Repair of Corroded Beam Web 2

[AK4S]

For an existing Highway Bridge we are reviewing, there is significant loss of section in the beam webs at the bearing location. I have attached some sample photos (these locations are not too bad, some others are worse).

The current proposal is to reinforce the beam web by bolting on new plates on either side of the existing web and extending the plate (away from the bearing) till the full web thickness is available in the original beam.

The idea is to provide new plate thickness to match the original web thickness of the beam(ignoring the deteriorated web thickness)and hence maintain the shear capacity of the section.

For example:
Existing web thickness =0.625"
reduction due to chamfer =1.0625"
New Plate thickness required = (0.625"/2) + 1.0625" = 1.375". Hence provide 1.5" thick plate on either side of existing web.
[ul]
[li]I found similar details (Link)shared earlier in this forum and so I guess the philosophy makes sense. Also See attached file with details from one of the responses.[/li]

[li]How should I go about evaluating/preparing calcs for the proposed repair? evaluate New plate thickness (match or thicker than existing web?), Connection bolts (check for shear only?), extent/length of plate required? Does AASHTO have any guidance?[/li]
[/ul]
[li]What can I use to Seal the edges of the new plate to prevent moisture from getting between the new plates and the existing web[/li]

Would appreciate any guidance and feedback.
Thanks

 

[AK4S]

@retired13;
Thank you for the response. The forum has been a really good learning experience for me and I really appreciate the time and effort by folks like yourself who are keen on sharing your wealth of knowledge and experience. There are many things which are not straight forward answers and the back n forth is fruitful. You personally have contributed to all of my posts, Thank you
I am still learning and trying to contribute to the forum where I can
Curious to know are the Bridge Experts missing for the day or longer?

Regarding your responses:
(1)We are trying to avoid welding on these existing beams,so sticking to bolted connections.
(2)To clarify, the repair is still on paper, so the changes I mentioned to the sketch are just changes in my approach.

To understand the load path here:
[ul]
[li]Vertical component of Shear is transferred from existing web to the new web-plates. The new web-plates "need" to be bearing on the flanges in order to transfer the force to the bearing? Else they will stress the bolts when trying to follow the path via the vertical leg of the angle.[/li]
[li]The Horizontal component of shear is transferred from the web-plates to the angle and to the bottom flange of the beam via the connecting bolts.[/li]
[/ul]
What is your opinion?

 

[r13]

Theoretically I couldn't find anything wrong on both statements. In the field, I just wish there is adequate sound material (of the existing web) left to produce required resistance. I think large stiff plate washer on each side of the connection may produce better result (to ensure larger contact face).

 

[AK4S]

@retired13: Thanks for the confirmation of the basic load path. I did not understand regarding the plate washer, are you referring to connection b/w the new web-plate and existing web?

 

[r13]

Yes. I try to make sure there is adequate contact surface, provided that there was defect around.

 

[bridgebuster]

@AK4S - I don't think you need to worry about your new detail. There are so many differing opinions on web repairs. Bending stress is low; the shear stress is probably low; steel has a lot of bearing strength. Think of the repair as a bearing stiffener design; under the Standard Spec you can spread your load over 18t[sub]w[/sub]. With 2 repair plates you have a very beefy web.

 

[AK4S]

@bridgebuster: Thanks for your response. In my first detail with the 1.5" thick beveled plate, I had the required portion of plate thickness (Total-bevel) with full bearing on the bottom flange to transfer the Vertical component of Shear.
In the revised detail (See sketch below) with 0.75" plate not bearing on the bottom flange, the vertical shear load path will be through web-plate -> bolts -> vertical leg of the angle -> bottom flange. Is this advisable?
Per my first detail I had spaced these bolts only based on transfer of horizontal component of shear.If the revised detail is ok, I will have to space these connection bolts to take both Vertical+Horizontal components of shear acting simultaneously.