W-beam Rail Research Articles

Design and Testing of MASH Test Level 3 Thrie-Beam Guardrail System for Roadside and Median Applications

Thrie-beam guardrail systems are used when enhanced Test Level 3 (TL-3) protection above that typically provided with a W-beam guardrail is desired. The currently available Manual for Assessing Safety Hardware ( MASH)-compliant modified thrie-beam system incorporates components that are more costly to fabricate, and the installation creates a wider footprint than a standard W-beam guardrail. The goal of this study was to develop a cost-effective thrie-beam guardrail system (TGS) for roadside and median applications under MASH TL-3 requirements. The roadside and median TGS configurations were developed using computer simulations, and their crashworthiness was evaluated through full-scale crash testing. Additionally, transition designs from a TGS to a standard W-beam system were developed. The TGS uses all the Midwest guardrail system (MGS) standard components except for the thrie-beam rail; it has a thrie-beam rail mounted at 34 in. in height as opposed to the MGS, with a W-beam rail mounted at 31 in. The two systems are attached using a symmetric W-to-thrie-beam transition segment. Based on the results of three successful full-scale crash tests and a computer simulation, both roadside and median TGS configurations meet all safety requirements for MASH TL-3.

Multi-objective optimization design of post-soil system for enhanced W-beam guardrail containment performance

In the W-beam guardrail system, the post can provide sufficient lateral force through interaction with the subgrade and can create the necessary containment function by connecting with the W-beam rail panel. The purpose of this study is to evaluate the best embedment depth and section size of two different posts in the same subgrade from the perspectives of maximum lateral force and occupant ridedown acceleration for enhanced the containment performance of guardrail protection system in China. An accurate lateral force measurement method is used for the inertia effect in collision problems. And the exact finite element model of post-soil interaction is built by combining dynamic impact test with detailed finite element study. Then the Genetic algorithm (GA) was used to determine the optimum value of spread and then the GA-RBF was applied to construct the surrogate models of the analytical objective, which increased the accuracy of fitting. Finally, the embedment depth and structure size were obtained using multi-objective genetic algorithm. Full-scale crash test results show that the optimum design results meet the requirements. Through optimization design, W-beam guardrail has been greatly improved, which improves the crash safety of corrugated beam guardrail.

Investigation and MASH Full-Scale Crash Testing of the Practice of Raising Blockouts on W-Beam Rail Systems

The Federal Highway Administration (FHWA) clarifies appropriate height measures for W-beam guardrails. Identification of existing locations where rail height is lower than recommended by FHWA is common. A research study was conducted to investigate the crashworthiness of raising blockouts on posts to restore barrier height and provide clarification on implementation of such methodology. The researchers evaluated the crashworthiness of raising blockouts by conducting a full-scale Manual for Assessing Safety Hardware (MASH) Crash Test 3-11 of a 28-in. W-beam guardrail system with composite blockouts raised 4 in. on posts. The 28-in. W-beam guardrail system with raised composite blockouts contained and redirected the 2270P vehicle, and it performed acceptably for MASH Test 3-11. The results of this study include guidance on the procedure for raising blockout mounting height on steel posts to achieve recommended rail height for a W-beam guardrail.

Evaluation of the Midwest Guardrail System stiffness transition with curb

ABSTRACTA 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 AASHTO's 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.

Design and Full-Scale Testing of Low-Cost Texas Department of Transportation Type T631 Bridge Rail for MASH Test Level 2 and 3 Applications

The purpose of this project was to design and test a low-cost bridge rail system that would be compatible with the Midwest Guardrail System (31 in. height) and minimized or eliminated deck damage when impacted by errant vehicles. The Texas Type T631 bridge rail developed for this project is a flexible, low-cost bridge rail system for Test Level 2 (TL-2) applications. The Texas Department of Transportation Type T631 bridge rail designed and developed for this project was evaluated under Manual for Assessing Safety Hardware (MASH) TL-2 in 2013. The bridge rail incorporated S3X5.7 steel sections designed to yield at the post baseplate. The post baseplate was designed to distribute the baseplate bearing and shear forces without causing damage to the 8-in.-thick reinforced concrete deck. The welds on the posts were designed such that the post yielded without tearing away from the top of the baseplate. The rail element consisted of a 12-gauge W-beam rail element. The rail element was attached to the post with a bolt of diameter 5/16 in. This bolt was designed to break away without adversely affecting vehicle performance. The posts were spaced 6 ft 3 in. on centers for TL-2. The post spacing was reduced to 3 ft 1½ in. on centers and evaluated for MASH Test Level 3 (TL-3) specifications in 2014. At the smaller post spacing, the T631 met all the performance requirements of MASH TL-3. Details of the design and testing of the T631 for MASH TL-2 and MASH TL-3 specifications are provided in this paper.

