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Bolt Specifications for Attachment of Thrie Beam to Concrete Parapet

Question
State WI
Description Text

I'm working on updating our standards on attaching thrie beam to rigid barriers. I understand that A325 bolts and A449 bolts are acceptable alternatives.


We have situations where we will need to drill through parapets and bolt on the back side. In general, we would need a bolt about 14.5 inches long. In some of these situations, a standard A325 bolt may not have enough threading to allow for a tight connection between the thrie beam and concrete barrier.


I know that we could specify the following to solve these situations:


Use a shorter A325 bolt.

Specify an A449 bolt that is fully threaded.


I did some searching around on the web. I had some difficulties finding standard sizes of A325 or A449 bolts. Many of the bolts I found where too short to be used (9 inches or shorter) or where a different standard (SAE...)


The questions I have are:


What are the standard bolt lengths for A325 and A449? Or what source should I get to verify standard bolt lengths?

Are there other standards of bolts that we could use?

Would it be possible to specify a galvanized threaded rod?

Could we use some of the research on epoxy into bridge deck research to connect thrie beam to a bridge parapet.


From my brief look on the web, if galvanized threaded rods are common. If a galvanized rod could be used instead of a specially ordered A449 or A325 bolt, the department could save some costs.

Keywords
  • Guardrail
Other Keywords none
Date July 1, 2011


Response
Response

I have put some responses below in red.

 

What are the standard bolt lengths for A325 and A449? Or what source should I get to verify standard bolt lengths?

I don't know of standard bolt lengths for A325 and A449. A325 is a structural bolt standard that generally uses shorter thread lengths to increase the shear strength of bolts used in structural connections. It also uses a heavy hex head standard. On many websites, such as Portland Bolt and Fastenal, they recommend that if you cannot find an A325 bolt that meets your need, then you can switch to A449. In fact, in Section 1.5 of the A325 specification it states "for bolts of other configurations and thread lengths with similar mechanical properties (to A325), see Specification A449."

 

From past experience, we have custom ordered variable length A325 bolts from various manufacturers. As such, you should be able to obtain quotes for most reasonable lengths for 1-in. increments. Second, if thread length is an issue, you could use several ¼"¢â‚¬Å“in. thick plate washers on the back side of the parapet to allow for the nut to be tightened on the threads. It may also be possible to epoxy longer female inserts into the concrete parapet for use with the bolts, although further investigation would be required. Can you let us know what bolt lengths would typically be required to pass through the concrete parapets? With this information, we could assist with obtaining quotes for your required lengths.

 

That said, I cannot find much on standard lengths for A325 bolts. The longest lengths I could find were 14" and 10.5". There were no in between sizes. Thus, I would try contacting Fastenal, Portland Bolt, and Bennett Bolt to see what options are available.

 

Are there other standards of bolts that we could use?

If you are looking for a substitute for A325, then A449 is the best replacement grade available as the A325 spec noted above. SAE Grade 5 also has similar mechanical properties, but like A449 may not have the exact same bolt head specification.

 

If you want to stick with A325 bolts, Portland Bolt's website notes that they can custom build A325 bolts. I am guessing that will cost more, but you will likely be able to spec a length and thread length.

 

Would it be possible to specify a galvanized threaded rod?

In terms of capacity, there are several threaded rod material grades that would work. However, I have concerns that the extra threaded rod that would protrude on the traffic side face of the connection would become a vehicle snag hazard. Thus I would not recommend the use of the threaded rods. SAE Grade 5 and ASTM A193 B7 would be sufficiently strong.

 

Could we use some of the research on epoxy into bridge deck research to connect thrie beam to a bridge parapet.

There is some potential to use the epoxy anchor research or other inserts to anchor the thrie beam. We did just that with the TCB transition to anchor the thrie beam to the single slope barrier. However, we have not done this to date with approach guardrail transitions. In order to do so, we would need to look at the type of attachment (epoxied threaded rod, epoxied threaded insert with a bolt, or a mechanical anchor), the depth of the section, and the effect of edge distance and anchor spacing. Thus, I believe that there is a potential to do this kind of attachment, but we would need to do some additional analysis.

 

 

 

Date July 1, 2011


Response
Response

As a follow on question, WiSDOT had a question regarding the use of fully threaded A325T bolts versus partially threaded A325 bolts for connection of thrie beam and W-beam to concrete parapets.

Date July 2, 2011


Response
Response

There was a question regarding the use of fully threaded A325T bolts versus partially threaded A325 bolts for connection of thrie beam and W-beam to concrete parapets.

 

The only concern that I had was that a fully threaded section would have reduced shear capacity as compared to a partially threaded one.

 

In order to check this concern I calculated the capacity of the end shoe versus the capacity of the 7/8" A325T bolts. I examined the tensile capacity of the thrie beam end shoe versus as well as the bearing failure of the end shoe anchor holes. It turns out that the bearing failure of the end shoe holes is the limiting value (i.e. the end shoe will fail under bearing failure at the anchor holes long before its tensile capacity is exceeded). As such, the A325T bolts should be acceptable as long as the shear capacity of the 7/8" A325T bolts is greater than the bearing capacity of the end shoe anchor holes.

 

The shear capacity of the 7/8" A325T bolts is several times greater than the bearing capacity of the thrie beam end shoe bearing capacity, thus the use of the 7/8" A325T bolts should be acceptable.

Date July 2, 2011


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