Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A Guide (2022)

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89   4.1 Research Questions The final design developed and tested under this project is site-specific, so its layout may not be appropriate at all locations. Alternative conditions may include a different (but crashworthy) transition design, different curve radii, or a location warranting a curved barrier with no bridge nearby (or an intersecting road farther away from a bridge). The following sections address these concerns based on computer simulation only. 4.2 Application Guidelines Given that there are many locations where the site geometry differs from that tested under this project, the general guidelines discussed in this section are based on simulation analyses under the following three conditions: • Different transition designs, • Larger radii, and • No bridge near side road. 4.2.1 Different Transition Designs The following guidelines convey how agencies can use SRGS with Thrie-beam or W-beam transition designs. • Thrie-beam Transition Design. The length and height of the Thrie-beam design must meet MASH TL-3 criteria, in keeping with the design tested under this project: 18 ft, 9 in. long and 31 in. high. Connect both cables used in the system to the back side of the Thrie-beam rail, and attach the additional 18 ft, 9 in. 10-gauge W-beam rail with the rounded end section to the back of the Thrie-beam posts, the asymmetrical section, and 37½ in. of the W-beam along the main road, similar to the testing done under this project. • W-beam Transition Design. The length and height of the W-beam design must meet MASH TL-3 criteria, in keeping with the design tested under this project: 18 ft, 9 in. long and 31 in. high. Attach the bottom cable of the SRGS through the post nearest to the upper cable con- nection, similar to how the lower cable is anchored through a post at the opposite end along the side road. Attach the top cable to the back side of the W-beam transition, and attach the additional 18 ft, 9 in. 10-gauge W-beam rail with the rounded end section on the back side of the transition posts and a segment of the W-beam along the main road as needed, as in the tested design. C H A P T E R 4 Development of Guidelines on Application and Installation of SRGS

90 Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A Guide 4.2.2 Larger Radii Some site conditions may require a radius greater than 8 ft. As Figure 4.1 shows, the project team created computer models with three radii (8, 16, and 24 ft) to assess SRGS performance. All aspects of this design were kept the same as the final design (outlined in the section on SRGS design), except the larger radii necessitated using additional sections of curved rail and longer cables. Simulations were run using the 16 and 24 ft radius layouts, and then results were compared to the 8 ft radius design (see Table 4.1). Figure 4.2 shows the locations where rail-to- post bolts were omitted for each simulation. The results of these simulations are described and depicted in the following section. Table 4.1 shows predicted yaw, pitch, and roll angles as well as the occupant-risk numbers from the three simulations. The occupant risk factors were relatively constant in all three simula- tions, and they satisfied MASH evaluation criteria. Figures 4.3 and 4.4 show sequential pictures from the three simulations. Note: A higher vehicle yaw angle was seen in the 24 ft radius design simulation than in the tested design. All simulations were conducted for an impact speed of 62 mph (100 km/hr). Improved performance would be expected at lower impact speeds. Figure 4.1. SRGS computer models of bridge with 8, 16, and 24 ft radii. Occupant Risk Factor 8 ft Radius Simulation 16 ft Radius Simulation 24 ft Radius Simulation Occupant Impact Velocity (OIV), m/s Longitudinal Lateral Occupant Ridedown Accelerations, G Longitudinal Lateral Maximum Roll, Pitch, and Yaw Angles, degrees Roll Pitch Yaw 9.7 1.7 9.4 7.7 5.2 9.3 74.6 9.2 0.7 9.6 6.7 8.3 17.9 83.7 9.7 0.5 10.3 6.0 6.2 18.7 121.4 Table 4.1. Occupant risk factors from with-bridge simulations.

Development of Guidelines on Application and Installation of SRGS 91   4.2.3 No Bridge near Side Road If there is no bridge on the main road but shielding is needed for an embankment or other hazard, or if the side road is farther from the bridge than the tested design, then the SRGS should be installed symmetrically. The section along the main road should be the mirror image of the side road installation. The project team conducted computer simulations with the three different radii (8, 16, and 24 ft) to assess the SRGS performance for cases where it is connected at one or both ends to a standard 31 in. high W-beam system. Figure 4.5 shows models with the three radii. All three models were symmetrical relative to the center of the curved section. The angle between the main and side road for all three cases was the same as the test design (i.e., 90 degrees). The cable connections on both ends of the SRGS are similar to the connec- tions used on the side road of the tested design. For the simulations, the lengths of the tangent section along the main road in all three models are the same as the side road installation in the tested design. The locations where the curved sections of rail are bolted to the posts are the same as those shown in Figure 4.2. For the side road, the end treatment for the simulations is a modified cable end anchor (no strut), as used during the actual crash testing, but it is not crashworthy. As stated in the following section on installation guidelines, adding a crashworthy terminal to the end of the second 10-gauge W-beam section from the radius, or extending the guard- rail along the side road if roadside conditions warrant additional shielding, is acceptable. In these cases, use a standard steel line post to replace the timber breakaway cable terminal Post 2 of the cable end anchor; field drill a hole at the base of the steel line post web and use the same connection (bearing plate) to anchor the lower cable anchor. Along the main road, the SRGS would also be connected to a 31 in. high W-beam that could be extended, as needed, to shield a given hazard (e.g., a steep embankment or a parallel drainage structure along the road). The cables would be anchored as a mirror image of the anchorage described along the side road. Figure 4.2. Locations (circled) where rail is not bolted to posts.

