate from the as-tested configuration (e.g., by missing posts); this deviation reduces the desired lateral stiffness and strength of the transition system. Validated BARRIER VII computer models of 18-ft 9-in. (5.7-m)-long and 31-ft 3-in. (9.5-m) long systems of NCHRP Report 350 crashworthy approach guardrail transitions were used to gain an understanding of how they would perform, with and without deficiencies, when subjected to Test Level 3 impacts at various locations throughout each system. Each simulation was evaluated on the basis of three criteria: (a) maximum wheel-rim snag on the upstream edge of the bridge rail, (b) maximum dynamic deflection within the nested Thrie section, and (c) maximum vehicle pocketing angle within the nested Thrie section. According to simulation results, when transition posts were missing, installed adjacent to sloped terrain, or exposed more than 3 in. (76 mm), excessive dynamic deflection or vehicle snag on the upstream end of the bridge rail could occur. Recommendations and retrofits are provided to upgrade approach guardrail transitions for the safest performance.

Development of Transition between Free-Standing and Reduced-Deflection Portable Concrete Barriers

Portable concrete barriers (PCBs) are often used in applications in which limited deflection is desired during vehicle impacts, such as bridge decks and work zones. In an earlier study, a reduced-deflection, stiffening system was configured for use with non-anchored, F-shape PCBs and was successfully crash tested under Manual for Assessing Safety Hardware (MASH) safety performance criteria. However, details and guidance for implementing this barrier system outside the length-of-need, including within transitions to other barrier systems, were not provided. The focus of this study was to develop a crashworthy transition design between the reduced-deflection, F-shape PCB system to free-standing, F-shape PCB segments using engineering analysis and LS-DYNA computer simulation. First, the continuous steel tubes in the reduced-deflection system were tapered down to the surface of the free-standing PCB segments to reduce the potential for vehicle snag. In addition, steel tube spacers were added at the base of the two joints upstream from the reduced-deflection system to increase the stiffness of adjacent free-standing PCBs. Simulations were performed to determine the critical impact points for use in a full-scale crash testing program. It was recommended that three full-scale crash tests be conducted, two tests with a 2270P pickup truck vehicle and one test with an 1100C passenger car, to evaluate the proposed design system with impacts at the recommended critical impact points.

Development of a Standardized Buttress for Approach Guardrail Transitions

Approach guardrail transitions (AGTs) incorporate increased post and rail sizes, reduced post spacings, and specialized buttress end geometries to smoothly transition from deformable W-beam guardrail to rigid barriers. This transition in barrier stiffness makes AGTs sensitive systems that require specific combinations of these components to function properly. Changing components, or even the removal of a curb below the rail, can negatively affect the safety performance of an otherwise crashworthy system. However, recent full-scale crash testing has indicated that a properly designed buttress at the downstream end of an AGT may be utilized with multiple AGT systems. Thus, the objective of this project was to develop a standardized buttress to reduce vehicle snag and be compatible with a wide variety of previously developed Thrie beam AGT systems, either with or without a curb. The standardized buttress was designed with a dual taper on its front upstream edge. A longer lower taper was designed to mitigate tire snag below the rail, while a shorter upper taper was designed to prevent vehicle snag and limit the unsupported span length of the rail. This buttress design was evaluated in combination with a critically weak AGT without a curb, which represented the worst-case scenario. The standardized buttress was successfully crash tested to MASH TL-3. Guidance was provided for both the attachment of the buttress to various Thrie beam AGTs as well as how to transition the shape of the buttress to adjacent bridge rails or rigid parapets downstream of the AGT.

Development of retrofit, low-deflection portable concrete barrier system

ABSTRACT A retrofit stiffening mechanism was developed for use in reducing the deflection of an F-shape portable concrete barrier (PCB) system without requiring anchorage of the barrier segments to the road surface. The research effort included development and analysis of mechanisms for limiting deflections through engineering analysis and finite element analysis with LS-DYNA. Deflection-limiting mechanisms investigated included increased barrier mass, increased barrier-to-ground friction, reduction of the joint gap, and composite action. Following analysis of the candidate designs, an initial prototype design was developed based on using composite action to provide moment continuity across the barrier joints. This design was successfully evaluated in full-scale crash tests. Following the first crash test, the low-deflection PCB system was modified to further reduce deflections and full-scale crash tested a second time. The final version of the low-deflection PCB system was capable of reducing dynamic barrier deflections almost 50% over free-standing PCB installations while still safely redirecting errant vehicles.

Development and Testing of the Manitoba Constrained Width Tall Wall Barrier

This project in Manitoba, Canada, developed a single-slope concrete barrier system with a height of 1,250 mm and a base width of no more than 600 mm. Configurations for bridge rail, roadside, and median barrier applications were developed and optimized to minimize installation costs while satisfying the AASHTO Manual for Assessing Safety Hardware (MASH) Test Level 5 performance standards. Additionally, a bridge deck was developed for the overhang portion of the deck supporting the bridge rail. To evaluate the new barrier system, a 45.7-m-long section of the bridge rail was constructed on a simulated bridge deck and subjected to a full-scale crash test according to MASH Test 5-12. During the test, the 36,000-kg vehicle was safely redirected with minimal roll to the cab and trailer. Damage to the barrier and deck was minor, consisting of concrete gouging, hairline cracks, and some spalling to the top of the barrier. Thus, the Manitoba constrained width tall wall was deemed crashworthy to MASH Test Level 5 standards.

