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We have an existing bridge that currently has w-beam
attached to the side of the parapet. The parapet on the traffic side is 9
inches tall and 1'-6" wide.  

Below is a diagram and photograph of this location. I have
also attached additional photos of the site location.  

Short of replacing the structure, we are looking for the
best that can do design understanding that this is a situation were there are
no designs that would meet crash testing requirements due to the 9 inch tall
curb. 

Do you have any suggestions for a design at this location?

After reviewing your information, there are a few thoughts that come to mind.

First, there may be potential to remove the W-beam rail and post system. Then, a reinforced concrete parapet could be attached to the top surface of the concrete curb. Concrete buttresses may be needed at the ends with appropriate tapers when adapting approach guardrail transitions. Additional reinforcement would be needed to anchor the buttresses as only one yield line would be available to develop sufficient redirective capacity for impacting vehicles.

Many years ago, we crash tested a retrofit parapet placed on a curb that formerly supported an aluminum beam and post bridge rail. This work was completed for the Iowa DOT. Several links are provided below to guide access to the pertinent reports on our website.

http://mwrsf.unl.edu/reportresult.php?reportId=203&search-textbox=iowa%20bridge

http://mwrsf.unl.edu/reportresult.php?reportId=80&search-textbox=iowa%20bridge

http://mwrsf.unl.edu/reportresult.php?reportId=200&search-textbox=iowa

In recent years, we provided guidance to NDOR regarding the attachment of retrofit parapets to weak deck that have old bridge rails cut off. I am asking that Scott Rosenbaugh forward that information to you.

Second, there may be some potential to attach crashworthy beam and post systems to your curb as long as it has sufficient structural capacity. There is a recent TTI testing effort on the RC 131 bridge rail. The link is provided below.

https://tti.tamu.edu/publications/catalog/record/?id=38552

https://tti.tamu.edu/publications/catalog/record/?id=37169