Bridges_Repairing Cracked Welds in Box Girder Int Stiffener

[Enjoy learning_not working]

Hi Everyone,

I work as an EIT and currently working on a bridge repair project for a State DOT. One of the common defects I found while going through the bridge Insp. Reports was cracked weld at the connection plate / vertical intermediate stiffener to top flange or web connection on a twin steel tub girder bridge. Attached are the pictures.

I am trying to come up with a repair plan for these defects. So, before actually planning the repair, I tried understanding the cause of the cracked welds. But I have not found any resources or references to why such cracks are caused and what would be a suitable repair plan. The closest I could find and think as to why the cracks are caused was either i) distortion induced fatigue cracking (web gap) or ii) insufficient weld capacity. I searched typical recommended details for steel girder stiffener connection detail from Caltrans and other agencies and it does look like the original design followed the recommended details.

Could you guys point me towards a good guidance / material / reference to better understand this. Help is appreciated.

Thanks.

https://files.engineering.com/getfi...560-41da-bd9a-945c53c502e9&file=Capture_2.PNG

https://files.engineering.com/getfi...-b6c4-1150689528f9&file=Caltrans_-_Detail.pdf

 

[BridgeSmith]

I don't have much experience with tub girders, but I would suspect distortion or restraint induced fatigue cracking. Essentially, overstress of the weld that's trying to restrain flexure of the top flange.

Before you set about to come up with a fix for these, I suggest you explore whether the weld there is needed. Granted, my experience pretty much exclusive to welded plate I girders, but we've found that those stiffener plates only need to be welded to the flanges if there are crossframes or diaphragms attached to them, that would transfer out-of-plane bending forces to the web if they were not restrained at the ends. Are these used as connection plates for internal crossframes or diaphragms? I don't see anything attached in the picture, but it may be because it's too close.

 

[Enjoy learning_not working]

Thanks BridgeSmith,

After going through a lot of resources, I am aware of recent recommendations of not welding to tension flanges. But was not aware of not welding to flanges if they are not connected to crossframes or diaphragms. For this particular bridge, the cracks at connection welds at either i) stiffener plate to top flange or ii) stiffener plate to web was observed regardless of whether it was just a vertical stiffener or a connection plate to internal diaphragms.

I suddenly remembered that I had the As-Builts for this particular bridge. And looks like most of the location of crack welds are at the region of tension flanges (See pdf attached). "On the tension flange, the effects of stress concentration increase the fatigue or brittle fracture possibilities...". This was from one of the references. So, I am beginning to think that this might be the primary reason for the cracks. And the repair to most of these locations would simply necessitate removing / grinding the existing weld and leaving it as is.

 

[BridgeSmith]

the cracks at connection welds at either i) stiffener plate to top flange or ii) stiffener plate to web was observed regardless of whether it was just a vertical stiffener or a connection plate to internal diaphragms.

The cause of the cracks was most likely flexure of the top flange, which the weld was too small to restrain. The good neews is, most likely, it was never expected to.

I was just trying to convey that stiffeners not used as connection plates are not typically subjected to much, if, any lateral forces, so they don't usually require a connection to the flanges.