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I have some comments for you regarding post type and grade.

Currently, there are two variables at play. One is the post section and the other is the material grade. W-beam guardrail systems are typically tested with W6x8.5 or W6x9 posts. In recent years, we have primary tested the MGS and other W-beam guardrails with W6x8.5 posts as it is what states are typically supplied by the guardrail manufacturers. Especially if the posts were standard lengths. For non-standard post lengths or special posts like the UBSP posts or culvert mounted strong posts, we have received W6x9 as this is a common structural element. W6x9 posts have about a 9% increase in bending strength, but we generally allowed either for use with the MGS.

The second item is the material grade which currently may vary between A36 to A992 (or A572). A709 is a grade 50 steel used for rolled steel sections on bridges, but is not really relevant for this discussion on guardrail posts. Currently, rolled structural steel shapes are trending towards the higher A992 grade material and older steels with yield strengths of 36 ksi have been replaced with higher strength materials with Fy = 50 ksi.  Please refer to the attached documents describing this transition. Additionally – please see relevant ASTM Specifications and look at section 1.1 of each:

From ASTM A36 … no longer ANY mention of structural steel (beam):

1.1 This specification2 covers carbon steel shapes, plates, and bars of structural quality for use in riveted, bolted, or welded construction of bridges and buildings, and for general structural purposes.

From ASTM A992 … indicates rolled structural steel (beam):

1.1 This specification covers rolled steel structural shapes for use in building framing or bridges, or for general structural purposes.

From ASTM A709 … indicates structural steel (beam):

1.1 This specification covers carbon and high-strength low alloy steel structural shapes, plates, and bars and quenched and tempered alloy steel for structural plates intended for use in bridges. Seven grades are available in four yield strength levels as follows:

From ASTM A572 … indicates structural steel (beam):

1.1 This specification covers five grades of high-strength low-alloy structural steel shapes, plates, sheet piling, and bars.  Grades 42 [290], 50 [345], and 55 [380] are intended for riveted, bolted, or welded structures. Grades 60 [415] and 65 [450] are intended for riveted or bolted construction of bridges, or for riveted, bolted, or welded construction in other applications.

There is a lot of overlap between these material specifications which allows for a particular steel lot/heat/batch to qualify under multiple of these specifications.  For example, A36 requires only a minimum yield and tensile strength, there is no maximum values.  As such, it has been easier to manufacture steel at grade 50 and label it as A992, A572, and A36. It may still be possible to obtain grade 36 steel posts, but it becoming increasingly difficult to find, especially when ordering anything other than W6x8.5 guardrail posts. Over the past 5-10 years, MwRSF has typically received A572 or A992 when ordering guardrail posts (even when A36 was requested). You can see this in the attached tables that lists out the materials we have received for recent guardrail and AGT testing.

Note that we receive both A992 and A36 in W6x8.5 posts and only get A992 in other standard structural sections. It should also be noted that the A36 material we receive typically has yield strengths in the 45-50 ksi range. Thus, it is at or very near the A992 specification.

Based on this, we have typically allowed both W6x9 and W6x8.5 posts for use in the MGS and in AGT’s as the difference in section and material strength appears to be minimal and we believe that the effect on the overall barrier performance is also minimal.

Within drawing sets and system details, MwRSF has been listing multiple specifications as equivalent steel materials for use as guardrail posts. However, we have made the decision to stop listing grade 36 steels in current and future projects due to a lack of 36 ksi steel availability and the push tin the structural steel community towards 50 ksi material. MwRSF will only be listing grade 50 steel (A992). We also believe that it is simpler to have a single material grade moving forward.

Ron’s previous comments regarding bridge structures referred directly to steel post bridge rails systems. There is a possibility for increased deck damage from bridge rails designed/tested with 36 ksi steel if the grade is increased to a 50 ksi material.  The increased strength of the post will transfer more load to the deck. Damage to the deck would also depend upon the deck strength, concrete strength, and rebar configuration, so increased damage is not a certainty.  Increased deck damage is a concern and systems specifying A36 posts should be evaluated on an individual basis.