Development of Low-Cost, Energy-Absorbing Bridge Rail

A new, low-cost bridge railing was designed to be compatible with the Midwest Guardrail System (MGS). The barrier system was configured to reduce bridge deck width and its associated cost. Several concepts for an energy-absorbing bridge post were developed and tested; the concepts included strong-post designs with plastic hinges and weak-post designs with bending near the bridge deck attachment. The final railing concept incorporated S3 × 5.7 (S76 × 8.5) steel posts housed in a tubular bracket placed at the outside vertical edge of the deck and anchored to its top and bottom with one through-deck bolt. The W-beam rail section was attached to the posts with a bolt that was designed to fracture during an impact event. Two full-scale crash tests were performed in accordance with the Test Level 3 impact conditions provided in the Manual for Assessing Safety Hardware. The bridge rail system met all safety performance criteria for both the small car and pickup truck crash tests. Barrier VII computer simulations, in combination with the full-scale crash testing programs for the bridge railing and MGS, demonstrated that a special-approach guardrail transition was unnecessary.

Design and simulation of two wooden-post W-beam guardrails to eliminate wheel snagging

Recent crash tests on strong-post round- and rectangular-wood W-beam guardrail systems demonstrate that wheel snagging can be a serious concern for vehicle stability and impact severity. There are several methods that exist to minimise wheel snagging in strong-post guardrail systems. This paper aims to investigate the effect of one of those methods: the increased offset distance between post and W-beam rail. Extensive simulation studies are performed to determine optimum offset distances between the post and W-beam in both systems. Different designs with varying offset block depths are evaluated and their impact performances are compared. LS-DYNA, a versatile, nonlinear, large deformation, finite-element program is utilised to analyse different alternatives. Guardrail models previously validated against full-scale crash tests were used in the analysis. Simulation findings suggest that tendency to wheel snagging reduces with increased offset depths. 260-mm depth was determined to be the optimum offset distance between the wooden posts and W-beam. Simulation results show that when a nominal 260-mm offset distance is provided, wheel snagging and associated vehicle instability and impact severity can be alleviated in wooden-post guardrail systems.

Guardrail Connection for Low-Fill Culverts

A W-beam guardrail system was developed for attachment to the top slab of a low-fill concrete culvert. The guardrail design was constructed with a single, 2.66-mm-thick W-beam rail totaling 53.34 m in length. Over the culvert, W150×13.5 steel posts 946 mm long spaced 952.5 mm on center supported the W-beam rail. The research study included dynamic testing with a bogie vehicle and steel posts attached to a rigid foundation, computer simulation modeling with BARRIER VII, and two full-scale vehicle crash tests. The crash tests used three-quarter-ton pickup trucks and were conducted in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The first test was successfully conducted on the guardrail system with the back sides of the posts positioned 457 mm away from the front of the culvert’s headwall. The second test was unsuccessfully performed on the guardrail system with the back sides of the posts positioned 25 mm away from the front of the headwall. The safety performance of the W-beam guardrail system attached to the top of a low-fill concrete culvert was determined to be acceptable according to the TL-3 criteria found in NCHRP Report 350. Recommendations for the final placement of the guardrail system with respect to the culvert headwall are also made.

Tests and simulation of a w-beam rail-to-post connection

The bolted connection of a w-beam rail to a guardrail post can have a significant affect on the performance of a guardrail system. For example, if the connections are too strong, the w-beam is likely to be pulled to the ground with the post and result in the vehicle overriding the guardrail. If the connections are too weak, the rail can pull away from the posts too soon allowing the rail to drop and the vehicle to penetrate behind the system. In recent years, finite element simulation has rapidly become a fundamental part of the analysis and design of roadside safety hardware systems, and as such, the finite element models must be capable of accurately simulating the response of these bolted connections. One of the challenges of simulating guardrail collisions is obtaining accurate models of each of the distinct components of the system, such as the various types of bolted connections, and properly modelling their interaction with each other. This study investigates the failure mechanism of the bolted connection of a w-beam rail to a guardrail post using laboratory experiments and uses that information to develop computationally efficient and accurate finite element models of the rail-to-post connection that can be used in routine analysis of guardrail system performance using LS-DYNA.

