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I believe you worked with our group on standard drawing
MGS-3.1.  From past e-mails, I see that she used Iowa’s standard drawing
as a template.  I looked at the Iowa website, but didn’t see a connection
detail like the one shown below.  This is the MGS thrie-beam connection to
twin steel tube bridge railing.  I received a call from a contractor
asking if the washers (highlighted below) are necessary.  Do you know if
this connection detail was based on research from Midwest Pooled Fund or
another state?  I would normally assume that the washers are necessary,
but this particular contractor does a large amount of work for us and his
question makes me wonder whether I’m missing something.

Thanks,

http://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/roadway/Standard%20Construct%20Drawings/MGS-3.1_7-18-2014.pdf

This issue has come up in the past regarding the use of the washers underneath the end shoe and nested thrie beam attachment. We have been recommending that washers be used based on the size and length of the slots in the current thrie beam end shoe pieces. We have some concerns that the size of the slots in the end shoe might allow the nuts to pull through. TTI has been using washers as well based on similar concerns. I believe that they have been using rectangular washers, but I do not have the spec.

In our recent tests, we have been using 5/8” F844 washers on the backside of the end shoe. That has worked fine to date. These are more standard parts and are easier to obtain.

http://www.portlandbolt.com/products/washers/standard-flat/

Thanks