92 Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A Guide 8 ft Radius 16 ft Radius 24 ft Radius 0.00 s 0.00 s 0.00 s 0.25 s 0.25 s 0.25 s 0.50 s 0.50 s 0.50 s 0.75 s 0.75 s 0.75 s 1.00 s 1.00 s 1.00 s Figure 4.3. Time sequence of simulation results—with a bridge at different radii, overhead view.

Development of Guidelines on Application and Installation of SRGS 93   8 ft Radius 16 ft Radius 24 ft Radius 0.00 s 0.00 s 0.00 s 0.25 s 0.25 s 0.25 s 0.50 s 0.50 s 0.50 s 0.75 s 0.75 s 0.75 s 1.00 s 1.00 s 1.00 s Figure 4.4. Time sequence of simulation results—with a bridge at different radii, isometric view.

94 Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A Guide Table 4.2 shows yaw, pitch, and roll angles, as well as the occupant-risk values from the three simulations. It is notable that higher yaw, pitch, and roll angles were observed for the simulations but were still acceptable. All of the occupant-risk values are below the MASH maximum allow- able values. Figures 4.6 and 4.7 show sequential pictures from the three simulations. All the simulations used the MASH 2270P vehicle with an impact speed of 62 mph (100 km/hr). 4.3 Installation Guidelines The many simulation runs and the outcomes of the crash tests described in Chapter 3 prove the efficacy of the final design. Minor changes were implemented in the design process to improve SRGS functionality, which led to successful tests demonstrating compliance with MASH guide- lines for a TL-3 barrier design. Computer simulations used in design, development, and testing provided some basis for developing guidelines on applying SRGS in situations different from the tested condition. However, final guidelines must be promulgated by agency staff relative to its use and installation within established agency practices. Occupant Risk Factor 8 ft Radius Simulation 16 ft Radius Simulation 24 ft Radius Simulation Occupant Impact Velocity (OIV), m/s Occupant Ridedown Accelerations, G Maximum Roll, Pitch, and Yaw Angles, degrees Longitudinal Lateral Longitudinal Lateral Roll Pitch Yaw 9.8 1.6 7.5 7.4 22.1 45.6 120.8 9.0 0.7 8.7 7.2 14.3 23.1 110.1 9.2 1.4 9.0 5.8 7.1 8.5 67.7 Table 4.2. Occupant risk factors from no-bridge simulations. Figure 4.5. SRGS computer models without a bridge at 8, 16, and 24 ft radii.

Development of Guidelines on Application and Installation of SRGS 95   8 ft Radius 16 ft Radius 24 ft Radius 0.00 s 0.25 s 0.50 s 0.75 s 1.00 s 0.00 s 0.25 s 0.50 s 0.75 s 1.00 s 0.00 s 0.25 s 0.50 s 0.75 s 1.00 s Figure 4.6. Time sequence of simulation results—no bridge at different radii, overhead view.

96 Roadside Barrier Designs near Bridge Rail Ends with Restricted Rights-of-Way: A Guide 8 ft Radius 16 ft Radius 24 ft Radius 0.00 s 0.25 s 0.50 s 0.75 s 1.00 s 0.00 s 0.25 s 0.50 s 0.75 s 1.00 s 0.00 s 0.25 s 0.50 s 0.75 s 1.00 s Figure 4.7. Time sequence of simulation results—no bridge at different radii, isometric view.

Development of Guidelines on Application and Installation of SRGS 97   Agencies can fabricate this SRGS system from standard guardrail components and hardware. The following guidelines cover various site conditions where the system can be installed. • Different Transition Design. Refer to the section on different transition designs in Chapter 4. • Different End Anchor. The section on SRGS design in Chapter 3 describes the end anchor as the “as tested” anchor used for crash testing, but it is not appropriate for use with two-way traffic. Replace this anchor by either continuing the rail or replacing with a crashworthy ter- minal using the following guidelines. – Continuing the Rail. Bolt the half-bracket used to anchor the upper cable to the first 12-gauge W-beam rail, and add an additional MGS rail as warranted to shield any iden- tified roadside hazards along the secondary roadway. Note: The breakaway wood posts and soil tubes used in the test installations are not needed when the W-beam is extended. Connect the lower SRGS cable through the base of the first post, supporting the 12-gauge W-beam section using a bearing plate, washer, and nut. – Replacing with a Crashworthy Terminal. Replace the end anchor with a MASH terminal that requires a TL-3 application. Place at least 12 ft, 6 in. of standard 12-gauge rail before attaching the terminal, or place the terminal as specified by the manufacturer. • Different Blockout Size. The system as tested used 8 in. wooden, routed blockouts; based on simulation, 12 in. blockouts can also be used. Both wood and recycled composite blocks can be used. Note: Because of the large vehicle intrusion into the system for the nose impact (MASH Test 3-33), keep an area immediately behind the system free of rigid objects. For the retest— FOIL Test 20004—that area was approximately 30 ft from the side road and 15 ft from the main road. It is important that installers and maintenance supervisors/crews understand how the system functions so that it is properly installed and maintained.