Tests and simulation of a w-beam rail-to-post connection

Abstract The bolted connection of a w-beam rail to a guardrail post can have a significant affect on the performance of a guardrail system. For example, if the connections are too strong, the w-beam is likely to be pulled to the ground with the post and result in the vehicle overriding the guardrail. If the connections are too weak, the rail can pull away from the posts too soon allowing the rail to drop and the vehicle to penetrate behind the system. In recent years, finite element simulation has rapidly become a fundamental part of the analysis and design of roadside safety hardware systems, and as such, the finite element models must be capable of accurately simulating the response of these bolted connections. One of the challenges of simulating guardrail collisions is obtaining accurate models of each of the distinct components of the system, such as the various types of bolted connections, and properly modelling their interaction with each other. This study investigates the failure mechanism of the bolted connection of a w-beam rail to a guardrail post using laboratory experiments and uses that information to develop computationally efficient and accurate finite element models of the rail-to-post connection that can be used in routine analysis of guardrail system performance using LS-DYNA.

Flared Energy-Absorbing Terminal Median Barrier

The design and crash test results of a median barrier version of the Flared Energy-Absorbing Terminal, known as FLEAT-MT, are presented. This energy-absorbing terminal is designed for use with a W-beam, strong-post median barrier. The FLEAT-MT terminal uses two standard FLEAT terminals, one for each of the two W-beam rail elements. The energy-absorbing capability of the FLEAT-MT terminal is based on the sequential kinking concept, similar to that used with the Sequential Kinking Terminal and FLEAT guardrail terminals. Three full-scale vehicle crash tests were conducted to evaluate the impact performance of the FLEAT-MT terminal in accordance with guidelines set forth in NCHRP Report 350: Test 3-35—pickup truck redirection test (Test No. FMT-1), Test 3-31—pickup truck head-on test (Test No. FMT-2), and Test 3-39—pickup truck reverse-direction test (Test No. FMT-3M). The terminal performed as designed. The FLEAT-MT terminal meets all evaluation criteria for a Test Level 3 median barrier terminal set forth in NCHRP Report 350. The FLEAT-MT terminal is being evaluated by FHWA for approval to be used on the National Highway System.

W-Beam Guardrail Adjacent to a Slope

A W-beam guardrail system was developed and successfully crash tested for use on a 2:1 foreslope. The guardrail design was constructed with W-beam rails 2.66 mm thick (12 gauge) totaling 53.34 m in length, and it incorporated a half-post spacing section of 17.15 m. The W-beam rail was supported by 15 W150 × 13.5 steel posts 1829 mm long, spaced 1905 mm on center, and 19 W150 × 13.5 steel posts 2134 mm long, spaced 952.5 mm on center. Routed, 150 × 200 × 360 mm wood spacer blockouts were used to block the rail away from each post. The research study included bogie testing on steel posts placed in sloped fill, computer simulation modeling with BARRIER VII, and one full-scale vehicle crash test, using a 2000-kg pickup truck. The test, impacting at a speed of 100.7 km/h and an angle of 28.5 degrees, was conducted and reported in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350. The safety performance of the W-beam barrier system was determined to be acceptable according to TL-3 criteria.

Performance of W-Beam Splices

Structural failure of post-and-beam W-beam guardrails during impact sometimes is due to the rupture of the W-beam rail where two sections are spliced together with bolts. Summarized is a study of the mechanics of failure of the splice connection. The causes of rupture are identified, and a design alternative is formulated that will reduce the likelihood of rupture of the splice connection. The tensile forces in the W-beam rail and the mode of deformation of the splice connection during impact were critical factors considered in the study. The results of full-scale crash tests, laboratory tests, and finite element analysis indicate that relocating splices to midspan locations would greatly reduce the chance of observing a rupture of the guardrail in full-scale crash tests and in real-world collisions.