Safe placement of breakaway luminaire poles behind Midwest Guardrail System

ABSTRACT Luminaire poles are commonly installed along highways to provide proper illumination in critical areas. When placing light poles in close proximity to guardrail, the poles may affect the guardrails ability to safely contain and redirect vehicles. The interaction between a deflected guardrail system and a closely-positioned light pole may create unwanted stiffening or hinging of the barrier system around the pole. The pole may also present a snag hazard to impacting vehicles and induce vehicle instabilities. In this study, the barrier clearance distance, i.e. the lateral offset away from a breakaway light pole was investigated and evaluated. The minimum safe lateral offset away from the pole with respect to the Midwest Guardrail System (MGS) was determined to be 508 mm (20 in.) through crash testing and computer simulation with non-linear finite-element analysis. Two full-scale crash tests were conducted according to the American Association of State Highway Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) Test Level 3 (TL-3) impact safety criteria. In test no. ILT-1, a 2268-kg (5000-lb) pickup truck impacted the combination MGS with light pole system laterally offset 508 mm (20 in.) from back of posts at a speed of 100.7 km/h (62.6 mph) and an angle of 25.0°. In test no. ILT-1, the pickup truck was captured and safely redirected while impacting the light pole and disengaging the pole away from the base. In test no. ILT-2, a 1098-kg (2420-lb) small car impacted the combination MGS with light pole system laterally offset 508 mm (20 in.) from back of posts at a speed of 100.9 km/h (62.7 mph) and an angle of 25.6°. In test no. ILT-2, the car was safely contained and redirected while minimally contacting the light pole. The MGS with a lateral pole offset of 508 mm (20 in.) away from back of posts to front face of pole provided an acceptable safety performance to MASH TL-3 when critically impacted by a pickup truck and a small car. Thus, a minimum offset of 508 mm (20 in.) between the back of the MGS post and front face of the breakaway pole was sufficient to assure a safe performance of the MGS during vehicle impacts without undesired interaction with the pole. Accordingly, guidance for the safe pole placement behind the MGS was provided.

Manual for Assessing Safety Hardware Test Level 4 Design and Evaluation of a Restorable Energy-Absorbing Concrete Barrier

A new, high-containment longitudinal barrier was designed to reduce the acceleration imparted to passenger vehicles during impacts and to be restorable and reusable. Elastomer support posts were designed to translate laterally and absorb energy when struck and then to restore to their initial position after impact events. A hybrid concrete beam and steel tube combination rail was optimized to minimize weight, provide sufficient structural capacity, maintain a height to contain and redirect single-unit trucks, and prevent passenger vehicles from snagging on the posts. Three full-scale vehicle crash tests were conducted according to the Manual for Assessing Safety Hardware (MASH) Test Level 4 (TL-4) safety performance requirements on a barrier 240 ft long with nominal height of 38⅝ in. In the Safer for Highway Test 1 (SFH-1), a 5,021-lb pickup truck was redirected with minimal damage to the barrier. The peak lateral acceleration was reduced 47% compared with similar impacts on rigid barriers. In the SFH-2 test, a 2,406-lb small car was redirected by the barrier, and the peak lateral acceleration was reduced 21%compared with similar impacts on rigid barriers. In the SFH-3 test, a 21,746-lb single-unit truck was successfully contained and redirected, resulting in only minor damage to the concrete rail. Therefore, the barrier met all the MASH TL-4 safety performance criteria. The paper provides recommendations about the performance, future design refinements, and installation requirements of the barrier.

Minimum Effective Length for the Midwest Guardrail System

The recommended minimum length for the standard Midwest Guardrail System (MGS) is 175 ft (55.3 m) based on crash testing according to NCHRP Report 350 and AASHTOs Manual for Assessing Safety Hardware (MASH) specifications. However, varying roadside hazards and roadway geometries may require a W-beam guardrail system to be shorter than the currently tested minimum length. The effects of reducing system length for the MGS were therefore investigated. The research study included one full-scale crash test with a Dodge Ram pickup truck striking a 75-ft (22.9-m) long MGS system. The barrier system satisfied all MASH Test Level 3 (TL-3) evaluation criteria for Test Designation Number 3-11. Test results confirmed that the reduced system length did not adversely affect overall system performance or deflections. Simulations that used BARRIER VII and LS-DYNA were also conducted to analyze system performance with reduced lengths of 50 ft (15.2 m) and 62 ft 6 in. (19.1 m). Both system lengths exhibited the potential for successfully redirecting an errant vehicle at MASH TL-3 test conditions. However, these reduced-length systems would have a narrow window for redirecting vehicles and would be able to shield hazards of only a limited size. Owing to limitations associated with the computer simulations, full-scale crash testing is recommended before these shorter systems are installed.

Analysis of Existing Work-Zone Sign Supports Using Manual for Assessing Safety Hardware Safety Performance Criteria

Over the years, numerous work-zone, portable sign support systems have been successfully crash tested according to the Test Level 3 safety performance guidelines provided in the National Cooperative Highway Research Program Report 350 and accepted for use along our nations highways. For this study, several crashworthy sign support systems were analyzed to predict their safety performance according to the new evaluation criteria provided in the Manual for Assessing Safety Hardware (MASH). More specifically, this analysis was conducted to determine which hardware parameters negatively affect a systems safety performance. To verify the accuracy of the analysis, eight systems, four with the 2270P pickup truck and four with the 1100C small car, were evaluated according to the MASH criteria. Five out of the eight tested systems failed the MASH criteria, and the other three systems performed in an acceptable manner. As a result of the analysis and verification, several hardware parameters were deemed critical for contributing to system failure under MASH and included sign panel material, top mast height, presence of flags, sign-locking mechanism type, base layout, and system orientation. Flowcharts were developed to assist manufacturers with the design of new sign support systems.