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Fence Mounted on Concrete Barrier

Question
State	IN
Description Text	Has there been any high speed testing of chainlink fence attached to F-shape railing? We’ve got a railroad that’s mandating a 7ft+ fence on top of a 32” F-shaped rail…on the interstate. Typically we only consider fence where there is significant pedestrian activity. The use on an interstate structure seems like a bad idea, so I’m looking for documentation to allay my fears or to use as supporting documentation to push back.

Question

State

Description Text

Has there been any high speed testing of chainlink fence
attached to F-shape railing? We’ve got a railroad that’s mandating a 7ft+
fence on top of a 32” F-shaped rail…on the interstate. Typically we only
consider fence where there is significant pedestrian activity. The use on
an interstate structure seems like a bad idea, so I’m looking for documentation
to allay my fears or to use as supporting documentation to push back.

System Performance Evaluation

System Types
Bridge Rails
Permanent Concrete Barriers

Applications

System Features

Date March 14, 2019
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Attachment Fence Mounted on a Barrier.pdf Attachment link.php

Response
Response (active)	We are aware of the need for crash-worthy debris fences, particularly for railroad shielding applications. Limited crash testing exists regarding debris fences attached to concrete parapets. As such, the significance of the structural strength of the debris fence and its offset from the front face of the barrier are largely unknown. Debris fences attached to bridge rails are subject to two major concerns. If the debris fence is located within the Zone of Intrusion (ZOI), which is the area behind the traffic-side face of the barrier into which a vehicle may protrude during impact, it must not produce excessive occupant compartment deformations, vehicle snag, nor occupant risk due to stiff beam and post members. However, in contrast, the fences must be strong enough to withstand live and dead loads from the bridge, and should not fall onto railroad tracks below when impacted. Additionally, there is concern that vehicle impacts involving the debris fence, especially impacts with heavy truck vehicles analogous to MASH TL-4 or higher, may have the potential to disengage components or sections of existing fence designs. TTI researchers successfully crash tested a chain link fence attached to a New Jersey safety shape concrete barrier which was intended as a vandalism deterrent. However, this design is similar to a debris protection fence. The chain link fence was attached to the back side of the 32-in. tall, New Jersey shape concrete barrier using two U-shaped brackets with threaded rods epoxied into the concrete and nutted to the U-brackets. TTI’s test no. 472070-6 was conducted according to AASHTO’s Guide Specifications for Bridge Railings PL-2 test specification, consisting of a 5,397-lb Ford F250 pickup truck impacting at 62.8 mph and 20.2 degrees. This system is shown in Figure 2. The vehicle’s right-front A-pillar and the upper right sill of the right-side window contacted the chain link fence and middle structural bar, but the high stiffness of the truck frame and the 20-degree impact angle limited vehicle extension over the top of the barrier. To date, no debris fence designs mounted on concrete parapets have been tested to TL-3 according to MASH. Many state DOTs have developed standardized designs for pedestrian rails or debris fences for installation in conjunction with bridge rails. Although most, if not all, of the designs have not been full-scale crash tested according to MASH TL-3 impact conditions, many of the designs were based on historically-successful systems tested under NCHRP Report No. 350, AASHTO’s Guide Specifications for Bridge Railings, or NCHRP Report No. 230. MwRSF currently has a funded project with Iowa DOT to develop a MASH TL-3 debris fence design. The project is currently in the design phase. Feel free to contact Bob Bielenberg for more information. Thanks

Response

Response
(active)

We are aware of the need for crash-worthy debris fences, particularly for railroad shielding applications. Limited crash testing exists regarding debris fences attached to concrete parapets. As such, the significance of the structural strength of the debris fence and its offset from the front face of the barrier are largely unknown.

Debris fences attached to bridge rails are subject to two major concerns. If the debris fence is located within the Zone of Intrusion (ZOI), which is the area behind the traffic-side face of the barrier into which a vehicle may protrude during impact, it must not produce excessive occupant compartment deformations, vehicle snag, nor occupant risk due to stiff beam and post members. However, in contrast, the fences must be strong enough to withstand live and dead loads from the bridge, and should not fall onto railroad tracks below when impacted. Additionally, there is concern that vehicle impacts involving the debris fence, especially impacts with heavy truck vehicles analogous to MASH TL-4 or higher, may have the potential to disengage components or sections of existing fence designs.

TTI researchers successfully crash tested a chain link fence attached to a New Jersey safety shape concrete barrier which was intended as a vandalism deterrent. However, this design is similar to a debris protection fence. The chain link fence was attached to the back side of the 32-in. tall, New Jersey shape concrete barrier using two U-shaped brackets with threaded rods epoxied into the concrete and nutted to the U-brackets. TTI’s test no. 472070-6 was conducted according to AASHTO’s Guide Specifications for Bridge Railings PL-2 test specification, consisting of a 5,397-lb Ford F250 pickup truck impacting at 62.8 mph and 20.2 degrees. This system is shown in Figure 2. The vehicle’s right-front A-pillar and the upper right sill of the right-side window contacted the chain link fence and middle structural bar, but the high stiffness of the truck frame and the 20-degree impact angle limited vehicle extension over the top of the barrier. To date, no debris fence designs mounted on concrete parapets have been tested to TL-3 according to MASH.

Many state DOTs have developed standardized designs for pedestrian rails or debris fences for installation in conjunction with bridge rails. Although most, if not all, of the designs have not been full-scale crash tested according to MASH TL-3 impact conditions, many of the designs were based on historically-successful systems tested under NCHRP Report No. 350, AASHTO’s Guide Specifications for Bridge Railings, or NCHRP Report No. 230.

MwRSF currently has a funded project with Iowa DOT to develop a MASH TL-3 debris fence design. The project is currently in the design phase. Feel free to contact Bob Bielenberg for more information.

Thanks

Date March 15, 2019
Previous Views (355) Favorites (0)