The performance of non-proprietary, or untested, steel guardrail systems has been observed and commented on by many sources within the Middle East with regards to their vehicle containment. The common observation is that the impacting vehicle has broken through, or “split” the w-beam guardrail. The use of a system tested to standards applicable to the vehicle fleet (American NCHRP350 or MASH), such as Ezy-Guard mitigate and manage this risk. Below are the performance findings from a site visit: Ezy-Guard and a non-proprietary system were both installed on a new road and provided a suitable comparison of barrier containment performance.
Several barrier collision sites were observed where the impact angle and collision were light, the barrier had been damaged and had redirected the vehicle. However, on a location where the angle had clearly been more severe, it was noted that the barrier damage was short in length and that the W-beam had split open, failing to contain the vehicle.
Start of impact point as observed with scrape marks on w-beam.
Damaged section of w-beam completely removed.
Section of crumpled w-beam detached and showing signs of compression and “pocketing”.
Adjacent line posts only lightly deformed near to the collision point
Summary In this example the spacing is a “strong post” every 4m and the collision point indicates little post deformation and therefor absorption of energy. Heavy damage to the w-beam, that can be described as crumpling, indicates that it is being subjected to excessive forces that is leading to tearing and splitting of the beam. The posts are too rigid before and after the collision point which, when combined with a larger post spacing, result in the w-beam being subjected to a higher redirection angle through the interaction with the vehicle. During heavier collisions by larger vehicles this is likely to over-stress the w-beam and lead to containment failure as seen here. Several collision points were observed. All had been successfully contained:
Point of probable impact and approximate angle judging by tyre marks.
Posts deforming and deflecting ahead and beyond the impact point.
Review of System Rear:
Deforming posts absorbing energy and providing a measured lateral resistance.
W-beam has remained intact and redirected vehicle. No crumpling of beam but beam now laying on sand after impact as no longer supported by posts.
Partial deformation of post.
Heavy leading to complete deformation of posts showing movement of sliding carriage upward and off the supporting post.
Complete detachment of sliding carriage away from post, but still securely attached to the intact w-beam which is able to perform as intended.
The Ezy-Guard posts are installed with a “weak post” every 2m and are designed and tested to deform on collision in a way that enables the w-beam to smoothly redirect the impacting vehicle without significantly increasing the stress on the w-beam.
The deforming posts continue to offer lateral resistance through the sliding carriage without subjecting the w-beam to forces that either significantly increase the angle of interaction or are attempting to pull the w-beam down as the post rotates/deforms in the soil. The w-beam can smoothly redirect the vehicle back to the road and contain the collision as was seen from the site visit.