Long-Span Guardrail System for Culvert Applications

A long-span guardrail for use over low-fill culverts was developed and successfully crash tested. The guardrail system was configured with 30.48 m of nested, 12-gauge W-beam rail and centered around a 7.62-m-long unsupported span. The nested W-beam rail was supported by 16 W152×13.4 steel posts and 6 standard CRT posts, each with two 150-mm×200×360 mm wood block-outs. Each post was 1830 mm long. Post spacings were 1905 mm on center, except for the 7.62-m spacing between the two CRT posts surrounding the long span. The research study included computer simulation modeling with Barrier VII and full-scale vehicle crash testing, using 3/4-ton (680-kg) pickup trucks in accordance with the Test Level 3 (TL-3) requirements specified in NCHRP Report 350. Three full-scale vehicle crash tests were performed. The first test was unsuccessful because of severe vehicle penetration into the guardrail system. This penetration resulted from a loss of rail tensile capacity during vehicle redirection when the swagged fitting on the cable anchor assembly failed. A second test was performed on the same design, which contained a new cable anchor assembly. During vehicle redirection, the pickup truck rolled over and the test was considered a failure. The long-span system was subsequently redesigned to incorporate double block-outs on the CRT posts and crash tested again. Following the successful third test, the long-span guardrail system was determined to meet TL-3 criteria.

Design and Analysis of Approach Terminal Sections Using Simulation

Turned-down guardrail terminal sections were analyzed using LS-DYNA3D, a dynamic, nonlinear, large deformation finite-element modeling package with capabilities for simulating vehicular impacts into roadside hazards. A baseline simulation was conducted on the existing turned-down approach terminal section, as well as on various retrofit options. Simulation findings were used to identify potential design changes and to select the two most promising options. Modified designs were subjected to six low-speed and one high-speed full-scale crash tests with a minisize automobile. The crash testing verified that one of the retrofit designs would allow the W-beam rail to drop down without causing vehicle rollover when impacted end on by a minisize automobile. However, the revised design did not meet recommended safety standards when one of the weakened posts failed to break away as designed. It is believed that by revising the post installation procedures, the modified turned-down terminal section would perform satisfactorily.

Development of Metal-Cutting Guardrail Terminal

A crashworthy terminal for strong-post W-beam guardrail systems was developed at the Midwest Roadside Safety Facility at the University of Nebraska—Lincoln. The terminal incorporates an impact head that is placed over the end of a tangent section of W-beam rail. The impact head is designed to be pushed down the rail and to dissipate impact energy by cutting the W-beam along the peaks and valley to produce four essentially flat strips of steel. These flat strips are then deflected out of the path of the vehicle, striking the end of the rail. Static and dynamic component tests as well as full-scale developmental crash tests conducted during the development of this system are described. Finally, the results of the three full-scale compliance crash tests are presented and discussed. The metal-cutting guardrail terminal was shown to meet NCHRP Report 230 safety performance standards.

Development of Metal-Cutting Guardrail Terminal

A crashworthy terminal for strong-post W-beam guardrail systems was developed at the Midwest Roadside Safety Facility at the University of Nebraska—Lincoln. The terminal incorporates an impact head that is placed over the end of a tangent section of W-beam rail. The impact head is designed to be pushed down the rail and to dissipate impact energy by cutting the W-beam along the peaks and valley to produce four essentially flat strips of steel. These flat strips are then deflected out of the path of the vehicle, striking the end of the rail. Static and dynamic component tests as well as full-scale developmental crash tests conducted during the development of this system are described. Finally, the results of the three full-scale compliance crash tests are presented and discussed. The metal-cutting guardrail terminal was shown to meet NCHRP Report 230 safety performance standards.

Impact Behavior of Barriers on Nonlevel Terrain

Six full-scale crash tests were conducted to evaluate the impact behavior of two widely-used roadside barriers when placed on a 6:1 side slope. Four of the six tests involved a standard W-beam rail on metal post varies directly as G4(1S) system triple prime and the other two tests involved a three-cable barrier mounted on metal posts (G1 system). The tests were conducted and evaluated in accordance with national guidelines for testing of roadside appurtenances. Based on the results, it is recommended that the G4(1S) system not be placed on 6:1 or steeper side slopes. Placement of the G1 system on a 6:1 side slope is acceptable provided ample space exists between the barrier and the hazard it is shielding. Language: en