We have had similar discussions with state DOTs previously. You can see that discussion here. http://mwrsf-qa.unl.edu/view.php?id=1128

Let me know if you need anything else.

Thank you for your very detailed answer.  In summary from your email below:

• Based on this, we have typically allowed both W6x9 and W6x8.5 posts for use in the MGS and in AGT’s as the difference in section and material strength appears to be minimal and we believe that the effect on the overall barrier performance is also minimal.
• However, we have made the decision to stop listing grade 36 steels in current and future projects due to a lack of 36 ksi steel availability and the push tin the structural steel community towards 50 ksi material. MwRSF will only be listing grade 50 steel (A992). We also believe that it is simpler to have a single material grade moving forward.
• Ron’s previous comments regarding bridge structures referred directly to steel post bridge rails systems. There is a possibility for increased deck damage from bridge rails designed/tested with 36 ksi steel if the grade is increased to a 50 ksi material.  The increased strength of the post will transfer more load to the deck. Damage to the deck would also depend upon the deck strength, concrete strength, and rebar configuration, so increased damage is not a certainty.  Increased deck damage is a concern and systems specifying A36 posts should be evaluated on an individual basis.

Hi Dave

Response below in red.

Thanks

From: Bizuga, Dave [mailto:David.Bizuga@dot.nj.gov]
Sent: Thursday, June 14, 2018 11:16 AM
To: Robert Bielenberg <rbielenberg2@unl.edu>; swright@gregorycorp.com
Cc: Potapa, John <jpotapa@arorapc.com>; Goessel, Charles <cgoessel@arorapc.com>; Tang, Hung <Hung.Tang@dot.nj.gov>; Durkos, John <jdurkos@roadsystems.com>; Bligh, Roger (R-Bligh@tti.tamu.edu) <R-Bligh@tti.tamu.edu>; Ronald Faller <rfaller1@unl.edu>; Warren, Joseph <Joseph.Warren@dot.nj.gov>
Subject: RE: NJ / Post / W6x8.5 vs W6x9# Beam

Bob,

Thank you for your very detailed answer.  In summary from your email below:

• Based on this, we have typically allowed both W6x9 and W6x8.5 posts for use in the MGS and in AGT’s as the difference in section and material strength appears to be minimal and we believe that the effect on the overall barrier performance is also minimal.
• However, we have made the decision to stop listing grade 36 steels in current and future projects due to a lack of 36 ksi steel availability and the push tin the structural steel community towards 50 ksi material. MwRSF will only be listing grade 50 steel (A992). We also believe that it is simpler to have a single material grade moving forward.
• Ron’s previous comments regarding bridge structures referred directly to steel post bridge rails systems. There is a possibility for increased deck damage from bridge rails designed/tested with 36 ksi steel if the grade is increased to a 50 ksi material.  The increased strength of the post will transfer more load to the deck. Damage to the deck would also depend upon the deck strength, concrete strength, and rebar configuration, so increased damage is not a certainty.  Increased deck damage is a concern and systems specifying A36 posts should be evaluated on an individual basis.

Not sure what “the push tin” means in the second bullet. 

Poor Typing by me. It should read “the push by the structural steel community”.

So in the second bullet above, you would be specifying a post section of W6X8.5 or W6X9 steel at Grade A992 instead of Grade A36. 

Yes. Moving forward, we plan to list those steel sections as A992 to be consistent with structural steel guidelines. We also feel that having a single steel grade makes more sense.  

In the third bullet for steel post bridge rail systems, are you also specifying a post section of W6X8.5 or W6X9 steel at Grade A992 instead of Grade A36?  It sounds like you want A36.

For steel bridge posts, we believe that you would have to look at the individual bridge rail system, its connection to the bridge deck, and the bridge deck reinforcement. If an older design was built and tested with a steel that yielded near 36 ksi, there would be concern that switching to the higher grade may overload the post to deck connection or the bridge deck itself and affect the rail performance.  It doesn’t mean that you couldn’t use A992, but you would need to check the loading into the deck.

Steve,